Subsurface Investigations PDCA Professor s Driven Pile Institute. Loren R. Anderson Utah State University June 25, 2015

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1 Subsurface Investigations PDCA Professor s Driven Pile Institute Loren R. Anderson Utah State University June 25, 2015

2 Ralph B. Peck (1962) Subsurface engineering is an art; soil mechanics is an engineering science. We would do well to recall and examine the attributes necessary for the successful practice of subsurface engineering. There are at least three: knowledge of precedents, familiarity with soil mechanics, and a working knowledge of geology...

3 Geotechnical Engineering Process (Worth, 1972) 1. Define the Project Concept 2. Project Site Reconnaissance. 3. Develop a Working Hypothesis of the Subsurface Conditions. 4. Plan a Field Investigation to Test the Working Hypothesis. 5. Develop a Model for Analysis.

4 Geotechnical Engineering Process (cont) 6. Evaluate Alternative Schemes. 7. Make Specific Recommendations 8. Prepare Plans and Specifications 9. Construction Inspection and Consultation 10. Performance Feedback

5 PDCA Design and Construction of Driven Pile Foundations, Chapter 4, Subsurface Explorations Chapter 5, In-Situ Testing Chapter 6, Laboratory Testing Volume I

6 Subsurface Exploration Planning the Exploration (Office) Field Reconnaissance Survey Detailed Subsurface Exploration

7 Subsurface Investigation Pile capacity (shear failure) Lateral capacity Driving resistance Pile length Pile group settlement What do we need?

8 Subsurface Investigation Guidelines Minimum Program Number and location of borings may change Drilling method Depth of borings may change Type of samples to take Standard Penetration Test ASTM T206, also consider liquefaction Engineer is in charge Extend boring into rock say 10 ft. Proper field logging Water level at time of drilling and future Backfill borings

9 Subsurface Exploration, In Situ Testing and Laboratory Testing Reference Manual Chapters 4, 5, & 6 Lesson 3

10 Subsurface Explorations Foundation design requires adequate knowledge of the subsurface conditions With the appropriate information, an economical system can be designed

11 Subsurface Explorations Absence of thorough geotechnical data often leads to: Large factor of safety, generally more expensive and/or difficult to construct An unsafe foundation Construction disputes & claims

12 A thorough foundation study consists of: Subsurface exploration program Laboratory testing Geotechnical analysis of all data Design recommendations

13 Boring Plan Guidelines One boring / substructure unit More borings for substructures > 30 m (100 ft) Stagger boring locations Confirm suitability of boring depth for design purpose early Extend through unsuitable layers, terminate in hard or dense materials

14 Boring Plan Guidelines (cont.) Thoroughly explore the affected depth SPT samples at 1.5 m (5 ft) intervals and at strata changes Undisturbed sample locations/frequency to meet project needs NX size rock core obtained for a depth of 3 m (10 ft) where rock is encountered

15 Boring Plan Guidelines (cont.) Crews should maintain a field drilling log Samples should be properly labeled, sealed, and transported Water level readings made and recorded Bore holes properly backfilled & sealed

16 Soils Samples Disturbed Identification and Classification Tests Undisturbed Consolidation, Shear Strength, and Permeability Tests

20 SPT Split-Barrel Sampler

21 Standard Penetration Test Advantages Widely used Substantial data available Simple & inexpensive Provides disturbed soil samples Disadvantages Highly variable N-value determined from test is influenced by many factors

22 SPT Hammer Types Donut Safet Automatic

23 Safety Automatic

24 SPT N Value Comparison for Safety and Automatic Hammers

25 SPT Hammer Calibration N 60 = N (ETR/60) ETR = EMX / 350 ftlbs

26 SPT N Values SPT hammer type & operational characteristics have a significant influence Type of hammer should be clearly noted on all boring logs

27 SPT Error Sources Effect of overburden pressure Variations in hammer drop heights Interference with hammer free-fall Damaged or worn sampler drive shoe Failure to properly seat sampler at bottom of hole

28 SPT Error Sources Inadequate cleaning of loose material at bottom of hole Failure to balance hydrostatic pressures inside & outside of borehole Unreliable results in gravelly soils Samples from dilatant soils may cause plugging Careless work by drill crew

29 N = C N (N) N = corrected SPT N value C N = correction factor for overburden pressure N = uncorrected or field SPT N value

30 TABLE 4-5 EMPIRICAL VALUES FOR, D r, AND UNIT WEIGHT OF GRANULAR SOILS BASED ON CORRECTED N' (after Bowles, 1977) Description Very Loose Loose Medium Dense Very Dense Relative density D r Corrected Standard Penetration N' value Approximate angle of internal friction * Approximate range of moist unit weight,, kn/m 3 (lb/ft 3 ) 0 to 4 4 to to to (70-100) (90-115) ( ) ( ) Correlations may be unreliable in soils containing gravel. See discussion in Section 9.5 of Chapter 9. * Use larger values for granular material with 5% or less fine sand and silt ( )

31 TABLE 4-6 EMPIRICAL VALUES FOR UNCONFINED COMPRESSIVE STRENGTH (q u ) AND CONSISTENCY OF COHESIVE SOILS BASED ON UNCORRECTED N (after Bowles, 1977) Consistency Very Soft Soft Medium Stiff Very Stiff Hard q u, kpa (ksf) 0 24 (0 0.5) ( ) ( ) ( ) ( ) 384+ (8.0+) Standard Penetration N value (saturated), kn/m 3 (lb/ft 3 ) ( ) ( ) ( ) ( ) ( ) ( ) The undrained shear strength is 1/2 of the unconfined compressive strength. Note: Correlations are unreliable. Use for preliminary estimates only.

32 Undisturbed Samplers Thin wall open shelby tube Piston Hydraulic piston Pitcher Denison core barrel

33 Shelby Tube Samplers

34 Ground Water Monitoring Observation well Piezometer

35 Soil Profile Development Visual presentation of subsurface conditions Uncertainties in profile indicate need for more borings & lab tests Develop in stages as data is available Identify soil layers, then lab test determinations

36 Soil Profile Development Final soil profile includes: Soil physical properties (, q u, C c,, etc.) Visual soil description Note ground water, boulders, voids, artesian pressures, etc. Well developed soil profile is necessary to design a cost effective foundation

38 IN-SITU TESTING Reference Manual Chapter 5

39 In Situ Testing Provides design parameters in conditions where high quality undisturbed samples cannot be obtained In-situ tests are performed to obtain foundation design parameters

40 Primary In-Situ Tests CPT Cone Penetration Test CPTU CPT with pore pressure measurement PMT Pressuremeter Test DMT Dilatometer Test VST Vane Shear Test

45 Interpretation of CPT/CPTU Results Provides a continuous profile of subsurface stratigraphy Soil classification from cone tip resistance & friction ratio CPT correlations for evaluation of: D r q u

48 A Series of Exploration Events Setup at the Site

49 A Series of Exploration Events Push the Cone

50 A Series of Exploration Events Into the ground

51 A Series of Exploration Events Induce a Shear Wave

52 A Series of Exploration Events Interpret the Results

53 A Series of Exploration Events Leave the Site

54 A Series of Exploration Events Plug the hole from China

55 A Series of Exploration Events Drive a Pipe

56 A Series of Exploration Events It s dark and the water flows

57 A Series of Exploration Events We even used our pants

58 Advantages of CPT/CPTU Rapid & economic development of continuous profile of subsurface conditions Determination of in situ strength parameters Reduce the number of conventional borings, or focus attention on discrete zones for sampling & testing

59 CPT/CPTU Disadvantages Cannot be pushed in dense soils CPT must be pushed in borehole advance through dense deposits Soil samples not recovered Local correlations are important in data interpretation

60 Pressuremeter and Dilatometer Limited applicability for vertically loaded pile foundation design Pressuremeter useful for p-y curve determination for lateral load designs Dilatometer has potential usefulness for lateral load design

62 Vane Shear Testing In situ test to determine undrained shear strength of soft to medium clays Measures peak & remolded strength Most accurate method for q u < 50 kpa (1 ksf) Very useful data for driveability analysis & soil setup evaluation

65 LABORATORY TESTING Reference Manual Chapter 6

66 Laboratory Testing The trend to higher capacity piles & greater pile penetration depths for special design events reinforces the importance of accurate determination of soil shear strength & compressibility.

67 Laboratory Testing Quality of results far more important than quantity of test results Inaccurate results may lead to design misjudgements &/or construction problems

68 Cohesionless Soils: Laboratory Testing SPT & CPT primary tools for and D r, complimented by index testing Cohesive Soils: Traditional tests on undisturbed samples yield best results for q u and C c

69 Lab QC Procedures Sample handling & storage Sample prep Adherence to procedures Equipment calibration Qualification of personnel Result review & checking Reporting of test results

71 Types of Lab Tests Soil classification & index Shear strength Consolidation Electro chemical classification

72 Classification & Index Tests Moisture content Particle size analysis Atterberg limits Unit weight

73 Shear Strength Tests Unconfined compression Direct shear Triaxial compression

74 Consolidation Tests Amount of settlement Time rate of settlement

75 Electro Chemical Classification ph Resistivity Sulfate content Chloride content

76 Lab Tests for Driveability Evaluations Remolded shear strength of cohesive soils Sensitivity S t = q u-undist / q u-remold ( Sensitivity qualitative not quantitative indicator of soil setup ) Gradation of cohesionless soils Fine content Angularity

77 Lesson 3 Learning Outcomes You will be able to: Explain what field & lab test results are needed to develop a design soil profile for pile design. Identify SPT hammer types and their influence on N values. Discuss the importance of quality subsurface information & lab test results in pile design.

78 About the Site

79 USU Drainage Farm Infrastructure Engineering Earthquake Engineering Dynamic Testing Rehabilitation with composite materials Wind Engineering Pile Test Site

80 Any Questions

81 Recruiting Strategy High School Bridge Contest 10 to 19 schools Promotes USU and Engineering Hospitality Tours Coordinate with Math/Science Teachers Follow up letter 5 games, 16 HS, students High School visits and tutoring (Envir)

82 Purpose of the I-15 Testbed I-15 Corridor Window of opportunity Old Structures a destructive testing opportunity New construction Behavior of soft clays Performance of innovative structures Instrumentation

83 Sometimes we worked late

84 Sometimes it was overwhelming

85 There was always a bright side

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

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