Contrast Analysis of the Reinforcement Effect of Pile-Net Composite Foundation

To investigate the effect of consolidation soft soil, three groups of model tests were designed. The first group was PVC pile-net composite foundation, the second was pile-cap-net composite foundation, and the third was PVC and sand pile composite foundation. Butter was coated and plastic membrane was covered on inner side wall of model cast to reduce border effect. The gauges were glued with epoxy on the surface of the model with PVC piles and geogrids to measure the stress of PVC piles and geogrids. Soil pressure cells were installed in the middle of piles and the top of the sand piles, and dial indicators were installed in the middle of road and road shoulder to measure deformations. It is that shown: 1) as for the distribution of the road settlement and the differential settlement, the settlements of the third group are the largest and those of the second group are the least; 2) in terms of the stress ratio of PVC pile and soil, the values of the first group and the third group are similar, while the value of the second group is much larger; 3) the change of geogrid strain is disorderly. There are periodic peaks in the strain of geogrid of pile top and periodic troughs in the soil between the piles. The geogrid strain of the second group measured in the corresponding spot is much larger than those of the other two groups. The results of three groups of tests illustrate that if the condition is permitted, it would be the best to adopt the scheme of pile-cap-net composite foundation, which has better reinforcement effect for soft soil.     

Numerical simulation analysis on small clear spacing crossing viaduct pile foundation of shielded subway tunnels

Aimed at the problem of the in partial section of the Nanjing Metro Line 3, the three-dimensional pattern of tunnel, segment and pile foundation was established after appropriate simplification. The simulation results showed that, the Overpass pile foundation of Shield Tunneling to Adjacent Metro Shield Tunnel will have effect on the force and deformation of the earth's surface and pile foundation, the maximum deformation value of the earth's surface is larger than that of the pile foundation top, stress concentration appeared in right working slope lower side segment of tunnel. Through the comparison with field monitoring results, the field dates is consistent with the Numerical Simulation Results, the execution parameters are advised to be well controlled in the further construction, in the same time strengthing the track monitoring, tracking grouting reinforcement should be carried when necessary. The research results could provide reference for the smooth going of the project.     

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.     

Discussion on Methods for Determining Cracking Angle of Rock Slope

Many mountainous cities are facing slope problems during project construction. At present, there are two methods to determine cracking angle for rock slope, namely, the method from "Technical Specification for Retaining Structure in Excavation" and the method from "Handbook of Engineering Geology". However, there is obvious difference between cracking angles of rock slope by these two methods. In this paper, the theoretical formulas of these two methods are derived and compared. Based on analyzing the results of FLAC numerical simulation for soft rock slope, it is concluded that the cracking angles of rock slope determined by the "Handbook of Engineering Geology" are more reasonable and safe.     

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。     

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.     

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.     

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.     

Analysis on key problems of initiative decompression pre-reinforced structure

In slope engineering, the shear resistance of rock and soil can never be exerted themselves by general pre-reinforced structure, through the coupling mechanism between reinforced structure and slope, an initiative decompression pre-reinforced structure consists of soft stuffing and pre-reinforced structure is presented. The setting and thickness of soft stuffing are both key questions during the design of initiative decompression pre-reinforced structure. On one hand, the setting of soft stuffing assure that parts of initiative decompression pre-reinforced structure cannot interact each other under reinforcing; on the other hand, the thickness of soft stuffing can assure that the shear resistance of rock and soil can be exerted by themselves, the sliding thrust which is endured by pre-reinforced structure alone is changed to be endured by soil and pre-reinforced structure together. Then the sliding thrust endured by pre-reinforced structure minimizes, accordingly the effect of initiative decompression is achieved. In the end, the calculation procedure of thickness is illustrated by a practical project and the result is rational.     

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.     

The Application of Pre-splitting Blasting to Excavation on High Slope in Soft Rock Section

Based on analyzing about blasting mode of slope in the construction of road, the paper shows that pre splitting blasting is mostly suitable in the section of severely weathering soft rock with developed joints and fractures, introduced the laying out about the hole of pre splitting blasting that can apply in the high slope of the expressway in the section, and designed the parameter. The practice shows that it gained favourable effect by this method.     

Asphalt pavement structure design of expressway on soft soil foundation

Non homogenous settlement will occur while the expressway is constructed on soft ground. The differential settlement can cause the bigger additional stress inside the asphalt pavement structure accelerating bituminous pavement destruction. Therefore,we must choose reasonable pavement structure when constructing road on soft base in order to reduce the influence on surface layer structure from the differential settlement. Based on ABAQUS finite element method and through analysis, this article draws the conclusion that establishing unbound graded aggregate sandwich structure under the asphalt pavement structure can effectively reduce the horizontal additional stress of the stress controled layer and better prevent crack reflection which is beneficial for constructing the asphalt pavement structure on the soft ground.     

Influence of heat storage mode of domestic hot water on the performance of ground heat exchanger in ground-source heat pump system

The vertical U-tube ground-coupled heat pump system provides cold and heat for the controlling of indoor environment. Under the air-conditioning condition, the vertical U-tube ground-coupled heat pump system with heat recovery can provide domestic hot water. The influence of supplying domestic hot water on the heat transfer performance of ground heat exchangers is different under different operating modes in summer and winter. Through a project design of ground-source heat pump system, the influence of supplying domestic hot water under heat storage mode on the heat transfer performance of ground heat exchangers in summer and winter is respectively analyzed. The dynamic performance of heat exchangers under different working conditions is analyzed, and through numerical calculation, the heat transfer performance parameters of ground heat exchangers under different operating modes are obtained. From the calculation results, the adjusting methods based on the load characteristics of this project represent.     

植物根系固土作用模型研究进展

植物根系固土作用模型研究已历经近40年,从简单的极限平衡模型到复杂的有限元和离散元数值模型,已发展到10余种。总结这些根系固土作用模型不仅对揭示根系加固土壤作用的力学机制和分析林地边坡的稳定性具有重要意义,对根系固土作用模型未来的研究方向也具有积极指导意义。笔者对根系固土作用模型分2部分进行综述,第一部分主要介绍根系固土作用的理论模型,包括：Wu模型、倾斜根系模型、位移模型、纤维束模型、根束增强模型和能量模型,以及这些模型的应用条件、模型优缺点、适用范围等。第二部分主要综述根系固土作用的数值模型,包括：有限元数值模型、离散元数值模型和造林边坡稳定性分析数值模型,并详细比较了有限元与离散元数值模型的优缺点和在造林边坡稳定性分析上的应用。最后探讨了目前根系固土作用模型研究中存在的不足以及未来的发展方向。     

Development and Failure Principle of Differential Weathering Overhanging Rock

Differential weathering overhanging rock by hard rock and soft rock interlayer is common for geological failure.To study the influence of ground stress in rock slope and cave deepness to differential weathering overhanging rock,a mechanical model was proposed.And hollow cylinder stress meter was used to test and analyze on site ground stress at Hongyadong in Chongqing.Moreover, the development range of overhanging rock was determined.And a case studywas used to analyze the relationship among tension ground stress, cave deepness and growth of controlling crack.A method for forecasting overhanging rock failure pattern was proposed.     

Comparative Analysis of Heat Exchange Performance ofEnergy Piles and Borehole Heat Exchangers in GSHP System

Due to their enhanced cost-effectiveness and efficiency over traditional borehole exchangers, energy piles are increasingly used in Ground Sourced Heat Pump (GSHP) projects. In this paper, the structural characteristics of these two types of heat exchangers and their heat transfer mechanism were discussed firstly. The thermal response tests (TRT) were performed on two testing energy piles in one GSHP project in Nanjing, China. The TRT results were then used to verify the numerical simulations, which suggests that the heat exchange performance of energy piles is superior to that of the traditional borehole exchangers. Meanwhile, the numerical simulation method used in this paper was considered applicable to the optimization design of ground heat exchangers in GSHP system.     

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.     

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.     

Parameter Analysis of Effects of Axial Load on the Lateral Response of Piles

Based on the small deformation assumption, the equations of the laterally loaded piles influenced by the axial load were established. The effect of axial load on the lateral response of piles was studied with parameter analysis. The analysis shows that internal force and deformation of laterally loaded pile under axial loading is actually closely linked with the values of axial and lateral loads. In general, the high level axial load should be focused on. It is more significant that the effect of axial load on the internal force and lateral deflection of the upper part of flexible piles, while there is little effect on deep of long-thin pile foundation. The effect of axial load on the lateral response of pile is the largest as coefficient form of subgrade reaction increases linearly, while the effect is minimal as coefficient form of subgrade reaction is a constant. Except in case of buckling, the changes of axial load along the pile direction have little influence on the magnitudes of deflection and moment. The assumption that the axial load is constant with depth can meet the requirements of engineering.     

Strain rate effects on dynamic behavior of reinforcement concrete columns with various reinforcement ratio

The mechnical characteristics of concrete is sensitive to the strain rate and it is crucial to consider the effect of load rates on the behavior of reinforced concrete (RC) structures subjected to dynamic loads such as severe earthquakes. In this study, numerical simulations on the dynamic behavior of typical RC column specimens under dynamic loadings with different load rates were performed. Concrete constitutive model considering the strain rate effects proposed by the CEB code was employed with a fiber model to characterize the nonlinear strain rate dependent behavior of RC columns. The developed dynamic fiber element model was validated by comparing the simulated results of four RC column specimens with the fast loading test results. Results show that the developed fiber element model can predict the behavior of RC columns with acceptable accuracy. After valiating the proposed fiber elemen model considering the strain rate effect, the load carrying capacity of different RC columns with various longitudinal reinforcement ratios and volumetric stirrup ratios were simulated. Results show that the trends of the influences of longitudinal reinforcement ratios and volumetric stirrup ratios on the load carrying capacity of the RC columns under dynamic loadings are different.