土钉加固黏性土坡加载的离心模型试验研究

进行了不同坡度土钉加固边坡坡顶加载的离心模型试验,观测了土坡的破坏过程并测量土坡的位移场,研究了土钉加固黏性土坡的承载力、变形和破坏规律以及坡角对其破坏规律的影响。试验结果表明,坡顶荷载的增加引起土坡变形的增加,变形的集中产生和发展导致滑裂面的形成并使土坡发生破坏。土钉变形规律受加载阶段和加载底板的综合影响,坡顶荷载越大,接近坡顶的土钉弯曲挠度越大,钉土间的相互作用越强。土坡的坡角越大,承载力越低,土体呈现出更显著的向坡面位移的趋势。     

水位下降条件下土钉加固土坡破坏特性研究

水位下降是导致滑坡的重要原因之一,而土钉是加固土坡的有效手段。进行离心模型试验,再现了水位下降时土钉加固土坡的变形和破坏过程,测量了土坡的位移变化。试验结果表明,水位下降条件下土钉加固土坡的破坏模式以绕钉破坏为主,滑裂面从坡顶逐渐向下发展至坡面;土钉加固土坡的破坏过程与变形局部化过程表现出显著的耦合变化;土钉加固机制主要表现为通过土钉与坡体的相互作用,减小土坡的变形和变形局部化程度,从而提高土坡的稳定性。增加土钉长度使得滑裂面向坡内部移动,显著减小土坡的变形及变形局部化程度,从而提高了土坡安全性。     

土工织物加筋黏性土坡坡顶加载的离心模型试验研究

土工织物加筋技术在工程中得到了广泛的应用,取得了良好的加固效果。但对于土工织物加筋机制尚缺乏明确和统一地认识,加筋理论研究落后于工程实践。为此,进行了坡顶加载条件下土工织物加固黏性土坡和素土边坡的离心模型试验,记录和再现了素土边坡和加筋土坡在坡顶加载条件下的变形破坏过程。主要基于变形分析探讨了黏性土坡在土工织物简单加固条件下的加固效果和加筋机制。结果表明,土工织物加筋可以有效地提高黏性土坡的极限承载力,加筋带的存在改变了土体的位移场,扩大了坡顶加载的影响区域,加筋后滑裂面明显后移。加筋带对土体的局部作用和作用范围,随着土体变形的增大而增大和扩展     

土钉墙变形规律及其相关性的实测研究

根据基坑坡顶水平位移与沉降的实测数据,讨论了土钉墙坡顶水平位移和沉降以及水平位移与沉降之比的规律,并利用统计方法对其相关性进行了分析,根据实际施工工况与实测数据对比,指出影响土钉墙变形的关键因素及控制土钉墙变形的有效措施。实测数据分析结果表明：基坑坡顶变形的空间效应明显;采用放坡或坡顶卸载可以有效地控制土钉墙的变形;在基坑上部设置预应力锚杆对基坑变形控制具有明显的效果;基坑坡顶的沉降随其水平位移呈非线性增加,沉降与水平位移比与其水平位移基本呈线性增加;土钉基坑发生破坏时的坡顶水平位移的警戒值为0.8 %～1.0 %H。     

黄土边坡开挖与支护效应的离心模拟试验研究

黄土边坡在开挖卸载过程中的稳定性分析及其防护在边坡工程中占有重要地位。采用西南交通大学土工离心机进行了1组非支护边坡和2组土钉支护边坡的离心模型试验,研究了开挖卸载过程中黄土边坡的变形特性、稳定性变化规律及土钉的加固效应。离心模型试验研究表明,土钉能够显著提高黄土边坡的稳定性。土钉支护的边坡土体,因土钉的锚固效应,边坡的变形范围更大,但变形量较小,最大变形量并不在坡面,而是发生在坡面下的锚固区域内,非支护黄土边坡的潜在滑移面产生于距坡顶约40 cm处,土钉支护后,黄土边坡基本不会发生破坏。对于抵抗边坡发生变形而言,不等长土钉支护的效果要优于等长土钉支护,研究成果为黄土边坡的开挖与防护提供了参考。     

荷载作用下黏性土坡位移场应变场分析

通过室内土坡模型试验,研究了在荷载作用下黏性土坡竖向位移随深度的变化规律、土坡大主应变与最大剪应变分布、土坡的蠕变特性及裂缝作用机制。结果表明,随着荷载的逐渐增大,土坡微结构蠕变不断增加,土体的蠕变过程实质上是土体损伤过程,是土坡微结构能量耗散的过程。土坡的蠕变和损伤积累随着加荷时间延续而增大,损伤各向异性更加明显。坡顶和斜坡面处的损伤程度较大,在坡顶和斜坡面出现裂缝,坡顶的竖向位移大于侧向位移,相反坡底处侧向位移大于竖向位移。     

地形地貌对地震波放大效应数值模拟研究

采用FLAC3D 软件进行大量数值模拟,研究了地形地貌对地震波放大效应规律。结果表明:对于单面坡模型,斜坡较低时,坡体对天然地震波和简谐波的峰值加速度在竖直向和顺坡面向产生线性放大效应。斜坡较高时,若坡角低,两种波形的加速度等值线近似平行于坡面,天然地震波坡顶正下方极值性不明显,但随坡角增大而明显,坡面正下方可见若干条与坡面相平行具节律性的极小值条带,随坡角增大向一条极值带转化,简谐波在高低坡脚时坡顶面正下方区域内都出现等间距相间分布具节律性的极值条带,坡面正下方的极值带状性不如天然地震波明显,随坡角增大而消失; 若坡角高,两波形加速度放大系数顺坡面呈相间的极值圈分布。双面坡坡顶宽度越小,山脊越单薄,加速度放大效应越强烈,随坡顶宽度增大,坡肩加速度放大系数趋于稳定,双面坡对加速度放大效应强于单面坡。对加速度放大效应,多峰形双峰形单峰形,坡顶越不规则,加速度放大效应越强烈。V形河谷坡面上半部分加速度放大效应要强于U形河谷,U形河谷的谷底中部对地震波动力响应要强于V形谷。坡面局部不规则性只影响到坡面局部范围内的峰值加速度分布,坡高、坡角、坡顶几何特征为整个峰值加速度分布的控制因素。     

削坡作用土质边坡变形分布式光纤监测试验研究

采用高空间分辨率的PPP-BOTDA光纤感测技术,研发出一种适合于土体变形监测的特种感测光缆。通过水平向和垂直向感测光缆植入,对边坡模型在坡顶局部加载和削坡过程土体内部变形场进行了分布式监测,获得了荷载和削坡作用下坡体变形场的分布规律,并对边坡模型进行了有限元数值分析和计算评价。分布式光纤感测技术监测结果表明:在坡顶局部加载作用下土体水平向拉张变形最大值发生在坡体中部,这与数值模拟结果一致;但在削坡作用下,坡体水平向拉张变形最大值发生在坡体上部,表明削坡作用改变了边坡模型的变形规律,上层土体在坡顶局部荷载作用下易发生倾倒变形。研究结果也表明,作者研制的特种感测光缆具有良好的感测性能,可以对土体变形场进行准确有效监测。     

黄土高边坡土钉-预加固桩复合支护体系性状分析

土钉-预加固桩复合支护技术已在基坑及边坡工程中取得了大量应用,但在黄土高边坡开挖中的应用相对较少。基于详细的现场监测数据并辅以有限元数值计算,分析了边坡开挖过程中支护体系受力及变形随时间和空间的变化规律。结果表明：预加固桩的水平位移随着时间的推移与开挖深度的增加呈增大趋势,并最终趋于稳定,同时,桩身剪力及弯矩亦随开挖的进行而不断增大;剪力最大值的位置不断下移,说明边坡的潜在滑动面有不断向下扩展的趋势。与深基坑支护桩的土压力分布相比,土钉-预加固桩复合支护体系中桩后土压力随开挖呈不断减小的趋势,但桩前土压力随着开挖深度的增加,有增有减。随着施工开挖深度的增加,土钉所测得的应力有着明显的增大,说明土钉对抑制坡体变形起到了一定作用。在预加固桩的影响下,桩上方坡体的最危险破裂面为圆弧状,其剪出口位于预加固桩桩顶处。开挖深度较浅时,土钉对整体稳定性的贡献较大,而随着开挖深度的变大,预加固桩的加固效果开始占主导地位。     

黄土台塬顶部建筑物安全距离计算——以韩城黄河观光休闲生态园建设项目

韩城市黄河生态园酒店修建于不稳定斜坡顶部,距离坡顶线较近,酒店建成后对坡顶加载,加剧坡面变形,危及上部建筑物安全。在对不稳定斜坡的发育现状、地层详细调查的基础上,通过计算不稳定滑动面距离,结合坡率法,计算基础底面至坡顶安全距离,算出酒店基础底面距离至坡顶线安全距离,确保建筑物建成后在不稳定斜坡变形影响范围之外,保证坡顶建筑物的安全。通过计算得出酒店基础底面外边线到原始坡缘安全距离不小于54 m。     

循环荷载及静载下土工格室加筋路堤模型试验研究

为探究土工格室加筋路堤在循环荷载及静载下的各种性能,利用美国GCTS公司的USTX-2000加载装置进行加载,通过改变加筋层数、格室高度,格室焊距对土工格室加筋路堤进行一系列模型试验。对各种工况下加筋路堤极限承载力、长期循环荷载及固定振次循环荷载后极限承载力的变化进行研究。试验表明,土工格室加筋能显著提高地基极限承载力并能显著减小坡顶和坡中临界破坏时的法向累积变形,在加筋间距一定的情况下,加筋层数增加和格室高度增大均可不同程度提高极限承载力并减小临界破坏时坡顶法向累积变形,格室焊距的减小也可在一定程度提高极限承载力,格室焊距对边坡法向变形影响不大;长期循环荷载下固定间距加筋层数对路堤竖向累积沉降量影响不大,而对边坡坡顶法向累积变形有一定影响,格室高度增大和格室焊距减小均可不同程度减小路堤竖向累积沉降量和坡面法向累积变形;越靠近加载点处,路堤土压力值受加筋影响越显著,加筋提高了土体刚度和密实度,使加筋路堤土压力值较无筋路堤明显增大;对于无筋路堤,改变动载幅值和振次均导致振后极限承载力有不同程度的降低,而对于加筋路堤,当动载幅值≥30 kPa或动载振次≥1 000时,振后极限承载力均有不同程度的提高。     

Block reinforcement behavior and mechanism of soil slopes

In recent years, blocks created by pressure grouting of cement into soil were used to reinforce slopes by targeting specific weak areas. A clear understanding of the block reinforcement mechanism is essential for the accurate evaluation of the stability of block-reinforced slopes and reasonable design of block layouts. A series of centrifuge model tests was conducted to investigate the bearing capacity and the full deformation and failure behavior of block-reinforced slopes, with a focus on the influence of block layouts on the reinforcement effect. A block reinforcement with a reasonable layout was confirmed to increase the stiffness and the ultimate bearing capacity of the slope. The block reinforcement significantly changed the failure mode to the complex disturbance and destruction from slippage failure in an unreinforced slope. The block reinforcement restrained the deformation localization around the blocks and thus prevented the development of the coupling effect between the deformation localization process and the failure process in an unreinforced slope during loading. Such a reinforcement mechanism could be used to explain why the block reinforcement increased the bearing capacity and changed the failure mode of the slope. The blocks exhibited significant motion along with the development of deformation localization in the slope during loading. The block reinforcement effect was significantly affected by the rotation of blocks, which was determined by the block layout.     

Seismic stability analysis of soil nail reinforced slope using kinematic approach of limit analysis

Prediction of the critical seismic yield acceleration coefficient and the seismic permanent displacement of soil nail reinforced slope under seismic loading has been playing an important role in helping design in the earthquake-prone areas. In this paper, the seismic stability of soil nail reinforced slope is analyzed using the kinematic theorem of limit analysis. The log-spiral failure mechanism is considered and the corresponding analytical expressions are derived to calculate the critical seismic yield acceleration coefficient and the permanent displacement of slope subjected to earthquake loading. A series of calculations are carried out to illustrate the influence of inertial force on the stability of a nail-reinforced slope. Parametric studies indicate that the strength and geometry of slope as well as characteristic parameters of soil nail have a significant effect on the critical seismic yield acceleration coefficient and the permanent displacement of soil nail reinforced slope.     

加卸载作用下加筋垫层变形特征试验研究

加筋垫层由于具有诸多优点而被广泛应用于反复加卸载作用下公路、铁路路基等工程构筑物中。为研究加卸载作用下加筋垫层结构的变形特征,针对加筋与未加筋垫层2组模型,开展了单次加卸载静力试验。测试并获得了不同荷载作用下垫层竖向变形、筋材应变变化规律,对比分析了加筋与未加筋垫层的变形特征,并从能量角度对加筋垫层工作机制进行了探讨。结果表明:与未加筋情况相比,荷载作用下加筋垫层(加载板处)的沉降变形和残余变形更小。加筋后垫层表面(加载板范围外)的竖向变形及其受影响范围均增大,且在卸载过程中垫层表面竖向变形的水平分布曲线特征由"凹"型变为"凸"型,其加卸载曲线呈"∞"型。格宾网筋材应变沿横向呈现非均匀分布特点,其最大应变小于0.06%,筋材始终处于弹性变形状态。加筋垫层中筋材具有储存、释放及横向传递应变能效应,这使得加筋后垫层具有更好的承载能力与弹性性能,进而可降低循环加卸载作用下垫层的塑性变形或累计变形。     

基于光纤传感技术的土工格栅变形及受力研究

光纤传感技术具有精度高、灵敏度高的特点,在变形测量方面具有独特优势。但由于缺乏有效的封装保护技术,目前将光纤传感器用于土工合成材料变形监测的应用和研究比较少。文章通过对光纤传感器的封装结构进行设计,较好地解决了光纤传感器与被测物体间的协调变形问题,并延长了光纤传感器的使用寿命。基于此封装结构,通过室内土工格栅加筋边坡模型试验,选取土工格栅的加筋层数及筋材的布设方式作为变量,研究了土工格栅在加筋过程中的变形及受力特性。研究结果表明:在垂直方向上,上层筋材的应变大于下层筋材的应变;在水平方向上,单层变形最大处位于加载点正下方范围内。增加加筋层数,能够使得各层格栅的变形得到分担,同时有效限制坡面的法向位移,尤其是坡面中上部分的法向位移;土工格栅能够显著提高边坡的极限承载力。通过对光纤传感器的研究,表明其能够灵敏监测被测物体的微小变形与受力,实际使用中较为稳定,验证了本文封装结构设计的可行性,弥补了传统测量方法的缺陷。     

Bearing capacity tests of strip footings on reinforced layered soil

The ultimate bearing capacity of strip footings resting on subsoil consisting of a strong sand layer (reinforced/unreinforced) overlying a low bearing capacity sand deposit has been investigated. Three principal problems were analysed based on results obtained from the model tests as follows: (1) the effect of stratified subsoil on the foundations bearing capacity; (2) the effect of reinforcing the top layer with horizontal layers of geogrid reinforcement on the bearing capacity; (3) effect of reinforcing stratified subsoil (reinforced and unreinforced) on the settlement of the foundation. It has been observed that reinforcing the subsoil after replacing the top layer of soil with a well-graded soil is beneficial as the mobilization of soil-reinforcement frictional resistance will increase.     

Bearing capacity of square footings on reinforced layered soil

In the present study, an approximate method has been suggested to calculate the ultimate bearing capacity of a square footing resting on reinforced layered soil. The soil is reinforced with horizontal layers of reinforcement in the top layer of soil only. The pre requisite to the method is the ultimate bearing capacity of unreinforced layered soil, which can be determined from the methods already available in literature. The results have been validated with the model tests conducted on two layered soil compacted at different densities and the top layer reinforced with horizontal layers of geogrid reinforcement.