岩土锚固工程的若干力学概念问题

SEVERAL MECHANICAL CONCEPTS FOR ANCHORED STRUCTURES IN ROCK AND SOIL

我国当前某些岩土锚固工程存在力学概念模糊、设计施工方法不当,导致锚杆失效、工程失稳现象频频出现,工程坍塌破坏等事故也时有发生。通过对岩土锚固的典型工程及事故工程调查、理论分析和试验研究,研究显著影响锚固工程的稳定性与健康发展的若干力学概念问题,旨在为提高锚固工程的设计施工水平,改善锚固工程的安全性与经济性提供依据。主要研究结果为:(1)预应力锚杆(索)具有提供主动抗力、能将结构的拉力传至深部稳定地层等力学特征,凡抵抗倾倒、竖向位移、沿基础底面、地层剪切面破坏和洞室坍塌的结构锚固均应采用此类锚杆。(2)适应张拉控制应力要求的锚杆筋体截面,足够的自由段长度和能充分调动地层抗剪强度的锚固体形式是提高锚杆受拉承载力的基本要素。(3)压力分散型锚固体系显著改善了锚杆的荷载传递机制与防腐保护性能,具有良好的力学与化学稳定性。(4)施锚时机滞后是影响锚固工程稳定性的主要因素之一。及时施作低预应力(张拉)锚杆和发展预制的钢筋混凝土块件作锚杆的传力结构,可有效控制和避免施锚时机滞后现象。(5)为改善高应力低强度岩层中的大型洞室的稳定性,应全面采用低预应力锚杆作初期支护,严格控制高预应力锚杆施作滞后,提高锚杆拉力设计值与初始预应力值和加强围岩变形–锚杆抗力(刚度)相互作用失衡的调控力度。

The misconception in soil and rock mechanics,the irrational methods of design and construction for anchored structures in ground exist in China,which frequently lead to accidents such as anchor failure,instability and even collapse of engineering structures. According to geotechnical investigations of typical engineering and engineering accidents,theoretical analysis and experimental studies,some mechanical conceptual problems which significantly affect the stability of ground anchorage were studied. The prestressed anchor has the advantages of providing the active resistance and transferring the tensile stress of structures to the deep stable strata and can be widely used to resist dumping,vertical displacement,shear failure along the foundation base and openings collapse. The section of anchor meeting the requirements of tensile stress,the length of free end of the anchor being long enough and the anchoring formations being able to fully mobilize the ground shear strength are basic elements for raising the tensile bearing capacity of anchors. The pressure-dispersive anchor significantly improve the load transfer effect and the anti-corrosion protection performance and has excellent mechanical and chemical stability. The time delay in anchor installation can be effectively controlled and avoided after excavation in the slopes and openings by timely applying tensile anchors and prefabricated reinforced concrete blocks as the high bearing capacity transfer structures. In order to improve the stability of large openings in high stress and low-strength rock,it is necessary to adopt the low prestressed anchors as the initial support,to strictly control the time delay of the installation of high prestressed anchor,to raise the initial prestressed value in design and to strengthen the control of the interaction between the surrounding rock deformation and anchorage resistance(stiffness).