Wireless remote spatiotemporal monitoring of high-fill foundation deformation

The spatial and temporal deformation patterns and deformation control indicators of highfill foundations directly affect the design,construction and operational safety of high-fill projects.In situ monitoring can comprehensively reflect the deformation of high-fill during and after construction.In this paper,we have first designed and installed an integrated wireless remote monitoring system for high-fill to achieve real-time dynamic monitoring of settlement,pore water pressure and soil pressure of the fill foundation.Based on the monitoring results of nearly one year of the construction period and two years after construction,it was found that the deformation amount and deformation rate of the high-fill foundation showed a non-linear growth relationship with the filling rate and filling height.The settlement deformation of the high-fill foundation during the loading period was mainly dominated by the original foundation soil,accounting for 54.4%of the total settlement on average;the settlement deformation during the post-construction period was mainly dominated by the filling body,accounting for 77.04%of the total settlement on average,and the settlement deformation during the post-construction period mainly occurred in the first year after construction.The analysis of the deformation mechanism suggests that the deformation of the filling body is dominated by exhaust consolidation during the loading period and drainage consolidation during the post-construction period;the deformation of the original foundation soil is dominated by drainage consolidation during the loading period and drainage consolidation develops slowly during the post-construction period.It is recommended that the original foundation should be reinforced before the large area filling construction,and that the filling rate should be strictly controlled during construction.The research results can provide a scientific basis for deformation calculation and stability assessment of high-fill foundations.

Soil erosion and its causes in high-filling body:A case study of a valley area on the Loess Plateau,China

Large-scale land consolidation projects(LCPs)have been carried out on the Loess Plateau to increase the area of agriculture land.The newly created land is prone to soil erosion under the effects of water and gravity.Taking a typical high-filling body(HFB)formed by LCPs in Yan’an,China as the subject,this study comprehensively investigated the types and causes of soil erosion with multiple methods of field investigation,on-site monitoring and laboratory tests.Results showed that the HFB presented a composite pattern of soil erosion with multiple types mainly including underground erosion,mixed water-gravity erosion,seepage erosion,and scouring erosion.The type of erosion varied spatially in different parts of the HFB depending on the dominant factors,mainly including the groundwater state,rainfall,runoff,gravity action,topography,and soil erodibility.The underground erosion mainly occurred at the positions with higher groundwater level and larger hydraulic gradient,while scouring erosion mainly occurred at the positions with extensive interactions of surface runoff,channel slope gradient and soil properties.And near the leading edge of the top of the slope,a band of mixed watergravity erosion occurred owing to the effects of water and gravity.In addition,nearly saturated soils at the toe of HFB displayed groundwater exfiltration and slope-face slumping.Based on our findings on the causes and variation of soil erosion for the HFB,we proposed the following erosion prevention and control measures to protect the LCPs on the Loess Plateau:to construct drainage ditches and blind ditches to form a complete drainage system,plant alfalfa on the top platform to increase rainfall interception and reduce surface runoff,set seepage ditches and plant deep-rooted plants at the toe of the slope to improve slope toe stability,monitor groundwater level and slope deformation to learn the erosion dynamics and slope stability,and optimize the geometry of HFB such as the slope gradient and slope steps to reduce soil erosion.

Static load test and load transfer mechanism study of squeezed branch and plate pile in collapsible loess foundation

As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundation failure. Pile is a popular foundation used in collapsible loess. The squeezed branch and plate pile is a new type of pile developed in recent years and has not be used in a project before. In this paper three squeezed branch and plate piles are tested in collapsible loess after immersion processing. The results may be used for reference in similar construction project, and to provide theoretical references for de- signing of the squeezed branch and plate piles in engineering practice.

Influence of Collapsible Loess on Foundation and its Treatment Strategy

The properties of collapsible loess are complex.The self-gravity of overlying soil,sei gravity stress and additional stress act together,which will damage the soil structure and lead to the deformation of the soil structure.Collapsible loess is widely distributed in Northwest and Northeast China.A series of problems caused by its structural characteristics will affect the quality of foundation construction.Therefore,construction enterprises need to deeply study the foundation treatment measures of collapsible loess,so as to avoid the uneven settlement after the construction of collapsible yellow soil foundation.This paper analyzes from the judgment and classification of collapsible loess,studies the impact of collapsible loess on building fbxmdation construction,and explores the specific construction treatment measures of collapsible loess,in order to promote the effective application of foundation construction.

Numerical study on settlement of high-fill airports in collapsible loess geomaterials:A case study of Lüliang Airport in Shanxi Province,China

Foundation settlement is of great significance for high-fill engineering in collapsible loess areas.To predict the construction settlement of Lüliang Airport located in Shanxi Province,China,a plane strain finite element method considering the linear variation in the modulus,was carried out in this paper based on the results of geotechnical tests.The stress and deformation of four typical sections caused by layered fill are simulated,and then the settlement of the high-fill airport is calculated and analyzed by inputting three sets of parameters.The relative soft parameters of loess geomaterials produce more settlement than the relatively hard parameters.The thicker the filling body is,the greater the settlement is.The filling body constrained by mountains on both sides produces less settlement than the filling body constrained by a mountain on only one side even the filling thickness is almost the same.The settlement caused by the original subbase accounts for 56%−77%of the total settlement,while the fill soils themselves accounts for 23%−44%of the total settlement,which is approximately consistent with the field monitoring results.It provides a good reference for predicting the settlement of similar high-fill engineering.

黄土基坑斜直桩支护结构受力及变形特性模型试验研究

为深入探究斜直桩支护的工作机理及变形特性,通过模型试验对比斜直桩和传统支护在开挖和降雨阶段桩顶位移、桩身弯矩及坑外沉降变化规律。研究结果表明:斜直桩受力及变形均小于悬臂和双排直桩,其极限挖深更大,对周边环境影响更小,其中内斜直支护性能最优。部分直桩改为斜桩可使受力更合理,除了受到弯剪还有拉压,有效提高支护刚度。降雨阶段下支护结构受力及变形增幅较开挖更大,还会引发土体塌陷、坑内外土体表面开裂等破坏。研究结果可为斜直桩黄土基坑施工风险防控提供参考。

改进的分层总和法在黄土地区高填方地基沉降变形中的应用研究

黄土高填方沉降变形控制是工程建设的重点和难点。通过室内侧限压缩试验和加湿试验,总结了重塑黄土在自重应力和含水率变化下的变形特征。基于分层总和法的思想,引入了Gunary模型和割线模量法,将黄土高填方地基的沉降分为荷载引起的施工沉降和含水率变化引起的施工后沉降,并提出了黄土高填方地基沉降变形的计算方法。结合实际工程背景,预测了高填方工程的沉降变形。结果表明:黄土高填方沉降的主要来源是施工期荷载引起的沉降;随着填土高度的增加,工后沉降占总沉降的比例逐渐增大;在最优含水率条件下,当施工期压实度达到95%以上时即可完成土的排气固结,施工后期为土的排水固结;压实度的控制对高填方工程至关重要;该研究成果丰富了黄土高填方地基沉降变形的计算理论,为黄土高填方工后沉降和湿陷性沉降的研究提供了理论依据,并对黄土高填方工程的施工及工后沉降控制具有一定的参考价值。

黄土地基不均匀沉降对现浇管廊影响的试验研究

湿陷性黄土地基浸水后的不均匀沉降会使现浇管廊结构产生附加内力,造成管廊结构开裂甚至破坏,严重威胁其运营安全.为深入研究黄土地层湿陷变形对现浇管廊的影响,开展了黄土地层局部浸水湿陷的模型试验.在试验中,设定局部浸水范围,以地基浸水深度为变量,对管廊结构底部位移、土体接触压力、表面应变和地表沉降进行了监测,并分析了其发展趋势.试验结果表明:当局部基底浸水深度达到20 cm,管廊结构在浸水区出现明显的弯曲变形,结构在湿陷区内的最大下沉达到0.57 mm;结构与土体接触压力变化较大区域为湿陷区边缘的管廊底板处;在管廊底部局部浸水发生不均匀沉降时,结构受力形式表现为底板受拉,顶板受压,且越远离管廊中部,所产生的应变越小,拉压应变在湿陷区边缘发生转变;地表也会发生沉降现象,最大沉降值为2.24 mm.试验结果可为湿陷黄土地区现浇管廊的设计和相关病害的防治提供参考.

气动振杆密实法加固湿陷性黄土的模型试验研究

气动振杆密实法是湿陷性黄土地基处理的一项全新技术。采用自行研制的气动振杆密实模型试验装置,进行了单一激振力、气体射流协同激振力两种条件下的模型试验,评价了土体加固效果,研究了振杆贯入过程中土体水平向土压力、土颗粒垂直振动速度和土体中气体压力值的变化规律。试验发现,处理后各深度土层的密度均有明显提高,湿陷系数降低;增设气体射流后,100 mm深度以下土层密度进一步提高,水平向土压力最大提高20.4%,同时放大了振杆密实法引起的土体振动响应。研究揭示了气体射流在土体加固过程中的作用机理,探讨了气动振杆密实法加固湿陷性黄土机理,为推广气动振杆密实法处理湿陷性黄土地基技术的应用提供了理论依据。

不同工作荷载下能量桩热-力耦合特性模型试验

本文通过黄土地基中能量桩在3种不同荷载工况下的温度循环荷载试验,以及在此基础上进行的能量桩竖向承载特性试验,对比分析了冷热循环过程中热交换效率、桩顶竖向荷载、桩土沉降、桩身轴力、桩侧摩阻力及桩端反力等变化规律。试验结果表明:桩顶竖向荷载随温度循环次数的增加而逐渐减小,桩顶沉降呈现出收敛特性;热循环时桩身受压,冷循环时受压区范围与工作荷载和冷循环次数成正比;桩顶工作荷载较小时,冷热循环对侧摩阻力的影响更大,冷循环时的侧摩阻力更大;工作荷载的大小是桩-土相对位移的控制因素;温度位移零点的位置与荷载大小无关,以此点为界冷热循环对侧摩阻力及桩-土相对位移有不同影响。

湿陷性黄土地基大跨度桩基承载特性模型试验

城市车辆段上盖开发工程中的大跨度桩基具有单桩竖向承载较大、桩间大跨度范围内土体受荷较小的特点。以西安地铁某车辆段大跨度桩基为研究对象,制备人工湿陷性黄土作为相似材料,开展了湿陷性黄土地层大跨度桩基的室内模型试验,研究大跨度桩基在湿陷性黄土地层中的荷载传递机制与变形规律。结果表明:制备的人工湿陷性黄土与现场原状黄土性质接近,将其应用于模型试验时可以得到良好的效果;大跨度桩基在未浸水时,荷载沉降曲线为陡降型,桩身轴力在桩顶附近显著下降,未达到极限承载力时,桩顶沉降、桩端阻力线性增大;在黄土浸水湿陷后,桩身轴力沿埋深方向呈“D”字型分布,随着浸水时间的增加,桩顶沉降、桩端阻力先缓慢增加后显著增加,中性点位置不断向桩身下部移动。

黄土介质微波加热机理及效果研究

针对土木工程领域软弱黄土地基热固结效果的问题,基于COMSOL Multiphysics分别建立了电阻式热传导、理想微波辐射、实际天线辐射的黄土加热模型,对加热速率和范围进行了仿真和分析,并探讨了不同微波频率对加热效果的影响。结果表明:微波加热效果优于电阻式热传导,而对于实际天线,由于热传导和微波加热两种机制共同作用,加热效果最佳。此外,通过对工作频率进行分析研究,得出微波加热效果随频率增大不断恶化的特性。在实际工程中,应用天线辐射对黄土地基进行热加固处理,可以提升加热效率,确保黄土地基稳定性。

复杂参数条件下基于空间应力解的重塑黄土沉降计算方法

基于J.Boussinesq推出的弹性半空间在荷载作用下内部任意一点的应力分量解析式,得到任意一点土体的空间应力状态,并将其引入沉降计算模型,从而提出将围压参数引入重塑黄土沉降计算的方法。通过应力式加载三轴试验分析了重塑黄土基于偏应力、含水率、围压在内的3个参数对应变发展的影响,得到了重塑黄土在不同参数下的应变规律,提出了重塑黄土应变受多个参数影响的沉降计算公式,并通过工程实例验证了公式的可靠性。结果表明:偏应力、含水率、围压均对重塑黄土的应变有显著影响,其中偏应力、含水率均与重塑黄土的压缩变形正相关,而围压与重塑黄土的压缩变形负相关,且3个参数拟合的重塑黄土应变经验公式效果良好。通过实际工程案例验证,沉降计算结果和实际沉降监测结果基本一致,表明提出的计算方法可以更为合理且便利地应用于重塑黄土工程场地的沉降计算及分析。

急速增湿条件下湿陷性黄土中桩基的承载性状

入渗增湿条件下,湿陷性黄土地区中桩基的承载性状会因桩周土基质吸力减小和湿陷变形而显著劣化,进而诱发一系列的工程问题。为了研究浸水前后湿陷性黄土中桩基承载性状的变化规律,进行模型桩的入渗试验,同时对桩周土体的变化(包括沉降、体积含水率、基质吸力)以及桩基承载性状的变化(包括桩顶沉降、桩侧摩阻力和桩端承载力)进行监测。将入渗过程中桩周黄土基质吸力变化与桩基承载性状的变化相关联,从非饱和土力学的角度阐明入渗前后桩基承载性状的变化规律和变化机理。研究结果表明,入渗过程中的桩顶沉降和桩端承载力不断增加,桩身轴力大致呈“D”字形分布,最大轴力出现在入渗过程中。入渗过程中桩周黄土的基质吸力减小,产生湿陷变形,使桩侧摩阻力大小和方向发生改变,进而导致桩基承载性状的变化。基于非饱和土力学原理对传统的剪切位移法进行简化和修正,提出考虑桩周黄土湿陷变形影响的单桩沉降预测模型,并结合试验结果对理论模型进行验证。研究成果有助于进一步完善复杂环境荷载作用下湿陷性黄土地区的桩基设计理论和工程性状评估。

基于物联网技术的PHC管桩加固湿软黄土地基自动化监测现场试验

预应力高强度混凝土(Pre-stressed High-strength Concrete:PHC)管桩作为一种常用的处理湿软黄土地基方法,质量稳定可靠。但是,在传统PHC管桩施工过程中,对管桩贯入位移的记录存在频率不足、效率不高等问题,未能满足预期的地基处理施工监测效果。鉴于此,基于物联网的基本框架和技术,依托甘肃安临高速PHC管桩处理湿软黄土地基工程,设计了一套PHC管桩施工质量自动化监测系统,采用自行研发的监测装置与系统,针对管桩在施工过程中的贯入位移质量控制指标进行了现场监测试验。结果表明:该监测系统可实时输出管桩贯入土层过程中贯入位移随锤击次数的响应情况,并将管桩贯入持力层的信息及时反馈于现场施工作业区。同时借助地质雷达与低应变检测技术验证了该监测系统的可靠性。该研究成果可为PHC管桩在施工过程中实现贯入信息采集的智能化提供一定的技术支撑。

不同夯击能相同夯沉量条件下黄土填方地基强夯处理效果分析

为了评价不同夯击能、相同夯沉量控制条件下的黄土填方地基强夯处理效果,在晋中市某工程填方区开展了夯击能4 MN·m、6 MN·m、8 MN·m和10 MN·m共四种能级的强夯试验,测试强夯前后填土的干密度、压缩模量、湿陷系数、瑞雷波波速等物理力学性质指标。试验结果表明,夯击能6 MN·m、8 MN·m、10 MN·m分别在夯点处7 m、9 m、7 m深度内,夯间处8 m、7 m、6 m深度内,密实度提高、压缩性降低的效果与夯击能4 MN·m接近;夯击能4 MN·m、6 MN·m、8 MN·m、10 MN·m分别消除了5 m、4 m、7 m、5 m深度内的湿陷性;与夯击能4 MN·m试验相比,夯击能6 MN·m、8 MN·m、10 MN·m总耗时分别缩减12.5%、37.4%、40.7%,油耗分别减少7.9%、26.9%、23.1%,表明高夯击能与低夯击能相比所用时间与设备耗油有大幅度降低。

考虑荷载及含水率变化的黄土高填方地基沉降变形计算

黄土高填方的沉降变形控制是工程建设中的重点和难点,基于分层总和法的思想,通过引入Gunary应力应变模型和割线模量法,提出考虑荷载变化和含水率变化的黄土高填方地基沉降变形计算方法。结合算例,对高填方地基的沉降变形进行预测及验证。结果表明,黄土高填方沉降变形的主要来源是施工期间因荷载变化而引起的沉降。随着填土高度的增加,因含水率发生变化产生的广义增湿湿陷沉降占总沉降的比例逐渐增加。压实度控制对高填方工程至关重要,压实度越高,总沉降量越小。研究成果丰富了黄土高填方地基沉降变形的计算理论,为黄土高填方工后沉降和湿陷沉降的研究提供理论依据,对黄土高填方工程的施工和工后沉降控制具有一定的参考价值。

湿陷性黄土场地大型储罐基础设计

结合在湿陷性黄土场地上建设的10万方大型钢储罐工程,从基础选型、承载力设计、地基处理、充水预压、沉降观测等方面进行了深入的分析和研究,并从经济性、施工可操作性等方面进行地基处理方案比选,确定采用孔内深层强夯桩+灰土石垫层,提出对含水率较低的湿陷性土层进行预增湿技术,使土层达到最优含水率,解决桩沉管不易、拔管困难、较难消除湿陷性的问题,充水预压后进行沉降观测,结果表明地基沉降随充水荷载增大而增大,在15d后趋于稳定,且储罐四周沉降大于中心点,但沉降量均小于估算值,地基处理效果达到预期。

饱和软黄土地层深基坑支护与降水施工技术

以西安市某医院改造项目深基坑工程为背景,对饱和软黄土区域基坑支护设计及施工时遇到的问题进行了分析总结,并提出了相应的处理措施。介绍了设计以及施工过程中基坑深度调整应采取的设计对策,提出优先采用刚度较大的咬合桩止水帷幕原则,同时强调了“分层开挖、分层支护、严禁超挖”的重要性。

基于改进云模型的湿陷性地基渡槽稳定状态评估

【目的】由于跨湿陷性黄土区的输水渡槽因服役期内的地基变形和建筑物老化,造成渡槽的服役安全性和结构稳定性难以定量评估,为对湿陷性地基渡槽的稳定状态进行评估,以宁夏固海扩灌灌区的清水河渡槽为研究对象,构建了基于湿陷性黄土地基稳定状态与渡槽建筑物稳定状态的多级评估体系耦合的湿陷性黄土地基渡槽稳定状态综合评估体系,【方法】使用云模型对湿陷性黄土地基渡槽稳定状态进行综合评估,使用AHP-熵权法对云模型进行改进,研究中使用拉格朗日乘子法将AHP法与熵权法进行耦合后计算指标权重,以提高模型权重的合理性使其更加客观精确。【结果】研究结果显示:现役清水河渡槽的湿陷性黄土地基稳定状态、渡槽建筑物稳定状态及湿陷性黄土地基渡槽整体稳定状态的云数字特征参数分别为W_(1)=(4.608,0.766,0.228)、W_(2)=(6.094,0.674,0.214)和W=(5.307,0.720,0.221)。【结论】结果表明:现役清水河渡槽的湿陷性黄土地基稳定状态、渡槽建筑物稳定状态及湿陷性黄土地基渡槽整体稳定状态分别处于V_(3)(中等)稳定状态、V4(较为)稳定状态以及V_(3)(中等)稳定状态。该评估模型可为同类湿陷性黄土区域的水工建筑物的稳定状态评估提供参考。