Loren R. Anderson

Investigation of a cyclic laterally loaded model pile group

Abstract In certain regions of the world, designing deep foundations to withstand seismic loading is a reality. Seismic loading of structures and foundations reaches its most critical state as a cyclic lateral force. The response of soils and foundations to repetitive lateral forces is highly complex, relegating most design methods to be based upon overly conservative rules-of-thumb. The primary objective of this research was to analyze the mechanics of seismic loading on pile groups in clay soils. To achieve this a model testing facility was constructed to house a fully instrumented 1×5 model pile group that was subjected to cyclic lateral loading. An empirically based method for pile group design is suggested based upon the results generated from model pile group testing.

Risk Assessment of Success Dam, California: Flood Related Potential Failure Modes

Potential seismic deficiencies of Success Dam, California have been identified and a remediation plan for the dam is in the process of development. The dam is currently operated under reservoir pool elevation restriction to reduce risk until the long-term remediation is implemented. Justification of operation restrictions and establishing the priority of remediation activities required preparation of a baseline risk assessment. Seepage and piping failure modes made a significant contribution to the baseline risk, but were little affected by the operating restrictions that were used to reduce the earthquake-related failure modes. This paper describes the role of the flood-induced failure modes in the risk assessment and particularly the evaluation of the piping and seepage failure modes. The USACE Piping and Seepage Toolbox was used as an aid in estimating the probability of failure by the various piping and seepage failure modes.

Risk Assessment of Success Dam, California: Earthquake Induced Potential Failure Modes

Seismic deficiency of Success Dam, California has been determined and the need of remediation for improving the performance of the dam under earthquake loading has been identified. Consequently, the dam is currently operated under reservoir pool elevation restriction, pending rehabilitation implementation. Justification of operation restrictions and establishing the priority of remediation activities required preparation of a baseline risk assessment. This paper describes the estimation of the inputs to the estimation of the probability of failure (breach of the dam) from earthquake loading using an event tree risk model. The inputs that are described include earthquake loading, liquefaction and deformation analysis and the development of the system response probability relationships for above core erosion, seepage erosion through cracks and tower induced failure modes. Two companion papers describe the potential failure modes related to flood events (Anderson et al 2011)and the overall risk assessment and justification of operation restrictions (Bowles et al 2011).

Instrumentation for Laterally Loaded Model Piles

Utah State University is involved with a research project funded by the Utah Department of Transportation and the Mountain Plains Consortium. The reaction of model piles subjected to lateral loading is the subject of ongoing research. The measured response of laterally loaded model pile is compared with predicted results. The model piles are 1524 mm (60 in.) long with approximately 1219.2 mm (48 in.) embedded in a soft clay soil. The piles consist of 1-in. Schedule 40, 33.40 mm (1.315 in.) OD aluminum tubes, with a wall thickness of 8.407 mm (0.331 in.). To measure the pile response to the lateral loads, each pile is instrumented with 14 pairs of foil strain gauges mounted at 91.875-mm (3.75-in.) spacings. The gauge pairs were mounted on the inside wall of the seamless tube. A special installation tool was designed and fabricated at Utah State University for this purpose. A wedge-scissors device was used to mount the gauges to the inside wall. The strain gauges (CEA-13-250UW-120) are each wired into a 1/4...

Cylinder Direct Shear: A New Test Method

The Cylinder Direct Shear is a new test method that has been developed for determining large displacement interfacial shear strengths of geosynthetics. The significance of the new test method is that many geosynthetics interfaces lose shear strength with increasing displacement. The new method is patented and is designed around the current 0.3-m (12-in.) direct shear per ASTM D-5321. It consists of testing the geosynthetic interface mounted on a cylinder instead of on a flat plate. The Cylinder Direct Shear has one geosynthetic mounted on the surface of the rigid cylinder and the second geosynthetic anchored to a stationary anchor bar and contained within a latex rubber membrane. The test assembly is mounted within a pressure chamber and a normal force is applied using the chamber pressure acting on the latex rubber membrane. Friction resistance is measured by recording the torque to rotate the cylinder while the normal force is applied and displacement is determined by measuring the rotation of the cylinder relative to the stationary anchor bar. Comparable results have been obtained using the same geosynthetic interfaces at similar displacements when compared with current 0.3-m direct shear testing. The primary difference of the Cylinder Direct Shear with the 0.3-m direct shear has been the ability to measure interface shear strengths using continuous unlimited displacement testing in the machine direction to displacements far beyond the 7.5 to 10 cm limitation of the current 0.3-m direct shear. Interface shear strengths of geosynthetics have been measured at displacements in excess of 6 m using the Cylinder Direct Shear Test.