The current research on the energy distribution characteristics of supercritical CO2 phase transition fracturing (CDPTF) is relatively lacking, particularly for effective quantitative calculation methods. This study develops models to calculate CO2 shock wave and gas expansion energy, quantifying their roles in rock damage and energy distribution. Five field tests measured acoustic wave velocity, rock damage, and energy distribution during CO2 rock fracturing. The results indicate that supercritical CO2 creates large rock fragments, with a small crushing zone, forming numerous through-cracks on the surface and causing weak seismic effects. Additionally, the radius of rock failure ranges from 4.3 to 5.6 m, with gas expansion energy accounting for 84.36 % and shock wave energy only 15.64 %. Specifically, the average energy proportion of the shock wave used for rock fragmentation, crack formation, and surface vibration is 2.57 %, 12.13 %, and 1.94 %, respectively. The average energy proportion of gas expansion used for crack propagation is 42.15 %, while the energy used for gas ejection (i.e., wasted energy) accounts for 41.21 %, reflecting a relatively high overall energy efficiency. Furthermore, reducing the initial phase change pressure or increasing the tensile strength of the rock can effectively improve energy utilization efficiency. Minimizing gas leakage or applying the method in high-strength rock areas can further enhance the efficiency of gas expansion energy in rock fracturing. This study provides a theoretical basis for optimizing CDPTF energy utilization in rock fracturing.

With the increasing attention paid to three-dimensional numerical limit analysis, there is an urgent need to develop a new Drucker-Prager (DP) criterion suitable for geomaterials under conventional triaxial stress condition. Yet, an exact DP criterion for geomaterials under conventional triaxial stress condition does not exist. Instead, an approximate equal-area-circle DP-3(1) criterion has been used traditionally, which is relatively safe. This study developed a new DP-3(2) criterion for geomaterials under conventional triaxial stress condition based on the tri-shear energy yield criterion. The theoretical formulation was derived to determine the highest point of the criterion (i.e., the tangent point between the criterion and the Mohr-Coulomb criterion). Then, the conventional triaxial DP-3(2 )criterion was established through the highest point. Thereafter, this new criterion was used to determine the ultimate load of soil under conventional triaxial condition and slope stability analysis. The ultimate load of soil under conventional triaxial condition determined by the DP-3(2) criterion was found to be about 87%-97% of the measured value. Moreover, the maximum ratio of ultimate load computed by the DP-3(2) criterion to the DP-3(1) criterion was 1.19, and it increased with decreasing confining pressure, increasing cohesion c, or increasing internal friction angle phi. The factor of safety (FOS) of soil slopes determined by the DP-3(2) criterion was approximately 1.01-1.04 times that determined by the DP-3(1) criterion. Furthermore, the difference increased at larger slope angles. These results suggest that the DP-3(2) criterion is suitable for numerical limit analysis of geomaterials under conventional triaxial stress condition.

In this paper, a numerical model for solving the coupling problem of fluid flow and solid mechanics in porous media is established based on the Biot’s consolidation theory, and the numerical analysis and calculation are carried out by a new strong-form finite element method（Element Differential Method, EDM）. Compared with the weak-form methods, the control equation of poroelastic problems can be discretized directly the Element Differential Method without any numerical integration calculation. Therefore, the method has a relatively simple discrete format when solving the multi field coupling problem, and it shows high efficiency when calculating the coefficient matrix. The numerical method uses the Lagrange element in the finite element method, which can obtain relatively more accurate and stable results compared with the strong-form meshless method.By introducing the Element Differential Method and the implicit time iteration scheme, the displacement and pore pressure of each time step in the porous media can be calculated directly. In this paper, two classical numerical models are selected, one is the one-dimensional Terzaghi column model, and the other is the two-dimensional saturated soil zone model. For these two problems, the accuracy and stability of the method are verified by comparing with the results of analytical solution and finite element method.

高切坡支挡工程的健康运营对三峡库区移民迁建区人民的安居乐业和社会的和谐稳定至关重要,目前关于服役期混凝土材料高切坡挡墙运营安全的分析缺少基于力学机制的定量分析方法,为此文章基于数值极限分析方法开展了服役期高切坡挡墙整体稳定性和工作性能的定量分析.首先,采用有限元强度折减法进行了混凝土材料强度衰减过程中高切坡挡墙工程整体稳定性的动态评价.然后,基于数值极限应变法建立的混凝土材料破坏标准,通过数值计算结果直观显示服役期内挡墙结构的易损关键部位和损伤特征.服役期高切坡挡墙整体稳定性和工作性能定量分析方法的提出,可以掌握安全管理的主动权,为其安全评价和监测预警,以及养护管理决策等提供了新思路和新方法.

1975年后有限元数值极限方法的出现和计算机的应用和发展,使得工程材料的弹塑性解析计算进入到数值极限计算的新时代.文章所研究的岩质隧道就是采用了这一新方法,即强度折减法与荷载增量法,以及最近提出的极限应变法.为解决岩体隧道围岩力学参数的不确定性,提供较为科学合理的围岩力学参数,必须做好理论、勘察和经验相结合的围岩分级工作.以轨道交通隧道围岩分级为例提升分级的水准,包括强度指标的改进,以定量分级为主的分级方法,合理确定岩体基本质量指标BQ值,增加围岩分级数量,制定区间隧道与车站隧道的围岩分级表,定性与定量分级方法的协调与统一.最后,确定围岩自稳能力量化指标,通过反算提出较为科学合理的围岩物理力学参数.

According to the different stress paths, similar model test and PFC simulation test of tunnel surrounding rock are designed to compare the failure mechanisms at macroscopic and mesoscopic scales. The following conclusions are drawn. 1) Excavation unloading will disturb the surrounding rock to form a certain excavation damaged zone. 2) Under the loading path, the stress of surrounding rock failure is 1.500 MPa; under the unloading path with initial stress of 60％ σZmax and 100％ σZmax, the failure stress is 1.583 and 1.833 MPa respectively in the model test. 3) In terms of the failure mode of rocks under different stress paths, tensile fractures first appear in two sides of the vertical walls;thereafter, the spandrel and arch foot are loosened due to the stress concentration. The fractures gradually coalesce with those occurring in the vertical walls. 4) In the process of excavation unloading, the proportion of shear cracks is 35.3％, and the rock is subject to strong shear effect. The final failure surface is approximately V-shaped. 5) The tangential peak stress on the vertical walls at the free face is the lowest; the vertical walls at the free face show the poorest bearing capacity and are easily subjected to tensile failure.

土的应力方向依赖性包含材料方向性(各向异性)与应力方向性(应力绕主轴旋转)两层含义,是土力学领域的热点和难点问题.试验和理论研究均表明,土的各向异性是应力主轴旋转效应的内在原因,复杂的应力状态是各向异性的外部条件,因此,本构模拟须加以综合考虑.相关本构模型可大致分为3类:(1)基于连续介质力学理论和宏观试验现象所建立的宏观本构模型;(2)基于细观机理分析的细观本构模型;(3)基于细观机理与宏观现象合理关联的宏细观结合的本构模型.通过梳理代表性本构模型的建模思路,分析了土的应力方向依赖性的处理方式,总结了不同建模方法之间的优缺点,以期深化对土应力方向依赖性的理解与认识,为广大岩土工作者提供参考.

土的应力方向依赖性是指土的力学特性随应力方向改变而改变的性质,包含两层含义:一是材料的方向性,即土的各向异性,是应力方向依赖性产生的内在原因;二是应力的方向性,即通常所说的"应力主轴旋转效应",是应力方向依赖性的外部客观条件.以材料各向异性主轴和应力主轴的位置关系分类,相关试验研究可划分成"应力不转、试样旋转"和"旋转应力、试样不转"两类.诸多证据表明,材料的方向性与应力的方向性之间存在某种密切的关联.随着各向异性主轴和应力主轴发生相对旋转,试样所表现出的力学性质存在显著的差异.旋转角度相同时的剪切试验研究表明(包括直剪试验、三轴试验、定轴剪切试验等),旋转角度、潜在滑移面位置和试样的强度与变形之间存在某种特定的关系.通过对比梳理两类试验的试验原理与重要结论,明晰了 土应力方向依赖性的试验研究框架,为相关研究提供一些新的思路,以期抛砖引玉,引起广大岩土工作者对该问题的思考.

Due to the restriction of the traditional constitutive theory and the lack of in-depth studies on the common change laws of the basic mechanical characteristics of soils, most of the constitutive models established at present cannot reflect the actual deformation mechanism of soils well. A big data processing platform of Hadoop and Spark is built. By using the functional network and the AIC criteria, a distributed adaptive auto-regressive algorithm is proposed for deep mining of big data of tests on dilative soils. Based on the big data characteristic relationship of each plastic coefficient, combined with its significant and secondary influence factors, the constitutive model for dilative soils is established based on the theory of generalized plastic mechanics. Through the model verification experiments, the results show that the proposed model is better than the modified Cambridge model and the similar Cambridge model considering the dilatancy, and has strong adaptability to the expression of the mechanical properties of the dilative soils under different stress paths. The big data technology and generalized plastic mechanics are applied to the studies on the constitutive relationship of soils, which effectively breaks through the shackles of the traditional constitutive theory, and is of more extensive theoretical significance. At the same time, it also provides a new idea for the studies on the constitutive relationship of soils.

A similarity model with a volumetric similarity ratio of 1:100 and a granular flow model for the tunnel were designed. By comparing macroscopic and mesoscopic information (such as fracture process, strain evolution, stress transfer, crack propagation, and stress distribution) of the tunnel models under load, the failure mechanism of the metro tunnel under load was investigated. The result showed that: 1) under the loading path, the instability area of the tunnel is mainly distributed in the straight wall on both sides. When the load is 1.5 MPa, a large number of cracks on both sides of the straight wall run through, resulting in the initial failure of the rock mass; 2) the surface rock mass of arch bottom is under tensile stress and the deep rock mass is under pressure stress, therefore, the fracture does not develop continuously. The surface of straight wall produces continuous development crack under the action of tensile stress; 3) the arch bottom first responds during the stress redistribution of the small-span tunnel; the top and middle parts of the side walls of the running tunnel with greatest potential for damage respond most; 4) in the process of stress redistribution, the peak stress of the deep measuring points of the straight wall is greater than that of the free surface; 5) at the initial stage of loading, tensile cracks account for a high proportion of all cracks found. When the load is 1.5 MPa, the proportion of shear cracks increases to 28%, and when the load is 1.6 Mpa, the proportion of shear cracks increases to 31%. Finally, the tensile-shear effect triggers the failure of the tunnel.

The failure mode analysis of surrounding rock is the basis of stability analysis, control, and support design of surrounding rock in underground engineering. The excavation of surrounding rock is a complex loading and unloading process with radial stress decreasing and axial stress increasing, but the failure mode of surrounding rock of tunnels is often studied by overloading tests. As an important factor affecting its failure mode, the stress path of surrounding rock in overload test is different from that of confining pressure unloading with axial compression. To compare the failure modes of tunnel surrounding rock under different stress states, the strain evolution law and failure surface development process of tunnel surrounding rock during overload and excavation unloading process were studied by utilizing the WE–600B hydraulic universal testing machine and self-designed tunnel model tester. In terms of strain evolution law, both conditions produced a certain tensile strain at the bottom of the arch, while the strain growth rate of the side wall and arch waist in the excavation and unloading mode was higher than that in the overload mode, and the deformation speed of surrounding rock towards the blank surface was faster and the failure was more severe in the excavation and unloading mode. In the development of the failure surface, the surrounding rock on both sides of the straight wall was peeled off under tunnel overloading, and the peeled body remains intact, however it was extruding and crushing to free space and the integrity was very poor during excavation unloading, indicating that the crushing degree of surrounding rocks under the excavation and unloading path was greater. During overloading condition, the failure process from the tensile cracks of arch bottom under low stress state transits into the tensile-shear coupling “V” shape peeling failure of the side walls under high stress state. The failure model was wedge failure and vertical tension fracture coupling “V” shape splitting failure when the tunnel was under two kinds (60%${\sigma _{{{{\textit{z}}\max}}}}$ and 100%${\sigma _{{{{\textit{z}}\max}}}}$) unloading conditions.

Geo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC 2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V − shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge.

Due to sedimentation, irregular particles of sand arrange anisotropically in nature. Anisotropy diversifies the internal friction angles between relative research planes at different directions in soil material. Thus, to analyze the mechanical mechanism of strength anisotropy, except for conventional inherent anisotropy of the material, stress distribution caused by external loads should also be considered in addition. The level and direction of the inherent strength anisotropy of geomaterials can be measured by a modified anisotropic variable, which is derived from the stress tensor and the fabric tensor. It is assumed that the overall shear strength of the material depends on the shear strength of the most mobilized plane, which is the spatially mobilized plane (SMP) and has a closely relationship with the stress state according to the SMP criterion. Therefore, the orientation of the most mobilized plane builds a bridge that connects the anisotropy of geomaterials and the magnitude and direction of stress. On this basis, a general description of anisotropic strength, considering both the magnitude and directions of the principal stresses, is given, of which the parameters can be easily obtained by triaxial tests. Besides, the variation of the sliding plane along with the direction of the major principal stress is approached. Furthermore, three types of tests, including the direct shear test, the true triaxial test and torsion shear test, were performed to prove the reliability of the new criterion. It shows that both the anisotropic shear strength and the orientation of the sliding plane can be predicted accurately by the newly built anisotropic strength criterion.

研究生教育是国家人才竞争和科技竞争的集中体现.研究生教材是研究生培养质量的重要保障.充分考虑研究生的培养规律,以建构主义学习理论为依据,从科学范式与内容模块化设计、研究方法与内容深度融合、创新过程"非理性突跃"和"预见性"创新特质培养等角度,重塑岩土塑性力学教材新体系,充分激发研究生自主学习潜力,建构研究生的创新基因,形成基于研究生培养规律的教材建设理论.通过40余年的努力,新教材取得了良好的教学效果,在国内外均有较大影响,对提升研究生教育质量具有一定的推动作用.

The dilatancy of soils is an important basis for constitutive models, and the current dilatancy models do not fully reveal their common laws, which is also an important reason why the existing constitutive models cannot well reflect the deformation mechanism of soils. Based on the Hadoop and Spark computing platform, a distributed Levenberg Marquardt regression (DLMR) algorithm for deep mining of big data with strong global optimization, fast convergence and computational stability is proposed. Based on a large number of experimental data of dilatancy characteristics of dilatant soils, according to the DLMR algorithm and the basic mechanical properties of soils, the big data characteristics of dilatancy of dilatant soils are obtained. It is found that there are obvious nonlinear characteristics between dilatancy ratio and stress, strain and stress increment, and the correlation functions between them are established respectively. On this basis, a dilatancy model which can reflect the common law of dilatancy characteristics of dilatant soils is constructed. Through model comparison, it is shown that the proposed model is superior to the dilatancy model of modified Cambridge model and Rowe model. By simulating the triaxial compression experimental data of dilatant soils under different stress paths, it is shown that the new model can well reflect the dilatancy under different stress paths.

数值极限分析方法既有很广的适用性,又有很好的实用性.该文通过有限元荷载增量法和极限应变法计算条形地基的极限承载力,并和传统经验公式的计算结果进行对比分析,验证了数值极限分析方法的可靠性.基于有限元荷载增量法求解地基承载力系数的数值解,可以解决采用经验公式计算可信度不高的问题,并能综合考虑基础宽度和地基土内摩擦角的影响.修正后的地基极限承载力经验公式具有更明确的物理意义,基于数值极限分析方法构建的地基承载力系数取值表格更具实用性和可操作性.

采用有限元强度折减法对埋入式抗滑桩加固的滑坡模型进行了数值分析.模拟结果表明,在设计工况下埋入式桩承担的滑坡推力与全长桩承担的滑坡推力相当,推力大小与设计安全系数有关.在极限破坏工况下,桩悬臂段越长,滑体越顶滑动破坏时对应的稳定安全系数也越大,桩承担的滑坡推力越大.由此提出埋入式抗滑桩加固滑坡设计时,埋入式桩的合理桩长可采用强度折减数值方法根据设计安全系数确定,埋入式桩应承担的滑坡推力可用传统极限平衡法按全长桩计算,也可用有限元强度折减法进行校核.

The effect of unloading stress levels on the unloading failure mechanism is explored from both macro- and microscopic perspectives by carrying out tests to load axial compression and unload confining pressures on marble samples under different unloading stress levels and with the simulation of particle flow. The results reveal four points. First, the lower the prepeak unloading level, the lower the peak bearing capacity of rock samples after unloading; while the closer the unloading level to the peak bearing capacity, the later the occurrence of inflection point for the negative increase of volumetric strain. Second, bond energy and strain energy mainly fluctuate due to changes in unloading levels. The lower the prepeak stress level, the lower the inflection point where bond energy first increases and then decreases and the more obvious the fluctuations in strain energy from the unloading point onwards. Third, the acoustic emission (AE) event count rate increases after unloading from different stress levels. The lower the prepeak unloading stress level of specimens, the smaller the axial strain corresponding to the maximum AE event count rate. Fourth, the evolution of cracks with such a slow-rapid-slow increase does not vary with the changes in unloading stress levels. Moreover, the damage to failure caused by tensile cracks in specimens is more serious than that caused by compression-shear forces during unloading failure. There are a finite number of secondary failure surfaces inside the model at high unloading levels and the cracks caused by tensile failure are distributed over a large area. Relevant experimental results can provide theoretical basis for surrounding rock deformation control of rock underground engineering.

传统的深埋与浅埋隧道划分方法以普氏压力拱理论为基础,由于普氏理论的局限性,这种划分方法不尽合理.鉴于此,文章将有限元极限分析法应用于隧道深浅埋划分中,提出了隧道深浅埋划分的三条原则.对于Ⅳ级、Ⅴ级围岩的岩质隧道,根据隧道的破坏模式划分深埋与浅埋,破裂面贯通至地表即为浅埋隧道,破裂面没有贯通至地表即为深埋隧道,并利用有限元强度折减法求出浅埋隧道压力拱高度,以此作为深浅埋分界线;对于围岩等级高的岩质隧道,以无衬砌隧道稳定安全系数来划分深浅埋,安全系数大于等于1.5时为深埋隧道,安全系数小于1.5时还要根据破坏模式进行深浅埋判断.此外,深浅埋隧道划分还应考虑环境、施工、地质构造、不稳定块体等因素的影响,由此可能造成围岩整体塌落,形成松散压力.最后,文章建议对于深埋隧道可按弹塑性数值分析计算,而对浅埋隧道除按弹塑性数值分析外,还需按浅埋松散荷载依据荷载-结构模式分析,以确保安全.

The elastic model of geomaterial is the mechanical model based on the elastic theory. There are two purposes to study the elastic model of geomaterial: one is to describe the elastic part of elastoplastic deformation, and the other is to calculate the integral calculation of geomaterial deformation.