拉压复合型锚杆的锚固机理及设计方法研究

Anchors play an important role in the country basically construct program as a core component of anchorage engineering. Considering the fact that stress concentration between the rock mass and grouting body in tension-type anchor and compression-type anchor can soft shear strength on the interface and result in progressive damage, and that load-dispersive anchors have problems of complex structure and complicated construction. A new tension-compression composite anchor is proposed, with advantages of uniform distribution of shear stress on the interface, high bearing capacity, low cost, convenient construction, etc. So, this project intends to study the anchorage mechanism and design method of this tension-compression composite anchor systematically with the method of combining numerical simulation, model test, theoretical research and engineering application. The major research of this project is regard to the influence of different parameters on the interface between rack mass and grouting body, establishment of stress-strain constitutive relationship model on the interface. Considering the compatibility of deformation between anchorage section in compression and tension, calculation methods for the ratio of tension capacity to compression capacity are proposed. Discriminated methods for different failure models are proposed, taking into account of the influence of different parameters. Then a complete design method is presented for tension-compression composite anchor, combining the results from comparative tests and in-situ tests. Results from this project can provide theoretical basis and technical guidance for the promotion and application of tension-compression composite anchor.

锚杆作为锚固工程的核心组成部分，在国家基本建设中发挥着重要作用。针对荷载集中型锚杆岩土体与灌浆体界面的应力集中容易引起界面剪应力软化，导致渐进式破坏，以及荷载分散型锚杆结构复杂和施工繁琐的问题。提出了一种新型拉压复合锚杆，它具有界面剪应力分布均匀，承载力高，造价低，施工便捷等优点。为此，本项目拟通过数值模拟、模型试验、理论研究和工程应用相结合的研究方法，系统地研究拉压复合型锚杆的锚固机理及设计方法。主要研究内容包括不同参数对岩土体与锚固体界面力学性能的影响；建立界面剪应力-应变本构关系模型；基于承压锚固段与受拉锚固段的变形协调，建立拉压承载比的计算方法；研究不同参数对拉压复合锚杆破坏模式的影响，建立不同破坏模式的判别方法；结合对比试验及原位测试研究结果，提出一套完整的拉压复合锚杆设计计算方法。为拉压复合锚杆的推广和应用提供理论依据和技术指导。

针对新型拉压复合型锚杆，假定锚固体与岩土体之间的剪应力呈三角形分布，对其锚固机理进行了研究。推导得出了拉压复合型锚杆的抗拔承载力计算公式，及其与拉力型锚杆抗拔承载力之比N。对承载比N值的曲线分析结果表明：N随锚固段长度的增加而增加，当锚固段长度系数k1 =2.0时，N达到最大值2.0；N整体随承压锚固段长度系数k2呈碟碗形对称分布，且随k2的增加而先增加后减小，并在k2=0.5时最大；当k1≥2.0时，N的最大值不再随锚固段长度增加而继续增加，但是满足N达到最大值的k2取值区间变大。对比拉压复合型锚杆室内试验成果，本文推导的承载比计算值与试验值吻合较好。在相同锚固段长度下，拉压复合型锚杆抗拔承载力可达拉力型锚杆2.0倍，具有良好的工程应用前景。.通过对传统拉力型锚杆及拉压复合型锚杆开展静力加载试验，研究了不同锚杆的极限抗拔承载力及其特性。研究结果表明：拉压复合型锚杆的荷载位移曲线可分为加载上升段，峰后下降段及残余稳定段三个阶段；拉压复合型锚杆的极限抗拔承载力比拉力型锚杆有显著提高，最高达2.61倍，且当拉压长度比为1:2和2:1时，极限抗拔承载力提高十分显著；拉压复合型锚杆的残余抗拔承载力水平较高且稳定性较好。本文研究成果对拉压复合型锚杆的进一步研究及工程应用具有很好的参考价值。