兰州红砂岩极限承载力深度修正方法试验研究

兰州地区红砂岩处于泥质胶结和极弱的钙质胶结状态,由于该层砂岩具有半成岩的特性,其极限承载力的深度修正与一般土体和岩体不同。本文结合实际工程对半胶结红砂岩的极限承载力深度修正方法进行探究,通过对不同的压板面积、不同的试验深度、不同超载条件下平板载荷试验和剪切试验的试验结果进行统计分析发现:载荷试验因差异性局部破坏,容易低估其岩基极限承载力,不能完全反映其承载特性;红砂岩峰值抗剪强度和残余抗剪强度随正应力有增大趋势,但残余抗剪强度在增大到一定程度后趋于稳定;根据岩基的初始围压以及初始应力可对其极限承载力进行深度修正,但不能等效于砂土;本文中提出的修正后的Vesic公式能对胶结状红砂岩的极限承载力进行较好的预测。

Experimental Investigation on Red Sandstone Depth Correction Method of Ultimate Bearing Capacity

The red sandstone in Lanzhou is in the state of argillaceous cementation and very weak calcareous cementation. Because of its performance of half diagenesis, its depth correction of the ultimate bearing capacity is different from the soil and rock mass. This paper explored the depth correction of the ultimate bearing capacity of the semi-cemented red sandstone combined with practical engineering. Through analyzing the result of the test with designing the different pressure plate, different depth and different overload conditions of plate load test and in-situ shear test, this paper finds that using batholith load test due to differences in local damage is easy to underestimate the ultimate bearing capacity, which can not fully reflect the load-bearing characteristics. The peak intensity residual shear stress and the residual shear strength of the red sandstone would increase along with the normal stress, but the residual shear strength would tend to be constant after the normal stress reaches certain extent. According to the initial confining pressure and initial stress of rock foundation, the ultimate bearing capacity can be modified in depth, but not equivalent to sandy soil. The fixed Vesic formula proposed in this paper can predict the ultimate bearing capacity of the Lanzhou red sandstone.