Stability analysis of karst tunnel surrounding rock considering spatiotemporal effects
During tunnel construction,various geological problems may be encountered,and karst development can cause great harm to the tunnel.Because the lithology of the rock mass in the karst area is poor and its structure is relatively broken,it is likely to occur the deformation of surrounding rock and even the instability and damage for the whole tunnel during the tunnel excavation.Due to the limitation of exploration technology and exploration cycle,as well as the irregularity of karst development itself,it is difficult to determine the karst morphology and properties.Therefore,it is very important for us to accurately detect the geometric characteristics of karst so as to propose a reasonable scheme of karst disposal and tunnel excavation,which can ensure the stability and construction safety of the surrounding rock in karst tunnel excavation.The deformation of the surrounding rock of tunnel follows the evolution law of"accelerated deformation-rapid deformation-slow deformation-stable deformation".The longitudinal deformation curve of the convergence-constraint method reveals the spatial effect of deformation of surrounding rock during tunnel excavation,and provides a theoretical basis for us to determine the best time for tunnel excavation support by analyzing the interaction between the surrounding rock and the supporting structure.In Maojiapo tunnel,a single-line single-hole railway tunnel from Dangyang to Yuan'an,a large karst cave is situated at the position of the bottom plate on the right side of the tunnel face.To ensure a clear understanding of the location and size of the cave,and the directions of cave branches,a holographic 3D laser scanner was used to obtain the 3D point cloud data on accurate survey of the karst cave,such as the basic data of geometric characteristics and spatial distribution of the karst cave.In this large and dry karst cave,there are long extended pipelines impacting little on the overall stability of the tunnel.In addition,the karst hall is located under the tunnel.Based on the distribution characteristics of the karst cave and the relative position of the tunnel,this study adopted different reinforcement schemes for the karst hall,and proposed four tunnel karst treatment measures,namely,bridge span,backfill with C20 concrete,backfill with C20 rubble concrete,and ballast backfill.After the four schemes were compared in terms of construction technology and economic benefits,the scheme of backfill with C20 concrete was adopted for karst cave treatment.MIDAS/GTS-NX was used to numerically simulate and analyze the excavation and support of the karst section of Maojiapo tunnel after the karst cave treatment had been completed.An empty-cave model was established based on shape,location and size of the karst cave detected by high-precision 3D laser scanning.The longitudinal deformation law of the surrounding rock during the karst tunnel excavation was obtained by the convergence-constraint method,and the stress and failure characteristics of surrounding rock before and after the tunnel excavation of the karst section were studied.The supporting stability of surrounding rock in the karst section and the non-karst section was analyzed.The results show that compared with the vault subsidence and peripheral convergence of the non-karst section and the karst section of the tunnel,the occurrences of vault subsidence and horizontal peripheral convergence of the karst section reduced after treatment,which indicated the treatment measures of the karst section were reasonable and feasible.Compared with the longitudinal deformation of surrounding rock at different footage of karst tunnel excavation,the footage is negatively correlated with the force of supporting structure.Choosing optimal excavation footage can not only ensure that the deformation of surrounding rock meets the requirements of the specification,but can also contribute to the reasonable use of supporting.This study makes a more complete evaluation of the treatment effect of karst caves and the basis of karst tunnel excavation.
karst tunnelspatiotemporal effect3D laser scanningstability of surrounding rock
国家科技期刊平台
NSTL
万方数据
