复合土钉墙实例分析和变形评估

Case studies of composite soil-nailing walls and movement estimate

尽管复合土钉墙在实际工程中广泛应用,但是由于复杂的土层性质和变化多样的挡土结构形式,一直没有能够找到实用的、被广泛认可的变形估算方法。通过分析我国已竣工的26个典型的复合土钉墙支护基坑实例,探讨了复合土钉墙的最大水平位移、沉降与地质条件、支护设计参数之间的关系。统计分析表明,复合土钉墙最大水平位移、最大沉降大多分别在0.4%,0.2%倍的基坑开挖深度附近变化。其中,最大水平位移是桩排和地下连续墙支护的两倍左右。设有预应力锚杆或微型桩的复合土钉墙,最大水平位移值会有所减小。基于Mohr-Coulomb强度准则提出的土层单位抗剪强度的新概念,反映了土层总的强度特性。当基坑主要土层单位抗剪强度增加时,基坑变形有明显减小的趋势。

The displacement evaluation method for composite soil-nailing walls has not been discovered due to the complicated properties of soils and various retaining structures although composite walls have been widely applied. 26 typical case histories of composite soil-nailing walls in deep excavations are presented. The maximum lateral displacements and settlements are analyzed in these cases to find out the relationships between geology and retaining structures. The statistical results show that the maximum lateral displacements and settlements for composite soil-nailing walls are 0.4% and 0.2% of excavation depths, respectively. The former is about twice that for piles and diaphragms. The maximum lateral displacements are reduced slightly for the composite soil-nailing walls with prestressed anchors and micro-piles. The new concept, the unit shear strength of soil, is proposed based on the Mohr-Coulomb failure criterion to quantify the whole shear strength of soil. The maximum displacements are found to decrease significantly as the unit shear strength for the main strata increases.