稳定分析之地震参数求教

在规范规定的稳定分析方法——拟静力法中，对于地震荷载的考虑是如下Fh＝ah*$*G*ai /g ，其中ah为水平地震加速度，$为地震作用效应折减系数，ai为动力分布系数，G为土条容重。 其中$规范直接规定为0.25。没有说明数据来源，查目前接触到的国外软件（slide和slope/w）中的地震力说明，基本没有发现有折减系数这个说法，仅在slope/w里说明了边坡坡脚存在淹没，或者说坡外有水时会通过专门的地震分析软件计算出水平地震力会比ah*G直接算的值会小，例子中大概小了0.5左右。

现在求教各位，我们规范中的0.25是怎么来的，国外相应的规范是不是也存在这样的系数。（前苏联国家应该是有的。我们的规范是继承他们的。指欧美日等国家）


以下为slide软件中对地震力的描述

Seismic Force
If seismic coefficients are defined, a seismic force will be applied to each slice as follows:
Seismic Force = Seismic Coefficient * Slice Weight
= Seismic Coefficient * area of slice * Unit Weight of slice material
Note that the acceleration due to gravity (g = 9.81 m/s2 for metric units) is already incorporated into the material Unit
Weight entered in the Define Material Properties dialog (remember that the dimensions of Unit Weight are kN / m3),
and therefore does not explicitly appear in the above equation.
The seismic force is applied through the centroid of each slice.
Horizontal Seismic Coefficient
The HORIZONTAL seismic coefficient is always POSITIVE, and represents a horizontal seismic force directed OUT OF the slope (i.e. in the direction of failure).
Since the HORIZONTAL seismic force in Slide is always directed OUT OF the slope, a HORIZONTAL seismic coefficient should always DECREASE the safety factor, for a given slip surface, compared to the same model with NO seismic load applied.

附件为slope/w软件中对地震力的描述。