地下连续墙成槽成墙阶段槽壁稳定和变形的三维数值分析

泥浆护壁成槽施工中槽壁的稳定是保证地下连续墙顺利施工及其墙体施工质量的关键,结合上海十六铺改造工程深基地下连续墙围护施工,采用理论与数值分析相结合的方法对该工程地下连续墙泥浆护壁成槽施工和混凝土浇筑过程中的槽壁稳定与变形进行模型计算,并与实测结果对比,印证了计算与实测类似规律性。     

超深地下连续墙槽壁稳定分析与工程实践

对某工程超深地下连续墙进行了成槽期间槽壁稳定的计算分析,结果表明:高地下水位的影响较大,槽壁稳定最危险区段在-4～-12m间。考虑到三维土体结构所形成的拱效应的有利影响,采取了在最危险区段深度范围进行单轴水泥土搅拌桩槽壁加固的处理措施,现场施工实践证明该方案适合可行。     

地下连续墙成槽施工槽壁整体稳定性分析

地下连续墙槽壁稳定是确保成槽安全及成槽质量的关键前提,为从理论上分析其整体失稳机制,建立了槽壁整体破坏滑动体模型,基于土体相关联流动法则及塑性极限破坏理论,采用极限平衡分析法,得到槽壁整体失稳的最小泥浆重度及安全系数计算方法,并从安全系数角度对比分析两种计算方法的参数敏感性,最后结合工程实例对两种泥浆重度计算方法进行对比分析和验证。研究结果表明:本文方法相较于常用方法更适用于黏土地层槽壁稳定性分析,且安全系数主要受槽段长度、泥浆重度、土体内摩擦角及泥浆-水液面相对高差影响。实际成槽泥浆重度介于理论计算的控制范围之内,理论分析得到现场超声波检测验证,其结果可为今后地下连续墙成槽施工提供理论参考。     

搅拌桩加固作用下地下连续墙的槽壁稳定分析

在深厚的砂层或软土层中进行地下连续墙施工,往往需要采用搅拌桩对地下连续墙的槽壁进行加固处理。本文针对地下连续墙成槽施工过程中的槽壁稳定性及失稳现象,分析了地下连续墙槽壁失稳的主要机理。基于库伦理论的滑动体模型,对搅拌桩加固作用下的槽壁稳定性进行受力平衡分析,并导出了槽壁稳定安全系数的计算公式,结合计算实例分析了搅拌桩的强度、加固宽度对槽孔稳定安全系数和泥浆比重的影响规律,提出了搅拌桩的强度和加固宽度建议值,可供其它类似工程参考。     

泥浆护壁临界深度的计算

地下连续墙成槽或灌注桩成孔,常采用泥浆护壁方法。泥浆对槽壁主要起液体支撑作用,保护开挖槽面的稳定,它是确保挖槽机成槽的关键。泥浆护壁稳定槽壁的临界深度,可借助于楔形土体滑动的假定分析的结果进行计算。一、在粘性土中成槽的计算     

深厚砂层中地下连续墙槽壁稳定性分析

随着经济的发展,基坑开挖深度越来越深,而这些深大基坑紧邻交通干道、地铁隧道及各种地下管线,施工场地紧张,工期紧迫。地下连续墙由于其施工噪声小、刚度大、整体性好和良好的抗渗能力等优点得到广泛的应用。结合工程实例分析地下连续墙成槽过程中的槽壁稳定问题,计算出槽壁稳定最小安全系数Fsmin的临界角θcr,分析了槽壁稳定的影响因素,提出保证槽壁稳定的技术措施,为地下连续墙的设计与施工提供参考。     

深基坑地下连续墙的泥浆槽壁稳定分析

首先对深基坑地下连续墙槽壁失稳机理进行探讨,然后基于库仑理论对槽壁整体稳定性进行滑动体受力平衡分析并导出了槽壁稳定安全系数的计算公式,结合算例与半圆柱法、抛物线法以及对比法等进行了对比分析,并对影响槽壁稳定的主要因素进行了分析,最后提出了控制槽壁稳定的一系列具体措施。     

泥浆护壁监界深度的计算

地下连续墙成槽或灌注桩成孔，常采用泥浆护壁方法。泥浆对槽壁主要起液体支撑作用，保护开挖槽面的稳定，它是确保挖槽机成槽的关键。泥浆护壁稳定槽壁的临界深度，可借助于楔形土体滑动的假定分析的结果进行计算。     

地下连续墙槽壁稳定性探讨

地下连续墙施工中的槽壁稳定性控制是地墙施工的关键，直接关系到基坑施工的安全。论述了地下连续墙槽壁稳定的机理，分析了影响槽壁稳定的关键因素，并通过工程实践进行验证，取得良好的效果。     

江苏某港口码头地下连续墙泥浆槽壁稳定性研究

地下连续墙的成槽稳定性制约着地下连续墙的发展,通过分析影响槽壁土体稳定性的各影响因素及失稳机理,并对槽壁土体进行稳定性分析,得出槽壁稳定性与地面超载、土体黏聚力、内摩擦角、泥浆液面标高、地下水位等因素的关系。同时结合实体工程进行分析计算,并辅以成槽检测进行了验证。     

复杂地层地下连续墙施工实例分析

地下连续墙工法的广泛应用使得深基坑技术日益成熟,特别是在地质条件恶劣区域。以复杂地层情况下地下连续墙施工实例为背景,介绍地下连续墙施工过程中难点及注意事项。同时,在基坑开挖阶段对地下连续墙实时监测,对监测数据进行适当地处理,反映地下连续墙变形的实际情况。结合地下连续墙变形监测数据,表明该工法的应用效果良好,期望能对类似工程有一定的参考。     

TRD技术在超大基坑中的应用

武汉市长江航运中心属超大面积深基坑工程,地质勘查发现,对基坑开挖影响最大的软～流塑、高压缩性、强度较低的粉质粘土夹粉土在整个场地均有分布,因紧邻长江,基坑工程还将面临极为严峻的承压水影响问题。基于地质水文条件,地下二层区域采用常规的钻孔灌注桩结合三轴水泥土搅拌桩止水帷幕作为支护体。对于地下三层区域,其受承压水影响严重,止水帷幕深度较大。TRD工法地下连续墙可施工的深度较大,而且地层适应性也广,可满足本工程隔断地下水的要求,因此,地下三层区域选择地下连续墙（TRD工法）支护体。Ⅰ区和Ⅱ区的水平支撑均采用对撑结合边桁架支撑。     

Effects of slurry on stickiness of excavated clays and clogging of equipment in fluid supported excavations

Mechanized excavation of tunnels and fabrication of deep foundation elements in soft ground often requires a fluid support of the temporarily created openings. The supporting fluids are generally mixtures of bentonite with water, enhanced by chemical additives for difficult geological conditions. The properties of the slurries are chosen to guarantee the stability of the excavation, in particular providing sufficient support to the coarse grained soil layers. When these are interlaid with clayey layers, excavation can be hindered by clogging problems, requiring time consuming cleaning works and causing construction delays. Clogging is caused by the stickiness of the excavated clay, which can be affected both by the clay mineralogy and the composition of the supporting slurry. The paper investigates these effects by means of a laboratory experimental study using novel stickiness tests: the mixing test and a model TBM cutter-head test. For bentonite slurries, the stickiness of the excavated soil was found to correlate with the shear resistance of the slurry. Therefore, increased slurry strength, while beneficial for excavations in coarse soils, may lead to increased susceptibility to clogging under mixed face conditions. In contrast, some pure polymer slurries can help to combine high slurry resistance with low clogging potential by protecting clay aggregate surface from penetration of water.     

泥浆减阻技术在粉土地层长距离曲线顶管中的应用

上海世博北京西路～华夏西路电力电缆隧道三标工程采用Ф3500F型钢筋混凝土管和大刀盘泥水平衡顶管掘进机施工。该工程分为6个区间顶程,全部是大直径长距离曲线顶管,其中11～10区间顶管穿越的地层主要为夹砂粉土层。该区间顶管实施过程中,施工技术人员对顶管触变泥浆材料、配方、搅拌方法、注浆工艺等,尤其是对触变泥浆在粉土地层中的抗渗透性能和稳定性进行了深入的研究。通过研究结果在施工中的运用,成功地将混凝土管道外壁与粉砂土之间的单位面积侧向摩阻力控制在1kPa以内,保证了顶管顺利贯通的同时,该研究与应用成果还为今后类似顶管工程的设计和施工提供了参考。     

Opening the excavation chamber of the large-diameter size slurry shield: A case study in Nanjing Yangtze River Tunnel in China

Shield tunnel construction in a dense strata often encounters malfunction of shield-tunneling machine or abrasion of cutters. Accessing to an excavation chamber under compressed air is a main method to repair and replace worn cutters. And many safety issues such as stability of the excavation face were involved. However, the face stability due to opening an excavation chamber was not fully studied. To overcome this shortcoming, face support scheme and stability analysis were presented in a case history of opening the pressure chamber for a large-diameter (up to 14.93 m) slurry shield tunnel constructed underneath Nanjing Yangtze River. Since most of the damaged cutters were distributed along the edge of cutting wheel, only top 3 m of tunnel face within the chamber needed to be supported by compressed air, and remaining area would also to be supported by slurry pressure. A series of simple primary laboratory tests were carried out to design an optimum slurries mixing scheme to support the tunnel face as accessing to the pressure chamber in the project. The face stability was analyzed in terms of the pressure equilibrium (i.e., internal and external pressures) as well as three-dimensional numerical analysis by adopting properties of soils and filter cakes from laboratory tests. By injecting lower density slurry into the sand to form a stable infiltration zone, followed by using higher density slurry to create a filter cake at tunnel face, compressed air-support system could ensure face stability during maintenance of cutter wheel. The success of applying the mixed slurry and compressed air-support scheme in this project is valuable to shield tunnel constructions in similar ground conditions.     

Storage temperature affects distribution of carbon, VFA, ammonia, phosphorus, copper and zinc in raw pig slurry and its separated liquid fraction

Chemical-mechanical separation of pig slurry into a solid fraction rich in dry matter, P, Cu and Zn and a liquid fraction rich in inorganic N but poor in dry matter may allow farmers to manage surplus slurry by exporting the solid fraction to regions with no nutrient surplus. Pig slurry can be applied to arable land only in certain periods during the year, so it is commonly stored prior to field application. This study investigated the effect of storage duration and temperature on chemical characteristics and P, Cu and Zn distribution between particle size classes of raw slurry and its liquid separation fraction. Dry matter, VFA, total N and ammonium content of both slurry products decreased during storage and were affected by temperature, showing higher losses at higher storage temperatures. In both products, total P, Cu and Zn concentrations were not significantly affected by storage duration or temperature. Particle size distribution was affected by slurry separation, storage duration and temperature. In raw slurry, particles larger than 1 mm decreased, whereas particles 250 μm-1 mm increased. The liquid fraction produced was free of particles >500 μm, with the highest proportions of P, Cu and Zn in the smallest particle size class (<25 μm). The proportion of particles <25 μm increased when the liquid fraction was stored at 5 °C, but decreased at 25 °C. Regardless of temperature, distribution of P, Cu and Zn over particle size classes followed a similar pattern to dry matter.     

高速公路稀浆封层施工质量控制

近年来稀浆封层被广泛应用于新建高速公路,但施工过程中还存在一些问题影响着稀浆封层的施工质量。结合工程实践,本研究对影响稀浆封层施工质量的因素进行分析,提出相应的施工质量控制方法,从而提高了施工质量。     

The role of slurry TBM parameters on ground deformation: Field results and computational modelling

This paper examines the role of slurry TBM operational parameters, namely face, annulus and grout pressures, on ground deformation. The analysis includes both field data and computational modelling. Field data from the very successful Queens bored metro tunnels (6.9 m diameter) project in New York City is employed to illustrate phenomenologically how ground deformation was controlled via slurry TBM parameters. Computational modelling is then employed to support the experimental findings and to further investigate the relative influence of TBM parameters through parametric analysis. The results quantify the importance of the various pressures on controlling ground deformation.     

Impact of chemical amendment of dairy cattle slurry on phosphorus, suspended sediment and metal loss to runoff from a grassland soil

Emerging remediation technologies such as chemical amendment of dairy cattle slurry have the potential to reduce phosphorus (P) solubility and consequently reduce P losses arising from land application of dairy cattle slurry. The aim of this study was to determine the effectiveness of chemical amendment of slurry to reduce incidental losses of P and suspended sediment (SS) from grassland following application of dairy cattle slurry and to examine the effect of amendments on metal concentrations in runoff water. Intact grassed-soil samples were placed in two laboratory runoff boxes, each 200-cm-long by 22.5-cm-wide by 5-cm-deep, before being amended with dairy cattle slurry (the study control) and slurry amended with either: (i) alum, comprising 8% aluminium oxide (Al₂O₃) (1.11:1 aluminium (Al):total phosphorus (TP) of slurry) (ii) poly-aluminium chloride hydroxide (PAC) comprising 10% Al₂O₃ (0.93:1 Al:TP) (iii) analytical grade ferric chloride (FeCl₂) (2:1 Fe:TP), (iv) and lime (Ca(OH)₂) (10:1 Ca:TP). When compared with the study control, PAC was the most effective amendment, reducing dissolved reactive phosphorus (DRP) by up to 86% while alum was most effective in reducing SS (88%), TP (94%), particulate phosphorus (PP) (95%), total dissolved phosphorus (TDP) (81%), and dissolved unreactive phosphorus (DUP) (86%). Chemical amendment of slurry did not appear to significantly increase losses of Al and Fe compared to the study control, while all amendments increased Ca loss compared to control and grass-only treatment. While chemical amendments were effective, the reductions in incidental P losses observed in this study were similar to those observed in other studies where the time from slurry application to the first rainfall event was increased. Timing of slurry application may therefore be a much more feasible way to reduce incidental P losses. Future work must examine the long-term effects of amendments on P loss to runoff and not only incidental losses.     

Experimental evaluation of the performance of a geotextile for a pressure-grouted soil nail

A new idea that adopts a geotextile instead of a latex membrane to improve the performance of a pressure-grouted soil nail, was proposed. First, based on the self-developed device, a series of cement slurry filtration tests were carried out to study the influence of the water-cement ratio, slurry volume, and grouting pressure on the geotextile's filtration performance. The variations in filtration time and water-cement ratio, derived from the changes in the aforementioned influencing factors, during pressure grouting were obtained. Second, corresponding penetration tests for the surrounding sands after filtration tests were conducted, and the strength improvement due to infiltration of cohesive substances was subsequently evaluated. Third, uniaxial compression tests were carried out for cement blocks before and after the filtration tests. The grout bulb strength (cement block) was largely increased because the water-cement ratio in the grout bulb was significantly reduced during filtration of the geotextile. This study can help optimize the design of pressure-grouted soil nails using geotextiles.