Model test study of frost heaving pressures in tunnels excavated in fractured rock mass in cold regions

Based on the similarity theory, taking the horseshoe, city-gate and round linings as examples, the value and distribution regularities of normal frost heaving pressures （hereinafter as frost heaving pressures） in tunnels excavated in fractured rock mass in cold regions under different constraints and freezing depths were studied by a test model. It was found that the larger the frozen depth, the larger the frost heaving pressure, and the stronger the top constraint, the larger the frost heaving pressure. For the horseshoe lining and city-gate lining, the top constraint has a greater effect on the frost heaving pressures on the arch and the inverted arch. For the round lining, the influences of the top constraint on the frost heaving pressure in all linings are almost the same. The frost heaving pressure is maximum on the city-gate lining and minimal on the round lining. The largest frost heaving pressure all occur near the foot of the inverted arch for the three kinds of lining. Thus, the test data basically coincide with the observed in situ data.

MEASUREMENT AND RESEARCH OF SURROUNDING ROCK PRESSURE OF DEEP SHAFT

The whole depth measuring plan and its implementation method of surrounding rock mass pressure on the wall′s of a shafts are described, which is in Suncun Coal Mine with a depth of 1 000 m.Then with the combination of data processing, it is discussed the effects of such factors on the distribution law of shaft surrounding rock pressures as rock quality,burying depth, end effect due to excavating, rock stratum dip, shaft wall structure form and regression formulae relating to the shafts surrounding rock pressures as well as to several other factors.And finally, the measured results were verified according to the comparison between analyses of stress strain of side walls and side wall strain measurements.

A thermal stress loading technique for large-sized hot dry rock mechanical tests

Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host frames and hydraulic pumps,which could lead to great investment.Low-cost testing machines clearly always have great appeal.In this study,a new approach is proposed using thermal expansion stress to load rock specimens,which may be particularly suitable for tests of deep hot dry rock with high temperatures.This is a different technical route from traditional mechanical loading through hydraulic pressure.For the rock mechanics test system of hot dry rock that already has an investment in heating systems,this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes.This paper presents the basic principle and a typical design of this technical solution.Preliminary feasibility analysis is then conducted based on numerical simulations.Although some technical details still need to be resolved,the feasibility of this loading approach has been preliminarily confirmed.

A Test Model of Water Pressures within a Fault in Rock Slope

This paper introduces model test results of water pressure in a fault, which is located in a slope and 16 different conditions. The results show that the water pressures in fault can be expressed by a linear function, which is similar to the theoretical model suggested by Hoek. Factors affecting water pressures are water level in tension crack, dip angle of fault, the height of filling materials and thickness of fault zone in sequence.

Assessment of cyclic deformation and critical stress amplitude of jointed rocks via cyclic triaxial testing

Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress amplitudes.The samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 Hz.At each level of confining pressure,the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was observed.Analysis of the test results indicated that there existed a critical cyclic deviatoric stress amplitude(i.e.critical dynamic deviatoric stress)beyond which the jointed rock specimens yielded.The measured critical dynamic deviatoric stress was less than the corresponding static deviatoric stress.At cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress,minor cumulative residual axial strains were observed,resulting in hysteretic damping.However,for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress,the plastic strains increased promptly,and the resilient moduli degraded rapidly during the initial loading cycles.Cyclic triaxial test results showed that at higher confining pressures,the ultimate residual axial strain attained by the jointed rock specimen decreased,the steadystate dissipated energy density and steady-state damping ratio per load cycle decreased,while steadystate resilient moduli increased.

Numerical analysis of stress distribution in the upper arm tissues under an inflatable cuff：Implications for noninvasive blood pressure measurement

An inflatable cuff wrapped around the upper arm is widely used in noninvasive blood pressure measurement.However, the mechanical interaction between cuff and arm tissues, a factor that potentially affects the accuracy of noninvasive blood pressure measurement, remains rarely addressed. In the present study, finite element（FE） models were constructed to quantify intra-arm stresses generated by cuff compression, aiming to provide some theoretical evidence for identifying factors of importance for blood pressure measurement or explaining clinical observations. Obtained results showed that the simulated tissue stresses were highly sensitive to the distribution of cuff pressure on the arm surface and the contact condition between muscle and bone. In contrast, the magnitude of cuff pressure and small variations in elastic properties of arm soft tissues had little influence on the efficiency of pressure transmission in arm tissues. In particular, it was found that a thickened subcutaneous fat layer in obese subjects significantly reduced the effective pressure transmitted to the brachial artery, which may explain why blood pressure overestimation occurs more frequently in obese subjects in noninvasive blood pressure measurement.

Influence of dynamic pressure on deep underground soft rock roadway support and its application

Due to high ground stress and mining disturbance, the deformation and failure of deep soft rock roadway is serious, and invalidation of the anchor net-anchor cable supporting structure occurs. The failure characteristics of roadways revealed with the help of the ground pressure monitoring. Theoretical analysis was adopted to analyze the influence of mining disturbance on stress distribution in surrounding rock,and the change of stress was also calculated. Considering the change of stress in surrounding rock of bottom extraction roadway, the displacement, plastic zone and distribution law of principal stress difference under different support schemes were studied by means of FLAC3D. The supporting scheme of U-shaped steel was proposed for bottom extraction roadway that underwent mining disturbance. We carried out a similarity model test to verify the effect of support in dynamic pressure. Monitoring results demonstrated the change rules of deformation and stress of surrounding rock in different supporting schemes. The supporting scheme of U-shaped steel had an effective control on deformation of surrounding rock. The scheme was successfully applied in underground engineering practice, and achieved good technical and economic benefits.

Micro-failure process and failure mechanism of brittle rock under uniaxial compression using continuous real-time wave velocity measurement

In this study,the micro-failure process and failure mechanism of a typical brittle rock under uniaxial compression are investigated via continuous real-time measurement of wave velocities.The experimental results indicate that the evolutions of wave velocities became progressively anisotropic under uniaxial loading due to the direction-dependent development of micro-damage.A wave velocity model considering the inner anisotropic crack evolution is proposed to accurately describe the variations of wave velocities during uniaxial compression testing.Based on which,the effective elastic parameters are inferred by a transverse isotropic constitutive model,and the evolutions of the crack density are inversed using a self-consistent damage model.It is found that the propagation of axial cracks dominates the failure process of brittle rock under uniaxial loading and oblique shear cracks develop with the appearance of macrocrack.

Theory and application of rock burst prevention using deep hole high pressure hydraulic fracturing

In order to analyze the mechanism of deep hole high pressure hydraulic fracturing, nonlinear dynamic theory, damage mechanics, elastic-plastic mechanics are used, and the law of crack propagation and stress transfer under two deep hole hydraulic fracturing in tectonic stress areas is studied using seepage-stress coupling models with RFPA simulation software. In addition, the effects of rock burst control are tested using multiple methods, either in the stress field or in the energy field. The research findings show that with two deep holes hydraulic fracturing in tectonic stress areas, the direction of the main crack propagation under shear-tensile stress is parallel to the greatest principal stress direction. High-pressure hydraulic fracturing water seepage can result in the destruction of the coal structure, while also weakening the physical and mechanical properties of coal and rock. Therefore the impact of high stress concentration in hazardous areas will level off, which has an effect on rock burst prevention and control in the region.

盾构壁后注浆窜浆模型试验及发生条件研究

全断面围岩管片壁后注浆因向开挖面方向的窜浆现象会引起盾尾空隙注浆不饱满,管片上浮、错台及开裂,螺机喷涌等事故常有发生,已经引起广泛重视。通过设计自制壁后注浆液窜浆模型装置进行试验,分析浆液性质、缝隙厚度、注浆压力差对是否发生窜浆及窜浆量的影响,并探讨了不发生窜浆的临界条件。结果表明:(1)浆液压力与窜浆距离呈线性衰减,当浆液稠度较低时,窜浆量与缝隙厚度、浆液稠度呈近似线性正相关、与浆液的剪切屈服应力呈近似线性负相关,窜浆距离与注浆压力差呈近似线性正相关;当浆液稠度增大时,以上关系将逐渐转化为非线性关系;(2)通过极差分析表明浆液的窜浆量受盾壳与岩层间缝隙厚度影响最大,注浆压力与开挖面压力差影响其次,最后是浆液本身的性质;(3)建立了窜浆临界分析模型和计算公式,得到了窜浆发生条件和判别方法,可用于指导稳定围岩地层中盾构掘进时浆液的配制。

双封隔取样压力数据深入解释方法研究

双封隔器是一种地层测试测压取样工具,取样过程通常需要泵抽几小时甚至十几小时,取得地层流体样品,获得压力和流量数据,但无法真实反映地层渗透率的探测范围。利用油藏模拟软件模拟双封隔器泵抽取样过程,引入Schroeter算法和Levitan算法这两种压力/流量数据反褶积算法,反演渗透率参数波及半径从几厘米到上百米,并使用数值模拟案例验证了只利用取样完成后的压力恢复数据进行反褶积方法的准确性和合理性。该研究应用于双封隔现场测井数据,采用反褶积方法得到渗透率探测半径31m,反褶积处理后的数据可用于产能预测,对正确认识油气藏具有重要意义。

黄土盾构隧道开挖围岩扰动特性模型试验研究

为了探究不同含水率和埋深等工况下的黄土盾构隧道开挖对围岩的扰动作用特征,采用相似模型试验,首先通过三轴试验测定了不同含水率下原状黄土物理参数及强度指标,通过大量试配得到了不同含水率下与原状黄土强度指标参数相似的试验用土。其后,考虑盾构隧道盾尾间隙特征,开展不同含水率及埋深等组合工况下盾构开挖模拟试验,通过微型土压力传感器、百分表等监测元件以及数字图像技术等手段,分析了不同工况下地层变形、地表沉降和围岩应力的变化规律。研究发现:含水率较低时,围岩的自稳能力强;含水率越高,埋深越大,开挖对地层的扰动作用也越大;地表最大沉降值与含水率呈正相关,与埋深呈负相关;围岩剩余应力随含水率和埋深的增大而增大,但当含水率增大至一定值(26.6%)时,围岩剩余应力骤减;基于不同含水率下的围岩应力及变形发展规律,可将黄土含水率分为自稳、形变以及松动含水率,基于含水率和埋深引起的围岩松动情况,可将不同工况下的黄土盾构隧道围岩压力作用模式按照形变压力和松动压力计算,以更加适应黄土地层的特性。

不同埋深条件下盾构施工扰动试验研究

随着城市地下空间开发规模不断扩大,盾构施工诱发的地层扰动对地下既有建(构)筑物及周边环境的安全产生了重要的影响。通过自主研发盾构掘进试验装置,实现了不同地层应力水平的加载,分析了不同埋深条件下盾构施工地层扰动的变化规律及影响范围。研究结果表明:隧道周围地层中土压力变化率随着距隧道水平距离的增大而逐渐递减;盾构掘进完毕后土压力相对于初始土压力减少了约20%~40%;埋深比变化对拱顶、拱底处的土体应力路径影响较小;定义了基于土压力力变化的地层扰动度,随埋深比的增大,地层扰动度逐渐减小,说明深埋条件会降低盾构开挖对地层的扰动作用;盾构掘进完毕后,扰动作用的竖向影响范围高度介于隧道上下0.5D~0.8D(D为隧道直径)之间,当盾构到达监测断面时水平扰动范围宽度约为0.5D,盾构穿越远离后近似为1.2D~1.5D。

径向让压系统对软岩隧道围岩力学特性影响研究

为处理深部软岩隧道存在的大变形问题,一般采取强支护或支护后进行修复,但收效甚微。在三维地质力学模型的基础上,提出以径向让压为核心的主动支护,先释放围岩应力,后抵抗围岩变形,改善挤压型大变形隧道的力学特性,有效地控制隧道开挖过程中的位移变形。文章以公路隧道典型大变形段为研究对象,建立三维地质力学模型,分析径向让压支护对围岩变形和支护承载能力的控制效果。结果表明:径向让压支护段相对正常支护段能有效控制围岩相对变形,从锚杆变形看出,最大拉应变减小了75.8%,最大压应变减小了67.6%;从围岩与初支接触压力看,将拱底、拱脚压力降低80%,验证了径向让压支护对于围岩塑性区发展和应力释放的有效控制。研究成果可为同类深部软岩隧道围岩控制技术提供数据参考。

桩网复合地基离心模型试验中桩顶轴力测试方法研究

桩网复合地基是常见的软土加固措施。在开展桩网复合地基离心模型试验时,为了分析桩土应力比,需要测量桩顶轴力和桩间土压力。微型土压力计在离心模型试验中已经得到广泛应用,但尚无成熟的微型桩顶轴力测试传感器。利用模型桩的桩帽,开发了一种离心模型试验专用桩顶轴力测试方法,标定结果显示该方法测试线性度好。通过某桩网复合地基离心模型试验和数值分析的桩土应力比结果对比分析,验证了该方法的测试效果。

基于模型试验的某矿区地下开采过程中采场稳定性研究

目的:围岩稳定性是岩土工程界重要研究内容之一,较差的围岩可能会使地下工程如隧道、矿井等发生坍塌。因此,为了确保地下工程的安全施工和稳定性,对围岩稳定性的研究至关重要。方法:本研究在充分调查某矿区某矿段采场结构参数及对地压控制研究分析后,基于矿体的赋存条件、地质产状以及顶底板的实际情况,选取了某矿段中比较有代表性的剖面,采用相似模型试验的方法,围绕点柱控顶建立室内相似试验模型,对该矿地下开采过程中采场的稳定性进行模拟分析。结果:随着矿体倾角的增大,围岩变形随之增大。在完全空场条件下,即只留中段矿柱,不留点柱,顶板会发生大面积破坏,并有可能出现地表塌陷,造成安全事故。结论:本研究要预留点柱控制地压,防治冲击地压。意义:研究成果对指导该矿区矿体的安全开采和利用具有重要的理论和实践意义。

湖南省桂阳抽水蓄能电站高压引水隧洞稳定性分析

为研究湖南桂阳抽水蓄能电站高压引水隧洞稳定性,在工程区开展了高压压水试验和地应力测试,定量描述了隧洞围岩在高内水压力作用下的渗透特性,分析了整个工程区特别是重要工程部位的岩体应力状态,在此基础上根据围岩条件、抗抬理论准则、最小主应力准则、渗透准则评价了高压引水隧洞的渗透稳定性。结果表明:(1)工程区水平主应力大小总体上随深度的增加而增大,3个主应力之间的关系为SH>SZ>Sh,属于走滑型应力状态,钻孔附近地壳浅表层的最大水平主应力方位平均为NW32°,高压岔管及厂房区域属中等-低地应力区。高压压水试验结果显示隧洞围岩属于弱至微透水岩体;(2)高压引水隧洞各洞段具有足够的埋深条件,满足抗抬理论准则,同时隧洞围岩的抗渗透能力及抗水力劈裂能力均较好,基本满足钢筋混凝土衬砌方案的要求。

束状孔与当量大孔爆破应力波在节理岩体中的衰减规律

束状孔当量球形药包爆破技术是基于大直径深孔采矿法的新型爆破技术,与单孔爆破技术相比,其炸药能量利用率更高。为了探究节理岩体中束状孔与当量大孔爆破应力波衰减规律的不同,开展束状孔与当量大孔爆破模型试验研究。试验采用混凝土制作相似模型并用无缝钢管将炮孔包围以忽略爆生气体的作用,同时考虑不同节理厚度的影响,得到了爆炸应力波峰值速度与节理厚度的关系,并将两种布孔方式在相同节理条件下进行对比分析。结果表明:两种布孔方式的爆炸应力波峰值速度均随着节理厚度的增加而逐渐降低,在相同节理厚度条件下,束状孔爆破的应力波衰减相对更小。

土岩地层无岩肩吊脚墙基坑开挖变形与破坏特征模型试验

依托某深基坑工程开展室内模型试验,分析基坑开挖至加载破坏全过程吊脚墙顶沉降、支撑轴力、墙后土压力、墙体弯矩等变化规律,并揭示基坑破坏特征形态。结果表明:墙顶沉降量随基坑开挖逐渐增大,基坑开挖深度小于吊脚墙高度时,墙顶沉降量增长速率较小,大于吊脚墙高度时,墙顶沉降增长速率增大;支撑轴力随开挖深度增大逐渐增大,其中第2道最大,第1道最小;墙后土压力在开挖过程中由静止土压力转化为主动土压力,地面超载作用下的墙后附加土压力基本一致;墙体最大弯矩随开挖深度增大逐渐增大,最大弯矩位置随基坑开挖下移,最终位于第2道支撑与第3道支撑之间;12 kPa超载作用下,基坑沿岩壁段底部呈现滑动破坏,岩壁段隆起坍塌,岩层相似材料出现明显贯穿剪切裂缝。

满足试样内部环境参数测量的试样制备模具设计

随着深部资源开采和深地空间利用等工程活动的日益普遍,岩土工程面临越来越多复杂环境下岩石力学问题和挑战,亟须开展高温高压原位环境下的岩石力学测试研究,要求岩石力学测试具备更为准确和更多维度的数据测量采集能力。为此,该文开发设计了一种满足试样内部环境参数测量的试样制备模具,并形成了一套内置传感器及其信号传输通道的浇筑方法,最终制备出若干内置温度传感器及其信号传输通道的混凝土试样,且内置传感器通过导线信号传输正常,表明该试样制备模具能满足试样内部环境参数测量的试验要求。该试样浇筑模具操作方便简单,预设传感器位置可调,且可配套多种内置传感器使用,具有较强的操作性、可行性和适用性。该装置的开发和使用将有利于更多高精度多维度岩石力学测试的顺利开展。