既有建筑地基承载力时间效应评价的试验研究

Experimental study on time effect of bearing capacity of foundation soil for existing buildings

通过大比尺室内模型试验,对既有建筑地基承载力随时间变化的规律进行了分析研究。试验中分别对模型进行持载3d、7d、14d、28d、35d、49d的载荷试验,选定以持载后继续加载产生的附加沉降占加载前总沉降的3%、5%、10%为允许变形控制指标,结合p-s曲线数据得到了在不同的允许变形控制指标下地基承载力随持载时间增长的提高数值,地基承载力在模型持载一周时间内提高的幅度较大,土体的压密效应效果显著。在实际工程中应根据工程允许的沉降变形与载荷板试验的沉降变形的对应关系,通过现场足尺的载荷板持载试验,选择适当的允许变形控制指标来确定地基承载力。通过双曲线拟合进一步得到了既有建筑地基承载力与时间的变化规律,提出了不同允许变形控制指标下的地基承载力提高的极限值。

The variation regularities of the bearing capacity of the foundation soil with time for existing buildings are systematically studied through the large scale indoor model tests. The experimental model loading tests are constructed which have different sustained load time including three days, seven days, fourteen days, twenty-eight days, thirty-five days and forty-nine days. The three percent, five percent and ten percent which is the additional settlement after sustained load accounts for the percentage of the total settlement before loading are chosen for the allowed deformation index, the values of the bearing capacity of foundation soil under the allowed deformation index are gained through the test data, the compaction effect of the soil is basically completed and the bearing capacity of foundation soil is improved to a larger extent after the model has seven sustained load days. The appropriate allowed deformation index can be chosen to confirm the bearing capacity of foundation soil with the full scale loading plate test according to the corresponding relation between the engineering allowed settlement deformation and the settlement deformation from loading plate tests in practical projects. The hyperbolic-fit method is used to get ihe changing values between the increasing percentage of the bearing capacity of foundation soil and the time, and the improved limit values of the bearing capacity of foundation soil are put forward under different allowed deformation index.