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现场孔隙压力测量表明,地基中一点上的超静孔隙压力以一定的速率随地面荷重而线性地增长,直达某个临界荷重。这个临界荷重在该点上引起的剪应力达到其抗剪强度,使它发生局部屈伏。此后,该点孔隙压力随着荷重进一步线性地增长,但其速率较大。在局部屈伏前,超静孔隙压力主要是由压应力引起的,剪应力的影响较小;局部屈伏后,剪应力的影响剧烈增大,孔隙压力系数a大致为屈伏前的四倍左右。利用刚发生局部屈伏时的临界荷重和孔隙压力,反算原地的有效应力强度,结果与室内试验十分符合。
The on-site pore pressure measurement shows that the excess pore pressure at a point in the ground increases linearly with the ground load to a certain critical load. This critical load causes the shear stress at this point to reach its shear strength, causing it to locally yield. Thereafter, the pore pressure at this point increases further linearly with the load but at a higher rate. Before the local buckling, the excess pore pressure is mainly caused by the compressive stress, and the influence of the shear stress is small. After the local buckling, the influence of the shear stress increases dramatically. The pore pressure coefficient a is approximately four times that before the buckling. Using the critical load and pore pressure just after the occurrence of local buckling, the in-situ effective stress intensity was backcalculated and the results were in good agreement with the laboratory tests.