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.     

Time Effect Experimental Analysis of the Soil Arch Effect of Anti sliding Pile

Soil arching effect is important for stabilizing the soil behind anti sliding pile. The creep of soil mass will inevitably lead to the formation of soil arching, which has time effect. In this analysis, an indoor thrust pile model test is proposed. The characteristics of stress distribution in the soil and the time effect of soil arching behind anti sliding pile are analyzed. The experimental data acquired by the soil pressure cells arranged along the normal direction of the thrust show that soil arching effect is enhanced with the increase of thrust.The thickness of soil arch increases with time.And the data obtained by soil pressure cells arranged along the direction of the thrust show that the horizontal soil arching effect increases and then gradually extends.The scope of stress dispersion has very large growth along the normal direction as time goes on.     

Analyisis of Arching Mechanism in Compacted Rockfill

As the main material in constructing dams,arching mechanism in compacted rockfill is aways the focus of safety problem in compacted rockfiu dams. Compacted rockfill has different engineering characteristics according to stack forms and constructing techniques,and the failure of compacted rockfill conforms to Coulomb_Mohr criterion.Compacted rockfill is the main material in protecting embankment for the migration movement in Fuling city zone.The arching action is theoretically studied and numercally modelled especially for constructing techniques.It is found out that the arching action begins and numerically of settlement and burdens part of load and deadweight of upper soil.Earth pressure applied to the arch is smaller than the weight of overburden.     

Analysis on Deformation Characteristics of CFG Piles-Gravel Cushion Composite Foundation of the Deep Embedded Secret Passage

In order to investigate the issue in the field of the application of CFG pile application of CFG pile composite foundation technology in deep embedded secret passage of such special structure ground treatment, the settlement deformation of CFG pile composite foundation according to deep are studied and detailed analysis are given in the field test and indoor model test of the gravel cushion with different thickness. Moreover it points out that the cushion compressive deformation must be taken into account, and that the settlement deformation calculation cannot simply consider the amendments of composite foundation. The amendments of cushion deformation must be considered. The effect of the different thickness of cushion on pile-soil stress ratio, total settlement of composite foundation, cushion compression and axial stress of pile body were analysed by using ABAQUS finite element method. Through the analysis of the field test, indoor model test and the numerical simulation of CFG piles-gravel cushion composite foundation of the deep embedded secret passage, a settlement deformation monitoring method has been described and the selection principle of the cushion has determined so as to provide the cushion design basis in the process of composite foundation design.     

FEM Analysis of Differential Settlement of Gravel Pile Foundation Under Large scale Oil Tank

In order to reduce the differential settlement of gravel pile foundation under large scale oil tank, axisymmetric numerical simulation method and finite element method was employed to study the pile length, the exchange rate of length, the length of the cushion course to the influence of differential settlement and the relationship of negative lateral displacement and the settlement. It is found that: differential settlement has a minimum range of pile length. For the oil tank foundation center, by keeping the pile diameter, increasing pile spacing can increase the rate of exchange and obtain smaller differential settlement in relatively smaller displacement rate conditions. And by keeping replacement rate unchanged, the larger the pile diameter(namely the looser pile spacing) is, the smaller the differences settlement of the gravel pile foundation is. Moreover, pile length adjustment and the exchange rate have obvious effects on different subsidence and not obvious effects on the length of the cushion course. The appearance of oil tank foundation negative lateral displacement is one of the most important features of differential settlement adjustment.     

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.     

3D Dynamic Coupled Mechanical and Hydraulic Analysis of Geogrid-reinforced Pile-supported Embankments

In order to investigate the dynamic behaviors of geogrid-reinforced pile-supported embankments under traffic loading, three-dimensional coupled mechanical and hydraulic numerical simulations are conducted using FLAC 3D. Four cases are studied including unreinforced and no-pile embankments, reinforced embankments, pile-supported embankments, and geogrid-reinforced pile-supported embankments. The behaviors of vertical displacement, horizontal displacement, pile-soil stress ratio, excess pore water pressure and acceleration under four cases are analyzed. It is found that the vertical displacement, nonuniform settlement and horizontal displacement of geogrid-reinforced pile-supported embankments are smaller than those of other cases due to soil arching effect and reinforcement effect. Pile-soil stress ratio decreases with the increase of loading number. The crest value of acceleration and the time for acceleration to be steady are also smaller than those of other cases. The dissipation velocity of excess pore is quicker than that of unreinforced embankments.     

Face Stability Analysis of Shield Tunneling in Sandy Cobble Stratum

When shield crossed the sandy cobble stratum in Chengdu metro line 1, ground subsidence reached as high as dozens of times. The losing stability of excavation face caused excessive ground loss. Conditions of engineering geology and hydrogeology about sandy cobble stratum in Chengdu were analyzed. Mechanical characteristics of sandy cobble were obtained via large-scale triaxial test. According to the low cohesion and heavily discrete characteristics of sandy cobble, numerical computation was conducted by discrete element method. Based on numerical simulation of the large scale triaxial test, the micro parameters of the sandy cobble were calibrated. The influence of support pressure on shield excavation face deformation, surface settlement, max horizontal displacement and stress of soil was analyzed. The results show that: 1) Collapse pattern of excavation face by numerical simulation coincides with result of centrifuge model test in sand. 2) When supporting pressure is small, contact forces of particle in front of excavation face is low. The tendency of particle flow is apparent. Since over-excavation is easily brought out, cavity in the ground is caused after shield tunneling. 3)Soil arching effect in shield construction is obvious. Shield excavation forms cavity in deep ground and obvious earth surface collapse is not observed. This is main reason for lagged settlement phenomena of shield tunneling in Chengdu.     

Analysis of the Lateral Deformation of Structural Soft Dredger Fill with True Triaxial Test

In order to study the mechanical properties and structural properties of soft dredger fill under lateral deformation. Based on true triaxial and WF stress path apparatus, lateral unloading undrained tests were carried out. The results derived from true triaxial test, WF stress path test and routine triaxial shear test were analyzed. The contrastive conclusions are as follows: The stress-strain curve of true triaxial unloading test shows a softening behavior, which is different from the hardening behavior for that of conventional triaxial shear test. With the increase of initial confined pressure, the dilatancy of soil transfers from shrinkage to expansion. The structural yield stress of the unloading soil with true triaxial test method is dramatically larger than that with the latter two tests due to the effect of intermediate principal, which exhibits a nonlinear growth as the coefficient of intermediate principal bd stress jumps. The shear strength indexes of unloading soil with true triaxial test is larger than that with WF stress path test. Compared with the results of routine triaxial test, the internal friction angle of true triaxial test is bigger while the cohesion is smaller.     

High-Speed Railway CFG Pile Composite Foundation Settlement Influence Factors Analysis

Because of high bearing capacity and small settlement of CFG pile, CFG pile have been used widely in foundation treatment of engineering construction, but it has applicant in high-speed railway roadbed only in the initial stage. In this paper, based on the project of Beishahe of Hada high-speed rail, simulated with the finite element model by ADINA by changing the parameters of CFG pile and roadbed height in the situation of permafrost and unpermafrost of foundation, obtained the relationship of parameters and foundation settlement, it has the directive significance for high-speed railway with CFG pile composite foundation.     

小麦堆压缩特性的实验研究

利用回弹模量仪对小麦堆（河南产）（水分为11.7%,13.33%,15.18%,16.55%,18.18%w.b）的密度和无侧向膨胀压缩体变模量进行了实验测定,实验选定加在样品顶部的压应力为：50 kPa、100 kPa、150 kPa、200 kPa、250 kPa、300 kPa,通过计算得出对应的样品平均竖直压应力为：36.8 kPa、74.8 kPa、110.9 kPa、153.4 kPa、184.7 kPa、221.0 kPa。进而得到样品所受的平均压应力为：18.3 kPa、41.9 kPa、66.7kPa、91.0 kPa、110.9 kPa、133.248 kPa。实验结果表明：在同一水分下,随着平均压应力的增大,小麦堆的密度也增大。在同一水分下,随着平均压应力的增大,小麦堆的体变模量也增大。拟合方程为y=axb,其中参数a、b随水分的不同而变化。     

Numerical Simulation and Field Monitoring Research of Reinforcement Range of Soft Ground on One Side Road Widening Project

As one of common reinforcement measure, cement mix pile is widely used in soft ground treatment of road widen project, while relevant studies on reinforcement range is insufficient. According to the one side road widening project, the cross-section of deep soft ground is analyzed. When fill is simplified as trapezoid load, the conclusion that reinforcement depth of cement mix pile should greater than load breadth can be gained by addition stress distribution. Based on the numerical simulation of different reinforcement measures, the slope stability, road settlement and horizontal deformation are influenced greatly by reinforcement range. Comparison research indicates that when the soft ground from slope toe to road shoulder is strengthened, the improvement effect is obvious. The numerical simulation and field monitoring resules show that reinforcement measure is suitable. Meanwhile, this study can provide reference to similar project.     

Effective Unloading Area between Cantilever Piles

The formation mechanism of the arching effect between cantilever piles is studied according to their stress characteristics. The soil arch is classified into three types based on its position in a space coordinate system, namely, a horizontal arch, a vertical arch and a free face arch. The master factor for distribution of unloading area between piles is the horizontal arch effect. The range of effective unloading area is defined. Based on the failure pattern of soil arches and the relationship between soil strength theory and the static equilibrium principle of soil arches, a calculation model is established by considering the presence of geostatic stress and sliding thrust force. The relation between soil strength and critical height is studied by variation of cohesion and friction angle. In addition, the impact of canonical distributions of the earth pressure to the vector height of unloading area is also discussed. Finally, the calculation model is verified by an example from real engineering work.     

甜瓜常温运输不同堆高层次的三维轴向振动强度差异

西州蜜17号甜瓜采用发泡网单个包装,置于瓦楞纸箱(4个/箱)内,共2 849箱11层堆高,用货车后挂载装,设置底层(2箱高)、中层(6箱高)和顶层(10箱高)三个堆高层次处理,使用振动记录仪监测载重33 t、时速57 km/h、54 h运输全程的X轴向(左右方向)、Y轴向(前后方向)和Z轴向(上下方向)振动的响应加速度,分析不同堆装高度三维轴向振动加速度的差异,为采后甜瓜适宜的运输条件提供理论依据。试验结果表明,甜瓜运输全程85.87%~92.33%的X轴向振动加速度为0.020~0.058 g,70.85%~91.63%的Y轴向振动加速度为0.033~0.083 g,67.33%~74.91%的Z轴向振动加速度为0.093~0.140 g。常温运输的甜瓜垂直方向振动强度最高,前后方向次之,左右方向最低。堆装高度的增加将提高三维轴向的振动强度,中层和顶层堆高存在水平方向对垂直方向的振动递增效应。中层堆高瓜箱内的温度与相对湿度较低;顶层堆高的相对湿度较大,底层堆高的温度偏高。     

Behavior Analysis of Laterally Loaded Single Pile under Large Deflection

Based on the simplified elastoplastic constitutive model of soil, the calculation method for the laterally loaded single pile with large deflection was submitted. The coefficient of subgrade reaction was presumed to increase linearly with depth, which simulates the soil resistance close to ground well. The relevant program was then developed using FORTRAN language. The examples show that (1)the displacement and bending moment increase nonlinearly when the lateral load and the moment load increase. (2)The pile displacement decreases with depth. (3)The pile displacement at the point which is over ten times pile diameter from ground is so small that can be neglected. (4)The pile head condition is the key factor, which influences the distributions of pile responses along depth. (5)By improving the mechanical properties of soil around pile, the maximum lateral displacement and bending moment can be decreased efficiently. The calculation results are in good agreement with the field test results and are better than those obtained using the pre existing solutions, which shows the presented solutions are reliable.     

m法下的双曲线型p-y曲线

工程中基桩大多处于复杂的成层地基中,鲜有位于单一土层中,从宏观角度出发,引入初始地基比例系数,提出了基于m法的双曲线型p-y曲线。某现场7根试桩地基土非线性显著,实测和理论计算的地面处桩身水平位移水平荷载关系曲线均呈良好的二次抛物线关系,且理论与实测曲线吻合良好,验证了本文p-y曲线模型。地基土非线性对桩身最大弯矩、桩侧地基土压力影响显著,不容忽略。工程实际中采用m法计算基桩最大弯矩值偏小,建议乘以1.05~1.25的系数,以计入地基土非线性影响。     

水平荷载作用下斜坡刚性桩非线性分析

在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。     

A study on lateral deformation calculation of foundation under embankment

Embankment load causes not only vertical settlement of foundation but also lateral deformation of foundation, and lateral deformation is one of the important factors for foundation settlement. In order to analyze lateral deformation of foundation under th     

Effect of Soil Content on Dynamic Modulus in Filling Sand Subgrade

To analyse the effect of the soil content on dynamic modulus in filling sand subgrade, the portable falling weight deflectometer (PFWD) test and degree of compaction test in field were carried out at first. The relationship of the soil content and the dynamic modulus was analysed as well. Based on the test data, the regression models among the dynamic modulus, degree of compaction, consistency and the soil content were established. Then combining with the out-and-indoor test results, the controlling standard of soil content in filling sand embankment was presented. The results turn out that the soil content in the embankment is 3.0%~5.5%. The dynamic modulus increases with the soil decreasing, and there is a good power function regression between them. There is also a good regression among dynamic modulus, degree of compaction, consistency and soil content. When the soil content is within 10%, the dynamic modulus increases then turn to decrease with the soil content increasing. When soil content is smaller than 3% or larger than 8%, the dynamic modulus are significantly smaller than others. So the controlling standard of soil content in filling sand embankment is recommended at 3%~8%.     

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。