Investigating Effect of Tunnel Gate Shapes with Similar Cross Section on Inserted Forces on Its Coverage and Soil Surface Settlement

According to technology development and relative facilitation in digging and underground structures, ways, highways, all types of tunnels, underground train network, and other underground settle, storage are number of structure built and developed in advanced countries. In most situation, tunnel digging operations are done years after its construction or are not recorded in new structures regulations;therefore, this research investigates soil settlement and inserting force to tunnel coverage by limiting studies about effects of tunnel shapes on soil settlement using Plaxis, Seismo Signal, and Seismo Aspect. This study shows that rectangular tunnel has the most settlement in soil surface and circular tunnel has the least settlement but horseshoe tunnel has similar behavior to circular tunnel;however, earth subsidence level by digging this tunnel is more than circular tunnel. In addition, sectional shape has direct effect on inserting forces on tunnel coverage.

Dynamic Mechanisms for Evolution of Mountain Rural Settlements and Soil Conservation in Upper Yangtze River Basin

This paper presents the logic relationship between rural settlement reconstruction and soil conservation in the Upper Yangtze River. Firstly, by introducing the concepts of ＂flow＂ and ＂intercepted flow＂, we probe into the dynamic mechanism on interaction between ecological and environmental system, and then point out that the ＂intercepting sites＂ are physical conditions for establishment of human settlements in mountains. Secondly, by using ecological theories, ＂flow＂, ＂source＂, and ＂sink＂, material cycle and energy flow in mountains have been discussed. Thirdly, according to dissipative structure theory and thermodynamic laws, a hypothesis has been proposed that ＂entropy flow＂ is a dynamic force for settlement evolution. Finally, it is argued that a project for soil conservation is set to control and utilize flows so rural settlements can be supported and farmers＇ life improved.

Settlement prediction and behaviour of pile foundations in deep clayey soil deposits

A new measurement technique is used to determine the settlement of bridge pile foundation and the thickness of deep compressed soft layer. The finite element Plaxis 3D foundation program is used in the analysis with a proposed empirical equation to modify the input parameters represented by the soil compression modulus. The results of the numerical analysis using the proposed empirical equation provide insight to the settlement analysis of pile groups in soft clayey soils; consequently, the finite element Plaxis 3D program can be a useful tool for numerical analysis. The numerical analysis is modified by adjusting the calculation of compression modulus from those obtained under pressure between 100-200 kPa by which the results of the settlement are modified and thus matching the realistic measurements. The absolute error is 3 mm which is accepted compared with the last researches. This scenario can be applied for the similar problems in the theoretical applications of deep foundations.

Analysis of nonlinear settlement for an unsaturated soil under stage continuous loading

A new approach was proposed to describe settlement behavior of an unsaturated soil with subgrade filling for high-speed railway. Firstly, based on Terzaghi consolidation theory, equations considering the variation coefficient of consolidation with void ratio and saturation for consolidation of an unsaturated soil under stage continuous loading were derived, and according to analytical solutions of equations, a formula for settlement computation under stage continuous loading was obtained. Then, combined with the width-to-height ratio of subgrade to compute ground reaction, and by means of in-situ plate loading curves, a correctional approach was presented for the analysis of nonlinear settlement of foundation. Also, the comparison between calculated and measured loadsettlement behavior for an unsaturated soil in Qingdao-Ji'nan high-speed railway was given to demonstrate the effectiveness and accuracy of the proposed approach. It can be noted that the presented solution can be used to predict the settlement of an unsaturated soil foundation under stage continuous loading in engineering design.

Utilization of soil nailing technique to increase shear strength of cohesive soil and reduce settlement

This article deals with the assessment of the soil nailing technique with a vertical inclusion to improve the geotechnical parameters of cohesive soil. A series of unconfined compression tests and direct shear tests were carried out to establish the stressestrain relationship and strength characteristics of the reinforced clay sample by vertical steel nails. The shear strength performance of the new composite material was tested by varying the number of vertical inclusions, the embedment depth and the alignment radius. The results confirmed that the vertical bars/inclusions shared the vertical applied load with clay. Increase in the number of vertical inclusions significantly increases the shear strength and the stiffness with a remarkable reduction in settlement. When the clay samples were reinforced with six inclusions along the perimeter, the shear strength was increased to 231% for the embedment depth ratio equal to 0.85. To obtain the optimum effect in eliminating shear failure, the vertical inclusions should be extended to a deeper zone with sufficient numbers. It has been found that the vertical inclusions significantly influence the shear strength, and the brittle or general shear failure of the unreinforced sample can be diverted to partial/plastic shear failure.

Effect of Wet Settlement on Mercury in Alpine Soil in Mercury Mining Area

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Study on temperature field and settlement of thawing soil under static and dynamic loading

A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The results demonstrate： （1） the temperature field distribution of the thawing soil was not significantly influenced by the loading form under the tested loading conditions; similar results were obtained for samples at different dynamic loading frequencies and different dynamic loading ampli- tudes, which verified the independence of loading form and temperature field; （2） changed temperature field distributions were found in thawing soil with different cooling and thawing temperatures, and the cooling and thawing temperature of the samples were the main factors affecting their temperature distributions; （3） under the tested conditions, thawing set- tlements were little influenced by the thawing temperature and the dynamic loading frequency; and （4） a linear relation- ship existed between the thawing settlement and the cooling temperature, and a logarithmic function could be used to describe the relationship between the thawing settlement and the loading amplitude.

A new approach for time effect analysis of settlement for single pile based on virtual soil-pile model

A new approach is proposed to analyze the settlement behavior for single pile embedded in layered soils.Firstly,soil layers surrounding pile shaft are simulated by using distributed Voigt model,and finite soil layers under the pile end are assumed to be virtual soil-pile whose cross-section area is the same as that of the pile shaft.Then,by means of Laplace transform and impedance function transfer method to solve the static equilibrium equation of pile,the analytical solution of the displacement impedance function at the pile head is derived.Furthermore,the analytical solution of the settlement at the head of single pile is theoretically derived by virtue of convolution theorem.Based on these solutions,the influences of parameters of soil-pile system on the settlement behavior for single pile are analyzed.Also,comparison of the load-settlement response for two well-instrumented field tests in multilayered soils is given to demonstrate the effectiveness and accuracy of the proposed approach.It can be noted that the presented solution can be used to calculate the settlement of single pile for the preliminary design of pile foundation.

Nonlinear analysis of pile load-settlement behavior in layered soil

A simplified approach is presented to analyze the single pile settlement in multilayered soil. First, a fictitious soil-pile model is employed to consider the effect of layered soil beneath pile toe on pile settlement behavior. Two approximation methods are proposed to simplify the nonlinear load transfer function and simulate the nonlinear compression of fictitious soil-pile, respectively. On this basis, an efficient program is developed. The procedures for determining the main parameters of mathematical model are discussed. Comparisons with two well-documented field experimental pile loading tests are conducted to verify the rationality of the present method. Further studies are also made to evaluate the practicability of the proposed approach when a soft substratum exists, and the results suggest that the proposed method can provide a constructive means for assessing the settlement of a single pile for use in engineering design.

长期堆载预压处理软土地基效果评价

为评估某园区10 a长期堆载预压后,场地后续沉降对拟建管线的影响,通过室内试验和现场试验对堆载预压处理后的场地进行系统评价,分别采用双曲线法与有限元法对后续沉降进行预测。结果表明:场地堆载预压10 a后各地层物理力学参数明显改善,但其中淤泥层性质相对较差,是场地后续沉降发生的主要地层;经过10 a堆载,场地主固结沉降基本完成,固结度达到95.5%,说明长期堆载预压效果较好;对于堆载多年后的场地,在进行后续沉降数值计算时,采用弹性模型并选用现场试验获得的参数进行计算,计算结果与实测数据较好吻合,场地剩余平均沉降量在15.4 cm左右;园区道路管线可采取常规预防措施。

上覆软弱路基加固对既有地铁隧道沉降的影响规律

为研究道路施工引起下方既有地铁隧道的沉降问题,在地铁隧道上方斜穿施工道路的基础上,进行了现场隧道沉降变形实测研究,分析了道路在路基注浆加固、路床和路面结构层施工阶段中地铁隧道的沉降曲线。建立地铁隧道-土体-道路模型对道路施工的注浆加固过程及路床和路面结构层施工进行模拟,通过比较地铁隧道沉降计算结果与现场实测值,验证了该精细化模型的准确性。基于此,分析了路床和路面结构层总施工厚度、道路土体性质、隧道下卧土层、隧道衬砌强度等关键参数对地铁隧道的沉降影响规律。结果表明:地铁隧道的沉降值与施工厚度呈正相关关系;道路的存在对隧道的沉降影响越小,其弹性模量和泊松比对地铁隧道沉降几乎没有影响;卧土层的弹性模量越大,土层越不易变形,且地铁隧道沉降越小;衬砌弹性模量增大对地铁隧道沉降影响反而越小。

基于桩-土界面剪切特性的单桩沉降和承载问题研究

近年来,西北地区出现了许多高填方场地,为减小建筑物基础的不均匀沉降,基础类型广泛使用桩基础。与一般场地不同,黄土填方场地中的单桩桩周土受力后仍会产生较大的变形,该类场地单桩沉降机制复杂。桩顶总沉降计算是桩基设计的重要依据,为此,建立了高填方黄土场地单桩桩顶总沉降计算模型。基于传统的荷载传递法和剪切位移法,分别考虑桩-土界面的桩-土相互作用和桩-土界面外剪切带土体的剪切变形。依据桩端边界,将单桩类型分为摩擦桩和端承摩擦桩,分别建立桩周土弹性阶段和塑性阶段的桩身位移控制微分方程,结合边界条件进行求解,得到桩身位移、轴力、侧摩阻力,并通过弹塑性理论求解了桩周土剪切带土体剪切变形,进而通过叠加原理求得桩顶总沉降。用桩长与桩周土塑性发展深度的比值,定义了桩基承载力安全系数K。通过算例分析与现场试验数据对比分析,研究结果表明:使用新的模型计算得到的桩顶总沉降与现场试验结果相近;当桩顶荷载较小、桩周土处于弹性阶段时,桩端边界对桩身轴力、位移和侧摩阻力影响很小,但桩周土进入塑性滑移阶段后,桩端边界的影响开始变大,考虑桩端土的承载能力会极大提高单桩极限承载力;建立了将荷载传递法和剪切位移法综合起来的计算模型,不仅可以考虑桩-土界面的相对滑移,还可以计算桩-土界面外土体剪切带的剪切变形,使得桩顶总沉降计算更加精确,可为类似场地中单桩沉降的分析与控制提供一定的参考。

Study on Optimization of Design Parameters for Precast Pipe Pile Treatment of Soft Soil Subgrade on the Jianghan Plain

The soft soil in the Jianghan Plain is characterized by a high water content, liquid limit, sensitivity, porosity ratio, and organic matter content and low strength and is commonly known as “five highs and one low” soft soil. Thus, the construction of expressways in this area is likely to cause subgrade settlement. The manuscript investigated the influence of the design parameters of precast pipe piles on the soft ground treatment in the Jianghan Plain based on the case of the soft soil subgrade project of the Xiaogan south section of the Wuhan city ring expressway, China. Midas GTS NX 2019 finite element software was used to analyse the settlement pattern of the subgrade under the variations in pile length, pile spacing and pile diameter. The results show that precast pipe piles are effective in reducing the settlement of soft soil subgrades with a high compressibility and water content;the soft foundation settlement decreases with increasing pile length and pile diameter and decreasing pile spacing. As the pile tip is embedded in the bearing stratum, the settlement of the soft foundation is greatly affected by the variations in pile length and pile spacing while slightly influenced by the variation in pile diameter;in combination with the curve fitting obtained from the real-time monitoring data, the analysis concludes that the soft foundation treatment plan with a pile length of 15 m, pile spacing of 1.2 m to 1.5 m and pile diameter of 0.6 m can better contain the soft soil subgrade settlement in this section.

河谷区多层软土地基强夯处治分析

文章依托高速公路多层软土地基强夯处治项目,在施工现场选取具有代表性的监测断面开展现场监测,检验河谷区多层软土地基强夯处治效果。由监测数据得出,在强夯处治和路基填筑施工阶段,地基分层沉降、土压力、孔隙水压力和侧向位移增幅均较大,工后逐渐趋于稳定,可说明强夯处治后软基承载力得到有效提升,路基整体结构稳定,加固效果良好。

虹吸排水法处理软土地基的水位与沉降计算模型

软土具有渗透性差、承载力低等特性,软土地基的处理一直是岩土工程中的一大难题。利用虹吸免动力排水的特点,可将虹吸排水法应用于软土地基处理中,达到改善土体性质的目的。本文针对虹吸排水法独特的定降深降水模式,先基于离散化的Theis井流模型以及非线性的分层总和法,构建了以孔隙率为核心、渗透系数与压缩模量随固结情况改变的水位与沉降动态计算模型,并与数值模拟结果对比,然后从土体渗透系数、排水板间距以及场地大小3个方面对虹吸排水法处理软土地基的效果进行了分析。结果表明:数值模拟结果验证了计算模型的可靠性,对于浙江沿海不同渗透系数的土体,虹吸排水法均可起到良好的排水固结作用;调整排水板间距可对排水固结时间以及地下水位线起到显著控制作用;排水带来的附加应力随着场地面积的增大向土体深处延伸,对于面积50 m×50 m大小的场地,有效影响深度可达到地表以下27.31 m,远远超出虹吸扬程的极限。在实际的大面积软土地基处理中,虹吸排水法可发挥更好的作用。

类矩形盾构隧道开挖引发土体沉降解析解研究

类矩形盾构隧道施工可能会导致明显的土体沉降,并进一步影响周围既有建筑物的安全。基于Verruijt解和积分法推导得到类矩形盾构隧道开挖作用下的土体响应解析解,并充分考虑土体等量径向收缩、类矩形隧道竖向、水平向以及旋转位移4个变形分量的影响,以全面描述复杂施工或地层情况下类矩形盾构开挖引发的土体位移模式。利用实际工程实测数据验证解析解的有效性,并通过参数分析研究各个变形参数对地表土体沉降的影响。研究结果表明,解析理论计算结果与实测数据较为吻合,可较好地评估类矩形盾构引发的土体沉降,类矩形隧道的水平位移和旋转位移会使地表沉降呈现非对称形态,并会使最大地表沉降增大。

砂砾土振动体变评价方法与离心机模型试验验证

2008汶川地震出现了砂砾土大范围液化致灾现象,现场震害调查表明砂砾土场地存在砾石效应影响,现有砂土场地的震后沉降评价方法不适用于砂砾土场地。对此,在“张-社本”振动体变评价方法的基础上进一步发展了考虑砾石含量的砂砾土振动体变评价方法,然后开展动三轴试验确定评价方法中的相关参数,最后开展3组典型砾石含量的砂砾土地基离心机振动台模型试验对评价方法的可靠性进行验证。试验结果表明,砾石含量越高,振动引起的场地沉降变形越小;砂砾土振动体变评价方法可以较为准确地预测新近沉积砂砾土场地的震后沉降,但对存在地震历史影响的砂砾土场地,本文提出的评价方法较为保守,建议进一步发展考虑地震历史效应的砂砾土振动体变评价方法。

冲击荷载下层状饱和无粘性土动孔压发展模式研究

为揭示饱和无黏性土层在冲击荷载作用下动孔压发展模式及其受土层条件的影响,基于自主研制的冲击荷载加载台装置,开展了不同土层条件层状饱和土冲击试验,对动孔压发展特征及土体沉降等进行了分析。结果表明:冲击荷载作用下,无粘性饱和土体动孔压发展呈明显两阶段,即瞬态响应和稳态响应阶段,其中稳态响应阶段动孔压发展又经历缓慢下降及快速下降两过程。单层土情形下,饱和砂土在冲击荷载后动孔压发生骤增,随着粒径的增大,动孔压峰值越大,但其消散用时则随粒径的增大而减小;双层土情形下,动孔压稳态响应阶段因上下土层渗透系数变化,在其下层土动孔压下降过程产生明显变化;当含有相对弱透水夹层时,受弱透水层影响,各测点动孔压下降段几乎在同一时刻均出现明显转折平台,使其下降的速率明显变小,且该现象弱透水层以上土体较其下部土体更为显著;含夹层时,试验过程出现明显非均匀分布的“水膜”,最大厚度可达2 cm左右。同时,每次冲击荷载下均伴随明显的土体沉降,随着冲击次数增加,土层沉降变化量逐渐减小。

软土场地双线盾构地铁隧道施工数值模拟分析

以天津软土场地某双线盾构地铁隧道为研究对象,数值模拟了地铁盾构隧道掘进过程,研究不同计算方法、不同隧道埋深以及不同双线净距对地表沉降的影响。研究结果表明,双线净距越大、隧道埋深越小时,等效圆法所得的地表沉降结果与工程经验相差较大,不适用于双线隧道盾构施工地表沉降预测;叠加法能考虑双线隧道的相互干扰作用,获得地表W形沉降曲线;双线净距较大且隧道埋深较小时,地表沉降呈W形沉降模式,其他情况下均为V形沉降模式,地表沉降最大值随着隧道埋深和双线净距的增大而减小。

地下管廊深基坑回填土层沉降特征研究

为研究城市地下综合管廊回填后路面的沉降规律,依托雄安新区某管廊工程,运用现场回填土层沉降变形物联网智能监测与数值模拟计算方法,建立了综合管廊基坑回填施工过程的力学计算模型,对不同工况下的路面沉降与管廊结构的应力、应变情况进行分析。研究结果表明:1)回填土体的累积沉降量及各土层间的沉降差随着回填土层厚度的增大而增大。2)在阶梯法回填施工中,施工回填段数越多,路面沉降量及不均匀沉降程度越小,管廊结构变形越大。3)施工后的路面沉降量随着压实度的增大而显著减小。相关模拟方法与研究成果可为类似综合管廊回填工程的方案设计提供参考依据。