OBJECTIVES OF SUBSURFACE EXPLORATION

Transcription

1 OBJECTIVES OF SUBSURFACE EXPLORATION Three (3) General Objectives for Subsurface Exploration: 1. Define Soil and Rock Stratigraphy and Structure within Proposed Construction Zone of Influence. 2. Obtain Groundwater Data. - Level at Time of Testing. - Seasonal Fluctuations. 3. Determine Engineering Properties of Subsurface Materials for Use in Foundation Design. - Collect samples for laboratory testing. - Determine insitu engineering properties. Photograph courtesy of Slide 1 of 73

2 GENERAL SUBSURFACE INVESTIGATION METHODS METHOD Abbrv. ASTM SAMPLING MAX. DEPTH (ft) Hand Auger Borings HAB D a D (06) Yes Typ (w/difficulty) Test/Excavation Pits TP None Yes Limits of equipment (Typ. 20 ft) Soil Test Borings STB D420-98(03) D a D (06) Yes ~ 300 ft (dependent of various factors) D420-98(2003) Standard Guide to Site Characterization for Engineering, Design, and Construction Purposes Green Near Surface : Red Near and Deep Slide 2 of 73

3 Requires Manual Labor. Typical Depths up to 6 to 8 ft. Standard Diameter: 3¼ in (Other Diameters Available). Allows for soil samples (disturbed) to be collected for classification and laboratory testing (if desired). HAND AUGER BORINGS (HAB) Will be conducting HAB s in CIVL402 Typical HAB Cross-Section Figure courtesy of WPC Engineering Inc. Two Man Operation Photograph courtesy of Slide 3 of 73

4 TEST/EXCAVATION PITS (TP) Requires Appropriate Construction Equipment (e.g. backhoe). Typical Depths up to 20 ft (limited by equipment). Pit size determined by needs. Allows for soil samples (disturbed) to be collected for classification and laboratory testing (if desired). Allows for greater examination of insitu soils by geotechnical engineers and engineering technicians. Photographs courtesy of photos.orr.noaa.gov, & Slide 4 of 73

5 SOIL TEST BORING (STB) RIGS Failing Truck Mounted Rig CME750 All-Terrain Rig Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 5 of 73

6 SOIL TEST BORING (STB) RIGS MoDOT Track Mounted Rig Wireline Rig for Kaolin Mines Macon, GA Water Boring from Barge for Bridge Crossing Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 6 of 73

7 Continuous flight augers, added in 5-ft increments. Limited to non-caving soils and depths < 30 ft. Solid flight augers are removed prior to soil sampling, thus labor-intensive. Auger diameters from 4 in to 8 in. Front end has finger or fish-tail bit to loosen soil. Spoil collects around top of borehole. SOIL TEST BORINGS (STB) Solid Flight Augers Solid Auger and Drill Bit Text & Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 7 of 73

8 SOIL TEST BORINGS (STB) Solid Flight Augers Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 8 of 73

9 Continuous hollow flight augers, added in 5 ft increments. Hollow stem augers allow soil sampling without removal. Act as temporary casing to stabilize borehole. Center stem and plug are inserted down the hollow center during boring advance. HSA range from about 6 to 12 inch O.D. with 3 to 8 inch I.D. HSA generally limited to depths < 100 ft. HSA should not be used in loose silts and sands below the GWT. SOIL TEST BORINGS (STB) Hollow Stem Augers (HSA) Truck-Mounted Rig with Hollow-Stem Augers HSA outer and inner assembly with stepwise center bit Text & Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 9 of 73

10 SOIL TEST BORINGS (STB) Rotary Wash Borings Rotary wash techniques are best for borings extending below GWT. Rotary wash can achieve great depths > 300+ ft. Drilling bits: Drag bits for clays Roller bits for sand In rotary wash method, borehole is stabilized using either temporary steel casing or drilling fluid. Fluids include water, bentonite or polymer slurry, foam, or Revert that are re-circulated in tub or reservoir at surface. Truck Rig conducting rotary wash boring Text & Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 10 of 73

11 SOIL TEST BORINGS (STB) Rotary Wash Borings Schematic (Hvorslev 1948) Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 11 of 73

12 Bucket auger drills are used for obtaining large disturbed or undisturbed samples. Diameters range from 0.6 m (2 ft) to 1.2 m (4 ft). Increment of 0.3 m to 0.6 m depths (1 to 2 feet). Good for gravelly soils and cobbles. SOIL TEST BORINGS (STB) Bucket Auger Borings Same rigs used for constructing Drilled Shafts. Setup of rig for Bucket Auger Boring (ASTM D4700) Text and Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 12 of 73

13 Disturbed Sampling (Most Common) Bulk samples (from auger cuttings or TP excavations). Bucket samples (borrow pits). Drive samples (e.g. split-spoon). Laboratory Tests: Grain size, Atterberg Limits, Specific Gravity, Organic Content, Hydraulic Conductivity (coarse grained), Shear Strength (coarse grained). Partially Undisturbed (ASTM D1587) Continuous Hydraulic Push. SOIL SAMPLING Split Spoon Sampler Undisturbed Sampling (ASTM D1587) Push Tubes (e.g. Shelby, Piston, Laval) Rotary & Push (e.g. Denison, Pitcher) Block Samples Laboratory Tests: Consolidation, Hydraulic Conductivity (cohesive), Shear Strength (cohesive) Thin Wall Samplers Text & Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 13 of 73

14 UNDISTURBED SAMPLES Sampling Disturbance Photoelasticity Studies Radiography (X-rays) of Tubes Photographs courtesy of FHWA NHI Course Subsurface Investigations Slide 14 of 73

15 INSITU TESTING METHODS METHOD Abbrv. ASTM SAMPLING MAX. DEPTH (ft) Dynamic Cone Penetrometer DCP D Yes (via HAB) 6 8 Typ. 20 (w/difficulty) Standard Penetration Test SPT D a Yes > 300 ft (dependent on boring method) Cone Penetration Test CPT D D No > 300 ft (typically ft max) Flat Plate Dilatometer DMT D No > 300 ft (typically ft max) Pressuremeter PMT D Vane Shear Test VST D Yes (via boring) Yes (via Boring) > 300 ft (dependent on boring) > 300 ft (dependent on boring) Green Near Surface : Red Near and Deep Slide 15 of 73

16 Labor Intensive (Can be done with one person, better with two). Several types in use: - Scala (1956) DYNAMIC CONE PENETROMETER (DCP) - Sowers (Sowers and Hedges, 1966) (Common in Southeast US) - Dual Mass (Army COE) Mainly used for residential construction and pavement subgrade evaluations. Conducted in conjunction with HAB s (therefore, soil samples can be collected). Depth limited by soil type. 6 8 ft typical, 20 ft maximum (if lucky). Figure courtesy of WPC Engineering Inc. Slide 16 of 73

17 INSITU TESTING METHODS Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 17 of 73

18 STANDARD PENETRATION TEST (SPT) (ASTM D a) Marking of 6 inch Increments for SPT Test Photograph courtesy of physics.uwstout.edu Very common test worldwide Colonel Gow of Raymond Pile Co. Split-barrel sample driven in borehole. Conducted on 2½ to 5 ft depth intervals. ASTM D1586 guidelines Drop Hammer (140 lbs falling 30 inches) Three increments of 6 inches each; Sum last two increments = SPT N value" (blows/ft) Correlations available with all types of soil engineering properties. Disturbed Soil Samples Collected Text courtesy of FHWA NHI Course Subsurface Investigations Slide 18 of 73

19 STANDARD PENETRATION TEST (SPT) (ASTM D a) Split Spoon Dimensions (after ASTM D1586) Typical Setup Figures courtesy of J. David Rogers, Ph.D., P.E., University of Missouri-Rolla & FHWA NHI Course Slide 19 of 73

20 STANDARD PENETRATION TEST (SPT) (ASTM D a) Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 20 of 73

21 STANDARD PENETRATION TEST (SPT) (ASTM D a) Figure courtesy of Slide 21 of 73

22 STANDARD PENETRATION TEST (SPT) Factors Affecting SPT (after Kulhawy & Mayne, 1990 & Table 8. FHWA IF ) Cause Inadequate Cleaning of Borehole Effects SPT not made in insitu soil, soil trapped, recovery reduced Influence on N Value Increases Failure to Maintain Adequate Head in Borehole Bottom of borehole may become quick Decreases Careless Measure of Drop Hammer Energy varies Increases Hammer Weight Inaccurate Hammer Energy varies Inc. or Dec. Hammer Strikes Drill Rod Collar Eccentrically Hammer Energy reduced Increases Lack of Hammer Free (ungreased sleeves, stiff rope, more than 2 turns on cathead, incomplete release of drop, etc.) Hammer Energy reduced Increases Sampler Driven Above Bottom of Casing Sampler driven in disturbed soil Inc. Greatly Careless Blow Count Recording Inaccurate Results Inc. or Dec. Use of Non-Standard Sampler Correlations with Std. Sampler Invalid Inc. or Dec. Coarse Gravel or Cobbles in soil Sampler becomes clogged or impeded Increases Use of Bent Drill Rods Inhibited transfer of energy to sampler Increases Slide 22 of 73

23 CARE & PRESERVATION OF SOIL SAMPLES Mark and Log samples upon retrieval (ID, type, number, depth, recovery, soil, moisture). Place jar samples in wood or cardboard box. Should be protected from extreme conditions (heat, freezing, drying). Sealed to minimize moisture loss Packed and protected against excessive vibrations and shock. Text and Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 23 of 73

24 STANDARD PENETRATION TEST (SPT) (ASTM D a) TEST RESULTS (i.e. BORING LOG) Shows the following: Soil Profile (determined from sampling and boring information) with respect to depth and/or elevation. Groundwater Table (GWT). SPT N Values. Laboratory Test Results (if available). ASTM D Standard Guide for Field Logging of Subsurface Explorations of Soil and Rock Boring Log courtesy of WPC Engineering Inc. Slide 24 of 73

25 CONE PENETRATION TEST (CPT) (ASTM D ) Electronic Steel Probes with 60 Apex Tip Hydraulic Push at 20 mm/s No Boring, No Samples, No Cuttings, No Spoil Continuous readings of stress, friction, pressure With Pore Pressure Measurements (CPTu) With Shear Wave Measurements (SCPT) Text and Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 25 of 73

26 CONE PENETRATION TEST (CPT) (ASTM D ) V s Shear Wave Velocity (V s ) f s Sleeve Friction (f s ) u 2 Penetration Porewater Pressure (U 2 ) q c Cone Tip Resistance (q c ) Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 26 of 73

27 CONE PENETRATION TEST (CPT) RIGS Figures courtesy of FHWA NHI Course Subsurface Investigations & WPC Engineering Inc. Slide 27 of 73

28 CONE PENETRATION TESTING (CPT) RESULTS q c f s u o, u 2 F R Soil Profile CPT Results courtesy of WPC Engineering Inc. Slide 28 of 73

29 CONE PENETRATION TESTING (CPT) Factors Affecting CPT Results Figure 9-2. FHWA NHI Course Subsurface Investigations V s f s U 2 q c Slide 29 of 73

30 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Direct push of stainless steel plate at 20-cm intervals; No borings; no cuttings. Introduced by Marchetti (1980). 18 o angled blade Pneumatic inflation of flexible steel membrane using nitrogen gas Two pressure readings taken (A and B) within about 1 minute A B Figures and Text courtesy of FHWA NHI Course Subsurface Investigations Slide 30 of 73

31 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 31 of 73

32 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Calibrations: ΔA, ΔB (positive values) Readings: contact pressure "A" and expansion pressure "B" with depth Corrections for membrane stiffness in air: p 0 = 1.05(A + ΔA) (B - ΔB) p 1 =B -ΔB DMT INDICES: I D = material index = (p 1 -p o )/(p o -u o ) E D = dilatometer modulus = 34.7(p 1 -p o ) K D = horizontal stress index = (p o -u o )/σ vo A B Text courtesy of FHWA NHI Course Subsurface Investigations Slide 32 of 73

33 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Manual Reading System (Standard) Marchetti Device (ASCE JGE, March 1980; ASTM Geot. Testing J., June 1986) Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 33 of 73

34 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Computerized System (Standard) Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 34 of 73

35 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Results Charleston, SC Project Raw Data & Calibrations Soil Behavior Classification E D with Depth DMT Results courtesy of WPC Engineering Inc. Slide 35 of 73

36 FLAT PLATE DILATOMETER (DMT) (ASTM D (2007)) Results - Piedmont Residuum, Charlotte, NC DMT Results courtesy of FHWA NHI Course Subsurface Investigations Slide 36 of 73

37 SPT-CPT-DMT COMPARISON From Local Project in Charleston, SC Area (2000) Also see Hajduk, E.L., Meng, J., Wright, W.B., and Zur, K.J. (2006). Dilatometer Experience in the Charleston, South Carolina Region, 2nd International Conference on the Flat Dilatometer, Washington, D.C. Slide 37 of 73

38 PRESSUREMETER TEST (PMT) (ASTM D ) Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 38 of 73

39 PRESSUREMETER (PMT) (ASTM D ) Results Utah DOT Project PMT Results courtesy of FHWA NHI Course Subsurface Investigations Slide 39 of 73

40 Performed at bottom of boring or by direct push placement of device Four-sided blade pushed into clays and silts to measure following: s uv (peak) = Peak Undrained Strength VANE SHEAR TEST (VST) (ASTM D ) s uv (remolded) = Remolded Strength (after 10 revolutions) Sensitivity, S t = s uv (peak)/s uv (remolded) Scandinavian Vanes Pictures and text courtesy of FHWA NHI Course Subsurface Investigations Slide 40 of 73

41 VANE SHEAR TEST (VST) (ASTM D ) Figure courtesy of FHWA NHI Course Subsurface Investigations Slide 41 of 73

42 VANE SHEAR TEST (VST) (ASTM D ) Vane Shear Devices Dutch Vane Equipment, Holland VST in Upstate NY Pictures courtesy of FHWA NHI Course Subsurface Investigations Slide 42 of 73

43 VANE SHEAR TEST (VST) (ASTM D ) Results - San Francisco Bay Mud, MUNI Metro Station VST Results courtesy of FHWA NHI Course Subsurface Investigations Slide 43 of 73

44 INSITU TEST METHOD ADVANTAGES/DISADVANTAGES Method Advantages Disadvantages DCP Quick Low cost Limited depth range Limited correlations of DCP values to soil properties. SPT Obtain Sample + Number Simple & rugged device at low cost Suitable in many soil types Can perform in weak rocks Available throughout the U.S. and worldwide. Many correlations with soil engineering properties exist Obtain Sample + Number Disturbed sample (index tests only) Crude number for analysis Not applicable in soft clays and silts High variability and uncertainty Many correlations with soil engineering properties exist Slide 44 of 73

45 INSITU TEST METHOD ADVANTAGES/DISADVANTAGES Method Advantages Disadvantages CPT DMT Fast and continuous profiling of strata. Economical and productive. Results not operator-dependent. Strong theoretical basis for interpretation. Particularly suited to soft soils. Simple and Robust Equipment. Repeatable and Operator- Independent. Quick and Economical. Theoretical Derivations for elastic modulus, strength, stress history. High capital investment Requires skilled operator for field use. Electronics must be calibrated & protected. No soil samples. Unsuited to gravelly soils and cobbles. Difficult to push in dense and hard materials. Primarily established on correlative relationships. Needs calibration for local geologies. Slide 45 of 73

46 INSITU TEST METHOD ADVANTAGES/DISADVANTAGES Method Advantages Disadvantages VST Assessment of undrained shear strength of clays. Simple test and equipment. Measure inplace sensitivity. Long history of use in practice, particularly embankments, foundations, & cuts. Limited to soft to stiff clays & silts with s uv < 200 kpa Slow & time-consuming Raw s uv needs empirical correction Can be affected by sand seams and lenses Slide 46 of 73

47 Geophysical Methods Geologic Mapping (need qualified geologists) Drilling and Coring ROCK EXPLORATION Exploration Test Pits Emerging Tech. Center Sitework Lowell, MA Slide 47 of 73

48 ROCK EXPLORATION Drilling and Coring STB Refusal Auger refusal SPT refusal (> 50 blows per 1 inch penetration) Coring (ASTM D2113) Noncore Drilling Sinkhole in Limestone Terrain Orlando, FL Percussive Methods ASTM D Standard Practice for Rock Core Drilling and Sampling of Rock for Site Investigation Text and Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 48 of 73

49 ROCK EXPLORATION Percussive Drilling Air-Tracks Drilling for Dynamite Placement Penobscot, Maine Photograph courtesy of FHWA NHI Course Subsurface Investigations Slide 49 of 73

50 ROCK EXPLORATION Drilling Rotary Wash Drill Rig Tricone, Roller, Plug Bits Roller Bits Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 50 of 73

51 ROCK EXPLORATION Coring Diamond Bits. Best and hardest, producing high quality core. Fastest cutting rates. Expensive. Synthetic Bits. Less expensive. Generally good quality cores. Tungsten Carbide Bits. Least expensive. Slower coring rates. Diamond Diamond, Carbide Tungsten, Sawtooth Carbide Type Bits Photograph courtesy of Slide 51 of 73

52 Most rugged, least expensive. Consists of head section, core recovery tube, reamer shell, & cutting bit. Often used as starter when beginning core operations ROCK EXPLORATION Coring Single Tube Core Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 52 of 73

53 ROCK EXPLORATION Coring Double Tube Core Inner Barrel Assembly Outer Barrel Assembly Double tube core barrel is the standard. Outer barrel rotates with cutting bit. Inner barrel is either fixed or swivel type (with bearings) that retains core sample. Core diameters generally range from 21 to 85 mm (0.85 to 3.35 inch). NX core: standard diameter = 54 mm (2.15 inches). ASTM C42: The diameter of cores for determining f c in load bearing structural members shall be at least 3.70 in. Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 53 of 73

54 ROCK EXPLORATION Coring Triple Tube Core Good for obtaining core samples in fractured rock and highly weathered rocks. Outer core barrel for initial cut and second barrel to cut finer size. Third barrel to retain cored samples. Reduces frictional heat that may damage samples. Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 54 of 73

55 ROCK EXPLORATION Coring Drilling Fluids Notes Rotary wash with water, foam, or drilling mud (bentonitic or polymeric slurries). Fluids reduce wear on drilling and coring bits by cooling. Fluids remove cuttings & rock flour. Re-circulate to filter fluids and to minimize impact on environment Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 55 of 73

56 Stabilizes boreholes Driven casing Drilled-in casing Dual wall reverse circulation method Use in areas with expected large losses in drilling fluid Inner section for sampling ROCK EXPLORATION Coring Casing Outer casing maintains fluids for drilling Drilled-In Dual Wall Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 56 of 73

57 ROCK EXPLORATION Core Recovery Core Runs taken in either 5- or 10-foot sections. Log the amount of material recovered. Core Recovery is percentage retained. RQD (Rock Quality Designation) is a modified core recovery. Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 57 of 73

58 ROCK EXPLORATION Core Recovery Cores should be stored in either wooden boxes or corrugated cardboard box. Box marked with boring number, depth of core run, type core, bit type, core recovery (CR), rock type, RQD, and other notes. Core operations should be documented: Loss of fluid Drilling rates Sudden drop in rods Poor recovery Loss of core Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 58 of 73

59 ROCK EXPLORATION Core Recovery The RQD is a modified core recovery. Measure of the degree of fractures, joints, and discontinuities of rock mass RQD = sum of pieces > 100 mm (4 inches) divided by total core run. Generally performed on NX-size core. Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 59 of 73

60 Routine: Core boxes Special: Plastic sleeves General: Avoid exposure to shock and vibration during handling and transport. Non-natural fractures may result from excessive movements, temperatures, and exposure to air. Store for future reference ROCK EXPLORATION Care & Preservation Text & Figures courtesy of FHWA NHI Course Subsurface Investigations Slide 60 of 73

61 GEOPHYSICAL METHODS MECHANICAL WAVES Seismic Refraction (SR) (courtesy of Also Available: Downhole Tests (DHT) Spectral Analysis of Surface Waves (SASW) Crosshole Tests (CHT) (FHWA NHI Figurer 5-25) Slide 61 of 73

62 GEOPHYSICAL METHODS ELECTROMAGNETIC WAVES Electrical Resistivity (ER) Survey Results (FHWA NHI Figurer 5-35) Electromagnetic (EM) Survey (FHWA NHI Figurer 5-35) Ground Penetrating Radar (GPR) (photographs courtesy of Other Methods: Magnetometer Surveys (MS) Resistivity Piezocone (RCPTu) Slide 62 of 73

63 ADVANTAGES OF GEOPHYSICS Nondestructive and/or non-invasive Fast and economical testing Theoretical basis for interpretation Applicable to soils and rocks GEOPHYSICAL METHODS GPR Results for UST (FHWA NHI Figure 5-33) MS Results for Oil Well Location (FHWA NHI Figure 5-37) DISADVANTAGES OF GEOPHYSICS No samples or direct physical penetration Models assumed for interpretation Affected by cemented layers or inclusions. Results influenced by water, clay, & depth. Slide 63 of 73

64 SUBSURFACE EXPLORATION PLANNING Subsurface Exploration Plan: Function of - Type and Critical Nature of Structure - Foundation Loads - Topographical Information - Site Geology (Soil and Rock Formations) - Location of Bedrock 1.5 m core to confirm >3 m core required for foundations on rock - Engineer s Experience - Project Requirements USACE EM There are no hard and fast rules stating the number and depth of samples for a particular geotechnical investigation. ASTM D420-98(2003) Standard Guide to Site Characterization for Engineering, Design, and Construction Purposes Consequences of Poor Subsurface Explorations (photographs courtesy of NHI 13231) Slide 64 of 73

65 SUBSURFACE EXPLORATION PLANNING IBC (2006) Section The scope of the soil investigation including the number and types of borings or soundings, the equipment used to drill and sample, the insitu testing equipment and the laboratory testing program shall be determined by a registered design professional. YOU WILL NEED 1 BORING TO 100 ft TO DETERMINE SEISMIC SITE CLASSIFICATION FOR IBC 2006 LET THE ENGINEER DECIDE! Are Soil Explorations as Costly as the Repair? (Photographs courtesy of Slide 65 of 73

66 Photograph courtesy of TTU Center for Multidisciplinary Research in Transportation ( The Massachusetts State Building Code (7 th Edition) 780 CMR FOUNDATION AND SOILS INVESTIGATIONS Borings, Sampling and Testing. The scope of the subsurface exploration, including the number and types of borings, soundings or test pits, the equipment used to drill and sample, the in-situ testing equipment and the laboratory testing program, shall be determined by a registered design professional. LET THE ENGINEER DECIDE! Slide 66 of 73

67 SUBSURFACE TEST LAYOUT GUIDELINES Structure FHWA USACE NAVFAC (NHI ) (Table 2-4 EM ) (DM7.01) Min. # Spacing Min. # Spacing Min. # Spacing Rigid Frame Structure 1 per 230m² 50 ft spacing Low-Load Warehouse Isolated Rigid Ftg < 2500ft² Isolated Rigid Ftg < 10,00ft² Corners O.C. 3 around Per. Houses Subdivisions 1 per 8000m² 200 to 400 ft Houses Individual Lots Bridge Piers 1 (< 30m wide) 2 (> 30m wide) 1 per lot 1 Retaining Walls 1 60 m Roads 2 Lane 60 m 1 per 150 CL Roads Multi Lane 1 per 75 CL Cuts and Embankments 1 60 m Culverts 1 60 to 120 m Levees 6 to 12 m high Levees 12 to 18 m high 230 m 150 m 100 to 200 ft Slide 67 of 73

68 SUBSURFACE TEST LAYOUT GUIDELINES SCDOT Geotechnical Design Manual (2010) Foundation Type Min. Geotechnical Site Investigation Reference Bridge Pile Foundation Minimum one testing location per bent 1 Table 4-1 Bridge Single Foundation Drilled Shaft Minimum one testing locations per foundation location Table 4-1 Bridge Multiple Foundation Drilled Shaft 2 Minimum two testing locations per bent location Table 4-1 Bridge Shallow Foundation Founded on Soil Minimum three testing locations per bent location Table 4-1 Bridge Shallow Foundation Founded on Rock Minimum two testing locations per bent location Table 4-1 Retaining Wall (within 150 of bridge abutment) Minimum one testing location at least every 75 ft Section Retaining Wall (within 150 of bridge abutment) Minimum one testing location at least every 75 ft Section Embankments Minimum one testing location at least every 500 ft Section Cut Excavations Minimum one test locations every 300 ft along cut area Section Culverts Minimum one testing each end of culvert and at every 100 ft of new crossline culvert 2 Section Sound Barrier Walls Dependant on shallow or deep foundation used 2 Section Misc. Structures (Light poles, overhead signs) Minimum of one test location per foundation location Section NOTES: 1. Spacing between testing locations may be increased, but shall be approved prior to field operations and shall include justification. Spacing may not exceed 100 ft. 2. See SCDOT Geotechnical Manual for additional details. Slide 68 of 73

69 SUBSURFACE TEST DEPTH GUIDELINES Structure Spread Footings Deep Foundations (Soil) Deep Foundations (Rock) Roadways FHWA (NHI ) L f 2B, Min. Depth = 2B L f 5B, Min. Depth = 4B 2B < L f < 5B, Extrapolate Min. Depth = 6m below anticipated foundation tip elevation Min. Depth = 3m, 3D, or 2B group below foundation tip Min. 2m USACE (Table 2-4 EM ) Min. Depth = 1½B (4.5m for houses or to unweathered rock) Min. Depth = 1½B of imaginary 2/3 expected pile depth Min. 3m below finished grade (0.75m into rock) Embankments/Culverts Min. 2x Embankment Height Height of Levee Cuts Min. 5m below cut elevation NOTE: B = Footing Width Slide 69 of 73

70 SUBSURFACE TEST DEPTH GUIDELINES SCDOT Geotechnical Design Manual (2010) Foundation Type Minimum Depth Reference Deep Foundation Bridge Shallow Foundation Retaining Walls Embankments Cut Excavations Culverts Borings shall extend below the anticipated pile or drilled shaft tip elevation a minimum of 20 ft or a minimum of 4 times the minimum pile group dimension, whichever is deeper. L 2B, Minimum test depth = 2B L 5B, Minimum test depth = 4B 2B L 5B, Minimum test depth = 3B At least 2X wall height beneath the anticipated bearing elevation or to auger refusal, whichever is shallower. At least 2X embankment height beneath the anticipated bearing elevation (i.e. to a depth sufficient to characterize settlement and stability issues) or to auger refusal, whichever is shallower. At least 25 feet below the anticipated bottom depth of the cut or to auger refusal, whichever is shallower. At least 2X the embankment height beneath the anticipated bearing elevation or in accordance with the bridge spread footing criteria, whichever is deeper (or auger refusal) Section Table 4-2 Section Section Section Section Sound Barrier Walls Dependant on shallow or deep foundation used 1 Section Misc. Structures (Light poles, overhead signs) Same depth criteria as specified for the bridge test locations for the same type of foundation. NOTES: 1. See SCDOT Geotechnical Manual for additional details. Section Slide 70 of 73

71 TEST LOCATION PLAN (EXAMPLE) Other Useful Data: - North Arrow - Topographic Information Shows test locations relative to site Symbol key differentiates between test types Project Information Scale Test Location Plan Example (Courtesy of WPC Inc.) Slide 71 of 73

72 SUBSURFACE TEST LAYOUT & DEPTH GUIDELINES Other Guidelines HUD Directive Rev 2 (1995) Shallow Foundations: 1 boring per 2,500 ft² Deep Foundations: 1 boring per 1,600 ft² Borings must be at least to the bottom of proposed footings and deep enough to locate bearing strata that will support the proposed structure. When rock is encountered, depth of drilling into rock shall be at least 5 feet or enough to establish rock quality regarding voids, fissures and strength, or whether it is a boulder. Hospital and Office Buildings (Sowers and Sowers, 1970) Boring Depth = 3(Number of Stories) 0.7 (for light steel or narrow concrete buildings) Boring Depth = 6(Number of Stories) 0.7 (for heavy steel or wide concrete buildings) Slide 72 of 73

73 SUBSURFACE TEST LAYOUT & DEPTH GUIDELINES Other Guidelines ASCE (1972) 1. Determine Δσ for planned foundation. 2. Determine σ' o with Depth. 3. Determine Depth D 1 at which Δσ = 0.1q (q = applied footing load) 4. Determine Depth D 2 at which Δσ/σ' o = Minimum Depth is the smaller of D 1 and D 2. Figure Das FGE (2005) Slide 73 of 73