Study On Creep Characteristics And Roadway Stability Of Argillaceous Limestone

Rheological effect is the critical factor which may induce the deformations and even failures in surrounding rocks. Therefore rheological effect should be taken into consideration sufficiently in the designs and construction processes of tunnels. Based on the research of speedy drivage in the San Menxia bauxite mine in Henan province, theoretical study, field geological survey, experimental tests and numerical simulations are conducted to investigate the stability of surrounding rocks and tunnel supports in the tunnels located in argillaceous limestone. Above studies may provide critical references to the safety and excavation rate in the tunnel constructions. The main results obtained are written as:(1) Considering the existence of the randomly distributed inner cracks in rocks, investigations of the damage mechanism in the creep process are conducted based on damage mechanics. And then the statistical damage variable of the rock microelement strength which follows Weibull distribution is introduced to improve the Nishihara model. In the modified Nishihara model, the long-term strength is treated as the threshold stress which will ensure that the rate of steady creep is a nonzero value, and the strain at the starting point of accelerated creep is viewed as the threshold strain of accelerated creep. The deficiency in depicting the characteristics of the accelerated creep in former Nishihara model is conquered, and the entire creep curve is deduced excellently in this improved model.(2) Combining with the Mohr-Coulomb criterion, the form of finite element difference in three-dimension is proposed, and then the constitutive development of Nishihara model in FLAC3D is accomplished. The creep curve of Nishihara model is fitted excellently with Kelvin model curve when the elements are not in the yielded states, and the creep curve is characterized by a steady creep with constant creep rates when the elements are in the yielded states. Based on above characteristics of the creep curve, the accuracy of Nishihara model applied in FLAC3D is verified.(3) Investigation on the characteristics of the surrounding rocks in the tunnels located in argillaceous limestone is performed by applying the advanced geological detection system (TRT6000) in the study. Based on the experimental test, basic mechanical parameters of argillaceous limestone are obtained. And then, according current technical codes and the engineering reduction methods of mechanical parameters, the reasonable mechanical parameters adopted in simulations are also proposed.(4) Numerical analysis based on FLAC3D is conducted on the comparisons among the supporting schemes adopted in the tunnels which are not supported, spraying-concrete supported and bolt-concrete supported in argillaceous limestone. It can be concluded from numerical analysis that the crown settlement and the convergences resulted from the deformation of floor and lateral walls are encountered after the tunnel excavation. The deformation and the expansion of plastic zones in the surrounding rocks are tending to be stable in30days after the excavation; the stability of the tunnel is improved by controlling the deformation and constraining the development of plastic zones of surrounding rocks in both of the supporting patterns. Although the bolt-concrete supporting schemes acquire the better supporting effects than the spraying-concrete supporting schemes, but due to the small creep deformation and small loose circle in the tunnels located in argillaceous limestone, spraying-concrete support is an economical supporting pattern which can also meet the requirement of speedy drivage.