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.

中文翻译：

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加载条件下软硬复合岩层锚固系统荷载传递机理的仿真研究

在运输，岩土和地下工程中经常遇到软硬复合岩石地层。但是，目前的大多数支护是为均质岩体设计的，而忽略了软硬复合岩层中不同的锚固效果。本文对软，硬复合岩层中全注浆岩壁锚杆的拉拔特性进行了数值研究。通过实验室测试，分别获得了锚固在软岩和硬岩中的锚固砂浆界面的非线性粘结滑动关系。然后，将非线性粘结滑移关系放入数值模型中。数值结果表明与实验测试和所提出的模型非常匹配。岩性序列，层厚比，数值模拟模型考虑了层数和层数。在相同层数的情况下，较浅层软硬复合岩层（HSCRS）具有更高的承载力和抗变形能力。随着SHCRS中软硬层厚度比的增加，载荷-位移曲线的初始刚度和峰值载荷不断降低。对于HSCRS中不同的硬硬厚度比，载荷-位移曲线显示出相同的初始刚度。随着硬对软厚度比的增加，峰值载荷和峰值载荷下的位移增大。因此，硬岩石越靠近载荷端，载荷-位移曲线的初始刚度就越大。硬岩厚度越大，峰值负载越大。在相同锚固长度下，随着层数的增加，峰值载荷和峰值载荷下的位移减小，但减小幅度减小。本文对软，硬复合地层锚固系统的荷载传递机理有更好的理解，为科学的支护设计和评价方法提供参考。