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RE: Soil Pressure
[Subject Prev][Subject Next][Thread Prev][Thread Next]- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Soil Pressure
- From: "Horning, Dick/CVO" <dhorning(--nospam--at)CH2M.com>
- Date: Tue, 26 Jan 1999 18:06:00 -0700
First of all, if this is a basement wall it's not free to rotate about the bottom, so the soil lateral pressure will be *at-rest* pressure, not active. The pressure distribution is approximately linear downward from the ground surface, increasing at a rate of Ko times the soil density lbs/sq ft/ft depth. Ko depends on the soil strength parameters friction and cohesion, but might typically be 0.5 for a good, cohesionless granular backfill. The uniform pressure would be appropriate if there is a surcharge loading on the soil, and again it would be Ko times the vertical surcharge. Seismic soil pressure is often characterized by an "upside-down" triangular pressure distribution, with the peak pressure at or near the ground surface, and the resultant force at 0.6H above the base of the wall. The geotechs should probably be more complete in their explanation, but it sounds as if you need to review the soil mechanics you learned in college to be better able to understand the explanation. -----Original Message----- From: Francisco Duarte [SMTP:fduarte(--nospam--at)leasung.com] Sent: Tuesday, January 26, 1999 4:03 PM To: seaint(--nospam--at)seaint.org Subject: Soil Pressure Hi, I am working on a project for which I am designing a retaining wall. The report describe the loading as fallow: The basement wall should be design to resist a lateral earth pressure equivalent to a fluid weight of 35 pound per cubic foot , and an additional uniform pressure of 15H pound per square foot, where H= back fill height above the base of the basement wall footing in feet.... Additionally the basement wall should be designed to resist lateral pressure induced by earthquake. An additional earthquake -induce pressure equivalent to a fluid weight of 20 pounds per cubic foot may be used in design. However, distribution of the lateral pressure should be taken as an "invert triangle " with its resultant force acting at a point two third of the wall height above the base of the wall. Now I have tried to calculate the active overall presure and I came up with 75 psf(no including the 15H), which I think is to high and the soils engineer says there is something wrong in my calculations. When I ask him/her to give me his calculated number, the only thing I recieved was a diagram in which he/she shows the 15H psf rectangle , 20H psf rectangle and a 15H psf triangle I guess I am missing something here. 1- Why can he/she give me a straight foward numerical answer? 2- What will the answer be for a 8 feet wall ? -- Francisco Duarte Lea and Sung Engineering, Inc. Tel: 1-510-887-4086 Fax: 1-510-887-3019
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