对比弹性支点法的狭长基坑围护结构施工优化研究

Study on Construction Optimization of Narrow and Long Foundation Pit Retaining Structure Compared with Elastic Fulcrum Method

【目的】弹性支点法将基坑假定为平面应变问题进行分析,即假设狭长基坑长距离一次开挖,但在实际施工中有分段开挖的现实情况,所以需要对分区段开挖对基坑围护结构的影响进行研究。【方法】结合新建哈牡客专爱民隧道出口明挖段狭长基坑,建立不同单次开挖长度工况下的三维有限元模型,研究围护结构内力及变形随单次开挖长度的变化规律。【结果】随着单次开挖长度的增加,围护桩水平位移和桩身弯矩逐渐增大并趋近于弹性支点法的计算结果,一次开挖20 m、30 m、40 m时,水平位移比开挖10 m时的水平位移分别增大8.75%、12.2%和13.6%,桩身弯矩分别增大12.1%、14.9%和16.8%;一次开挖10 m、20 m、30 m、40 m时安全系数分别为弹性支点法的1.3、1.17、1.13、1.12倍。【结论】弹性支点法安全储备过大,在实际工程中可结合不同的开挖工况,在对围护结构进行合理优化或满足条件的情况下,合理调整单次开挖长度。

[Purposes]The elastic fulcrum method is used to analyze the foundation pit as a plane strain problem,and that is,it is assumed that the long and narrow foundation pit is excavated once in a long distance.However,there is a reality of segmented excavation in the actual construction,so it is necessary to study the influence of segmented excavation on the retaining structure of the foundation pit.[Methods]Combined with the narrow and long foundation pit in the open-cut section of the newly-built Aimin tunnel exit of Ha-Mu passenger special line,a three-dimensional finite element model under different single excavation length conditions was established to study the variation of internal force and deformation of the retaining structure with the single excavation length.[Findings]With the increase of single excavation distance,the horizontal displacement and bending moment of retaining pile gradually increase and approach to the calculation results of elastic fulcrum method.When the excavation is 20 m,30 m and 40 m,the horizontal displacement increases by 8.75%,12.2%and 13.6%respectively,and compared with that when the excavation is 10 m,and the bending moment of pile body increases by 12.1%,14.9%and 16.8%respectively.When the excavation is 10 m,20 m,30 m and 40 m,the safety factors are 1.3,1.17,1.13 and 1.12 times of the elastic fulcrum method respectively.[Conclusions]The safety reserve of the elastic fulcrum method is too large.In practical engineering,the enclosure structure can be reasonably optimized according to different excavation conditions,or the single excavation length can be reasonably adjusted when the conditions are met.