Earthquake Engineering Support. Phase 5

• Main Author: Steedman, R S
• Format: Report
• Language: English
• Subjects: ARMY EQUIPMENT; ARMY RESEARCH; DAMS; DEEP DEPTH; DEEP WATER; DYNAMIC RESPONSE; EARTHQUAKE ENGINEERING; EARTHQUAKES; FOREIGN REPORTS; GRAVITY; HIGH DENSITY; LIQUEFACTION; PERMEABILITY; PORE PRESSURE; RESEARCH MANAGEMENT; Seismology; SOIL DYNAMICS; STRENGTH REDUCTION FACTOR; STRESS ANALYSIS; Structural Engineering and Building Technology; STRUCTURAL INTEGRITY; UNITED KINGDOM; WATER TABLE

This report summarizes the findings of an experimental study supported by the U.S. Army Centrifuge Research Center and Engineer Earthquake Engineering Research Program (EQEN) into the behavior of saturated sands under high initial effective confining stresses subjected to strong ground shaking. The research was conducted using the Army Centrifuge at the U.S. Army Engineering Research and Development Center (ERDC), located in Vicksburg, MS. A large dataset of the response of saturated sand to dynamic shaking under level ground' conditions has been compiled and a series of verification models have been conducted. Several techniques were used to investigate the response of deep soil sites (in excess of 70 m) including surcharges, lowered water table and higher acceleration (gravities). The most effective approach was to test specimens at higher gravity, as the interpretation of data from specimens tested using a heavy surcharge on the ground surface, or a deep water table has proved difficult. Many deep samples showed a limit to the excess pore pressure generated during shaking at a level much less than 100% of the initial vertical effective stress. A range of explanations has been proposed, including container effects, saturation, compression of the soil, redistribution of pore pressure and dynamic response of the surcharge. The verification tests eliminated container effects, and parallel research by others has shown that there are several reasons for pore pressure generation at depth to be limited. However, as postulated in earlier stages of this research, there is no absolute limit: in a fully saturated specimen of broadly uniform permeability, liquefaction was observed within a few cycles of strong shaking throughout (to an equivalent field depth of around 65 m). A second key finding indicates that dense layers overlying loose layers may still be readily liquefied as a consequence of the high excess pore pressures generated below.