Bootlegger Cove Formation Research Articles

Stiffness and strength anisotropy of overconsolidated Bootlegger Cove clays

This paper presents the evaluation of the stiffness and strength anisotropy of overconsolidated (OC) Bootlegger Cove Formation (BCF) clays at the Port of Alaska, formerly known as the Port of Anchorage. The stiffness and strength anisotropic material response was evaluated based on triaxial samples equipped with internal instrumentation including a submersible load cell and three subminiature linear variable displacement transducers (LVDTs). Three sets of bender elements were used in this research to measure shear wave velocities for different propagation and polarization directions. The effects of reproducing the stress history of the soil deposit on the stiffness cross-anisotropic behavior of the material are discussed. The laboratory test results are compared with in situ measurements of shear wave velocities based on suspension logging and crosshole and downhole soundings. The results of the experimental program showed that BCF clay is a cross-anisotropic material. Mean stiffness anisotropy ratios ranged from 0.90 to 1.22 and 0.93 to 1.46 for lightly OC and OC conditions, respectively. Strength anisotropy ratios, defined as the ratio of undrained shear strength under triaxial extension to compression, varied between 0.8 and 0.5. It is found that reproducing the stress history of the OC soil deposit during the laboratory reconsolidation stage did not have a significant impact on the initial stiffness anisotropy ratios of the BCF clay.

Stress history and sampling disturbance effects on monotonic and cyclic responses of overconsolidated Bootlegger Cove clays

This paper examines the influence of reproducing the stress history of a natural soil deposit during laboratory reconsolidation on the subsequent response and behavior of heavily overconsolidated Bootlegger Cove Formation (BCF) clays under both monotonic and cyclic loadings. The results are compared with a conventional reconsolidation technique wherein a specimen is directly K0-reconsolidated to the in situ effective stresses, and no stress history of the overconsolidated soil deposit is reproduced. Monotonic and cyclic experiments under triaxial conditions were conducted and their results compared in terms of stress–strain–strength responses with emphasis on shear stiffness degradation, to show the significant difference in the responses between the stress-probe sets. Additionally, comparison with field and in situ measurements are presented to validate procedures, judge the accuracy of the experiments, and evaluate the effects of tube sampling.

Effects of Construction-Induced Stresses on Dynamic Soil Parameters of Bootlegger Cove Clays

This paper presents the influence of construction-induced stress changes on the dynamic soil parameters of Bootlegger Cove Formation (BCF) clays at the site of the Port of Anchorage (POA) expansion project. Results are presented based on numerical simulations of the POA wharf construction and laboratory experimentation where both free-field and postconstruction conditions are reproduced. The postconstruction stability of the foundation clay is considered under both static and dynamic loadings. For the dynamic case, a cyclic triaxial loading equivalent to the contingency-level earthquake (CLE) established for design was used, whereas for the static case, undrained triaxial compression and extension loadings to failure were employed. The results from numerical simulations and laboratory experiments are presented and compared with field measurements and performance data collected during the project construction. The results obtained from specially designed cyclic triaxial probes show the large effects that the construction-induced stresses can have on the dynamic soil parameters and illustrate the importance of adequately considering such effects. Testing protocols and procedures are proposed for quantifying postconstruction soil parameters to better reflect field values and values at small (and otherwise appropriate) strain levels.

Defining Y2 Yielding From Cyclic Triaxial Tests

Abstract This paper presents the yielding characteristics of overconsolidated Bootlegger Cove Formation (BCF) clays extracted from the Port of Anchorage construction site. Additionally, it extends the critical shear strain concept to define the point at which irrecoverable deformations begin (Y2 yielding) to the case of fully reversed loadings during undrained cyclic triaxial (CyTX) tests. On-specimen linear variable differential transformers (LVDTs) and an internal load cell with high accuracy were employed to define stress–strain responses and yield points of the specimens. This paper also presents Y2 yield points obtained using standard procedures available in the technical literature based on monotonic triaxial testing to show that the size and location of the Y2 yield surface can be determined from undrained CyTX tests.

Determination of S-wave Site Response in Anchorage, Alaska in the 1-9 Hz Frequency Band

Site response was estimated at 19 sites in the Anchorage basin in south-central Alaska, using 15 local earthquakes recorded with good signal-to-noise ratio by a temporary weak motion network. The receiver-function-type horizontal-to-vertical spectral ratios (HVSR) were computed at 1-9 Hz frequency band and the resulting HVSR contour maps at 1, 5 and 9 Hz are presented here. The spatial site response distribution shows considerable variation from the foothills of the Chugach Mountains in the east to the western part of Anchorage. The site response increases by a factor of 3 and 3.5 at 1 and 5 Hz, respectively, from the area of older glacial deposits in the eastern part of the city to the area occupied by the Bootlegger Cove formation, particularly in the section adjoining Knik Arm. At 9 Hz, the variation of HVSR from the east to the west is smaller, approximately by a factor of 2. Moreover, the trend of the HVSR variation at 1 and 5 Hz shows good correlation with that of the soil class obtained from surface measurements of S-wave velocity in the 0-30 m depth range and available results on ground failure susceptibility of Anchorage.

Sensitive strata in Bootlegger Cove Formation : Olsen, H W J Geotech Engng Div ASCEV115, N9, Sept 1989, P1239–1251

Sensitive strata in Bootlegger Cove Formation : Olsen, H W J Geotech Engng Div ASCEV115, N9, Sept 1989, P1239–1251