裂隙网络模拟与REV尺度研究

研究了利用平面四边形模拟节理岩体三维裂隙网络的方法。在生成裂隙网络时,同时考虑结构面几何参数和力学参数的随机性。利用裂隙网络研究了确定岩体REV尺度的指标。在此基础上,编制了岩体裂隙网络模拟程序、裂隙网络图形输出程序和岩体REV尺度指标分析程序。通过算例分析,验证了研究成果及程序的合理性,并得出了岩体REV尺度约为各组裂隙中最大迹长期望值3~4倍的结论。研究成果为后续计算岩体等效力学参数奠定了基础。     

S-wave velocity images of the Dead Sea Basin provided by ambient seismic noise

Based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small-scale array, we have obtained shear wave velocity images of the uppermost materials that make up the Dead Sea Basin. We extracted empirical Green’s functions from cross-correlations of long-term recordings of continuous data, and measured inter-station Rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0.1–0.5 Hz bandwidth. A tomographic inversion of the travel times estimated for each frequency is performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved. Subsequently, the velocity-frequency curves are inverted to obtain S-wave velocity images of the study area as horizontal depth sections and longitude- and latitude-depth sections. The results, which are consistent with other previous ones, provide clear images of the local seismic velocity structure of the basin. Low shear velocities are dominant at shallow depths above 3.5 km, but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the Lisan Peninsula. The lack of low speeds at the sampling depth of 11.5 km implies that there are no sediments and therefore that the basement is near 10–11 km depth, but gradually decreasing from south to north. The results also highlight the bowl-shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin. The structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north–south direction. Infill materials down to ∼8 km depth are observed in the hollow of the basin, unlike what happens in the north and south where they are spread beyond the western Dead Sea shore.     

平推式滑坡多级拉陷槽形成过程及成因机理分析

通过对中江县冯店垮梁子滑坡的现场调查和室内物理模拟试验研究,发现滑坡滑动过程中存在诱发次级拉裂缝产生甚至贯通的现象,结合滑坡的变形历史迹象,进行受力分析,论证拉裂缝产生形成过程及位于拉裂缝间滑带局部贯通现象,提出U形槽模式多级平推式滑动理论; 对比宣汉天台乡滑坡已有对多级平推式滑坡研究,针对多级平推式滑坡后缘多级拉陷槽的形成过程和成因机理进行分析,提出多级平推式滑坡存在牵引后退式和推动前进式两种不同启动和运动模式,就两种模式各自岩性组成、构造裂隙发育情况、启动水头、启动速度、及多级滑动启动水头变化对比分析,建立地质力学机制模型。     

陕西宝鸡市三趾马红土工程地质特性及灾害效应

陕西宝鸡市渭河北岸地区厚层黄土底部普遍存在一套三趾马红土,其物理力学特性控制着滑坡灾害的发生。通过试验分析发现：①三趾马红土粘粒含量高（一般在37%~55%之间）、蒙脱石或伊利石/蒙脱石类膨胀性粘土矿物含量大（相对含量55%~75%,绝对含量21.99%~33.98%）、有效蒙脱石含量为18.61%~27.56%,比表面积平均值为204.7m2/g,最高达262.9m2/g,属于膨胀性粘土,物理化学活性强;②三趾马红土微裂隙发育、胶结程度差、易崩解,天然状态下为坚硬粘土,饱水后呈现可塑—软塑态,具显著膨胀性;③三趾马红土的天然强度相对较高,而遇水饱和后,粘聚力和内摩擦角明显降低,峰值强度和残余剪强度降幅在47%~63％之间。因此,三趾马红土在地下水作用下强度显著降低,成为高陡斜坡中的软弱地层,形成剪切带,控制着渭北黄土塬边地区滑坡的发育与分布。     

土钉与锚杆联合支护在深基坑工程中的应用

结合深圳市星海阁办公楼的工程实例,从周边环境对深基坑支护的特殊要求及复杂的地质条件出发,论述了采用土钉与锚杆联合支护形式的依据.介绍了在深基坑支护施工中采取的具体措施后期效果.同时分析了这种联合支护结构形式的力学特点,通过将两者联合使用,可实现锚杆支护结构水平侧移小和土钉支护结构受力合理的优点.且土钉与锚杆联合支护,使得上部锚杆和中下部的土钉墙两者形成了统一的受力整体,共同抵抗荷载和变形.     

考虑裂尖塑性区影响的水力压裂缝高计算模型

储层可压性的准确评价是储层压裂设计和压后产能评估的重要前提。目前,采用岩石力学参数进行页岩可压裂性评价取得了较好的现场应用效果。因此,如何准确获取岩石力学参数成为至关重要的问题。通过建立一种基于物理信息约束的神经网络模型,该模型采用物理和数据双驱动,仅使用少量数据就能够实现岩石力学参数的准确预测。为验证模型性能的优异性,采用人工神经网络、随机森林和XGBoost模型与之进行对比。结果表明,物理信息约束的神经网络在少量数据下预测岩石力学参数的平均准确率高于95%,性能远优于其他模型。采用物理信息约束的神经网络预测得到弹性模量、泊松比、抗拉强度和断裂韧性4种岩石力学参数,基于岩石力学参数对储层可压性的影响,建立了基于脆性指数和力学参数的可压性评价方法。最后,以渤海湾盆地沧东凹陷K2段不同储层可压性为例进行验证。结果表明：研究区整体可压性较好,其中,纹层状混合质页岩可压裂指数高于0.7,可压性良好;纹层状长英质页岩、厚层状灰云质页岩和薄层灰云质页岩可压裂指数均处在0.4~0.7,可压性中等。评价结果与实际施工现场各储层日采油量进行对比,证实了可压性智能评价方法的可靠性,该方法可以推广至页岩储层可压性评价工作中。

     

用于颗粒土微观力学行为试验的微型三轴试验仪

颗粒土的微观力学行为（如土颗粒的运动与破碎等）决定着其宏观应力-应变行为,如应变局部化、应力硬化等。为研究颗粒土的微观力学行为,开发了一台微型三轴试验装置。它的轴向加载系统由伺服控制的步进转动马达与涡轮传动的减速器组成,围压由GDS压力控制器提供,压力室采用高透光率,高强度的轻质材料制成。借助于X射线显微CT及图像处理分析技术,该装置能实现对干砂土微尺寸试样（直径为8 mm,高度为16 mm）在三轴剪切条件下微观特性的无损检测。采用该三轴试验装置对粒径为0.60～1.18 mm 的LBS（Leighton Buzzard sand）试样在1.5 MPa的围压下进行了试验。结果显示,试验装置测得应力-应变曲线合理,显微CT 图像特征清晰,能够用于颗粒土体微观土力学行为的试验研究。     

DEM simulations of methane hydrate exploitation by thermal recovery and depressurization methods

Methane hydrate (MH, also called fiery ice) exists in forms of pore filling, cementing and load-bearing skeleton in the methane hydrate bearing sediment (MHBS) and affects its mechanical behavior greatly. To study the changes of macro-scale and micro-scale mechanical behaviors of MHBS during exploitation by thermal recovery and depressurization methods, a novel 2D thermo-hydro-mechanical bonded contact model was proposed and implemented into a platform of distinct element method (DEM), PFC2D. MHBS samples were first biaxially compressed to different deviator stress levels to model different in-situ stress conditions. With the deviator stress maintained at constant, the temperature was then raised to simulate the thermal recovery process or the pore water pressure (i.e. confining pressure for MH bond) was decreased to simulate the depressurization process. DEM simulation results showed that: during exploitation, the axial strain increased with the increase of temperature (in the thermal recovery method) or decrease of pore water pressure (in the depressurization method); sample collapsed during MH dissociation if the deviator stress applied was larger than the compression strength of a pure host sand sample; sample experienced volume contraction but its void ratio was slightly larger than the pure host sand sample at the same axial strain throughout the test. By comparison with the laboratory test results, the new model was validated to be capable of reproducing the exploitation process by thermal recovery and depressurization methods. In addition, some micro-scale parameters, such as contact distribution, bond distribution, and averaged pure rotation rate, were also analyzed to investigate their relationships with the macroscopic responses.     

温度-渗流-应力耦合作用分类

根据耦合作用实现方式的不同,将温度-渗流-应力耦合作用分为“力学”耦合和“参数”耦合两大类,“力学”耦合通过场之间的某种力学作用或过程实现,而“参数”耦合则通过场的控制参数的变化而体现出来。     

边坡岩体软弱夹层力学特性试验研究

采用自制试验装置,进行边坡岩体中的软弱夹层的力学特性试验。分析实测的剪应力-变形曲线发现,该曲线有明显的比例极限、屈服点和峰值点,表明在试件受力变形初期,剪切力-变形近似呈线性关系,剪切刚度为常量;随法向应力的增大,峰值剪应力呈线性增长,达到峰值强度之后,随剪切变形增大,抗剪强度变化不大,残余强度近似等于峰值强度,表明试样发生剪切破坏,其破坏类型呈“塑性”破坏型。软弱夹层的剪切变形可分为3个阶段,各个阶段的强度参数不同,对边坡工程来说,为保证其有足够的安全系数,建议软弱夹层强度参数取低值。根据试验结果得到的法向应力-压缩位移关系曲线近似呈双曲线型,当法向相对位移小于3.4 mm时与理论结果更为接近。