基坑支护设计中常见问题分析

为保障基坑支护设计方案的安全可行,对基坑支护设计方案中常见问题进行分析,论述了解决杂填土不利影响的方法和泄水管合理设置方法。结果表明,降、排水后的黏性土的土压力、水压力仍采用水、土合算的方法。对砂质土、砂土、碎石土等含水层在已采取降水措施的情况下应不再考虑地下水的影响,土的抗剪强度指标应采用有效应力强度指标C'、φ'进行计算。对于厚度2 m及以下的杂填土,宜将支护结构的起点设置在浅埋的杂填土层底以下位置,同时将杂填土视作附加荷载进行支护设计计算;对于厚度2 m以上的杂填土,土钉或锚杆的锚固段应进入下卧天然地层中,提前对锚固段区域进行注浆等加固措施以改良土性,提高杂填土的极限黏结强度。在含水层与隔水层间特别是有低位汇水的地段加密泄水孔的数量,保障泄水管滤水段部分处于下卧隔水层,在黏性土等隔水层中可少量或不设置泄水装置。 In order to ensure the safety and feasibility of design of foundation pit,the common problems in the design of foundation pit was analysed,and methods to solve the adverse effects of miscellaneous fill and reasonable setting of the drainage pipe were discussed.Results show that earth and water pressure of cohesive soil after precipitation and drainage are still calculated by combined calculation of earth and water pressure.In the case of aquifers such as sandy soil,sand,gravel soil and other aquifers,effect of groundwater should no longer be considered in the case of precipitation measures.The shear strength index of soil should be calculated by the effective stress intensity index C'and φ'.For the miscellaneous fill with thickness of 2 m and below,the starting point of supporting structure should be set at the bottom of the shallow buried fill layer,and the clutter is considered as an additional load for the support design.The anchorage section of soil nailing or anchor should enter the lower lying natural stratum and anchorage section shoule be grouting reinforcement in advance to improved soil property and ultimate bond strength of miscellaneous fill with a thickness of 2 m or above. The number of drainage holes are encrypted in aquifer and aquifers,especially in the low water catchment area.The drainage section of the discharge pipe is in the lower lying layer,and a small amount or no discharge device can be set in the clay and other aquifers