土压平衡盾构施工中渣土改良技术的应用

地铁隧道工程施工时,经常会采用盾构施工法进行施工,在施工期间,需要结合地质情况及施工进度对渣土的状态进行改良和调整,保证盾构施工顺利开展。以实际工程为例,首先对渣土改良的重要性进行了分析,然后提出渣土改良的方案,并根据实验室配比进行研究,探讨土压平衡盾构施工过程中渣土改良施工技术的应用,确保项目工程的顺利施工,为同类工程施工提供参考与借鉴。     

南昌富水砂砾石地层土压平衡盾构渣土改良技术研究

以南昌轨道交通1号线土建六标工程项目的彭家桥站—师大南路站区间施工所采取的渣土改良技术为背景,对富水砂砾石地层条件下土压平衡盾构施工渣土改良系统的优化创新、渣土改良剂的选择、配合比试验、添加剂注入量的确定等措施进行了详细的研究试验,实践结果表明,通过该项渣土改良技术改良出的渣土具有良好的流塑性和止水性,有效地减小了刀盘扭矩,控制了地表沉降,并安全地下穿了浆砌块石基础的老石拱桥。     

砂性地层盾构施工渣土改良试验研究

土压平衡盾构机在砂性地层中掘进时,因颗粒间的摩擦阻力、渗透系数大等原因需要进行渣土改良,但目前国内尚未系统地制定某类地层渣土改良的技术标准,因此采用室内试验和现场论证的方法进行渣土改良试验,以泡沫土的搅拌（扭矩）、坍落度、压缩性、直剪性能和渗透性5个方面作为渣土改良的评价依据。通过对泡沫剂改良渣土的主要性能指标进行量化研究,得出了泡沫剂改良渣土的最佳注入比;通过实际工程应用,验证了泡沫剂在渣土改良中效果较明显,推力、刀盘扭矩、螺旋输送机扭矩、土仓压力等施工参数都得到了改善,为实际工程提供了助力。     

南宁泥质粉砂岩地层中土压平衡盾构掘进渣土改良技术

南宁地铁1号线泥质粉砂岩地层中土压平衡盾构掘进土施工中,为使仓渣土达到塑性流动状态以提高掘进效率,采用泡沫剂作为渣土改良材料,通过发泡率、稳定性、坍落度等室内试验确定渣土改良参数并应用于施工,达到了预期效果。     

哈尔滨地区富水砂层盾构施工的渣土改良技术研究

针对哈尔滨地区的富水砂层盾构施工难题,进行了实验室内的渣土改良研究。试验采用膨润土泥浆和高分子吸水树脂等添加剂,以改善渣土性状,并测试渣土的坍落度和渗透系数。其后,将实验室研究的配比结果应用于现场盾构施工,并设置试验段来测试盾构采用不同渣土改良手段后的扭矩变化。研究结果表明:采用1.05 g/ml的膨润土泥浆,配合质量百分数为0.3%的高分子吸水树脂溶液,注入量为渣土质量的5%～7%,可以满足盾构在富水砂层施工中的渣土改良要求。     

北京地区典型地层土压平衡盾构渣土改良技术

北京地区地层条件复杂,土压平衡盾构施工过程中渣土改良困难,易发生刀具磨损严重、地表塌陷等风险事故。在分析北京地区典型地层工程特点的基础上,结合主要渣土改良材料的特性及作用原理,对典型地层渣土改良技术进行了研究,得出了北京地区3种典型地层在不同水文地质条件下的土压平衡盾构渣土改良技术。     

地下综合管廊盾构法施工渣土改良系统研究

盾构法施工过程中,经常会遇到复杂的地质情况,针对不同的地质情况进行不同的渣土改良则是一大难点,研究盾构法施工过程中渣土改良系统则为重中之重,结合沈阳市地下综合管廊(南运河段)工程,通过对不同地质情况渣土改良系统的详尽阐述,为同类工程提供参考。     

生石灰膨润土泥浆土压盾构渣土改良试验研究

土压平衡盾构在砂性地层施工中,常出现盾构刀盘磨损严重、扭矩过大、土压舱土体难形成塑流状态等问题,施工中常使用膨润土泥浆作为土体改良剂对切削渣土进行改良来解决上述问题。本文以膨润土和生石灰为原料配制土体改良剂,通过采用泥浆粘度和相对密度为参考指标优选出合适的泥浆作为土体改良剂对渣土进行改良,并对改良渣土开展坍落度试验和剪切试验来综合评价生石灰含量对渣土改良效果的影响。试验结果表明:对于生石灰掺量为0%~2.8%的膨润土泥浆,随着生石灰含量的增加,泥浆的粘度和相对密度有所增加,改良后渣土的抗剪强度有所降低,在生石灰含量为1.4%时坍落度能较好的满足施工要求。     

浅埋富水全断面砂层盾构施工渣土改良初步研究

在隧道工程施工过程中,对于富水全断面砂层一般使用盾构进行施工。在施工的过程中,对渣土进行改良是施工中的重点和难点。本文以实际工程为例,对富水全断面砂层盾构施工渣土改良技术进行研究。     

地铁隧道穿越砂-黏地层沉降控制技术研究

依托广州地铁区间隧道下穿条形浅基础密集民居建筑群工程,通过渣土改良试验,明确各改良参数对渣土力学性能的改良效果及其合理范围。利用FLAC3D软件模拟盾构穿越松散富水砾砂、粉质黏土和风化花岗岩复合地层的施工过程,探究可有效控制地层沉降变形的盾构施工参数范围。研究表明:基于室内渣土改良试验用发泡剂浓度为3%的泡沫剂进行渣土改良,控制渣土含水率在16.95%、20.95%左右,泡沫剂掺入比分别为21%~46%、71%~92%,可将渣土塌落度、渗透性等力学性能改良至理想状态;根据盾构实况,应调整土仓压力大于原应力平衡体系静水土仓压力;通过增大注浆压力,最大化密实地层空隙与盾尾脱空间隔,提高加固层弹性模量,控制地层不均匀沉降;对比分析试验段、下穿段和危害建筑物的沉降监测数据,施工过程中采取渣土改良措施与设定优化的盾构参数,可将地层与危害建筑物的变形控制在规定的安全范围内。为类似盾构隧道提供技术指导。     

路堤土质边坡土性参数的变异性分析

对土的物理参数、力学参数的变异性进行了分析,并探讨了土性参数的变异性对路堤边坡稳定性的影响,得出对于边坡的稳定性分析应在定值法分析的基础上进行可靠度分析,而不应当仅仅进行简单的力学定值分析而判定边坡质量状态的结论。     

离子土固化剂改良膨胀土的机理研究

以河南安阳典型弱膨胀土为研究对象,分别对素土及离子土固化剂（Ionic Soil Stabilizer,简称ISS）改良土进行一系列的理化试验研究,通过标准吸湿含水率试验分析土体吸湿持水能力的变化;通过X射线衍射、傅立叶红外光谱测试、阳离子交换量及可交换阳离子成分测定、Zeta电位、比表面积,扫描电镜试验分析土体矿物组分、晶体结构、电化学性质及表面属性等反映土体胀缩本质因素的变化规律。试验结果表明：膨胀土经离子土固化剂处理后,吸湿持水能力下降,膨胀能力变弱,土样矿物成分未发生明显变化,但蒙脱石类矿物d₀₀₁晶层间距变小,层间水合度降低;通过离子交换,ISS置换出膨胀土体颗粒表面亲水性阳离子,促使土体阳离子交换量减小,可交换阳离子主要成分为Ca²⁺;改良土体ξ电位降低,土颗粒间连接力增强,比表面积减少。ISS改良机理可解释为通过离子交换,吸附,包裹等一系列复杂的表面物化反应,降低黏土矿物晶层间“水敏性”,改变土颗粒表面的双电层结构,促使结合水膜厚度减薄,从而降低了土体的膨胀性,水稳定性。     

非饱和土的性状及膨胀土边坡稳定问题

主要叙述非饱和膨胀土及其边坡稳定研究方面的新进展。首先讨论了非饱和土研究中与土坡稳定性有关的若干重要特性,指出非饱和土的气 水形态问题是非饱和土研究的一个基本问题。并提出随含水率由小变大,非饱和土存在四种气 水形态,不同气 水形态的土具有不尽相同的性状。然后,对非饱和土的吸力和土水特征曲线以及不同气 水形态下的强度作了讨论,并对非饱和土的本构关系作了简要的介绍。接着以南水北调中线膨胀土渠道工程为背景,以吸力问题为中心,对非饱和膨胀土边坡滑动的各种内在的和外界的因素进行了分析,尤其对新近研究的降雨入渗和裂隙影响的研究进行了定量的分析,改变了以往对这方面只进行定性研究的情况。在此基础上对边坡失稳的机理和考虑裂隙及雨水入渗的稳定分析方法进行了研究。     

水泥稳定土处治盐渍土软土地基试验研究

通过 S201线水泥稳定土处治试验盐渍土软土地基研究,找出了水泥稳定土处治盐渍土软土地基的合理厚度,以完善盐渍土地基处治设计及施工工艺,为盐渍土湿软地基处治提供参考.     

脂肪族离子固化剂改性水泥土的机理研究

水泥基材料加固土(水泥土)存在早期强度低、易开裂变形等性能缺陷。为对其改性,在水泥土中掺入含水率体积1/300～1/50不等的新型土壤固化材料,离子固化剂(ISS)。通过无侧限抗压强度试验、体积化学减缩试验,探究了ISS改性水泥土的可行性,并通过对表面吸附特性、物相构成演变、微结构特性的表征及分析,对ISS改性水泥土的机理进行了系统的研究。结果表明:ISS分子对于水泥土各组分具有显著的选择吸附性;ISS掺入水泥土后,能够提升体系内各组分的分散性并降低黏土矿物结合水的能力,进而加速土体内水化反应产物的生成,优化土体孔隙结构,提升土体强度并增大体积化学减缩;最优ISS掺量为1/150,过量的掺入会减弱ISS的改性效果,但可降低水泥土体积的化学减缩。相关成果可为离子固化剂应用于水泥土的改性提供一定的参照。     

非饱和土土水特性试验研究

在改进的非饱和土三轴仪上对洛阳地区非饱和土开展了三轴试验,并依此对非饱和土土水特性、试样重塑对基质吸力的影响进行了分析研究。研究表明:试件的基质吸力随围压的增大而非线性减小,基质吸力随饱和度的增大而连续减小,饱和度与基质吸力的关系是连续的。     

土钉支护技术在软土基坑中的应用

土钉支护技术近年来已在我国高层建筑的深基坑开挖施工中得到愈来愈多的应用，本文作者通过对具体项目的实践，透析了该技术在运用中的一些问题，具有一定的借鉴作用。     

Effect of cation exchange capacity of soil on stabilized soil strength

While a certain correlation between the cation exchange capacity (CEC) of the soil and the strength of the cement stabilized soil has been reported, the mechanism remains unclear. In this research, a set of soil samples with different CECs were stabilized with different proportions of cement and calcium hydroxide (Ca(OH)₂, CH). The influence of soil CEC on the strength of the stabilized soil was investigated by analyzing the CH saturation in the pore solution and measuring the strength of the stabilized soil specimens. It is revealed that cation exchange in the soil can reduce the CH saturation of the stabilized soil. If the CEC of the soil is too high, the CH in the pore solution of the stabilized soil cannot reach the saturation level, and further cation exchange would then consume the Ca²⁺ ions which should be originally used to generate calcium silicate hydrate, thus result in the poor strength of the stabilized soil.     

European soil sampling guidelines for soil pollution studies

The soil sampling guidelines used in European countries (ESSG), as kindly provided by the national institutions which participated in the project, have been recorded, studied, evaluated and presented in this paper. The aim has been to ascertain what soil sampling guidelines exist in Europe; to detect similarities and differences (comparable results), advantages and deficiencies; to identify incompatible strategies and evaluate how methodologies might affect data quality; to investigate sources of deviations or uncertainties; to improve comparability and representativeness of soil sampling; to investigate the need for harmonised sampling guidelines; and to develop suggestions for standard operating procedures (SOP). Soil sampling guidelines throughout Europe differ as to whether they are applied by law, or used throughout the country. In some countries these are ISO/DIS related or based (ISO 10381-1, 1995; ISO 10381-2, 1995), or are produced by a scientific society or a standardisation body. As far as sampling strategy is concerned, not all sampling guidelines clearly describe the sampling scale, the specifications for contamination risk precautions, the sampling plan and protocol structure and the pre-analysis treatment of the soil samples. The purpose for sampling, in descending order of frequency, is soil pollution, soil fertilisation, general soil monitoring, background risk assessment, or else it is not specified. The majority of countries do not sample the top organic matter separately. Sampling depth is either related to the morphogenetic horizon or to ad hoc sampling depth, which is not specified in all cases. They suggest mass- and volume-related soil sampling, while the sampling pattern is not presented in all national guidelines. The criteria for area, site, unit, sub-unit, and point selection are mainly based on pedology and land use, following the history and pre-screening information or geology, or is site related. Some guidelines suggest the division of sampling units into sub-units. The sampling pattern is mainly grid sampling, grid and random sampling, or not mentioned. Sampling density inside the sampling unit either varies greatly or it is not mentioned, while the size of the sampling unit varies widely. Most guidelines require the collection of composite instead of simple samples, while some prefer sampling soil profiles. In the European SSG many technical details and steps are either not defined or vary, while in the pre-analysis treatment quality assurance (QA) and quality control (QC) approaches are used either both in the lab and in the field, or only in the field, or are not mentioned. The common points and the points in which harmonisation could be started or achieved are discussed.     

Influence of relative density of soil on performance of fiber-reinforced soil foundations

An experimental study has been carried out for studying the influence of combinations of relative densities of two layered soil system. The model tests have been performed for the case of circular and ring footings resting on randomly distributed fiber reinforced sand (RDFS) layer overlying unreinforced sand bed. The influence of relative density on, different type of footings i.e. circular and ring (r_i/r_o = 0.3, 0.4, 0.5, 0.6) footings; percentages of fiber in RDFS layer i.e. 0.5%, 0.75%, 1.00%, and 1.25%; and thickness of RDFS layer i.e. 0.5B, 0.75B, and 1.00B have been studied. Results have indicated that relative density, of both the RDFS layer as well as the bottom unreinforced sand layer, significantly influences the ultimate bearing capacity as well as the settlement. Improvement in terms of bearing capacity ratio (BCR) is more when top RDFS layer is compacted at 70% relative density with bottom unreinforced sand having 30% relative density. Moreover, in terms of settlement reduction, maximum improvement is observed when both the layers were compacted at 70% relative density.