Experimental and numerical interpretation on composite foundation consisting of soil-cement column within warm and ice-rich frozen soil

Affected by climate warming and anthropogenic disturbances, the thermo-mechanical stability of warm and ice-rich frozen ground along the Qinghai-Tibet engineering corridor(QTEC) is continuously decreased, which may delay the construction of major projects in the future. In this study, based on chemical stabilization of warm and icerich frozen ground, the soil-cement column(SCC) for ground improvement was recommended to reinforce the foundations in warm and ice-rich permafrost regions. To explore the validity of countermeasures mentioned above, both the original foundation and the composite foundation consisting of SCC with soil temperature of -1.0℃ were prepared in the laboratory, and then the plate loading tests were carried out. The laboratory investigations indicated that the bearing capacity of composite foundation consisting of SCC was higher than that of original foundation, and the total deformation of original foundation was greater than that of composite foundation, meaning that overall stability of foundation with warm and ice-rich frozen soil can be improved by SCC installation. Meanwhile, a numerical model considering the interface interaction between frozen soil and SCC was established for interpretating the bearing mechanism of composite foundation. The numerical investigations revealed that the SCC within composite foundation was responsible for the more applied load, and the applied load can be delivered to deeper zone in depth due to the SCC installation, which was favorable for improving the bearing characteristic of composite foundation. The investigations provide the valuable guideline for the choice of engineering supporting techniques to major projects within the QTEC.

Pile-soil stress ratio in bidirectionally reinforced composite ground by considering soil arching effect

To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.

Development of the nano-composite cement:Application in regulating grouting in complex ground conditions

Improvement of the fluidity and setting time of grouting materials has been recognized as an effective approach of seepage prevention in foundation works, and it is quite common to be used for handling severe leakages in complex ground conditions, such as loose, broken and fully fissured stratum. For the purposed of better meeting the engineering requirements, experimental studies were conducted in this study with focus on the nanocomposite grouting materials and the related controlled grouting technology. As compared with the commonly used silicate-sulpho-aluminate composite cement, which is characterized by relatively poor rheological property, quick setting time and low strength, the most suitable nano-material with proper reactants were selected intentionally to improve the mentioned attributes of composite cement. Due to the setting time and strength of the targeted cement slurry behaving with poor performance of harmonization to engineering construction problems, hydration synergistic effect of these composites were investigated in our experiments. Results showed that the properties of grouting materials, including initial fluidity, setting time, ideal right-angle thickening, and early strength and late strength were sufficient to produce an expected grouting application. It is therefore advocated that the refined grouting material could provide a better solution to fix grouting problems in complex ground cementing operations.

Single-phase earth fault current distribution between optical fiber composite overhead ground wire and ordinary ground wire in transmission system

It is important for the safety of transmission system to accurately calculate single-phase earth fault current distribution.Features of double sided elimination method were illustrated.Quantitative calculation of single-phase earth fault current distribution and case verification were accomplished by using the loop method.Influences of some factors,such as single-phase earth fault location and ground resistance of poles,on short-circuit current distribution were discussed.Results show that:1) results of the loop method conform to those of double sided elimination method;2) the fault location hardly influences macro-distribution of short-circuit current.However,current near fault location is evidently influenced;and 3) the short-circuit current distribution is not so sensitive to the ground resistance of poles.

Research and Application of Ecological Outdoor Ground Structure with Composite Water Storage and Drainage Function

In order to solve the problems of surface runoff increase,water accumulation in rainy days and urban heat island effect,an ecological outdoor ground structure with composite water storage and drainage functions was studied and applied in this paper:Through the comprehensive design of road ground,road inspection well,garden inspection well and drainage pipe network,it can quickly store and drain ground water,alleviate the urban heat island effect,realize plant infiltration irrigation,and achieve the purpose of saving water and energy.

Verification of Seismic Performance of Pile Foundation in Composite Ground through Experimental and Numerical Methods

A new construction method of pile foundation in composite ground, in which, prior to installing piles, the ground is improved around the heads of the piles in soft ground or ground subject to liquefaction, which is introduced in this paper. This construction method uses a combination of pile foundation construction together with common ground improvement methods, including deep mixing, preloading and sand compaction piling, and it is referred to as the composite ground pile method. Since an artificial ground with relatively high rigidity comparing with that of the original ground was formed around the pile in this method, and the seismic performance has not been made clear, thus the seismic performance of piles in composite ground was systematically analyzed through a series of centrifuge model tests and numerical analyses by using dynamic nonlinear finite element method, and a verification method for the seismic performance of piles in composite ground was proposed on the basis of the experimental and numerical results.

Microstructure and Composition of Hydration Products of Ordinary Portland Cement with Ground Steel-making Slag

The effect of ground steel-making slag on microstructure and composition of hydration products of ordinary Portland cement (OPC) was investigated by mercury intrusion porosimetry (MIP),X-ray diffraction (XRD) and differential thermal analysis (DTA).Results show that ground steel-making slag is a kind of high activity mineral additives and it can raise the longer-age strength of OPC mortar.The total porosity and average pore diameter of OPC paste with ground steel-making slag increase with the increase of the amount of ground steel-making slag replacing OPC at various ages,while after 28 days most pores in OPC paste with ground steel-making slag do not influence the strength because the diameter of those pores is in the rang of 20 to 50nm.The hydration mechanism of ground steel-making slag is similar to that of OPC but different from that of fly ash and blast furnace slag.The hydration products of ground steel-making slag contain quite a lot of Ca(OH) 2 in long age.

Consolidation analysis of composite foundation with partially penetrated cement fly-ash gravel(CFG) piles under changing permeable boundary conditions

Based on the double-layered foundation theory, the composite ground with partially penetrated cement fly-ash gravel(CFG) piles was regarded as a double-layered foundation including the surface reinforced area and the underlying untreated stratum. Due to the changing permeability property of CFG piles, the whole consolidation process of the composite ground with CFG piles was divided into two stages, i.e., the early stage(permeable CFG pile bodies) and the later stage(impermeable pile bodies). Then, the consolidation equation of the composite foundation with CFG piles was established by using the Terzaghi one-dimensional consolidation theory. Consequently, the unified formula to calculate the excess pore water pressure was derived with the specific solutions for the consolidation degree of composite ground, reinforced area and underlying stratum under instant load obtained respectively. Finally, combined with a numerical example, influencing rules by main factors(including the replacement rate m, the treatment depth h1, the permeability coefficient Ks1, Kv2 and compression modulus Es1, Es2 of reinforced area and underlying stratum) on the consolidation property of composite ground with CFG piles were discussed in detail. The result shows that the consolidation velocity of underlying stratum is slower than that of the reinforced area. However, the consolidation velocity of underlying stratum is slow at first then fast as a result of the transferring of effective stress to the underlying stratum during the dissipating process of excess pore water pressure.

Deformation and failure modes of composite foundation with sub-embankment plain concrete piles

With the development of high-speed railway in China, composite foundation with rigid piles has become a stamdard solution of meeting the high requirements of stability and post-construction settlement of embankment on soft subgrade. Among several im- provement pattems, plain concrete piles have been extensively used to treat soft ground supported embankment. To investigate the deformation and failure modes of unimproved soft ground and soft ground reinforced by sub-embankment plain concrete piles, and to learn the influences of track and vehicle load, the effect of pile spacing, as well as the compression moduli of soil layers and upper load condition on the failure modes, a series of centrifuge model tests were performed. Test results indicate that the dis- placement of unimproved soft ground under the embankment increases continuously as embankment, track and train loading, and slip circle failure takes place. The deformation law of soft ground reinforced by sub-embankment plain concrete piles depends on pile spacing, compression modulus of the soft ground, and loading conditions. It was also found that plain concrete piles show displacement and failure patterns depending on its location, compression modulus of soft soil around the pile, and loading condi- tions. Furthermore, the evaluation of improved ground stability as well as the model test procedure is also presented.

Failure analysis and control measures of deep roadway with composite roof:a case study

There is great variation in the lithology and lamination thickness of composite roof in coal-measure strata;thus,the roof is prone to delamination and falling,and it is difficult to control the surrounding rock when developing roadway in such rock strata.In deep mining,the stress environment of surrounding rock is complex,and the mechanical response of the rock mass is different from that of the shallow rock mass.For composite-roof roadway excavated in deep rock mass,the key to safe and efficient production of the mine is ensuring the stability of the roadway.The present paper obtains typical failure characteristics and deformation and failure mechanisms of composite-roof roadway with a buried depth of 650 m at Zhaozhuang Coal Mine(Shanxi Province,China).On the basis of determining a reasonable cross-section shape of the roadway and according to the failure characteristics of the composite roof in different regions,the roof is divided into an unstable layer,metastable layer,and stable layer.The controlled unstable layer and metastable layer are regarded as a small structure while the stable layer is regarded as a large structure.A superimposed coupling support technology of large and small structures with a multi-level prestressed bearing arch formed by strong rebar bolts and highly prestressed cable bolts is put forward.The support technology provides good application results in the field.The study thus provides theoretical support and technical guidance for ground control under similar geological conditions.

Strong motion simulation by the composite source modeling:A case study of 1679 M8.0 Sanhe-Pinggu earthquake

In this study, a composite source model has been used to calculate the realistic strong ground motions in Beijing area, caused by 1679 Ms8.0 earthquake in Sanhe-Pinggu. The results could provide us the useful physical parameters for the future seismic hazard analysis in this area. Considering the regional geological/geophysical background, we simulated the scenario earthquake with an associated ground motions in the area ranging from 39.3°N to 41. 1°N in latitude and from 115.35°E to 117.55°E in longitude. Some of the key factors which could influence the characteristics of strong ground motion have been discussed, and the resultant peak ground acceleration （PGA） distribution and the peak ground velocity （PGV） distribution around Beijing area also have been made as well. A comparison of the simulated result with the results derived from the attenuation relation has been made, and a sufficient discussion about the advantages and disadvantages of composite source model also has been given in this study. The numerical results, such as the PGA, PGV, peak ground displacement （PGD）, and the three-component time-histories developed for Beijing area, have a potential application in earthquake engineering field and building code design, especially for the evaluation of critical constructions, government decision making and the seismic hazard assessment by financial/insurance companies.

Mica Filled PVC Composites: Performance Enhancement in Dielectric and Mechanical Properties with Treated/Untreated Mica of Different Particle Size and Different Concentration

Polyvinyl chloride (PVC) of different grades is the second most commonly used polymer for fabrication of electric cables and wires after polyethylene. Cables of domestic and industrial use of various capacities are fabricated using different compounds of PVC. Mica is useful particulate filler extensively used to enhance the performance of many polymeric materials. It surface resistance and arc resistance improving its mechanical properties. In the present research work mica filled PVC composites of different concentrations were prepared using untreated and surface treated water ground mica of different particle size. Mica filled PVC composites were compounded for various compositions and test samples were prepared using compression moulding process. These samples were tested for electrical insulation and mechanical properties. The results shows enhancement in dielectric properties with improvement in Young’s modulus, stiffness, reduction in elongation at break and slight increase in shore D hardness of composites. Scanning electron microscopy was used to test the morphology of the samples which has shown proper distributions and adhesion of the filler mica in PVC matrix. There was some effect of surface treatment of mica on its mechanical and dielectric properties of the composite.

Consolidation of high replacement ratio stone column-reinforced ground:Analytical solutions incorporating clogging effect

The utilization of stone columns has emerged as a popular ground improvement strategy,whereas the drainage performance can be adversely hampered by clogging effect.Despite the ample progress of calculation methods for the consolidation of stone column-improved ground,theoretical investigations into the clogging effect have not been thoroughly explored.Furthermore,it is imperative to involve the column consolidation deformation to mitigate computational error on the consolidation of composite ground with high replacement ratios.In this context,an analytical model accounting for the initial clogging and coupled time and depth-dependent clogging of stone columns is established.Then,the resulting governing equations and analytical solutions are obtained under a new flow continuity relationship to incorporate column consolidation deformation.The accuracy and reliability of the proposed model are illustrated by degradation analysis and case studies with good agreements.Subsequently,the computed results of the current study are juxtaposed against the existing models,and an in-depth assessment of the impacts of several crucial parameters on the consolidation behavior is conducted.The results reveal that ignoring column consolidation deformation leads to an overestimate of the consolidation rate,with maximum error reaching up to 16%as the replacement ratio increases.Furthermore,the initial clogging also has a significant influence on the consolidation performance.Additionally,the increment of depth and time-clogging factors a and b will induce a noticeable retardation of the consolidation process,particularly in the later stage.

Study on Ground Fissures and Land Subsidence Induced by Seepage Deformation in Xi'an

There are lots of theories about the causation of ground fissures in Xi’an,such as the tectonics theory,the excessive groundwater exploitation theory and the compositive theory. Based on the construction of the geologic environment monitoring network in Guanzhong urban agglomeration,the latest survey of ground fissures and land subsidence in Yuhuazhai in Xi’an shows that the extensive piping and quicksand in self-supply wells is a factor to induce ground fissures and land subsidence. It is suggested that the seepage deformation caused by high hydraulic gradient leads to sand gushing and changes some aquifers into the composite aquifer,which is the main factor to induce ground fissures and land subsidence. The development characteristics of ground fissures and land subsidence caused by seepage deformation were summarized. The results will supply new schemes and methods for the causation of land subsidence and ground fissures in Xi’an and lay out a clear road map of measures to control land subsidence and ground fissures.

On Composition Devices in Modernist Architecture： The Case of De Vore House and House II

This paper examines general composition problems in modernist architecture by means of a close analysis of the formal principles and devices at work in two exemplary mid twentieth century projects, De Vore House by Louis Kahn （1901-1974） and House II by Peter Eisenman （1932）. The goal of the paper is to inaugurate a larger research project into the design processes and spatial-formal effect at work in modernist architecture. The methodology is primarily visual, and postulates a range of form relationships for the creation and interpretation of works of architecture. Following an introduction to the research problem, an analysis of the case study projects is undertaken according to three themes： plan disposition, ambiguity in wall and column relations, and volume as impacting on movement. A concluding section summarizes the findings and suggests future lines of research. The paper＇s significance lays in its contributions to discussions around architectural practice at a specific moment in modernist architecture＇s mid twentieth century trajectory, to our understanding of a number of formal strategies and their resulting architectural effects, and to scholarship on the practice and theories of Kahn and Eisenman.

地基处理技术现状与发展

近年来我国的基础设施建设规模不断扩大,坚实的地基是确保工程建设安全与韧性的关键。因此,地基处理技术与工程品质之间的关联性愈发受到关注,这促进了地基处理技术的持续进步与发展,进而不断涌现出新的理论、技术和设备。文章简要阐述了地基处理的分类方法与发展特点,回顾了各类地基处理技术的研究现状,具体介绍了近年来复合地基技术、排水固结法、土工合成材料、高聚物注浆、固化剂、特殊土地基、大面积高填方地基和抗震地基处理技术等方面的新进展,归纳总结了地基处理智能设备、设计理论、评价方法和规范编制的发展情况。在现阶段信息化浪潮不断来袭、可持续发展作为永恒主题的新形势下,提出了地基处理技术应不懈追求“韧性、绿色、智能、人文”的品质提升的核心议题,探讨了地基处理行业各个方面的发展方向与未来展望,以期为地基处理领域的研究与技术人员提供参考和借鉴。

路堤下CFG桩复合地基稳定性分析方法及试验验证

路堤下CFG桩复合地基稳定性分析方法尚不完善。基于桩体抗滑段受力平衡条件,开展考虑桩承水平净推力、桩承轴力和桩顶筋带约束作用的桩体抗滑效应分析。由CFG桩弯曲强度确定桩承极限水平净推力,通过引入桩体破坏不同步性的桩承水平净推力系数,提出能良好反映CFG桩弯曲破坏模式下复合地基稳定性分析的桩承综合力矩法,并结合土工离心模型试验进行验证。案例研究表明:路基工程CFG桩复合地基的抗滑力矩中,土体抗滑力矩占比54.8%~79.8%,桩体抗滑力矩占20.2%~35.5%,筋带抗滑力矩约9.7%;对于桩体抗滑力矩,由桩承轴力提供的抗滑力矩占比达86.9%~91.9%,由桩体弯曲强度和桩顶筋带约束作用引起的抗滑力矩占比约8.1%~13.1%;针对离心模型试验的极限和临界状态,采用桩承综合力矩法计算的地基稳定系数在0.98~1.06之间,适用性较好。

碎石桩复合地基非等应变非线性固结特性分析

现有碎石桩复合地基固结理论通常基于等应变假设,与工程实际情况有出入。基于分段线性差分法,建立了一种考虑非等应变刺入修正和任意桩土非线性本构关系的碎石桩复合地基非线性固结模型。该模型可以考虑桩土自重、涂抹区、井阻效应和变荷载,可以计算碎石桩向垫层或下卧层的刺入并对等应变假设进行修正,可以分析桩土附加应力沿深度方向的衰减,以及任意的非线性压缩性及渗透性关系。与工程实测数据对比发现,考虑非等应变修正的模型计算值与工程实测值基本吻合。结合算例分析,进一步研究了垫层及下卧层模量、桩土竖向应力衰减和应力路径对碎石桩复合地基土体固结特性的影响,结果表明:碎石桩向垫层或下卧层刺入使复合地基桩土应力比减小、沉降量增大、固结速率减缓;忽略桩土竖向应力衰减虽对固结速率影响不大,但会高估复合地基沉降变形;不同应力路径对碎石桩复合地基固结特性影响显著,简化的土层压缩性关系将对分析结果带来较大误差。

多胞圆管夹芯组合板落锤冲击试验及数值仿真

为了应对煤矿巷道冲击地压下支架结构破坏严重的问题,提出了一种多胞圆管夹芯组合板。该组合板可与煤矿巷道金属支架结合,通过溃缩变形吸能共同抵御冲击荷载。共设计了4个不同芯层厚度夹芯组合板试件的落锤冲击试验,并建立了有限元模型,基于试验验证了该数值模型,开展了多胞圆管夹芯组合板的冲击响应和吸能特性的参数分析。研究结果表明,冲击作用下,多胞圆管夹芯组合板面板呈现圆盘状凹陷,芯层胞体和十字肋发生了褶皱和下陷变形,各个腔室协同工作、相互支撑,并通过塑性变形吸能。同时底部冲击反力的峰值总是滞后且低于落锤冲击荷载峰值,在多次冲击条件下,该组合板也能展现出良好的吸能缓冲效果。多胞圆管夹芯组合板可吸收超过90.00%的冲击能量,其中65.00%以上能量由芯层结构吸收。芯层厚度从0.5 mm增加到2.0 mm,芯层部分吸收能量的占比增大了24.17%,相反面板吸能效率递减,减幅为17.17%,芯层厚度减小可降低峰值冲击荷载,芯层厚度为1.0 mm时吸能效果较好。面板厚度对吸能性能影响较小,建议其厚度选择与芯层厚度相近。冲击能量一定情况下,改变落锤质量和冲击速度对结构动力冲击性能和吸能效率的影响很小。

地震和高铁共同作用下桩网复合地基振动特性

为研究地震和高铁列车荷载共同作用下桩网复合地基振动特性,通过建立轨道-路堤-桩网复合地基三维有限元计算模型,分别与实测数据和一维波动理论对比验证模型的正确性。通过对比不同荷载工况下地面位移和加速度时频振动曲线,分析地震和高铁两动载共同作用时不同车速下桩网复合地基时频振动特性,研究桩体模量对桩网复合地基减震效果的影响。研究表明,Hollister地震荷载和高铁荷载共同作用下,距轨道中心1 m处地面振动位移由地震荷载主导,地面振动加速度由列车荷载主导;20 Hz以下地面低频振动由高铁和地震荷载共同控制,地面高频振动主要由列车荷载控制。Lytle Creek地震荷载和高铁荷载共同作用下,桩网复合地基地面振动位移和加速度峰值均大于高铁荷载单独作用下的值;增加桩体模量对高铁荷载单独作用和两动载共同作用下桩网复合地基地面振动均有减振效果,但两动载共同作用下增加桩体模量对地面减振效果比高铁荷载单独作用下弱。