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.

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.

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.

Analytical and Numerical Study of the Hydro-Mechanical Behavior of a Cantilever Retaining Wall in Upward Seepage Conditions

Poor design of ground water evacuation mechanisms is often blocked and leads to the rise of ground water behind the wall. As a result, free water behind the wall that is not quickly evacuated, increases the lateral pressure and thus favors overturning failure. The resolution of the overturning problem in cantilever retaining walls caused by hydro-mechanical interaction was studied. An analytical and numerical method was used to study this type of wall-floor interaction. Then Coulomb’s design criterion against overturning to develop a mathematical model that compute analytical factor of safety against overturning in different water conditions and heel lengths was used. The modeling and simulation of this system in the Cast3m software which took into account a wide variety of floor and wall properties were performed. The numerical factor of safety against rollover was obtained, and the graphs for the factor of safety versus heel length and immersion depth for both methods were plotted. From (0 ≤ Hw ≤ H/3), water effect is not dangerous to wall stability against overturning and from (H/3 Hw ≤ H), water effect is very dangerous to wall stability against overturning. For analytical and numerical methods, the heel can be predimensioned against overturning as: Lc: [0.27H 0.38H], [0.29H 0.43H] for 0 ≤Hw ≤ H/3;[0.33H 0.45H], [0.39H 0.53H] for H/3 Hw ≤ 2H/3;[0.5H 0.6H], [0.50H 0.67H] for 2H/3 Hw≤ H. The numerical method guaranteeing more safety than the analytical method, Cantilever retaining walls can thus be pre-dimensioned considering Clayey-Sand soil in hydro-mechanical conditions.

Electron theory study on the effect of Mn on as-cast structure of Fe-C-Cr-Mn cast irons

The valence electron structure of alloying austenite of 3C-15Cr high chromium white cast iron with different Mn contents from 1% to 6% is analyzed by BLD method and EET. Results show that the addition of Mn has major influence on the valence electron structure of the alloying austenite, especially on that of Fe-C, Fe-C-Cr and Fe-C-Cr-Mn unit cells of it. The effect becomes weak when Mn content is over 4%. Based on the effect of n~, F~~, the weighting of each unit cell and the degree of undercooling on phase transition of the aus- tenite, we can calculate the retained austenite content of as-cast structure of the high chromium white cast iron. The calculation results coincide well with those of the experiment. The phase transition characters of the austenite in high chromium white cast iron can be forecasted through valence electron structure analysis of alloying austenite by BLD method and EET on the basis of Fe-C-Cr equilibrium phase diagram.

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.

紧邻在建城市轨道交通特别保护区开口基坑支护实践

基坑北侧距离济南市在建城市轨道交通R2线特别保护区仅1.9 m,特别保护区内严禁支护结构进入,务必在该有限的空间内实现支护桩和止水桩的布置,因此济南市常规的桩锚支护体系难以应用。基坑南侧为先开挖到底的居住地块基坑,因其邻近本基坑侧采用放坡支护,导致本基坑在南侧形成开口,难以满足支撑支点设置要求。通过在居住地块侧设置专门的支撑传力结构作为支座,在解决支撑支点设置问题的同时还增加了地下室的实际使用面积,使本基坑成为R2线特别保护区边首个采用钢管支撑的地下2层深基坑,在确保基坑本身安全的同时,满足了R2线的建设控制要求。

Research and application of mechanical models for the whole process of 110 mining method roof structural movement

For the 110 mining method,it is challenging to accurately calculate the support resistance of the roadway due to the lack of understanding of the dynamic movement of the overlying strata in this method.The consequential excessive support results in a significant increase in the cost of roadway support.The authors explored the overlying strata movement and roadway deformation of the gob-entry retaining in the 110 mining method to solve this problem.First,the typical stages of the roof-cutting gob-side entry were defined.Second,the mechanical model and calculation formula of the support resistance on the roof were explored.Then,using numerical simulation software,the starting ranges of the specific supports at different stages were verified and the feasibility of the support scheme was examined.Finally,combined with the field measurement data,the stress and the deformation of the gob roadway at different stages under the influence of two mining processes in the 110 mining method were obtained.The numerical simulation results obtained are consistent with the field test results,providing a theoretical basis for precision support at different stages by the 110 mining method.

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.

护圈和石笼结构防护下桥墩局部冲刷试验研究

桥墩基础局部冲刷是造成涉河桥梁水毁最主要因素,对可能冲刷区域进行防护是降低基础冲刷危害的主要措施。文章选取矩形墩和双排圆柱形墩,基于主动和被动防护机理的护圈和石笼防护结构,考虑防护范围和流速因素,进行了桥墩基础局部冲刷试验;采用极差分析和相关性分析的方法,对墩型和防护措施结合后的基础局部冲刷演化过程和抗冲刷防护性能进行深入研究,探究防护效果与不同影响因素间的关系。结果表明:外径因素对防护效果的影响程度大于措施因素的影响程度;对矩形墩进行防护时,低流速下优先选用护圈结构,中高流速下两者均可采用;对双排圆柱形墩进行防护时,优先选用石笼结构;在护圈或石笼结构防护下的矩形墩、双排圆柱形墩局部冲刷深度计算中,基底修正系数K_(D)与防护比D_(p)/D更符合二次函数关系。

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。

基于装配式设计理念的Ⅱ型挡土墙研究

基于装配式挡土墙的设计理念,提出两种Ⅱ型挡土墙的结构型式:型式一为上一层挡墙结构单元支撑在下一层结构单元的肋板上,型式二为上一层挡墙结构单元面板支撑于下一层结构单元的肋板顶部,肋板支撑在上下结构单元之间的填土上,上层结构单元通过下层突起面板形成水平位移限定机制传递水平推力。采用数值模拟方法,验证这种挡墙机制的科学性和可靠性。研究表明:Ⅱ型挡土墙结构单元之间的接触应力满足结构抗压强度;结构刚度及水平变形满足要求;结构整体稳定性满足要求;相较于传统的衡重式、扶臂式挡土墙,Ⅱ型挡土墙结构施工便捷,具有较为明显的造价优势。