深长群桩基础沉降计算深度确定的新方法

New approach to determining the calculation depth for the pile foundation settlement

高速铁路沉降直接关系到高速铁路的安全运营和舒适度,而计算深度(即压缩层厚度)是能否准确计算沉降量的关键。以京沪高速铁路天津段和河北沧州段大桥基础为例,分别进行了现场试验和沉降量的理论计算。现场试验采用液位沉降计和单点沉降计联合监测的方法,得到总沉降量和不同深度土层的压缩量,根据不同深度每延米的压缩量确定压缩层厚度;以3个代表性工点(DK124、DK152、DK240)为例来理论计算其沉降量,经过比较分析得出,需同时满足以下两个条件才可确定压缩层厚度:一是某深度处土层满足压缩层厚度确定方法σi<0.1σzi;二是在该深度以下,土层相临深度间均有Δs/Δh<0.1 mm/m的土层深度。这样既考虑了应力对沉降的影响,也考虑了各土层的应变对沉降的影响。将理论计算值与现场监测数据进行对比,吻合较好。

The present paper is inclined to introduce a new approach to determining the depth calculation for the pile foundation settle- merit, which directly involves the high-speed railway transportation safety and the comfort degree of the passengers in the case of China high-speed railway system. However, one of the key impediments for determining the depth of the settlement （the compressed strata thick- ness） is to solve the problem of field tests and conduct theoretical cal- culations for the three leading sites （DKI24, DKI52, DK240） with the bridge-building foundation in the Tianjin-Cangzhou section of Bei- jing-Shanghai high-speed railway. To solve the liquid level settlement problem, it is also necessary to monitor the entire settlement level and the compression degree of the soil strata at the pile-up tips and make up for the great variety of the thicknesses of the compressed strata in the different parts of the construction sites by using the liquid leveling settlement gauge and the single point settlement gauge in accordance with the per-meter compression degree. For this purpose, it is neces- sary to work out the theoretical settlement of the pile foundation con- gregations through comparison and analysis, for the depth calculation for the settlement can only be satisfied with the next two conditions： 1 ） The additional stress has to be done less than 0.1 time as much as the gravity stress, and, 2 ） The per meter compression under the depth has to reach no more than 0.1 mm. To satisfy the aforemen- tioned demands, it is necessary to compare the testing data with the theoretical values in addition to analysis of the relative errors between them. And, finally, the comparison and analysis results demonstrate that the amount of compression calculated are well in accord with those from the on-spot in-situ tests with the compression depths being larger than the theoretical calculation one. Therefore, it has been made possible to find the original cause of the high compressed depth from the testing data comes from the great depth of the monitoring, which proves that the method of determining the thickness of com- pressed strata is reasonable for the soft soil area in the section of engi- neering project section from Tianjin to Cangzhou, wherein it is neces- sary to take into account the impact of stress and strain of each soil stratum on the settlement. Thus, the above situation can be over- comed if the settlement of foundation can be reduced with the increase of the depth wherein the thickness of compressed strata can be deter- mined by the compression modulus equivalent value in the current specifications.