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发表于 2006-6-1 22:34:49
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来自 广东深圳
The uplift induced by the excavation of a cavern in an elastic material is reasonable and understandable, given the effect of weight reduction noted above. However, in practical cases of tunnel excavation, uplift is rarely observed. There may be several reasons, all of which can be accounted for in a numerical
model, if required. First, more-realistic material behavior, such as plastic flow, anisotropy and microfracturing, may cause the subsidence to be much greater than the uplift (which therefore is unnoticed). Second, there may be an erroneous effect of an artificial lower model boundary. In a uniform, elastic material, the uplift will increase continuously as the lower boundary is placed further away from the upper surface, for a 2D plane-strain simulation. In most field situations, the modulus of rock or soil increases with depth. By representing this correctly in the numerical model, the effect of the artificial lower boundary may be minimized.
Finally, if it is required to eliminate the uplift effect completely, a set of forces can be applied to the excavation boundary that are exactly equal to just the forces that were exerted by the weight of material removed (but not the forces due to non-gravity stresses).
就是这句话。实际上,如果不是要计算开挖引起上部土层的沉降(比如隧道),对于基坑开挖,就可以在开挖的面,施加一个和上面土体重量一样的力,从而限制土体的上浮。
FLAC的其他方法,比如分布开挖,采用逐步施加反力(ZONK.FIS),对控制土体的上浮都没有什么用。 |
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