土遗址加固中木锚杆锚固机理的现场试验研究

木锚杆锚固机理的研究对于土遗址传统材料与工艺的科学性挖掘和当今的保护加固具有重大价值。选择代表性的土遗址（交河故城）开展现场锚固测试,包括锚固性能测试和第一界面层（杆体-浆体）剪应变监测。试验结果表明：①鉴于杆体的自然选材,不同杆体的锚固性能差异较大,但锚固潜力巨大;②受力状态下,剪应力沿着界面呈现含峰值非均匀分布;③荷载逐步增大时,界面剪应力峰值逐步向末端转移;④剪胀作用明显,增强了锚固性能;⑤兼有拉力型和压力型锚固系统的复合特征。     

夯筑土遗址木锚杆四锚系统锚固机制物理模型试验研究

选择夯筑土遗址木锚杆四锚系统为研究对象,构建尺寸为2 m×2 m×0.5 m室内试验模型,运用自主研发的拉拔试验测试系统,获得四锚锚固系统的荷载位移关系与破坏模式。基于三维有限差分数值模拟方法,分析夯筑土体的位移场与应力场、单根锚杆轴应力以及锚杆–浆体界面的应力分布特征。研究结果表明,荷载位移关系前期处于弹性阶段,后期进入塑性阶段。单根锚杆周围土体的破坏半径约为26cm,杆间裂纹相互贯通,群锚系统呈现典型的复合锥形破坏。数值模拟结果表明,所选取的四锚对角线L_1、边线L_2、中线L_3三条测线位移分布特征相同,均呈对称的抛物线分布。四锚锚固系统的受力区集中在试样中部土层。随着荷载增加,锚杆–浆体界面的剪应力向锚杆末端转移,上部界面脱黏破坏。受到夯筑工艺影响,夯筑土遗址群锚破坏模式可能会沿着土层分离。研究结果对夯筑土遗址木锚杆群锚锚固系统设计具有较高的参考价值。     

土遗址用变径木锚杆锚固机理数值模拟研究

基于室内拉拔试验的物理模型,利用FLAC3D建立变径木锚杆拉拔数值计算模型,分析了变径木锚杆锚固系统的荷载传递规律、界面剪应力分布和传递规律、浆体土体应力场和位移场,并通过数值试验研究锚孔直径、锚杆直径和锚固长度对锚固效果的影响。研究结果表明:数值试验结果与室内拉拔试验结果较为吻合,证明数值模拟木锚杆拉拔过程的可行性和科学性;木锚杆浆体界面剪应力沿锚固段分布不均,主要集中在锚固段顶端和末端的0.1m范围内,末端界面剪应力呈增大的趋势与其变径的结构特征有关,其变径的特点在一定程度上提高了木锚杆的抗拔力;变径木锚杆同时具有拉力型和压力型锚杆的特征,径向具有剪胀作用;锚固影响因素中锚孔直径、锚固长度对木锚杆抗拔力影响显著,而锚杆直径对其影响相对较小;提出了木锚杆极限抗拔力计算公式。     

烧料礓石改性浆体–遗址土体界面抗剪性能试验

为研究土遗址锚固系统中浆体–土体界面抗剪性能,揭示锚固系统内部受力机制。试验选择目前土遗址锚固工程中常用的烧料礓石、粉煤灰、石英砂及遗址土作为主要浆体材料,同原状遗址土制成黏结试样。根据实际工作条件,对试样进行室外土体掩埋养护。通过浆体–土体界面直接剪切试验,得到不同配比浆体–土体界面的剪应力–位移关系曲线、抗剪强度参数及浆体–土体界面剪应力–位移拟合曲线。试验结果表明,浆体–土体界面未能有效黏结,界面抗剪强度主要依靠滑动摩擦及咬合摩擦承担;烧料礓石改性遗址土浆体与遗址土体黏结试样内摩擦角最大,浆体材料兼容性对界面抗剪强度的提高具有重要意义。室外掩埋养护土体温湿度的频繁波动和PS溶液的固化作用对界面黏结能力影响显著。因此,土遗址锚固工艺是保证锚固质量的关键因素之一。     

风化岩地基GFRP抗浮锚杆力学与变形特性现场试验

利用光纤光栅传感技术,对10根GFRP抗浮锚杆进行现场拉拔破坏性试验,研究了风化岩地基中GFRP抗浮锚杆的承载性能与变形特性。试验结果表明:发生滑移破坏的锚杆杆体、锚固体荷载-位移差曲线高于同型号发生断裂破坏的锚杆;锚固长度接近临界锚固长度的试验锚杆荷载-位移差曲线上升较平稳;增加杆体直径有助于提高锚杆承载能力、限制杆体位移并且降低杆体、锚固体的位移差。此外,杆体横截面轴应力沿锚固深度呈"反S型"分布,由孔口沿锚固深度方向递减;锚杆轴向界面剪应力沿锚固深度呈先增大后减小的趋势,且剪应力在锚固体内按斜向上方向由第一界面传递至第二界面。最后,利用剪应力分布简化模型求得杆体、锚固体位移差与发生滑移破坏的锚杆试验结果较为一致,可为GFRP锚杆的推广应用提供理论基础。     

南竹加筋复合锚杆加固土遗址研究

 南竹加筋复合锚杆是专门针对大体量土遗址加固设计的一种新型锚杆。通过试验证明,采用PS系列灌浆、南竹加筋复合锚杆加固土遗址符合文物保护的原则。当采用水泥砂浆作为灌浆材料时南竹加筋复合锚杆单位锚固力可采用30 kN/m,当采用PS-(F+C)浆液灌浆时单位锚固力可采用20 kN/m。南竹加筋复合锚杆加固土遗址时的薄弱界面是锚杆杆体与锚固体之间,水泥砂浆和PS-F灌浆材料的强度都可以满足南竹加筋复合锚杆锚固时的要求,水泥砂浆锚固体与锚杆杆体的黏结强度标准值为187 kPa,特征值为85 kPa;12%PS-F与粉煤灰锚固体与锚杆杆体的黏结强度标准值为114 kPa,特征值平均为52 kPa。     

拉力型锚杆锚固性能与界面力学传递试验分析

锚杆锚固段界面剪应力的传递规律是锚杆设计和锚固性能评价的重点。通过采用不同锚固参数进行拉力型锚杆的拉拔试验,分析在不同类型围岩中各界面及围岩中距锚固体表面2 cm处的应变片的实测值,得到了锚固系统在不同围岩条件下沿锚杆轴向和径向的应力传递规律和第二界面剪应力传递规律。结果表明:1)锚固系统各界面的剪应力衰减过程沿杆体和径向两个正交方向衰减,分布不均匀;合理选择锚固段长度可以提高锚固系统的承载能力;2)围岩强度降低后,第一界面剪应力沿锚杆轴向的分布相对更加均匀,同时也使锚杆的作用范围增大。     

地下洞室全长黏结式锚杆动力有限元模拟EI北大核心CSCD

基于锚固体基本受力方程,推导了锚杆与围岩荷载传递控制方程,并采用有限差分格式将其转化为线性方程组,结合围岩自由变形位移,考虑锚固体界面的损伤进行修正,通过迭代求解获得锚固体位移,进而得到锚固体正应力和界面剪应力沿杆长分布规律,形成了一种考虑地震作用下锚固体界面剪切损伤的锚杆动力算法。首先通过静力算例计算,验证了该算法的合理性;然后应用于工程实例的动力计算,结果表明,该算法能较好地模拟锚杆支护效果,锚固体受力符合中性点理论,地震过程中锚杆正应力随时间呈不断增加的趋势,锚头附近部位的界面剪应力较大,地震作用下最易损伤破坏。     

地下洞室全长黏结式锚杆动力有限元模拟

基于锚固体基本受力方程,推导了锚杆与围岩荷载传递控制方程,并采用有限差分格式将其转化为线性方程组,结合围岩自由变形位移,考虑锚固体界面的损伤进行修正,通过迭代求解获得锚固体位移,进而得到锚固体正应力和界面剪应力沿杆长分布规律,形成了一种考虑地震作用下锚固体界面剪切损伤的锚杆动力算法。首先通过静力算例计算,验证了该算法的合理性;然后应用于工程实例的动力计算,结果表明,该算法能较好地模拟锚杆支护效果,锚固体受力符合中性点理论,地震过程中锚杆正应力随时间呈不断增加的趋势,锚头附近部位的界面剪应力较大,地震作用下最易损伤破坏。     

基于钢筋粘结滑移模型的灌浆-锚杆界面力学性能分析

为了研究锚杆-灌浆体系界面应力-应变关系,提高预应力锚杆锚固效应,运用前人提出的钢筋粘结滑移模型来模拟灌浆-锚杆之间力学性能。重点分析了锚杆全长范围内应力状态中的弹性阶段、弹性软化阶段两种应力状态下,锚杆沿杆长分布的轴力-位移关系。最后通过拉拔试验进行验证和校准,得出锚杆与灌浆界面的剪切力呈非线性力学特征,并与理论推导出的锚杆-灌浆界面切应力变化趋势一致,这对于研究锚杆围岩的受力和变形具有参考意义。     

Effects of bolt profile and grout mixture on shearing behaviors of bolt-grout interface

Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system.In this paper,direct shear tests on bolt-grout interfaces under constant normal load(CNL) conditions were conducted to investigate the effects of bolt profile(i.e.rib spacing and rib height) and grout mixture on the bolt-grout interface in terms of mechanical behaviors and failure modes.Test results showed that the peak shear strength and the deformation capacity of the bolt-grout interface are highly dependent on the bolt profile and grout mixture,suggesting that bolt performances can be optimized,which were unfortunately ignored in the previous studies.A new interface failure mode,i.e.'sheared-crush' mode,was proposed,which was characterized by progressive crush failure of the grout asperities between steel ribs during shearing.It was shown that the interface failure mode mainly depends on the normal stress level and rib spacing,compared with the rib height and grout mixture for the range of tested parameters in this study.     

纤维加筋土坯的蒸发过程及抗拉强度特性

土坯作为一种生态、低碳和环保的建筑材料,其力学性能是学界和工程技术人员关注的重点。为了提高土坯的综合抗拉特性,提出采用纤维加筋技术对土坯进行改性处理。通过模拟土坯的形成过程,制备了一系列不同纤维掺量(0~0.2%)、初始含水率(16.5%~20.5%)和干密度(1.50~1.70 g/cm³)的压实土坯试样,进行自然干燥处理,并对干燥后的土坯试样开展了一系列劈裂试验,重点分析了纤维掺量和初始压实状态对土坯干燥失水过程及抗拉强度的影响。结果表明:(1)纤维加筋对土坯的干燥失水过程没有明显影响,但加筋土坯的残余含水率随纤维掺量呈"先降后升"趋势;(2)纤维加筋能显著提高土坯的抗拉强度,但其对抗拉强度的贡献随掺量的参加呈"先升后缓"趋势,对南京地区的下蜀土而言,其最优纤维掺量为0.1%,且纤维加筋能有效抑制土坯的脆性破坏模式,改善土坯的残余抗拉强度和韧性;(3)提高土坯制作时的初始含水率和初始干密度对改善土坯的抗拉强度和纤维加筋效果有较好的正面作用;(4)纤-土界面的微观力学作用及纤维的"桥梁"作用是控制纤维加筋土坯综合抗拉特性的关键因素。     

First exploratory study on dynamic characteristics of rammed earth buildings

Rammed earth construction is attracting a renewed interest throughout the world thanks to its “green” characteristics in the context of sustainable development. Several studies have been carried out to investigate this material and evaluate its durability along with its mechanical, thermal and earthquake capacities. This paper presents a study on the parameters needed for the seismic design of rammed earth buildings in accordance with current earthquake standards. First, the dynamic parameters of buildings such as natural frequencies and damping ratios-which were necessary to determine the equivalent static seismic force-were identified using in-situ dynamic measurements. Then, these experimental values were compared with the values calculated by empirical formulas suggested in Eurocode 8 to demonstrate that these formulas were applicable for the cases of rammed earth structures. Then, modeling was done to find a simple suitable model for rammed earth structures. Laboratory experiments were developed to measure the Poisson’s ratio which was necessary for the models. The results provided by the shear-beam model were close to that of in-situ experiments, which showed a shearing behavior of rammed earth structures. Elements which influenced the dynamic behavior of this structural type were also discussed. Understanding the dynamic characteristics of rammed earth structures will help engineers in their design of new rammed earth buildings but also in earthquake analyses of existing rammed earth buildings.     

当代国外生土材料的复合应用与现代表达研究

生土材料由于低碳、环保、经济的优势而备受社会各界人士的青睐。近年来,伴随着建筑材料的革新,当代国外生土建筑涌现了生土和其他可持续性材料相结合的新型生土建筑形式。以当代国外生土材料作为研究对象,探讨其与新型材料组合应用所创造的“低成本”与“高品质”两种不同的发展方向,并分析生土建筑现代性表达的途径,谨此希望对我国生土建筑的发展与革新提供一定的借鉴与启发。     

Laboratory investigation into effect of bolt profiles on shear behaviors of bolt-grout interface under constant normal stiffness (CNS) conditions

Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering. It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system. Previous studies have proposed some optimal rib parameters (e.g. rib spacing); unfortunately, the interface shear behaviors are generally ignored. Therefore, determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible. The load-bearing capacity and deformation capacity vary as bolt profiles differ, suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles. The aim of this study is to investigate the effects of bolt profiles (with/without ribs, rib spacing, and rib height) on the shear behaviors between the rock bolt and grout material using direct shear tests. Thereby, systematic interfacial shear tests with different bolt profiles were performed under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does, in particular at the post-yield stage. The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions, and optimize selection of rock bolts under in situ rock conditions.     

国贸中心三期基坑支护工程监测研究

北京地区深基坑开挖监测及理论研究尚显不足。对北京国贸三期深基坑开挖过程中的监测结果进行分析、研究,结果表明：正常情况下,桩锚支护的位移一般不会超过0.1%H;护坡桩钢筋的应力一般仅达钢筋设计强度值的1/10～1/8;锚杆的实际拉力值较小,说明目前支护设计采用的土压力值大于护坡体系实际受到的土压力;各排土钉的拉力均在38 kN以下,远小于按现行规程计算出的土钉的设计拉力值。由此看出,实际钢筋应力、锚杆拉力、土钉拉力均比按目前规程计算理论拉力小。研究结果为类似工程的设计提供参考,也为以后规程的修订提供依据。     

软质岩中压力型锚索锚固段应力分布特征

为了研究软质岩中压力型锚索锚固段应力分布和传递规律,进行了足尺现场试验.制作了与实际工程条件相似的试验锚索,在试验锚索的锚固段砂浆体中按一定间距设置了应变砖,记录了在不同张拉荷载下各测点的应变情况,测得压力型锚索锚固段的轴向应变和径向应变分布曲线.通过对试验结果进行分析处理,得到了锚固段与围岩界面剪应力分布曲线.测试结...     

Durability of rammed earth walls exposed for 20 years to natural weathering

This paper presents a study on the durability of different types of stabilised and unstabilised rammed earth walls. These rammed earth walls were constructed and exposed for 20 years to natural weathering, in a wet continental climate. None of these walls have shown complete collapse to date. A method to measure the rammed earth walls erosion by stereo-photogrammetry has been developed. The result shows that the mean erosion depth of the studied walls is about 2 mm (0.5% wall thickness) in the case of rammed earth wall stabilised with 5% by dry weight of hydraulic lime and about 6.4 mm (1.6% wall thickness) in the case of unstabilised rammed earth walls. The stabilisation enables to not use any plaster to protect the walls. In the case of the unstabilised rammed earth walls, an extrapolated lifetime longer than 60 years can be assessed. This shows a potential for the use of unstabilised rammed earth in the similar climatic conditions with this study. The method of stereo-photogrammetry used to measure the erosion of rammed earth walls on site may also help to calibrate and develop more pertinent laboratory test to assess the durability of rammed earth wall.     

土楼夯土在模拟风雨环境下的风洞侵蚀试验研究

福建土楼作为世界文化遗产,宏大的夯土墙体显出土楼的建筑特色,但这种生土结构易受雨水侵蚀,闽西南地处亚热带温湿海洋气候,雨量充足,台风频发,长期风雨侵蚀严重影响土楼的安全性和耐久性.从永定县非世遗客家民居土楼割取原始夯土块,进行了风驱雨模拟环境下的风洞侵蚀试验研究,研究表明:夯土侵蚀受风速和雨强影响,其侵蚀量随风速与雨强的增加而增加,而风速增加产生的夯土侵蚀量明显大于雨强增加产生的侵蚀量,结合当地风雨气象资料,可计算福建土楼的风雨侵蚀寿命,为土楼保护提供理论依据,具有较强的应用价值.