陶粒粉煤灰混凝土在桥涵台背回填中的应用研究

通过材料性能试验、土工离心模型试验和数值计算,研究陶粒粉煤灰混凝土的物理力学性能及其在桥涵台背回填的应用效果。首先,通过材料性能试验研究不同配合比的陶粒粉煤灰混凝土的物理力学性能;其次,通过土工离心模型试验和数值计算研究陶粒粉煤灰混凝土用作桥涵台背回填材料时,作用于台背的土压力和回填体的变形特性。研究发现：陶粒粉煤灰混凝土具有轻质、高强度、高模量和易施工等诸多优点;陶粒粉煤灰混凝土回填体作用于台背的土压力明显小于常规回填材料;回填区和地基的沉降变形亦明显小于其他材料。结果表明：陶粒粉煤灰混凝土作为台背回填材料具有明显的优越性,是一种值得推荐的桥涵台背回填材料。     

基于小生境遗传算法软土地基上加筋路堤稳定性分析

在软土地基加筋路堤稳定性分析方法中,传统分析方法(如瑞典法和荷兰法)因对加筋材料的加筋作用估计不足,导致计算结果过于保守,与实际不符。本文在充分考虑加筋体的加筋作用下,提出了新的加筋路堤稳定性分析计算方法,并采用小生境遗传算法搜索临界滑动面和最小安全系数。算例计算结果表明,本文提出的加筋路堤稳定性分析方法与工程实际情况吻合较好,并且小生境遗传算法能有效地搜索到边坡所有的临界滑动面。     

土工格栅路堤加筋效果的影响因素分析

土工格栅作为一种新型的土工合成材料,由于具有高强度、低延伸率等特点而被选作主要的路堤加筋材料,在路堤中适当位置加入土工格栅能有效地减少路堤的沉降和侧向变形。本文采用通用非线性有限元程序ABAQUS分析了加筋前后的路堤底部的竖向位移、堤址点垂线下地基深度的水平位移和地表的水平位移,计算中采用D rucker-Prager模型和C lay p las-tic ity模型模拟土体的非线性,土工格栅采用一维杆单元来模拟。通过对加筋层数、筋材模量、软基模量、填土高度和软土层厚度等影响加筋效果的因素进行对比分析,从计算结果分析可知,路堤加筋虽然对软土地基的竖向位移影响不大,但加筋能有效抑制侧向位移的发展,这样增大了路堤边坡的稳定性,分析结果与大多数实际工程的实测资料相吻合。     

防波堤土工织物加筋地基离心模型试验及数值模拟

以黄骅港北防波堤工程为依托,对土工织物加筋软粘土地基及斜坡式防波堤体系的固结过程进行了离心模型试验和有限元数值模拟,通过分析地基土体固结过程中防波堤-加筋垫层-基体系的位移场和应力场的发展及织物拉应力分布和发展,验证离心试验及数值模拟方法的合理性,并得出以下几点主要结论:(1)土工织物加筋垫层的作用机理为其抗拉性限制自身横向变形,通过与附近土体的摩擦作用限制其侧向变形;(2)加筋减小防波堤-垫层-地基体系的高应力水平区,避免堤身与地基高应力水平区域的连通,增强系统稳定性;(3)在离心试验采用的分层地基的条件下,加筋减小了浅层软基和堤身的侧向位移量,对系统总位移有抑制作用;(4)试验中织物替代材料的极限拉伸强度发挥程度较低,其与砂垫层间摩擦强度的发挥水平约为23.8％。     

用非线性模型评价加筋柔性台背路堤

在考虑土的固结和土体的非线性应力应变关系的基础上,利用非线性有限元数值方法对土工织物加筋柔性台背路堤的受力性状和破坏机理进行了分析。分析结果表明,将铺有土工合成材料的桥台路堤,看作由土体、土工合成材料、土体-土工合成材料界面组成的、独立的平面应变三层连续体系,进行数值计算是行之有效的。计算结果显示,土工织物加筋可以有效减少桥台路堤50%的均匀沉降和66%的非均匀沉降,并能增加台背路堤的稳定性。现场监测表明,本文采用的数值模拟方法与实际工程具有一致性。     

软土地基上土工织物加筋堤的离心模型试验研究

以黄骅港防波堤工程为依托,对有、无土工织物加筋垫层及不同织物加筋条件下堤坝和软土地基的变形与稳定进行了离心模型试验对比研究。得到了地基土体的竖向与水平位移分布规律以及孔隙水压力的消散特性。研究表明：土工织物加筋垫层的加筋机理源于其对土体的侧限效果,铺设土工织物后能有效地减小地基的沉降,并能够限制浅层土体的侧向变形;为使土工织物的加筋效果能够得以充分发挥,要求织物的强度及模量要与垫层的界面强度相匹配。     

基于ABAQUS仿真分析的高填粗粒土路基边坡稳定性研究

高填方粘性土边坡的稳定性以往研究较多,为了研究变形特性与强度都不同于粘性土的高填方粗粒土边坡,运用ABAQUS软件,采用强度折减法对多级加筋粗粒土边坡工程做了有限元数值模拟,分析了整个边坡的稳定性.研究结果表明,加筋不仅提高了各个台阶的局部稳定性,也加强了边坡的整体稳定;边坡中都存在水平位移,最大值出现在边坡底部坡脚附近,在坡脚处出现小部分沿x轴正向的负位移;水平位移随着填土高度的增加而减小,第一台阶的水平位移最大;越靠近边坡,土工格栅和土体的位移均越大,变大的趋势近似一致,但土体的水平位移明显大于土工格栅的水平位移.     

土工格室加筋垫层路堤破坏模式和稳定性评价

采用土工格室加筋垫层提高软土地基上填方路堤的稳定性已得到认可,但其破坏模式和稳定性分析方法仍未取得共识。作者通过室内物理模拟试验,识别软土地基上无筋垫层路堤、土工格栅加筋垫层路堤和土工格室加筋垫层路堤的失效模式,并在此基础上探讨土工格室加筋垫层路堤的稳定性和临界填筑高度分析方法。研究结果表明:软土地基上无筋垫层路堤和土工格栅加筋垫层路堤发生穿过垫层的圆弧滑动破坏;土工格室加筋垫层路堤呈整体破坏模式,滑动面虽呈似圆弧状但未穿过加筋垫层,破裂面在软土地基中形成和发展,而且位置更深。在识别破坏模式的基础上,通过土工格室加筋垫层的工作机理分析,提出了软土地基上土工格室加筋垫层路堤稳定性和临界填筑高度分析方法。     

土工格栅加筋土地基平板载荷试验研究

在近年来的岩土工程实践中,土工合成材料加筋土技术得到越来越广泛的应用。采用平板载荷板试验方法,进行了多组加筋砂土地基模型试验,监测和分析了不同加筋材料（双向格栅与四向格栅）和加筋层数对土工格栅加筋土地基承载特性的影响。研究结果表明：土工格栅加筋土地基与无筋地基相比,承载性能得到改善,双层加筋明显优于单层加筋;土工格栅加筋限制了浅层地基的侧向变形,相同荷载下地基沉降减小,可恢复变形增大;模型试验中测得加筋材料应变和拉力很小,与土工格栅强度相比,拉伸模量对加筋土地基承载力的贡献更大。     

条形基础加筋砂土地基极限承载力计算

基于传统的极限平衡条分法,利用临界滑动场法计算了条形基础的加筋地基极限承载力。假定土体处于极限平衡状态时,土体与筋材间存在均匀的摩擦力,通过建立土体条块极限平衡方程,推导了地基承载力的递推关系式。首先,设定计算土体范围,并划分条块和离散状态点;其次,根据递推公式计算各个状态点的参数,并搜索临界滑面;最后,根据搜索出的滑面计算地基承载力。通过实例比较进一步验证了计算结果的可靠性,并分析了首层筋带埋深、铺设层数和长度对地基承载力和滑面位置的影响。研究结果表明：地基承载力随着筋带埋深的增加先增大后减小;随着层数和长度的增加先逐渐增大,最后趋于稳定;滑面位置的变化规律主要是垂直影响深度和水平影响范围增大或减小。该方法原理简单、易于编程,为条形基础加筋地基承载力的计算提供了一种新思路,是临界滑动场法在地基承载力计算中的推广应用。     

Slope stability analyses for materials with a non-linear failure envelope

Upper bound techniques are used to analyse the stability of slopes of material failing according to a non-linear failure criterion, such as closely jointed rocks. The global, extremal nature of upper bound calculations is discussed, as is the inverse use of such procedures for obtaining safe lower bound estimates for material strength properties in back analyses. Specific results are presented for the material model proposed by Hoek and Brown.     

Performance evaluation of soil mixtures treated with graphite and used as barrier fill material for high-level radioactive waste repository

Buffer/backfill material is an important engineering barrier in a deep geological repository of high-level radioactive waste (HLW). Its thermo-hydro-mechanical (THM) performance is very important for the safe and stable operation of the HLW repository system. Natural graphite powder mixed with sodium bentonite forms a buffer/backfill material that can dissipate heat quickly and provide strong isolation. In this paper, the THM characteristics of bentonite–sand–graphite–polypropylene fiber (BSGF) mixtures, used as a buffer/backfill material, were studied through a series of laboratory tests. The influence of graphite and polypropylene fiber contents on thermal conductivity, swelling pressure, hydraulic conductivity, and strength properties of BSGF mixtures with different sand contents was analyzed. Experimental results indicated that the graphite content, the maximum graphite mesh number, and the initial dry density of bentonite–graphite mixtures influenced the thermal conductivity of bentonite–graphite mixtures. The addition of polypropylene fiber was found to enhance the shear strength and inhibit cracking without significantly affecting the expansivity, permeability, and thermal conductivity of the BSGF mixtures. This study provides a new buffer/backfill material that can improve the stability, functionality, and thermal efficiency of the HLW repository.

     

Upper bound finite element analysis of slope stability using a nonlinear failure criterion

In this study, upper bound finite element (FE) limit analysis is applied to stability problems of slopes using a nonlinear criterion. After formulating the upper bound analysis as the dual form of a second-order cone programming (SOCP) problem, the stress field and corresponding shear strength parameters can be determined iteratively. Thus, the nonlinear failure criterion is represented by the shear strength parameters associated with stress so that the analysis of slope stability using a nonlinear failure criterion can be transformed into the traditional upper bound method with a linear Mohr–Coulomb failure criterion. Comparison with published solutions illustrates the accuracy and feasibility of the proposed method for a simple homogeneous slope stability problem. The proposed approach is also applied to a seismic stability problem for a rockfill dam to study the influence of different failure criterions on the upper bound solutions. The results show that the seismic stability coefficients obtained using two different nonlinear failure criteria are similar but that the convergence differs significantly.     

考虑强度各向异性的边坡稳定有限元分析

天然沉积的土层总是表现出一定程度的强度各向异性,但现有的边坡稳定有限元分析极少考虑各向异性的影响。对大型有限元软件ABAQUS进行二次开发,使其能够考虑土体黏聚力随大主应力方向的变化,动态更新增量迭代求解过程中边坡不同位置处的抗剪强度,进而提出具备安全系数自动搜索功能的各向异性边坡稳定分析方法。计算结果表明,均匀边坡的有限元解与极限分析上限解相差很小。如果采用土体固结方向的黏聚力并按各向同性评价缓坡的稳定性,可能严重高估安全系数,尤其是在黏聚力较高的情况下。与极限分析不同,建立的强度更新有限元模型能够分析成层边坡的稳定性。     

风积砂质高浓度胶凝充填材料性能与粉煤灰掺量关系分析

充填材料是决定煤炭充填开采效益、效率、效果的最主要因素。为了掌握风积砂质高浓度胶凝充填材料的性能变化规律,本文以粉煤灰的质量掺入比作为变量,试验研究和理论分析了粉煤灰对该充填材料性能的影响规律。结果表明,粉煤灰的适量添加可以提高充填材料的强度,大掺量导致强度相对降低; 泌水率随着粉煤灰掺量的增大总体上呈减小趋势,较大掺量试样泌水速率相对较低; 分层度随着粉煤灰掺量的增大线性降低; 凝结时间随着粉煤灰掺量增大呈现指数增大; 坍落度总体上随粉煤灰掺量的升高而增大,但大掺量会使其出现相对降低。分析认为,适量粉煤灰的掺入,使风积砂质高浓度胶凝充填材料的颗粒粒度、水分分布和水泥分散均匀,而使材料的强度和输送性能适度改变,但掺量过大会稀释胶结料和改变颗粒相对级配而导致性能下降。     

陡倾矿体充填法采矿充填体稳定性研究

理论研究是分析力学问题基本手段,应用理论方法分析充填体整体稳定性的前提条件是存在明确的滑移面。前人许多研究成果基于考虑充填体与围岩接触面即为滑移面,但将接触面作为滑移面分析充填体稳定性缺少数据支持。本文结合前人研究成果,并根据金川二矿区地表变形特征,考虑倾斜（直线和曲线）滑移面,进而解析得到充填体内部竖向应力微分表达式;根据二矿区开采分层充填体的实际情况,考虑为简支梁模型,求得分层充填体局部稳定性的理论解析解;运用数值模拟软件分析二矿区充填体底板最大、最小主应力,判断了充填体发生破坏失稳的可能性。结果表明:充填体不会发生整体失稳垮塌,但充填体局部发生变形破坏的可能性还是存在的,对于双中段开采的上部采空区,充填体发生变形破坏的可能位置位于两侧角点,对于双中段开采的下部采空区,变形破坏位置稍有扩大,但也集中在两侧角点附近,应及时采取合理的支护措施,防止发生充填体局部失稳破坏。     

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

This paper is an attempt to relate the microstructure to long-term mechanical properties of the cemented paste backfill produced from a hard rock mine tailing from North Queensland in Australia bound with flyash-based geopolymer (geopolymer), flyash-blended cement (FBC), and general purpose cement (GPC). A relatively high slump (260 mm) paste backfill mix with 74 wt% solids has been used to prepare cylindrical paste backfill samples with a diameter of 50 mm and a height of 100 mm. The uniaxial compressive strength tests were conducted on all samples after curing for 112 days to obtain their strength, failure strain and Young’s modulus. Fractured samples were examined under scanning electron microscope to understand the failure mechanisms at the microstructural scale. The results show that binders significantly affected the mechanical properties of paste backfills (ANOVA, p < 0.05). The paste backfill bound with geopolymer gave the lowest strength and Young’s modulus, while the paste backfills bounded with FBC and GPC showed comparable higher strength and modulus values. This was attributed to the relatively well-packed paste backfills with less cracks and smaller pore sizes in these paste backfills bound with FBC and GPC binders. In particular, needle-shaped particles, which were originally identified in GPC, highly influenced the mechanical property of paste backfills. These results indicate that fly ash can be used to partially replace the cement as a binder for paste backfills to achieve economic and environmental benefits.     

多因素组合影响下向进路充填顶板稳定性计算

下向分层进路充填采矿法中,进路充填顶板的稳定对回采过程安全性至关重要,而分层充填体叠加载荷计算一直是顶板稳定性分析的难点。在充分考虑采动岩体荷载、矿体倾角、相邻分层间回采进路的交错布置、充填体与围岩的接触等工程实际后,推导了进路顶板平衡微分方程,求解得到进路顶板静荷载的理论值。结合回采工艺建立了“多跨梁”力学模型,并得到了回采进路顶板拉应力的理论计算公式,分析得到影响进路顶板稳定性的4个重要理论因素：顶板上部载荷σ v、回采进路跨度l、1:4充填体的厚度h、充填体自身抗拉强度[σt]。为充分考虑进路顶板静载荷和回采爆破动载荷影响,利用FLAC^3D对多因素影响下的顶板稳定性进行了数值模拟正交计算。根据模拟结果,分析了各因素对顶板拉应力的影响规律,利用多元非线性回归的方法建立了多因素组合影响下顶板稳定性评价模型。该模型应用到某铜矿试验采场的实际生产,具有较好的指导作用。     

Limit analysis solutions for three dimensional undrained slopes

This paper uses numerical finite element upper and lower bound limit analysis to produce stability charts for three dimensional (3D) homogeneous and inhomogeneous undrained slopes. Although the conventional limit equilibrium method (LEM) is used more often in practice for evaluating slope stability, the accuracy of the method is often questioned due to the underlying assumptions that it makes. Using the limit theorems can not only provide a simple and useful way of analysing the stability of slopes, but also avoid the shortcomings and arbitrary assumptions under pinning the LEM. The rigorous limit analysis results in this paper were found to bracket the slope stability number to within ±9% or better and therefore can be used to benchmark for solutions from other methods. In addition, it was found that using a two dimensional (2D) analysis to analyse a 3D problem will lead to a significant difference in the factors of safety depending on the slope geometries. This is of particular relevance to any back analyses of slope failure as it will lead to an unsafe estimation of material strengths.