花岗岩直板轴向压缩的分层破坏及围岩失稳探讨

基于弹性稳定理论,确定抗拉强度较低的板状构件因拉伸分层而轴向压缩失稳的条件;利用宽80 mm、长270~420 mm、厚8~20 mm的花岗岩直板,以刚性压头或垫入5~10 mm橡胶模拟端部的固支和铰支进行单轴压缩。厚16 mm及以上直板会发生分层破坏,强度约为标准试样的40%而不再随厚度增加;而较薄直板可以Euler压缩失稳估计其破坏载荷。从围压对强度的影响趋势看到,花岗岩标准试样单轴压缩强度明显偏低,这同样源于拉伸分层引起的压缩失稳。岩体抗拉强度较低,深部巷道围岩在轴向应力作用下可能发生结构失稳和分区破裂而出现片帮和底鼓,平面应变状态下应力分析和强度校核不足以确认工程安全。

LAMINATED FAILURE OF GRANITE PLATES UNDER AXIAL COMPRESSION AND INSTABILITY OF SURROUNDING ROCK

The instable failure of laminated plate with low tensile strength was explained with the theory of elastic stability. The granite plates of 80 mm in width,270–420 mm in length and 8–20 mm in thickness were compressed using the rigid loading heads with or without the soft rubber cushions of 5–10 mm in thickness. The plates with thickness over 16 mm failed in laminated style and the strength did not increase with the increase of the thickness and was about 40% of the uniaxial compressive strength of standard cylinder sample. The thinner plates were described with Euler?s instability of compression. Similarly,the uniaxial compressive strength was much lower than that from the trend of strength with confining pressure due to axial instability of laminated rock. The surrounding rock with low tensile strength may be structurally instable and zonal disintegrated in deep tunnel under the axial stress.