含充填物的厚壁圆筒砂岩的力学性质研究

基于单轴和常规三轴压缩试验,采用完整试样、空心及铝棒充填的厚壁圆筒试样,模拟研究支护对圆形巷道的强度、变形和破坏特征的影响。结果表明:充填试样和完整试样的单轴压缩强度和弹性模量大致相同,而厚壁圆筒试样的强度和弹性模量则偏低31.8%和22.4%;厚壁圆筒试样三轴压缩时出现沿圆周层状破坏,其剪切面积随着围压的增大而减少,围压40 MPa时出现明显塌孔;充填试样进入塑性屈服阶段后,充填物才会对试样的力学性质产生明显影响;充填物改变了孔道内部应力状态,使孔道内壁由原来的二维应力状态恢复到三维应力状态,抑制了孔道内壁的侧向变形,防止自由面岩石的脱落;岩石破坏并不代表承载能力消失,充填试样岩石破坏后失去黏结力,载荷主要通过充填物与岩石、岩石裂隙之间摩擦力共同承载。     

Numerical evaluation of the deformation behaviour of thick-walled hollow cylinders of shale

The stability of tunnels and boreholes in shales is a major problem. For example in the oil and gas industry, wellbore instability problems cost the industry many millions of dollars annually. In an attempt to minimise instability problems, detailed and careful analyses of the excavation process are often carried out at the planning stage. However, the accuracy of these analyses is highly dependent on the constitutive model adopted for the shale. One important feature of the constitutive behaviour is the dissipation of pore pressure within the shale. In this paper, two FLAC-based models are used to investigate the influence of induced pore water pressure and its dissipation on borehole deformation of a thick-walled hollow cylinder of synthetic shale. The two models are: a time-dependent model that incorporates coupled flow-mechanical interaction and a steady state time-independent analysis that only accounts for mechanical-induced pore pressure. In both models, a linear elastic-plastic constitutive model (Mohr–Coulomb) is used. Non-linear elastic-plastic and strain-softening constitutive models are also investigated in the coupled flow-mechanical analyses. The numerical predictions obtained using linear coupled Mohr–Coulomb, non-linear elastic-plastic and strain-softening constitutive models are assessed against experimental observations. The FLAC predictions use material parameters obtained from conventional laboratory tests.The investigation shows that there are large differences between predictions obtained from the coupled flow-mechanical analysis and the mechanical-induced pore pressure only simulation. The non-linear coupled Mohr–Coulomb numerical model is shown to be in good agreement with the results of the laboratory tests. The investigation also shows that the simple Mohr–Coulomb constitutive model can adequately predict the deformation in thick-walled hollow cylinders of shale. Further work needs to be done before the simple strain-softening constitutive model developed in this paper can be used confidently for shale. Otherwise, more sophisticated strain-softening constitutive models may have to be used.     

Experimental investigation on longitudinal residual stresses for cold-formed thick-walled square hollow sections

This paper presents the experimental study on cold-formed thick-walled square hollow sections with thickness greater than 6 mm. Square hollow sections are formed using two different forming processes of a “direct square” way and an “indirect way from circular to square”. Two test methods of the hole-drilling method and the X-ray diffraction method are used to measure the magnitudes and distributions of longitudinal residual stresses. The magnitudes and distributions of longitudinal residual stresses along the section perimeter as well as along the section thickness are obtained in this study. It is shown that the longitudinal residual stresses are in tension at outer surface and in compression at inner surface, and present nonlinear distributions, which seems like “sine” curve along the section thickness. Furthermore, the effects of forming process and cross-section geometry on the magnitudes and distributions of longitudinal residual stresses for cold-formed thick-walled square hollow sections are discussed. At last, two distribution patterns have been proposed for the square hollow sections formed using two different forming processes, respectively.     

新疆且末县红沙湖一带三叠系地层划分及特征

在新疆维吾尔自治区且末县西昆仑地区1∶5万区域地质调查工作中,针对工作区中出露地层开展地质剖面测量和区域地质填图,系统收集其岩性岩相、岩石组合、分布特征、接触关系、基本层序等资料,并开展地层划分及对比研究和沉积环境分析工作。通过研究将工作区内三叠系出露地层划分为群鸭湖组(T_(1-2)q)和云雾岭组(T_3y),岩性组合主要为砂岩与泥页岩组成的巨厚层复理石建造,间夹有少量条带状灰岩和极薄层硅质岩及透镜状砾岩。并依据其岩性岩相组合特征和接触关系将群鸭湖组至下而上划分为T_(1-2)q~1、T_(1-2)q~2、T_(1-2)q~3三段,将云雾岭组组划分为T_3y~1和T_3y~2两岩性段。进一步分析认为群鸭湖组地层为深水环境重力流沉积,云雾岭组地层则为浅海陆棚-半深海相沉积。     

基于非线性反演的井壁稳定随钻预测方法

常规井壁稳定预测方法计算量大、操作繁琐、适用范围有限,严重影响其实钻应用效果。通过考察声波速度、地震记录及井壁稳定参数之间的定量关系,建立起利用地震资料直接反演孔隙压力、地应力、岩石强度的模型。根据反演模型的非线性特征,结合井壁稳定参数的地质统计特性,运用随机地震反演方法预测待钻地层的孔隙压力、地应力、岩石强度,并根据反演结果进一步预测井壁稳定性。在实钻过程中,利用录井资料的实时分析和井壁稳定参数的分层地质统计模型,对钻头前方地层的井壁稳定性进行随钻预测。在川东北元坝气田的应用情况表明,本方法的综合性能相比常规方法有明显提高,具有较强的随钻预测能力。     

基于渗流-应力-损伤耦合模型的泥页岩井壁稳定性研究

石油钻井过程中,泥页岩地层井壁稳定性研究十分复杂。本文在连续损伤力学理论基础上,将塑性损伤演化及渗流相互耦合的概念引入Mohr-Coulomb破坏准则,建立了基于等效塑性应变的损伤演化模型,给出了泥岩的渗透性的演化方程。以中国西部某油田实际钻井过程为例,建立了井壁稳定分析模型。计算过程中考虑了围岩损伤引起的弹性模量、黏聚力和渗透系数的变化,得到了井壁围岩损伤、渗透系数、应力、塑性应变、孔隙压力和位移的分布规律。结果表明,井壁附近岩石的损伤演化对围岩塑性区的塑性应变和应力分布有明显影响。钻井液密度的高低,会造成井壁在水平最小主应力方向上的剪切损伤或在水平最大主应力方向上的拉伸损伤。当损伤达到极限时,会造成井壁围岩的破坏。     

大光包滑坡滑带碎裂岩体原位钻孔剪切试验研究

安县大光包滑坡是汶川地震触发的最大规模滑坡,滑坡南侧暴露长约1.8 km顺层滑带,其岩体高度碎裂化,引起广泛关注。为准确评价滑带碎裂岩体的强度参数,笔者在前人研究的基础上开展了细致的野外调查工作,采用法国Phicometre岩土两用原位钻孔剪切试验仪对大光包滑坡滑带碎裂岩体进行了原位剪切试验。将试验结果与Hoek–Brown岩体强度准则估值和基于工程地质类比法的力学参数建议值进行了对比分析。基于以上研究,提出了大光包滑坡南侧顺层滑带碎裂岩体力学参数建议值:内聚力为245~480 k Pa,内摩擦角为25.0°~26.5°。     

Experimental study on compressive strengths of thick-walled cold-formed sections

This paper describes an experimental study on the compressive strengths of cold-formed thick-walled steel sections. A total of 18 stub columns with plate thickness ranging from 8 to 12 mm were tested to determine the section capacities of the cold-formed thick-walled steel columns. Material properties were obtained from flat and corner tensile coupon tests. Effects of cold forming on material properties were investigated. The stub column test strengths were compared with the design compressive strengths specified by the Australian/New Zealand and Chinese standards for cold-formed steel structures. It has been shown that the design strengths predicted by these two standards using material properties obtained from the flat coupon tests are quite conservative, while the design strengths based on the average design yield stress of the full section are less conservative.     

粉喷桩桩周土施工效应室内模型试验研究

粉喷桩在高速公路软土地基处理工程中得到广泛应用,但是目前对粉喷施工效应问题没有清晰的认识。针对粉喷桩施工效应问题,设计了粉喷桩室内模型试验机并采用大直径PVC管开挖取原状样进行粉喷桩施工试验。通过粉喷桩施工的模型试验,发现对于天然沉积的软土而言施工后桩周土的物理性质没有产生变化,但是桩周土的强度在距桩边一定的范围内强度降低,并且随着喷粉压力增大而增大,离桩边距离减小而增大。     

Mechanical tests on a new non-cementitious grout, silica sol: A laboratory study of the material characteristics

This introductory study on mechanical properties aims to characterize silica sol and to improve knowledge of the suitability of silica sol as grout. Silica sol is a non-cementitious grout that consists of spherical particles of amorphous silica, with a diameter of 5–100 nm. For a testing period of six months, specimens of silica sol were kept at 8 °C with three relative humidities: 75%, 95% and 100%. During the test period measurements of the drying shrinkage, compressive strength, modulus of elasticity (Young’s modulus), shear strength and flexural strength were made. The results show that the strength of silica sol continues to increase for a long time and during the test period of six months the strength kept increasing. The increase of strength depends on the humidity to which silica sol is exposed but the humidity also affects the drying shrinkage. A lower humidity results in a faster increase in strength but also a larger shrinkage.     

爆炸引起饱和砂地表沉降的试验研究

通过观察，分析模型试验的现象和结果，讨论了爆炸加密饱和砂的机理，研究了药量与地表下沉量的规律，指出在爆炸加密砂基的问题中比药量不是主要的物理参数。总结出了地表下沉量及爆炸作用范围的计算公式。研究结果表明，爆炸振动引起砂体的破坏与再排列是砂基密实的主要原因。     

基于围岩本体Mogi-Coulomb强度准则的层理性岩层斜井井壁稳定模型

 层理性地层中进行大斜度井施工的井壁失稳问题较为突出,在传统井壁稳定模型基础上,以弱面对岩石强度的弱化作用实验为依据,引入欧拉变换充分考虑三维地应力方向的任意性,利用Mogi-Coulomb准则强化中主应力对围岩本体强度的影响,结合单弱面强度准则建立分析层理性地层斜井井壁稳定问题的模型,并进一步给出计算斜井坍塌压力与破裂压力的方法与公式。实验与计算结果表明：当加载方向与弱面夹角为30°时岩石强度最低;Mogi-Coulomb准则因考虑了中主应力的影响而对围岩本体强度的估计更为有效;考虑层理弱面影响的井壁坍塌破坏区域明显增大,破坏位置也发生改变;取得最小坍塌压力值的钻井方向在空间中与层理面并非简单的垂直关系;空间中关于地应力主平面对称的井孔破裂压力相同。利用所建模型进行安全泥浆压力窗口的计算可为安全钻井以及斜井轨迹设计提供理论依据。     

Furnace tests on unprotected and protected concrete filled structural hollow sections

The accurate prediction of cross-sectional temperatures within concrete filled steel hollow (CFS) sections is critical for the accurate prediction of fire resistance. Whilst there have been many thermal and structural tests conducted on CFS columns, there are few that report the full cross-sectional thermal profile, and when they are reported, the sensor density is low, hindering the ability to validate models. This paper presents furnace tests and thermal modelling on 14 unprotected and 20 protected CFS sections, and examines the effect of several parameters on cross-sectional thermal profiles, as well as assessing the accuracy of both Eurocode thermal analysis guidance and intumescent fire protection design guidance. This paper shows that; (a) the assumptions within the Eurocode guidance can lead to large over-estimations in cross-sectional temperatures; (b) proposes new thermal modelling assumptions in three key areas; and (c) shows that the current intumescent fire protection design guidance is very conservative.     

A case study in evaluating the status of consolidation of a soft soil deposit by incomplete piezocone dissipation tests using laboratory and field data

By using the piezocone penetration test (PCPT or CPTu), one can develop not only a better understanding of the soil stratification, but also an understanding of soil behavior parameters related to soil compressibility, as well as soil strength. This paper describes a case study that utilizes incomplete piezocone dissipation test to estimate status of consolidation of a soil deposit. Incomplete pore pressure dissipation record of PCPT is extrapolated on an inverse time scale (1/t method) to estimate the “in situ” pore pressure and “residual excess” pore pressure. No case study has been reported in open literature where this methodology has been utilized to estimate the status of consolidation of the soil deposit. In this paper, the 1/t method was verified using dissipation data from rigorous calibration chamber tests and field test data.     

自平衡试验与传统试验的比对研究

本文介绍了原位试验过程,对一根原型桩分别进行了自平衡试验、抗压试验和抗拔试验,抗压试验过程中测量了荷载箱在分级荷载下的荷载,同时用钢筋计测量了桩身应力,分析了自平衡试验与传统静载荷试验中极限承载力的差异,得到了自平衡承载力转换为抗压、抗拔承载力的转换系数。试验结果表明,上桩的抗压承载力最大,自平衡承载力次之,抗拔承载力最小;有桩端支撑时,桩侧承担的荷载增加了29.04%,说明增加桩端阻力可以增加桩侧摩阻力;在自平衡载荷试验和抗压试验均达到极限状态时,自平衡试验的荷载箱受力荷载大于抗压试验时的荷载,说明自平衡试验对应的极限端阻力大于抗压状态下的极限端阻力;上桩在没有端承条件下的抗压承载力与自平衡承载力相等,说明在相同端承条件下,上桩的自平衡摩阻力与抗压摩阻力不存在明显差异。     

降雨条件下压实黄土水分入渗规律模型试验研究

以西北地区黄土高填方工程为研究背景,在自行研发水分迁移特性测试设备的基础上,开展了重塑压实黄土在降雨入渗条件下的水分迁移特性室内模型试验,获得了不同压实度下黄土的"电阻率–饱和度"Archie模型和"饱和度–基质吸力"Fredlund-Xing模型及参数变化规律,建立了基于土电阻率的基质吸力幂指数预测公式;研究了不同压实度黄土在不同雨型条件下的入渗特征及其入渗速率、饱和度、电阻率等随时间和土层深度的变化规律。研究结果表明:(1)雨型不同,压实黄土的入渗特征各异,小雨下入渗线呈"Y"型(最大入渗深度Hmax=0.20~0.35 m),大雨下呈"D"型(Hmax=0.55~0.65 m),暴雨下呈倒"V"字型(Hmax0.8 m),入渗速率与雨量正相关,与土层深度和压实度反相关;(2)土体电阻率变化规律与饱和度变化过程相反,基质吸力预测值和实测电阻率变化方向一致;(3)采用土电阻率方法可以为深入探索黄土高填方的长期变形机制和稳定性预警或灾害防治提供一个新的途径。     

全风化花岗岩地层岩芯钻探孔壁稳定性分析

使用回转钻探取芯工艺的地质勘探中,在遇到全风化花岗岩地层时,易产生塌孔埋钻事故,导致取芯失败。本文对孔壁被水浸泡和未被浸泡两种状态进行了受力分析,探讨了影响孔壁稳定性的一些因素。然后从钻井液、钻具及施工操作三方面提出了使全风化花岗岩孔壁稳定性的措施。通过上述分析,对全风化岩层这些特殊类岩土的钻探工作提供了参考,有利于取芯钻进的顺利进行。