列车荷载对下穿盾构隧道影响的模型试验

为研究地面线路运营对下穿盾构隧道结构的影响规律,基于相似比理论建立室内大型试验模型,模拟上部列车荷载作用下土层及其内部盾构隧道结构的受力变形过程,总结变形规律。结果表明,模型试验能够较好地反映外部荷载影响下土层以及内部盾构隧道结构的受力和变形特性;地表列车荷载在土层传递过程中,同一层面上沿地面线路方向的土压力大于两侧土压力,远离线路的地层受列车荷载影响相对较小,同一竖向截面土压力变化量由上至下逐渐减小,即外部荷载对浅层土的影响明显大于深层土;盾构隧道在地表列车行驶过程中,环向出现背车面受拉迎车面受压的受力特性,呈斜向压扁,纵向应变从中间交叉点向盾构隧道两侧逐渐减小,呈下凹压弯;盾构隧道埋深越小,受地表荷载影响越显著,增大一倍埋深对应纵向应变最大值减小约44.5%。     

Excavation collapse of Hangzhou subway station in soft clay and numerical investigation based on orthogonal experiment method

This paper studies the excavation collapse at the Xianghu subway station on Hangzhou metro line 1. The objective is to present an overview of this case study and discuss the cause of the failure. Through field investigation and preliminary analysis, the reasons for the excavation collapse were the misuse of the soil parameters, over excavation, incorrect installation of steel struts, invalid monitoring data, and inadequate ground improvement. Finally, a small strain constitutive model was used for further analysis. In order to estimate damage efficiently, the orthogonal array (OA) was introduced for screening the key factor in the numerical experiments. Six estimated indexes including deformations and internal forces of the excavation were taken, and the effectiveness of four factors which may cause the collapse was evaluated. Through numerical experiments and interaction analysis, it is found that the deformation and internal force can be well controlled by jet grouting of the subsoil under the final cutting surface, but increasing the improvement ratio of the jet grouting cannot help optimize the excavation behavior efficiently, and without jet grouting and the fourth level struts, the deformation and internal force of the excavation in this case will far surpass the allowable value.     

盾构施工参数对地层变形的影响

以南宁地铁一号线南湖段下穿隧道为工程背景,建立隧道开挖的三维有限元模型,通过数值分析,得到盾构施工过程中地层变形的分布规律,讨论盾构施工过程中注浆压力对地表沉降、水平位移及拱顶位移的影响,分析掌子面压力对地表隆起的影响规律。研究结果表明,注浆压力对地表变形会产生明显的影响,随着注浆压力的增大,地表沉降及水平位移明显减小。当掌子面压力大于0.1 MPa时,会引起掌子面前方土体产生向上的位移,地表隆起量随掌子面压力的增加而增大。     

SMW工法桩在深基坑支护中的应用

以福州市某房地产公司综合楼地下室基坑工程为例,计算、分析了基坑开挖各工况下SMW桩的侧向变形以及地表沉降量等变形规律,对比了SMW围护结构与一般围护结构的支护效果。结果表明: SMW工法桩在基坑支护中限制变形效果好,对周围地基影响小,综合效果优于一般支护形式。     

浅谈水泥土搅拌桩在南水北调工程中的应用

水泥土搅拌桩是利用水泥（或石灰）等材料作为固化剂,通过特制的搅拌机械在地基中将软士和固化剂强制搅拌,使软士硬结成具有整体性、水稳性和一定强度的水泥加固士,从而提高地基士强度,增大变形模量。此方法适用于软基处理,效果显著。使用水泥士搅拌法加固地基也有其局限性,这点更应该引起设计单位的重视。当采用水泥士搅拌法用于处理无类似工程经验的地区或工程时,必须有针对性的进行地质勘探补探工作,按规范通过设计前期的现场试验确定其适用性。     

Elastoplastic numerical analysis of layered soil foundation under the rectangular shallow footing subjected to vertical load

1 Introduction a Shallow foundation is widely used in civil engineering. Its bearing capacity and settlement are important research subjects in soil mechanics and foundation engineering [1]. Because of the complexity of soil engineering properties, the subject is still under development and improvement. Now the rigid-plastic limit equilibrium method based on the classic plasticity theory is widely used in the engineering practice in China. But soil is not rigid- plastic actually. Hence, the …     

调心球轴承动态特性参数分析

基于Jones-Harris方法建立了调心球轴承的动力学模型,应用Newton-Raphson方法对轴承动力学方程组进行了求解,开发了相应的计算程序.完成了该轴承的离心力、陀螺力矩、接触载荷、接触角、径向变形与径向刚度等动态特性参数分析.分析结果表明：转速与载荷是影响接触角大小与接触载荷分布最主要的2个因素;滚子的离心力与陀螺力矩随着转速的上升而增大,在此影响下外圈接触载荷增大而内圈接触载荷减小;受离心力的影响,外圈的接触角减小而内圈的接触角增大,且随着转速的增加,内外圈接触角的差值越来越大;轴承的径向刚度随着转速的上升而下降,而滚道沟曲率系数也对轴承径向刚度有一定程度的影响.     

狭长深基坑开挖引起的地表沉降变形及影响因素分析

狭长深基坑的开挖会对周边环境产生较大影响。鉴于此,文章基于有限元软件MIDAS GTS建立三维模型,重点分析基坑开挖过程中周围地表沉降的发展规律,并将数值模拟结果与施工现场监测数据进行对比,结果表明二者数据吻合良好。在此基础上对狭长深基坑开挖引起的地表沉降变形的影响因素进行分析,结果表明:基坑周围地表沉降值对基坑开挖深度敏感,且随着基坑开挖深度的增加而逐渐增大;地表最大沉降值出现在离墙后约8 m的位置,地表沉降的主要影响范围为0.5He~1.5He;增大地连墙厚度和嵌入深度、减小内支撑水平和竖向间距均使地表沉降值呈现减小趋势。     

The Applicability of the Risk and Resilience Model to Social Problems of Students with Learning Disabilities: Response to Bernice Wong

The purpose of this article is to respond to Bernice Wong's questions regarding the efficacy of the risk and resilience model for studying social problems in students with learning disabilities. Two factors render this framework particularly inviting to special education researchers. First, it is inherently optimistic because it assumes that once we identify factors that contribute to resilience, we can train less‐resistant individuals to be more resilient. As such, it moves us away from deficit models to empowering models. Second, the model forces us to look beyond the characteristics of the individual to consider external factors that have a significant influence on development and behavior. At the same time, however, we still need to advance our knowledge regarding the basic dimensions of social problems among students with learning disabilities. Hence, this article argues for multiple approaches to advancing knowledge about students with learning disabilities.     

路堤下土体侧向变形性状研究

分析了路堤荷载作用下土中水平向附加应力随深度的变化特征,得出了侧向变形沿深度"弓"形分布的变化规律,大量实测结果也证明了这一点.在此基础上提出了符合该变形规律的预测模型,分析了模型曲线随其中3个参数a,b 和 c的变化规律,并且通过3个实测点的侧向变形数据(s0,0),(s1,h0) 和 (s2,2h0)就可以简单地定出模型中这3个参数.将该模型应用到2个工程实例当中,预测结果和实测数据比较吻合,取得了较好的效果.     

Elastoplastic pipe-soil interaction analyses of partially-supported jointed water mains

Water distribution networks are essential components of water supply systems. The combination of pipe structural deterioration and mechanics leads to the failure of pipelines. A physical model for estimating the pipe failure must include both the pipe deterioration model and mechanics model. Winkler pipe-soil interaction （WPSI）, an analytical mechanics model developed by Rajani and Tesfamariam （2004）, takes external and internal loads, temperature changes, loss of bedding support, and the elastoplastic effect of soil into consideration. Based on the WPSI model, a method to evaluate the elastic and plastic areas was proposed in the present study. An FEM model based on pipe-soil interaction （PSI） element was used to verify the analytical model. Sensitivity analyses indicate that the soft soil, long pipe and high temperature induced the axial plastic deformation more likely, which, however, may not occur in normal scenarios. The soft soil, pipes in small diameters, long unsupported bedding are prone to form flexural plastic area. The results show that the pipes subjected to the same loads have smaller stresses in the elastoplastic analysis than elastic analysis. The difference, however, is slight.     

钢管复合土钉墙支护在城市深基坑中的应用研究

本文以北京三峡大厦深基坑开挖支护为工程背景,结合理论分析、现场监测和数值模拟等方法,对钢管复合土钉墙支护的作用机理和应用效果进行了研究。根据土力学和基坑支护相关原理确立力学机理模型,采用有限差分数值模拟方法进行开挖支护模拟,将数值模拟结果与实测基坑变形数据进行分析比较,二者结果基本一致,说明数值模拟方法应用于基坑开挖支护过程是比较可靠的,且从塑性区和变形分析可知用钢管桩复合土钉墙进行支护后的基坑是稳定的,即钢管桩复合土钉墙能很好地满足基坑支护稳定性的要求。     

Model test and numerical analysis on long-term mechanical properties of stepped reinforced retaining wall

Model tests and numerical analyses of stepped reinforced retaining wall were performed to investigate the effects of rheology of backfill and creep of geogrids on the long-term performance of the structure.The geogrid tensions,soil pressures,wall deformations and foundation pressure were measured during model construction and loading.A visco-elasto-plastic model and an empirical nonlinear visco-elastic model were utilized to simulate the stresses and deformations of geogrid-reinforced earth-retaining wall under long-term loads.By comparing test data with numerical results,it is shown that the foundation pressure distribution is nonlinear,and the lateral constraint of geogrids for backfill can cause a redistribution of foundation pressure.The curve of soil pressure is outside convex at each step initially,and it is close to the distribution for the case of vertical wall subsequently.The variation trend of geogrid tensions at different heights is obtained.Moreover,the failure mechanism and development mode of potential slip surface in retaining wall are proposed.     

词汇衔接理论在大学英语阅读教学中的应用

英语语篇的词汇衔接手段分为两大类:复现关系和同现关系。本文根据词汇衔接理论的主要内容,阐述了词汇衔接在英语阅读教学中的具体应用。     

盾构开挖顶推力对下平行隧道影响的数值分析

以滨海软土地层中盾构隧道平行上穿既有隧道为背景,通过数值仿真软件对开挖动态过程进行了精细化模拟,研究盾构隧道施工顶推力对周边地层及其内部既有隧道受力变形的影响。结果表明,在新建隧道上穿施工过程中,开挖扰动对地层的影响范围主要集中在距离开挖面-1.0~1.5D区域内(D为盾构隧道外径),扰动效果以新建隧道轴线为中心呈环状向外扩散,盾构顶推力从0.1MPa增至0.4MPa时,地表变形及1.0D范围内地层压力均增大20%以上;新建隧道平行上穿既有隧道过程中,既有隧道断面变形从横向鼓曲变为竖向拉伸,且整体出现上浮现象,顶推力达0.3MPa后,既有隧道拱底和拱顶隆起速度增加,以拱底为基准,顶推力自0.1MPa增加至0.4MPa时,隧道上浮量增大34.2%;施工过程中除保证常规地表变形监测外,对于近接平行上穿施工还需加强对既有隧道竖向变形的监控,必要时采取结构加固措施和施工参数综合调整办法,以降低开挖扰动对周边地层和结构物的影响。     

Bearing Capacity and Technical Advantages of Composite Bucket Foundation of Offshore Wind Turbines

Based on mechanical characteristics such as large vertical load,large horizontal load,large bending moment and complex geological conditions,a large scale composite bucket foundation (CBF) is put forward.Both the theoretical analysis and numerical simulation are employed to study the bearing capacity of CBF and the relationship between loads and ground deformation.Furthermore,monopile,high-rise pile cap,tripod and CBF designs are compared to analyze the bearing capacity and ground deformation,with a 3-MW wind generator as an example.The results indicate that CBF can effectively bear horizontal load and large bending moment resulting from upper structures and environmental load.     

广州嘉洲翠庭深基坑支护结构方案探讨

本文通过对钢管桩加喷锚网的基坑支护方案的技术经济分析比较，探讨合理深基坑支护形式，对结构的安全可靠性、经济性具有一定影响，并供同行们进一步探讨。     

Reduction rate of dragload and downdrag of piles by taper angles

Taper angle is one of the effective methods to reduce the dragload and downdrag of piles under the surcharge load. The model tests on the tapered pile and uniform cross-section pile embedded in sand were carried out under the surcharge load. The values of dragload and downdrag of piles versus the surcharge loads were measured. Based on the concentric cylinder shearing theory, a simplified theoretical model for calculating the dragload and downdrag of tapered piles with small taper angles under the surcharge load was proposed considering the angle effect. The correctness of the developed theoretical model was validated through comparing with the model test results obtained in this study and previous literature. Then the parametric studies of the taper angle, surcharge, strength and modulus of soil were discussed. It is shown that the tapered pile with the taper angle of 3° can reduce approximately 65% of the maximum dragload value and 30% of the downdrag value compared with a uniform cross-section pile. The value of downdrag can be decreased by approximately 50% compared with a uniform crosssection pile in the same average pile diameter.     

近代石家庄铁路枢纽的特点

近代石家庄是因路而兴的城市典型,石家庄铁路枢纽的形成具有一些与众不同的特点,对日后石家庄的兴起与发展产生了重要的影响。石家庄铁路交通枢纽的城市化是零起点,城区发展自然以铁路车站为中心,逐步向四周外延拓展;作为不同轨距枢纽,京汉路与正太路的机车与车厢不能过轨,给联运造成难以克服的困境,而相对石家庄的城市化而言,却具有“楚弓楚得”的效应;近代石家庄铁路枢纽呈现由丁字形向十字形的过渡,相比之下,丁字枢纽存在的时间更长,对石家庄的影响更大一些;伴随着城市的发展,铁路枢纽所占空间对城市的切割愈演愈烈。     

大型螺旋锥齿轮热处理变形的数值模拟与测量

应用计算流体力学软件Flow3D对大型螺旋锥齿轮在淬火过程中的变形情况进行数值模拟,并通过逆向反求和数模比对技术测定实际的热处理变形量,结果表明数值计算与实际测量结果较吻合,数值模拟可以有效地预测热处理后轮齿的变形情况。轮齿的热处理变形具有不均匀性,大端的变形量大于小端的变形量。凸齿面和凹齿面表现出不同的变形趋势,凸齿面主要产生负偏移,凹齿面主要产生正偏移。