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发表于 2007-9-21 14:37:56
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来自 上海徐汇区
在SLOPE/W2007的用户手册，有专门对于水位骤降的说明：
3.15 Rapid Drawdown Analysis Methods
Using SLOPE/W, stability during rapid drawdown can be modeled in two approaches, namely the “effective strength” approach (simple and rigorous) and the “staged undrained strength” approach.
In the effective strength approach, the effective stress parameters are used to compute the effective shear strength of the embankment during rapid drawdown. The advantage of this approach is that effective shear strength parameters are used which are fundamentally better. The disadvantage of this approach is the extra work required to estimate the pore water pressures within materials during the drawdown process.
In the staged undrained strength method, the shear strength is evaluated based on the total stress parameters and consequently, the requirements associated with the estimation of the pore water pressure conditions for effective stress analysis can be avoided. The disadvantage of this approach is that total stress parameters are used and these total stress parameters are not commonly available. Furthermore, the hydraulic properties of the materials are ignored and the stability of the embankment dam at different times during the drawdown process cannot be evaluated.
rigorous “effective strength” approach需要借助SEEP/W2007计算水位骤降后坝体内的水压力消散，实际上simple “effective strength” approach是最危险的情况，即库区水位降了，但坝体内的水压力还保持不变。
The Staged Undrained Strength Method
The “3-stage” undrained strength method proposed by Duncan, Wright and Wong (1990) has been implemented in SLOPE/W. In short, the 3-stage analysis method can be summarized as follows:
The first stage involves the stability analysis of the embankment before drawdown when the water level is high and the pore water pressures in the materials are at a steady state condition. Both the effective normal stress and shear stress along the slip surface are used to determine the undrained shear strength for materials that do not drain freely.
The second stage involves the stability analysis of the embankment after drawdown when the water level is low and the pore water pressures in the materials are at a steady state condition. The effective normal stress obtained from stage two together with the effective strength parameters are used to compute the drained (effective) strength along the slip surface.
Both the drained and undrained strengths at the slice base along the slip surface are then compared, and the smaller strength is chosen as the computed shear strength which will be used in the third stage. The comparison is needed in order to avoid using undrained strengths greater than drained strengths, which cannot be mobilized if cavitation or drainage occurs (Duncan, Wright and Wong (1990).
The third stage involves conducting a stability analysis using the computed shear strengths and the final drawdown water level. The computed factor of safety from the first and second stages are ignored and only the factor of safety computed from the third stage analysis is used to represent the stability after rapid drawdown.
[ 本帖最后由 basara 于 2007-9-21 14:41 编辑 ] |
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