DEM Analysis of Soil Arching of Pile Supported Embankment

Pile supported embankment has been widely used in road, airport and dam engineering due to effective construction and economic advantages which can effectively control the settlement and differential settlement. The soil aching effect is a key factor in the load transfer mechanism of pile supported embankment. Based on the current laboratory model test, a series of numerical simulations were conducted with the particle flow code PFC2D to study the contact force, principal stress, vertical and lateral displacements in embankment. The embankment fill and subsoil were simulated by the Disk,andthe pile and model box were simulated by the WallThe multi-layer compaction method was used to establish the Discrete Element Method models. The micromechanical properties of the embankment fill and subsoil were obtained from numerical biaxial compression test and simple compression test, respectively. The simulation results indicated that the soil arching in pile supported embankment was composed by multiple hemispherical arches with different centers, and the height of arching was about 5(s-a)/6. Within the soil aching height, the deflection of principal stresswas obvious, and the vertical and lateral displacements were significant.     

The Core in Performance -Based Building Fire Protection Study and Its Development

The core of performance-based building fire protection design consists of the establishment of fire scenario,the enactment of fire and the simulation of fire and smoke-flow development.These are most important for performance-based building fire protection design.An unreasonable enactment or pre-digestion could result in a biggish error between the simulation outcome and the actual condition.In this paper,several emphases and some issues worth much attention are introduced and analyzed.In addition,a few important issues in simulating the fire and smoke-flow development related to Field Model are analyzed in detail.     

基于向日葵DUS测试的遗传多样性分析及代码分级

通过对来源于全国各地的253份向日葵种质资源进行相关、回归、遗传多样性分析,为向日葵种质资源开发、利用、评价提供参考;利用2倍标准差法对数量性状进行代码分级,并采用频次分析对代码分级的科学性进行探讨,为向日葵DUS测试[对申请保护的植物新品种进行特异性（distinctness）、一致性（uniformity）和稳定性（stability）的栽培鉴定试验或室内分析测试]指南的修订提供依据。通过相关分析和回归分析发现叶片大小与叶长、叶宽,瘦果大小与瘦果长度、瘦果宽度存在极显著相关关系且存在着一定的线性函数关系。通过性状代码分级和频次分析发现苞叶密度、舌状花密度、叶长、瘦果厚度分级比较少,且数据较为集中,不利于区分不同品种。瘦果长度、瘦果宽度、瘦果大小虽然分级较多,但不符合正态分布,表明代码分级不够科学合理。而主茎叶数、叶宽、叶片大小、花盘直径、株高这些性状数据分布符合正态分布,代码分级较为科学,便于区分不同品种。造成代码分级不合理的主要原因是人工选择的结果,同时也受品种保护意识淡薄、法律法规不完善的影响。     

Simulation of thermocapillary flow in a two dimensional cavity with lattice Boltzmann method

Thermocapillary flow driven by an unbalanced surface tension plays the most important role for mass and heat transport in floating zone melt crystal growth under microgravity. The authors develop both a serial and a parallel codes with lattice Bhatnagar-Gross-Krook(BGK) model using two distribution functions, and numerically study the thermocapillary flow in a two dimensional square cavity with a single free surface under microgravity condition. The serial code is developed by combining collision and propagation step, using a temporary array to continuously read distribution functions, and its performance is improved two times faster than the code with separating the collision and propagation step. The MPI parallel code is proposed utilizing one dimensional partitioning and non-blocking communication. The accurate and reliable results are achieved with both the serial and parallel codes by comparing with CFD results simulated by the finite volume method; the MPI parallel code has high performance.     

An Equivalent Shear Displacement Method of Single Capped Pile in Layered Soil

Based on the interaction of single pile, cap and soil, the load transfer matrixes of single pile and soil were proposed to establish an equivalent shear displacement method of single capped pile in layered soil. With the compatibility of displacement at the interface between the pile and the soil, equilibrium equations of pile and soil could be derived. With the increase of the total load on the pile cap, the lateral friction at the interface of the pile and the soil becomes so large that the occurrence of the sliding takes place. While there is little sliding at the interface between the soil under cap and the soil outside of the cap because of the less lateral friction, which gives rives to less settlement of the soil outside of the cap. Eventually, the results of the finite element method, existing theoretical method and the model tests were compared with those from the analytical method and were found to be in good agreement. The increase of the ratio of length to diameter does not infinitely enlarge the overall stiffness of the single capped pile, because the pile cap would afford part of the loading all the time.     

Stability Analysis of Multiple Long Pile Models based on the Lateral Static Load Test of Pile

A mathematical model was established by using the transfer matrix based on Winkler elastic subgrade and spring supports in Newmark method. In simplification for subgrade reaction with discrete spring supports, the unequal displacements of two ends for pile section were included in the model. Lateral displacement and cross-section angle of the pile were determined by lateral static load test and the values of parameters of multiple subgrade reaction models were calculated by computer programming. By identifying the stability of long pile in different subgrade reaction models, the change patterns of three factors were analyzed, including effective length of long pile, restrictions on pile top and extensive length on the ground.     

A Construction Example of Pile Amending by Consolidation Grouting

In this paper the amendment of No.18 pile in 19th pier of Citong Bridge in Quanzhou city is presented. There is a soft layer 6.41m thick in No.18 pile,a site cast concrete pile,due to breakdown of guide tube during casting. Amended by consolidation grouting, the pile stood up to tests. The construction technology, adopted steps and test method were introduced. It can serve as reference to similar engineering.     

Dynamic Behavior of Geogrid Reinforced Pile Supported Embankments under Moving Load

In order to investigate the dynamic behavior of geogrid reinforced pile supported embankments (GRPS) under moving load, a three dimensional coupled mechanical and hydraulic model was built by FLAC 3D. The results from two cases including unreinforced and no pile embankments, and geogrid reinforced pile supported embankments were presented. The behaviors of vertical displacement, pile soil stress ratio, excess pore water pressure, and vertical acceleration under two cases were compared and discussed. Additionally, studies on the effect of speed and weight of the moving load were performed. It is indicated that the value of vertical displacement, pile soil stress ratio, excess pore water pressure, and vertical acceleration of GRPS decrease evidently compared with those of unreinforced and no pile embankment, which is caused by the soil arching effect and the reinforcement effect. It is also shown that the greater the axle load value is, the less the beneficial effect of GRPS on the vertical displacement. With the increase of the moving speed of the load, the vertical displacement increases.     

简谐SH波作用下管桩的振动特性

在一维波动模型的基础上得到了简谐SH波作用下桩周土和桩芯土的位移。在三维轴对称的情况下,运用势函数和分离变量法求解了简谐水平集中荷载和SH波引起的管桩桩周土和桩芯土的振动问题,得到了桩周土和桩芯土的径向位移和环向位移。考虑管桩土动力相互作用和管桩土的连续性边界条件对简谐水平集中荷载和SH波作用下管桩的振动进行了研究,得到了管桩桩顶的动力放大因子。通过数值算例分析可知,简谐SH波作用下管桩存在共振现象;管桩管壁过薄宜导致桩基失稳;相同外径情况下采用管桩要比实芯桩的抗震性能更好。     

Model Investigation of Sliding Resistence Mechanism for h type Anti slide Pile

In order to improve the understanding of the mechanism of h type anti slide pile to reinforce the slope, this type of anti slide pile with different anchorage depth and distance between fore pile and back pile was investigated through model test by specially designed experimental apparatus. The test results indicate that the distribution of resistence and thrust acting on fore pile is triangular, and the resistence acting on back pile is rectangular. For the landslide thrust acting on back pile, there are three types of distribution: parabolic, parabolic with upper center of gravity and rectangular. Therefore, when the calculation pattern for the part of h type pile above the potential slip surface is defined, the distribution of resistence and thrust acting on fore pile can be fixed as triangular, and the resistence acting on back pile can be fixed as rectangular. Whilst the distribution of landslide thrust acting on back pile should consider the influence of property of soil, anchorage depth and the distance between fore pile and back pile. Some conclusions drawn from this test can provide useful reference for the design of h type anti slide pile.     

Longitudinal Vibrations of a Single Pile in Saturated Viscoelastic Soil

Based on Biot's theory, the longitudinal vibrations of a single pile in saturated viscoelastic soil are investigated in the frequency domain subject to the harmonic load. By the Novak plane strain model, the control equations for the saturated viscoelastic soil are derived. Regarding the pile as the one-dimensional rod model, the vibration equation of the pile is established. Based on the continuity conditions of the pile and soil, the dynamic stiffness and dynamic damping of the pile top are obtained. It is compared with the solution for Novak, and the influence of different physical parameters of the pile and soil on the longitudinal vibrations of the soil and pile system is examined. It is shown that the dynamic characteristics of the pile in the dry soil as well as the saturated soil have some differences; the resonance effect of dynamic stiffness factor and equivalent damping is obvious weakening with the increase of the ratio of the length to radius of the pile. The resonance effect and natural frequency are increasing when the modulus ratio of the pile to soil increases; the interaction coefficient of the flow-solid and the damping ratio of soil skeleton have few influences on the responses.     

Bearing Capacity Behavior of Roll Forming Filling Screw Pile

Bearing capacity behavior of roll forming filling screw pile (screw pile for short) is investigated through numerical calculation and static load test. The influence of pile-type parameters, such as width of thread tooth and thread pitch, on the ultimate bearing capacity of crew pile is studied; furthermore, the bearing capacity behavior of screw pile and that of pile with the same diameter are compared and analyzed through static load test. The results show that the ultimate bearing capacity of screw pile is a bit higher than that of pile with the same outside diameter; width of thread tooth has a distinct effect on ultimate bearing capacity which increases with the increment of width of thread tooth. When the screw pile is tested under light load, the resistance on pile side is distributed along screw pile, and tip resistance is small, but the resistance rises considerably with load increasing. Besides, the design formula of bearing capacity of screw pile is proposed.     

玉米堆摩擦角的测定与研究

利用直剪仪对玉米(水分率为11.05%、12.34%、16.72%、17.57%w.b)的内摩擦角进行了实验测定与分析。结果表明:玉米的内摩擦角变化范围是22.81°~35.20°,玉米的内摩擦角随剪切速度的增加而减小,随法向压应力的增加而减小,随水分的增加而增加。     

门架式抗滑桩结构模型试验研究

为了对门架式抗滑桩的结构特性有进一步的认识和提升,进行了门架式抗滑桩三维地质力学模型试验与门架式抗滑桩结构模型试验。通过在桩身内部贴置应变片以及桩身的关键位置处放置千分表,来测量在推力荷载施加过程中,门架式抗滑桩的桩身应力变化特点及关键位置点的位移变化特征。试验结果表明：门架式抗滑桩桩前、后排桩桩顶位移大于滑动面处位移,后排桩桩身位移大于前排桩桩身位移;前、后排桩桩身内力均呈现明显的“s”型分布,桩顶应力不为零,其数值随着推力荷载的增大的而增大。     

城市污泥堆肥及农用前后重金属形态变化的研究

笔者以城市污水处理厂污泥为研究对象,添加不同种类及不同比例的调理剂对A、B和C堆污泥进行高温堆肥试验,分析了堆肥成品的种子发芽指数和基本理化性质,用顺序提取法分析堆肥、种植小白菜前后重金属形态的变化,为城市污水厂污泥资源化利用及堆肥中重金属形态变化提供相关参考。结果表明,城市污水厂污泥经过堆肥处理,添加剂种类及添加比例对污泥的腐熟程度有一定影响,且堆料中重金属Cu、Zn的X-(KNO3+H2O)态均有所降低,其中Cu的X-(KNO3+H2O)态下降比例顺序是C堆(53.71%)＞A堆(24.64%)＞B堆(2.55%),Zn的X-(KNO3+H2O)态下降比例是A堆(80.58%)＞B堆(71.09%)＞C堆(66.34%);堆肥处理后的土壤中,Cu、Zn的X-(KNO3+H2O)态的比例则有所增加。试验结果对污水厂污泥堆肥土地利用及重金属形态在土壤中的形态转化具有实用价值。     

Field Comparative Experimental Study on Bearing Capacity of Both Bored Pile with Branches and Plates and Column Bored Pile at the Same Site

Compared with column bored pile,the bored pile with branches and plates is a new type of piles with higher bearing capacity and lower settlement.Field comparative tests related to ultimate bearing capacity of both the bored piles with branches and plates and column bored piles at the same site in Huzhou city of province Zhejiang in China were studied through self-balanced method under static pressure.The results testify that,compared with column bored pile under the same geological conditions,the bored pile with branches and plates can obtain better economic benefit such as: increasing ultimate compressive bearing capacity and ultimate extraction bearing capacity used per cubic meter concrete over 75.3%and 118.9%respectively,while dropping consumption of reinforced concrete upwards of 41.9%and 44.1% respectively,reducing settlement and pile length under the same loading.The tests will present an objective reference to the new type of piles in both theoretic study and application to analogous engineering.     

Foundation pile test by self-balanced method of rock-socketed piles and friction piles in multilayer soil geological structure

结合检测工况对测试数据的影响,对自平衡“精确转换法”进行改进,提出摩擦桩位移协调转换法和嵌岩桩的荷载协调转换法,实际应用结果说明两种转换方法合理。所得测试结果表明湄公河大桥桩基承载力符合设计要求;分析湄公河大桥试桩的侧摩阻力和端承力分布,嵌岩桩和摩擦桩纵向承载均以侧阻力为主。