Soil Borings. 14.485 CAPSTONE DESIGN OVERVIEW REVIEW OF 14.431 FOUNDATIONS & SOILS ENG. Geotechnical Report (not covered). Bearing Pressure Calculations. Settlement Calculations. Lateral Earth Pressure Calculations. Retaining Wall Design Review. Slide 1 of 43
OVERVIEW: BORINGS Slide 2 of 43
STANDARD PENETRATION TEST (SPT) (ASTM D1586-11) Marking of 6 inch Increments for SPT Test Photograph courtesy of physics.uwstout.edu Very common test worldwide 1902 - 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) 3 or 4 increments of 6 inches each Three (3) Increments: Sum of last two increments = SPT N value" (blows/ft) Four (4) Increments: Sum of last two increments = SPT N value" (blows/ft) Correlations available with all types of soil engineering properties Disturbed Soil Samples Collected Text modified from FHWA NHI Course 132031 Subsurface Investigations Slide 3 of 43
STANDARD PENETRATION TEST (SPT) (ASTM D1586-11) 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 132031 Slide 4 of 43
STANDARD PENETRATION TEST (SPT) (ASTM D1586-11) Figure courtesy of FHWA NHI Course 132031 Subsurface Investigations Slide 5 of 43
STANDARD PENETRATION TEST (SPT) (ASTM D1586-11) Figure courtesy of http://www.civil.ubc.ca Slide 6 of 43
STANDARD PENETRATION TEST (SPT) Factors Affecting SPT (after Kulhawy & Mayne, 1990 & Table 8. FHWA IF-02-034 ) 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 7 of 43
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 132031 Subsurface Investigations Slide 8 of 43
c u = undrained strength T = unit weight I R = rigidity index ' = friction angle OCR = overconsolidation K 0 = lateral stress state e o = void ratio V s = shear wave E' = Young's modulus C c = compression index q b = pile end bearing f s = pile skin friction k = permeability q a = bearing stress 14.485 CAPSTONE DESIGN STANDARD PENETRATION TEST (SPT) CLAY N SAND D R = relative density T = unit weight LI = liquefaction index ' = friction angle c' = cohesion intercept e o = void ratio q a = bearing capacity p ' = preconsolidation V s = shear wave E' = Young's modulus = dilatancy angle q b = pile end bearing f s = pile skin friction What Do We Need? How Do We Get It? Courtesy of FHWA NHI Course 132031 Subsurface Investigations Slide 9 of 43
14.485 CAPSTONE DESIGN CORRECTIONS TO SPT N VALUE N measured = Raw SPT Value from Field Test (ASTM D1586-11) N 60 = Corrected N values corresponding to 60% Energy Efficiency (i.e. The Energy Ratio (ER) = 60% (ASTM D4633-10) SPT Corrections (From Table 9, FHWA IF-02-034) Note: 30% < ER < 100% with average ER = 60% in the U.S. N 60 = C E C B C S C R N measured Factor Term Equipment Variable Correction Energy Ratio C E = ER/60 Donut Hammer Safety Hammer Automatic Hammer Borehole Diameter C B 150 mm 65 155 mm 200 mm Standard Sampler Sampling Method C S Non-Standard Sampler Rod Length C R 3 4 m 4 6 m 6 10 m > 10 m For Guidance Only. Actual ER values should be measured per ASTM D4633 0.5 to 1.0 0.7 to 1.2 0.8 to 1.5 1.00 1.05 1.15 1.0 1.1 to 1.3 0.75 0.85 0.95 1.00 Slide 10 of 43
CORRECTIONS TO SPT N VALUE TWO BORINGS/ONE SITE EXAMPLE: Measured N-values Corrected N 60 4 0 10 20 30 40 50 4 0 10 20 30 40 50 Depth (meters) 6 8 10 12 14 16 ER = 34 (energy ratio) 55 45 60 56 40 41 63 41 63 39 63 47 Donut 64 56 Saf ety 69 Sequence Depth (meters) Donut 6 Safety Trend 8 10 12 14 16 Data from Robertson, et al. (1983), Courtesy of FHWA NHI Course 132031 Subsurface Investigations Slide 11 of 43
NORMALIZED SPT N VALUE (N 1 ) 60 (N 1 ) 60 = N 60 values normalized to 1 atmosphere overburden stress. (N 1 ) 60 = C N N 60 Where: C N = (P a /' vo ) n P a = Atmospheric Pressure (1 atm = 14.7 psi = 2116 psf) ' vo = Insitu Vertical Effective Stress n = 1 (clays) and 0.5 to 0.6 (sands) Slide 12 of 43
EFFECTIVE FRICTION ANGLE (') FOR SANDS - SPT 55 Triaxial Database from Frozen Sand Samples Friction Angle, ' (deg) 50 45 40 35 30 25 ' = [15.4(N 1 ) 60 ] 0.5 +20 Sand (SP and SP-SM) Sand Fill (SP to SM) SM (Piedmont) H&T (1996) 20 0 10 20 30 40 50 60 Normalized (N 1 ) 60 Figure 9-12. FHWA NHI Course 132031 Subsurface Investigations Slide 13 of 43
SOIL SHEAR STRENGTH CORRELATIONS FROM IN-SITU TESTING Shear Strength Parameter Insitu Testing Method SPT CPT DMT Effective Soil Friction Angle ( ) See Slide 15 arctan[0.1+0.38log(q t / vo )] 28 +14.6 log(k D )-2.1 log 2 K D See Slide 15 Robertson and Campanella (1983) Marchetti et al. (2001) ISSMGE TC 16 Report Undrained Shear Strength (S u ) NO ACCEPTABLE CORRELATIONS (q t - vo )/N kt (N kt = 15 for CHS) Aas et al. (1986) 0.22 vo (0.5K D ) 1.25 Marchetti et al. (2001) ISSMGE TC 16 Report NOTES: 1. (N 1 ) 60 = N 60 (P a / vo ) 0.5 for sands. P a = Atmospheric Pressure = 1 bar 1 tsf. 2. vo = Insitu Effective Overburden Pressure = Insitu Vertical Effective Stress. 3. vo = Total Overburden Pressure = Insitu Vertical Total Stress. Slide 14 of 43
SOIL SHEAR STRENGTH CORRELATIONS FROM IN-SITU TESTING Effective Soil Friction Angle ( ) Summary from NCHRP Report 651 (2010) Equation ' = 54-27.6034*exp(- 0.014(N 1 ) 60 ) Reference Peck, Hanson, & Thorton (1974) from Kulhawy & Mayne (1990) ' = [20*(N 1 ) 60 ] 0.5 + 20 for 3.5 (N 1 ) 60 30 ' = 27.1 +0.3*(N 1 ) 60 0.00054(N 1 ) 2 60 ' = [15.4(N 1 ) 60 ] 0.5 + 20 ' = [15(N 1 ) 60 ] 0.5 + 15 for (N 1 ) 60 > 5 and 45 Hatanaka & Uchida (1996) Peck, Hanson, & Thorton (1974) from Wolff (1989) Mayne et a. (2001) based on Hatanaka & Uchida (1996) JRA (1996) Slide 15 of 43
SOIL ENGINEERING PROPERTY CORRELATIONS FROM IN-SITU TESTING (TABLE 1) Soil Density/Consistency N q t (MPa) t (pcf) V. Loose 0-4 0-2 90-105 <30 Loose 5-10 2-5 95-110 30-35 ( ) SANDS Medium Dense 11-30 5-15 105-120 35-38 Dense 31-50 15-25 115-130 38-41 Very Dense >50 >25 125-140 41-44 Very Soft 0-2 0-0.5 90-100 COHESIVE SOILS Firm 2-8 0.5-1.5 90-110 Stiff 9-15 1.5-3 105-125 Very Stiff 15-30 3-6 115-135 Hard >30 >6 120-140 after Fang et al. (1991) and EM 1110-1-1905. NOTE: 1 MPa = 10.44 tsf NA Slide 16 of 43
NORMALIZED SPT N VALUE N1 60 (AASHTO 2010) N1 60 = C N N 60 Where: C N = [0.77log10(40/' vo )] (C N < 2.0) ' vo = Insitu Vertical Effective Stress (ksf) N 60 = SPT Blow Count corrected for hammer eff. Table 10.4.6.2.4-1. N1 60 vs. f (after Bowles, 1977). N1 60 f ( ) <4 25-30 4 27-32 10 30-35 30 35-40 50 38-43 * Assume ER = 60% (Cathead) & 80% (Automatic) Slide 17 of 43
AASHTO (2010) 10.6 SPREAD FOOTINGS 10.6.1.3 Effective Footing Dimensions B = B 2e b L = L 2e L Where: e b = Eccentricity parallel to Dimension B. e L = Eccentricity parallel to Dimension L. Figure C10.6.1.3.1. Reduced Footing Dimensions. Slide 18 of 43
AASHTO (2010) 10.6 SPREAD FOOTINGS 10.6.3.1 Bearing Resistance of Soil q R = φ b q n Where: q R = Factored Resistance φ b = Resistance Factor (see Article 10.5.5.2.2) q n = Nominal Bearing Resistance = q ult in 14.431 Slide 19 of 43
REVIEW BEARING CAPACITY EQUATION (after Meyerhof, 1963) q u = c'n c F cs F cd F ci + qn q F qs F qd F qi + 0.5BN F s F d F i Cohesion Component Where: c' = Soil Cohesion N c = Bearing Capacity Factor - Cohesion q = Surcharge = D f N q = Bearing Capacity Factor - Surcharge = Soil Unit Weight N = Bearing Capacity Factor Soil F cs, F qs, F s = Shape Factors F cd, F qd, F d = Depth Factors F ci, F qi, F i = Inclination Factors Soil Component Soil Below Footing Surcharge Component Soil Above Footing B = Footing Width Slide 20 of 43
BEARING CAPACITY FACTORS (Dimensionless, based on ') N q N c N q N tan 2 45 1cot N 1tan 2 q e 2 tan Bearing Capacity Factor (Nc, Nq, N) 100 80 60 40 20 10 8 6 4 2 0 5 10 15 20 25 30 35 40 45 N q N c N c N q N 100 80 60 40 20 10 8 6 4 2 Also see Table 12.1, Das FGE (2006) for Tabular Data 1 N 0 5 10 15 20 25 30 35 40 45 Effective Friction Angle (') ( ) 1 Slide 21 of 43
BEARING CAPACITY FACTORS (Table 12.1 Das FGE 2006) Slide 22 of 43
BEARING CAPACITY FACTORS Factor Cohesion Surcharge Unit Weight Shape (De Beer, 1970) Depth (D f /B 1) (Hanson, 1970) Depth (D f /B >1) (Hanson, 1970) Inclination Hanna & Meyerhof (1981) F F q B cs 1 B N B F qs 1 tan F L N s 1 0. 4 c L L F cd 1 0. cd 4 F ci 1 0.4 tan 1 D f B 1 90 D f B 2 F F qd qd 1 2 tan 1 sin 1 2 tan F qi D 1 f 1 sin 2 tan B 1 90 2 2 D f B F d F d F i 1 1 1 = Inclination of Load with respect to vertical The factor tan -1 (D f /B) is in radians Slide 23 of 43
BEARING CAPACITY EQUATION (AASHTO LRFD Design Specifications, 5 th Ed., 2010) q n = cn cm + D f N qm C wq + 0.5BN m C w Cohesion Component Where: c = Undrained Shear Strength N cm = N c s c i c N c = Cohesion BCF for undrained loading (see Table 10.6.3.1.2a-1) s c = Footing Shape Correction Factor (see Table 10.6.3.1.2a-3) i c = Load Inclination Factor (Eq. 10.6.3.1.2a-5 or 6) This is Munfakh et al. (2001) for determining φ b Surcharge Component Soil Above Footing = Moist Unit Weight of soil above footing D f = Footing Embedment Depth N qm = N q s q d q i q N q = Surcharge BCF (see Table 10.6.3.1.2a-1) s q = Footing Shape Correction Factor (see Table 10.6.3.1.2a-3) d q = Depth Correction Factor (see Table 10.6.3.1.2a-4) i q = Load Inclination Factor (Eq. 10.6.3.1.2a-7) C wq = Groundwater CF (Table 10.6.3.1.2a-2) Soil Component Soil Below Footing = Moist Unit Weight of soil below footing B = Footing Width N m = N s i N = Unit Weight BCF (see Table 10.6.3.1.2a-1) s = Footing Shape Correction Factor (see Table 10.6.3.1.2a-3) i = Load Inclination Factor (Eq. 10.6.3.1.2a-8) C w = Groundwater CF (Table 10.6.3.1.2a-2) Slide 24 of 43
14.485 CAPSTONE DESIGN PRESUMPTIVE MAXIMUM ALLOWABLE BEARING PRESSURES (from Table 1804.2, IBC 2006) Material USCS q all (ksf) Crystalline Bedrock 12 Sedimentary and Foliated Rock 4 Sandy Gravel and/or Gravel GW & GP 3 Sand, Silty Sand, Clayey Sand, Silty Gravel, & Clayey Gravel Clay, Sandy Clay, Silty Clay, Clayey Silt, Silt, and Sandy Silt Mud, Organic Silt, Organic Clays, Peat, and Unprepared Fill SW, SP, SM, SC, GM, GC CL, CH, ML, MH 1.5 See also Table 1 NAVFAC DM7.02 (p. 142) and Table C10.6.2.6.1-1 AASHTO (2010). 2 TBD Slide 25 of 43
AASHTO (2010) 10.6 SPREAD FOOTINGS Other Bearing Capacity Considerations Figure C10.6.1.3.2b-1. Punching Failure (Reduction in Shear Strength) Figure C10.6.1.3.2c-1 (& c-2). Footing on Slopes (Reduction in Bearing Factors) Figure C10.6.1.3.2e-2. Footing on Two Layer Soil Systems (Dependent). Slide 26 of 43
AASHTO (2010) 10.6 SPREAD FOOTINGS 10.6.2.4.2 Settlement Analysis S S S S t e c s Where: S t = Total Settlement S e = Elastic Settlement S p = Primary Consolidation Settlement S s = Secondary Consolidation Settlement Slide 27 of 43
AASHTO (2010) 10.6 SPREAD FOOTINGS 10.6.2.4.2 Settlement (Cohesionless Soils) Elastic Half-Space Method: Where: S q o(1 2 ) e 144E s z A S e = Elastic Settlement q o = Applied Vertical Stress (ksf) A = Effective Area of Footing (ft 2 ) E s = Young s Modulus of Soil (ksi) (See Article 10.4.6.3 if direct measurements are not available) = Soil Poisson s Ratio (See Article 10.4.6.3 if direct measurements are not available) z = Shape Factor (dimensionless) (As specified in Table 10.6.2.4.2-1) Unless E s varies significantly with depth, E s should be determined at a depth of about ½ to 2/3 of B below the footing. If the soil modulus varies significantly with depth, a weighted average value of E s should be used. Slide 28 of 43
ELASTIC SETTLEMENT OF SOIL (DMT) Uses Direct Measurement of Soil to Calculate Settlement Figure courtesy of Marchetti (1999) - The Flat Dilatometer (DMT) and It's Applications to Geotechnical Design Slide 29 of 43
ELASTIC SETTLEMENT OF SOIL (DMT) S e M DMT Z Stress Distribution Where: S e = Elastic Settlement = Change in Stress M DMT = Constrained Modulus Z = Depth Figure courtesy of Marchetti (1999) - The Flat Dilatometer (DMT) and It's Applications to Geotechnical Design Slide 30 of 43
LATERAL EARTH PRESSURES COULOMB OR RANKINE REVIEW Coulomb Wedge Theory: Accounts for wall friction. Unique failure angle for each design. Used by National Masonry Concrete Association (NCMA) & USACE. Inaccurate passive earth pressures w/large wall angles or friction angle (particularly for ' > ' /2). Decreased accuracy w/ depth. Calculates lower active earth pressure than Rankine for level backslope. Rankine State of Stress Theory: Does not account for wall friction. Requires vertical wall. Conservative relative to other methods. Fixed plane of failure. Favored by the transportation agencies (AASHTO and FHWA). See AASHTO Standard Specifications for Highway Bridges. Slide 31 of 43
14.485 CAPSTONE DESIGN LATERAL EARTH PRESSURES COULOMB OR RANKINE REVIEW Coulomb Rankine 1 sin Ka 1 sin K K K K a p p p tan tan 1 K a 2 2 (45 / 1 sin 1 sin (45 / 2) 2) Slide 32 of 43
LATERAL EARTH PRESSURES COULOMB OR RANKINE? Figure C3.11.5.3-1 Application of (a) Rankine and (b) Coulumb Earth Pressure Theories in Retaining Wall Design (AASHTO 2012). Slide 33 of 43
REVIEW: RETAINING WALL DESIGN ANALYSES Overturning Sliding (Strength) Bearing Capacity (Strength) Overall Stability (Service) Figure 13.4. Das FGE (2005) and Figure C11.6.2.3-1 (AASHTO 2012). Slide 34 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.5.2 Service Limit States Abutments, piers, and wall shall be investigated for: Excessive vertical and lateral displacements Vertical: Dependent on wall Lateral: < 1.5 inches (C11.5.2) Overall Stability Can use Modified Bishop, Simplified Janbu, and Spencer Analysis Methods (11.6.2.3) Slide 35 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.5.3 Strength Limit States Abutments and walls shall be investigated at the strength limit states using Eq. 1.3.2.1-1 for: Bearing Resistance Failure (i.e. bearing capacity) Lateral Sliding Excessive Loss of Base Contact Pullout Failure of anchors and soils reinforcements Structural Failure Slide 36 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.5.5 Load Combinations & Load Factors Where: DC = Dead Load of Structural Components DW = Dead Load of Wearing Surfaces and Utilities EH = Horizontal Earth Pressure Load ES = Earth Surcharge Load EV = Vertical Pressure from Dead Load of Earth Fill WA = Water Load and Stream Pressure Figure C11.5.5-2 Typical Application of Load Factors for Sliding and Eccentricity. Slide 37 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.5.5 Load Combinations & Load Factors Where: DC = Dead Load of Structural Components DW = Dead Load of Wearing Surfaces and Utilities EH = Horizontal Earth Pressure Load ES = Earth Surcharge Load EV = Vertical Pressure from Dead Load of Earth Fill WA = Water Load and Stream Pressure Figure C11.5.5-2 Typical Application of Load Factors for Sliding and Eccentricity. Slide 38 of 43
AASHTO (2010) 11 ABUTMENTS 11.5.5 Load Combinations & Load Factors Where: LS = Live Load Surcharge Figure C11.5.5-3 Typical Application of Live Load Surcharge. Slide 39 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.6.3.2 BEARING RESISTANCE (SOIL) v V B 2e Where: V = Sum of Vertical Forces B = Footing Width e = Eccentricity Figure 11.6.3.2.-1 Bearing Stress Criteria for Conventional Wall Foundations on Soil. Slide 40 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.6.3.6 Sliding (refer to 10.6.3.4 Failure by Sliding) R R = φr n = φ R + φ ep R ep Where: R R = Factored Resistance against Failure by Sliding R n = Nominal Sliding Resistance φ = Shear Resistance Factor (see Table 10.5.5.2.2-1) R = Nominal Shear Resistance (=V*tan) φ ep = Passive Resistance Factor (see Table 10.5.5.2.2-1) R ep = Nominal Passive Resistance Slide 41 of 43
AASHTO (2010) SECTION 11 ABUTMENTS 11.6.3.5 Passive Resistance Neglected in Stability Calculations Unless base of the wall extends below the depth of maximum scour, freeze-thaw, or other disturbances Neglected is soil providing passive resistance is, or is likely to become, soft, loose, or disturbed, or if contact between the soil and ground is not tight. Slide 42 of 43
INTERFACIAL FRICTION ANGLES (NAVFAC DM7.02) NOTE: ⅓' ' < ⅔' 14.485 CAPSTONE DESIGN Section 10.6.3.4: Concrete Cast against Soil: tan = tan f Precast Concrete Footing: tan = 0.8*tan f Slide 43 of 43