拉伸状态下充填体损伤演化及本构方程研究

1引言抗拉强度是充填体的重要力学性能之一。充填体中存在有微裂隙,如裂纹、气泡、孔穴和离析等,这些内部的微观缺陷或不连续现象对充填体宏观力学性能起决定性作用。对于矿山胶结充填体的内部微开裂和由微开裂引起的各类力学行为的研究很少。为计算和预测安庆铜矿大体积充填体     

不同纤维作用下尾砂胶结充填体早期力学特性及损伤本构模型研究

为了提高某金矿尾砂胶结充填体材料的稳定性,保障矿山采空区充填效果,对加入不同纤维(聚丙烯腈纤维(JBX)、玻璃纤维(BL)、聚丙烯腈和玻璃混合纤维(HJB))的尾砂胶结充填体的早期力学性能和损伤特征进行研究,通过单轴压缩试验得到了不同纤维作用下充填体损伤本构模型.试验结果表明:在不同纤维作用下尾砂胶结充填体单轴抗压强度...     

粉煤灰膏体充填材料水化动力过程与水化机制

明确粉煤灰膏体充填材料的水化动力学特性及胶结过程演变机制,有助于剖析充填材料早期强度低、变形量大及泌水严重等缺陷存在的原因,进而为科学调控充填材料结构形成过程和合理制定充填工艺参数提供指导。本文采用TAM Air等温微量热仪测定充填材料的水化放热速率和放热量,基于Krstulovic-Dabic水化动力学模型,计算充填材料的水化动力学参数,对水化动力过程各阶段的变化特征进行分析。利用水泥水化建模软件模拟了充填材料在不同水化程度下的水化过程,并对水化机制作进一步解释。结果表明:充填材料水化动力过程可通过结晶成核与晶体成长(NG)、相边界反应(I)和扩散(D)进行描述。水化初期NG过程控制水化反应的进程,随着水化程度的提高逐渐转变为由I过程和D过程控制。与纯水泥水化动力过程变化特征相比,充填材料水化动力过程的转变则需要更高的水化反应程度。水化过程模拟结果为描述和探讨粉煤灰充填材料的水化特征与微结构演变提供了有益参考。通过对粉煤灰膏体充填材料水化机制的研究,揭示了充填材料结构及其形成过程的一般规律。     

沿空巷旁分层充填留巷试验研究

煤矿目前在高地应力或覆岩运动剧烈的条件下,采用巷旁充填留巷方式有2点不足：刚性材料充填易造成墙体应力集中,使充填体被压裂乃至失效,裂隙发育使采空区与巷道连通引起火灾或CH4,CO等有毒有害气体泄漏;柔性材料充填易造成巷内顶板下沉过大乃至发生冒顶。为此,在华恒煤矿11508运输巷留巷时进行改进。首先建立沿空留巷巷旁侧向覆岩结构模型,计算充填体可缩量,制定巷旁分层充填留巷方案：即巷旁支护体采用2种强度等级的材料充填,上分层材料起密封作用,适应覆岩运动产生的冲击载荷,下分层材料起支护作用。通过建立力学模型计算得出下分层材料必需的支承强度,通过结构模型确定各自充填厚度。现场试验达到了预期效果。     

胶结充填体早期损伤对后期力学性能影响机制研究

为探究胶结充填体早期损伤对后期力学性能影响机制，将龄期3,7,14,21 d的充填体施加4种不同程度的静载损伤，养护28 d后开展单轴压缩试验、超声波测试、电镜微观结构扫描，从宏–细–微三个尺度探讨充填体早期损伤对后期力学性能影响机制。结果表明：损伤对龄期3和7 d充填体后期抗压强度影响较小，在一定压损条件下充填体后期抗压强度上升，对龄期14和21 d充填体后期抗压强度均产生弱化作用，对各个龄期充填体后期弹性变形能力起到强化作用；基于波速变化建立损伤程度与充填体力学特性之间的定量关系，发现损伤龄期3和7 d充填体存在损伤阈值和修复阈值；随着损伤程度的增大，充填体内部结构由数量较多的细小裂隙逐渐扩大为单一裂隙，裂隙断面处的连接物质主要为水化产物C-S-H网状凝胶；龄期3和7 d充填体内部存在大量未完全水化的水泥颗粒，养护后期产生的凝胶产物足以填充大部分损伤裂隙，故损伤对其后期抗压强度影响较小，而龄期14和21 d充填体未完全水化的水泥颗粒减少，后期产生的凝胶产物不足以填充损伤裂隙，内部结构颗粒之间联系较差，故损伤对其后期抗压强度弱化作用显著。研究结果可为矿山充填体工作提供指导意义。     

充填体与岩体三维能量耗损规律及合理匹配

 根据灰砂配比为1∶4,1∶8,1∶10和1∶12的4种胶结充填体力学试验结果,揭示不同配比充填体三维损伤耗能规律。针对矿床开采岩体应力转移并释放能量特征,探索矿床开采过程中岩体三维能量释放规律。研究结果表明,矿体埋藏越深,开挖岩体释放能量越高;岩体弹性模量越高或泊松比越低,岩体释放能量越小。根据充填体与岩体耦合作用的三维能量耗损特征,探讨充填体与岩体的合理匹配,并用该匹配模型验证安庆铜矿采用最低充填配比1∶12开采矿石是可行的。研究发现,充填体与岩体的匹配系数K和三维原岩应力、岩体及充填体力学参数相关,不同开采技术条件必须设计合适的充填体抗压强度才能实现与岩体匹配。     

新型巷旁充填材料的研究

本文介绍了一种新型巷旁充填材料——煤矸石膏体巷旁充填材料,由煤矸石、粉煤灰、PL膏体胶结料和水组成。通过试验,改变各组分用量,测定充填材料的力学性能参数,得出了一种较为合理的配比方案,为巷旁充填材料的选择与应用提供了有效的途径。     

沿空留巷围岩结构模型的建立及其稳定性分析

综合考虑沿空留巷围岩变形、采场覆岩运动规律及巷旁支护结构的特点,将沿空留巷顶板结构简化为采空区矸石、巷旁充填体及巷帮煤体共同作用的弹性力学模型,计算了该条件下的支护反力,利用控制变量的方法分析了影响支护反力的主要因素是充填体宽度和充填体弹性模量,得出了巷旁充填体压缩量计算公式。在此基础上,通过UDEC数值模拟方法,模拟了沿空留巷顶板关键岩块在弹性支撑条件下的应力状态,分别得出了充填体宽度及弹性模量与顶板下沉量的关系。     

远场爆破水平应力波扰动下分层胶结充填体矿柱的动力响应机制

为研究远场爆破扰动下分层胶结充填体矿柱的动力响应机制,综合分层充填体的结构特征及其与围岩、周边充填体的相互作用,首次构建不同灰砂比的分层充填体多自由度结构响应模型方法,以冬瓜山铜矿3分层矿柱为例进行计算分析,与数值模拟及现场监测的结果进行对比验证,预判其稳定性,并研究不同应力波频率对其作用机制。结果表明:在远场水平爆破应力波作用下,结构响应模型法的分析结果与数值模拟、现场监测结果基本吻合。灰砂比大小严重影响分层胶结充填体的速度、位移响应,及不同灰砂比充填体的响应峰值大小;灰砂比越小,分层充填体振动周期越大,速度、位移响应峰值越大,结构稳定性越差;低灰砂比分层充填体是矿柱结构中的最薄弱区域,容易发生失稳现象。应力波频率明显影响充填体的速度、位移响应峰值,二者变化趋势线均呈"单峰"特征,前者滞后后者出现拐点;在低频阶段,充填体的振动周期增加,二者增加速率先小后大;当频率接近充填体自振频率时,充填体将发生共振现象,二者峰值达到最大值;在高频阶段,二者峰值不断衰减。研究成果为远场爆破扰动下充填体矿柱稳定性判定提供理论支撑。     

不同充填体材料在沿空留巷中的应用综述

对沿空留巷的充填体材料进行了论述,总结了材料的力学性能和充填工艺,传统的巷旁充填技术仅适用于条件较好的薄而中厚的煤层中,而新型的充填材料与传统相比,稳定性能好,能够有效地提高充填体和围岩的强度,说明巷旁充填材料的性能高低在沿空留巷的技术中是非常重要的,并提供了理论的依据。     

城市道路沥青路面损坏的调查及分析

结合对上海市浦东新区一临近东海的城市道路沥青路面状况的详细调查,描述了沥青路面的损坏类型。其中横向裂缝、车辙和沉陷是沥青路面的主要破坏形式,占到总破坏面积的80.9%。最后分析了产生的原因,提出了今后城市道路在设计和施工中应着重注意的几个问题,并建议在路面施工中应提高沥青压实度标准,在路基施工中应注意采取切实措施确保沟浜回填质量。     

经编土工格栅施工损伤现场试验研究

经编土工格栅因施工损伤导致强度折减现象较为严重,但国内现场试验较少。比较了双向拉伸经编格栅在4种填料下压实后的纵横向拉伸强度、伸长率、应力应变曲线,对施工损伤导致的强度折减影响因素进行了分析,并给出了相应的折减系数,为设计人员提供了适合国内施工工艺、施工器械、经编格栅产品的施工损伤折减系数的参考值。     

Seismic analysis of semi-gravity RC cantilever retaining wall with TDA backfill

The seismic behavior of Tire Derived Aggregate (TDA) used as backfill material of 6.10 m high retaining walls was investigated based on nonlinear time-history Finite Element Analysis (FEA). The retaining walls were semi-gravity reinforced concrete cantilever type. In the backfill, a 2.74 m thick conventional soil layer was placed over a 3.06 m thick TDA layer. For comparison purpose, a conventional all soil-backfill model was also developed, and the analysis results from the two models under the Northridge and Takatori earthquakes were compared. The FEA results showed that both models did not experience major damage in the backfill under the Northridge earthquake. However, under the Takatori earthquake, the TDA-backfill model developed substantially large displacement in the retaining walls and in the backfill compared with the soil-backfill model. Regions of large plastic strain were mainly formed in the TDA layer, and the soil over the TDA layer did not experience such large plastic strain, suggesting less damage than the soil-backfill model. In addition, the acceleration on the backfill surface of the TDA-backfill model decreased substantially compared with the soil-backfill model. If an acceleration sensitive structure is placed on the surface of the backfill, the TDA backfill may induce less damage to it.     

Seismic motion response and fragility analyses of cantilever retaining walls with cohesive backfill

The seismic motion response of a cantilever retaining wall with cohesive and cohesionless backfill materials was evaluated using fully dynamic analysis based on finite difference method. The dynamic analysis was validated based on experimental test results and then compared to analytical and empirical correlations based on Newmark sliding block method. Seven different earthquake events and the backfills with low to high levels of cohesion were considered. Nonlinear regression analyses were carried out to provide correlations between free-field peak ground acceleration (PGA) and maximum relative displacement of the retaining wall. These results were compared to results from empirical and analytical methods. Furthermore, fragility analyses were conducted to determine the probability of damage to the retaining wall for different free-field PGAs and backfill cohesions. It is demonstrated to what extent a small amount of cohesion in backfill material can influence displacement of the retaining wall and probability of damage in seismic conditions.     

Evaluation of Extent of Damage to Geogrid Reinforced Soil Walls Subjected to Earthquakes

The aim of this study is to establish a simple method for evaluating the extent of damage to geogrid reinforced soil walls (GRSWs) subjected to earthquakes. Centrifuge tilting and shaking table tests were conducted to investigate the seismic behaviour of GRSWs, with special focus on the effects of the tensile stiffness of the geogrids, the pullout characteristics and the backfill materials. As a result, it was found that GRSWs showed large shear deformation in the reinforced area after shaking, that such deformation was influenced by the tensile stiffness of the geogrids, the pullout resistance and the deformation modulus of the backfill material, and that finally slip lines appeared. However, the GRSWs maintained adequate seismic stability owing to the pullout resistance of the geogrids, even after the formation of slip lines. It is considered that such slip lines appeared due to the failure of the backfill material. Since the maximum shear strain occurring in the backfill can be roughly estimated from the inclination of the facing panels, using a simple plastic theory, it is possible to evaluate whether the backfill has reached its peak state or not. The formation of slip lines observed in the centrifuge model tests could be well explained by this method. Finally, the method is proposed to estimate the failure sections in the GRSWs using a Two Wedge analysis.     

董志塬区黄土高填方地基工后沉降特性试验研究

黄土高填方地基工后沉降量大,容易引起建筑物开裂破坏。本文以庆阳市西峰区某小区填沟造地项目为背景,对董志塬区黄土高填方地基的工后沉降特性进行了分析研究,研究结果表明,⑴黄土高填方地基在回填后200天到250天左右工后沉降量较大,最大沉降量可达到79cm。⑵黄土高填方地基工后沉降在沟谷处较大,距离沟谷越远,沉降量越小。⑶干密度是影响黄土高填方地基工后沉降的主要因素,可以通过提高干密度的方法提高黄土的回填质量,对于超厚的黄土高填方地基,宜采用高能级强夯进行分层回填。     

Case history on failure of geosynthetics-reinforced soil bridge approach retaining walls

Six geosynthetic-reinforced soil (GRS) retaining walls supporting bridge approach roads of an overpass bridge in China exhibited a series of structural problems after 18 years of service. Field investigations demonstrated that the major structural problems consist of excessive lateral facing displacement, settlement and damage of facing panels, and pavement cracks above the GRS retaining walls. The structural problems were mainly caused by inadequate backfill compaction behind the facing, rain water infiltration, the settlement of foundation soil, and reinforcement ageing. Among the six GRS walls, a 22-m-long section collapsed after mild rain in July 2016, and the failure surface in the collapsed zone was mainly located 0.5–0.9 m away from the back of facing panels along the wall height. The field investigation found that external water filtration into the backfill behind the facing panels, and the breakage of connection between reinforcement and facing panels were the main causes of the failure. The connection breakage resulted from the ageing of PP reinforcement strips, and the critical issue of PP reinforcement ageing in complex backfill environment was pinpointed. Remedial measures of the failed section and reinforcing techniques of the remaining GRS walls were briefly presented in the end.     

Analysis of installation damage tests for LRFD calibration of reinforced soil structures

North American design codes are now committed to the development of load and resistance factor design (LRFD) for reinforced soil structures including internal stability limit states. Reliability-based analysis is required to carry out these calibrations. A framework for LRFD calibration has been proposed by the writers that requires bias statistics for load and resistance terms for each limit state function. In this paper the formulation of the limit state for reinforcement tensile rupture is developed and the component strength-reduction bias statistics identified. The paper describes how to compute bias statistics from project-specific installation damage trials for use in reliability-based design for the reinforcement rupture limit state or using data from multiple sources for LRFD calibration. A database of results from field installation damage trials on 103 different geosynthetic products was collected from 20 different sources. A total of 799 and 2248 in-air tensile test results were reviewed for undamaged and damaged geosynthetic specimens, respectively. This database is used to compute installation damage bias statistics for six different categories of geosynthetic and four categories of backfill soils classified according to the D₅₀ particle size. A practical outcome is that for analysis purposes, bias statistics can be grouped into two ranges for each geosynthetic type based on D₅₀ of the soil greater than or less than 19 mm. The paper shows how bias statistics together with load and resistance factors for the geosynthetic rupture limit state function recommended by AASHTO (2010) can be used to calculate probability of failure using Monte Carlo simulation and demonstrates the sensitivity of probability of failure to magnitude of installation damage bias statistics. The installation damage data is valuable for future LRFD calibration to select resistance factors for use in design codes for the geosynthetic rupture limit state in reinforced soil structures.