Experimental Study on Reduction of the Horizontal Subgrade Reaction due to Liquefaction

It is important to evaluate resistance strength of foundation and the subgrade reaction of soil surrounding the foundation during an earthquake when a bridge is constructed on liquefiable ground. In this study, we evaluated reduction coefficient of the horizontal subgrade reaction during liquefaction DE based on shaking table tests. We examined the influence of liquefaction resistance factor FL, subgrade shear strain amplitude and velocity of the ground on the reduction coefficient DE from the test results. We made model grounds varying relative soil density in a container, which was placed on a shaking table. A piston was installed on the side wall of the container, and penetration force was measured as horizontal subgrade reaction when the piston was penetrated into the liquefied soil

Compressional and Shear Waves Tests Through Upper Sheet of Low Angle Thrust Fault

Compressional and shear wave tests were conducted on the upper thrust sheet of the low angle Little Salmon thrust fault. The study was conducted on the campus of the College of the Redwoods. The campus is located approximately 8 miles south of Eureka and 24 miles north-northeast of Cape Mendocino and the Mendocino Triple Junction (MTJ) in Northern California. The MTJ is the point of transition from strike-slip faulting of the San Andreas transform system to low-angle reverse (thrust) faulting and folding associated with the convergent margin of the Cascadia Subduction Zone. The campus is located on the southwest limb of the Humboldt Hill anticline, one of the folds in the fold and thrust belt. The Little Salmon fault zone is a low angle thrust fault that day lights on the south side of the campus and then projects underneath striking northwest and dipping northeast. A boring was drilled down to the fault plane located at a depth of 200 ft. in the upper thrust block to develop a mode1 of the stratification as well as the material properties. The boring also revealed the trunk of a redwood tree located at a depth of 180 feet. Results of compressional and shear wave velocities as a function of depth that were determined using an downhole geophysical technique. Results indicated two shear wave velocity units. Unit 1 was from 0 to 120 ft. with a shear wave velocity ranging from 950- 1400 fps. Unit 2 ranged from 120 to 190 ft. with a shear wave velocity ranging from 2300 to 2600 fps. Compression wave velocity measurements obtained from the same test boring also depict a change in velocity in the 100 to 120 foot range. A response spectra was generated based on this in-situ mode1 using SHARE91 and compared against one developed using the Boore, Joyner and Fumal empirical model

Use of Microzonation to Site Facility on Low Angle Thrust and Associated Fault Bend Folding

The campus of the College of the Redwoods is located completely within the Little Salmon Fault Zone, designated by the State of California as an active fault. The College has been extensively investigated for fault rupture and other seismic hazards in 1989, 1993, 1997, 1998, and 1999. The Little Salmon Fault Zone bounds the College and consists of two main northwest-striking, northeastdipping, low-angle thrusts. The west splay daylights along the southwest edge of the campus and projects beneath it. A recurrence interval of 268 years and slip rate of 5+/-3 mm/yr is estimated by CDMG. Individual dip-slip displacements along the west trace are reported to be 12 to 15 feet (3.6 to 4.5 m). Movement on the Little Salmon fault (LSF) is accompanied by growth of broad asymmetric folds in the upper thrust sheet resulting in surface rupture, localized uplift and discreet fault-bend fold axial surfaces. College of the Redwoods is located approximately 8 miles (13 km) south of Eureka and 25 miles (40 km) north-northeast of Cape Mendocino and the Mendocino Triple Junction (MTJ) in northern California. The \u27MTJ is the point of transition fi-om strike-slip faulting of the San Andreas transform system to low-angle thrust faulting and folding associated with the convergent margin of the Cascadia Subduction Zone. Campus infrastructure is located along the base of the Humboldt Hill Anticline (HHA), a major faultbend fold of the Cascadia fold and thrust belt. A new learning resource center (LRC) is proposed for a location 400 feet (120 m) northeast of where the west trace of the LSF daylights and 200 feet (60 m) above the low-angle fault plane. Building setback and design recommendations to mitigate for both fault rupture hazards and fault-generated folding hazards are presented