EXPERT SYSTEM AND ITS APPLICATION IN THE SELECTION OF PIT RETAINING STRUCTURES

This paper describes the development of an expert system(ES) on earth retaining structures for the selection and design.The ES retaining is an interactive menudriven system and consists of two main parts—the selection part,selectwall and the design part.Selectwall is developed using the knowledge base and it makes a choice of the most appropriate retaining structure.The design part is developed by three independent subprograms which perform detailed design including strength,deformation,stability of the retaining structure.The calculation results are illustrated by plotting the diagram.Using this program,the design procedure of the retaining structure can be performed automatically.

A Slip-Force Device for Maintaining Constant Lateral Pressure on Retaining Structures in Expansive Soils

Expansive soils can pose tough issues to civil engineering applications. In a typical year, expansive soils can cause a greater financial loss than earthquakes, floods, hurricanes and tornadoes combined. Various means have been studied to tackle problems associated with expansive soils. The majority of the methods are based on treatment of the soils. While the methods may be effective in some cases, their limitations are also obvious: The treatment normally involves complex processes and may not be eco-friendly in the long run. In many cases, the effectiveness of the treatment is uncertain. A retaining system that maintains a constant lateral pressure is proposed, which consists of three components: the retaining sheet, the slip-force device and the bracing column. The retaining sheet bears the pressure exerted by expansive backfills and is not embedded into the soils. Placed between the retaining sheet and bracing column, the slip-force device permits displacement of the retaining sheet but keeps the force on the sheet and the bracing column constant. The governing equation of the motion of the piston in the slip-force device is derived and a numerical simulation of a practical case is conducted based on the derived governing equation. Numerical results show that as the expansive soil swell, the spring force will increase and the piston will move accordingly. When the pressure of the oil in chamber reaches the open threshold of the unidirectional relief valve, the valve will open and the spring force and the oil pressure in the chamber will keep constant. The results also show that some parameters, such as damping ratio, have very slight influences on the device behavior, say 2 × 10-6 or even 4.8 × 10-9. Theoretical and numerical studies prove the effectiveness of the proposed retaining system.

An Overview of Recently Developed Coupled Simulation Optimization Approaches for Reliability Based Minimum Cost Design of Water Retaining Structures

This paper reviews several recently-developed techniques for the minimum-cost optimal design of water-retaining structures (WRSs), which integrate the effects of seepage. These include the incorporation of uncertainty in heterogeneous soil parameter estimates and quantification of reliability. This review is limited to methods based on coupled simulation-optimization (S-O) models. In this context, the design of WRSs is mainly affected by hydraulic design variables such as seepage quantities, which are difficult to determine from closed-form solutions or approximation theories. An S-O model is built by integrating numerical seepage modeling responses to an optimization algorithm based on efficient surrogate models. The surrogate models (meta-models) are trained on simulated data obtained from finite element numerical code solutions. The proposed methodology is applied using several machine learning techniques and optimization solvers to optimize the design of WRS by incorporating different design variables and boundary conditions. Additionally, the effects of several scenarios of flow domain hydraulic conductivity are integrated into the S-O model. Also, reliability based optimum design concepts are incorporated in the S-O model to quantify uncertainty in seepage quantities due to uncertainty in hydraulic conductivity estimates. We can conclude that the S-O model can efficiently optimize WRS designs. The ANN, SVM, and GPR machine learning technique-based surrogate models are efficiently and expeditiously incorporated into the S-O models to imitate the numerical responses of simulations of various problems.

Study on Liquefying Simulation Test of Retaining Structure Ground of Kobe Port

In order to clarify the deformation and failure mechanism of retaining structure ground under liquefying, a series of shaking table tests was performed. The test results suggest that the strength decrease and local liquefaction of subsoil are the leading factors in the deformation and failure of retaining structures. The movement of the ground mainly manifests the lateral displacement under liquefaction. At the backfill layer, liquefaction will be rapidly reached in far field whereas the excess pore pressure is slowly increased nearby the wall under shaking.

Rapid excavation with a newly developed retaining system: Spiral assembly steel structure

The spiral assembly steel structure, a newly developed retaining wall for the rapid excavation of small-sized foundation pits in unsaturated soil, is presented. This new type of retaining structure is prefabricated in the factory and is assembled on site in the excavation of a pit. This retaining structure is composed of several prefabricated steel structural units, in which the adjacent steel structural units are joined with connectors. Each steel structural unit has one steel pipe in the radial direction and is welded to a single piece of steel plate. After full installation in situ, the retaining structure becomes a cylindrical steel structure. With the protection afforded by this new type of retaining structure, excavation work can be completed within 24 h to a depth up to 5 m. In order to verify the reliability and effectiveness of this new retaining structure, field construction tests were conducted in Beijing, China. The test construction was monitored. The monitoring program included measuring stress in the structure, lateral earth pressure, and lateral deformation of the surrounding soil. The monitoring data from the field test were compared with the theoretical results. The results show that the proposed new structure is reliable and effective.

Effects of Nano-carbon Humic Acid Water-retaining Fertilizer on Citrus Growth and the Soil Bacterial Community in Citrus Field

[Objective] In order to reveal the effects of reducing the amount of novel nano-carbon humic acid water-retaining fertilizer(CSF) on soil microbial community structure and citrus growth. [Method]In this study,conventional fertilization was as the control(KC1) in Wanzhou citrus orchard of Three Gorges Reservoir area. CSF reductions by 0%(KC2),10%(KC3),20%(KC4),30%(KC5) and 40%(KC6) were used to analyze the changes of soil bacterial community structure,citrus yield and quality. [Result]The results showed that the observed species,Shannon index,Chao1 index and PDwholetree of KC6 were higher than those of KC1,and were the same as KC2. The abundance of Xanthomonadaceae was the highest in KC5. Compared with KC1,the Xanthomonadaceae in KC3,KC4 and KC6 was significantly decreased,and the levels of Nitrosomonadaceae and Pseudomonasaceae were higher than that of KC1 after the treatment of KC6. Sphingomonas in different reduction treatments was lower than that of KC1,but Burkholderia and Pseudomonas were significantly higher than those of KC1. It was found that the similarity among treatments was small after bacterial community similarity clustering analysis,and citrus yield increased somewhat after CSF fertilization reduction.When CSF fertilization reduced by 30%,citrus yield increased by 4. 50%. When CSF fertilization reduced by 40%,citrus yield decreased by4. 14%. After CSF fertilization,citrus quality did not change significantly in CSF conventional fertilization and reduction of 10% and 40%,while significantly decreased in 20% and 30% of fertilization reduction. [Conclusion] CSF fertilization reduction changed the diversity of soil bacterial community structure and the yield and quality of citrus.

盾构始发与接收对工作井围护结构的影响研究

[目的]一般情况下,盾构机均在盾构工作井主体结构施工完成后才进行始发或接收,由于诸多因素的限制,往往需要考虑盾构工作井主体结构尚未施工时进行盾构始发或接收的情况,因此需研究盾构始发与接收对盾构工作井围护结构的影响。[方法]以成都地铁某标准地下三层岛式车站为例,研究盾构工作井在未施作主体内衬结构状态下实现盾构始发与接收时的围护结构受力及变形情况,并分析了盾构始发与接收对围护结构稳定性的影响。[结果及结论]研究结果表明:无内衬状态工作井盾构始发与接收时,围护结构桩体水平位移最大值及弯矩最大值均发生在盾构工作井端墙中跨第4道钢支撑处,围护结构剪力最大值发生在盾构工作井端墙中跨底板处;当盾构工作井未施作主体内衬结构时,围护结构桩体变形及受力均有所增大,但其位移及力学指标均满足规范要求;围护结构在剪力及弯矩作用下能够满足承载能力及强度要求;无内衬状态下的工作井盾构始发与接收可提高施工效率,有效节省工期,节约工程成本。

弹性环梁支撑下圆形深基坑支护结构变形解析解

将环梁和支护结构分别视为弹性圆环和弹性圆柱薄壳,基于环梁和圆柱壳的变形协调,得到了具有任意数目弹性环梁支撑圆形深基坑支护结构变形的解析解.在验证解析解合理性和可靠性的基础上,针对某一实际圆形基坑工程,比较了在刚性和弹性环梁支撑下支护结构变形和内力的差异,并分析了支护结构底部边界条件、环梁弹性模量、尺寸和数量以及位置等参数对支护结构变形和内力分布的影响.研究结果表明:相对于刚性环梁支撑,弹性环梁支撑处内力变化较小,环梁弹性模量和尺寸的改变只对基坑挖掘面以上支护结构变形和内力影响显著,而对挖掘面以下的支护结构变形和内力几乎没有影响.该研究成果为圆形基坑支护结构设计提供了理论依据和指导.

基于力学模型构建的留巷切顶高度确定与围岩控制技术

以顺和煤矿2401运输巷道沿空留巷为工程背景,分析巷道围岩结构特征,基于巷道局部空间结构稳定性,分别构建了沿空留巷未切顶与切顶力学结构模型,并以巷道不同切顶高度进行物理相似模拟试验。结果表明:巷旁采空区切落的矸石增加对关键块的支撑力,同时弱化关键块对直接顶悬壁端部挤压,巷旁支护阻力减少35.78%;随着切顶高度增加,巷道顶板采空区侧端部悬臂由F型缓慢过渡到大I型,同时大保护结构具有向上平移趋势,相比于未切顶1巷,4 cm切顶2巷、8 cm切顶3巷与16 cm切顶4巷叠加应力峰值分别下降9.38%,28.13%,25.00%。结合巷道顶板岩性,最终确定切顶高度为8.2 m,留巷段采用三列单体液压支柱作巷旁支护,长短锚索超前补强,巷道围岩稳定,较好满足使用要求。

基于遗传算法的空箱式挡土墙多目标优化设计

为高效、准确、自动化地实现空箱结构的优化设计,以空箱式挡土墙为研究对象,基于Python语言和ABAQUS软件进行参数化建模,实现了结构建模及有限元计算分析全套流程的自动化。结合某水闸工程中的一座空箱式挡土墙结构,以多个强度和稳定性指标的最优化和混凝土体积的最小化为目标,以规范要求的指标阈值、几何尺寸和体积限制为约束条件,采用非支配排序遗传算法(NSGA-Ⅱ算法)进行空箱式挡土墙多目标优化设计。为进一步提高计算效率,基于人工神经网络算法建立了代理模型,实现了与实际有限元模型的高度近似。结果表明,依据所提出的优化设计方法进行空箱式挡土墙多目标优化设计,可以在有效控制强度和稳定性的前提下尽可能地缩减混凝土用量,具有显著的经济效益。

基于人工神经网络的深基坑支护结构侧移预测

为了更精准地预测基坑开挖引起的支护结构侧移,采用支持向量机模型、传统人工神经网络模型及2种考虑时序性输入的循环神经网络模型,建立了不同基坑支护结构最大侧移、同一基坑不同工况支护结构侧移的预测模型.结果显示,人工神经网络可以根据工程实测数据实时更新和预测支护结构变形,有助于及时规划工程下一步施工工艺.在支护结构不同工况侧移的预测上,考虑了时序性输入的循环神经网络模型效果优于传统人工神经网络模型.

基于拉压杆模型的装配式混凝土挡墙结构设计方法

为了研究装配式混凝土箱体挡墙结构在水压力和土压力共同作用下的受力机理,提出了一种基于拉压杆模型的装配式混凝土挡墙结构设计方法.以体积和应变能为优化目标,采用Tosca软件对数值模拟得到的主要受力骨架进行拓扑优化.构建拉压杆模型,结合箱体挡墙结构的破坏机理,分析并推导出侧墙受压、临水面挡墙和集束连接受拉3种主要破坏模式的承载力公式.实际工程对比分析结果表明:进行900次模型优化后,优化形态和应变能基本保持不变;基于拉压杆模型的装配式混凝土箱体挡墙结构的承载能力低于规范值和有限元模拟值,但误差均保持在16%范围内,从而验证了该方法的合理性.

砂质泥岩巷道顶板定向爆破不耦合装药系数优化与应用

聚能爆破技术在沿空留巷工程项目中有着重要的作用,装药结构问题一直是目前讨论的热点及难点。对于目前沿空留巷顶板超前预裂装药长度尚没有明确的指标情况下,以孟津煤矿二_2-11031工作面轨道顺槽为研究背景,提出了等长装药顶板预裂技术,为明确最优装药结构,本文通过LS-DYNA数值模拟软件建立了三维定向聚能爆破模型,改变轴向药柱的长度,以裂纹扩展长度和应力衰减速率为分析指标,通过数值模拟可知,轴向不耦合系数在1.25~1.7之间径向切缝距离约为40 cm,轴向切缝距离约为80 cm,相比轴向不耦合系数在2~3之间,切缝距离分别提高了25%和12.5%;轴向不耦合系数在1.25~3之间,应力衰减速度均小于1,能量利用最为合理;将轴向不耦合系数α=1.25~2的装药结构在孟津煤矿二_2-11031工作面轨道顺槽进行顶板定向爆破实验,对预裂爆破后的两炮孔中线进行钻孔窥视,观察到4种爆破方案,两炮孔之间沿切缝方向裂纹均已经完全贯通,裂纹光滑平整,现场应用效果良好,结合经济性、安全性两方面考虑,不耦合系数α=1.7为最优;研究结果表明等长装药结构可以代替传统的三段式装药结构。研究结果可以为今后类似的项目提供参考。

基于三维激光扫描的高陡边坡勘查与支护设计

以广东清远银湖城复杂高陡边坡为依托,采用三维激光扫描技术,查明边坡的空间展布形态、优势结构面的空间分布特征,为边坡设计提供依据。基于三维激光扫描调查和边坡稳定性评价结果,对挖方土岩组合高边坡,上部土体采用“放坡+锚杆格构梁”,中下部岩体采用“削坡+马道挡石墙”的治理措施;对填方边坡,采用“强夯加固+扶壁式或重力式挡墙直立式支挡+坡率加筋土+坡面浆砌石格构梁防护相结合”的治理措施。生态修复效果良好,经济效益显著。

地铁深基坑围护结构渗漏病害规律分析

为掌握深基坑围护结构渗漏病害规律,本文阐述了杭州地铁工程概况和工程地质背景,基于2015—2021年渗漏病害资料开展统计研究,分析渗漏与地质、地理、结构和变形等因素的关系。结果表明:(1)工程地质层③、⑥在渗漏病害发育的地层岩性中占据主要地位,孔隙潜水则是渗漏的主要地下水来源。(2)补给基坑渗漏的邻近河流侧向比降分为少发(i≥0.117),多发(0.022≤i<0.117)和易发(0.006≤i<0.022);5 d累积降雨量分为低雨强(0~25.4 mm/5d)、中雨强(25.4~67.1 mm/5d)和高雨强(67.1~82.3 mm/5d),并分别能够诱发Ⅰ~Ⅱ、Ⅲ和Ⅳ级渗漏。(3)深基坑围护结构转角接缝是渗漏易发部位,5 d累积降雨量较小的Ⅳ级病害站次围护结构多具有严重缺陷。(4)渗漏分布在开挖面以上5 m范围内,最浅临界埋深与开挖深度、最浅临界开挖深度与基坑设计深度均呈指数关系;渗漏位于最大侧向变形以上6.0 m、以下2.5 m范围内,二者深度整体呈线性正相关;渗漏深度与最大侧向变形/变形深度关系呈分区线性负相关,不同分区拟合直线斜率相近。讨论渗漏病害发育规律的机制,选取典型工程实例判别渗漏风险,验证规律分析的可靠性,研究结果可为富水砂层深基坑工程渗漏预防提供参考。

软土地层基坑群模型试验相似材料研制及应用

针对基坑群连续开挖存在的耦合效应问题,首先确定相似材料配比方案,通过正交试验得出合理的配比材料,进而设计基坑群模型试验来研究两侧基坑叠加作用影响下车站基坑的围护结构和土体表层变形.研究结果表明:满足该软土地层相似常数的土层材料配比为(石英砂∶滑石粉∶双飞粉∶膨润土∶水=0.27∶0.27∶0.232∶0.058∶0.17);基坑群开挖时由于相邻墙体引起的墙后土拱效应叠加导致坑间土体水平应力降低,围护结构受力和变形量减小,坑间土体沉降量增大;基坑间距是支护结构变形的主要影响因素,两侧基坑间距位于1H~2H之间(H为基坑深度),接近1倍开挖深度一侧的叠加影响大于接近2倍开挖深度一侧.

铁路泡沫轻质土路基挡护结构的优化设计研究

泡沫轻质土在施工场地受限的路基帮宽工程中发挥了独特优势,为进一步优化铁路泡沫轻质土路基挡护结构,在商合杭(商丘—合肥—杭州)铁路肥东站开展工程现场试验,获得了挡护结构的受力特征与变化情况。结果表明:泡沫轻质土浇筑完成后具有良好的自立性及强度,挡护结构所受侧向压力显著降低,挡护结构承受的侧向土压力仅2~5 kPa,土压力系数逐渐减小趋近于0.1,因此泡沫轻质土路基挡护结构主要作用是防止泡沫轻质土的劣化、保护轻质土性能,兼作施工模板,可以根据泡沫轻质土填筑固化前的侧压力和风荷载进行结构优化设计。

组合扶壁式挡土墙结构设计及稳定性分析

扶壁式挡土墙作为一种轻型、柔性的挡土结构,具有方便施工和受力性能好等特点,但对支挡高度却有一定的限制。为此,本文以威海龙润国际项目为依托,提出一种新型的组合扶壁式挡土墙结构,并结合数值模拟方法对挡墙结构的受力特征进行了分析研究。结果表明:组合扶壁式挡土墙可有效提高抗倾覆抗滑移能力,将原有的肋板受力转变成箱体受力,提高了边坡的整体稳定;在满足组合扶壁式挡土墙最大基底压力的前提下,位于0.5H(挡墙高度)处的5.0m盖板宽度的弯矩最小,边坡稳定系数为1.62。现场监测结果得到挡土墙填筑及使用期间最大水平位移为18.3mm,验证了支护方案的合理性,可为今后同类工程的计算及设计提供一定的参考。

加筋保土柔性污染阻隔管控技术在历史遗留废渣堆治理中的应用

历史遗留废渣堆的治理是目前环保治理工作中的难点和热点,特别是对于堆存场地受限、边坡陡的废渣堆,原位污染防控与生态恢复的协同治理技术是当下历史遗留废渣堆污染防治的难题之一。以某关停矿山生态恢复项目渣堆管控项目为例,提出了一种新型的历史遗留废渣堆原位污染防控及生态恢复技术,即废渣堆加筋—保土—水平与垂直柔性阻隔—生态恢复治理方案,简称“加筋保土柔性阻隔生态恢复技术”,该技术对废渣堆采用土工袋+格栅加筋的方式稳固边坡,堆体表面设置HDPE膜为主防渗的阻隔层,并挂设土工格室进行保土绿化,并在渣堆四周设置柔性垂直污染防控阻隔墙,将废渣堆进行三维立体阻隔,有效防控废渣堆对周边地下水及土壤的污染。同时废渣堆表层阻隔采用的是HDPE膜,其渗透系数小于1×10^(-13) cm/s,四周采用的柔性垂直阻隔墙整体渗透系数小于1×10^(-7) cm/s,HDPE膜表层通过钢制花管HDPE管靴固定土工格室,钢制花管HDPE管靴可与HDPE膜实现热熔焊接,渗透系数满足1×10^(-7) cm/s,最终实现污染阻隔与生态绿化相互协同,达到废渣堆原位污染防控和生态恢复的双重效果。

考虑空间效应的大型异形基坑开挖变形分析

城市紧张的用地环境及复杂的主体结构需求,导致异形基坑越来越常见。目前国内基坑规范推荐的分析方法均不能满足形状对基坑变形的影响。本文以北京某超大异形基坑为依托,建立异形基坑Midas-GTS仿真计算模型,并结合现场实测变形数据,对异形基坑的坑外地表沉降及围护结构变形特征展开研究。结果表明,受基坑形状特征影响,地表沉降及支护结构变形均存在明显的空间效应:地表不均匀沉降现象显著,基坑长边附近沉降大于短边,沉降量随着离坑角距离的增加而显著增大;围护墙长边中间区域变形较大,短边中部次之,结构角点处变形最小。因此,在进行基坑设计支护时,应充分考虑基坑变形的空间效应,节约工程成本,提高基坑整体稳定性。