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Basic Geotechnical Earthquake Phần 8

Động đất là một thiên tai khó có thể dự báo trước được, cho nên những người sống ở một nơi gần những nơi thường có động đất không thể tránh nó được. Tuy nhiên, có một số điều ta có thể làm để trước, trong lúc, và sau động đất để tránh thương tích và thiệt hại do động đất gây ra. | 10 Chapter RETAINING WALL ANALYSES FOR EARTHQUAKES 10.1 introduction Retaining wall is a structure whose primary purpose is to provide lateral support for soil or rock. It may also support vertical loads. They could be of gravity cantilever counterfort and crib wall type. Basement walls and bridge abutments are typical examples. Performance of retaining wall during earthquake is very complex. Due to seismic forces walls can move by translation and or rotation depending on wall design. Magnitude and distribution of dynamic wall pressure is influenced by mode of wall movement. Maximum soil thrust acts on wall when the wall translates or rotates towards the backfill. It is minimum when the wall translates or rotates away from the backfill. The shape of earthquake pressure distribution and the point of application of resultant changes as the wall moves. Dynamic wall pressure and permanent wall displacement increase significantly near the natural frequency of wall backfill system under earthquake loading. Increased residual pressure may remain on wall after episode of strong shaking has ended. It has been stated that the allowable bearing pressure and allowable passive pressure should be increased by a factor of one-third while performing seismic analysis. This increase is appropriate if retaining wall bearing material and soil in front of wall consists of massive crystalline bedrock and sedimentary rock that remains static during earthquake soils which dilate due to earthquake soils having little reduction in shear strength with strain clay with low sensitivity and soils located above water table. However the increase is not recommended if the soil consists of foliated rock that fractures in earthquake loose soil located below water table sensitive clays and soft clays. Former group of soils do not loose shear strength during seismic shaking while later group of soils loose shear strength during seismic shaking. This chapter deals with methods of retaining wall .