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lmnqqy:这个是库仑？朗肯土压力考虑的大小主应力吧。 (2013-09-12 09:58) 

jijian:Do you know when the backfill is horizontal, Coulomb reduces to Rankine? (2013-09-12 10:02) 

lmnqqy:沙土内部有摩擦角，并不是垂直于滑动面的。
这个库仑解法有详细解释。
你把土压力简单分成下滑力和垂直力滑动面的力不可取吧。
tana的摩擦系数没考虑。 (2013-09-12 10:16) 

jijian:No need to con-sider the sliding force on the failure surface, since the moment by this force becomes zero. Am I right? (2013-09-12 10:20) 

lmnqqy:按照力矩的话，确实啊
只考虑垂直滑动面的重力，那滑动面以下对力矩的贡献呢，
那个也是有贡献的哦。
不考虑这个力的力矩平衡不全面吧。 (2013-09-12 10:37)

jijian:haha, I think you need to review your basic mechanics of materials.
The forces perpendicular to slip plane are a pair of equilibrium force. They never contribute to the moment calculation.
(2013-09-12 10:44)

jijian:Attached is illustration for Rankine failure zone theory.
In this problem, the issue is to talk about passive failure.
[图片]
 (2013-09-12 10:17)