Stiffness Degradation of Undisturbed Saturated Soft Clay in the Yangtze Estuary Under Complex Stress Conditions

Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.

Research on characters of surrounding rock in complex geology conditions and supporting time

The methods combined by test, field monitoring and theoretical analysis were adopted to do the systemic research on the rock mass from micro-structure to macro-deformation, and rheological model of Jinchuan rock mass was established to discuss the reasonable supporting time. Resuhs show that supporting after suitable stress and displacement release can benefit for the long-term stability of surrounding rock.

Effect of intermediate principal stress on strength of soft rock under complex stress states

A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/softening constitutive model based on the unified strength theory(UST) were used to simulate both the consolidated-undrained(CU) triaxial and the consolidated-drained(CD) true triaxial tests. Based on the results of the true triaxial tests simulation, the effect of the intermediate principal stress on the strength of soft rock was investigated. Finally, an example of an axial compression test for a hard rock pillar with a soft rock interlayer was analyzed using the two-dimensional finite difference code FLAC. The CD true triaxial test simulations for diatomaceous soft rock suggest the peak and residual strengths increase by 30% when the effect of the intermediate principal stress is taken into account. The axial compression for a rock pillar indicated the peak and residual strengths increase six-fold when the soft rock interlayer approached the vertical and the effect of the intermediate principal stress is taken into account.

Influence analysis of complex crack geometric parameters on mechanical properties of soft rock

Soft rocks, such as coal, are afected by sedimentary efects, and the surrounding rock mass of underground coal mines is generally soft and rich in joints and cracks. A clear and deep understanding of the relationship between crack geometric parameters and rock mechanics properties in cracked rock is greatly important to the design of engineering rock mass struc‑tures. In this study, computed tomography (CT) scanning was used to extract the internal crack network of coal specimens. Based on the crack size and dominant crack number, the parameters of crack area, volume, length, width, and angle were statistically analyzed by diferent sampling thresholds. In addition, the Pearson correlation coefcients between the crack parameters and uniaxial compression rock mechanics properties (uniaxial compressive strength UCS, elasticity modulus E) were calculated to quantitatively analyze the impact of each parameter. Furthermore, a method based on Pearson coefcients was used to grade the correlation between crack geometric parameters and rock mechanical properties to determine threshold values. The results indicated that the UCS and E of the specimens changed with the varied internal crack structures of the specimens, the crack parameters of area, volume, length and width all showed negative correlations with UCS and E, and the dominant crack played an important role both in weakening strength and stifness. The crack parameters of the angle are all positively correlated with the UCS and E. More crack statistics can signifcantly improve the correlation between the parameters of the crack angle and the rock mechanics properties, and the statistics of the geometric parameters of at least 16 cracks or the area larger than 5 mm2 are suggested for the analysis of complex cracked rock masses or physical reproduction using 3D printing. The results are validated and further analyzed with triaxial tests. The fndings of this study have important reference value for future research regarding the accurate and efcient selection of a few cracks with a signifcant infuence on the rock mechanical properties of surrounding rock mass structures in coal engineering.

Critical Cyclic Stress Ratio of Undisturbed Saturated Soft Clay in the Yangtze Estuary under Complex Stress Conditions

There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index dis-tinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus de-veloped by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consoli-dation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress,initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio wereinvestigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientationangle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate prin-cipal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic cou-pling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stressdirections during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does.

NEW THEORY IN TUNNEL STABLILITY CONTROL OF SOFT ROCK──MECHANICS OF SOFT ROCK ENGINEERING

Tunnel stability control is a world-wide difficult problem. For the sake of solving it,the new theory of soft rock engineering mechanics has been estabilished. Some key points,such as the definition and classification of soft rock, mechanical deformation mechanism of a soft rock tunnel, the critical support technique of soft rock tunnel and the new theory of the soft rock tunnel stability control are proposed in this paper.

Development and applications of the quasi‐dynamic triaxial apparatus for deep rocks

The mechanical behaviors of deep rocks have always posed a challenge for the implementation and safe operation of major underground engineering projects.To this end,this study modified the existing mainstream rock mechanics instruments equipped with a dynamic disturbance loading system and developed a second‐generation TFD‐2000/D triaxial instrument.The first‐generation device is equipped with an independent disturbance system and an advanced EDC‐580 all‐digital servo controller,which can apply disturbing load independently,implement the function of cyclic disturbance,and combine dynamic and static disturbances.The instrument was found to be reliable for use in analyzing the damage process of rocks in the disturbance test of marbles.The second‐generation instrument tackles three limitations of the first‐generation instrument:(i)it upgrades the strain measurement system and uses extensometers with linear variable differential transformers to accurately measure deformation;(ii)it uses the self‐balanced chamber to replace the Hoek–Franklin triaxial cell and auto‐balancing triaxial pressure chamber;and(iii)the loading rod is independently equipped with an EDC‐580 all‐digital servo controller,which measures precise loads.The experimental findings confirmed that the second‐generation instrument can be used for rock mechanics testing under cyclic disturbance loading,the disturbance–stress relaxation cycle,and the creep–fatigue cycle.In this sense,the second‐generation instrument can be a useful addition to deep rock mechanical instruments and provide a valuable reference.

西瓦里克地质区域条件下软岩高边坡施工技术

以尼泊尔某水电工程引水隧道TBM始发平台永久边坡工程为依托,介绍西瓦里克地质区域条件下软岩高边坡的设计方案与施工关键技术,通过稳定性计算,采用土钉锚杆+网格梁/喷锚支护+综合排水措施。通过施工监测结合永久监测数据分析,边坡整体稳定,满足设计要求。

软土地区某复杂边界条件深大基坑支护设计与分析

随着长三角城市化和地下空间的发展,地下空间逐渐呈现特大超深、布局复杂等特点。同时,在软土复杂边界条件下,仅采用单一的支护形式已较难以同时满足工程适用性、安全性、经济性和工期需求。以台州中心城区某布局复杂、深大基坑工程为背景,基于项目周边环境及地质条件,对基坑特点及难点、支护方案选型、设计思路和处理方法等进行了详细的介绍和分析。通过采用综合性合理的支护结构体系和分坑、分区技术,并在重点部位采取针对性的技术手段,有效解决了基坑布局复杂且挖深差异大、周边环境敏感复杂、软土强度低及变形大等难题。数值模拟分析和现场实际监测结果表明,采用此方案基坑整体变形小、对周边环境影响小,可为后续类似工程设计提供一定经验和参考。

综合楼施工深基坑变形多点视觉监测

以保障工程施工安全为目的,提出综合楼施工深基坑变形多点视觉监测方法。以某待测综合楼施工工程深基坑项目为研究标靶,在其周围设置测点并布设图像传感器采集深基坑支护桩顶、周围道路、管线等位置的相关图像,利用包围盒法重建三维深基坑图像,采用粗糙K均值聚类算法计算靶点范围与中心,通过对比原始图像与监测图像的标志点差异获取深基坑的变形位移值,利用所得深基坑图像的标志点位移变化量构建监测数据样本,通过训练RBF神经网络输出深基坑变形预测结果。实验结果表明:该方法可有效监测深基坑变形;深基坑周围道路沉降的变形量最大约为15.12 mm,未达到报警值40 mm;围护加固结构可有效约束深基坑变形。

软岩地质条件下巷道过断层支护技术研究

针对软岩巷道断层越来越严重的问题,王楼煤矿采用“锚杆+注浆”的二次支护形式进行软岩地质条件下巷道过断层的支护。首先在巷道过断层位置布置锚杆进行支护,然后注入浆液以增强支护效果。通过实例结果可以看出,采用设计支护技术施工后,巷道过断层左帮围岩变形36.8 mm,右帮围岩变形39.3 mm,达到了预期的支护效果。研究软岩地质条件下巷道过断层支护技术对于确保煤矿开采工作的安全和顺利进行具有重要意义。

复杂软岩条件下综采工作面液压支架创新回撤方法

针对清水营煤矿110206综采工作面顶底板为泥岩和砂质泥岩的复合特性,以及工作面煤层较软和顶板淋水等特点,在工作面收尾期间支护方式及设备回收方法的选择尤为重要。通过分析工作面收尾、设备回撤通道及工作面上下口支护方式存在的问题,提出了复杂软岩条件主动锚索梁支护+锚索桁架加强支护+锚索注浆全长锚固+工作面出口反底拱联合支护方案。通过现场实施表明,这种支护方式在工作面回撤期间能较好地控制回收通道及工作面上下口的顶板及底板发生下沉及底鼓现象。针对液压支架回撤情况,设计了一种专用模块化钢板,首尾相接铺设在回撤通道软弱底板上,将支架拉移至钢板上,采用绞车将支架拖运至工作面上口,用单轨吊回收。掘进面扇形带采用掩护支架支护顶板,待抽支架采用自拉自的方式,抽出时利用掩护支架的护帮板作为其防倒装置,实现了抽架及调向不用绞车,同时也减少了作业人员,实现了安全高效回撤。110206综采工作面采用这种回撤模式,安全高效地完成了设备回撤工作,取得了较好的使用效果,为复杂软岩及类似条件下工作面液压支架回撤提供了一种创新回撤方法。

西延高铁长大复杂隧道建造关键技术

针对新建西延高铁隧道数量多、地质条件差、施工环境复杂等特点,采取理论分析、室内试验、现场监控量测、数值模拟以及专家咨询等手段,展开典型长大复杂隧道建造关键技术研究,形成了较为完整的西延高铁隧道建造关键技术,主要包括:浅埋软塑黄土隧道变形控制技术、全断面大型机械化配套快速掘进技术、缓倾层状围岩隧道特殊支护技术、微弱振动非爆掘进技术和机械化作业空间布设调整技术措施等,推动软弱围岩隧道机械化、信息化、智能化建造技术升级,为西延高铁安全顺利施工提供重要保障和支撑。

复杂地应力条件下软岩隧道施工关键技术研究

软岩强度低、自稳能力差,在复杂地应力作用下更易出现大变形、支护结构破坏等灾变现象。文章以复杂地应力隧道施工为切入点,分析了软岩隧道地应力分析方法,重点阐述现场测试手段、初始模拟分析方法与围岩应力应变特性试验,帮助施工单位真实了解工程现场地应力条件,客观评估复杂工况对隧道施工形势造成的实际影响。文章还阐述了复杂工况下的软岩隧道施工路径,旨在有效控制施工过程中的围岩大变形问题,保证施工安全和施工进度,减小地应力对围岩的影响。

极端降雨工况下库岸软岩边坡综合防护措施工程效果分析

采取工程加固措施是保证边坡安全稳定的重要手段,具有十分重要的意义和作用。文中以碧流河水库上游软岩边坡为例,利用数值模拟的方式对不同加固措施组合方案的效果进行对比分析,结合计算结果和工程的实际,建议综合运用三维网植草护坡、锚杆框格梁支护和坡面固化土处理等3种措施对边坡进行加固处理。

复杂地质条件下盾构隧道掘进中岩土分层施工难点与解决对策

通过实地勘察和室内试验,分析了不同地质条件对盾构掘进的影响。研究表明:地层软硬不均、地下水丰富和断层破碎带是主要难点。针对这些问题,提出了优化刀具配置、改进注浆工艺和采用变量控制等对策。实践证明:这些措施能有效提高施工效率和质量,为复杂地质条件下盾构隧道施工提供了可靠的技术支持。

亚热带复杂海域区间隧道精准勘察与评价

结合厦门轨道交通2号线五缘湾隧道工程,下穿存在残积砂质黏性土,全、强风化花岗岩层等,发育有可液化砂土、软土、残积土和全风化岩等特殊岩土,土质均匀性较差的复杂海域地质段,通过海上测绘、合理布置勘探孔、物探、现场测试、室内试验、理论计算等综合技术,研究其工程地质和水文地质条件,评价场地的稳定性和适宜性,提出针对性的工程防治措施,为设计和施工提供依据。

特殊条件下大采高工作面回撤通道稳定性控制研究

为了实现特殊条件下大采高工作面设备快速安全回撤,以赵庄矿5310工作面回撤通道为工程背景,综合采用现场调研、数值模拟、理论分析等方法,研究了基本顶不同断裂位置和周期来压步距对回撤通道的影响,进而确定合理的回撤通道位置;根据回撤通道赋存特征和围岩条件,坚持"顶帮协同控制"的原则,在提高支架初撑力的基础上,顶板采用全锚索支护、煤帮为锚网索联合支护。现场监测表明,该支护方案能够实现工作面设备顺利回撤,可为类似条件下工作面回撤通道的稳定性控制提供借鉴和参考。

复杂条件下巷道围岩控制技术研究进展

煤炭资源开采正不断向深部迈进,面临的复杂地质条件问题也日益突出。深部资源开采、地下空间开挖等深部岩石工程活动迅速增加,而这些工程活动的开展和巷道的稳定性密切相关。重点总结了复杂条件下煤矿巷道围岩控制领域的相关成果,梳理了当下巷道围岩控制面临的主要复杂条件,划分了工程地质条件和开采技术条件2类巷道复杂条件。阐明了各类复杂条件下巷道围岩的变形破坏特征,指出了围岩应力、围岩性质和支护结构是巷道围岩控制的3类基本对象,明确了围岩应力环境恶化、围岩性质劣化和支护体性能弱化3种失稳形式,在此基础上揭示了不同地质环境与采掘时空关系下回采巷道的失稳机制。分析了现阶段困难巷道围岩控制基本机理:改善围岩应力环境、改良围岩性质与强化围岩承载结构;详述了基于卸压、改性、支护与协同控制的围岩控制技术在不同复杂条件巷道的阶段性理论研究与技术应用现状。同时,分析了泥质采动巷道渗流失稳与围岩控制的典型工程案例,揭示了该类复杂困难条件的巷道围岩失稳机理,提出了疏水泄压、泥岩置换、分级注浆、高强度封层支护结构与底板结构等多种方法协同作用的高强度综合修复与控制技术体系。最后,基于上述4方面研究,结合工程实践,展望了未来复杂条件下巷道围岩控制技术的发展趋势。

五河杂岩的变质岩石学及P-T条件分析——来自蒙城南ZK02钻孔的研究

五河杂岩是华北克拉通东部陆块东南缘最重要的岩石单元.然而,直至今日,人们对于该组杂岩一直缺乏足够的研究,特别是对于其形成的变质条件分歧较大.本文通过对蒙城南ZK02钻孔中五河杂岩的构成和地质特征详细研究表明五河杂岩分为上、下两段.上段主要为一套由云母片岩、大理岩和花岗片麻岩组成的变质表壳岩系;下段为一套基性变质岩,主要岩性为斜长角闪岩、角闪岩、石榴斜长角闪岩和少量的混合岩.同时,针对下段特征岩石（石榴斜长角闪岩）,进行了较为详细的岩相学和矿物化学分析,并应用不同的温压计进行P-T条件评价和比较,结合岩相学限定和前人的研究成果,认为五河杂岩的主体普遍经历了高压角闪岩相变质作用,其温压范围为：T=671℃～700℃和P=0.82～0.95 GPa,地温梯度约为25～28℃/km,与典型陆壳地温梯度类似.与同邻区主要岩石单元的变质级别相比,五河杂岩应当形成于板内变质环境,并不具备造山带变质特征.