【作者】 任非凡；

【导师】 韩文峰； 谌文武；

【作者基本信息】 兰州大学 ， 地质工程， 2009， 博士

【摘要】 目前,国家加大了文物保护力度,特别是保存在我国西北丝绸之路上的土遗址,由于遭受严重的风蚀和雨水冲刷、构造裂隙的破坏,大批的土遗址濒临破坏,范围急剧收缩,已经成为广大专家学者最为关注的问题之一。锚固作为提高岩土体稳定性和解决复杂岩土工程问题最经济、有效的方法之一,它可以提高土体的强度及其自稳能力,易于施工,正被广大的文物保护单位所采用。南竹加筋复合锚杆作为一种新型锚杆以其自身的优越性虽已被应用于一些土遗址保护加固工程中,但其加固技术尚属首创,其施工工艺和流程、锚固机理、锚固效果尚未得到科学合理的阐释,结构的多界面性以及界面各介质的交互作用为系统地研究复合锚杆带了很大的挑战。因此,对其进行系统的研究不但可填补南竹加筋复合锚杆锚固机理研究的空白,为复合锚杆自身优化提供依据,而且也可为干旱半干旱地区土遗址高陡边坡复合锚杆加固技术的推广应用提供科学依据,并对其他类型工程锚杆的锚固机理研究具有一定的借鉴意义。论文阐释了交河故城遗址的工程地质环境和崖体边坡的破坏模式,对现有的复合锚杆锚固工艺进行优化。应用弹塑性力学、断裂力学、数学、变形监测、数值分析等理论、技术手段,从理论、试验、数值模拟三个方面,对南竹加筋复合锚杆的锚固机理及变形破坏进行系统的研究。并以交河故城崖体边坡41-5亚区为例,用强度折减有限元法,对其锚固前、后的边坡稳定性进行分析对比。主要研究成果如下：(1)研究区地处吐鲁番盆地中央隆起构造带上,构造运动强烈,崖体坡度大,构造裂隙、卸荷裂隙发育且相互交错,河流侵蚀切割现象严重,加之特殊气候下形成的携砂风对崖面软弱地层的掏蚀所形成的临空面,极大地破坏了交河故城崖体的稳定性。(2)结合交河故城锚固工程,对现有复合锚杆施工工艺进行现场调查、统计、对比,针对复合锚杆自身特性及土遗址加固的特殊性,分别从布孔定位、临时支护、钻孔、清孔、上锚杆、插入锚杆、注浆、安设锚具、锚孔封堵、表面作旧、锚杆养护等多方面进行优化研究。(3)基于三线型剪切-滑移理论模型,对南竹加筋复合锚杆的锚固机理进行了分析,将整个受力阶段分为四个阶段,即弹性阶段、弹性-软化阶段、弹性-软化-解耦阶段以及软化-解耦阶段,并获得了锚杆界面各个受力阶段所对应的荷载-位移关系、剪应力分布、轴向应力分布的闭合解。通过对试验所获取的荷载-位移曲线进行分析,获取三个特征点,继而对剪切-滑移模型进行参数标定,预测锚杆的荷载-位移曲线、各个受力阶段的剪应力分布以及轴向应力分布。经过对比锚杆拉拔试验与理论分析结果,两者符合较好。对锚固理论进行的参数分析结果表明：①随着锚杆长度的增加,最大承载力也随之增大,但当锚杆长度大于有效锚固长度后,最大承载力增幅不大；②随着锚杆轴向刚度的增大,锚杆的最大承载力呈近似线性的增长；③随着残余强度因子k值的增加,最大承载力不断增加。(4)通过在钢绞线、南竹管材内、外表面粘贴电阻应变计,利用静态应变仪、锚杆拉力计,对南竹加筋复合锚杆进行拉拔试验,总结分析出了以下规律：a)复合锚杆的主要破坏形式为钢绞线-复合材料界面发生软化、滑移。随着荷载的增大,拉拔力首先克服锚杆近端的粘结力,继而远端的粘结力也被克服直至破坏。b)复合锚杆轴向应力分布呈指数状分布,并随荷载的增大而增大。当荷载较小时,界面剪应力分布呈指数状分布,剪应力从锚杆的近端向远端逐渐减少；随着拉拔荷载的增加,剪应力峰值逐渐向远端转移,但弹性部分仍呈指数状分布。c)钢绞线上轴向应力明显高于南竹管材的轴向应力,且复合锚杆在循环拉拔的过程中,呈现明显的材料记忆功能。南竹内表面的应变值总体上高于同一截面竹子外表面的应变值,这是由于南竹内外表面弹性模量不同所致。d)经对比,在锚杆尾部安设锚具和垫板提高了锚杆的极限承载力,可为南竹加筋复合锚杆的改进提供有益的参照。(5)用Cohesive单元模拟南竹加筋复合锚杆的界面断裂破坏,对复合锚杆拉拔试验进行数值模拟。研究结果一方面验证了现场拉拔试验所获得规律性,另一方面对现场试验由于应变计无法粘贴或者应变计提前脱落监测较差的部位进行了分析,得到了一些新的结论：a)南竹-复合材料、南竹-水泥砂浆界面的剪应力同样遵从指数分布的规律,且界面剪应力峰值随着主控面——钢绞线-复合材料界面的剪应力峰值的转移而转移。但南竹轴向应力分布较钢绞线有所不同,其峰值轴向应力分布在南竹的中部。b)水泥砂浆-土体界面由于其边界条件与其他界面的不同,其剪应力分布正好相反,即剪应力沿锚杆轴向从近端至远端不断增大。c)经分析,除主控面钢绞线-复合材料界面外,其他界面均未发生软化、破坏,而是随着主控面的软化、破坏,它们的轴向应力、界面剪应力进行相应的调整。d)钢绞线的轴向应力明显高于南竹的轴向应力,同一横截面处,主控面钢绞线-复合材料界面的剪应力最大,复合材料-南竹、南竹-水泥砂浆、水泥砂浆-土体界面剪应力依次减小。e)通过对比数值模拟结果与现场试验测量结果,两者复合较好,因此,本次数值模拟是可靠的,规律性是可信的。(6)结合强度折减弹塑性有限元法,对研究区中的41-5亚区锚固前、后的边坡稳定性进行了模拟计算,结果表明：①边坡在为锚固之前,其安全系数为1.002,处于极限平衡状态,破坏形式表现为沿裂隙下端塑性区贯通。②锚固后边坡的应力分布状况得到了极大的改善,边坡稳定性系数可达1.31,满足了设计的要求,同时也验证了复合锚杆的工程实用性。更多还原

【Abstract】 At present, China has paid more attention to protection of cultural relics, because a large number of earthen sites, especially those in the Silk Road of China, have being destroyed due to severe wind and rain erosion, structural fissures. And it has become one of the most issues that many experts focus on. As an effective and economical measure, rock-soil anchoring technique can increase the strength of soil and its self-stability. Therefore, it has been widely used by the departments of cultural relic protection.As a new type of rockbolt, Bamboo-steel composite rockbolts have been successfully applied in some soil relic projects. However, its anchorage mechanism and construction technology have not been studied systematically yet, and it will be much difficult to research the composite rockbolt because of its complicate structure and multi-interfacial feature. Therefore, a systematic study on this new rockbolts will not only fill the blank of the anchorage mechanism and technology, but also it can provide a scientific basis for applying this composite rockbolts in the steep slopes of the arid and semi-arid region, meanwhile, it has a reference meaning for learning other types of rockbolts.First of all, basing on collecting literature and field investigation, this paper demonstrates the geological environment of the study area, and anchorage techniques are optimized through investigating and comparing the present techniques. Then, combining with the theoretical and technological methods, such as the elastic-plastic mechanics, fracture mechanics, mathematics, deformation monitoring and numerical analysis and so on, the anchorage mechanism of the composite rockbolt is systematically studied by the theoretical, experimental and numerical means respectively. Finally, taking the 41-5 sub-region of Jiaohe ancient city as an example, the slope stability analysis before and after anchoring with composite rockbolts is respectively studied using the strength-reduction finite element method. The main results of the paper are listed as below: (1) The study area is located in the central uplift structure belt of the Turpan Basin, which is influenced by strong tectonic movement. The cliff is very steep with many tectonic fissures and unloading fissures, and its base has been eroded severely by the river. The weak strata at the cliff have also been eroded by the sand-carrying wind, which is formed in the special climate. As a result, many free faces have been formed. Therefore, the stability of the cliff has been greatly undermined by these unfavorable factors.(2) Combining with the anchor engineering of Jiaohe ancient city, the existing construction techniques have been investigated and compared. Considering the characteristics of the composite rockbolt and the earthen site, this paper summarizes and optimizes the construction techniques, including the location of anchor hole, hole-creating, lifting rock-bolts, installing rock-bolts, grouting, installing anchor devices, blocking the anchor holes, imitation of ancient surface, curing the rock-bolts etc.(3) Based on a realistic tri-linear bond-slip model with residual bond strength at the grout-bolt interface, this paper presents an analytical solution for predicting the full-range mechanical behaviour of grouted rockbolts in tension. The full-range behaviour consists of five consecutive stages: elastic stage, elastic-softening stage, elastic-softening-debonding stage softening-debonding stage and debonding stage. For each stage, closed-form solutions for the load-displacement relationship, interfacial shear stress distribution and bolt axial stress distribution along the bond length were derived. The ultimate load and the effective anchorage length were also obtained. The analytical model was calibrated and validated against two pullout experimental studies. The predicted load-displacement curves as well as the distributions of the interfacial shear stress and the bolt axial stress are in close agreement with test results. A parametric study is also presented, providing insights into the behaviour of the rockbolts:①the ultimate load increases quickly with the bond length before the effective bond length l_e is reached, beyond which the ultimate load increases at a much slower rate.②the ultimate load clearly increases but the ductility decreases as the bolt axial stiffness increases.③a larger k increases both the ductility and the ultimate load.(4) Through fixing strain gauges on the surfaces of the strand and the bamboo, which are monitored by a static strain meter, some pull-out tests to the composite rockbolt are carried out. Some conclusions have been developed:a) The main failure mode occurs in the strand-composite material interface. As the load increases, the adhesive force at the proximal end will be overcame first and then the damage will move to the distal end until all interface are overcame.b) The axial stress is distributed exponentially along the bond length, and it increases with the increment of the load. When the pull-out force is small, the interfacial shear stress is also distributed exponentially along the bond length. With the load increasing, the peak shear stress is gradually transferred to the distal end.c) The axial stress in the strand is significantly higher than that in the bamboo. During the cycling pull-out process, the composite rockbolt has an apparent function of material memory. The value of the strain on the inner-surface is larger than that on the outer surface of the bamboo due to the difference of elastic modulus in these two surfaces.d) By contrast, through installing anchorage and anchor plate at the end of the composite rockbolt, the ultimate bearing capacity is greatly increased, which can provide a useful reference to improve the bamboo-steel composite rockbolt.(5) This study develops a finite element model to analyse the full-range nonlinear behaviour of the bamboo-steel composite rockbolt. The finite element model uses cohesive elements in Abaqus characterised by a tri-linear bond-slip model to simulate debonding along the grout-bolt interface. The parameters in the bond-slip model are calibrated using the analytical solution from the experimental pullout tests. On the one hand, its results verify the conclusions derived from the experiments. On the other hand, some new conclusions are also obtained about the positions which can not be monitored by the in-situ experiments.a) The shear stress on the bamboo-composite material and bamboo-cement mortar interface are also distributed exponentially along the bond length, and the peak shear stress is transferred to the distal end with the increment of the pull-out force. However, it is totally different from the strand-composite interface, the shear stress transfer is influenced by the peak shear stress development of the control interface, i.e. the strand-composite interface, other than their own softening and debonding. In addition, the axial stress distribution is different from the steel strand, and its peak is distributed in the middle of the bamboo.b) Due to different boundary conditions, the shear stress distribution along the cement mortar-soil interface is different from that of other interfaces, just the opposite direction, that is, the shear stress along the interface increases from the distal end to the proximal end.c) All of the interfaces are not softened or damaged except for the control interface, and the axial stress and shear stress along other interfaces adjust corresponding to the softening and debonding development of the control interface.d) The axial stress in the steel strand is significantly higher than that of the bamboo. At a same cross-section, the shear stress in the control surface is larger than the composite-bamboo, bamboo-mortar, mortar-soil interface, and the shear stress on these interfaces decreases in order.e) By comparing the numerical results and experimental data, they are in close agreement with the experimental results. Therefore, the conclusions derived from numerical simulation are reliable and credible.(6) Combined with the strength reduction elastic-plastic finite element method, the slope stability of the sub-region 41-5 before and after anchorage is analyzed using Abaqus. The results show that:①the safety factor before anchoring is only 1.002, and the slope is in the limit equilibrium state. The failure mode is that the plastic zone develops from the bottom of the fissure to the free surface.②after anchoring, the stress distribution in the slope has been improved greatly. And the safety factor is up to 1.31, which meets the requirements of the engineering design. Meanwhile, the engineering practicability of the bamboo-steel composite rockbolts is also validated by this study.更多还原