Simulation Research on the Load Transfer Mechanism of Anchoring System in Soft and Hard Composite Rock Strata under Tensile Loading Conditions

Abstract

Soft and hard composite rock strata are frequently encountered in transportation, geotechnical, and underground engineering. However, most of the current support is designed for homogeneous rock masses, which ignores the different anchoring effect in soft and hard composite rock strata. A numerical study is presented in this paper on the pull-out behavior of fully grouted rock bolts in soft and hard composite rock strata. The nonlinear bond-slip relationship of bolt-grout interface that is anchored in soft rock and hard rock is obtained from laboratory test, respectively. Then, the nonlinear bond-slip relationship is put into the numerical model. The numerical result shows a close match with the experiment tests and the proposed model. Lithological sequence, layer thickness ratio, and layer numbers are taken into consideration in numerical simulation models. Under the same layer number, the shallower-soft and deeper-hard composite rock strata (SHCRS) have a higher bearing capacity and deformation resistance than the shallower-hard and deeper-soft composite rock strata (HSCRS). As the soft-to-hard thickness ratio in SHCRS increases, the initial stiffness of the load-displacement curve and peak load decreases continuously. The load-displacement curve shows the same initial stiffness for different hard to soft thickness ratios in HSCRS. As the hard to soft thickness ratio increases, the load peak and the displacement at the peak load increase. Therefore, the closer the hard rock is to the loading end, the greater the initial stiffness of the load-displacement curve is. The greater the hard rock thickness, the larger the peak load. Under the same anchor length, the peak load and the displacement at the peak load decrease with the increase of layer numbers, but the reduction magnitude decreases. This paper leads to a better understanding of the load transfer mechanism for the anchoring system in soft and hard composite strata and provides a reference for scientific support design and evaluation method.

Investigation on the pullout bearing properties and stress characteristics of fully grouted bolts in layered rock mass

“…Previous studies have shown that bonded bolts in different rocks have different shear strength parameters of the anchorage interface. 47,48 In coal mines, the layered rock mass structure are composed of different types of rocks, such as hard rock and soft rock. Therefore, to investigate the pullout bearing performance of fully grouted bolts in layered rock mass, hard rock and soft rock were set up in the layered rock mass, and different shear strength parameters of the anchorage interface were used to simulate the interface mechanical behavior of fully grouted bolts in hard rock and soft rock, as shown in Figure 5.…”

“…According to the bearing mechanism of the bonded anchorage system, the shear strength parameters of the anchorage interface determine the bearing performance of fully grouted bolts. Previous studies have shown that bonded bolts in different rocks have different shear strength parameters of the anchorage interface 47,48 . In coal mines, the layered rock mass structure are composed of different types of rocks, such as hard rock and soft rock.…”

Simulation Study on Mechanical Characteristics of Rock Bolt in Rock Mass with Bedding Separation Based on the Nonlinear Bond Slip Relationship

“…This model is rewritten and implemented as a subroutine by FISH language in Flac3D Version 5.0. Then, the nonlinear bond slip relationship is putting into the numerical simulation model by user-defined cs_cstable for expressing the nonlinear characteristics of the anchoring interface [27,29].…”

Finite Element Analysis Model Design on the Mechanical Properties of Prefabricated Shear Wall Structure

“…After unloading, the deformation of the structure cannot be completely recovered and there will be residual deformation and energy dissipation. According to "The technical specification for concrete structures of tall buildings," the energy dissipation capacity of specimens should be measured by the area enclosed by the load-displacement curve [11][12][13][14]. Figure 5 is a schematic diagram for calculating the energy dissipation and equivalent viscous damping coefficients of specimens.…”