围岩侧限对自膨胀锚杆性能影响效应研究

Effect of Surrounding Rock Confinement on the Performance of Self-expanding Bolt

大掺量膨胀剂水泥浆作为锚固体的新型自膨胀高强预压锚固技术可显著提升锚杆抗拔力,为研究该技术在围岩侧限条件下的锚固性能,研发了模拟地应力条件下岩体锚固的装置及方法,并开展了不同围岩侧限等级、不同膨胀剂掺量条件下锚固体膨胀应力实时监测及拉拔试验,分析了膨胀应力演化规律、锚固破坏形态及抗拔力提升机理、锚杆界面力学特性及锚固系统破坏耗能规律。结果表明:(1)内界面应力存在随时间的损失效应,损失率随掺量呈线性递减的关系;定义了协同应力,指出内界面应力峰值与协同应力峰值存在滞后时差,并从应力传递的角度解释了其力学机制。(2)拉拔过程中微扩头“卡”在锚孔内并不断上移形成了该锚固体系独特的“荷载平台效应”,极大提升了锚固系统的延性及破坏极限耗能值,并绘制了该效应的力学机制图;建立了自膨胀锚杆的极限抗拔力预测模型,指出初始侧限应力值对极限抗拔力呈指数式影响,表明在工程运用中侧限约束强的围岩能大幅提升锚杆极限抗拔力。(3)引入自膨胀影响系数λ、围岩侧限影响系数k,建立了自膨胀锚固体系的锚杆界面力学公式及能量方程,并结合算例验证了公式的可行性;得出0.7 MPa初始侧限应力条件下,ω=30%的锚固极限抗拔力较普通锚固提升了2.38倍,锚杆峰前位移量提高了1.08倍,锚固系统峰前耗能值提升了6.34倍。

A new type of self-expanding high-strength pre-compression anchorage technology with a large amount of expansion agent cement slurry as an anchor can significantly improve the pull-out force of anchor bolts.To study the anchorage performance of this technology under the condition of the surrounding rock lateral limit,the device and method for simulating rock mass anchorage under the condition of in-situ stress were developed,and the real-time monitoring and pull-out tests of anchorage solids under the condition of different surrounding rock confinement grades and different amounts of expansion agent were conducted.The evolution law of expansion stress,the failure form of anchorage and the lifting mechanism of the pull-out force,the mechanical properties of the bolt interface,and the law of failure energy consumption of the anchorage system were analyzed.The results show that the internal interface stress has a loss effect over time,and the loss rate decreases linearly with the dosage.Moreover,the coordinated stress is defined.It is reported that there is a lag time difference between the peak of the internal interface stress and the peak of the coordinated stress,and the mechanical mechanism is explained from the perspective of stress transfer.During the drawing process,the micro-expanded head sticks to the anchor hole and moves upward continuously,forming the unique “load platform effect” of the anchorage system,which greatly improves the ductility of the anchorage system and the ultimate energy consumption value of damage;this helps draw the mechanical mechanism diagram of the effect.A prediction model for the ultimate pull-out force of self-expanding bolts is established.It is reported that the initial confining stress value has an exponential effect on the ultimate pull-out force,which indicates that the surrounding rock with strong confinement constraints can greatly improve the ultimate pull-out force of the bolt in engineering applications;by introducing the self-expanding influence coefficient λ and the surrounding rock confinement influence coefficient k,the bolt interface mechanics formula and energy equation of the self-expanding anchorage system are established,and the feasibility of the formula is verified using the calculation example.It can be concluded that under the initial confining stress condition of 0.7 MPa,the anchorage of ω=30% is 2.38 times higher than the ultimate pull-out resistance of ordinary anchoring,and the pre-peak displacement of the bolt is increased by 1.08 times.The pre-peak energy consumption of the anchoring system increases by 6.34 times.