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International Conferences on Recent Advances 2010 - Fifth International Conference on Recent in Geotechnical Engineering and Advances in Geotechnical Earthquake Dynamics Engineering and Soil Dynamics

26 May 2010, 4:45 pm - 6:45 pm

The Variable Damping Concept in Pile Capacity Prediction by Wave Equation Analysis

Mark R. Svinkin VIBRACONSULT, Cleveland, OH

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Recommended Citation Svinkin, Mark R., "The Variable Damping Concept in Pile Capacity Prediction by Wave Equation Analysis" (2010). International Conferences on Recent Advances in Geotechnical and Soil Dynamics. 5. https://scholarsmine.mst.edu/icrageesd/05icrageesd/session05b/5

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THE VARIABLE DAMPING CONCEPT IN PILE CAPACITY PREDICTION BY WAVE EQUATION ANALYSIS

Mark R. Svinkin VIBRACONSULT, Cleveland, Ohio-USA 44118

ABSTRACT

A wave equation method is applied for pre-driving analysis of driveability calculations and capacity prediction of driven piles. For the majority of piles, there are substantial differences between predicting results and pile capacities determined from static or dynamic tests. Correct calculations of the dynamic resistance are important for accurate prediction of the pile capacity. The dynamic resistance depends on the pile velocity and the damping coefficient, but both of them cannot reflect time-dependent changes of the pile-soil system after the end of driving. Variation of the pile-soil system after pile installation can be taken into account with a variable damping coefficient which should be considered as a function of time or other parameters characterizing around a pile. Wave equation analysis with the variable damping coefficients can provide the range of predicted pile capacities at a site. The existing wave equation programs can utilize the variable damping concept for improving of the prediction of pile capacities at construction sites.

INTRODUCTION variation are almost the same for both prediction methods, Hannigan et al. (1996). Wave equation analysis of driven piles is broadly used in pile driving calculations. The wave equation is an imperative tool An important direction in the application of the wave equation for a selection of proper driving equipment to ensure driven method is predicting pile capacity at the beginning of restrikes pile installation at satisfied depth keeping tolerable stresses in (BOR) performed at any time after EOD. However, this area is piles and to ascertain the penetration rate corresponding to the far beyond the scope of the original dynamic method required pile capacity. Beside driveability analysis, the wave developed for. Therefore, in spite of some successful equation method is applied for predicting the pile capacity prediction, computed pile capacities differ substantially from during the design stage and for the construction control of pile results of both static and dynamic pile tests in numerous cases, installation. Svinkin (1996b; 1997).

The wave equation method was originally suggested by Smith This paper describes the variable damping concept which (1960) to compute the pile capacity at the end of driving provides an opportunity to predict pile capacity by the wave (EOD). The Smith’s model was made on the basis of the equation method for any reasonable time after EOD. There are existing knowledge of pile driving at the time, and Smith several programs which provide wave equation solutions for supposed that his model could be improved with acquisition of driven piles. All these programs can employ the variable new data. Afterwards, the wave equation method has been the damping concept to predict pile capacity after EOD. subject of numerous research studies vastly referenced in GRLWEAP (2005) is one of the most commonly used wave Svinkin (1996b). equation programs, and this software was used to predict pile capacity with the variable damping concept. The main goal in using wave equation analysis is to provide a better prediction of the pile capacity, as a function of the pile penetration resistance, than can be obtained from classical PROBLEMS IN PREDICTION OF PILE CAPACITY dynamic formulas. However, statistical analysis of GRLWEAP results computed for 99 piles driven into various , has In prediction of pile capacity, it is necessary to consider demonstrated that a wave equation does not have an advantage variations of the pile-soil system with time and the ability of over the Gates dynamic formula. The mean and coefficient of wave equation analysis to reflect these changes.

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Soil Consolidation after EOD compared tests was not taken into consideration and soil properties around a pile were considered the same at EOD and During pile installation, soil around the pile experiences BOR. plastic deformations and pore pressure increases. After the completion of pile driving, soil consolidation and remodeling Correct calculation of the dynamic resistance is important for related to the dissipation of excess pore pressure at the pile- accurate predicting of the pile capacity. The existing dynamic soil interface zone are usually accompanied with an increase models of the pile-soil system use a velocity-dependent in pile capacity (soil set-up). A degree of the pile capacity approach for calculation of the dynamic resistance which is a increase depends on soil properties and pile characteristics. function of the pile velocity and the damping coefficient. The phenomenon of time-dependent strength gain in soils There are various linear and nonlinear relationships between related to piles has been studied and published in a number of velocity and damping coefficient. The pile velocity papers which are referenced in Svinkin (1996b), Svinkin characterizes a pile motion and should affect the dynamic pile and Woods (1998) and Komurka (2004). resistance. Laboratory tests performed for the velocity- dependent dynamic pile-soil resistance show contradictory Besides changes of excess pore pressure induced by pile results and cannot clearly identify the pile velocity effect on driving, two more substantial causes may influence the soil the soil resistance, Svinkin (1996b). For example in clays, strength after EOD. The first is age hardening, the phenomena some tests demonstrated enlargement of the shaft and toe of time-dependent strength gain in soil, Schmertmann (1991). resistances with an increase in a penetration velocity, but other The second is , a physicochemical phenomenon tests determined a very strong effect on the at low which causes a remolded soil to gain strength with time, velocities and very weak one at high velocities. Mitchell (1960). The phenomenon of thixotropy is mostly observed in fine-grained materials. Regain in the soil strength Data of measured pile velocities and corresponding blow after driving and the time required for return of equilibrium counts have been analyzed and displayed for 35 piles, Svinkin conditions are highly variable and depend mainly on a soil (1996a). For steel piles, velocities measured at EOD and BOR type. Case histories demonstrate that set-up can increases pile are in the similar ranges. The velocity range for concrete piles capacity up to about 2 times in for a period of 14-21 at EOD is narrower than that at BOR. However, there is no days and about 11 times in clays for a period of 22-35 days, obvious relationship between pile velocity and blow count for Svinkin (1996b). both pile groups. Velocity distributions computed along pile shafts are similar for different dynamic tests of each It is clear that the pile-soil system has various soil stiffness, considered pile. Obtained results reveal that the peaks of damping and involved in vibration soil mass at each restrikes. normalized velocities along pile shafts are mostly independent of a kind of dynamic testing and driving conditions with the For example, the frequency of the fundamental mode of pile exception of easy driving. Therefore, velocities measured at the vibrations increases after EOD. Modification of soil properties pile top and computed along the pile shaft almost do not reflect with an elapsed time after EOD can be taking into the soil consolidation with time after pile installation. consideration through damping and quake which represent the soil in the existing wave equation model. Though the pile-soil system changes with time after the completion of driving, the pile velocity is only a pile feature and remains in almost the same range for EOD and BOR. The largest The causes of wrong pile capacity prediction values of pile velocity measured at the pile head and calculated along a pile shaft depend on pile material, pile parameters and The actual efficiency of the hammer system is unknown energy transferred to the pile, and those velocity values cannot before pile installation, and therefore, wave equation reflect regain in soil strength and pile-soil adhesion after EOD. It calculations have some uncertainty. By adjusting the wave seems this is the first cause of unsatisfactory prediction of pile equation input with the results of dynamic measurements, capacity with time after EOD (Svinkin 1996b). some researchers obtained good correlation between computed and determined capacities for few piles, e.g. Hunt and Baker One of the major points of criticism of the Smith soil model is (1988). However, for the majority of piles there are substantial that soil constants cannot be determined from standard differences between computed capacities and capacities geotechnical laboratory or in-situ tests. There are numerous determined from static or dynamic tests. Adjustment of a wave experimental investigations of Smith soil parameters for equation input with the maximum measured values of driveability analysis. However, successful in-situ or laboratory velocity, force and energy improves obtained results, but determination of soil parameters does not necessarily ensure obviously it is necessary to consider the soil consolidation predicting the accurate pile capacity. The basic disadvantage of effect on wave equation solutions. Rausche et al. (1996) many models is an attempt to select the model parameters demonstrated results of the large wave equation correlation directly from actual soil properties. This can yield acceptable study. However, this research did not clarify a problem of the results for some cases, but in general, this approach is not accuracy of pile capacity prediction because the time between

Paper No. 5.05b 2 successful in finding good correlation between predicted and for pile capacity would be to vary the damping coefficient, while actual pile capacities after EOD. keeping the rest of the model parameters constant. This is a reasonable direction to improve the prediction accuracy of the Also, there are attempts to determine soil damping from dynamic resistance with the velocity dependent approach. Soil modified SPT (Standard Penetration Test) or signal-matching damping is the basic parameter for adjustment of wave equation solutions for dynamically tested driven piles. It could be solutions with time-dependent soil properties after adjustment of beneficial for some cases, but in general, such approaches are not calculated velocity, force and energy with their measured values. successful in finding proper damping values because of the scale The damping coefficient should be chosen to conform to the factor effect on the use of SPT results and complications caused predominant shaft or toe resistance. Variations of the pile-soil by the application of different models in pre-driving wave system after the completion of driving can be taken into account equation analysis and signal-matching technique. It is necessary with a variable damping coefficient which should be considered to point out that these approaches yield constant values of soil as a function of time or other parameters characterizing soil parameters and cannot be used in prediction of the pile capacity consolidation around the pile. It is assumed that the variable as a function of time after EOD. damping coefficient is independent of the pile velocity. The damping coefficient should be chosen for the predominant shaft It can be concluded that the use of the constant damping or toe resistance, Svinkin (1996b). The damping coefficient as a coefficients for calculation of the dynamic resistance is the function of time after pile installation can be found on the basis second cause of unsatisfactory prediction of pile capacity with of wave equation back analysis of the pile-soil system with time after EOD. Neither the pile velocity nor the damping known pile capacity using an iterative time consuming process. constant can reflect time-dependent variations of the pile-soil The following scheme was used (Svinkin 2002). system after EOD (Svinkin 1996b, Svinkin and Woods 1998). Observation (PileCapacity) + Theory (Wave Equation) → (1) Although wave equation analysis is an excellent tool for Empirical Soil Parameter (Variable Damping Coefficient) driveability calculations, this method does not provide accurate prediction of pile capacity for various elapsed times after EOD This procedure is in agreement with Lambe's (1973) equation because the existing programs do not actually take into account modified for a general back analysis approach by Leroueil & changes of soil properties after pile installation. For example, Tavenas (1981). Since the variable damping coefficient is chosen GRLWEAP is a popular wave equation program. The writer ran as only one soil parameter for taking into account the soil this software for thousands of times. However, GRLWEAP consolidation process after pile installation, this parameter can be (2005) recommends a setup factor in the 1-2 range and does not successfully back analyzed. require wave equation analysis at restrikes for determining pile capacity. This simple approach is not productive for the reason The results of variable damping computation, obtained from that multiplication of set-up factors on pile capacities predicted at wave equation back analysis, can be used for analysis of soil EOD with unknown accuracy cannot enhance the accuracy of damping contribution to the dynamic resistance and for pile capacity prediction at BOR. Moreover such approach does prediction of pile capacity in pre-driving wave equation not demonstrate the great capabilities of wave equation analysis analysis at specified sites. to incorporate soil set-up in predicting the capacity of piles.

APPLICATION OF VARIABLE DAMPING CONCEPT THE VARIABLE DAMPING CONCEPT By way of illustration of the variable damping concept, the The existing procedure for computing the dynamic resistance to results of a variable damping study (Svinkin 1995) has been pile penetration into the ground does not consider changes of soil analyzed. The study was performed for five prestressed concrete properties around the pile after EOD, and therefore this approach piles driven on a site with predominant silty sands. At a lower cannot provide prediction of pile capacity as a function of time third of driven piles, soil consisted of dense clayey and very after pile installation. There is the necessity to take into account dense silty sand. The water table was at a depth of 0.6 m from soil consolidation around a pile after EOD for improvement of the ground surface. The results of static and dynamic pile tests the accuracy of pile capacities predicted by wave equation are shown in Table 1. Pile capacities and shaft friction values analysis. were taken from high strain dynamic pile testing results obtained for five considered piles. All tested piles had mainly the bearing For the idealized Smith wave equation model, it is important to point resistance at EOD and the dominant shaft resistance at find an appropriate combination of parameter values, mainly BOR. For the considered soil damping models, shaft damping paying attention to soil variables, in order to achieve the accurate coefficients at EOD and toe damping coefficients at BOR were prediction of pile capacity. A better way to obtain the best match considered as the constant values chosen in accordance with GRLWEAP recommendations.

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seen in Figure 1 for all five soil damping models (piles CT1 and CT2) and in Table 2 for the standard Smith damping (piles CT1, CT2 and CT4). Increasing the pile capacity at BOR 2 does not mean a necessary increase of the damping coefficient. It has been found in this study that the variable damping coefficient depends on the ratio of pile capacity to blow count per 0.3 m of pile penetration into the ground. For piles CT1 and CT2 the damping coefficient at BOR 2 is higher than at BOR 1, but there is an opposite picture for pile CT4, Figure 2. These results were received because the variable damping coefficient in wave equation analysis is used to fit predicted and measured pile capacities depending on the blow count.

Fig. 2. Variable damping as a function of the ratio of pile capacity to blow count. Fig. 1. Five soil damping models with variable damping for two

similar piles (modified from Svinkin 1995).

Table 2. Variable Standard Smith Damping (modified from

Svinkin 1995) The five soil damping options available in GRLWEAP program were studied. For each dynamic test, GRLWEAP was repeatedly run to match computed and measured values of velocity, force Pile Test Js Jt and energy. Then adjustment of the damping coefficient was s/m s/m made to correlate between pile capacity and blow count per EOD 0.164 1.200 0.3 m of pile penetration into the ground for attaining the best CT 1 BOR 1 3.428 0.492 match of the GRLWEAP solution and the measured pile BOR 2 2.690 0.492 capacity from dynamic testing with accuracy within 5 %. Such a EOD 0.164 0.554 procedure was performed for five kinds of damping: standard CT 2 BOR 1 1.378 0.492 Smith, viscous Smith, Case, Coyle-Gibson nonlinear approach, BOR 2 0.121 0.492 and combination of viscous and Coyle-Gibson models. Obtained EOD 0.164 1.378 results for two similar piles are shown in Figure 1. Additional CT 3 BOR 1 - - information about the soil damping models is available in BOR 2 0.623 0.492 Svinkin (1996b). A performed analysis has revealed resemblance EOD 0.164 1.312 of changes of all the damping coefficients for all the considered CT4 BOR 1 0.220 0.492 dynamic soil models and these alterations are independent of BOR 2 0.830 0.492 linearity of the soil damping models. EOD 0.164 3.084 For all tested piles, there is a strong trend of increasing the CT 5 BOR 1 0.558 0.492 damping coefficient at BOR 1 as compared with a conventional value taken at EOD. However, at BOR 2 in comparison with BOR 1, the damping coefficient differently Piles CT1 and CT2 were driven at the same site by a Kobe K25 changed: slightly altered for pile CT1, strongly decreased for hammer and the piles had the same cross-section areas. Pile CT2, and strongly increased for CT4. These changes can be embedment into the ground was 19.7 m for CT1 and 22.9 m for CT2. Due to the difference in pile embedment, CT2 had

Paper No. 5.05b 4 substantially larger capacity (57 %) than CT1 at BOR 2, but the In saturated sands, the variable damping coefficient changes damping coefficient for CT2 at BOR 2 was 22 times smaller than with time after EOD by analogy with the pile capacity as a one for CT1 at BOR 2 because the damping coefficient depends function of time presented in Svinkin (1996c). on the ratio of pile capacity to blow count. This example demonstrates problems in predicting the pile capacity of similar piles at the same site using close values of the damping DISCUSSION coefficient. The wave equation method connects a pile capacity with a pile Nevertheless, the variable damping coefficients obtained from set per a hammer blow or blow count per 0.3 m of pile adjusted wave equation solutions can be generalized to derive the penetration into the ground. It is known that the greater blow equations as a function of time after EOD for determining a count the higher pile capacity. In general, pile installation range of the variable damping coefficient values which demonstrates such a relationship. However, the soil resistance characterize a construction site, Figure 3. The variable standard does not always match this relationship at EOD and BOR Smith damping coefficient ranges between the upper and lower because of soil heterogeneity and uncertainty. Data presented boundaries which can be represented by the following power in Table 1 confirmed that. For pile CT1, the pile capacity functions. increased 48 % at BOR 2 as compared with BOR 1, but blow count was the same for both BOR. For pile CT2, the pile The upper boundary for values of the shaft damping coefficient capacity increased 23 % at BOR 2 as compared with BOR 1 is though blow count decreased 29 % at BOR 2. For pile CT4, the pile capacity increased 34 % at BOR 2 as compared with u 0.5 0.5 0.5 Js = 5 Jse 0.1 = 5 0.164 0.1 = 0.82 0.1 (2) BOR 1 and blow count increased 125 % at BOR 2. It is obvious that the same piles at the same site will have scattered values of pile capacities in a certain range. Jse = 0.164 s/m is a conventional value of the standard Smith shaft damping coefficient in non-cohesive soils. On the one hand due to idealized nature of the Smith model, wave equation analysis cannot provide accurate prediction of The lower boundary for values of the shaft damping coefficient pile capacity for each pile. On the other hand wave equation is analysis is a powerful and useful tool which can provide

l 0.6 0.6 determination of the range of the pile capacity predicted at a = = (3) Js Jse 0.1 0.164 0.1 site.

In Figure 3, the damping coefficient determined at BOR 1 for Soil damping is the key parameter for adjustment of wave pile CT1 is substantially higher the upper boundary that can be equation solutions with time-dependent soil properties in pre- explained by the low energy transferred to the pile. An driving analysis. The variable damping coefficient reflects efficiency of the energy transferred to the pile was 0.129 changes in soil damping as a function of pile capacity and blow (Table 1). count per 0.3 m of pile penetration into the ground. The use of the variable damping coefficient gives an opportunity to compute the time-dependent pile capacity by the wave equation method before different restrikes.

It is common that pile test programs are implemented before installation of production piles for large projects. The range of the variable damping coefficients, similar to graphs presented in Figure 3, can be determined on the basis of static and dynamic pile testing using wave equation back analysis.

For verification of pile capacity of production piles, the predicted pile capacity has to be compared with the results of static or dynamic tests. In such comparison, it is necessary to take into account the quality of test implementation and the time after pile installation because both tests determine pile capacity as a function of time after EOD. Fig. 3. Upper and lower boundaries of variable damping values for five piles tested in saturated sands (modified from The variable damping concept together with wave equation back Svinkin 1995). analysis of the pile-soil system with known pile capacity can be

Paper No. 5.05b 5 used to create a database of damping values for different soil A variable damping approach gives insight into the process of conditions and various times after pile installation. predicting pile capacity by the wave equation analysis. The use of the variable damping concept provides an opportunity to The variable damping concept has been confirmed by results of compute the time-dependent pile capacity by the wave equation statistical analysis of damping coefficients obtained from method, incorporate a soil set-up effect into predicted pile CAPWAP solutions performed by Liang and Zhou (1997) who capacity, and determine a range of the pile capacity predicted have found that the damping coefficient is affected by the time. at a site.

It is thought that the variable damping concept can be considered The variable damping concept together with wave equation back as the next step in the development of Smith's numerical model analysis of the pile-soil system with known pile capacity can be with the velocity dependent approach for representation of the used to create a database of damping values for different soil dynamic resistance in determination of the pile capacity. conditions and various times after pile installation.

Additional research is needed to examine the results of variable CONCLUSIONS damping computations obtained from wave equation back analysis. These outcomes can be used to study soil damping The Smith’s model was derived on the basis of existing contribution in prediction of pile capacities and extrapolate knowledge of pile driving at the time and Smith supposed this derived equations beyond the time of load test implementation, model could be improved with acquisition of new data. Results and also generalize relationships between the variable damping obtained by many researchers confirmed that the Smith's model coefficients and the time elapsed after EOD for different soil is simple and sensible but with some lack of proper presentation conditions. It seems the application of the variable damping of soil properties. concept can decrease limitations of pre-driving wave equation

The main goal in using wave equation analysis is to provide a analysis in predicting pile capacity. better prediction of the pile capacity, as a function of the pile penetration resistance, than can be obtained from classical dynamic formulas. Nevertheless, there are substantial REFERENCES differences between predicted results and capacities determined from static or dynamic tests for the majority of GRL and Associates, Inc. [2005]. GRLWEAP –Wave Equation piles presented in diverse publications. Analysis of Pile Driving, Manual, Cleveland, Ohio.

The existing dynamic models of the pile-soil system use a Hannigan, P.J., Goble, G.G., Thendean, G., Likins, G.E., and velocity-dependent approach for calculation of the dynamic Rausche, F., [1997]. Design and Construction of Driven Pile resistance which is a function of the pile velocity and the Foundations, II, Workshop Manual, Publication No. FHWA- damping coefficient. However, neither the pile velocity nor the HI-97-014. , Washington, D.C. damping constant can reflect time-dependent variations of the Hunt, S.W., and Baker, C.N., [1988]. Use of -wave pile-soil system after EOD. measurements to evaluate piles in high set-up conditions. B. Fellenius (ed.), Proceedings of the Third International Soil damping is the basic parameter for adjustment of wave Conference on the Application of StressWave Theory to Piles, equation solutions with time-dependent soil properties after BiTech Publisher, Ottawa, pp. 689-705. adjustment of calculated force, energy and velocity with their measured values. The damping coefficient should be chosen to Komurka, V.E., [2004]. Incorporating set-up into the design conform to the predominant shaft or toe resistance. and installation of driven piles. Proceedings of 5th Annual Design & Installation of Cost-Efficient Driven Piles Variation of the pile-soil system after the completion of driving Conference, PDCA, pp. 12-36. can be taken into account with a variable damping coefficient which should be considered as a function of time or other Lambe, T.W., [1973]. Predictions in soil engineering. 13th parameters characterizing soil consolidation around the pile. Rankine Lecture, Geotechnique, 23(2), pp. 149-202.

The variable damping coefficient in wave equation analysis is Leroueil, S., and Tavenas, F, F, [1981]. Pitfalls of back- used to fit predicted and measured pile capacities which are analysis. Proceedings of 10th International Conference on Soil contingent on the blow count. It has been found in this study mechanics and Engineering, ISSMFE, I, pp. 185- that the variable damping coefficient depends on the ratio of 190. pile capacity to blow count per 0.3 m of pile penetration into the ground.

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Liang, R.Y., and Zhou, J., [1997]. Probability method applied to dynamic pile-driving control. Journal of Geotechnical Engineering, ASCE, 123(2), pp. 137-144.

Mitchell, J.K., [1960]. Fundamental Aspects of Thixotropy in Soils. Journal of and Foundation Division, ASCE, 86(SM3), pp. 19-52.

Rausche, F., Thendean, G., Abou-Matar, H., Likins, G.E., and Coble, G.G., [1996]. Determination of Pile Driveability and Capacity from Penetration Tests, Final Report, FHWA Contract No. DTFH61-91-C-00047, Washington, D.C.

Schmertmann, J., [1991]. The Mechanical Aging of Soils. The 25th Terzaghi Lecture, Journal of geotechnical Engineering, ASCE, 117(9), pp. 1288-1303.

Smith, E.A.L., [1960]. Pile driving analysis by the wave equation. Journal of the Soil Mechanics and Foundation Division, ASCE, V. 86, pp. 35-61.

Svinkin, M.R., [1995]. Soil damping in saturated sandy soils for determining capacity of piles by wave equation analysis. Proceedings of 20th Annual Members’ Conference, DFI, Charleston, South Carolina, pp. 199-216.

Svinkin, M.R., [1996a]. Velocity-impedance-energy relationships for driven piles. Proceedings of Fifth International Conference on the Application of Stress-Wave Theory to Piles, Orlando, Florida, USA, pp. 870-890.

Svinkin, M.R., [1996b]. Soil damping in wave equation analysis of pile capacity. Proceedings of Fifth International Conference on the Application of Stress-Wave Theory to Piles, Orlando, Florida, USA, pp. 128-143.

Svinkin, M.R., [1996c]. Discussion of ‘Set-up and relaxation in glacial sand’ by York et al. Journal of Geotechnical Engineering, ASCE, 122(4), 319-321.

Svinkin, M.R., [1997]. Time-dependent capacity of piles in clayey soils by dynamic methods. Proceedings of the International Congress 2002, ASCE, Orlando, Florida, pp. 898-914.

Svinkin, M.R., and Woods, R.D., [1998]. Accuracy of determining pile capacity by dynamic methods. 7th International Conference and Exhibition on Piling and Deep Foundations, DFI, Vienna, pp. 1.2.1-1.2.8.

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Table 1. Data of Tested Piles (modified from Svinkin 1995).

Pile Test Time Penetration Ru Set-up Transferred Rated WEAP Friction after Resistance Measd Energy Energy Hammer No. Description Embt EOD Efficiency Efficiency m days blows/0.3 m kN kJ % CT1 Prestressed 19.7 EOD - 18 913 1 23.77 0.310 0.31 36 Concrete BOR 1 2 84 1145 1.25 12.46 0.129 0.12 58 457x457 mm BOR 2 11 84 1702 1.86 29.61 0.250 0.40 65 SLT 21 - 1666 1.85 CT2 Prestressed 22.9 EOD - 42 1907 1 28.77 0.340 0.35 40 Concrete BOR 1 2 84 2176 1.14 30.74 0.322 0.45 70 457x457 mm BOR 2 11 60 2668 1.40 28.20 0.238 0.40 69 SLT 21 - 2540 1.34 CT3 Prestressed 19.5 EOD - 34 1513 1 30.90 0.319 0.55 46 Concrete BOR 1 1 72 - - 20.64 0.252 0.34 90 610x610 mm BOR 2 10 108 2615 1.73 22.12 0.187 0.40 66 (267 mm D. SLT 22 - 2869 1.90 void, solid ends) CT4 Prestressed 22.9 EOD - 77 1986 1 25.85 0.271 0.40 28 Concrete BOR 1 2 96 2691 1.35 22.81 0.236 0.40 54 610x610 mm BOR 2 11 216 3617 1.82 27.68 0.254 0.53 64 (267 mm D. SLT 23 - 3724 1.90 void, solid ends)

CT5 Prestressed 22.3 EOD - 92 2949 1 50.25 0.249 0.50 44 Concrete BOR 1 6 60 4210 1.43 61.71 0.303 0.72 67 915x915 mm SLT 20 - 4900 1.66 (570 mm D. void, solid ends)

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