The stress-strain-permeability behaviour of clay rock during damage and recompaction

Characterisation and understanding of the stressestrainepermeability behaviour of a clay host rock during damage and recompaction are essential for prediction of excavation damaged zone and for assessment of its impact on the repository safety. This important issue has been experimentally studied in triaxial compression tests on the Callovo-Oxfordian clay rock in this study. The samples were sequentially loaded by(1) hydrostatic precompaction to close up sampling-induced microcracks,(2)applying deviatoric stresses to determine damage and permeability changes, and(3) recompression along different loading paths to examine reversibility of the damage. The critical stress conditions at the onset of dilatancy, permeability percolation, failure strength, and residual strength are determined. An empirical model is established for fracturing-induced permeability by considering the effects of connectivity and conductivity of microcracks. The cubic law is validated for the variation of permeability of connected fractures with closure. The experiments and results are also presented and discussed.

Cyclic constitutive equations of rock with coupled damage induced by compaction and cracking

In this paper,the cyclic constitutive equations were proposed to describe the constitutive behavior of cyclic loading and unloading.Firstly,a coupled damage variable was derived,which contains two parts,i.e.,the compaction-induced damage and the cracking-induced damage.The compaction-induced damage variable was derived from a nonlinear stress–strain relation of the initial compaction stage,and the cracking-induced damage variable was established based on the statistical damage theory.Secondly,based on the total damage variable,a damage constitutive equation was proposed to describe the constitutive relation of rock under the monotonic uniaxial compression conditions,whereafter,the application of this model is extended to cyclic loading and unloading conditions.To validate the proposed monotonic and cyclic constitutive equations,a series of mechanical tests for marble specimens were carried out,which contained the monotonic uniaxial compression(MUC)experiment,cyclic uniaxial compression experiments under the variable amplitude(CUC-VA)and constant amplitude(CUC-CA)conditions.The results show that the proposed total damage variable comprehensively reflects the damage evolution characteristic,i.e.,the damage variable firstly decreases,then increases no matter under the conditions of MUC,CUC-VA or CUC-CA.Then a reasonable consistency is observed between the experimental and theoretical curves.The proposed cyclic constitutive equations can simulate the whole cyclic loading and unloading behaviors,such as the initial compaction,the strain hardening and the strain softening.Furthermore,the shapes of the theoretical curves are controlled by the modified coefficient,compaction sensitivity coefficient and two Weibull distributed parameters.

Vibration compaction characteristics of rock filling embankment

The dynamic model experiment of the rock filling embankment was carried out to investigate the vibration compaction mechanism. The rock filling materials were compacted by the plate-vibrated compactor, and the characteristics of the rock filling materials, such as settlement, pressure change and response waveform, were measured by the dynamic earth pressure gauge and aceelerometer. Moreover, a new method for detecting the compactness of the rock filling embankment was proposed based on the maximum dry density and modulus of deformation. The results show that the process of vibration compaction includes compact, elastic deformation and loose stages, and the vibratory pressure transfers to the surroundings from the vibration center in non-linear rule. Furthermore, the test results obtained by the present method are basically in agreement with those obtained by the traditional method, and the maximum relative error between them is about 0.5%.

Compacting Deformation Engineering Characteristics of Weathered Soft Rock Mixture in Subgrade

The engineering characteristics of weathered soft rock are important contents of soft rock mechanics. They also play a significant role in compacting deformation, which has been known to exert a significant amount of influence on the stability of highway filling subgrade engineering. In an effort to investigate this aspect of the problem, compacting tests and unconfined compressive strength tests have been carried out on weathered argillaceous slate and pelitic siltstone rocks, which are broken and graded before the test. The testing results indicate that the relationships of both between stress and strain and between axial strain and tangent modulus are exponential relationships; the size of the grain plays some influence on the deformation modulus, whereas the water content impacts the compressive strength greatly, which shows quadratic function; the unconfined compressive strength is linear with the dry density of loose soft rock mixtures. Therefore, the water content must be controlled in both the design and the construction of subgrade engineering of soft rock filling, and at the same time some effective measures should be taken to reach the requirement of compaction.

Compaction and seepage characteristics of broken coal and rock masses in coal mining:A review in laboratory tests

Broken coal and rock(BCR)are an important component medium of the caving zone in the goaf(or gob),as well as the main filling material of fault fracture zone and collapse column.The compaction seepage characteristics of BCR directly affect the safe and efficient mining of coal mines.Thus,numerous laboratory studies have focused on the compaction seepage characteristics of BCR.This paper first outlines the engineering problems involved in the BCR during coal mining including the air leakage,the spontaneous combustion,the gas drainage,and the un-derground reservoirs in the goaf.Water inrush related to tectonics such as faults and collapse columns and surface subsidence related to coal gangue filling and mining also involve the compaction seepage characteristics of BCR.Based on the field problems of BCR,many attempts have been made to mimic field environments in laboratory tests.The experimental equipment(cavity size and shape,acoustic emission,CT,etc.)and experimental design for the BCR were firstly reviewed.The main objects of laboratory analysis can be divided into compression tests and seepage test.During the compaction test,the main research focuses on the bearing deformation characteristics(stress-strain curve),pore evolution characteristics,and re-crushing characteristics of BCR.The seepage test mainly uses gas or water as the main medium to study the evolution characteristics of permeability under different compaction stress conditions.In the laboratory tests,factors such as the type of coal and rock mass,particle size,particle shape,water pressure,temperature,and stress path are usually considered.The lateral compression test of BCR can be divided into three stages,including the self-adjustment stage,the broken stage,and the elastic stage or stable stage.At each stage,stress,deformation,porosity,energy,particle size and breakage rate all have their own characteristics.Seepage test regarding the water permeability experiment of BCR is actually belong to variable mass seepage.While the experimental test still focuses on the influence of stress on the pore structure of BCR in terms of gas permeability.Finally,future laboratory tests focus on the BCR related coal mining including scaling up,long term loading and water immersion,mining stress path matching were discussed.

Large-scale Rock Landslide Slip Surface Location Analysis and Strength Parameters Evaluation

Large-scale rock landslides have huge impacts on various large-scale rock engineering and project operations. They are also important aspects evaluating geological disasters. In the initial evaluations on the stability of large-scale rock landslides, in most cases, it is difficult to conduct evaluation or to have accurate evaluations because most of large-scale rock landslides are huge in size, high in slopes, and located in the canyon of mountains, which makes the exploration very difficult and thus hard to get credible data on slip surface form, location, depth and strength. This paper describes the Badi landslide happened along the Lancang River, and systematically introduces methods to analyze and verify large-scale slip surface form using terrain conditions surrounding the large-scale landslide, shape of the slide walls, and development patterns of streams and gully. This paper also introduces ways to obtain strength parameters of slip surface with the soil in the slide zone by using the principles of stress state, principles of gravity compaction, structure regeneration and strength regeneration. It is confirmed that analyzed results to the slip surface are basically consistent with the exploration results. The methods introduced here have been successfully applied to evaluate the stability of Badi large-scale rock landslide and have been applied in engineering practices.

Study on Improvement of Dumping Site Stability in Weak Geological Condition by Using Compacted Layer

Berau Basin, a sub-basin of Tarakan Basin, had been developed during Eocene to Miocene period. Rocks in Berau Basin consist of sedimentary, volcanic and igneous rocks aged from Pre-tertiary until Quaternary epoch. The youngest identified rock formation was alluvial deposit consists of mud, silt, sand, gravel and swamp with brown to dark color. This youngest rock formation is relatively weak geological condition and can cause problems in the coal mining operation. PT Berau Coal as one of the coal mining companies in Berau Basin area had experienced some problems related to the occurrence of alluvial deposit. A large failure has occurred at one of its out pit dumping?area which lies over the swamp material. The failure caused a higher operating cost since it made that the distance for waste rock dumping became to be farther than the designated area. Therefore, in order to prevent similar failure occurring at dumping area which lies above swamp material, an improvement of dumping site stability on weak geological condition has to be needed. The proposed method for improving the stability of out pit dumping area in weak geological condition is to construct the compacted layer of waste rock before the out pit dumping area construction. Based on experimental results, a minimum of 40 kPa pressure is needed to give a proper compaction to the waste rock. The result of numerical analysis by Finite Element Method (FEM) shows that construction of compacted layer on the base of out pit dumping area can improve its stability.

凸棱非平面聚晶金刚石齿的破岩机理及在含砾地层中的应用

为提高聚晶金刚石复合片(PDC)钻头在含砾、软硬交错等不均质地层中的抗冲击性能,开展了凸棱非平面PDC齿的研究。通过仿真和室内实验对比分析了凸棱非平面齿与常规平面齿的破岩机理。与平面齿相比,凸棱非平面齿与岩石的接触应力分布更均匀,切削破岩过程中的载荷波动幅度明显更小,切削稳定性更高。凸棱齿特殊的非平面结构改变了切削齿与岩石的互作用方式,在不均质地层得到成功应用。

软岩堆石料的击实特性与尺寸效应研究

软岩堆石料的干密度是土石坝设计和施工的重要控制指标,直接决定了土石坝施工期和运行期的沉降量。采用Φ950 mm×H1000 mm的超大型击实仪,针对强风化粉砂质泥岩、弱风化粉砂质泥岩、弱风化5∶5强风化粉砂质泥岩混合料,进行了483、992、1475、1957、2681 kJ/m^(3)共5种单位体积击实功下的击实试验,最大干密度成果与Φ300 mm×H285 mm的大型击实仪成果进行了对比。试验成果表明,击实干密度随单位体积击实功增加而增加,在击实功低于2000 kJ/m^(3)时,干密度随击实功增加较快,击实功超过2000 kJ/m^(3)后增加速率变缓,增量较小,再增加击实功并不能有效提高干密度。相同单位击实功下,超大型击实试验的最大干密度比大型击实试验成果略低0.01~0.02 g/cm^(3)。软岩堆石料在击实特性方面的尺寸效应不明显,在重型标准击实功能条件下,室内采用Φ300 mm的击实仪进行软岩堆石料的击实特性研究,是比较适宜的。

粗集料形态特征及含量对沥青混合料压密行为的影响

为探究粗集料形态特征及颗粒含量对沥青混合料压密行为的影响规律,利用智能颗粒对车辙试验进行测试,获取颗粒力学和运动响应数据,通过三维激光扫描设备及图像处理技术构建了不同形态特征的粗集料轮廓,利用离散元方法建立沥青混合料的车辙数字试件。对数字试件开展虚拟车辙试验,借助智能颗粒测试结果对模型预测精度进行校验,利用高精度模型研究粗集料形状及含量对混合料压密行为的影响规律,以数字试件内部应力与颗粒位移来评价混合料的抗变形性能,以单一集料平均接触点数量与力链大小为量化指标进行骨架接触特性分析。结果表明:智能颗粒测试结果能够有效验证预测模型的精度,加速度幅值实测与预测最大差异为0.0215 g;在车辙虚拟试验中,由立方体状集料成型的试件,其内部应力高于含其他形状集料的混合料,且具有较小的迁移自由度,在集料含量为40%时颗粒竖向及水平位移仅为3.65 mm、1.89 mm;集料含量会影响沥青混合料压密行为,沥青混合料抗车辙变形性能及骨架接触特性随立方体状集料含量的增加而提高,而当针状、片状或针片状集料颗粒含量大于20%时,性能出现明显衰变。

考虑温度作用的岩石统计损伤本构模型及验证

为了预测和评估深部高温岩体的稳定性,运用理论推导的方法研究温度作用下(后)岩石的本构关系。首先,基于已有的岩石统计损伤本构模型,考虑温度对岩石损伤变量的影响,引入了损伤变量修正系数、损伤起裂应力和起裂应变等参数;其次,假设微元体强度服从幂函数分布,并符合Hoek-Brown(H-B)强度准则,针对统计损伤本构模型无法反映峰前较强的微裂纹压密效应的弊端,引入了相应的模型修正系数;再次,建立了考虑温度作用的岩石统计损伤本构模型,并确定了模型参数的表达式;最后,对比不同温度作用下(后)的花岗岩在单轴和常规三轴压缩试验条件下所得的结果与文献中模型的计算结果,验证本文模型的准确性。研究结果表明:所提出的模型的计算结果与文献的试验结果在数值、分布规律和趋势上具有良好的一致性;对于全过程σ-ε曲线的各阶段,本文模型的计算效果较文献中本构模型计算效果更好,与试验曲线的贴合度更高,能够更好地反映高温作用下(后)岩石的损伤本构特征。该模型的参数具有常规性,适用于各类温-压组合作用工况下的岩石。

堆石混凝土劈裂抗拉破坏过程中声发射特征分析

【目的】通过研究堆石混凝土(RFC)和自密实混凝土(SCC)在劈裂抗拉破坏过程中产生的声发射信号,并进一步确定最终的裂缝形态,有助于深入了解RFC和SCC的劈裂破坏特征,从而确保结构的可靠性和安全性。【方法】制作了边长为600 mm的RFC和SCC立方体试件,研究了RFC和SCC在劈裂抗拉破坏过程中声发射参数(振铃计数和累计振铃计数)与位移荷载曲线的关系;利用声发射信号的统计方法(RA和AF)分析确定了RFC和SCC裂纹演化特征;基于RA-AF值的混合高斯模型(GMM)辨识了劈裂抗拉破坏过程中RFC和SCC的开裂模式(拉伸型开裂或剪切型开裂)。【结果】结果显示:在劈裂破坏过程中,RFC声发射振铃计数分布不均,呈现分段式变化特点,累计振铃计数呈现明显阶梯状上升,SCC声发射振铃计数分布均匀,累计振铃计数平缓上升;RFC和SCC的拉伸型裂纹区域对应RA-AF数据点向AF轴靠拢,剪切型裂纹区域对应RA-AF数据点向RA轴靠拢,均表现出明显的原点集中现象。【结论】结果表明:(1)RFC和SCC劈裂抗拉破坏强度分别为其立方体抗压强度的0.065、0.067;(2)在劈裂抗拉破坏过程中,RFC的破坏模式以拉伸型开裂为主,占89.4%,SCC以剪切型开裂主,占53.6%;(3)利用GMM方法,通过概率密度估计能对裂纹的分类特点进行更精确的捕捉。

堆石混凝土坝概述及下一代混凝土坝施工技术展望

Over the past few decades,one of the most significant advances in dam construction has been the inven-tion of the rock-filled concrete(RFC)dam,which is constructed by pouring high-performance self-compacting concrete(HSCC)to fill the voids in preplaced large rocks.The innovative use of large rocks in dam construction provides engineers with a material that requires less cement consumption and hydration heat while enhancing construction efficiency and environmental friendliness.However,two fundamental scientific issues related to RFC need to be addressed:namely,the pouring compactness and the effect of large rocks on the mechanical and physical properties of RFC.This article provides a timely review of fundamental research and innovations in the design,construction,and quality control of RFCdams.Prospects for next-generation concrete dams are discussed from the perspectives of envi-ronmental friendliness,intrinsic safety,and labor savings.

基于DIC技术的自密实混凝土界面裂缝扩展规律研究

采用自密实混凝土作为堆石混凝土坝的抗冲磨层并与坝体进行一体化浇筑成型是一种新构造,其中抗冲磨层与坝体的界面性能至关重要。通过制作600 mm×600 mm×600 mm自密实混凝土(SCC)试件(C40SCC、C25SCC)及C40、C25SCC分层浇注试件(C40-C25SCC),结合数字图像技术(DIC)开展劈裂抗拉试验,分析了自密实混凝土界面裂缝扩展规律。结果表明:SCC断面破坏形态表现为骨料劈裂和剥落2种破坏形式;C40SCC、C25SCC及C40-C25SCC劈裂抗拉强度分别为1.861、1.416和1.362 MPa;基于DIC技术获取了裂缝相关参数,其中C40-C25SCC裂缝最大开口宽度、扩展时间均为最大,分别为0.125 mm、10.667 ms,C25SCC裂缝最大扩展速度最快,为10.12 m/s。研究表明:骨料的存在及粒径大小改变了试件破坏形态,影响了裂缝开口宽度及扩展速度变化。

裂隙发育过程对采动裂隙椭抛带压实区的影响研究

采空区瓦斯抽采的关键是了解工作面上覆岩层裂隙的演化过程。为了研究综采工作面覆岩采动压实区演化规律,高效进行煤矿采空区瓦斯抽采工作,以神东某矿区2207工作面为原型,通过物理相似模拟实验,利用自主研发的覆岩裂隙监测系统将图像进行直方图均衡化增强和中值滤波去噪处理,获得二值化裂隙图像后利用分形理论定量描述裂隙率,对典型周期来压覆岩垮落裂隙率进行统计分析,建立了裂隙发育程度受工作面推进时间的时空函数和采动裂隙椭抛带压实区演变修正模型。结果表明:覆岩平均裂隙率变化符合DoseResp函数关系,裂隙的发育过程包括产生、扩展蔓延、压实闭合3个阶段,裂隙在产生、闭合这2个阶段发育速率较平缓,而在扩展阶段发育速率陡增。采空区上覆岩层裂隙场形成旧裂隙区、压实区和新裂隙区3个区域,裂隙发育周期的不同导致旧裂隙区与新裂隙区在发育状态、压实程度和空间形态上有着明显差异,这些差异导致了采空区覆岩非对称性下沉现象的发生。通过分析覆岩应力恢复与覆岩内部裂隙演变关系,进一步验证了采用DoseResp时间函数曲线可以很好的表现采空区上覆岩层裂隙异速演变特征。最后建立了考虑覆岩裂隙异速演变效应的采动裂隙椭抛带压实区修正模型,并结合现场工程实践,有效提高瓦斯抽取高位钻孔布置的准确性,为工作面的安全开采提供理论指导。

道路桥梁工程路基路面振荡压实施工技术研究

为解决道路桥梁工程路基路面压实度过低的问题,以某省级干线公路工程为例,进行路基路面振荡压实施工技术研究。首先,采用振荡压路机,对路基路面进行振动压实。其次,结合工程实际情况,确定压实速度与碾压作业段长度。最后,针对纵向接缝构造和横向接缝构造进行碾压,实现对路基路面的压实,促进压实度提升,提高道路桥梁工程施工质量。

海南滨海粉细砂路基压实工艺与质量控制

海南滨海粉细砂路基的压实及质量检测是施工中的技术难题。结合海南环岛旅游公路项目,提出滨海粉细砂路基的压实质量检测方法,铺筑试验路段,研究滨海粉细砂路基的压实工艺及压实质量。结果表明:滨海粉细砂地基压实适宜采用在碎石土垫层上进行冲压和振压相结合的方式;粉细砂路堤可随挖随填、快速填筑,采用双钢轮压路机压实,压实厚度不宜超过20 cm,振动碾压遍数不宜小于4;压实质量可采用预埋土样盒的检测方法,压实度控制标准为不宜小于88%。试验路段的工程效果良好。

填石路基快速施工工艺与压实质量控制

为分析采用快速施工工艺碾压的填石路基的压实质量,采用有限元软件ABAQUS建立长方体三维土基模型,模拟分析由36、22 t压路机在500、700 kN 2种激振力下压实填石路基的力学响应;在现场试验路段,采用36 t压路机碾压松铺厚度为75、85 cm的填石路基,26 t压路机碾压松铺厚度为40 cm的填石路基,采用土压力传感器测试土压力,选用孔隙率和沉降差控制路基的压实质量。结果表明:2种激振力下36 t压路机碾压路基后的应力分别为22 t压路机的1.9倍、1.5倍;土压力主要由压路机振动产生,土压力随距路表深度的增大而减小,土压力降幅随距地表深度的增大而减小,现场试验结果与数值模拟结果一致;压路机碾压6遍后,2种松铺厚度路基的孔隙率均小于22%,建议沉降差的控制指标为3.0 mm;采用36 t压路机碾压松铺厚度为85 cm路基的最优工作效率较26 t压路机提高60%,工程成本降低36%。

基于故障树与贝叶斯网络的路基压实质量智能评价

现场动态回弹模量作为间接表征路基工程压实质量的检测指标之一,与传统压实质量检测指标具备很好的相关性,但影响动态回弹模量测试数据的因素较多且主次有别。该文基于故障树与贝叶斯网络构建现场动态回弹模量异常数据分析模型,以实际工程测量数据为基础,计算故障树中影响动态回弹模量因素的先验概率,找出不同动态回弹模量影响因素的关联性,采用模糊预测的方法给出动态回弹模量数据异常时的现场处理措施。依托阜淮高速公路路基工程项目实测数据,采用基于故障树与贝叶斯网络的路基压实质量智能评价方法得出,动态回弹模量数据异常时,环境温度原因概率最高为0.806,碾压速度原因概率最低为0.148。

不同加载方式下沥青混合料的压实过程与集料运动特性研究

为探究不同加载方式下沥青混合料的压实过程与集料运动特性,利用智能骨料进行静态压实和旋转压实试验测试;同时采用三维激光扫描设备以及图像处理技术构建具有真实形态特征的粗集料,建立沥青混合料压实过程的离散元模型,并借助智能骨料测试结果对模型进行准确性验证;最后,分析了沥青混合料内部集料运动和接触状况。结果表明,均匀增长的竖向压实载荷无法有效地使颗粒沿水平方向运动,在持续性的竖向载荷以及周期性的揉搓作用下,颗粒水平方向上的迁移和旋转能力得到激发,最终实现材料的致密化;在均匀增长的竖向压实载荷下,试件骨料-骨料间接触力较大,周期性的揉搓作用减轻了试件高压实阻力的形成,使其在后期获得更好的压实效果;靠近载荷作用区域的颗粒所受的运动更加激烈,主动压实区的颗粒运动活跃度大于被动压实区,而边缘区域的颗粒运动变异系数较高。