National Academies Press: OpenBook

Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation (2024)

Chapter: APPENDIX C-3 CyDSS Testing Remolded Specimen

« Previous: APPENDIX C-2 Strain- and Stress-Controlled CyDSS Testing Intact Specimen of Silty Sand
Page 160
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 160
Page 161
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 161
Page 162
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 162
Page 163
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 163
Page 164
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 164
Page 165
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 165
Page 166
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 166
Page 167
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 167
Page 168
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 168
Page 169
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 169
Page 170
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 170
Page 171
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 171
Page 172
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 172
Page 173
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 173
Page 174
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 174
Page 175
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 175
Page 176
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 176
Page 177
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 177
Page 178
Suggested Citation:"APPENDIX C-3 CyDSS Testing Remolded Specimen." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation. Washington, DC: The National Academies Press. doi: 10.17226/27537.
×
Page 178

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

160 APPENDIX C-3 CyDSS Testing – Remolded Specimen 1. Overview This appendix documents two types of advanced laboratory testing performed on remolded specimens of silty sand and clay: (i) strain-controlled Cyclic Direct Simple Shear (CyDSS) testing; and (ii) saturated hydraulic conductivity testing. Testing was performed at the University of New Hampshire (UNH) per a testing matrix provided to the UNH by the Research Team (RT). RT also provided disturbed specimens of soil recovered from boreholes advanced by the RT at the Wildlife Liquefaction Array site (WLA) in southern California. Sampling locations, sampling intervals, specimen care, transportation procedures, and material description are provided in Appendix B-1. The tested soil was remolded in a respective testing device (in CyDSS for strain-controlled testing and in permeameter for hydraulic conductivity testing). The target values for the preparation of remolded specimens, i.e., unit weight and shear wave velocity, were provided by the RT. These values were established by averaging the results of laboratory testing performed on intact specimens (unit weight) and over the representative depth of the results of in-situ shear wave velocity measurement (see Appendix B-1). To allow for direct comparison between in-situ (i.e., at the WLA site, Appendix B-1), laboratory testing on intact specimens (Appendix C-2), and the centrifuge experiment (Appendix C-1), basic soil classification testing was performed on remolded specimens. This testing included soil moisture content, shear wave velocity (under the specified effective vertical stress; Bender Elements), dry, moist, and saturated unit weight, Atterberg limits, specific gravity, void ratio, and saturated hydraulic conductivity (two methods, constant head, and falling head). The results of CyDSS were interpreted in terms of nonlinear stress-strain and pore water pressure (PWP) response (required for the development of parameters of advanced constitutive models). Given that induced PWP was relatively low in the 2nd cycle, an attempt was made to interpret the rest results in terms of shear modulus reduction and equivalent viscous damping ratio. The same interpretation was also made for the 10th cycle to evaluate the impact of PWP on modulus reduction. This initial interpretation of CyDSS in terms of modulus reduction and damping revealed significant disagreement between interpreted and expected shapes of the curves. Therefore,

161 to eliminate possible system errors, the initial CyDSS testing (Test Series 1) was repeated. The repeated testing is referred to herein as “Test Series 2.” 2. Testing Requirements and Target Material Parameters The following testing requirements were provided to the UNH geotechnical laboratory prior to testing: • Perform strain-controlled undrained CyDSS tests in accordance with ASTM D8296 (2019) (Standard Test Method for Consolidated Undrained Direct Simple Shear Test under Constant Volume with Load Control or Displacement Control). • Target vertical (consolidation) effective stress (σ′v) in the middle of the silty sand layer (WLA site Unit B) is σ′v = 43 kPa. In the middle of the fat clay layer that overlies silty sand, σ′v = 28 kPa. • For specimen remolding, target (moist) unit weight is 18.4 kN/m3 (for both silty sand and fat clay). The target shear wave velocity is 175 m/s (middle of sand layer) and 100 m/s (middle of lean clay layer). Mimic the properties of the remolded soil in the centrifuge experiment (Appendix C-1) as closely as possible. • Check B-value to see if the specimens are fully saturated. Measure shear wave velocity (Vs) on in-device specimen by Bender elements. • Test at 0.01%, 0.0316%, 0.1%, 0.316%, and 0.5% single-amplitude uniform shear strain (0.01% and 0.5% are the lowest and the highest cyclic shear strain amplitudes that the CyDSS device in the UNH can apply). Excitation should be sinusoidal with a frequency equal to 1.0 Hz. • Apply 10 cycles at each strain level, except at the largest achievable strain level (0.5% in the UNH lab). When performing a 0.5% strain amplitude test, if needed, apply more than 10 cycles (apply as many cycles as needed for soil to liquefy). Allow for dissipation of excess PWP between loading stages. Record and report volumetric compression during excess PWP dissipation. • Perform a post-cyclic monotonic simple shear test (on each specimen). Run test up to the largest shear strain achievable. • Interpret the CyDSS testing results in the form of: (i) stress-strain loops; (ii) PWP plots; and (iii) modulus reduction and damping curves. • Perform the soil characterization, classification, and index testing on each specimen tested and compare the results to the target values provided. Perform saturated hydraulic conductivity testing as well. The above listed target values for specimen remolding correspond to the target values provided to Golder for the strain- and stress-controlled testing of “intact” specimens (Appendix C-2) and to the UNH for the Centrifuge experiment (Appendix C-1).

162 3. Testing Devices and Specimen Preparation Techniques 3.1. CyDSS Device and Test Layout The UNH owns and operates a custom built CyDSS device that was designed and built by late Professor Pedro De Alba. The design, with Teflon-coated aluminum rings, is intentionally similar to the design of a laminar box. In technical literature, this type of CyDSS is classified as a “Swedish-type” CyDSS device. The CyDSS ring cell schematic is shown in Figure C-1. Figure C-1. Ring Cell of the UNH CyDSS Device (Adapted from Mousavi, 2020). The schematic of the CyDSS set up is shown in Figure C-2. The soil specimens are prepared in the CyDSS ring cell (100-mm x 25 mm). Linear Variable Differential Transformers are used to measure the settlement of the specimen. Bender elements are used to measure the shear wave velocity directly on the specimen. The load cell, connected to the hydraulic actuator and pneumatic piston, is used for the application of horizontal and vertical loads to the specimen. The flow pump constantly regulates the water flow through the CyDSS ring cell top and bottom platens. Specimen saturation is controlled by enabling constant flow through porous circular disks embedded within top and bottom plates. Differential pressure transducers are used to monitor the PWP generated within the specimen during testing. Figure C-2: CyDSS Test Setup at UNH (Adapted from Mousavi, 2020).

163 3.2. Specimen Preparation Techniques Specimens are prepared in the CyDSS cell. First, the top and bottom plates are coated off to ensure that soil specimens from previous tests were not mixed with the current ones. The rubber membrane is placed to fit on the bottom plate and its interior oiled to ensure that other parts of the CyDSS specimen cell fit appropriately. The Teflon-coated aluminum rings are placed around the 25-mm high membrane, and the outer collars are placed around the rings for specimen preparation. Preparation of fat clay specimen requires presoaking with de-aired water for over 24 hours. The required soil mass is evaluated based upon the internal volume of the CyDSS ring cell. Upon specimen preparation, the specimen is quickly covered with the top plate to prevent moisture loss due to evaporation. Silty sand specimens are prepared using the dry pluviation technique. Before specimen preparation, the silty sand is dried in the oven. Prior to the specimen preparation, the soil is cooled to room temperature. The required soil mass is evaluated based upon the internal volume of the CyDSS ring cell. After the specimen preparation, the top platen is secured by threaded rods and nuts, and the outer collars around the Teflon-coated aluminum rings are removed. Finally, the threaded rods and nuts are released to allow for application of vertical stress to the specimen. 3.3. Bender Element Layout Bender elements are used for direct (i.e., on specimen) measurement of shear wave velocity. The excitation required for this type of measurement is generated and monitored by an oscilloscope. The peak-to-peak method is used to measure the travel time between the input and received waves. The shear wave velocity is calculated by dividing the thickness of the specimen by the travel time recorded during testing. Records of travel times are read from the oscilloscope screen. The specimen test log (oscilloscope screenshot) is shown in Figure C-3.

164 Figure C-3. Shear Wave Velocity Measurement with Bender Elements – Test Log. 4. Testing Results – Test Series 1 4.1. Unit Weight, Moisture Content, Grain Size Distribution and Atterberg Limits Soil properties of tested remolded specimens are listed in Tables C-1 and C-2. Table C-1. Unit Weight Soil Specimen Unit Weight (kN/m³ ) Effective Stress (kPa)Dry Moist Saturated Silty Sand 13.4 - 18.0 43 Fat Clay - 18.4 - 28 Table C-2. Moisture Content and Atterberg Limits Soil Specimen Moisture Content (%) Liquid Limit (wL) (%) Plastic Limit (wP) (%) Plasticity Index (PI) (%) USCS (-) Silty Sand 34.3 23 N/A N/A SM Fat Clay 40 66 37 29 CH UCSC = Unified Soil Classification System Grain size distribution curves are shown in Figure C-4(a) for Silty Sand and in Figure C-4(b) for Clay. The corresponding plasticity chart is shown in Figure C-6.

165 (a) (b) Figure C-4. Grain Size Distribution: (a) WLA Site Silty Sand; (b) WLA Site Clay Figure C-5. Plasticity Chart – WLA Site Fat Clay (CH) 4.2. Specific Gravity and Void Ratio Specific gravity measurements were made using a pycnometer. Approximately 50 g of oven- dried silty sand was placed in a 500 ml pycnometer where water was added to approximately one-third of the total volume of the container. Approximately 75 g of the moist clay was dispersed and placed in a pycnometer. The soil-water mixture was agitated by circular wrist motion until a slurry was formed. The slurry was then de-aired by boiling for two hours, and then water was added to the slurry to a total volume of 500 ml. The slurry for the silty sand and clay were oven-dried and cooled in a desiccator, and then the dry mass was recorded. The results obtained from the specific gravity test are shown in Table C-3. Also, based on the data in Table C-1 and Table C-2, the void ratios for the silty sand and fat clay as prepared in the centrifuge were computed and are shown in Table C-3.

166 Table C-3. Specific Gravity and Void Ratio Soil Specimen Specific Gravity Void Ratio Silty Sand 2.68 0.96 Fat Clay 2.66 0.99 4.3. Saturated Hydraulic Conductivity The constant head and falling head tests were performed on remolded specimens of silty sand and fat clay. The specimens were prepared using a specimen preparation method that is commonly used in centrifuge experiments. The porous stones were placed on both ends of the soil specimen. They were then sealed with greased o-rings to prevent water leakage in the permeameter. Following the sealing, the specimen was saturated with water flowing from bottom to top. The constant head test was performed by attaching a water fill tube to the top of the permeameter, and a drainage tube was attached to the bottom. Readings were taken once constant flow was established. This procedure was repeated three times. The average value is reported in Table C-3. Falling head tests were performed by switching the permeameter to the falling head test setup. The average test results are reported in Table C-4. Table C-4. Hydraulic Conductivity (Remolded Specimens) Soil Specimen Hydraulic Conductivity (Averages of Three Tests) Constant Head (cm/s) Falling Head (cm/s) Silty Sand 1.47 × 10-3 9.04 × 10-4 Fat Clay 1.15 × 10-6 2.04 × 10-7 4.4. Shear Wave Velocity – Test Series 1 Shear wave velocity was measured directly in the CyDSS device by means of bender elements. The corresponding oscilloscope screenshots for silty sand and fat clay are shown in Figures C-6 as output plots for the fat clay and silty sand. Summary results are presented in Table C-5. The corresponding interpretation of these test results in terms of the small-strain shear modulus (Gmax) is presented in Table C-6.

167 Figure C-6. Input and Reflected Waves for (a) silty sand at vertical stress = 43 kPa; and (b) Fat Clay at Vertical Effective Stress = 28 kPa. Table C-5. Summary of Shear Wave Velocity Measurements prior to CyDSS Test Soil Specimen Vertical Effective Stress (kPa) Arrival Time ( ) Specimen Height (m) Shear Wave Velocity (m/s) Silty Sand 43 120.44 0.0249 206.7 Fat Clay 28 112.95 0.0248 219.6 Table C-6. Low-Strain Shear Modulus (Gmax) Soil Specimen Vertical Effective Stress (kPa) Bulk Density (kg/m³ ) Gmax (MPa) Silty Sand 43 1835 88.5 Fat Clay 28 1876 80.1 4.5. Shear Wave Velocity – Test Series 2 (Repeated Tests) Shear wave velocity was measured directly in the CyDSS device by means of bender elements. The corresponding oscilloscope screenshots for silty sand and fat clay are shown in Figure C-7. Figure C-8. Input and Reflected Waves for (a) silty sand at vertical stress = 43 kPa; and (b) Fat Clay at Vertical Effective Stress = 28 kPa (Repeated Tests).

168 The results of the shear wave velocity measurements on saturated soil (by means of bender elements; peak-to-peak method) are presented in Table C-7. The calculated low-strain shear modulus (Gmax) is presented in Table C-8. Table C-7. Summary of Shear Wave Velocity Measurements prior to CyDSS Test (Repeated) Soil Specimen Vertical Effective Stress (kPa) Arrival Time (μs) Specimen Height (m) Shear Wave Velocity (m/s) Silty Sand 43 113.56 0.0260 229.0 Fat Clay 28 154.33 0.0249 161.3 Table C-8. Low-Strain Shear Modulus (Gmax) (Repeated Tests) Soil Specimen Vertical Effective Stress (kPa) Bulk Density (kg/m³) Gmax (MPa) Silty Sand 43 1835 98.3 Fat Clay 28 1876 47.8 5. CyDSS Testing Conditions and Parameters – Test Series 1 and 2 The CyDSS tests were performed on the fat clay subject to a vertical load of 28 kPa and on the silty sand subject to a vertical load of 43 kPa. The test strain levels included 0.01%, 0.0316%, 0.1%, 0.316%, and 0.5%. Testing at 1% could not be performed due to the constraints of the loading actuator operating in the UNH laboratory.

169 (a) (b) Figure C-9. Strain-Controlled CyDSS Test on Remolded Samples of WLA Site Silty Sand - Applied Shear Strain History (PWP was Allowed to Dissipate between Stages). The testing frequency was 0.1 Hz. 10 cycles were applied at each strain level as shown in Figure C-9 for silty sand. PWP was allowed to dissipate prior to the application of the subsequent loading sequence. 50 cycles were applied at the ultimate strain level of 0.5%. The sampling rate was 500 Hz, while pre-trigger and post-trigger times were 0.3 s. Table C-7. Shear Stress – Strain Loops - Silty Sand at ’ v = 43 kPa 0.01% strain level at 10 cycles 0.0316% strain level at 10 cycles - 1 0 1 Sh e a r St r a i n 1 0 - 4 - 0 . 2 - 0 . 1 0 0 . 1 0 . 2 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 4 - 0 . 4 - 0 . 2 0 0 . 2 0 . 4 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n

170 0.1% strain level at 10 cycles 0.316% strain level at 10 cycles 0.5% strain level at 10 cycles 0.5% strain level at 50 cycles Table C-8. Shear Stress – Strain Loops – Fat Clay at ’ v = 28 kPa 0.01% strain level at 10 cycles 0.0316% strain level at 10 cycles 0.1% strain level at 10 cycles 0.316% strain level at 10 cycles - 1 - 0 . 5 0 0 . 5 1 Sh e a r St r a i n 1 0 - 3 - 1 - 0 . 5 0 0 . 5 1 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 3 - 1 . 5 - 1 - 0 . 5 0 0 . 5 1 1 . 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 6 - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 3 - 2 - 1 0 1 2 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 1 0 1 Sh e a r St r a i n 1 0 - 4 - 0 . 1 - 0 . 0 5 0 0 . 0 5 0 . 1 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 4 - 0 . 2 0 0 . 2 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 1 - 0 . 5 0 0 . 5 1 Sh e a r St r a i n 1 0 - 3 - 0 . 5 0 0 . 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 3 - 1 . 5 - 1 - 0 . 5 0 0 . 5 1 1 . 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n

171 0.5% strain level at 10 cycles 0.5% strain level at 50 cycles 6. CyDSS Test Series 1 (This Testing Series was Rej ected by GLA) Tables C-11 and C-12 present plots of excess PWP (Δu) recorded during straining in CyDSS. The Δu was recorded using a differential pressure transducer. This information was processed in the form of the PWP ratio, ru. The ru was calculated in two ways: (i) by normalizing the excess PWP with the initial vertical effective stress; and (ii) by normalizing the excess PWP with the initial mean effective stress. The mean effective stress was evaluated using K0 (coefficient of lateral earth pressure at-rest) that was back calculated from assumed Poisson ratio. The Poisson ratio of 0.33 for silty sand and 0.41 for fat clay are from Karray and Lefebvre (2008). Based on the B-value check, the silty sand specimen was fully saturated. Therefore, ru and ru* values are shown for all the strain levels considered. However, the fat clay specimen was not fully saturated. Therefore, ru and ru* estimates are lower than what would be expected for fully saturated soil. PWP plots for fat clay are presented only for the largest strain tested (0.5%) and for 10 and 50 cycles of straining. Table C-11. Excess PWP Plots - Silty Sand at ’ v = 43 kPa 0.01% Strain; Plot for 10 Cycles: (a) u; (b) ru ; and (c) ru* - 6 - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 3 - 2 - 1 0 1 2 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n 0 2 0 40 6 0 8 0 1 0 0 T i m e ( s ) 0 1 2 3 0 2 0 40 6 0 8 0 1 0 0 T i m e ( s ) 0 0 . 0 2 0 . 0 4 0 . 0 6 0 . 0 8 ru 0 2 0 40 6 0 8 0 1 0 0 T i m e ( s ) 0 0 . 0 2 0 . 0 4 0 . 0 6 0 . 0 8 0 . 1 ru *

172 0.0316% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.1% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.316% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.5% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.5% Strain; Plot for 50 Cycles: (a) Δu; (b) ru; and (c) ru* 0 20 40 60 80 100 Time (s) 0 2 4 6 ΔU (k Pa ) 0 20 40 60 80 100 Time (s) 0 0.05 0.1 0.15 ru 0 20 40 60 80 100 Time (s) 0 0.05 0.1 0.15 0.2 0.25 ru * 0 20 40 60 80 100 Time (s) 0 5 10 15 20 ΔU (k Pa ) 0 20 40 60 80 100 Time (s) 0 0.1 0.2 0.3 0.4 ru 0 20 40 60 80 100 Time (s) 0 0.2 0.4 0.6 ru * 0 20 40 60 80 100 Time (s) 0 10 20 30 40 ΔU (k Pa ) 0 20 40 60 80 100 Time (s) 0 0.2 0.4 0.6 0.8 1 ru 0 20 40 60 80 100 Time (s) 0 0.5 1 1.5 ru * 0 20 40 60 80 100 Time (s) 0 10 20 30 40 ΔU (k Pa ) 0 20 40 60 80 100 Time (s) 0 0.2 0.4 0.6 0.8 1 ru 0 20 40 60 80 100 Time (s) 0 0.5 1 1.5 ru * 0 200 400 600 Time (s) 0 10 20 30 40 ΔU (k Pa ) 0 200 400 600 Time (s) 0 0.2 0.4 0.6 0.8 1 ru 0 200 400 600 Time (s) 0 0.5 1 1.5 ru *

173 The PWP plots shown above reveal that silty sand liquefies after approximately 10 cycles of shear strain equal to 0.5%. The corresponding ru = 0.91 and its ru* is > 1.0. Table C-12. Excess PWP Plots – Fat Clay at σ’v = 28 kPa 0.5% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.5% Strain; Plot for 50 Cycles: (a) Δu; (b) ru; and (c) ru* The PWP plots shown above reveal that cyclically induced PWP buildup in fat clay is very small, even after 50 cycles of 0.5% shear strain. Table C-13. Shear Stress – Strain Loops – Silty Sand at σ’v = 43 kPa (Repeated Tests) 0.01% strain level at 10 cycles 0.0316% strain level at 10 cycles 20 40 60 80 100 120 Time (s) 0 0.1 0.2 0.3 ΔU (k Pa ) 20 40 60 80 100 120 Time (s) 0 0.002 0.004 0.006 0.008 0.01 0.012 ru 20 40 60 80 100 120 Time (s) 0 0.005 0.01 0.015 ru * 0 200 400 600 Time (s) 0 0.2 0.4 0.6 0.8 ΔU (k Pa ) 0 200 400 600 Time (s) 0 0.01 0.02 0.03 ru 0 200 400 600 Time (s) 0 0.01 0.02 0.03 0.04 ru * -1 -0.5 0 0.5 1 Shear Strain 10 -4 -0.15 -0.1 -0.05 0 0.05 0.1 Sh ea r S tre ss (p si ) Shear Stress vs Shear Strain -4 -2 0 2 4 Shear Strain 10 -4 -0.2 0 0.2 Sh ea r S tre ss (p si ) Shear Stress vs Shear Strain

174 0.1% strain level at 10 cycles 0.316% strain level at 10 cycles 0.5% strain level at 10 cycles 0.5% strain level at 50 cycles Table C-14. Shear Stress – Strain Loops – Fat Clay at ’ v = 28 kPa (Repeated Tests) 0.01% strain level at 10 cycles 0.0316% strain level at 10 cycles 0.1% strain level at 10 cycles 0.316% strain level at 10 cycles - 1 - 0 . 5 0 0 . 5 1 Sh e a r St r a i n 1 0 - 3 - 0 . 5 0 0 . 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 3 - 1 - 0 . 5 0 0 . 5 1 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 5 0 5 Sh e a r St r a i n 1 0 - 3 - 1 . 5 - 1 - 0 . 5 0 0 . 5 1 1 . 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 1 - 0 . 5 0 0 . 5 1 Sh e a r St r a i n 1 0 - 4 - 0 . 0 5 0 0 . 0 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 4 - 0 . 2 - 0 . 1 0 0 . 1 0 . 2 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 1 - 0 . 5 0 0 . 5 1 Sh e a r St r a i n 1 0 - 3 - 0 . 5 0 0 . 5 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n - 4 - 2 0 2 4 Sh e a r St r a i n 1 0 - 3 - 1 - 0 . 5 0 0 . 5 1 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n

175 0.5% strain level at 10 cycles 0.5% strain level at 50 cycles 7. CyDSS Test Series 2 (Repeat of Test Series 1) The excess pore pressure from the CyDSS tests (Δu) was recorded using a differential pressure transducer. This information was processed in the form of the PWP ratio, ru. The ru was calculated in two ways: (i) by normalizing the excess PWP with the initial vertical effective stress; and (ii) by normalizing the excess PWP with the initial mean effective stress. The mean effective stress was evaluated using K0 (coefficient of lateral earth pressure at-rest) that was back calculated from assumed Poisson ratio. The Poisson ratio values of 0.33 for silty sand and 0.41 for fat clay are from Karray and Lefebvre (2008). Based on the B-value check, remolded specimen of the WLA site silty sand was fully saturated. Therefore, ru and ru* values are shown for all the strain levels considered. However, remolded specimen of the WLA site fat clay was not fully saturated. Therefore, ru and ru* estimates shown in Table C-18 are lower than what would be expected for fully saturated clay soil Table C-17. Excess PWP Plots - Silty Sand at ’ v = 43 kPa (Repeated Tests) 0.01% Strain; Plot for 10 Cycles: (a) u; (b) ru ; and (c) ru* - 5 0 5 Sh e a r St r a i n 1 0 - 3 - 1 - 0 . 5 0 0 . 5 1 Sh ea r S tre ss (p si ) S h e a r S t r e s s v s S h e a r S t r a i n 0 2 4 6 8 1 0 Cy c l e Nu m b e r 0 1 2 3 0 2 4 6 8 1 0 Cy c l e Nu m b e r 0 0 . 0 2 0 . 0 4 0 . 0 6 0 . 0 8 ru 0 2 4 6 8 1 0 Cy c l e Nu m b e r 0 0 . 0 2 0 . 0 4 0 . 0 6 0 . 0 8 0 . 1 ru *

176 0.0316% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.1% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.316% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.5% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.5% Strain; Plot for 50 Cycles: (a) Δu; (b) ru; and (c) ru* 0 2 4 6 8 10 Cycle Number 0 2 4 6 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.05 0.1 0.15 ru 0 2 4 6 8 10 Cycle Number 0 0.05 0.1 0.15 0.2 0.25 ru * 0 2 4 6 8 10 Cycle Number 0 5 10 15 20 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.1 0.2 0.3 0.4 ru 0 2 4 6 8 10 Cycle Number 0 0.2 0.4 0.6 ru * 0 2 4 6 8 10 Cycle Number 0 10 20 30 40 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.2 0.4 0.6 0.8 1 ru 0 2 4 6 8 10 Cycle Number 0 0.5 1 1.5 ru * 0 2 4 6 8 10 Cycle Number 0 10 20 30 40 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.2 0.4 0.6 0.8 1 ru 0 2 4 6 8 10 Cycle Number 0 0.5 1 1.5 ru * 0 10 20 30 40 50 Cycle Number 0 10 20 30 40 ΔU (k Pa ) 0 10 20 30 40 50 Cycle Number 0 0.2 0.4 0.6 0.8 1 ru 0 10 20 30 40 50 Cycle Number 0 0.5 1 1.5 ru *

177 The PWP plots shown above reveal that silty sand liquefies after approximately 10 cycles of shear strain equal to 0.5%. The corresponding ru = 0.91 and its ru* is > 1.0. Table C-18. Excess PWP Plots – Fat Clay at σ’v = 28 kPa (Repeated Tests) 0.01% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.0316% Strain; Plot for 50 Cycles: (a) Δu; (b) ru; and (c) ru* 0.1% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.316% Strain; Plot for 50 Cycles: (a) Δu; (b) ru; and (c) ru* 0 2 4 6 8 10 Cycle Number 0 1 2 3 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.02 0.04 0.06 0.08 0.1 ru 0 2 4 6 8 10 Cycle Number 0 0.05 0.1 0.15 ru * 0 2 4 6 8 10 Cycle Number 0 0.5 1 1.5 2 2.5 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.02 0.04 0.06 0.08 ru 0 2 4 6 8 10 Cycle Number 0 0.02 0.04 0.06 0.08 0.1 ru * 0 2 4 6 8 10 Cycle Number 0 1 2 3 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.02 0.04 0.06 0.08 0.1 ru 0 2 4 6 8 10 Cycle Number 0 0.05 0.1 0.15 ru * 0 2 4 6 8 10 Cycle Number 0 2 4 6 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.05 0.1 0.15 0.2 0.25 ru 0 2 4 6 8 10 Cycle Number 0 0.1 0.2 0.3 ru *

178 0.5% Strain; Plot for 10 Cycles: (a) Δu; (b) ru; and (c) ru* 0.5% Strain; Plot for 50 Cycles: (a) Δu; (b) ru; and (c) ru* The PWP plots shown above reveal that cyclically induced PWP buildup in fat clay is very small, even after 50 cycles of 0.5% shear strain. Volumetric compression during PWP dissipation was not reported by the UNH laboratory. References ASTM D8296 (2019), “Standard Test Method for Consolidated Undrained Direct Simple Shear Test under Constant Volume with Load Control or Displacement Control,” ASTM International, West Conshohocken, PA, 2011, www.astm.org. Hardin, B., & Drnevich, V. (1972). "Shear Modulus and Damping in Soils: Design Equations and Curves," J. Soil Mech. Found. Div., 98. https://doi.org/10.1061/JSFEAQ.0001760 Karray, M., and Lefebvre, G. (2008), "Significance and evaluation of Poisson’s ratio in Rayleigh wave testing," Canadian Geotechnical Journal, 45(5), 624–635. https://doi.org/10.1139/T08-016 Kramer, S.L. (1996), “Geotechnical Earthquake Engineering,” Prentice Hall, Upper Saddle River, New Jersey, 653 p. Mousavi, S. (2020), "Dynamic Performance of Partially Saturated and Unsaturated Soils," Ph.D. Dissertation, The University of New Hampshire, Durham, New Hampshire Tsuchida (1970). “Prediction and Countermeasure against the Liquefaction in Sand Deposits." Abstract of the Seminar in the Port and Harbor Research Institute, 3.1 - 3.33 (In Japanese). 0 2 4 6 8 10 Cycle Number 0 2 4 6 8 ΔU (k Pa ) 0 2 4 6 8 10 Cycle Number 0 0.1 0.2 0.3 ru 0 2 4 6 8 10 Cycle Number 0 0.1 0.2 0.3 ru * 0 10 20 30 40 50 Cycle Number 0 2 4 6 8 10 ΔU (k Pa ) 0 10 20 30 40 50 Cycle Number 0 0.1 0.2 0.3 0.4 ru 0 10 20 30 40 50 Cycle Number 0 0.1 0.2 0.3 0.4 0.5 ru *

Next: APPENDIX D-1 Sample Element Tests Treasure Island Site: Stress-Controlled Cyclic Direct Simple Shear Test on Medium Dense and Dense Sand »
Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation Get This Book
×
 Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

There are many seismic site response analysis programs that operate in either the time domain or the frequency domain. These programs are available as public domain software, as commercial products, and/or through direct contact with the authors.

NCHRP Web-Only Document 383: Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation, from TRB's National Cooperative Highway Research Program, is supplemental to NCHRP Research Report 1092: Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines.

Supplemental to the document is an Implementation Plan.

READ FREE ONLINE

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!