Although the geotechnical properties and its indexes of the clayey soils subjected to acid/base contamination were widely investigated by the researchers, the relationships between the physical indexes and mechanical indexes of the contaminated soils were rarely addressed. This study investigated the plasticity and mechanical properties of a natural silty clay subjected to sulphuric acid, hydrochloric acid and sodium hydroxide, as well as the relationships between the plasticity indexes (liquid limit plasticity w(L), plasticity index I-P, liquid index I-L) and mechanical indexes (compression index c(c), undrained shear strength c(u)). The plasticity of the two acid-contaminated soil samples exhibited opposing trends, which cannot be explained by the diffuse double-layer theory. The normalised compression curves, c(c )- w(L) relationships, and c(c) - I-P relationships were changed significantly, and the relationships established for clean soils are no longer valid for the contaminated soils. However, the c(u) - IL relationships were almost unchanged by contamination. The structure effect induced by the soil-water-chemical interactions, which cannot be accounted for by the diffuse double-layer theory, is a factor governing the plasticity and index relationships of the contaminated soils.

软黏土不排水剪切过程中的孔隙水压力分析是软土工程的一个重要研究方向.三轴试验是研究软黏土不排水剪切孔压及孔压系数的传统方法,而孔压以及孔压系数的大小与应力路径以及剪应变的大小有关.利用 GDS 应力路径三轴仪,对上海软黏土原状土样与重塑土样进行了三轴ICUC(等压固结压缩剪切),三轴ACUC(K0 固结压缩剪切)和三轴ACUE(K0 固结拉伸剪切)三种应力路径的不排水剪切试验,对比这三种试验的剪切孔压及孔压系数的大小及变化规律,给出结构性以及各向异性对剪切孔压的影响规律.最后根据试验结果给出了上海软黏土在变形较大情况下的剪切孔压—应变双曲线模型的参数,可供设计计算采用.

Aquifers in China's southeast coastal areas are protected by the overlying marine soft clays formed in Holocene transgression. However, a fundamental understanding of the characteristics of DNAPL (dense nonaqueous phase liquid) contamination in marine soft clays is limited. The study was conducted on the site of a former pharmaceutical factory in Shanghai, where serious 1,1,2-trichloroethane (DNAPL) contamination was detected up to the depth of 22.0 m below the existing grade. Partitioning calculation method was used to identify the presence of pure phase, and the results showed that pure 1,1,2-trichloroethane was accumulated at the interface of the upper soft silty clay and lower soft clay. The vertical transport was believed to be the pure DNAPL displacing pore water following the principle of two-phase flow, rather than the convection and diffusion of aqueous phase. The contamination (NAPL-soil interaction) impacted the soil properties slightly, and this effect could not account for the deep contamination. Soil structure analysis showed that these clays contained a proportion of large interaggregate pores, providing pathways for the transport of pure DNAPL. Considering their flocculated structure, the marine soft clays are not capable to perform as a barrier to prevent the downward migration of pure DNAPL.

Unloading in deep excavation in thick soft soil usually leads to large pillar uplift which may endanger the safety of the retaining system.In the pillar uplift analysis, complex interactions among soil, pillar（pillar pile） and struts are involved, and the soil heave behavior during undrained excavation shall be understood well, but there is no simplified calculation method available at present.Firstly, the interactions among soil, pillar（pillar pile） and strut are simplified, and a theoretical analysis model for pillar uplift estimation in practical design is proposed, in which the key point is the determination of the heave of the soil around the pillar.Based on the numerical analysis results, a normalized soil heave curve was proposed, and the soil heave could be estimated in terms of the maximum lateral displacement of the retaining wall.Finally, with the deep excavation of a subway station in Shanghai taken as an example, the design procedures with this new method were elaborated, and the rationality of the method was verified; the stress and deformation characteristics of the pillar and the design principles of uplift control of the pillar were also discussed in depth based on the calculation results.

Geopolymers are widely considered be low-carbon and cost-effective binders and are used for the stabilization of soft soils in recent years. The current study investigated the stabilization efficacy of low-calcium fly ash (FA) geopolymer for soft clay. The influence of FA content, initial water content, and curing time on stabilization efficacy was investigated. A range of laboratory tests were conducted to investigate the strength and permeability performance of the geopolymer-stabilized clay, including unconfined compressive strength (UCS), falling head permeability, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the mechanical performance of the soft clay at high water content was greatly improved by low-calcium FA geopolymer, exhibiting obvious characteristics of continuous long-term strength development and more ductility compared with cemented clay. A linear empirical relationship was proposed to overcome the shortcomings of the traditional logarithmic function for predicting the long-term strength evolution of low-calcium FA geopolymer-stabilized clay. The UCS of the mixtures increased rapidly with increasing FA content from 16% to 30% and from 25% to 30% for clay water content at liquid limit (LL) and 1.4 LL, respectively. Thirty percent FA content is needed for stabilizing soft clay at 1.0 LL by the deep soil mixing (DSM) method but is obviously not enough at higher initial water content. The major reduction in permeability of the geopolymer-stabilized clay occurred within 28 days of curing while the FA content reached 12%. Despite the increase in curing time up to 90 days and the increase in FA content to 30%, permeability decreased quite slowly. Comparing with the cemented clay, the stabilized clay showed better hydraulic performance but slightly lower permeability.

原位软土处于K0固结状态因此变形具有显著的非线性和各向异性,然而室内三轴剪切试验通常采用等向固结方式,目前对K0固结和等向固结两种方式下不排水剪切的模量Eu的差别还未系统的对比总结过.采用上海软黏土的原状土样和重塑土样,进行了三轴等向固结压缩(ICUC)、K0固结压缩(ACUC)和K0固结拉伸(ACUE)三种不排水剪切试验,对比分析了应力-应变曲线、不排水模量Eu的非线性特性以及双曲线模型的参数值.研究结果表明,同等应变下ICUC试验的Eu与ACUE试验相近,但要大于ACUC试验值;ACUC试验与ACUE试验具有相近的初始模量和破坏比.结合试验结果和双曲线模型,推导给出了适用于这三种试验的归一化模量的统一表达式,并给出了上海软黏土的参数值.

在弯曲元剪切波速测试中,试样尺寸是一个重要的影响因素.在以往的研究中,试样长度与激发波波长之比常被认为与消除近场效应有关,然而与试样长度相关的边界反射目前鲜有试验研究.由于近场效应与边界反射都与试样尺寸相关,文中将这种与试样尺寸相关的效应称为尺寸效应,且为在试验中尽量避免近场效应对试验的干扰,根据以往消除近场效应的研究成果,将试样长度与波长之比大多控制在2以上.采用弯曲元法在无侧限条件下测试了6个不同长细比的圆柱状试样,给出了各试样的接收波波形以及不同数据处理方法得到的剪切波波速.结果表明随着试样长细比的增大,测试波形出现复杂的形态,接收波起跳点提前出现导致测试误差,且该现象受测试频率的影响不明显.分析表明这些现象难以通过近场效应来解释,复杂的数据处理方法也无助于提高测试的精度,其中起跳点法造成的误差最大.基于P波的侧向边界反射分析,给出了临界长细比的理论表达式.该理论总体上能够解释试验中表现出的尺寸效应,但由于接收波形受多种因素的影响表现得更为复杂而有待进一步深入研究.

Wave attenuation is a widespread physical phenomenon in most acoustic tests, but there is a scarcity of quantitative investigations into the influence of wave attenuation on the determination of shear wave travel time in bender element tests. To ascertain this attenuation effect, a series of bender element tests were conducted on clay samples with different lengths under unconfined conditions. The experimental results suggest that the real first peak of the received signal attenuates gradually with the increase of the sample length and even becomes undistinguished when the sample length exceeds a limit. This phenomenon results in misinterpretation of the wave travel time using the time domain method. In this study, the shear wave travel time is misinterpreted when wave travel distance over approximately 80 mm, leading to underestimation of the VS by 17% for the peak-to-peak approach and 10% for the arrival-to-arrival method. Therefore, besides the near field effect and boundary reflection, the wave attenuation effect turned out to be an important factor influencing the determination of VS using the time domain method. Accordingly, it is advisable to predetermine the limit test distance for a specific testing system under conditions, particularly for long distance testing.

There is growing engineering concern about the base heave and post uplift phenomena in deep excavation in soft clay, which may pose a risk of instability of retaining systems. The purpose here is to conduct a detailed case study on the post uplift observed in a 17.6-meter-deep braced excavation of a subway station in thick soft clay (total thickness up to 42 m) in Shanghai. In this case, a large uplift up to 87 mm unexpectedly developed for the post founded on a 30-meter-long pile foundation. Efforts were first made to examine the complex relationships between the post uplift with the excavation depth (H), Terzaghi's safety factor against base heave (Fs) and maximum deflection of retaining wall. A simplified approach for soil-post-strut interaction analysis was then proposed and used for quantitative research. The working characteristics of the long pile foundation under low safety factor against base heave (Fs < 1.5) are summarized as following: (a) the back-analyzed neutral plane, where soil uplift equals the post uplift, lies at approximately 0.68 times the pile length from the pile top; (b) deep soil movement below the neutral plane results in the observed post uplift; (c) strut reaction plays a minor role in the restriction of post uplift. The influence of base treatment and excavation/construction procedures on post uplift and the principles of pile foundation design are also discussed in this paper.

The fact that the permeability and microstructure properties of clay will be changed by NAPL (Nonaqueous Phase Liquids) pollution draws high attention in the study of the interaction between NAPL and contaminated soil. Through in-field contaminated clay soils from vinyl chloride and 1, 1, 2-trichloroethane-contaminated site in Shanghai, the variation of the content of vinyl chloride and 1, 1, 2-trichloroethane pollutants in clay with depth was obtained. The change of plasticity, permeability, and microstructure properties of the clay samples contaminated by vinyl chloride and 1, 1, 2-trichloroethane were investigated in detail. The measured test results were compared with the uncontaminated clay and indoor soaked contaminated clay samples by TCE (Trichloroethylene). The test results showed that the microstructure characteristics of clay were changed under the influence of the content of TCE, vinyl chloride, and 1, 1, 2-trichloroethane. The total porosity, accumulative pore volume, and the content of the macroporosity percentage of clay soils showed an increasing trend. The flocculation structure of contaminated clay samples was observed, but there were no overhead pores and connected cracks. Volatile organic pollutants were detected in both field and indoor contaminated clay samples. The plastic limit and liquid limit of each layer of contaminated samples decreased slightly, the plastic index did not change significantly, and the pore ratio and permeability coefficient increased gently. At the same time, the clay shrinkage was aggravated by TCE pollution, and cracks appeared on the surface of soil samples. However, no connected cracks were formed. Test results indicated that the self-developed improved permeability test device can be used to test the permeability coefficient of clay samples with shrinkage and to crack by NAPL pollution. The permeability coefficient showed an increasing trend, though the increase was not at the level of magnitude.

The in-situ soft soil is usually the K0 consolidated one with the initial anisotropy, and laboratory triaxial tests usually uses the remolded soil with isobaric consolidation. The undrained shear tests (three kinds of tests: ICUC, ACUC, ACUE) about K0 consolidated and isotropic consolidated soils are carried out by using the original and remolded soil samples made by Shanghai soft clay, and the normalized intensity cu/ , normalized modulus Eu50/ , normalized modulus Eu /Eu50-εa under characteristics of the nonlinear two consolidation states are compared. The results show that the stress and strain of soils under the two consolidation modes possess obvious nonlinear characteristics, and there are differences in strength exertion and normalized strength. The normalized effect obtained by using Eu50 as the normalization factor is satisfactory, and the normalized curves of the undisturbed and remolded soil samples are almost the same.

采用基于总应力法(φ=0°法)的强度折减有限元法分析了圆锥形人造园林山体的稳定性,给出了圆锥形边坡的稳定因子Ns和安全系数Fs随坡角β变化的规律.并与几种形态相似的平面边坡(三角形平面边坡、无限平面边坡)的稳定因子和安全系数进行了对比,分析了边坡稳定性的几何效应.研究表明,由于几何形态的影响,圆锥形园林山体边坡的稳定因子及安全系数要明显大于平面边坡的稳定性.工程设计中可以采用三角形平面边坡的安全系数乘以修正值1.41来分析这种圆锥形边坡的稳定性.另外,滑动面形态也表现出一定的几何效应,圆锥形边坡的滑动面比平面边坡的浅一些,失稳时的影响范围也要小一些.

The flat dilatometer test (DMT) has been widely used in engineering such as geotechnical engineering investigation and evaluation of ground improvement effect at home and abroad. The test process of DMT is usually carried out after the blade insertion of DMT into test position, so the disturbance caused by the dilatometer penetration process will directly affect test results to a certain extent. However, the mechanism of dilatometer penetration and soil disturbance and its influence on test results caused by penetration process are not yet known. Homogeneous dry sand samples under different initial densities are prepared by the layered plate compaction method with low level rainfall, and several laboratory model tests of dilatometer penetration into these sand samples together with particle image velocimetry (PIV) are carried out to investigate the distribution characteristics of the soil displacement field during the blade penetration process. The test results show that (1) the extrusion effect caused by the penetration of both the wedge part and lateral expansion part of the blade mainly causes soil disturbance. (2) The surrounding soil is squeezed downward and sideward during the penetration of the wedge part of blade, resulting in small vertical displacement and a flat displacement field which mainly extends to both sides, while the surrounding soil is squeezed horizontally to the two sides during the penetration of the lateral expansion part of blade, resulting in a semi-elliptical horizontal displacement field with the distribution range being obviously larger, and meanwhile, the shear effect caused by side friction between the blade and soil produce a vertical displacement field with a narrow range. (3) Moreover, the displacement field of dry sand caused by dilatometer blade penetration is less affected by the initial sand density than that by cone probe penetration, and only the distribution range of displacement field around the wedge part of the dilatometer blade expands with the increase of the initial density to some extent.

回顾了饱和黏性土总强度Su的概念以及"φ=0法"的基本原理,指出直接将三轴固结不排水强度指标ccu、φcu和直剪固结快剪强度指标ccq、φcq代入朗肯土压力公式是一种错误的分析方法,由此导致了对水土合算土压力分析方法的误解.根据两种试验的原理,推导出了采用强度指标ccu、φcu和ccq、φcq表示的总强度Su,进而依据"φ=0法",给出了基坑开挖卸载下正确的水土合算土压力公式.结合该公式,对行业规范中采用的一些土压力计算方法进行了评述,并结合算例结果对计算分析中几种强度指标的应用进行了评价.

采用布辛涅斯克解,给出了圆锥形和圆台形荷载作用下地基中心竖向附加应力计算公式,发现竖向附加应力随深度衰减要远大于其他类型荷载下的结果;采用弹性有限元法,给出了圆锥形荷载作用下地基中任意位置的竖向附加应力系数图,解决了圆锥和圆台荷载下任意位置竖向附加应力以及地表沉降的计算问题。工程案例验证了采用该方法给出轴对称附加应力解的必要性;并通过一个算例分析了两个圆锥形山体作用下地基的竖向附加应力和地表沉降的相互影响规律。

采用室内微型十字板剪切试验对上海两种含水量(w=45.45％,w=34.93％)的饱和软黏土的触变特性进行了研究.结果表明,两种含水量的软黏土重塑扰动后,在触变恢复初期强度增长速度较快,7天后强度恢复速率明显变缓.上海饱和软黏土不是完全触变材料,触变性是其具有高灵敏性的原因之一,其中低水量土样触变性对其灵敏性的贡献明显大于高含水量土样.

基于COMSOL Multiphysics自动有限元软件开发了考虑两相流和对流弥散作用的重质非水相有机污染物(DNAPL)迁移分析模块.以氯苯为例,选取典型参数值,进行了均质饱和黏性土中DNAPL一维纵向迁移的数值分析.单一的对流弥散分析结果表明,在静水条件下,以分子扩散作用为主的溶解态的DNAPL的纵向迁移速度较为缓慢(每年约几厘米).DNAPL?水两相流和对流弥散的耦合分析结果表明,对于渗透系数k达到1×10-6 cm?s-1的饱和粉质黏土,受自重驱动的两相流所造成的自由相DNAPL的纵向迁移平均速率达到每年几十厘米;自由相DNAPL的溶解进一步导致土中溶解相DNAPL的浓度迅速增大到溶解度,直接影响了孔隙水中溶解相DNAPL的浓度.研究表明,两相流很可能是造成生产时间达几十年的旧农药厂的饱和黏性土地层深部出现DNAPL污染物的主要机理.

为得到室温下粉煤灰与碱激发剂质量比、水玻璃与氢氧化钠溶液质量比和氢氧化钠溶液摩尔浓度对粉煤灰地质聚合物力学性能的影响,以低钙粉煤灰为原料,制备了地质聚合物胶凝材料.采用正交试验方法,分析粉煤灰地质聚合物抗压强度,探讨碱激发剂配比对粉煤灰地质聚合物力学性能的影响,结合SEM、XRD和FTIR对试样进行表征,并对该材料的应力-应变曲线进行了研究.结果表明:粉煤灰地质聚合物的抗压强度随着激发剂掺量的减少而增大,水玻璃在激发剂中的比值与粉煤灰地质聚合物的抗压强度呈现正相关,其中粉煤灰与碱激发剂质量比为1.8,水玻璃与氢氧化钠溶液质量比为2.5且氢氧化钠溶液的浓度为10 mol/L时,120 d龄期的抗压强度可达51.98 MPa.对应力-应变曲线分析得出,在一定程度上,激发剂的掺入量对粉煤灰地质聚合物的破坏应变和弹性模量有较大影响.SEM、XRD和FTIR分析表明随着养护时间增长,胶凝材料体系内结构更致密,生成了更多的硅铝酸盐凝胶.

采用“两墙合一”设计的预制地下连续墙是其中一种较有推广前景的装配式综合管廊建造工艺,预制地下连续墙既可以作为管廊条形基坑施工的围护结构,还可以作为管廊的永久侧壁结构.以上海某综合管廊工程试验段为对象,对3幅预制地下连续墙槽段在基坑开挖中的弯矩、墙体水平位移以及坑内外土压力进行了监测,获得了大量的实测数据,为今后的推广工作积累了经验.

The behaviors of one-dimensional relaxation have been studied by many researchers. However, the method for deducing the stress relax formulas is usually complicated. Two simple stress relaxation formulas in single-logarithmic form and double-logarithmic form are derived, which are based on the Buisman secondary compression equation and the concept of the equal-time compression line proposed by Bjerrum. The relationships between the slopes of these two types of stress relaxation formulas and the parameter ca/cc are proposed, here ca is the secondary compression index and cc is the compression index. One-dimensional secondary compression and the stress relaxation tests using Shanghai clay are conducted. The reliability of the stress relaxation formulas is verified. Moreover, the one-dimensional stress relaxing rate of general cohesive soils is estimated according to the values of ca/cc proposed by Mesri and Godlewski.