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Developing Subsurface Exploration & Testing Programs Considering Geophysics & In-Situ Testing

Benjamin S. Rivers, P.E. Geotechnical Engineer FHWA Resource Center Purpose of a Site Investigation

• Assess Suitability of Site for Proposed Project • Enable Adequate and Economical Design – No Failures - No Conservatism • Foresee and Provide for Construction Problems that may Arise (Reduce Claims)

4/16/2008 2 Who looks at the results and do they get what they want?

• Geotech Engineers/Designers • Better characterization of engineering properties, less uncertainty • Contractors • Better characterization of construction needs, less uncertainty • Owners • Better value from engineers and contractors

Value is Economics • Less expensive, longer lasting projects through better understanding of engineering properties and their distribution • Less Uncertainty/Better Reliability in Characterization and Parameters • Faster investigations – “time is money”

4/16/2008 3 4 8 0 n 0

e 2 / o 6 r y s 1 r

d / r

i 4 a a a

F S G L “If you do not know what you should be looking for in site investigation, you are not likely to find much of value.”

R. Glossop-8th Rankine Lecture

4/16/2008 5 Rational Approach

4/16/2008 6 GEC #5 Figure 1: & Rock Property Selection Flowchart

4/16/2008 7 Planning Exploration & Testing Program • Gather & Analyze Existing Information; Conduct Site Visit; Develop Preliminary Site Model • Identify Material Properties required for Design & Construction; Estimate Scope of Field Program; Divide into Zones of Interest • Develop Site Exploration Program • Conduct Exploration & Field Testing • Perform Descriptions and Laboratory Index Testing • Summarize Data & Develop Subsurface Profile Are Results Consistent with Preliminary Model???

4/16/2008 8 Planning Exploration & Testing Program • Review Design Objectives and Initial Results; Identify “Critical Areas” Additional data needs??? • Identify Representative Samples for Performance Testing. • Conduct Performance Testing, Review Test Data, Summarize Are Results Consistant & Valid? Is a Phase II Investigation Necessary? • Select Material Properties and Final Model • Perform Design and Consider Constructability Issues

4/16/2008 9 Planning Exploration & Testing Program

Identify Data Needs V Identify Design & Constructability Requirements V Identify Performance Criteria & Schedule Constraints V Identify Areas of Concern on Site and Potential Variability V Develop Likely Sequence and Phases of Construction V Identify Engineering Analyses to be Performed V Identify Required Engineering Properties & Parameters V Evaluate Methods to Obtain Parameters V Evaluate Number & Locations of Tests/Samples Needed (GEC #5: Table 1) 4/16/2008 10 Planning Exploration & Testing Program

Exploration Tools ‹ Undisturbed Sampling ‹ Disturbed Sampling ‹ In-situ Testing ‹ Geophysical and Remote Sensing Methods

4/16/2008 11 In-Situ Geotechnical Tests for

4/16/2008 12 Standard Penetration Test (SPT)

4/16/2008 13 Standard Penetration Test Advantages Disadvantages • Obtain Sample + Number • Disturbed sample (index • Simple & rugged device at tests only) low cost • Crude number for analysis • Suitable in many soil • Not applicable in soft types clays and • Can perform in weak • High variability and rocks uncertainty • Available throughout the U.S. (worldwide)

4/16/2008 14 Test Results

• N – SPT Resistance Value (blows/foot) • Consistancy/Relative Density • Soil Properties for to φ, E, liquefaction potential • Must apply corrections for energy and for normalization

4/16/2008 15 Standard Penetration Test (SPT)

Measured N-values Corrected N60

0 10 20 30 40 50 0 10 20 30 40 50 4 4 Donut ER = 34 (energy ratio) 6 6 Safety 55 45 60 Trend

40 )) ))

ss 8

ss 8 rr rr 56 ee ee 41 tt tt ee ee 63

41 mm mm

(( 10 (( 10

63 hh hh tt tt 39 pp pp ee ee 63 DD DD 12 47 12

Donut 64 56 14 Safety 14 69 Sequence 16 16

Data from Robertson, et al. (1983) 4/16/2008 16 Cone Penetration Test (CPT) Cone Penetration Testing (ASTM D 5778) Geostratigraphy by Piezocone Tests, Blytheville, AR

qt (MPa) fs (kPa) u2 (kPa) 0 10 20 30 40 50 0 100 200 300 400 0 1000 2000 3000 0 0 0 Clayey

5 5 5

10 10 10

15 15 15 ) m (

Clean h t 20 20 20

p Sand e D

25 25 25

30 30 30

35 35 35

40 40 40 Cone Penetration Test Advantages Disadvantages • Fast and continuous profiling • Electronics must be of strata calibrated & protected • Economical and productive • No soil samples • Results not operator- • Unsuited to gravelly soils and cobbles. dependent • Strong theoretical basis for interpretation • Particularly suited to soft soils

4/16/2008 20 CPT/CPTu/SCPTu Results Common to all: • Tip Resistance (Force/Area) • Sleeve Resistance (Force/Area) CPTu: • Pore-water Pressure SCPTu: • Shear Wave Velocity Soil Properties:

Vs, Gmax, Emax, ρtot, eo Sands - φ’, Dr, σho’, uo/water table elevation Clays - su, σp’, ch, kh, OCR

4/16/2008 21 Vane Shear Devices

Scandinavian Vanes McClelland Offshore Vane

4/16/2008 22 Vane Shear Test (VST) Results from Vane Shear Tests San Francisco Bay Mud, MUNI Metro Station

Vane Strength, suv (kPa) Sensitivity, St 0 10 20 30 40 50 60 70 80 0 1 2 3 4 5 0 0

Peak 5 5 Remolded ) ) s 10 s 10 r r e e t t e e m m

( 15 ( 15

h h t t p p e 20 e

D 20 D

25 25

30 30 4/16/2008 24 Vane Shear Test Advantages Disadvantages • Assessment of undrained • Limited to soft to stiff

of clays clays & silts with suv < 200 kPa • Simple test and equipment • Raw s needs empirical • Measure inplace sensitivity uv correction • Long history of use in practice for embankments, • Can be affected by sand foundations, & cuts seams and lenses

4/16/2008 25 Flat Plate Dilatometer (DMT)

Blade, Pressure Panel, Tubing, and Nitrogen

4/16/2008 26 Flat Plate Dilatometer Test (DMT) DMT in Piedmont Residuum, Charlotte, NC

0 0 0 0

2 2 2 2

4 4 4 4

)) 6 ss 6 6 6 rr ee tt ee mm

(( 8 8 8 8 hh tt pp ee

DD 10 10 10 10

12 12 12 12

Po 14 14 14 14 P1 Clay Silt

16 16 16 16 0 500 1000 1500 0 1 10 0 200 400 600 800 0 5 10 15

Pressure (kPa) Material Index ID Modulus ED (atm) Horiz. Index KD 4/16/2008 28 DMT Results

• Pressure Readings (A, B, C) Soil Properties:

Sands – φ’, E, Dr, mv,

Clays – σp’, Ko, su, mv, E, ch, kh

4/16/2008 29 Dilatometer Test (DMT) Advantages Disadvantages • Simple and Robust • Difficult to push in very Equipment dense materials and not in • Repeatable and Operator- . Independent • Primarily established on • Quick and Economical correlative relationships • Theoretical Derivations for • Needs calibration for local elastic modulus, strength, stress history

4/16/2008 30 Pressuremeter Test (PMT) Pre-Bored Pressuremeters (ASTM D4719)

Menard Pressure Panel Texam Monocell Probe 4/16/2008 32 PMT Data - Utah DOT Project 5 Lim it Pressure, PL V0 = 1200 cc 4 )) ff ss tt

(( 3

ee rr uu

ss Shear Strength ss

ee 2 rr PP E = elastic m odulus 1

P0 = lift-off pressure 0 0 200 400 600 Volume Change (cc) 4/16/2008 33 Pressuremeter Test (PMT)

Advantages Disadvantages • Theoretically sound in • Complicated determination of soil procedures – requires parameters high level of expertise • Tests larger zone of soil mass than other • Time consuming in-situ tests • Delicate – easy to • Develop stress-strain- damage shear curves

4/16/2008 34 PMT Results

• Pressure vs. ∆Volume or Volumetric Strain

Soil Behavior • Load/Volumetric Displacement

Soil Properties

E, G, mv, su

4/16/2008 35 Geophysical Investigations

• Initial Site Exploration/Preliminary Surveys • Assist with Placement of Borings/In-Situ Tests • Difficult Locations • Gravels, Cobbles, Boulders, Debris • Difficult • Contaminated Sites • Supplementary Exploration • Observe Variations Between Borings/Soundings/Outcrop, etc. • Locate Anomalies

4/16/2008 36 Common Geophysical Methods Surface Methods Methods • Siesmic Refraction • Crosshole/Downhole • Spectral-Analysis-of- • Suspension Logger Surface-Waves (SASW) • Electrical Logging • Electrical Resistivity • Nuclear Logging • Electromagnetics (EM) • Optical and Acoustical • Ground Penetrating Radar Televiewer (GPR) • Microgravity 4/16/2008 37 Geophysical Investigations

• Stratification of Subsurface Materials • Profile Top of • Depth to • Limits of Types of Soil Deposits • Rippability of Hard Soil and Rock • Locate Voids, Buried Utilities, Substructures • Shear Velocity and Modulus Properties

4/16/2008 38 Geophysical Properties P - Wave Velocities

Steel Intact R ocks W eathered R ocks Ice T ill Sand Resistivity Values (ConeTec & GeoProbe, 1997) Clay W eathered R ocks Sea W ater

G lacial T ill Fresh W ater 0 1000 2000 3000 4000 5000 6000 7000 8000 Sands & G ravels

Com pression W ave V elocity, V p (m /s) Loose Sands S - W ave Velocities Steel C lay Intact Rocks 1 10 100 1000 10000 W eathered Rocks Ice Bulk R esistivity, ρ (ohm -m eters) T ill Sand Clay Sea W ater V s = 0 Fresh W ater }

0 1000 2000 3000 4000

Shear W ave V elocity, V S (m /s)

4/16/2008 39 Results from Seismic Refraction

4/16/2008 40 Electrical Resisitivity Measurements

4/16/2008 41 Electromagnetic Conductivity (EM) Televiewer

Source: Eliassen, et al

4/16/2008 43 Summary • Value – Reduce Uncertainty – Increase Reliability – Quicker • Rational Approach – Develop Preminary Model – Identify Data Needs – Develop & Execute Appropriate Exploration & Testing Program – Re-evaluate Data Needs – Evaluate Data – Select Properties and Finalize Subsurface Model

4/16/2008 44 GEC #5: Evaluation of Soil & Rock Properties http://www.fhwa.dot.gov/engineering/geotech /library_listing.cfm

Publication No. FHWA-IF-02-034

Highly Recommended

4/16/2008 45 Reference on Geophysics

• Application of Geophysical Methods to Highway Related Problems (FHWA Manual DTFH68-02-P-00083; Sept. 2003)

www.cflhd.gov/geoTechnical

4/16/2008 46 Subsurface Investigation Courses

• NHI Course 132031: Subsurface Investigations – Geotechnical Site Characterization • NHI Course 132079: Subsurface Investigation Qualification – QC/QA www.nhi.fhwa.dot.gov

4/16/2008 47