Fuzzy Decision of Ground Improvement Method

With the rapid development of expressway in China, the ground improvement is becoming more and more important. The decision of the ground improvement method often depends on the experience of an engineer. This paper sets up a module of multi-level fuzzy decision of the ground improvement method in the expressway construction which is mainly to set up multi-level structure module, to get value of the affected factors at rule level and index level, to set up the character index matrix of project level and to have a total evaluation on the projects. Combined with the project of ground improvement on the Second Cincture Road in Wuhan, a case study is carried out with satisfactory results.

Plate Load Tests on Municipal Solid Waste Dump Site to Assess Ground Improvement Alternatives

Urbanization is the physical growth of urban areas as a result of global change. As the land cost is increasing tremendously and decreasing availability of good construction site is building up pressure on the engineers to utilize even the poorest site either by providing special type of foundation or by improving ground in urban centres. In this context literature is reviewed for use of landfill site for housing. The site exploration for old dump site was carried out to assess subsoil characteristics. The objective was to evolve strategy for economical feasible ground improvement technique to obtain permissible bearing capacity of 150 kPa and total settlement not more than 50 mm. The tests carried out are load tests with geotextile mat and stone filled wire mess matress. The analysis was attempted to evaluate the soil response and bearing capacity. The site can be used for construction of low rise housing for rehabilitation of displaced persons under TP scheme within city area utilizing old landfill sites.

Consolidation of partially saturated ground improved by impervious column inclusion:Governing equations and semi-analytical solutions

This study focuses on the consolidation behavior and mathematical interpretation of partially-saturated ground improved by impervious column inclusion.The constitutive relations for soil skeleton,pore air and pore water for partially saturated soils are proposed in the context of partially-saturated ground improved by impervious column inclusion.Settlement equation and dissipation equations of excess pore air/water pressures for a partially saturated improved ground are then derived.The semi-analytical solutions for ground settlement and pore pressure dissipation are then obtained through the Laplace transform and validated by the existing solutions for two special cases in the literature and the numerical results obtained from the finite difference method.A series of parametric studies is finally conducted to investigate the influence of some key factors on consolidation of partially saturated ground improved by impervious column inclusion.Based on the parametric study,it can be found that a higher value of the area replacement ratio or modulus of the pile results in a longer dissipation time of excess pore air pressure(PAP),a shorter dissipation time of excess pore water pressure(PWP),and a lower normalized settlement.

Improved Ant Colony Algorithm for Vehicle Scheduling Problem in Airport Ground Service Support

Support vehicles are part of the main body of airport ground operations,and their scheduling efficiency directly impacts flight delays.A mathematical model is constructed and the responsiveness of support vehicles for current operational demands is proposed to study optimization algorithms for vehicle scheduling.The model is based on the constraint relationship of the initial operation time,time window,and gate position distribution,which gives an improvement to the ant colony algorithm(ACO).The impacts of the improved ACO as used for support vehicle optimization are compared and analyzed.The results show that the scheduling scheme of refueling trucks based on the improved ACO can reduce flight delays caused by refueling operations by 56.87%,indicating the improved ACO can improve support vehicle scheduling.Besides,the improved ACO can jump out of local optima,which can balance the working time of refueling trucks.This research optimizes the scheduling scheme of support vehicles under the existing conditions of airports,which has practical significance to fully utilize ground service resources,improve the efficiency of airport ground operations,and effectively reduce flight delays caused by ground service support.

Road Foundation Improvement by Explosive Force

A highway was constructed in Jiangxi Province, China, through mountainous area. Some sections of the highway went through valleys where a soft clay layer of 6,8.5 m deep was encountered. A new explosive method was developed and adopted for this project. In this method, blasting is used to remove and replace soft clay with crushed stones. Explosive charges are placed in the soil to be improved according to a certain pattern. Crushed stones are piled up behind the area where charges are installed. The explosion removes most of the soil in the exploded area and causes the pile of crushed stones to slide into the area where the soil is removed by blasting. A formular was suggested to calculate the charge weight used for improving a certain type of soil. The effectiveness of the method is evaluated using borehole exploration, plate load tests,and ground-probing radar tests.

Experimental Study on Improvement of Soft Clay Using Sand Columns

Sand Compaction Piles(SCP)commonly known as Sand Columns(SC)now has been vastly used for reinforcing the range of soft soils.The installation of sand columns results in enhancing the ultimate bearing capacity of soft soil,increase the rate of consolidation,prevention of liquefaction in loose sandy soils and provide lateral resistance against the horizontal movement.This research aims at investigating the effects of floating columns in clayey soil with silty deposits by developing small scale laboratory models.The laboratory tests were conducted on a circular column of 37 mm diameter and results of the treated ground are compared to the untreated ground.The effects of sand columns on soils of different shear strengths(low-medium-high),slenderness ratio(L/D)of columns and different loading pattern are investigated.Group effect was also investigated by varying the spacing between the columns.The equivalent entire area of test model was loaded to determine the stiffness of composite ground and axial capacity of sand column was determined by loading the column area alone.Based on current study,it was concluded that sand column can significantly enhance the engineering properties of soft clayey soil.Also,the group effect was studied and it was concluded that by increasing the spacing between the columns,the group efficiency decreases.The axial capacity of sand columns decreases while increasing the spacing between the columns.

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.

Influence of cement-fly ash-gravel pile-supported approach embankment on abutment piles in soft ground

Abutment piles in soft ground may be subjected to both vertical and horizontal soil movements resulting from approach embankment loads. To constrain the soil movements, the soft soil ground beneath the approach embankment is often improved using composite pile foundations, which aim at mitigating the bump induced by high-speed trains passing through the bridge. So far, there is limited literature on exploring the influence of the degree of ground improvement on abutment piles installed in soft soil grounds. In this paper, a series of three-dimensional （3D） centrifuge model tests was performed on an approach embankment over a silty clay deposit improved by cement-fly ash-gravel （CFG） piles combined with geogrid. Emphasis is placed on the effects of ground replacement ratio （m） on the responses of the abutment piles induced by embankment loads. Meanwhile, a numerical study was conducted with varying ground replacement ratio of the pile-reinforced grounds. Results show that the performance of the abutment piles is significantly improved when reinforcing the ground with CFG piles beneath the approach embankment. Interestingly, there is a threshold value of the replacement ratio of around 4.9% above which the effect of CFG pile foundations is limited. This implies that it is essential to optimize the ground improvement for having a cost-effective design while minimizing the risk of the bump at the end of bridge.

An Air Route Planning Model of Unmanned Aerial Vehicles Under Constraints of Ground Safety

With the rapid growth of the number and flight time of unmanned aerial vehicles(UAVs),safety accidents caused by UAVs flight risk is increasing gradually.Safe air route planning is an effective means to reduce the operational risk of UAVs at the strategic level.The optimal air route planning model based on ground risk assessment is presented by considering the safety cost of UAV air route.Through the rasterization of the ground surface under the air route,the safety factor of each grid is defined with the probability of fatality on the ground per flight hour as the quantitative index.The air route safety cost function is constructed based on the safety factor of each grid.Then,the total cost function considering both air route safety and flight distance is established.The expected function of the ant colony algorithm is rebuilt and used as the algorithm to plan the air routes.The effectiveness of the new air route planning model is verified through the logistical distribution scenario on urban airspace.The results indicate that the new air route planning model considering safety factor can greatly improve the overall safety of air route under small increase of the total flight time.

Analysis of ground deformation development and settlement prediction by air-boosted vacuum preloading

Vacuum preloading has been widely used to improve soft soils in coastal areas of China.An increasing amount of evidence from field operations has shown that conventional vacuum preloading is prone to clogging in prefabricated vertical drains(PVDs)and demands a large volume of sand fills.In recent years,air-boosted vacuum preloading has been developed to overcome these limitations;however,this method still requires more data to verify its performance.In this study,a field test for air-boosted vacuum preloading was conducted,and a large-strain two-dimensional(2D)finite element(FE)model was developed and validated against the field test data.Then,a series of FE parametric analyses was performed to assess key factors,i.e.the air injection pressure,the injection spacing,and the characteristics of cyclic injection,which affect the performance of the air-boosted vacuum preloading.The results showed that the ground settlement and lateral displacement of the soils increased due to an increase in the injection pressure,a decrease in the injection spacing,or increases in the number and duration of the injection cycles.Based on the parametric analyses,an empirical formula for ground settlement prediction was proposed and compared with a case history reported in the literature,showing good agreement.

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。

融合灭弧信息的有源串联接地配电网故障检测方法

为了优化有源全补偿消弧设备和挖掘灭弧状态信息包含的故障特征,该文提出基于串联分压的配电网消弧原理及融合灭弧状态信息的接地故障检测方法。提出采用单个H桥变流器与消弧线圈串联的有源降压消弧全补偿方法和灵活接入保护电容的有源消弧装置保护方案,在消弧原理与控制、设备承压与安全、功率输出与过压防护等方面表现出良好性能。提出融合有源降压消弧全补偿“伪正常”状态信息的接地故障检测方法,利用系统正常-故障-灭弧3种状态信息构造故障检测判据,在免受过渡电阻和分布参数不对称影响的基础上优化故障检测方式和提高故障检测效率,无需线路间信息的横向比较即可实现系统全域零序导纳测量、故障馈线独立判别和故障程度跟踪识别。仿真实验证实了方法的有效性,为优化配电网有源消弧和接地故障检测提供创新方案。

强震损伤格栅墙处理地基抗液化性能离心模型试验研究

水泥土格栅墙能有效减缓被围束土体在地震作用下的剪切荷载及变形,已广泛应用为一种高效的抗液化对策。针对其长期服役过程,开展了两组超重力离心模型试验以研究强振历史对水泥土格栅墙内被围束土体液化响应的影响。两组模型均由15 m厚的易液化含黏粒砂土和2.5 m厚的粗砂层组成。其中,一组模型采用水泥土格栅墙对易液化层进行加固;另一组模型则未进行处理,作为自由场地对照组。两组模型均经历振幅为0.15g的振动事件,且在0.15g振动事件前,对两组模型施加振幅为0.4g的振动事件作为强振历史。试验结果表明,格栅墙在强振下主要的损伤模式表现为竖向贯穿型裂缝,并部分伴随有局部斜向裂缝,且外侧格室对于中心格室表现出类似于群桩基础的“遮蔽效应”。强振历史后,格栅墙中心格室内被围束土体的超静孔压显著低于自由场地,损伤后格栅墙仍具有良好的抗液化效果。同时,格栅墙由于强振后整体刚度的削弱,其与下卧粗砂层间的剪切变形显著减小。

基于时间窗的机场地面保障车辆动态调度

机场各类地面资源的优化配置是机场场面运行优化的核心问题,而机场地面保障任务的调度是其中的关键一环。针对机场地面保障车辆的调度问题,考虑航班延误、提前等情况,构建了双阶段机场地面保障车辆调度模型,并设计双阶段启发式算法进行求解;基于中国某大型机场的实际运行数据,以清水车和食品车调度为例分别进行仿真实验。结果表明:对比先到先服务策略,清水车行驶总距离减少55.31%,食品车行驶总距离减少47.38%;对比传统遗传算法,清水车行驶总距离减少19.31%,食品车行驶总距离减少22.93%;动态调整后,清水车新增总行驶距离1.2%,食品车总行驶距离新增3.2%,均在可接受范围之内。可见,双阶段机场地面保障车辆调度模型能提高大型机场场面运行效率,为机场航班实际地面保障任务调度提供理论依据和决策支持。

基于改进粒子群算法的中深层地源热泵供暖系统运行优化

构建变工况运行且包含蓄热装置的中深层地源热泵供暖系统,基于改进粒子群算法,分别以运行费用、系统COP和地热能利用系数为目标函数对系统运行进行优化,并对优化结果进行比较和分析。结果表明:对应目标函数优化后的运行费用、系统COP和地热能利用系数分别为279.27元、6.4420和0.8527。以系统COP为目标函数的优化效果与运行费用相反,而与地热能利用系数相近。

森林消防救援起降点选择影响因素分析

为提高森林消防救援效率,针对森林消防救援的起降点选择,提出了一种改进DEMATEL-ISM法,对其影响因素进行深入分析。首先基于扎根理论建立面向森林消防救援起降点选择的影响因素体系,然后引入模糊集理论消除DEMATEL-ISM法中专家评分的主观性,通过分析起降点选择的影响因素间因果属性和影响程度,确定关键因素,通过合理设置阈值构建多级递阶结构模型。通过案例分析,得到了影响森林消防救援的5个关键因素、3个根本因素、3个直接因素以及10个间接因素,并提出起降点选择的相关建议。该研究成果可以加快林火救援时起降点选择的决策速度,提高森林消防救援效率,为起降点的选择提供理论依据和科学参考。

真空预压与真空井点降水用于软土处理的机理差异

真空预压与真空井点降水两种工艺均可用于软土地基处理,表观上两者都是通过抽真空使土体内孔隙水排出并使软土沉降,但目前对两者的工艺和机理等关键差异的认识不深入,难以有效指导现场施工。真空预压和真空井点降水在抽真空设备、竖向排水通道和密封边界等设备与工艺方面有显著差异;两者的的排水机理也有着本质区别。真空预压的加固机理是负压作用下土体发生塑料排水板水平向排水固结,同时塑料排水板内的水向上流动与重力无关;真空井点降水的加固机理是群井抽水引起地下水位降低,土体的浮重度变为湿重度导致荷载增大使土体沉降,同时井点管内的水向上流动受重力影响。在工艺和机理的差异分析的基础上,进一步明确了真空预压和真空井点降水在10个关键方面的差异,包括加固机理、影响深度、不同深度的真空传播、土体水平变形、竖向排水与重力的关系、抽真空位置影响、与外界是否连通、影响区成因、地下水位变化、是否形成非饱和带。

刚性桩复合地基的载荷试验问题

《建筑与市政地基基础通用规范》(GB 55003—2021)对刚性桩复合地基承载力验收的条文是:复合地基承载力的验收检验应采用复合地基静载荷试验,对有粘结强度的复合地基增强体尚应进行单桩静载荷试验。在实际工程中,可能会遇到这样的情况:(1)复合地基静载荷试验合格,单桩静载荷试验不合格,复合地基承载力真的不合格吗?(2)复合地基和单桩静载荷试验都合格,复合地基承载力就一定合格吗?本文对此进行了分析讨论,认为与地质条件有关,规范方法主要是针对单一均匀地基的情况,对于多层土地基,规范方法有局限性,由于试验压板尺寸小,压板试验还不能反映深层土的影响。对于大尺寸的基础,还要进行科学的分析,应对实际尺寸的基础沉降进行计算分析,才能判断和保证工程的安全,仅靠小尺寸的压板载荷试验是不够完善的。

Assessment of compressive strength of jet grouting by machine learning

Jet grouting is one of the most popular soil improvement techniques,but its design usually involves great uncertainties that can lead to economic cost overruns in construction projects.The high dispersion in the properties of the improved material leads to designers assuming a conservative,arbitrary and unjustified strength,which is even sometimes subjected to the results of the test fields.The present paper presents an approach for prediction of the uniaxial compressive strength(UCS)of jet grouting columns based on the analysis of several machine learning algorithms on a database of 854 results mainly collected from different research papers.The selected machine learning model(extremely randomized trees)relates the soil type and various parameters of the technique to the value of the compressive strength.Despite the complex mechanism that surrounds the jet grouting process,evidenced by the high dispersion and low correlation of the variables studied,the trained model allows to optimally predict the values of compressive strength with a significant improvement with respect to the existing works.Consequently,this work proposes for the first time a reliable and easily applicable approach for estimation of the compressive strength of jet grouting columns.