Fracture development in Paleozoic shale of Chongqing area (South China). Part two: Numerical simulation of tectonic stress field and prediction of fractures distribution

A tectonics sedimentation evolution has been researched in Southeast Chongqing, and the reasonable Longmaxi shale highstand system tract (HST) and transgressive system tract (TST) geological model were built respectively based on the rock mechanical test and acoustic emission experiment which the samples are from field outcrop and the Yuye-1 well. The Longmaxi shale two-dimension tectonic stress field during the Cenozoic was simulated by the finite element method, and the distribution of fractures was predicted. The research results show that the tectonic stress field and the distribution of fractures were controlled by lithology and structure. As a result of Cretaceous movement, there are trough-like folds (wide spaced synclines), battlement-like folds (similar spaces between synclines and anticlines) and ejective folds (wide spaced anticlines), which are regularly distributed from southeast to northwest in the study area. Since the strain rate and other physical factors such as the viscosity are not taken into account, and the stress intensity is the main factor that determines the tectonic strength. Therefore, the stronger tectonic strength leads the higher stress intensity in the eastern and southeastern study area than in the northwest. The fracture zones are mainly concentrated in the fold axis, transition locations of faults and folds, the regions where are adjacent to faults. The fragile mineral contents (such as siliceous rock, carbonate rock and feldspar) in the shelf facies shale from south of the study area are higher than in the bathyal facies and abyssal facies shale from center of the study area. The shales characterized by low Poisson’s ratio and high elastic modulus from south of the study area are easily broken during Cenozoic orogenic movement.     

Compaction of a Rock Fracture Moderated by Competing Roles of Stress Corrosion and Pressure Solution

Unusually rapid closure of stressed fractures, observed in the initial stages of loading and at low temperatures, is examined using models for subcritical crack growth and pressure solution. The model for stress corrosion examines tensile stress concentrations induced at the Hertzian contact of propping fracture asperities, and mediates fracture growth according to a kinetic rate law. Conversely, pressure solution is described by the rate-limiting process of dissolution, resulting from the elevated stresses realized at the propping asperity contact. Both models are capable of following the observed compaction of fractures in novaculite. However, closure rates predicted for stress corrosion cracking are orders of magnitudes faster than those predicted for pressure dissolution. For consistent kinetic parameters, predictions from stress corrosion better replicate experimental observations, especially in the short-term and at low temperature when mechanical effects are anticipated to dominate. Rates and magnitudes of both stress corrosion and pressure solution are dependent on stresses exerted over propping asperities. Rates of closure due to stress corrosion cracking are shown to be always higher than for pressure solution, except where stress corrosion ceases as contact areas grow, and local stresses drop below an activation threshold. A simple rate law is apparent for the progress of fracture closure, defined in terms of a constant and an exponent applied to the test duration. For current experimental observations, this rate law is shown to replicate early progress data, and shows promise to define the evolution of transport properties of fractures over extended durations.     

干砂强夯动力特性的细观颗粒流分析

通过引进和开发二维颗粒流程序,基于相似理论建立了可以模拟砂土地基强夯加固的细观颗粒流模型,结合小比尺室内细观模型试验,从颗粒细观力学角度入手对干砂在强夯冲击加固过程中的动力反应特性进行了数值模拟。结果表明,数值模拟结果与试验结果有较好的一致性,利用颗粒流模型可以很好地模拟干砂在冲击荷载作用下的锤底动接触应力、颗粒间动接触应力和颗粒位移场分布情况,并可以实时跟踪颗粒的变位及接触应力变化,实现从细观角度揭示干砂强夯动力响应特性,研究工作为今后砂土强夯加固宏细观机制研究提供了一条新的思路。     

基于一维和三维固结挤土桩沉降时效计算分析

饱和软黏土地基中的挤土桩,施工引起的桩侧土体超孔隙水压力消散和竖向荷载引起的桩底土体固结是导致其沉降的主要因素。基于三维固结理论,研究了桩侧地基土再固结沉降的变化规律,并从桩-土相互作用的原理出发,结合边界条件,推导出了在桩侧地基土再固结沉降的作用下挤土桩沉降的计算公式。运用太沙基一维固结理论并采用分层总和法计算竖向荷载作用下桩底土体的沉降。提出了饱和软土中挤土桩沉降时效的计算方法。并对工程实例进行了计算分析,其结果符合工程实际沉降规律。     

冲击荷载下土体位移特征研究

建立了冲击荷载作用下土体动力压密有限元方程及其数值计算方法。用Ansys-Ls-dyna软件包对山西化肥厂地基冲击荷载作用后土体的动力响应进行了分析,得出了冲击荷载作用下分层土体中的位移分布特征及其它们的变化过程,计算结果与实测结果吻合较好。研究结果表明：冲击荷载作用下土体位移的影响范围为一椭球体。侧向加固半径距荷载作用中心接近2D(D为夯锤直径),荷载作用中心下加固深度能达到2D甚至更大。     

深厚软土地基爆破挤淤效果检测方法及应用实例

爆破挤淤抛石置换断面的结构分层特点及电磁参数差异具备探地雷达检测的基本物理前提。通过浙江洞头某海涂围堤的检测表明,对于底部深度达35 m左右的深厚抛石层,可采用16 MHz低频天线和合适的测试参数探测,查明落底深度、宽度以及腰部宽度等堤身参数,突破探地雷达检测深厚抛石层的局限性。其底部泥石混合层难以识别。     

路基粒状填土的旋转压实试验

尽管击实试验是目前最流行的室内土体压实试验方法,但实际上与现场任何一种压实方法都无相似之处,且不适用于无粘性土（粒状土）的压实试验。无粘性土的振动击实试验方法也存在很多问题。现代重型压实设备的使用,路基粒状填土的压实密度达到了目前室内规范试验方法不可能达到的水平。介绍了美国采用供高性能沥青路面混合料设计与质量控制之用的旋转压实机对粒状土进行的压实试验。其结果表明,旋转压实试验能有效模拟路基粒状填土的现场压实特征;可采用压实压力200 kPa、旋转角为1.25°、旋转次数为90、旋转速度为20 rpm的试验结果来控制粒状填土路基的现场压实质量。     

粤连电厂拦灰坝土石混合料碾压试验研究

对拦灰坝土石混合料进行3种不同铺填厚度、3种不同加水量、5种振动碾压遍数组合的现场试验,通过测试碾压前后的颗粒组成,沉降量、变形模量、干湿密度等确定1组优化参数作为现场施工控制参数,并对试验结果进行了分析,提出了相应的处理措施和建议。     

高能级强夯在大型石化工程中的应用

大面积的多孔隙、粗颗粒非饱和土地基的加固处理宜采用强夯法。加固深厚地基,特别是大孔隙湿陷性地基、山区大厚度非均匀块石回填地基和抛石填海地基,应该施加高能级强夯进行处理。我国的高能级强夯主要用于石化工程施工中的生产装置和大型储罐地基。结合青岛重交沥青有限公司4座5万m3原油储罐和配套附属设施地基处理工程,对高能级强夯的关键技术、检测方法和综合评价进行了阐述,可供强夯设计施工参考。     

森林经营措施对土壤的扰动和压实影响

根据森林经营措施对林地土壤的扰动和压实及其对树木生长和森林生产力的影响 ,指出森林经营措施对土壤造成的干扰是长期存在的 ,干扰强度越大 ,对林地生产力的影响越严重。从伐区作业、林地清理、整地、幼林抚育等方面提出减少土壤受扰动和压实的具体措施 ,为减少经营措施对林地生态系统的影响 ,从而改进传统的森林经营措施 ,实现森林可持续经营提供借鉴。