Instability Mechanism of Cavity‐Bearing Formation under Tunnel Excavation Disturbance

Abstract

Urban subway construction inevitably causes disturbances to the rock strata. It can even cause ground collapse accidents when construction encounters a bad geological body in the stratum. To verify the influence of cavities on surface settlement and the mechanism of formation instability, the instability mechanism of cavity-bearing strata under tunnel excavation disturbance was herein studied by tests using self-designed indoor models and numerical simulations. This study was based on the concrete project case of Qingdao Metro. Two groups of experiments (with and without cavities) were designed to simulate the four-step excavation by staged unloading of an airbag. The results show that the settlement value in the cavity state was about twice as much as that in the nonvoid state at the same stage. Besides the first step of excavation, in the numerical simulation, the settlement value of the same stage is about 1.3 times that of the model test. Simulating the deformation process of the surrounding rock in model tests shows that, in the excavation of the tunnel, the collapse surface of the tunnel arch roof will be connected with the sliding surface of the formation cavity. The cavity will gradually change from a regular circle to an ellipse or may even close, resulting in a sudden increase in land subsidence or even ground collapse. This indicates that disturbance during tunnel excavation would cause greater instability in a stratum when bad geological bodies, such as cavities, exist in the stratum.

Influence of the Large-Span Pile-Beam-Arch Construction Method on the Surface Deformation of a Metro Station in the Silty Clay–Pebble Composite Stratum

“…Most of them are built in dense urban areas with complex geological conditions. Excessive stratum settlement is easily caused in the construction process, which adversely affects the safety performance of surrounding buildings [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Improper construction can even lead to serious accidents such as ground collapse and the collapse of surrounding buildings.…”

Experimental Investigation of the Anomalously Low Friction Phenomena in Blocky Rock Systems

“…Effective strengths of these faults are much lower than the rock blocks, which makes the faults turn into slip surfaces. And the effective strengths will be further reduced due to the anomalously low friction phenomena after external disturbances, which can be caused by a nearby blasting [4,12], a construction disturbance [13,14], an earthquake [15,16], and so on.…”