临近岩质边坡挡土墙主动土压力分析

以临近稳定岩质边坡的刚性挡土墙为研究对象,在平移模式下,假定极限平衡状态下墙后有限无黏性填土中形成圆弧形土拱,考虑水平土层间剪应力的影响,修正水平层分析法,得到非线性分布的主动土压力表达式。据此探讨墙背和坡面倾角及其与填土间摩擦角等参数对主动土压力的影响。计算结果表明,此时主动土压力沿墙高一般为非线性分布,其合力作用点的位置有可能高于或低于墙高的下三分点。而且在某些特殊情况下,主动土压力合力大小有可能大于库仑土压力理论计算值。     

刚性挡土墙粘性填土被动土压力简化计算

利用水平条分法计算刚性挡土墙粘性填土的被动土压力，得到了刚性挡土墙粘性填土时被动土压力的非线性分布表达式且计算模型满足切应力互等定理。根据摩尔-库仑准则得到侧压力系数的计算公式，并且得到了被动土压力合力的简便公式。通过两种计算模型讨论了土条带间切应力增量对被动土压力影响。将计算结果与现有经典理论进行对比分析，结果表明:当挡土墙墙背光滑且无均布荷载时该文计算公式退化为Rankine公式，当填土为无粘性土时，该文方法所得结果与考虑土拱效应的经典文献结论趋于一致，并且与现有的试验结论保持一致。     

砂土中刚性挡墙不同主动变位模式任意位移土压力计算

已有模型实验及现场实测表明,刚性挡墙随着变位模式和位移量的变化,主动土压力合力和分布均发生改变,有时甚至与经典理论的线性分布有很大不同。采用中间状态系数定义非极限状态,提出了砂土中刚性挡墙不同主动位移模式下非极限状态土压力合力系数的计算公式;将墙后土体简化为连续非线性弹簧和刚塑性体的组合体作用在挡墙上,得到了不同位移模式任意位移的土压力分布和合力作用点高度。与已有理论方法和实验结果对比表明,该文方法在三种典型位移模式下与实验数据吻合更好。研究还发现,平动模式土压力呈线性分布,其合力随挡墙位移量的增大易趋于稳定并到达极限状态;绕墙底和绕墙顶转动模式下土压力合力随着位移增大只能接近极限状态且呈非线性分布。绕底转动时,土压力分布曲线逐渐向上凹,合力作用点高度趋于降低;绕顶转动时,分布曲线则逐渐向上凸,合力作用点高度趋于升高,墙顶附近表现出明显的土拱效应。     

新溆高速公路高填土涵洞减载措施

结合新溆高速公路高填土涵洞设计及多年涵洞设计、施工心得,借鉴高填士涵洞方面前辈们在高填土涵洞科研、实验和理论总结。围绕如何挖潜高填方涵洞的土拱效应服务于工程,提出新溆高速公路高填土涵洞采用加筋桥减载的方法挖潜土拱效应服务于本项目。     

基于弹性抗力法的深基坑悬臂支护结构上土压力空间效应分析

深基坑是一个具有长度、宽度、深度的三维空间结构体系。现行设计规范中将其简化为二维平面应变问题进行分析计算,不能反映基坑的空间性状和尺寸效应。基于弹性抗力法引入土压力发挥系数的概念,提出了土压力发挥系数的计算方法。提出基坑悬臂支护结构顶部冠梁的水平位移与简支梁受均布荷载作用下的水平位移具有相似的形式,在此基础上计算深基坑悬臂支护结构上土压力发挥系数、支护结构变形和内力的空间分布规律。工程实例计算表明:考虑土压力空间效应得到的基坑变形与实测结果相符合。     

边坡工程抗滑桩合理桩间距初探

对边坡工程防滑桩的合理间距进行探讨,要考虑抗滑桩间存在的土拱效应因素桩间距的影响,在对土拱效应分析之后就可以根据桩间静力平衡条件、跨中截面强度状况以及拱脚处所在截面强度状况合理推断出桩间距。在掌握了合理桩间距的计算公式之后,就可以通过计算公式看出桩间距与决定条件的关系,通常而言,如果保持其他因素不变,桩间距与桩后土体粘聚力成正比,与内摩擦角成正比,而与桩后坡体推力成反比。实际工程应用中我们也发现,这个桩间距公式的推导比较合理,很好地考虑了各方面的影响因素,根据计算出来的结果设置抗滑桩的桩间距,防滑效果甚好,所以说该计算公式实用价值比较高。     

钢管桁架拱平面内失稳与破坏机理的数值研究

对两铰圆弧形钢管桁架拱的弹性及弹塑性失稳机理及承载性能进行了深入研究,考虑了全跨和半跨水平均布荷载、跨中及1/4跨集中荷载等多种类型的荷载效应。分析了钢管桁架拱在不同荷载作用下的失稳破坏机理,指出其会发生整体失稳、弦杆局部失稳、腹杆局部失稳以及局部与整体的相关失稳等多种破坏模式。考察了矢跨比、腹杆尺寸、腹杆夹角和截面宽高比等不同参数对钢管桁架拱稳定承载力的影响,为桁架拱稳定设计方法的建立奠定了重要基础。     

考虑异形效应Y形桩侧摩阻力产生附加应力研究

Y形桩作为一种新型反拱曲面异形桩,侧土压力和侧摩阻力具有沿桩周不均匀分布的特性,虽将侧摩阻力假定为均匀分布与假定为集中力相比,附加应力计算结果更符合实际分布规律,但仍存在一定偏差。基于球形孔扩张理论,建立了Y形桩桩侧侧土压力的不均匀分布模型,进而建立了侧摩阻力的不均匀分布模型,并用于附加应力的计算。以主要影响因素外包圆半径R、模板弧度θ为变量,分别对比研究了将Y形桩侧摩阻力假定为集中分布、均匀分布和考虑异形效应不均匀分布三种模式下附加应力的变化规律,并将考虑异形效应的侧摩阻力产生附加应力计算方法用于沉降计算,通过现场静载荷试验数据验证,考虑异形效应的侧摩阻力产生附加应力计算方法所计算的沉降值与实测值吻合度更高。     

土拱的形成机理及存在条件的探讨

结合土工离心模型试验，理论分析及实地调查，综合研究了土拱效应的形成机理及存在条件，分析了土中成拱洞室的稳定性；推导出土中洞室的上覆土厚度及相应的最大跨径公。计算所得的结果与试验成果相一致。     

矩形截面框架柱斜向受剪承载力计算模型

为避免矩形截面框架柱在斜向水平地震作用下发生脆性破坏,通过试验研究14根框架柱在斜向水平荷载作用下的受力性能和破坏机理。以桁架-拱模型为基础建立计算矩形截面框架柱斜向受剪承载力的空间桁架-拱模型,该模型主要考虑了框架柱截面面积、混凝土和箍筋材料强度、配箍率、轴压力以及混凝土强度折减系数对其斜向受剪承载力的影响。最后,利用该文以及其他试验共计30根矩形截面框架柱的斜向受剪承载力试验结果对此空间桁架-拱模型的可行性和适用性进行了验证,试验结果与计算值的对比表明利用该模型可以安全计算矩形截面框架柱斜向受剪承载力。     

全尾砂胶结充填体的爆破振动破坏机制和振动速度阈值研究

结合五矿矿业安徽李楼铁矿-425 m中段矿柱爆破回采工程实例,利用应力波理论,分析了爆炸应力波在全尾砂胶结充填体中的传播及其与介质界面的相互作用,基于充填体的冲击压剪、剪切和反射拉伸等不同破坏机制和破坏准则,研究了充填体的质点振动速度阈值。研究表明:在爆炸应力波作用下,矿柱与1∶8充填体的胶结面易发生剪切破坏,而胶结充填体易发生压剪破坏;在透、反射应力波作用下,1∶8和1∶20配比充填体的胶结面易发生拉裂破坏,而与1∶20充填体相邻侧的1∶8充填体则可能发生层裂破坏。具体的充填体质点振动速度阈值为:矿柱与1∶8充填体胶结面的剪切破坏质点振速阈值为27.6 cm/s,紧邻矿柱1∶8充填体的冲击压剪破坏质点振速阈值为172 cm/s;1∶8和1∶20配比充填体胶结面的拉裂破坏质点振速阈值为12.6 cm/s,而与1∶20充填体相邻侧1∶8充填体的层裂破坏质点振速阈值为52.6 cm/s。     

Damage mechanism of composite cemented backfill based on complex defects influence

In order to reduce mining waste discharge and realize efficient application of tailing material in underground backfilling, the characteristics and mechanism of backfill damage is analyzed, and also the composed behavior and failure characteristic of cemented backfill. Five types of backfills were tested under uniaxial compression loading in SHT4206 electro‐hydraulic servo testing system. Based on the experimental results, the damage constitutive equations of cemented backfills with five cement?tailing ratios were proposed on the basis of damage mechanics and then validated. Research shows that the damage growth rate of backfills with lower cement?tailing is lower before peak value of stress, but it grows more rapidly after that. In addition, four backfill combination schemes were designed for mechanical test. Combining with research results on fracture characteristic of different backfills, a defects coupled constitutive model based on continuum damage mechanics was established. Research shows that the piecewise nonlinear model can well embodies effect of complex defects in backfills on the stress‐strain curve. Accuracy of the model is well verified by measured curve of backfill composite members. The results of this work provide a scientific basis for failure process prediction of backfills and reasonable matching design of framed filling.     

Meso-scale strain localization and failure response of an orthotropic woven glass–fiber reinforced composite

The present work focuses on studying the multi-scale deformation and failure mechanisms of an orthogonally woven glass fiber reinforced composite as a function of fiber orientation angle using digital image correlation. The full-field displacement and strain localization are effectively captured at meso-scale. At continuum scale, a remarkable change in mechanical response is observed when the loading axis diverges from principal axes. The variation in the global mechanical response is observed to be most prominent in the change of stiffness and strain at failure. At meso scale, a high degree of local deformation heterogeneity is observed and the level of inhomogeneity is found to be more prominent in case of the 45° off-axis specimens. While fiber-pull out is the major failure mode in the case of specimen loaded parallel to 0° and 90° fiber orientation, the localized shear strain developed in polymer-rich regions is the driving failure cause in the case of 45° off-axis specimen.     

横观各向同性岩石类材料的破坏准则

对岩石类材料,各向异性状态参数定义为材料微观结构偏张量与标准化的偏应力张量之间的联合不变量。通过在扩展的Lade-Duncan破坏准则内耦合各向异性状态参数,建立起了横观各向同性岩土类材料的破坏准则,并结合Tournemire页岩的三轴试验资料进行了验证工作。当加荷方向与材料沉积方向的夹角 在30°~60°范围时,预测出的岩石强度处于最小区域,从而达到了较好地对横观各向同性岩石的破坏强度进行合理预测的目的。     

Single-bolt tension joint tests on pultruded GRP plate - effects of tension direction relative to pultrusion direction

The literature on single-bolt tension joints in structural grade pultruded GRP plate is reviewed and the differences between the main investigations are highlighted. Details are given of the test setup and the joint configurations used in a series 54 such tests on single-bolt joints in which the angle between the pultrusion and tension axes (the off-axis angle) and the joint geometry are varied. Ultimate strength, intial stiffness, initial bolt slip and bolt displacement at failure data are presented as functions of the joints' principal geometric ratios. The observed joint failure modes show that, for off-axis angles ≥ 30 °, bearing failure (a relatively benign failure mode) does not arise. Instead, tension mode failure predominates and cracks tend to propagate parallel to the rovings diagonally across the width of the joint. It is concluded that the rovings play a significant role in controlling the crack propagation and this has implications for joint layout and design in pultruded GRP plate.     

四步法三维编织预制件的渗透率

采用径向法测量了三维编织预制件的渗透率, 利用修正注入半径的循环方法, 基于Visual C + + 计算了渗透率的大小, 主渗透率方向分两步确定: 一是通过选择阈值的图像处理运算提取流动前沿; 二是采用Matlab中的非线性最小二乘法将所得轮廓进行椭圆拟合, 并计算该椭圆长轴方向与编织方向的夹角。结果表明: 编织参数影响渗透率, 当编织角一定时, 随着纤维体积含量的增加, 主渗透率降低; 当纤维体积含量一定时, 随着编织角的增加, 主渗透率降低, 但主渗透率的方向不随编织角的变化而改变, 始终保持与编织轴向一致。      

Effect of aggregate size distribution and confining pressure on mechanical property and microstructure of cemented gangue backfill materials

The use of gangue, cementitious materials, and water mixed to make cemented gangue backfill material (CGBM) can achieve solid waste recycling while reducing environmental problems caused by its accumulation. In this paper, the fractal dimension of particle size distribution (PSD) and the confining pressure were investigated on the compressive strength, elastic modulus, stress–strain behavior, dilatancy deformation, and failure mode of CGBM using uniaxial compression, conventional triaxial compression, and microscopic scanning tests. The mechanism of the PSD fractal dimension on the mechanical properties of CGBM was revealed from a microscopic perspective. The results demonstrate that the compressive strength and elastic modulus of CGBM are quadratic polynomial and positively linearly related to the PSD fractal dimension and confining pressure respectively, with the PSD fractal dimension characterizing the maximum compressive strength of CGBM ranging between 2.4150 and 2.6084. The volume strain variation of CGBM diminishes as the PSD fractal dimension grows and increases dramatically when the confining pressure rises. The PSD fractal dimension has a quadratic polynomial relationship with both the cohesive force and the internal friction angle of CGBM. A reasonable PSD fractal dimension can optimize the microstructure of CGBM, reduce the distribution of defects such as microcracks and micropores, and enable hydration products to effectively fill the defects, guaranteeing that the CGBM has sufficient load-bearing capacity.     

拼焊板焊缝方向对其单向拉伸性能的影响研究

为提高拼焊板成形性,用单拉实验来研究拼焊板焊缝方向对其拉伸性能的影响.采用解析、实验和有限元法研究了拼焊板焊缝方向对其综合延伸率、失效模式的影响.结果表明,当焊缝角度较小时,失效表现为焊缝开裂;随着焊缝角度增大,平均延伸率非线性减小,且变化速率逐渐减小.当焊缝角度超过一定值后,失效变为薄侧母材开裂,并随着焊缝角度增大拼焊板综合延伸率逐渐增大,且增大的速率逐渐减小.在失效模式转换时,焊缝角度相应存在一个临界点,这一临界角度大小主要依赖于焊缝和薄侧母材性能.适当的焊缝角度有利于拼焊板成形性能的提高和失效模式的控制.     

Experimental characterization of the stress–strain behaviour of cemented paste backfill in compression

It is of great interest for economical and security reasons to understand the compressive properties of underground cemented paste backfill. In this paper, the stress–strain behaviours of cemented paste backfill (CPB) subjected to uniaxial compression and conventional triaxial tests are presented and discussed. The effect of CPB basic components, strength, ageing and confining pressure on the deformation behaviour of CPB are evaluated and discussed. The results show that the stress–strain behaviour of CPB is strongly influenced by the confinement, the age and strength of CPB, and its components. The increase in confining pressure leads to a change in the mode of failure, in the stiffness, and an increase in the strength.     

Effect of inherent anisotropy on acceleration wave speeds in hypoplasticity

Generally, soils possess an inherent fabric with transverse isotropy on the bedding plane. As a consequence, the deformation-stress characteristics show a dependence on the loading direction. Anisotropy is characterized by a vector normal to the bedding plane. In this paper we investigate the speeds of acceleration waves in an inherently anisotropic hypoplastic material. For the incrementally nonlinear hypoplastic constitutive equation the wave speed spectrum is continuous in contrast to discrete spectra in incrementally linear constitutive models. The so-called flutter instability arises when the equation for the wave speeds has complex solutions. In the principal stress space, a surface of first occurrence of flutter instability can be identified by analogy with the failure surface defined by a vanishing stress rate. We analyse the influence of the anisotropy on these surfaces and the change in their shape and symmetries depending on the bedding angle.