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砂卵石地层高强度、高渗透性以及低黏聚力的力学特性使得砂卵石基坑工程安全等级划分与评价不同于一般基坑工程。为了对砂卵石基坑安全等级进行有效评价,首先选取基坑开挖深度、砂卵石层厚度及地下水位高度作为砂卵石基坑安全等级评价指标,制定砂卵石基坑安全等级划分及评价标准,然后建立砂卵石基坑本体安全等级物元可拓评价模型,采用有限元计算与层次分析相结合的方法确定指标权重,最后给出砂卵石基坑安全等级评价规范化流程。利用所建立的模型对长沙地区某砂卵石基坑工程进行评价。结果表明,所建立的物元可拓评价模型不但能够定量辨别基坑的安全等级,而且能够区分同一等级不同基坑的相对危险性。
Sandstone gravel formation strength, permeability and low cohesion of the mechanical properties of sand and gravel makes the construction of the safety classification and evaluation of pit excavation is different from the general pit project. In order to effectively evaluate the safety grade of sand-gravel foundation pit, firstly, the excavation depth of foundation pit, the thickness of sand-pebble bed and the height of groundwater table are selected as the evaluation indexes of the safety grade of sand-pebble foundation pit. The safety grade classification and evaluation criteria of sand- Then, the evaluation model of meta-extensibility of sand-pebble foundation pit is built, and the weight of the index is determined by the combination of finite element analysis and analytic hierarchy process. At last, the standardized flow of evaluation of the security level of the foundation pit is given. Using the model established, a sand and gravel foundation pit project in Changsha area was evaluated. The results show that the extrinsic evaluation model can not only quantitatively identify the safety level of foundation pit, but also distinguish the relative risk of different pit of the same grade.