Observed Tip Resistance at Eod & Bor Using Bottom Tip

OBSERVED TIP RESISTANCE AT EOD & BOR USING BOTTOM TIP GAGES FOR DRIVEN PILES

YIPENG XIE

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2011

To my well-beloved professor, Dr. Michael McVay, and to my parents, for their unconditional love

ACKNOWLEDGMENTS

I am indebted to my many of my colleagues to support me with this thesis. Most importantly, I sincerely thank Dr. Michael McVay for serving as my advisor. If I have ever learned how to do research, or come closer to a geotechnical engineer, it is because of his great teach by word and deed. There is no doubt that his guidance will accompany me for the rest of my life. I am impressed by his vast and versatile erudition, rigorous attitude towards research, and great personality throughout. To be his student is definitely one of my whole life’s landmarks. His valuable support and encouragement were what made this possible. Special thanks go to Dr. Reynaldo Roque for sitting on my supervisory committee. I would also like to thank other fellow graduate students for making the graduate study an enjoyable experience. A particular word of thanks goes to

Khiem Tran and Jiangpeng Xiang, for unselfishly sharing with me much of their knowledge.

I would like to thank my parents also, for their self-giving love. Without them, I can never become who I am today. I hope they will feel proud for me in the future.

TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...... 4

LIST OF TABLES ...... 7

LIST OF FIGURES ...... 8

ABSTRACT ...... 11

CHAPTER

1 FOUNDATION INTRODUCTION ...... 13

1.1 Background of Pile Foundations ...... 13 1.2 Pile Capacities ...... 14 1.2.1 Introduction of Pile Forces ...... 14 1.2.2 Side Shear Force and Tip Resistance ...... 15

2 PILE SET-UP ( FREEZE ) ...... 18

2.1 Introduction to Pile Set-up ( Freeze ) ...... 18 2.2 Principles of Pile Set-up ...... 19 2.2.1 Observation of Pile Set-up ...... 19 2.2.2 Findings and Conclusions ...... 20 2.2.3 Mechanisms of Pile Set-up ...... 22 2.3 Relationship between Pile Set-up and Logarithm of Time ...... 24

3 PILE LOAD TESTS ...... 28

3.1 Introduction to Pile Load Tests ...... 28 3.2 Slow and Quick Tests ...... 30 3.3 Four Load Test Methods ...... 30 3.4 Dynamic Forces vs. Static Forces...... 34 3.4.1 Dynamic Forces Recorded by PDA ...... 34 3.4.2 Match Calculated Forces to Measured Forces With CAPWAP ...... 38 3.4.3 Dynamic Tests Recorded by SmartPile Review ...... 40 3.4.4 Wave Theory ...... 41 3.4.5 Unloading Point Method ...... 44

4 ENERGY METHOD ...... 47

4.1 Theories of Energy Method ...... 47 4.1.1 Newton's Three Laws of Motion ...... 47 4.1.2 Force and Energy Equilibrium ...... 48

4.1.3 Process of Energy Method ...... 51 4.1.4 Examples of Energy Method ...... 59 4.1.4.1 Site – Dixie Highway ...... 59 4.1.4.1.1 Compression load test – end bent no.1 ...... 59 4.1.4.1.2 Compression load test – Pier no.8 ...... 64 4.1.4.2 Site – Caminada Bay ...... 68

5 OBSERVATIONS OF ENERGY APPROACH ...... 72

5.1 EOD vs. BOR Predicted Static Response of Dixie Highway ...... 72 5.2 EOD vs. BOR Predicted Static Response of Caminida Bay ...... 74

6 CONCLUSION ...... 88

6.1 Summary ...... 88 6.2 Recommendations ...... 89

APPENDIX: EXAMPLES OF ENERGY METHOD ...... 90

LIST OF REFERENCES ...... 102

BIOGRAPHICAL SKETCH ...... 105

LIST OF TABLES

Table page

5-1 EOD and BOR tip forces of dixie highway ...... 83

5-2 EOD and BOR tip forces of caminida bay ...... 84

5-3 EOD and BOR tip forces of I-95 DEsign Build US 192 bent3 pile5 & I-95 Eau Gallie bent1 pile1 ...... 85

5-4 EOD and BOR tip forces comparison ...... 86

5-5 EOD and BOR skin friction comparison ...... 87

LIST OF FIGURES

Figure page

1-1 Prestressed concrete pile ...... 14

1-2 Pile total capacity composed of side skin friction and tip resistance ...... 15

1-3 Forces along the pile ...... 16

1-4 Forces acting on pile segment during driving ...... 17

2-1 Seidel et at. (1988) relationship between pile capacity and log time ...... 26

3-1 Pile load test frame 1 ...... 29

3-2 Pile load test frame 2 ...... 29

3-3 Pile instralled with PDA strain gages and accelerometer ...... 35

3-4 Instrumentation at 18 in from pile tip: PDI (strain and accelerometers)...... 36

3-5 PDA Data acquisition systems...... 36

3-6 PDA analyzer ...... 37

3-7 CAPWAP analyze procedure...... 40

3-8 EDC software window ...... 41

3-9 WaveUp and WaveDown Forces passing along the pile ...... 41

3-10 Wave traveling in the pile ...... 41

3-11 Steps of Statnamic test ...... 45

3-12 Real field Statnamic test ...... 45

3-13 Statnamic measured load and calculated static force ...... 46

4-1 Mass-Spring-Damper model ...... 50

4-2 Excel configuration sheet from SmartPile Review ...... 52

4-3 Excel data sheet from SmartPile Review of one blow ...... 51

4-4 Excel sheet from Energy Method1 ...... 53

4-5 Excel sheet from Energy Method2 ...... 53

4-6 EDC Blow 777 Forces vs. Time at Pile Tip of Pier 8 ...... 55

4-7 EDC Blow 777 Forces vs. Displacement at Pile Tip of Pier 8 ...... 56

4-8 EDC Blow 777 Energy vs. Time at Pile Tip of Pier 8 ...... 57

4-9 EDC Blow 779 Forces vs. Time at Pile Tip of Pier 8 ...... 57

4-10 EDC Blow 779 Forces vs. Displacement at Pile Tip of Pier 8 ...... 58

4-11 EDC Blow 779 Energy vs. Time at Pile Tip of End Bent1 ...... 58

4-12 EDC Blow 740 Energy vs. Time at Pile Tip of End Bent1 ...... 61

4-13 EDC Blow 740 Forces vs. Displacement at Pile Tip of End Bent1...... 61

4-14 EDC Blow 740 Energy vs. Time at Pile Tip of End Bent1 ...... 62

4-15 EDC Blow 765 Energy vs. Time at Pile Tip of End Bent1 ...... 62

4-16 EDC Blow 765 Forces vs. Displacement at Pile Tip of End Bent1...... 63

4-17 EDC Blow 765 Energy vs. Time at Pile Tip of End Bent1 ...... 63

4-18 EDC Blow 751 Forces vs. Time at Pile Tip of Pier 8 Pile ...... 65

4-19 EDC Blow 751 Forces vs. Displacement at Pile Tip of Pier 8 Pile ...... 66

4-20 EDC Blow 751 Energy vs. Time at Pile Tip of End Bent1 ...... 66

4-21 EDC Blow 779 Forces vs. Time at Pile Tip of Pier 8 Pile ...... 67

4-22 EDC Blow 779 Forces vs. Displacement at Pile Tip of Pier 8 ...... 67

4-23 EDC Blow 779 Energy vs. Time at Pile Tip of Pier 8 ...... 68

4-24 EDC Blow 630 Forces vs. Time at Pile Tip of Caminida Bay Bent1 Pile1 ...... 69

4-25 EDC Blow 630 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1 Pile1 ...... 69

4-26 EDC Blow 630 Energy vs. Time at Pile Tip of Caminida Bay Bent1 Pile1 ...... 70

4-27 EDC Blow 660 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1 Pile1 ...... 70

4-28 EDC Blow 660 Energy vs. Time at Pile Tip of Caminida Bay Bent1 Pile1 ...... 71

4-29 EDC Blow 660 Forces vs. Time at Pile Tip of Caminida Bay Bent1 Pile1 ...... 71

5-1 Estimated tip resistance of Dixie Highway Bent 1 Pile1 blows before the load test ...... 72

5-2 Estimated tip resistance of Dixie Highway Bent 1 Pile1 blows after the load test ...... 72

5-3 Estimated tip resistance of Dixie Highway Pile8 blows before the load test ...... 73

5-4 Estimated tip resistance of Dixie Highway Pile8 blows after the load test ...... 73

5-5 Estimated tip resistance of Caminida Bay1 blows before the load test ...... 74

5-6 Estimated tip resistance of Caminida Bay1 blows after the load test ...... 74

5-7 Estimated tip resistance of Caminida Bay7 blows before the load test ...... 75

5-8 Estimated tip resistance of Caminida Bay7 blows after the load test ...... 75

5-9 Davisson’s Capacity of Dixie Highway Bent1 Pile1 ...... 76

5-10 Davisson’s Capacity of Dixie Highway Pier8 ...... 77

5-11 Davisson’s Capacity of Caminida Bay Bent1 ...... 77

5-12 Davisson’s Capacity of Caminida Bay Bent7 ...... 78

5-13 Predicted Tip Resistance at EOD for pile 5 at US 192 ...... 80

5-14 Predicted Tip Resistance at BOR for pile 5 at US 192 ...... 80

5-15 Predicted Tip Resistance at EOD and BOR for pile 5 at US 192 ...... 81

5-16 Predicted Tip Resistance at EOD of I95 Eau Gallie bent1 pile1 ...... 82

5-17 Predicted Tip Resistance at BOR of I95 Eau Gallie bent1 pile1 ...... 82

5-18 Predicted Tip Resistance at EOD and BOR I95 Eau Gallie bent1 pile1 ...... 83

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

OBSERVED TIP RESISTANCE AT EOD & BOR USING BOTTOM TIP GAGES FOR DRIVEN PILES

Yipeng Xie

May 2011

Chair: Michael McVay Major: Civil Engineering

Pile foundations are the important part of a structure used to carry and transfer the load of the structure to the bearing ground. To compute the total load that can be applied to a pile, it is necessary to compute both tip resistance and skin friction acting on sides of the pile. Researchers develop many different methods of measuring pile shear forces and tip force. Static testing and dynamic testing are common used today to get pile capacities during and after driving process. During restrikes following the initial installation, or changing cushions template removal and so on, piles may experience an increase of total capacity. This phenomenon nowadays is well known as soil/pile set-up

(freeze). With more and more test sites observe such phenomenon, researchers believe that pile set-up occures mostly because of pile shear force increase, where pile tip resistance seem not to change as much as shear force. In order to have a better evaluation of pile static tip resistance, a new method called energy method is developed and used to analyse different pile sites, providing with consistant and gauranteed results.

This thesis focused on the introduction of this new method, also from the static tip resistance forces measured from this approach, it shows pile set-up has less

relationship with pile tip force compared to the increase of pile shear force. The current application of energy method performed on different piles is considered successful.

CHAPTER 1 FOUNDATION INTRODUCTION

1.1 Background of Pile Foundations

Pile foundations are important part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface.

Foundations are generally broken into two categories: shallow foundations and deep foundations. Shallow foundation is usually, embedded a meter or so into soil. A shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, including spread footing foundations, mat-slab foundations, slab-on-grade foundations, rubble trench foundations, and earthbag foundations. A deep foundation is a type of foundation distinguished from shallow foundations by the depth they are embedded into the ground. Structural members made of steel, concrete, and/or timber.

They are expensive due to cost materials, placement (driving, drilling, etc.) vs. shallow foundations. They are used for following reasons: 1) If the upper soil layers are compressible or too weak to support the structural loads. 2) Structures subject to large horizontal forces – In Florida, a common design consideration is hurricane winds, ship impact on bridge piers, etc. 3) Foundations subject to adverse future influences: soil erosion or scour from streams or waterways during storms (Acosta 15’ in 25yrs).

Pile foundations have been used as load carrying and load transferring systems for many years. Two types of forces act on piles, tip resistance acts on the bottom of the pile and skin friction acts on the sides of the pile. Piles are heavy beams of timber, concrete, or steel, driven into the earth as a foundation or support for a structure.

Selection of a pile type is based on Cost – in south Florida commercial construction, auger cast concrete are prevalent – develop more side friction than driven steel or

concrete pile due to drilling into limestone (oolites) – resulting in cheaper cost.

Nowadays concrete piles are the most common piles used, which are driven into the ground to ensure that the foundation is deep. For concrete piles, they are divided into two categories based on construction and installation: 1) Precast prestressed concrete pile (18” – 66”) constructed in a casting yard (Standard, Gates, etc.) and installed with crane, leads and a hammer; 2) Cast insitu pile: Franki Pile, auger cast pile, continuous flight auger – constructed by drilling or other hole creation, filling with concrete and steel reinforcement.

Figure 1-1. Prestressed concrete pile

1.2 Pile Capacities

1.2.1 Introduction of Pile Forces

No matter which type the pile is, usually two kinds of forces act on it: 1) Tip resistance acts on the bottom of the pile. 2) Skin friction acts on the sides of the pile. To compute the total load applied to a pile, it is necessary to compute both the tip force and

the skin friction and add them together. A modified Terzaghi bearing capacity equation is used to find the pile capacity:

Pt = Fside + Ftip (1-1)

Figure below shows that side friction and tip resistance both composing the total capacity.

Figure 1-2. Pile total capacity composed of side skin friction and tip resistance

1.2.2 Side Shear Force and Tip Resistance

It is common to see a block is placed on a clay surface. Now if a force is applied to move the block, the adhesion between the block and the clay will resist the movement.

The adhesion coefficient between the clay and the block is c, and the weight of the block is W, the force F due to adhesion will be

F = W * c (1-2)

Figure 1-3. Forces along the pile

When load acts on the pile, it will in the same way generate side shear force along the pile surrounded by soil. The load transferred from pile skin to the surrounding clay soil is a function of the diameter and the surface roughness of the pile, clay properties

(cohesion, type of consolidation and level of disturbance). Generally, skin friction (FS, force) is characterized as unit skin friction (fs, stress), times the surface area it acts over.

The unit skin friction (fs) is usually characterized as a function of the pile displacement

[u(x,t)], e.g., T-Z curve in FB-MultiPier, FB-DEEP, etc. A secant stiffness (K) is defined as the unit skin friction per unit of displacement [u(x,t)]. Using the secant stiffness (K), the skin friction (FS) force acting on segment dx (Figure 1-4) may be found. Next, assuming a general damping form, i.e., viscous with coefficient (Cr), the damping force

(Fd) is obtained from particle velocity times density and surface area (Figure 1-4).

Summing the forces on the segment, results in:

  F v  0  F B  F T  F I  F S  F d (1-3)

B   Axial Stress 2 FT   A where A  B

d FS = Skin Friction Fd = Side dx F x Damping I Fd = Side Damping: FI = Inertia Force Asu   rf   dx Fd = Cr P dx s u(x,t)/t  x

   Particle F    dx A B   x  velocity, v   Radiation FS = Skin Friction: Damping Soil Density unit fs, frictionskin Coeff.

Pile Perimeter = 4B K ’

u(x,t), pile displacement

F = Skin Friction = fs A = K’ u(x,t) P dx Summing Forces on Segment S surf

Figure 1-4. Forces acting on pile segment during driving

CHAPTER 2 PILE SET-UP ( FREEZE )

2.1 Introduction to Pile Set-up ( Freeze )

For geotechnical engineers, they observed nearly 100 years ago that bearing capacity of a driven pile usually increases after its installation. During restrikes following the initial installation, or changing cushions template removal and so on, piles may experience a driving from easy to hard. This phenomenon nowadays is well known as soil/pile set-up (freeze). With more installation of driven piles, it is recognized as occurring in most parts of all the world, all driven pile types, and in all sorts of soils, which ranges from organic and inorganic saturated clay, and loose to medium dense silt, sandy silt, silty sand, and fine sand, and is related to both soil and pile properties.

And the timeline is from less than half an hour to several years or even longer. Over forty years ago, geotechnical engineers observed an averaged 70% pile capacity increase between 0.5 to 20 days. (Tavenas and Audy (1972)). They wrote the first well- documented summarization of set-up phenomenon about performing tension load test on steel pipe piles at sand site in France, claiming the long term set-up was in the region of 50 to 150% of initial pile capacity. In fact, pile set-up occurs much more quickly in sand than in clay. Usually, set-up (freeze) takes a few hours for the side-shear friction to restore in sand, where in clay it may takes months or even years for the piles to restore total capacity.

Although the phenomenon today is observed more and more and got recognised in nearly all sorts of soils, the increase capacity of pile with time is not mainly considered in pile foundation design. It can be imagined that by including the pile set- up (freeze) into the pile foundation design, the total cost of foundation can be reduced

as the number, length, size of the pile could be reduced. It may also generated big saving in the total cost as foundation cost ranging from 5% to 30% in the total cost.

Although geotechnical engineers realize such advantages as if they can fully use this phonomenon, but due to lack of understanding about the detailed mechanism, it is hard to tell how principal factors such as soil type, pile size and material as well as its installation method affect soil/pile set-up.

2.2 Principles of Pile Set-up

2.2.1 Observation of Pile Set-up

As mentioned before, pile set-up occurs in all kinds of soil. Many papers also present relating findings. For example:

Bullock et al. (2005) - final research report lasting from February 1993 to April

1999 investigated five fully instrumented piles driven into a variety of soils (sand, clay, mixed soils) at four different FDOT bridge sites. These five eighteen-inch square piles were instrumented with strain gages, lateral total stress cells, pore pressure sensors along their length and at their tips were cast Osterberg load cells. In the field SPT

Torque, piezo CPT and DMT stage testing were performed. Also in laboratory, they drove a model pile in the centrifuge in flight at 50gs and then perform a static pull out

(tension) test to determine if they could duplicate freeze effects. After 16 to 1727 days elapsed time using Osterberg cell tests separating side shear and end bearing, 12 to

32% side shear increase per log cycle of time were recorded.

C.S. Chen, S.S. Liew & Y.C. Tan (1998) - two case histories where the changes in pile capacity were observed with time are presented. One case shows the increase in pile capacity especially the shaft friction for piles driven into clayey deposit. The average unit shaft friction, determined from the high strain dynamic pile test, has increased from

33 kPa to 57 kPa from 3 days to 33 days after the installation of piles. The second case shows a tendency of increase in pile capacity for pile driven into sandy deposit over a period longer than needed for complete dissipation of excess pore water pressure induced by the driving process.

Gary Axelsson (2000) - two series of full scale field tests were performed on instrumented concrete piles, driven in loose to medium dense sand. In addition, laboratory rod shear chamber tests were performed on driven model piles and finally revealed that set-up is a major feature of driven piles in non-cohesive soil.

Kehoe (1989) - investigated two Florida mixed cohesive soils sites with driven square prestressed concrete piles. Static and dynamic tests showed capacities increases average from 58% to 200% within 11 days after driving.

W. K. Ng & M. R. Selamat, K. K. Choong (2010) - based on the assumption that the capacity increase of pile depends on various factors, the duration of full set-up is assumed to be dependent solely on soil type, a total 6 case studies (CS) and 11 numbers of test piles (P1 – P11) are presented to investigate from the aspect of soil/pile set-up. All the projects located in peninsular Malaysia. Two types of pile used in the cases such as RC square pile (with size 200 – 400mm) and spun pile (with diameter

250 – 500mm), results showing set-up effect is playing a role on time-dependent capacity of driven pile in Malaysian soil.

2.2.2 Findings and Conclusions

Van E. Komurka and Alan B. Wagner (2003) concluded in their final report

“Estimating Soil/pile Set-up” that through a thorough review of the literature and the state of the practice, set-up is predominately associated with an increase in soil resistance acting on the sides (shaft) of a pile. Unit set-up has units of force divided by

pile side area. The complete mechanisms contributing to set-up are not well understood, but the majority of set-up is likely related primarily to dissipation of excess porewater pressures within, and subsequent remolding and reconsolidation of soil which is displaced and disturbed as the pile is driven. Set-up is recognized as occurring in most parts of the world, for virtually all driven pile types, in organic and inorganic saturated clay, and loose to medium dense silt, sandy silt, silty sand, and fine sand, and is related to both soil and pile properties. In cohesive soils, the shear strength of the disturbed and reconsolidated soil has been found to be higher than the soil’s undisturbed shear strength. In fine-grained granular soils, the majority of set-up is related to creep-induced breakdown of driving-induced arching mechanisms, and to aging. The more permeable the soil, the faster set-up develops. Set-up rate decreases as pile size increases. As soil around and beneath the pile is displaced and disturbed, excess porewater pressures are generated, decreasing the effective stress of the affected soil. The increase in porewater pressure is constant with depth (Soderberg,

1961), and can exceed the existing overburden stress within 1 pile diameter of the pile

(Pestana et al., 2002; Randolph, et al., 1979). Decrease in excess porewater pressure is inversely proportional to the square of the distance from the pile (Pestana et al.,

2002). The time to dissipate excess porewater pressure is proportional to the square of the horizontal pile dimension (Holloway and Beddard, 1995; Soderberg, 1961), and inversely proportional to the soil’s horizontal coefficient of consolidation (Soderberg,

1961). Accordingly, larger-diameter piles take longer to set-up than smaller-diameter piles (Long et al., 1999; Wang and Reese, 1989). Excess porewater pressures dissipate slower for a pile group than for a single pile (Camp et al., 1993; Camp and Parmar,

1999). As excess porewater pressures dissipate, the effective stress of the affected soil increases, and set-up predominately occurs as a result of increased shear strength and increased lateral stress against the pile.

Bullock et al. (2005), Axelsson (1998a), and Chow et al. (1998) concluded that setup occurs primarily as a result of side shear increase, not end bearing. Penetration of the pile pushes soil outward and away from the pile, destructuring and shearing it to a greater extent adjacent to the side of the pile than at the pile tip, and thus reducing the side resistance during installation (and increased aging effects).

2.2.3 Mechanisms of Pile Set-up

Time-dependent pile capacity increase depends on many factors such as soil grain characteristics, insitu stress level, pile geometry, chemical processes and pile installation procedure. In cohesionless soil, the excess pore water pressure dissipated quickly. Excess pore water pressures induced by pile driving seldom exceed 20% of the effective overburden stress. Soil/pile set-up taking place in pile in cohesionless soil is thought to be due to the following reasons:

(a) chemical effects which may cause the sand particles to bond to the pile surface,

(b) soil ageing effects resulting in increase in shear strength and stiffness with time,

(c) gain in radial effective stress due to creep effects or relaxation on the established circumferential arching around the pile shaft during installation.

Pile installation in clay is different from pile driving in sand. Komurka et al. divided the soil/pile set-up mechanisms into the following three phases:

Phase I: logarithmically nonlinear rate of excess pore water pressure dissipationBecause of the highly disturbed state of the soil, the rate of dissipation of excess porewater pressures is not constant. During this first phase of set-up, set-up rate

corresponds to the rate of dissipation, and so is also not uniform (not linear) with respect to the log of time for some period after driving. During this phase of non- constant rate of dissipation of excess pore pressures, the affected soil experiences an increase in effective and horizontal stress, consolidates, and gains strength in a manner which is not well-understood and is difficult to model and/or predict. This first phase of set-up has been demonstrated to account for capacity increases in a matter of minutes after installation.

Phase II: logarithmically linear rate of excess porewater pressure dissipation

At some time after driving, the rate of excess porewater pressure dissipation becomes constant (linear) with respect to the log of time. During this second phase of set-up, set-up rate corresponds to the rate of excess porewater pressure dissipation, and so for most soils is also constant (linear) with respect to the log of time for some period after driving. During the logarithmically constant rate of dissipation, the affected soil experiences an increase in effective vertical and horizontal stress, consolidates, and gains shear strength according to conventional consolidation theory.

Phase III: Independent of effective stress

Infinite time is required for dissipation of excess porewater pressure to be complete. Practically speaking, there is a time after which the rate of dissipation is so slow as to be of no further consequence, at which time it is accepted that primary consolidation is complete. However, secondary compression continues after primary consolidation is complete, and is independent of effective stress. Similarly, since the rate of set-up corresponds to the rate of excess porewater pressure dissipation, it follows that in some cases infinite time would be required for set-up to be complete.

Again practically speaking, and as with primary consolidation, there is likely a time after which the rate of set-up is so slow as to be of no further consequence, and effective- stress-related set-up is effectively complete. However, as with secondary compression, it has been demonstrated that set-up continues after dissipation of excess porewater pressures. During this third phase of set-up, set-up rate is independent of effective stress. This is related to the phenomenon of aging.

For a given soil type at a given elevation along the pile shaft, there is likely some overlap between successive phases, so, more than 1 phase may be contributing to set- up at a time (e.g., aging may begin before essentially complete dissipation of excess porewater pressure). In addition, unless soil conditions are uniform along the entire length of the shaft and beneath the toe, different soils at different elevations will be in different phases of set-up at a given time.

2.3 Relationship between Pile Set-up and Logarithm of Time

Civil engineers generally assume a log-linear relationship between pile capacity and elapsed time. Following is Terzaghi’s one dimensional (radial) consolidation theory:

2 Th = 4* Ch * t / rp (2-1)

Where Th = Time Factor Ch = Coefficient of Radial Consolidation t = Elapsed Time since End of Driving rp = pile radius

Based on Terzaghi’s theory, Vesic (1977) found that in clays, pile capacity showed a linear trend against the logarithm of time except for short and long setup times, which is similar to a strain vs. log time oedometer consolidation curve. It was raised by them that due to the dissipation of excess pore pressure as the result of pile installation, set- up was developed because of the radial consolidation. Researchers further illustrate

that the consolidation set-up varies as the square of pile radius, suggesting reduce some of the variation of Set-up Factors such as pile size would warrant additional research.

Mohr-Coulomb Equation (2-2) describes side shear increment in the following form:

τ = σ' tan(υ') + c' (2-2)

Where σ' = (σ - u), known as the principle of effective stress. σ is the total stress applied normal to the shear plane, and u is the pore water pressure acting on the same plane. υ' = the effective angle of shearing resistance. c' = apparent cohesion, allowing the soil to possess some shear strength at no confining stress, or even under tensile stress. It may also be due to diagenetic affects caused by soil aging such as chemical bonding, cementation of grains and the effects of creep; indeed futher identified that soil possessed no cohesion when newly remoulded. When shear tests are conducted on an overconsolidated or dense soil, and peak strengths are plotted on a τ/σ plot, it appears that cohesion exists as the y-intercept is non-zero. Some feel that this is not due to true cohesion, but is the effect of interlocking of particles.

From this Mohr-Coulomb equation, some researchers have shown the possibility which a portion of the set-up is due to the increases in the effective horizontal stress during consolidation. Experiments demonstrated that at first near the pile the horizontal effective stresses near the pile are low and increase as time goes by, when the excess pore water pressure disappears. Also from the experiments done in sand, effective stress changed from low to high the same with in clay. In conclusion, piles driven both in clay and sand will have a change in effective stresses, and the increase of horizontal effective stresses will be a reason for pile set-up effect.

So far, although researchers have not come to a final conclusion of how to predict the pile set-up exactly and uniformly, it is demonstrated a strong relationship between pile capacity changes and the logarithm of time.

Figure 2-1. Seidel (1988) ploted relationship between pile capacity and log time

Skov and Denver (1988) reached a relationship between pile capacity and time from four case histories illustrating set-up, as following:

Q / Q0 – 1 = A * log10 ( T / T0 ) (2-3)

Where Q = pile capacity at time T; Q0 = pile capacity at initial time T0; T = time elapsed since end of driving; T0 = initial time elapsed since end of driving, a reference time before which there is no predictable Q0 increase as a function of elapsed time.

Skov and Denver (1988) use mostly dynamic tests to reach the A value falling between 0.2 and 5.0. But for this equation, it is hard to tell the portion of pile side friction and pile end bearing of the total capacity. As some researches results indicate, pile set- up occurs primarily due to side shear forces increase instead of pile end bearing. Skov and Denver, Kehoe and many other researchers found little change with time for pile

end bearing from dynamic tests. Also static tests showed such situation from Axelsson’s research. In Equation 2-3, Q is defined as the total pile capacity which includes the pile end bearing capacity. Since end bearing may not change a lot, it will cause the set-up factor lower than the true values. Also further researchers need to concern is the T0.

Because there are no specific criteria to define what time T0 will ends, A will be affected by it significantly, too. Bullock suggests using T0 = 1 day, so it will give an general standard criteria for future set-up calculation. Bullock summarized the side shear forces increase linearly with the log of elapsed time at five test site with different soil situation in Florida

Bullock et al. (2005) then reviewed all the assumption of set-up factor, further raised another Set-up factor Ashear as the side shear Semilog-Linear Setup factor to modify Equation 2-3. He suggests that use T0=1 day to remove the difficulty of finding the actual start of the semilog-linear set-up process, providing a global reference, also use Ashear to describe the side shear component only, because end bearing capacity doesn’t change a lot after end of driving. Finally, plot the EOD capacity at 1 min elapsed time. It may give a more reliable capacity measurements at fixed times.

Bullock modified Skov and Denver’s equation into set-up factor based on side shear, providing a more uniformly using equation:

Qs/Qs0=fs/fs0=Ashear * log ( t / t0 )+1 = ( ms / Qs0 ) * log ( t / t0) + 1 (2-4)

Where Ashear = Dimensionless set-up factor; Qs = Side shear capacity at time t; Qs0 = Side shear capacity at initial reference time t0; fs = Unit side shear capacity at time t; t = Time elapsed since EOD, days; t0 = reference time, recommended to use 1 day; ms = Semilog-linear slope of Qs vs log t

CHAPTER 3 PILE LOAD TESTS

3.1 Introduction to Pile Load Tests

Geotechnical engineers find this increase of pile capacity after static load test

(SLT) or dynamic load test (DLT) taken after initial driving. So for determing when pile set-up (freeze) actually happens or how much influence it affects the total pile bearing capacity, it is very important that after initial driving, a load test would be conducted later. Pile foundations are constructed depending on the stiffness of subsurface soil and ground water conditions with a variety of construction techniques. Due to the extensive nature of the subsurface mass that it influences, the degree of uncertainty regarding the actual working capacity of a pile foundation is generally very higher. Load testing is playing an important role in value engineering and the geotechnical and structural optimization of foundation solutions. It should be recognized not only in financial terms, but also with regard to sustainability. Load testing of piles is factored into the project cost plan and program at an early stage. To perform load tests successfully, it should allow sufficient time for an objective evaluation of the test results, and subsequent design revisions engineering to be carried out. A lack of clear objectives and understanding combined with poorly specified requirements can lead to problems that could have been avoided such as: 1) insufficient time to carry out tests and to evaluate the test results; 2) lack of flexibility in the testing regime; 3) no provision for value engineering; 4) unrealistic performance criteria specified; 5) inappropriate test method specified; 6) load test conditions are not representative of the working piles; 7) piles infrequently loaded to failure. It is obvious that continuous improvement in foundation design and construction practices, while at the same time fulfilling its traditional role of

design validation and routine quality control of the piling works can be assured. Data from pile tests has to be collected and analyzed to enable the piling industry run smoothly. The test pile, installation equipment and installation procedure should be identical to that intended to be used for production piles to the extent load. The piles should be loaded to at least two times the design load, and preferably to failure. Pile foundations, including helical screw foundations, that have been tested to their ultimate capacity should not be used as production piles.

Figure 3-1. Pile load test frame 1

Figure 3-2. Pile load test frame 2

3.2 Slow and Quick Tests

Regarding to pile load test, two most common tests are slow and quick maintained tests (see American Society for Testing and Materials 1143-81).

1) Slow Maintained:

– Load the pile in 8 equal increments (25%, 50%, 75%, 100%, 125%, 175% and 200%) of the design service load;

– Maintain each increment until the rate of settlement has decreased to 0.01 in/hour, but not longer than 2 hours;

– Maintain the 200% load for 24 hours;

– After the required holding time, remove the load in decrements of 25% with 1 hour between steps;

– After loading as above, reload pile to test load in 50% increments of design load, allowing 20 minutes between load increments;

– Then increase the load in increments of 10% of design load until failure, allowing 20 minutes between load steps.

2) Quick Maintained – Recommended by Federal Highway Administration (3 – 5 hours):

– Load the pile in 20 increments to 300% of the design load (i.e. each increment is 15% of design load);

– Maintain each load for 5 minutes with readings taken every 2.5 minutes;

– After reaching 300% - hold load for 5 minutes and then remove the load in 4 equal decrements (each 75% of design) with 5 minutes between decrements;

– Because of the quickness of the test, it is not generally recommended for settlement estimations – considered an undrained loading scenario.

3.3 Four Load Test Methods

Dynamic Pile Testing: Dynamic pile testing constitutes a comprehensive and economical means to quantitatively evaluate the hammer-pile-soil system based on the measurement of pile force and velocity records under hammer impacts. Measurements, data processing and analysis are performed in real time in the field by Pile Driving

Analyzer® (PDA) equipment from PDITM, or Smartpile ReviewTM which supplies both top and tip gages. Testing results include estimation of pile load capacity, dynamic pile stresses and structural integrity as well as driving system performance. The Pile Driving

Analyzer® is applicable on bored cast-in-situ, drilled shafts, continuous flight auger & driven piles, this applies for either test pile or working pile. Dynamic pile monitoring for construction quality control and verification testing are performed on hundreds of project sites in America. Main objectives of dynamic pile testing include obtaining information on the following: 1) Hammer and driving system performance for productivity and construction control; 2) Dynamic pile stresses during and after installation. To reduce the possibility of pile damage, stress must be kept within certain bounds; 3) Pile integrity during and after installation; 4) Static pile bearing capacity, at the time of testing. For the evaluation of long term capacity, piles are generally tested during re-strike some time after installation.

To enhance analysis, CAPWAP® is used combined with PDA, which enables people to correlate the measured data with the known pile / soil model elements. The end result of CAPWAP®, via a rigorous and repeated signal matching solution, produces a pile driving summary that contains pile capacity, percent end bearing / skin friction, measured pile compression and tension stresses. Using this type of empirical and analytical data assistance, it can validate a project's design requirements with superior accuracy and speed. With dynamic load test, researchers want to know:

(a) Estimates total bearing capacity of a pile or shaft (b) Soil resistance parameters (c) Resistance distribution along the shaft and at the toe (d) Static load–settlement curves from the measured force and velocity data (e) Total computed soil capacity – sum of Skin Friction and Toe Bearing (f) Computed load against settlement curve

(g)Stresses at any point along the shaft

Static pile load testing: it involves the direct measurement of pile head displacement in the response to a physically applied test load. It is the most fundamental form of pile load. Testing has been performed in the load range 100 kN to

12,000 kN. The SLT may be carried out for the following load configurations:

(a) Compression (b) Lateral (c) Tension (i.e. uplift)

For the Static Load Test the load is most commonly applied via a jack acting against a reaction beam, which is restrained by an anchorage system or by jacking up against a reaction mass (“kentledge” or dead weight ). The anchorage system may be in the form of cable anchors or reaction piles installed into the ground to provide tension resistance. The nominated test load is usually applied in a series of increments in accordance with the appropriate Code, or with a pre-determined load testing specification for a project. Each load increment is sustained for a specified time period, or until the rate of pile movement is less than a nominated value. Static load testing methods are applicable to all pile types, on land or over water, and may be carried out on either production piles or sacrificial trial piles. Trial piles are specifically constructed for the purpose of carrying out load tests and therefore, are commonly loaded to failure.

Testing of production piles however, is limited to prove that a pile will perform satisfactorily at the serviceability or design load, plus an overload to demonstrate that the pile has some (nominated) reserve capacity.

Loading is applied to the test pile using a calibrated hydraulic jack, and where required a calibrated load cell measures the load. During the SLT, direct measurements

of pile displacement under the applied loading are taken by reading deflectometers (dial auges reading to 0.01mm) that are positioned on glass reference plates cemented to the pile head. The deflectometers are supported by reference beams that are founded a specified distance away from both the test pile and any reaction points. Although SLT is generally held as the most reliable form of load testing a pile or pile group, it is important that interaction effects are minimized. These may result from interaction between the test pile and the anchorage systems, or between the measuring system and reaction points. For this reason, careful attention is given to performing the test in accordance with proper procedures.

Lateral load test: Lateral load test in one of the good means of estimating lateral capacity of pile. Piles are generally used to transmit vertical and lateral loads to the surrounding soil media. Piles are sometimes subjected to lateral loads due to wind pressure, water pressure, earth pressure, earthquakes, etc. when the horizontal component of the load is small in comparison with the vertical load (say, less than 20%), it is generally assumed to be carried by vertical piles and no special provision for lateral load is made. Piles that are used under tall chimneys, towers, high rise buildings, high retaining walls, bridges & other concrete elevated structures etc. are normally subjected to high lateral loads. These piles or pile groups should resist not only vertical movements but also lateral movements. Some of the measured are: 1) Efficiency of the pile group loads; 2) Soil stiffness degradation; 3) Bending moments 4) Lateral pile response; 5) Pile deflection and soil response; 6) Ultimate lateral resistance; 7)

Acceptable deflection at working lateral load.

Pull-out load test: many structures are constructed using deep piled foundations in order to transfer structural dead load through unstable ground to a solid stratum. Action of horizontal wind or wave forces on the structure and the behavior of the piles under these loads are much less well documented. The resistance of the concrete piles to pull-out comes from two major sources, skin friction between pile and soil and suctions generated at the base of the pile as movement occurs. Both of these effects are greatly affected by the generation of excess or suction pore pressures in the soil due to movement of the pile. Suctions are generated at the base of the pile in all soils owing to the opening up of a void as the pile moves. At the sides of the pile, un-drained shearing of the soil when the pile is pulled quickly will result in excess pore pressure generation in loose soils and suctions being generated in dense soils. These pore pressures will alter the effective stress state of the soil and will hence have a great impact on the force-displacement behavior of the pile. Pull-out tests are the ideal alternative because of their low cost, relative rapid execution, and reliability of results. The actual skin resistance between concrete and in-situ soil can be measured at different elevations within the soil profile. The greater certainty achieved from pullout testing eliminates overly conservative design values, which in turn reduces as-constructed costs.

Experience has shown that these savings far exceed the cost of pullout testing.

3.4 Dynamic Forces vs. Static Forces

3.4.1 Dynamic Forces Recorded by PDA

Usually performing a static load test after end of driving is a cost of time and money, needing additional equipment to install loads and measurement of movement and force. Sometimes pile load test frame’s installation may have some disturb to the soil. But the estimation of pile tip force is very important for testing pile integrity and

prediction of pile performance. Static load test can directly measure pile end bearing capacity, where provide civil engineers with open-and-shut results. Comparing to taking long time performing static load tests, people want to measure the static shear forces and tip resistances more quickly and economically. So getting static results from dynamic tests is what usually researchers prefer. Since dynamic tests do not disturb soil around pile during driving and feed back test data simultaneity, it is easy for engineer s to monitor whether pile driving is smooth or not as well as inspecting pile capacity at the same time. The need to predict and better understand the ultimate loads to which a cast-in-place pile foundation is capable is critical for pile design and optimization, as well as for quality assurance of such elements. The use of high strain dynamic testing of cast-in-place piles and drilled shafts has become a more frequent routine for bearing capacity evaluations in many countries around the world, increasing the levels of standardization and codification (Beim et al. 1998). To accurately predict static capacity from dynamic pile testing is always being researched by many geotechnical engineers, and has been the focus of dynamic pile tests on many project sites. Signal matching on the data seems to be the key of getting more accurately determine capacity.

Figure 3-3. Pile installed with PDA strain gage and accelerometer. Photo courtesy of Michael C. McVay

Figure 3-4. Instrumentation at 18 in from pile tip: PDI (strain and accelerometers). Photo courtesy of Michael C. McVay

Figure 3-5. PDA Data Acquisition Systems. Photo courtesy of Michael C. McVay

Figure 3-6. PDA analyzer

A new system of multiple dynamic strain sensors and accelerometers embedded in test piles provides direct synchronous measurement of force and acceleration at various locations within a pile during high strain dynamic pile testing. By timing the strain gage data with the elastic modulus and cross area of pile, forces act on the pile could be get very easily. From accelerometers, acceleration could be calculated from raw data, accordingly by integrating the acceleration, both velocity and movement could be reached. And all these data can be transmit to operators immediately after pile driving, giving people a direct idea of pile situation. Strain gages and accelerometers are often instralled near the top of the pile, usually away from the top in the distance of one diameter. They measure and record the instantaneous pile velocity and force generated by each hammer blow driving in the pile. Nowadays, PDA is a commonly used equipment of receiving dynamic force measurement from site. For each hammer blow, the PDA displayed time traces of the force and velocity on an osillloscope. Except for those measurements, it also calculate a number of other parameters such as maximum tension or compression forces, energy put into the pile and check the pile integrity. If use dynamic tests to get static forces after EOD, researchers need to wait a

similar time as performing static load test, waiting until pore water pressure dissipates and pile set-up increases.

3.4.2 Match Calculated Forces to Measured Forces With CAPWAP

After PDA collects raw data from test field, recorded force and velocity waves from selected hammer blows will be analyzed using the CAPWAP® computer program to separate the skin friction and tip resistance from the total force. CAPWAP® (CAse Pile

Wave Analysis Program) is a software program that estimates total bearing capacity of a pile or shaft, as well as resistance distribution along the shaft and at the toe. The program takes as input the force and velocity data obtained with a Pile Driving

Analyzer® (PDA). This instrumentation system creates an opportunity to explore side and end bearing pile resistance distribution with confidence and reliability than from top measurements alone. Because PDA measures the dynamic forces during pile driving, it is difficult to know exactly how much the static force is. Along with the popularization of

CAPWAP®, it is considered a standard procedure for the capacity evaluation from high strain dynamic pile testing data. CAPWAP® separates static and damping soil characteristics and also allows for an estimation of the side shear distribution and the pile’s end bearing. CAPWAP® is based on the wave equation model, which analyses the pile as a series of elastic segments and the soil as a series of elasto-plastic elements with damping characteristics, where the stiffness represents the static soil resistance and the damping represents the dynamic soil resistance. Typically the pile top force and velocity measurements acquired under high strain hammer impacts can be analyzed utilizing the signal matching procedure yielding forces and velocities over time and along the pile length. Using one pile top measurement which is easy to install and protected during pile driving from damage, recording both the downward stress

wave and upward stress wave, CAPWAP® alters the soil model to calculate and obtain a match with the complimentary wave.

What this program does is adjust the model of the surrounding soil originally entered by the person analyzing the data until the calculated results for the test match those measured. In other words, the model is adjusted until the signals match, and the program used for this analysis can be CAPWAP® or DLTWAVE or similar programs. All these programs have one thing in common: they help the person analyzing the test results in developing a possible solution. CAPWAP® models the pile into a number of segments, and by drill the segments downward into the soil, there are soil resistance activated because of the movement. Users who operate this program will have to give the information of pile properties, static soil resistance, soil quake and the soil damping ratio. Then by fitting the downward and upward waves transmitted in the pile which have been recorded by the PDA, CAPWAP® try to get the most possible forces and assume it is the real case. The calculated wave is compared to the measured wave, assigned a quantitative match quality, to increase the accuracy. So for this case, CAPWAP®’s results will not be exclusive. It depends on the experience of engineers to obtain a best wave match. It should be noticed that this program adjusts the model of the surrounding soil originally entered by the person analyzing the data until the calculated results for the test match those measured. It just helps the person analyzing the test in order to developing a possible solution. The final outcome is only a possible solution instead of the real solution, as there is no unique solution for this process. So it is highly possible that two engineers analyze the same data could lead to two totally different results. For that reason it is very important that people who run CAPWAP® should have

experience.

Figure 3-7. CAPWAP® analyze procedure

3.4.3 Dynamic Tests Recorded by SmartPile Review

SmartPile ReviewTM (EDC) also records dynamic forces when pile is driving into the soil. Through sensors embedded in the pile, the SmartPileTM system obtains accurate information on stress levels in a concrete pile from the moment it is cast. This provides the system with the unique ability to measure residual stresses during installation and provide an accurate assessment of the true conditions in the pile.

Multiple embedded sensors also collect accurate wave speed measurements, allowing a higher level of pile integrity monitoring. Consequently, accurate dynamic data on the shaft friction and tip resistance is available, so that an estimate of the ultimate static resistance (i.e. capacity of the pile) can be made. To enhance safety and ease of use, its patented design allows monitoring and recording of data from up to 500 feet from the pile, with no wires to connect. Powerful PC‐based software generates DOT‐formatted

reports, provides multi‐user access with password control, and allows data review from both current as well as past projects.

Figure 3-8. EDC software window

3.4.4 Wave Theory

When hammer hits the pile top, any point on pile has possibility of two waves passing up or down at any time. The passing waves will generate compression and tension forces in the pile, they are called the downward force (fd) and upward force (fu).

Fup = -Z Vup (-) = -Z (+)

Fup = -Z Vup Fd = Z Vdown F = -Z V F = Z V up up d d (+) = -Z (-) (-) = Z (-)

Figure 3-9. WaveUp and WaveDown Forces passing along the pile

Wave has its own velocity ( C = wave velocity), usually around 13000 ft/sec in concrete piles. It can be calculated by pile properties

C = sqrt (E /  ) (3-1) where E = pile elastic modulus;  = pile desity

Another velocity needed to be noticed is the particle velocity which is different from wave velocity. It can be measured directly from accelerometer, as it is the real velocity where the pile’s particle moves. Pile impedance Z is calculated from wave velocity

, Z = EA/C (3-2)

Where A is the pile cross-section’s area.

Compr ession C=Wave Speed = sqrt (E /  ) Wave V (particle velocity)

Downward Traveling Compression Downward Traveling Tension

Fd = Z Vd (+) = Z (+)

Figure 3-10. Wave travelling in the pile

As soon as collecting the field data after hammer blow, Data Acquisition System will supply operators with raw data as strain gage values and accelerometer. Pile total force (P) calculated from strain gage data is composed of two forces - Fd and Fu forces.

P =  E Across = Fd + Fup (3-3)

By integrating the acceleration, both particle velocity and pile movement can be reached:

VT =  a dt = Vd + Vup (3-4)

Where a = pile acceleration;

VT = pile total velocity; Vd = downward wave velocity; Vup = upward wave velocity

Also: P = Fd + Fup = Z Vd – Z Vup (3-5)

So wave passing up and Down pile a given point and time is calculated using the following two equations:

Fup = ( P – Z VT ) / 2 (3-6)

Since PDA and SmartPileTM Review are both dynamic testing equipment, total force contains static resistance ( Rs ) and dynamic resistance ( Rd ) showing in the following equation:

P = Rs + Rd (3-7)

And dynamic resistance is composed of damping force and inertial force. Damping is associated with particle velocity. Due to remolding effects, the major soil damping occurs at pile tip. SmartPile ReviewTM also installs a pair of strain gages and accelerometer at the pile tip, so it can directly calculate the total tip resistance:

Ptip = m a + c VT + K  (3-8)

Where Ptip = the total tip force measured from tip strain gage;

M = pile tip mass; a = tip acceleration measured from tip accelerometer; c = damping ratio; K = pile tip stiffness;  = pile tip movement, also measured from tip accelerometer.

3.4.5 Unloading Point Method

Full-scale testing can be an integral component of quality control/quality assurance for projects involving construction of deep foundations. Rapid load tests are being used in the deep foundation industry as a method for assessing the axial static behavior of deep foundations. Since rapid load tests involve dynamics, inertial and damping forces must be considered in analyzing measured pile response to estimate the static pile response.

The Statnamic load test is based on Newton’s second and third law, considering that force is equal to mass times acceleration. Every reaction has an equal and opposite reaction. Loads ranging from 5 tons to 5000 tons are generated by propelling a reaction mass upward off the foundation. The force associated with propelling of this mass acts equally and oppositely on to the pile. Statnamic load testing requires no reaction piles, no reaction beam,and no hydraulic jack. The statnamic device is set up on the pile top and includes a calibrated load cell and displacement measuring system. During a

Statnamic test, a high-speed data acquisition system scans and records the load cell, displacement transducers, accelerometers and embedded strain gages. Because the duration of the axial Statnamic test is adequately longer than the natural period of the foundation element, the foundation thus remains in compression. The measured

Statnamic force is not simply the pile capacity but including both inertia and damping forces.

Figure 3-11. Steps of Statnamic Test

Figure 3-12. Real field Statnamic Test

In the early years of Statnamic, a variety of methods were used to analyze the results, mostly leading to incorrect results. The Unloading Point Method (UPM) developed by Pter Middendorp in 1993 was a breakthrough in deciding pile capacity from Statnamic test. Now SmartPile ReviewTM, Statnamic and others employ the

“Unloading Point Approach” developed by Middendorp to assess static resistance from dynamic measurements. The approach uses force equilibrium and assumes that the

static resistance has reached a peak when the velocity trace passes through zero, going negative, resulting in small incremental displacements. For the force equilibrium equation:

Fstatic = Ftotal – ma – cv (3-9)

Where Fstatic = static pile resistance;

Ftotal = measured total Statnamic force (load cell); ma = measured inertia force; cv = soil damping force

For zero velocity, the damping force is zero and because the mass is known along with the applied dynamic force, the static resistance may be assessed [Ftotal – ma =

Fstatic ]. Subsequently, assuming that the static resistance is constant for later times, the damping is assessed based on force equilibrium. A major concern related to the approach is the assumption of constant Static resistance, Fstatic, when calculating viscous damping, c.

Figure 3-13. Statnamic measured load and calculated static force

CHAPTER 4 ENERGY METHOD

4.1 Theories of Energy Method

4.1.1 Newton's Three Laws of Motion

Before introducing energy method implemented in pile tip for accessing tip static resistance, it’s better to review Newton's Three Laws first which is the core of this brand new approach. They are three physical laws that form the basis for classical mechanics.

They describe the relationship between the forces acting on a body and its motion due to those forces. They have been expressed in several different ways over nearly three centuries, and can be summarized as follows:

(a) First law: Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force. This means that in the absence of a non-zero net force, the center of mass of a body either remains at rest, or moves at a constant speed in a straight line.

(b) Second law: A body of mass m subject to a force F undergoes an acceleration a that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass, i.e., F = ma. Alternatively, the total force applied on a body is equal to the time derivative of linear momentum of the body.

(c) Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear. This means that whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction. This law is sometimes referred to as the action- reaction law, with F called the "action" and −F the "reaction". The action and the reaction are simultaneous.

For the pile tip model, the body is the pile mass under the strain gages, all the forces are acted to the pile mass. The pile tip obeys Newton's Three Laws of Motion at any time during the pile driving.

4.1.2 Force and Energy Equilibrium

Focusing on the tip mass, the only unknowns at the pile tip are m (mass), c

(viscous damping) and k (stiffness). In physics and engineering, damping may be mathematically modeled as a force synchronous with the velocity of the object but opposite in direction to it. If such force is also proportional to the velocity, as for a simple mechanical viscous damper (dashpot), the force F may be related to the velocity v by

F = c v (4-1)

where c is the viscous damping coefficient, given in units of Newton-seconds per meter. This force is an approximation to the friction caused by drag. Generally, damped harmonic oscillators satisfy the second-order differential equation:

(4-2)

where ω0 is the undamped angular frequency of the oscillator and ζ is a constant called the damping ratio. For a mass on a spring having a spring constant k and a damping coefficient c,

(4-3) and

(4-4)

The value of the damping ratio ζ determines the behavior of the system. A damped harmonic oscillator can be:

(a) Overdamped (ζ > 1): The system returns (exponentially decays) to equilibrium without oscillating. Larger values of the damping ratio ζ return to equilibrium slower.

(b) Critically damped (ζ = 1): The system returns to equilibrium as quickly as possible without oscillating. This is often desired for the damping of systems such as doors.

(c) Underdamped (ζ < 1): The system oscillates (with a slightly different frequency than the undamped case) with the amplitude gradually decreasing to zero.

The damped natural (angular) frequency ωd, i.e., the frequency the oscillation occurs when the system is underdamped (ζ < 1) and under free vibration, with regards to the damping factor ζ and the undamped natural (angular) frequency ω0 is given by:

(4-5)

Back to the tip model, generally m may be assumed as the mass of pile below the tip gages. The stiffness, k, of a body is a measure of the resistance offered by an elastic body to deformation. Stiffness is the resistance of an elastic body to deformation by an applied force along a given degree of freedom (DOF) when a set of loading points and boundary conditions are prescribed on the elastic body. For an elastic body with a single Degree of Freedom (for example, stretching or compression of a rod), the stiffness is defined as:

(4-6)

Where: F is the force applied on the body;

δ is the displacement produced by the force along the same degree of freedom

(for instance, the change in length of a stretched spring).

In the International System of Units, stiffness is typically measured in newtons per metre. In English Units, stiffness is typically measured in pound force (lbf) per inch.

However, the stiffness, k, is generally not constant (i.e. nonlinear, varies with displacement) and the damping, c is assumed a constant. Assessing c and the variable k at the pile tip uses force equilibrium, or

F m x  F c x  F k x  Pt inertia damping static (4-7)

which must be satisfied for any time.

Figure 4-1. Mass-Spring-Damper model

A major improvement of the “Unloading Point Approach” which conserves force equilibrium is to also conserve energy or work of the single degree of freedom system.

For the typical dynamic pile problem, the energy going into the system may be

assessed by the Force measured by tip EDC strain gage and accelerometer. The input energy must be balanced by the inertia, damping and static energy that occurs as result of tip acceleration, or

m x  c x  k xdx  Ptdx   (4-8)

Where x is displacement and is velocity and is acceleration.

To assist with the implementation of the integration as well as improve accuracy

(accelerometer measurements), the integration variable can be changed to time (Liang

& Feeny, 2006) or,

tT tT  m x  c x  k xx dt   Ptx dt t t (4-9)

4.1.3 Process of Energy Method

To perform energy method, first thing needed is to generate SmartPile ReviewTM’s raw data sheet of each blow. As the figure shown below, SmartPile ReviewTM can provide users with pile information such as pile number, blow number, modulus of elastic and so on, as well as simultaneous measured driven information such as top/tip force, top/tip acceleration and so on.

Figure 4-2. Excel data sheet from SmartPile Review of one blow

Figure 4-3. Excel configuration sheet from SmartPile Review

SmartPile ReviewTM generates excel sheet containing pile information

(configuration sheet), raw data (data sheet) for each blow. Energy method exerts these two sheets to calculate parameters and finally plots each force.

Figure 4-4. Excel sheet from Energy Method 1

From Figure 4-4, C1 labeled Wt (kips) is pile weight, divided by B1 refered to g

(ft/s2) can get D1 which is pile mass M ( kips-s2/ft), that is used to calculate damping force. G1, H1 and I1 are stiffness coefficient, reflecting pile tip static resistance is changing along with time. Cells A5 to I21 are data copied from SmartPile ReviewTM’s raw data.

Figure 4-5. Excel sheet from Energy Method 2

From Figure 4-5, it shows all the forces calculated using the raw data from Figure

4-4. As mentioned before, forces acting on the pile tip model are forces input from hammer (in the energy method sheet, it is directly got from SmartPile ReviewTM called tip force), damping force (Column M, equals to velocity times damping ratio), static tip force (Column L, equals to stiffness times tip mass), inertia force (Column K, equals to acceleration times tip mass). From Column Q to Column T, they are energy measured from each force. Except for force equilibrium, another equilibrium of pile tip is energy balance. After calculating all these forces, it’s ready to draw all the forces or energy together and minimize the error force/energy.

To see an example of the approach consider EDC Blow 777 (Figure 4-6) which was a restrike blow after static load test on Dixie Highway Pier 8. The Purple line is the applied force, P(t) (Equation.4-7), dark blue is inertia force, Finertia,(Equation.4-7). The damping force, Fdamping, was found by multiply a viscous damping, c, 30 kip-sec/ft by the measured tip velocity. The static resistance, FStatic, (Equation.4-7) was found by multiplying a tangent stiffness, k, by tip displacement, Figure 4-6.

Figure 4-6. EDC Blow 777 Forces vs. Time at Pile Tip of Pier 8

The assessment of c and k begins where the damping and inertia forces are zero

(blue and green lines) in Figures 4-6 (at 0.175 sec 0.023sec and 0.0314sec) and 32 (at

0.0359 ft, 0.0523 ft and 0.0693 ft). For these times and displacements the applied force,

P(t) must equal the static resistance, Fstatic, from equilibrium eq.4-7. Knowing the Fstatic, the value of tangent stiffness, k may be assessed (slopes of red line Figure 4-6). Finally, the value of the viscous damping, c (30 kip-sec/ft) may be determined through the energy balance at the pile tip from Equation 4-9. Shown in Figure 4-8 is the computed energy for each component (applied, inertia, damping, and stiffness) as well as the error

(Eapplied – Einertia – Edamping – Estatic).

Figure 4-7. EDC Blow 777 Forces vs. Displacement at Pile Tip of Pier 8

Evident from the new energy plot (Figure 4-7), the inertia component is small and dies out with time. This is because the pile tips generally undergo significant harmonic motion (i.e. positive and negative motion – Figure 4-6). Consequently, the static energy plus the damping energy must equal the applied energy (Figure 4-8) especially for later times. Since points on the static force vs. displacements are known (Equilibrium), the viscous damping coefficient may be very accurately assessed.

The new combined Equilibrium and Energy Balance Equations at the pile tip results in very accurate assessment of the nonlinear static resistance vs. displacement

(Figure 4-7) at the bottom of the pile. Based on Figure 4-7, the static tip resistance at

0.07 ft (0.84 in) was 320 kips or 160 tons. The latter compares very favorably with the

measured static tip resistance of 336 kip at 0.9 in of movement.

Figure 4-8. EDC Blow 777 Energy vs. Time at Pile Tip of Pier 8

Another example here is blow 779 of Dixie Highway Pier 8, which also shows energy method performs well.

Figure 4-9. EDC Blow 779 Forces vs. Time at Pile Tip of Pier 8

Figure 4-10. EDC Blow 779 Forces vs. Displacement at Pile Tip of Pier 8

Figure 4-11. EDC Blow 779 Energy vs. Time at Pile Tip of End Bent1

4.1.4 Examples of Energy Method

Figures 4-12 to 4-29 below are examples using energy method. First example shown is blows analyzed from Dixie Highway Project.

4.1.4.1 Site ---- Dixie Highway

Introduction: Dixie Highway (CR-818) from South of Hillsboro Boulevard (SR-810) to North of the Hillsboro Canal (Design-build Project). Pile End Bent NO.1 and Pier

NO.8 have been performed with compression load test, Pier NO.4 has been performed with tension load test. Test pile installation work at the above referenced site was performed by Cone and Graham, Inc.

4.1.4.1.1 Compression load test – End Bent NO.1

Test Pile Installation: One 24-inch-square prestressed precast concrete compression test pile at End Bent Number 1 was installed about 45 feet below the ground surface at a non-production pile location on April 21, 2010. The pile was driven using and ICE (I-46), single acting diesel hammer.

Pile Load Test: The compression test pile was load tested to failure in accordance with ASTM D1143 (quick test). The load was applied against a frame anchored by four, 24-inch-diameter Auger Cast In-Place (ACIP) reaction piles.

Test pile deflection were monitored using: 1) dial gauges with accuracy of 0.001 inch, 2) piano wire 1/64 scale system, and 3) a survey level to read scale with accuracy of 1/64 inch attached to the tension test pile.

Compression loads were applied using two 500 ton hydraulic jacks. Cone and

Graham, Inc. set-up the load test reaction frames, provided the pre-calibrated jack, reference beams, pumps, and necessary personnel to run the equipment.

Compression Load Test Results: The compression load test was performed on

April 29, 2010. The test loads were applied in two cycles. The pile was loaded in 45 ton increments to the maximum load of 298 tons for the first cycle. Each load was held for at least 10 minutes. The maximum gross pile butt deflection, under the maximum test load of 298 tons after 10 minutes of sustained loading, measured 1.78 inch. The pile was subsequently unloaded in 90 ton decrements. For the second cycle, the pile was again loaded in 45 ton increments to a maximum load of 317 tons. Each load was held for at least 5 minutes. The maximum gross pile butt deflection, under the maximum test load of 317 tons after 5 minutes of sustained loading, measured 2.97 inch. The pile was subsequently unloaded in 90 ton decrements. The result of this load test is summarized in the attached Compression Load Vs Settlement plot.

Geokon 4911 vibrating wire sister-bar strain gauges were installed in the compression test pile. Eight (8) strain gauges were installed at four levels within the pile.

Two (2) strain gauges were installed at each level. The strain gauges were installed to monitor under the applied loads. This data was used to infer load transfer along the test pile. Based on the strain gauge data, at the maximum test load of 298 tons, about 77 percent of the load was transferred to the bottom of the pile. But temperature corrections and gage factors have not been applied while utilizing the strain gage data, and therefore, these load distribution values should not be taken as absolute values.

Figures 4-12 to 4-14 shown below are energy method performed on blow 740 which is one of end of driving blows. As pile set-up occurs, comparing the EOD and

BOR blows’ tip resistance and skin friction could reveal some information of how much these capacities change.

Figure 4-12. EDC Blow 740 Energy vs. Time at Pile Tip of End Bent1

Figure 4-13. EDC Blow 740 Forces vs. Displacement at Pile Tip of End Bent1

Figure 4-14: EDC Blow 740 Energy vs. Time at Pile Tip of End Bent1

Blow 765 was driven one week later, which is BOR of Dixie High End Bent1.

Figure 4-15. EDC Blow 765 Energy vs. Time at Pile Tip of End Bent1

Figure 4-16. EDC Blow 765 Forces vs. Displacement at Pile Tip of End Bent1

Figure 4-17. EDC Blow 765 Energy vs. Time at Pile Tip of End Bent1

For Dixie highway End Bent1, 10 re-strike blows just before and after the load test for comparison with one another as well as with the measured static tip resistance from the load test. The specific results of one of the re-strike blow are presented here in detail for discussion. Energy method performed for other 9 blows will be presented in

Apendix A.

4.1.4.1.2 Compression load test – Pier NO.8

Test pile installation: One 24-inch-square prestressed precast concrete compression test pile at Pier Number 8 was installed about 49 feet below the ground surface at a non-production pile location on May 6, 2010. The pile was driven using an

ICE (I-46), single acting diesel hammer.

Pile Load Test: The compression test pile was load tested to failure in accordace with ASTM D1143 (quick test). The load was applied against a frame anchored by four,

24-inch-diameter Auger Cast In-Place (ACIP) reaction piles.

Test pile deflections were monitored using: 1) dial gauges with accuracy of 0.001 inch, 2) piano wire 1/64 scale system, and 3) a survey level to read scale with accuracy of 1/64 inch attached to the hydraulic jack.

Compression loads were applied using two 500 ton hydraulic jackes. Cone and

Graham, Inc. set-up the load test reaction frames, provided the pre-calibrated jack, reference beams, pumps, and necessary personnel to run the equipment.

Compression Load Test Results: The compression load test was performed on

May 12, 2010. The test loads were applied in two cycles. The pile was loaded in 45 ton increments to the maximum load of 255 tons for the first cycle. Each load was held for at least 10 minutes. The maximum gross pile butt deflection, under the maximum test load of 255 tons after 10 minutes of sustained loading, measured 1.69 inch. The pile

was subsequently unloaded in 90 ton decrements. For the second cycle, the pile was again loaded in 45 ton increments to a maximum of 285 tons. Each load was held for at least 5 minutes. The maximum gross pile butt deflection, under the maximum test load of 285 tons after 5 minutes of sustained loading, measured 3.12 inch. The pile was subsequently unloaded in 90 ton decrements.

Geokon 4911 vibrating wire sister-bar strain gauges were installed in the compression test piles, Eight (8) strain gauges were installed at four levels within the pile. Two (2) strain gauges were installed at each level. The strain gauges were installed to monitor the strain at different depths within the pile under the applied loads.

This data was used to infer load transfer along the test pile. Based on the strain gauge data, at the maximum test load of 255 tons, about 65% of the load appeared to be transferred to the bottom of the pile.

Figures 4-18 to 4-21 shown below are energy method performed on blow 751 which is end of driving blows.

Figure 4-18. EDC Blow 751 Forces vs. Time at Pile Tip of Pier 8

Figure 4-19. EDC Blow 751 Forces vs. Displacement at Pile Tip of Pier 8 Pile

Figure 4-20. EDC Blow 751 Energy vs. Time at Pile Tip of End Bent1

Blow 779 was driven five days later which is BOR of Dixie High End Bent1.

Figure 4-21. EDC Blow 779 Forces vs. Time at Pile Tip of Pier 8 Pile

Figure 4-22. EDC Blow 779 Forces vs. Displacement at Pile Tip of Pier 8

Figure 4-23. EDC Blow 779 Energy vs. Time at Pile Tip of Pier 8

4.1.4.2 Site – Caminada Bay

Caminida Bay is in Louisiana, 70 km south of New Orleans. The site consists of 10 m of silty fine sand with clay (SPT N ~ 14) followed by 10 m of fine sand with silt (SPT N

~ 24); and high plasticity (40 < PI < 70) clays. The first pile (pile 1) analyzed was a 0.76- m-quare precast prestressed concrete pile driven 21 m below the ground surface (1m into clay) using a single acting diesel hammer. Re-strikes were conducted 7 days after installation, and the static compression load test was conducted 2 days after the restrikes.

Figures 4-24 to 4-26 below show blow 630 which is beginning of drive at Caminida

Bay Bent1.

Figure 4-24. EDC Blow 630 Forces vs. Time at Pile Tip of Caminida Bay Bent1 Pile1

Figure 4-25. EDC Blow 630 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1 Pile1

Figure 4-26. EDC Blow 630 Energy vs. Time at Pile Tip of Caminida Bay Bent1 Pile1

Figure 4-27. EDC Blow 660 Forces vs. Time at Pile Tip of Caminida Bay Bent1 Pile1

Figure 4-28. EDC Blow 660 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1 Pile1

Figure 4-29. EDC Blow 660 Energy vs. Time at Pile Tip of Caminida Bay Bent1 Pile1

CHAPTER 5 OBSERVATIONS OF ENERGY APPROACH

5.1 EOD vs. BOR Predicted Static Response of Dixie Highway

The predicted tip resistance for both EOD and BOR blows are shown below respectively. Figure 5-1 represents the static tip resistance for 5 blows at EOD and figure 5-2 are for 5 restrike blows ( BOR ), also combined with static load test result.

Figure 5-1. Estimated tip resistance of Dixie Highway Bent 1 Pile1 blows before the load test. Photo courtesy of Yipeng Xie

Figure 5-2. Estimated tip resistance of Dixie Highway Bent 1 Pile1 blows after the load test. Photo courtesy of Yipeng Xie

Figure 5-3. Estimated tip resistance of Dixie Highway Pile8 blows before the load test

Figure 5-4. Estimated tip resistance of Dixie Highway Pile8 blows after the load test

5.2 EOD vs. BOR Predicted Static Response of Caminida Bay

Next is the predicted tip resistance for both EOD and BOR blows of Caminida Bay respectively. Figure 5-5 represents the static tip resistance for 3 blows at EOD and figure 5-6 are for 5 restrike blows ( BOR ), also combined with static load test result.

Figure 5-5. Estimated tip resistance of Caminida Bay1 blows before the load test

Figure 5-6. Estimated tip resistance of Caminida Bay1 blows after the load test

Figure 5-7. Estimated tip resistance of Caminida Bay7 blows before the load test

Figure 5-8. Estimated tip resistance of Caminida Bay7 blows after the load test

To better compare the static load test results with estimated tip resistance, it is necessary to calculate Davisson’s Capacity first, to see how much displacement the pile tip moves under such load. Davisson method is a graphical method which defines the pile capacity as that load corresponding to the movement which exceeds the elastic compression of the pile by a value of 0.15 inches plus a factor equal to the diameter of the pile ( in inches ) divided by 120. Figures 5-9 to 5-12 below are Davisson’s capacity found in each pile:

Figure 5-9. Davisson’s Capacity of Dixie Highway Bent1 Pile1

Figure 5-10. Davisson’s Capacity of Dixie Highway Pier8

Figure 5-11. Davisson’s Capacity of Caminida Bay Bent1

Figure 5-12. Davisson’s Capacity of Caminida Bay Bent7

From Figure 5-1 to Figure 5-8 it is observed that the estimated tip resistances compares very favorable to the load test results. When calculating Davisson’s capacity on the static load test, it is found that pile tip movement is about 0.3 to 0.5 ft, less than the maximum observed displacement which is around 0.5 to 0.8 ft. For Dixie Highway

End Bent1 and Pier 8, in the displacement range of Davisson’s capacity movement, estimated tip resistance compares favorably to the load test. Dixie Highway End Bent1 the two capacities are around 300 kips, and Dixie Highway Pier8 they are about 220 kips. In the case of Caminida Bay, both beginning of drive blows compares favorably to the static load test. For Caminida Bay Bent1 they are both around 180 kips, for

Caminida Bay Bent 7 they are around 80 kips.

Considering pile freeze occurred after EOD, comparison of EOD and BOR blows for the Dixie Highway piles were not considered as the static load test used augured cast piles at 3D spacing from the tested piles which may have influenced the results between EOD and BOR. Refer to Caminida Bay piles, tip resistance of Bent1 piles drops 10%, Bent7 increases 20%. The increase in tip resistance may be associates with pile freeze, which is due to the dissipation in pore water pressure in clay soils.

Another interesting behavior between EOD and BOR tip response is shown in

Figures 5-13, 5-14, and 5-15 for the case of Florida Department of Transportation

Design Build US192 over I-95 (24”x24” x 105ft), and Figures 5-16, 5-17, and 5-18 for the case of Florida Department of Transportation I-95 Eau Gallie bent1 pile1. Figure 5-

13 shows five EOD blows analyzed with force/energy tip approach. From the figure 5-

13, EOD shows 400 kips of end bearing at 0.04 ft (0.48”) of tip movement.

Subsequently, after 2 days the pile was restruck, and Figure 5-14 shows the measured

BOR response for 5 blows. The restrike analysis shows a mobilized tip resistance of

300 kips at 0.025 ft (0.3 in). Notice, the maximum tip movement of the BOR blows are smaller (0.3”) vs. the EOD value (0.48”). A comparison of the mean EOD vs. mean BOR tip resistance is given in Figure 5-15. Evident of from figure 5-15, the EOD and BOR stiffness are quite similar, but the difference in tip resistance is due to the mobilized tip displacements. A possible explanation of the different mobilized displacement at EOD vs BOR strikes may be due to the rated energy of the hammer and the fact that the same hammer and energy is being delivered to the pile for the EOD and BOR blows.

However, in the case of EOD driving, there is a loss of skin friction (i.e. excess pore pressure, etc.) and more of the hammer energy arrives at the pile tip, mobilizing more

tip displacement and resistance, Figure 5-13. After 2 day wait time, pile freeze occurs, and the same hammer delivers the same energy to the BOR blows; however more of it is dissipated in mobilizing skin friction and less arrives at the pile tip to mobilize tip resistance, Figure 5-14. Another example of this effect is shown from the FDOT EDC database of Eau Gali Bridge on I-95 in Figure 5-18 for mean EOD and BOR (18 days) resistances. Again, the tip resistance of pile at EOD went from 280 kips at 0.043ft (0.5”) to 180 kips at 0.025 ft (0.3”) for the 18 day BOR restrikes. Obviously for the US 192 and

Eau Gali Bridge over I-95, the BOR blows may not identify the full Davisson capacity, if movements greater 0.025 ft (0.3”) are needed. To address the latter, the recent NCHRP

Synthesis Report “Developing Production Pile Driving Criteria from Test Pile Data,” has suggested using predicted tip resistance at EOD with the skin friction assessed from

BOR blows. Of course, this assumes that same error in predicting total capacity applies to estimation of skin or tip resistance. With tip monitoring and proposed force/energy analysis the latter may be viable.

Figure 5-13. Predicted Tip Resistance at EOD for pile 5 at US 192

Figure 5-14. Predicted Tip Resistance at BOR after 2 days for pile 5 at US 192

Figure 5-15. Predicted Tip Resistance at EOD and BOR for pile 5 at US 192

Figure 5-16. Predicted Tip Resistance at EOD of I95 Eau Gallie bent1 pile1

Figure 5-17. Predicted Tip Resistance at BOR of I95 Eau Gallie bent1 pile1

Figure 5-18. Predicted Tip Resistance at EOD and BOR I95 Eau Gallie bent1 pile1

Tables below are summation of each pile’s tip resistance calculated by energy method and total capacity recorded by SmartPile ReviewTM.

Table 5-1. EOD and BOR Tip Forces of Dixie Highway Pile No. Energy UF method UF method Pile No. Energy UF method UF method Method Tip Total Method Tip Total Static Tip Resistance Capacity Static Tip Resistance Capacity Resistance (kips) (kips) Resistance (kips) (kips) (kips) (kips) Dixie 300 350 449 Dixie Highway 177 250 522 Highway End Pier 8 Bent 1 Blow No. 754 Blow No. 740 Dixie 331 374 447 Dixie Highway 228 273 505 Highway End Pier 8 Bent 1 Blow No. 755 Blow No. 741 Dixie 305 405 456 Dixie Highway 243 270 471 Highway End Pier 8 Bent 1 Blow No. 756 Blow No. 742

Table 5-1. Continued Pile No. Energy UF method UF method Pile No. Energy UF method UF method Method Tip Total Method Tip Total Static Tip Resistance Capacity Static Tip Resistance Capacity Resistance (kips) (kips) Resistance (kips) (kips) (kips) (kips) Dixie 260 398 436 Dixie Highway 176 300 454 Highway End Pier 8 Bent 1 Blow No. 758 Blow No. 743 Dixie 300 395 434 Dixie Highway 229 290 432 Highway End Pier 8 Bent 1 Blow No. 759 Blow No. 744 Dixie 300 410 482 Dixie Highway 194 410 430 Highway End Pier 8 Bent 1 Blow No. 777 Blow No. 760 Dixie 280 450 450 Dixie Highway 240 418 425 Highway End Pier 8 Bent 1 Blow No. 778 Blow No. 765 Dixie 273 406 437 Dixie Highway 256 400 403 Highway End Pier 8 Bent 1 Blow No. 779 Blow No. 778 Dixie 308 438 438 Dixie Highway 226 383 416 Highway End Pier 8 Bent 1 Blow No. 780 Blow No. 779 Dixie 280 425 425 Dixie Highway 267 340 451 Highway End Pier 8 Bent 1 Blow No. 801 Blow No. 780 Time interval between EOD and BOR of Dixie Highway End Bent 1 is 12 days. Time interval between EOD and BOR of Dixie Highway Pier 8 is 8 days.

Table 5-2. EOD and BOR Tip Forces of Caminida Bay Energy UF method UF method Pile No. Energy UF method UF method Method Tip Total Method Tip Total Pile No. Static Tip Resistance Capacity Static Tip Resistance Capacity Resistance (kips) (kips) Resistance (kips) (kips) (kips) (kips) Caminida Bay 172 233 567 Caminida Bay 60 139 422 Bent1 Pile1 Bent 7 Blow No. 625 Blow No. 313 Caminida Bay 171 192 584 Caminida Bay 51 76 367 Bent1 Pile1 Bent 7 Blow No. 629 Blow No. 315 Caminida Bay 170 210 582 Caminida Bay 60 57 355 Bent1 Pile1 Bent 7 Blow No. 630 Blow No. 316

Table 5-2. Continued Energy UF method UF method Pile No. Energy UF method UF method Method Tip Total Method Tip Total Pile No. Static Tip Resistance Capacity Static Tip Resistance Capacity Resistance (kips) (kips) Resistance (kips) (kips) (kips) (kips)

Caminida Bay 185 67 585 Caminida Bay 60 53 352 Bent1 Pile1 Bent 7 Blow No. 660 Blow No. 317 Caminida Bay 210 70 595 Caminida Bay 54 58 362 Bent1 Pile1 Bent 7 Blow No. 661 Blow No. 318 Caminida Bay 192 60 573 Caminida Bay 70 44 502 Bent1 Pile1 Bent 7 Blow No. 664 Blow No. 331 Caminida Bay 190 30 530 Caminida Bay 60 57 539 Bent1 Pile1 Bent 7 Blow No. 665 Blow No. 336 Caminida Bay 195 40 502 Caminida Bay 62 43 539 Bent1 Pile1 Bent 7 Blow No. 666 Blow No. 343 Caminida Bay 80 45 538 Bent 7 Blow No. 345 Caminida Bay 60 75 499 Bent 7 Blow No. 350 Time interval between EOD and BOR of Caminida Bay Bent1 Pile1 is 6 days. Time interval between EOD and BOR of Caminida Bay Bent 7 is 7 days.

Table 5-3. EOD and BOR Tip Forces of I-95 DEsign Build US 192 bent3 pile5 & I-95 Eau Gallie bent1 pile1 Energy Energy Method Energy Energy Method Static Tip Method Method Pile No. Static Tip Pile No. Resistance Pile No. Static Tip Pile No. Static Tip Resistance (kips) Resistance Resistance (kips) (kips) (kips) I95 DEsign Build 270 I95 DEsign Build 287 I95 Eau Gallie 160 I95 Eau Gallie 202 US 192 bent3 US 192 bent3 pile5 bent1 pile1 bent1 pile1 pile5 Blow No. 972 Blow No. 1694 Blow No. 1716 Blow No. 953 I95 DEsign Build 258 I95 DEsign Build 300 I95 Eau Gallie 160 I95 Eau Gallie 200 US 192 bent3 US 192 bent3 pile5 bent1 pile1 bent1 pile1 pile5 Blow No. 973 Blow No. 1696 Blow No. 1717 Blow No. 954

Table 5-3. Continued Energy Energy Method Energy Energy Method Static Tip Method Method Pile No. Static Tip Pile No. Resistance Pile No. Static Tip Pile No. Static Tip Resistance (kips) Resistance Resistance (kips) (kips) (kips) I95 DEsign Build 270 I95 DEsign Build 288 I95 Eau Gallie 167 I95 Eau Gallie 203 US 192 bent3 US 192 bent3 pile5 bent1 pile1 bent1 pile1 pile5 Blow No. 976 Blow No. 1700 Blow No. 1719 Blow No. 956 I95 DEsign Build 270 I95 DEsign Build 300 I95 Eau Gallie 178 US 192 bent3 US 192 bent3 pile5 bent1 pile1 pile5 Blow No. 977 Blow No. 1702 Blow No. 960 Time interval between EOD and BOR of I95 DEsign Build US 192 bent3 pile5 is 2 days. Time interval between EOD and BOR of I95 Eau Gallie bent1 pile1 is 7 days.

Table 5-4. EOD and BOR Tip Forces Comparison Energy Energy Static Tip Energy Energy Static Tip Method Method Resistance Method Method Resistance Pile No. Pile No. Static Tip Static Tip Increase Static Tip Static Tip Increase Resistance Resistance Resistance Resistance EOD (kips) BOR (kips) (kips) (kips) Dixie Highway N/A N/A N/A I95 DEsign 267 290 8.61% End Bent 1 Build US 192 bent3 pile5 Dixie Highway N/A N/A N/A I95 Eau Gallie 166.5 197.5 18.61% Pier 8 bent1 pile1 Caminida Bay 171 194 13.45% US1 over St 196 217 10.70% Bent1 Pile1 Sebastian River I75 Bent2 Pile2 Caminida Bay 57 66.4 16.4% SR21 over 250 300 20% Bent 7 Black Creek Bent5 Pile6

Table 5-5. EOD and BOR Skin Friction Comparison

Skin Skin Skin Friction Skin Friction Skin Friction Skin Friction Pile Pile No. Friction Friction Increase EOD (kips) BOR (kips) Increase No. EOD BOR (kips) (kips) Dixie N/A N/A N/A I95 DEsign 251 377.33 50.33% Highway Build US 192 End Bent 1 bent3 pile5 Dixie N/A N/A N/A I95 Eau Gallie 311.5 562.5 80.51% Highway bent1 pile1 Pier 8 Caminida N/A N/A N/A US1 over St N/A N/A N/A Bay Bent1 Sebastian River Pile1 I75 Vanderbilt Bent2 Pile2 Caminida 314.6 457 45.2% SR21 over N/A N/A N/A Bay Bent 7 Black Creek Bent5 Pile6

CHAPTER 6 CONCLUSION

6.1 Summary

In this study, a completely new method of assessing pile tip static resistance called energy method has been raised, and by given different test sites for investigation, energy method is proved to be feasible and efficient. Advantages of this method are obvious:

It could be done by researchers manually. It based on excel sheet and easy to learn. The more experience researcher gains, the shorter operating time it takes. Or, it also could be done automatically by computer once the coding is finished.

Energy method’s results are shown both in the format of numbers and figures, researchers can read the forces directly from plots without confusion.

Comparing to static load test, dynamic test is convenient and less cost. To get static tip resistance from dynamic test is always reseachers’ preference. Energy method uses the data collected from dynamic testing, providing with a guaranteed static tip force.

As the theories of energy method is force equilibrium and energy equilibrium, and those equilibrium should be satisfied any time of driving, this method could be applied at each blow, which means it can calculated static tip resistance either from EOD or BOR.

As pile set-up observed and validated from more and more researchers nowadays, energy method’s finding can lead to a deeper understanding of it. From the piles analysed using energy method, static tip resistance seem not to change very much compared to the skin friction, which most geotechnical researchers agree that is the main reason contributing to the increase of the pile total capacities. Although pile set-

up’s mechanism is still under investigating, results from energy method can provide some clues of assessing the set-up factor. What we choose here is blows from EOD and BOR period, usually the time interval between these two phases are several days long. So it guarantees most of the pile set-up will develop during this time interval. At the same time, the time when hammer stops hitting is less than one hour is also considered, and pile set-up is still observed for most cases. Data performed with energy method compared to static load test results are quite agreeable, which means this method could be used in future studies.

6.2 Recommendations

For this thesis energy method’s raw data sources are all from SmartPile

ReviewTM’s excel sheets. PDA nowadays is common dynamic testing equipment around

America, so performing energy method with PDA’s outputs will be put into consideration. Also, to accelerate the calculation, computer automatically run will surely reduce the time cost, and also provide with more standardized results.

APPENDIX A EXAMPLES OF ENERGY METHOD

Figure A-1. EDC Blow 740 Forces vs. Time at Pile Tip of Dixie Highway Bent1

Figure A-2. EDC Blow 740 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1 Pile1

Figure A-3. EDC Blow 740 Energy vs. Time at Pile Tip of Caminida Bay Bent1 Pile1

Figure A-4. EDC Blow 778 Forces vs. Time at Pile Tip of Dixie Highway Bent1

Figure A-5. EDC Blow 778 Forces vs. Disp. at Pile Tip of Dixie Highway Bent1

Figure A-6. EDC Blow 778 Energy vs. Time at Pile Tip of Dixie Highway Bent1

Figure A-7. EDC Blow 756 Forces vs. Time at Pile Tip of Dixie Highway Pier8

Figure A-8. EDC Blow 756 Forces vs. Disp. at Pile Tip of Dixie Highway Pier8

Figure A-9. EDC Blow 756 Energy vs. Time at Pile Tip of Dixie Highway Pier8

Figure A-10. EDC Blow 779 Forces vs. Time at Pile Tip of Dixie Highway Pier8

Figure A-11. EDC Blow 779 Forces vs. Disp. at Pile Tip of Dixie Highway Pier8

Figure A-12. EDC Blow 779 Energy vs. Time at Pile Tip of Dixie Highway Pier8

Figure A-13. EDC Blow 625 Forces vs. Time at Pile Tip of Caminida Bay Bent1

Figure A-14. EDC Blow 625 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1

Figure A-15. EDC Blow 779 Energy vs. Time at Pile Tip of Dixie Highway Pier8

Figure A-16. EDC Blow 660 Forces vs. Time at Pile Tip of Caminida Bay Bent1

Figure A-17. EDC Blow 660 Forces vs. Disp. at Pile Tip of Caminida Bay Bent1

Figure A-18. EDC Blow 660 Energy vs. Time at Pile Tip of Caminida Bay Bent1

Figure A-19. EDC Blow 313 Forces vs. Time at Pile Tip of Caminida Bay Bent7

Figure A-20. EDC Blow 313 Forces vs. Disp. at Pile Tip of Caminida Bay Bent7

Figure A-21. EDC Blow 313 Energy vs. Time at Pile Tip of Caminida Bay Bent8

Figure A-22. EDC Blow 313 Forces vs. Time at Pile Tip of Caminida Bay Bent7

100

Figure A-23. EDC Blow 313 Forces vs. Disp. at Pile Tip of Caminida Bay Bent7

Figure A-24. EDC Blow 313 Energy vs. Time at Pile Tip of Caminida Bay Bent7

101

LIST OF REFERENCES

Airhart, T.P., Hirsch, T.J., and Coyle, H.M. (1967). “Pile-soil system response in clay as a function of excess pore water pressure and other soil properties.” Research Rep. No. 33-8. Texas Transportation Institute, Texas A&M Univ., College Station, Tex.

Axelsson, G. (1998). “Long term set-up of driven piles in non-cohesive soilsevaluated from dynamic tests on penetration rods.” Proceedings of the First International Conference on Site Characterization. P.K. Robertson and P.W Mayne, eds., Balkema, Brookfield, VT, 2, 895-900.

Bartolomey, A.A. and Yushkov, B.S. (1985). “Variation in time of capacity of pile foundation in clays.” Proceedings of the Eleventh International Conference on Soil Mechanics and Foundation Engineering. Balkema, Brookfield, VT, 3, 1517 – 1520.

Bullock Paul J., P.E., M. ASCE “The Easy Button for Driven Pile Setup: Dynamic Testing” pp. 471-488, (doi 10.1061/40962(325)17).

Camilo Alvarez, Brian Zuckerman, and John Lemke, “Dynamic Pile Analysis Using CAPWAP and Multiple Sensors.”

Chow, F.C., Jardine, R.J., Brucy, F., and Nauroy, J.F. (1996). “The effect of overburden on pile capacity in a calcareous marl.” Proc., 18th Annual Members’ Conf., Deep foundation Institute, Englewood Cliffs, N.J.

Chow, F.C., Jardine, R.J., Brucy, F., and Nauroy, J.F. (1998). “Effects of time on the capacity of pipe piles in dense marine sand.” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Reston, VA, 124(3), 254-264.Federation of Piling Specialists Handbook on Pile Load Testing.

Kehoe, S.P. (1989). “An analysis of time effect on the bearing capacity of driven piles,” Master Thesis, Department of Civil Engineering, University of Florida, Gainesville, FL.

Lukas, R.G. and Bushell, T.D. (1989). “Contribution of pile freeze to pile capacity”, Proceeding of the Congress, Foundation Engineering: Current Principles and Practices. Kulhawy, F.H., editor, ASCE, Reston, VA, 2, 991- 1001.

Majboor, B.M. (1996). “Evaluation of time effects on skin resistance from dynamic and static pile data analysis.” Master Thesis. Department of Civil Engineering, University of Florida, Gainesville, FL.

McVay, M.C., David Bloomquist, “Analyses of Embedded Data Collector (EDC)”, Final Report, Department of Civil and Coastal Engineering University of Florida.

102

McVay, M.C.,David Bloomquist, “Embedded Data Collector (EDC) Evaluation Phase II” Progress Report 3, Department of Civil and Coastal Engineering University of Florida.

McVay, M.C., Schmertmann, J. and Bullock, P. (1999). “Pile friction freeze: a field and laboratory study.” Research Report submitted to Florida Department of Transportation. Department of Civil Engineering, University of Florida, Gainesville, FL.

Pestana, J.M., Hunt, C.E., and Bray, J.D. (2002). “Soil Deformation and Excess Pore Pressure Field around A Closed-Ended Pile.” Journal of Geotechnical and Geoenvionmental Engineering, ASCE, Vol. 128, No.1, pp.1-12

Randolph, M.F., Carter, J.P., and Wroth, C.P. (1979). “Driven Piles in Clay – the Effects of Installation and Subsequent Consolidation” Geotechnique 29, No.4, pp. 361- 393

Samson, L. and Authier, J. (1986). “Change in pile capacity with time: case histories” Canadian Geotechnical Journal. Natiaonal Research Council of Canada, Ottawa, Ontario, 23(2), 174-180.

Schmertmann, J.H. (1981). “A general time-related soil friction increase phenomenon.” American Society for Testing and Materials, Philadelphia, PA, 456-484. Laboratory Shear Strength of soil, ASTM STP 740. Yong, R.N. and Townsend, F.C.

Schmertmann, J.H. (1991). “The mechanical aging of soils (25th Karl Terzaghi lecture).” Journal of Geotechnical Engineering, ASCE, Reston VA 117 (9), 1285-1330.

Seidel, J.P.,Haustorfer,I.J., and Plesiotis, S.(1988). “Comparison of static and dynamic testing for piles founded into limestone.” Proceedings of the Third International Conference on the Application of Stress-Wave Theory to Piles. Fellenius.

Svinkin, M.R., C.M. Morgano & M. Morvant 1994. Pile capacity as a function of time in clayey and sandy soils. Proc. Fifth Inter. Conf. and Exhibition on Piling and Deep Foundations, Bruges, 13-15 June: 1.11.1-1.11.8, Rotterdam: Balkema.

Skov, R., and Denver, H. (1988). “Time-dependence of bearing capacity of piles.” Proceedings of the Third international Conference on the application of Stress- Wave Theory to Piles. Felllenius, B.G., editor, BiTech Publishers, Vancouver, BC, 879-888.

Van E. Komurka , Alan B. Wagner, Wagner Komurka (2003) “Estimating soil/pile set- up” Final Report, (WHRP) by the Wisconsin Department of Transportation (WisDOT) and the Federal Highway Administration (“FHWA”) under Project #0092-00-14.

103

Waldle, I.F., G,Price & T.J.Freeman 1992 “Effect of time and maintained load on the ultimate capacity of piles in stiff clay.” Pilling: European practice and worldwide trends, Proc. Institution of Civil Engineers: 92-99, London: Telford.

W.K.Ng, M.R.Selamat, K.K. Choong, “Soil/Pile Set-up Effects on Driven Pile in Malaysian Soil”, Vol. 14 [2010], Bund. A

York, D.L., Brusey, W.G.,Clemente, F.M., and Law, S.K. (1994). “Setup and relaxation in glacial sands.” Journal of Geotechninal Engineering, ASCE, Reston, VA

104

BIOGRAPHICAL SKETCH

She was born on May 21, 1986. She finished her undergraduate study and got her

B.S. in Hohai University, Nanjing, China. In the August, 2008 She came to America to pursue her master’s degree in University of Florida, majoring in Geotechnical

Engineering. Here she met her favorite Professor Dr. McVay who she followed to do research and under his instruction finished this master thesis. She admires his profound knowledge of geotechnical engineering and pure-hearted character, determine to become a eligible engineer like him in the future.

105