Craig A. Davis

Numerical Simulations of Geotechnical Centrifuge Modeling of Seismic Earth Pressures on an Underground Restrained Structure

Centrifuge model tests on rectangular structures buried in unsaturated soils are being conducted to simulate an underground restrained wall subject to earthquake shaking. In order to compare the centrifuge testing results with soil-structure-interaction (SSI) results from a numerical modeling approach that is becoming increasingly common for practical design, a pre-centrifuge testing Class A prediction has been performed. This prediction will enable: (1) comparison of the blind numerical modeling with the centrifuge testing results; (2) engineers to identify any potential analysis issues with emerging numerical modeling approaches; and (3) developing design improvements for underground restrained walls. Class A prediction results are presented for a buried rectangular structure with zero and 5 feet of soil above the roof, respectively. The centrifuge results, additional analytical studies, and recommendations for seismic analysis and design improvements will be published elsewhere after completion of the centrifuge testing program.

Lifelines in Megacities Future Directions of Lifeline Systems for Sustainable Megacities

The sustainability of megacities and the ecosystems they influence are critical for ensuring quality of life and environment throughout the world. This sustainability requires infrastructure systems that provide a good and equitable quality of life, and a balance between consumption, disposal, and environmental capacity. Megacities must be strengthened and prepared to resist all hazards that may threaten them. Megacities function as a mega-system made up of many independent subsystems that have been developed in silos. However, the operations of each system depend upon other subsystems within the mega-system, under both extreme and usual circumstances. Lifeline systems are the basic infrastructure that supports all other systems needed for a megacity to function properly. The resiliency of lifeline systems is critical to the sustainability of megacities. Future directions in lifeline systems require improved interactions between the interdependent systems and improved inter-agency coordination. Megacities are extremely vulnerable to risks from natural and man made hazards. Transformative research is needed to better understand how interdependent systems interact and to develop decision support tools that help to understand the performances of complex systems under normal and extreme events. Examples from the Los Angeles megacity region are presented to show the makeup of megacities and mega-systems, and to illustrate their vulnerabilities to extreme events. The simulated performance of water supply and distribution systems in Southern California during a great earthquake scenario are summarized to show how advanced decision support tools may be used for improving the functionality of critical infrastructure systems under normal and extreme circumstances. This study indicates that resilience can be enhanced through multi-system integration and the risks and vulnerabilities to hazards can be overcome through integration of existing infrastructure.

Seismic Resilience Design for a Concrete Box Reservoir

The proposed 110-million-gallon reinforced concrete Headworks Reservoir structures are planned by the Los Angeles Department of Water and Power (LADWP) to be part of the water supply system of the City of Los Angeles, and resilience of the water supply system is crucial for continued water supply in the event of a disaster, such as an earthquake. The seismic resilience of the reservoir structure is a function of the cracking and associated leakage that would be expected due to static loading and during the design level earthquake. Evaluation of the seismic deformation of the structure was accomplished utilizing a soil-structure interaction (SSI) model to evaluate performance of the reservoir structure in an earthquake, after the initial design based on standard code-based design procedures. SSI was used to provide information on the structural behavior of the reservoir, and to understand relative movement of inlet and outlet pipelines. In addition, a leak detection system was incorporated into the design. PROJECT DESCRIPTION AND GEOLOGY The proposed Silver Lake Complex Replacement Project consists of the Headworks Reservoir Complex (East and West Reservoirs), a Hydropower Plant to be constructed on approximately 12 acres within the Headworks Spreading Grounds, and a series of new water conveyance pipelines to and around the existing Silver Lake Reservoir (not at the location of the proposed reservoir site). The current proposed location of the reservoir complex including major project components planned are

A Comparison of SASW Survey Results with In-Situ Field Investigation Methods

A geotechnical investigation of a site for two large buried water storage reservoirs was recently conducted. The geotechnical investigation used multiple insitu field methods to characterize the recent alluvial and fluvial deposits overlying bedrock that underlie the reservoir site. The recent deposits had a gravel, cobble and boulder content which made characterization of these deposits by the usual in-situ methods, such as the standard penetration test (SPT), more difficult. Because of the coarser grained materials, Becker Penetration Tests (BPTs) were performed to provide continuous penetration resistance at several locations throughout the large site. To provide additional information, Spectral Analysis of Surface Waves (SASW) testing was performed to characterize the thicknesses and shear wave velocity (Vs) profiles of the alluvial and fluvial deposits and the underlying bedrock. The SASW results were compared with the results of shear wave velocity profiling using the suspension logging technique performed in several rotary wash borings at the site. The SASW shear wave velocity profiles, in combination with the other investigation methods, were useful in determining the nature of the subsurface materials and refinement of the soil and bedrock profiles for liquefaction and soil-structure interaction analyses required in the design of the reservoir structures.