新填海场地深基坑设计淤泥强度的取值

对于欠固结淤泥土层,现有规范推荐的固结排水强度指标折减系数的方法因没有考虑不同固结度的影响而显得不合理。由于扰动对淤泥不固结不排水强度的影响大,深圳机场扩建项目新填海场地钻孔取样得出的不固结不排水强度只有十字板抗剪强度的1/4。利用十字板原位测试结果确定欠固结土层强度比较合理。由于需要提前进行基坑设计,而欠固结淤泥强度在增长,因此预测欠固结淤泥强度是基坑设计的关键技术问题之一。本文基于改进的估算排水固结强度增长量的有效固结应力法,提出了利用排水固结软基处理实测沉降曲线推算抗剪强度的方法。通过场地刚满载、开挖基坑前和开挖到基坑底3个施工阶段的十字板原位测试结果证明了该方法的合理性和可行性。

Determination of Design Silt Strength for Deep Foundation Pit in New Reclamation Site

For underconsolidated silt layer,the reducing coeff icient method of consolidation drainage strength index recommended by existing codes is unreasonable because it does not consider the inf luence of different consolidation degree.Due to the great inf luence of disturbance on the unconsolidated undrained strength of silt,the unconsolidated undrained strength obtained from borehole sampling at the new reclamation site of Shenzhen Airport Extension Project is only 1/4 of the shear strength of the cross plate.It is reasonable to determine the strength of underconsolidated soil layer by in-situ test results of cross plates.Because it is necessary to design the foundation pit in advance and the strength of underconsolidated silt is increasing,the prediction of underconsolidated silt strength is one of the key technical problems in the design of foundation pit.Based on the improved effective consolidation stress method for estimating the increase of drainage consolidation strength,a method for calculating the shear strength was proposed by using the drainage consolidation soft foundation to treat measured settlement curve in this paper.The rationality and feasibility of the method are proved by the in-situ test results of the cross plates in three construction stages,including full-loading of the site,excavation before foundation pit and excavation to the bottom of foundation pit.