Dynamic shear modulus of undisturbed soil under different consolidation ratios and its effects on surface ground motion

The dynamic shear modulus for three types of undisturbed soil under different consolidation ratios is presented by using the resonant column test method. Its effects on surface ground motion is illustrated by calculation. The test results indicate that the power function is a suitable form for describing the relationship between the ratio of the maximum dynamic shear modulus due to anisotropic and isotropic consolidations and the increment of the consolidation ratio. When compared to sand, the increment of the maximum dynamic shear modulus for undisturbed soil due to anisotropic consolidation is much larger. Using a one-dimensional equivalent linearization method, the earthquake influence factor and the characteristic period of the surface acceleration are calculated for two soil layers subjected to several typical earthquake waves. The calculated results show that the difference in nonlinear properties due to different consolidation ratios is generally not very notable, but the degree of its influence on the surface acceleration spectrum is remarkable for the occurrence of strong earthquakes. When compared to isotropic consolidation, the consideration of actual anisotropic consolidation causes the characteristic period to decrease and the earthquake influence factor to increase.

Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay

Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for both the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are both the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure.

Stiffness Degradation of Undisturbed Saturated Soft Clay in the Yangtze Estuary Under Complex Stress Conditions

Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.

Radial consolidation characteristics of soft undisturbed clay based on large specimens

In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a largescale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway(north of Sydney) were compared using measured settlements and excess pore pressures.Moreover, this paper highlights the implications of the smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of smear zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens.

Influence of moisture content on shearing strength of unsaturated undisturbed quaternary system middle pleistocene

The unsaturated undisturbed quaternary system middle pleistocene loess,a typical unsaturated soil,often occurs in the implementation of western development strategy.To obtain the shearing strength characteristics of this unsaturated undisturbed loess,based on the analysis of mineral composition,the triaxial shear test of undisturbed quaternary system middle pleistocene loess under different moisture contents is conducted with the specialized triaxial instrument for unsaturated soil.The test results show that the mainly mineral composition of undisturbed quaternary system middle pleistocene loess is quartz and albite.Under the same confining pressure,the matric suction increases with the decrease of moisture content.The smaller the moisture content,the larger the matric suction;the higher the moisture content,the lower the matric suction.Under the same moisture content,the matric suction increases with the confining pressure and reaches a maximum when the confining pressure is 100 kPa,and then decreases with the increase of confining pressure.This phenomenon is closely related to the grain contact tightness of soil mass under high confining pressure.According to the triaxial test of loess,the sample of loess experiences 4 stages from loading to failure:1) compaction stage;2) compression stage;3) microcrack developing stage;4) shear failure stage.The test sample is of brittle failure(weak softening)under low moisture content and confining pressure.With the decrease of matric suction and the increase of consolidated confining pressure,the stress-strain curve changes from softening type to ideal plastic type.In the shearing strength parameters of unsaturated undisturbed loess,the influence of moisture content on internal friction angle is small,but that on cohesive force is obvious.Therefore,the shearing strength of unsaturated undisturbed loess is higher than that of saturated undisturbed loess and varies with the moisture content.

In Situ Measurement of the Undisturbed Ground Temperature for Ground Source Heat Pump System

The undisturbed ground temperatures are important for design of the ground heat exchangers in ground source heat pump （GSHP） systems. In this paper, the undisturbed ground temperatures measured in two different methods are presented. The investigation was carried out in two cases. The temperature measured with the direct method is assumed to give the correct undisturbed ground temperature profile. The temperature measured with indirect method overestimates the undisturbed ground temperature by 2.1℃ and 1.7~C. This difference is mainly caused by the circulation pump and ambient air to the fluid. Therefore, the results that are decreased about 2℃ as compared with the indirect measured are recommended to estimate the undisturbed ground temperature in situ measuring. A smaller pump or deeper borehole or mild weather would result in a more correct temperature. Because the undisturbed ground temperature is affected by many factors. Whether or not these conclusions are correct to other areas, this would need further investigation.

Strength of undisturbed and reconstituted frozen soil at temperatures close to 0 ℃

The strength of warm frozen soils in permafrost is fundamentally significant to estimate and predict the ground settlements from construction activities. A study was therefore initiated to assess the strength and its behaviors of undisturbed and reconstituted frozen soils at temperatures close to 0 ℃. A series of triaxial compression tests(TCT) were performed by using a developed testing apparatus and a matching specimen-preparation method. The confinement was applied from air pressure, the temperature in the specimen was maintained using two-end refrigeration, and multi-stage loading on a single specimen was adopted to determine the strength. The test results showed that the strength, both for the undisturbed and reconstituted frozen-soil specimens, was significantly dependent on the temperatures and independent of the applied confining pressures. Additionally, the strength of undisturbed frozen soils was about 1.6 times more than that for reconstituted frozen soils. These observations were closely associated with the structures existing between pore-ice and gravels with large diameters.

Vibrocorer for undisturbed sampling of firn aquifer layers in Greenland: general concept

The firn aquifer beneath the Greenland Ice Sheet may play a significant role in rising sea level. Both traditional mechanical drilling and electric thermal drilling are poorly adapted for effective, low-disturbance sampling in firn aquifers. We propose using a vibrocoring technique for the undisturbed sampling of dry firn and firn aquifer layers. A remote-controlled vibrocorer is designed to obtain 1-m-long cores with a diameter of 100 mm. The depth capacity of the system is approximately 50 m. The total weight of the vibrocoring system with the surface auxiliary equipment is approximately 110 kg, and corer assembly itself weighs ~60 kg.

Comparison of Water Quality Status of Disturbed and Undisturbed Mangrove Forest at Awat-Awat Lawas Sarawak

Water quality testing was compulsory for management of safe and reliable water sources. Various sources of pollution and destruction of mangrove forest decrease the quality of river water. Thus a study was conducted to determine the water quality status of mangrove forest river water of Awat-Awat Lawas Sarawak and compare the water quality status of disturbed and undisturbed mangrove forest river in that area. Samples from twelve sampling stations were collected from both mangrove forest river from October 2013 to March 2014. In-situ data collected (pH, temperature, dissolved oxygen (DO), salinity, turbidity, total dissolved solid (TDS), conductivity) and laboratory analysis (biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammoniacal nitrogen (AN), total suspended solid (TSS)) were conducted according to the Standard method of Examination of Water and Wastewater AHPA 2005. Six water parameters: pH, DO, BOD, COD, AN and TSS value were used in calculating the Water Quality Index (WQI). Mean values for disturbed area were follows, pH (7.07), temperature (29.93°C), salinity (15.64 PSU), turbidity (55.13 NTU), DO (4.59 mg/L), BOD (0.73 mg/L), COD (10.16 mg/L), AN (0.14 mg/L), TSS (53.92 mg/L), TDS (23.14 mg/L) and conductivity (2.61 ms/m). Undisturbed area results were, pH (6.84), temperature (28.32°C), salinity (14.65 PSU), turbidity (35.41 NTU), DO (2.39 mg/L), BOD (0.55 mg/L), COD (15.82 mg/L), AN (0.13 mg/L), TSS (53.23 mg/L), TDS (22.82 mg/L) and conductivity (2.34 ms/m). There were no significant differences between two locations except for DO. Both water qualities of disturbed and undisturbed mangrove forest river were found under Class III, which describe that the water bodies are in moderate quality status.

Critical Cyclic Stress Ratio of Undisturbed Saturated Soft Clay in the Yangtze Estuary under Complex Stress Conditions

There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index dis-tinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus de-veloped by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consoli-dation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress,initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio wereinvestigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientationangle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate prin-cipal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic cou-pling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stressdirections during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does.

Internal erosion characteristics and microstructure effects of undisturbed loess

Loess internal erosion caused by preferential flow often leads to serious loess ground collapse,shallow loess landslides,and other geological disasters.However,there is a lack of quantitative evaluation of the internal erodibility of undisturbed loess under the action of preferential flow,and little is known about the correlation between the internal erodibility of loess and its microstructure.In this study,we carried out a series of hole erosion tests(HET)on undisturbed loess samples from 4 typical locations on China's Loess Plateau.The internal erodibility of loess was quantitatively evaluated through an improved HET method,and its association with initial water content,clay content,and initial water head difference was investigated.On the microscopic scale,the microstructure of loess with different clay content was measured by scanning electron microscopy(SEM).The correlation between pore and particle microstructure parameters and loess internal erosion parameters was established based on grey correlation theory.When the initial water content increased from 10%to 36%,the erodibility index increased from 1 to 2.5.When the clay content increased from 8%to 27.95%,the erodibility index increased 3.5 times.The increase of initial water head difference has a positive linear effect on the internal erodibility of loess.The microstructure analysis shows that with the increase of clay content,the microstructure of undisturbed loess changes from a mosaic structure to a cementation structure,which creates favourable conditions for controlling the internal erosion of loess.Through grey correlation analysis,it has been determined that the microstructure of undisturbed loess has a significant correlation with the critical shear stress,and the loess microstructure morphology strongly correlates with the erosion rate.Under normal circumstances,the higher the clay content,the better the erosion resistance,the better the mechanical stability,and the easier to form a stable cave in loess.This study can provide a reference for revealing the cave formation mechanism in the loess area in the future.

单轴压缩垃圾液污染黄土电阻率特征试验研究

为研究不同含水率、垃圾渗滤液浓度的原状污染黄土电阻率与压缩特征之间的关联,人工配置垃圾渗滤液对黄土进行预污染,制备了不同含水率、不同污染液浓度侵扰的黄土试样,并基于Fukue提出的固结仪-电阻率试验原理进行室内试验,分析了不同含水率和渗滤液浓度对电阻率的影响,进一步探讨了各含水率下不同污染试样压缩系数与电阻率特征值之间的定量关系。结果表明:污染液侵入后会导致土体电阻率急剧降低,不同污染浓度试样间电阻率的差值较小;低含水率时电阻率对水分的响应度更高,随含水率升高,响应度开始降低;在0~100 kPa应力下,电阻率出现骤降,当应力增加至100 kPa后,电阻率逐渐稳定;以垃圾渗滤液含水状态为中间变量,进一步拟合了压缩系数与电阻率特征值之间的关系,其呈现出指数递减趋势;最后提出不同孔隙水化学溶液下的利用电阻率特征值评价黄土受垃圾渗滤液污染程度影响的工程分级评价建议。

原状海砂对混凝土力学性能的影响

为探究高氯盐、高贝壳含量原状海砂混凝土的力学性能,以海砂的氯离子含量和贝壳含量为变量,设计并配制9组海砂混凝土,开展混凝土立方体抗压强度试验和单轴受压应力-应变全曲线试验。结果表明:随着氯离子含量增加,混凝土的孔结构细化,早期强度提高,单轴受压应力-应变全曲线峰值应力增大,峰值应变降低,弹性模量提高;随着贝壳含量增加,混凝土坍落度显著下降,混凝土的孔结构较疏松,强度降低,单轴受压应力-应变全曲线峰值应力降低,峰值应变增大,弹性模量降低。在现有模型基础上,提出关于氯离子含量、贝壳含量的模型参数计算式。

广州原状花岗岩残积土非饱和力学特性的试验研究

【目的】为了研究原状花岗岩残积土的表观黏聚力和有效内摩擦角随基质吸力的变化趋势,【方法】以广州市白云区某医院在挖基坑的原状花岗岩残积土为研究对象,通过室内试验研究原状花岗岩残积土的矿物成分、颗粒级配曲线、基本物理性质指标和微观结构等,借助变水头试验研究原状饱和花岗岩残积土的渗透性,结合非饱和三轴固结排水试验与原状土的微观试验,解释微观结构在宏观层面上对残积土的渗透系数、崩解及基质吸力等的影响,探讨了不同类型土体土水特征曲线差异的原因。【结果】结果显示,研究对象的花岗岩残积土为残积黏性土,主要由高岭土、石英和云母等组成,土体内部孔隙大小不均匀且相互贯通。饱和状态下原状花岗岩残积土的有效黏聚力和有效内摩擦角分别为29.17 kPa和20.99°。【结论】结果表明,非饱和状态下,随饱和度的减小,基质吸力对花岗岩残积土的表观黏聚力和有效内摩擦角均有着明显的影响;Khalili给出的非饱和抗剪强度方程式对花岗岩残积土较为合适。

循环球应力作用下黄土变形特性研究

针对西安某地铁车站基坑Q3原状黄土,开展偏应力恒定的循环球应力加/卸载试验,对不同固结应力与不同动应力幅值条件下原状黄土的轴向变形与体应变发展规律进行分析。结果表明:循环球应力作用下,黄土会产生一定的不可逆塑性变形与可逆弹性变形,其变形增长规律与偏压程度和动应力幅值成正比,与固结应力成反比;轴向变形规律符合Monismith C L幂函数模型,且其模型参数与固结应力条件具有显著的相关性;原状黄土在加载初期体应变累积较明显,之后逐渐趋于稳定;固结应力比对体应变影响较小,固结球应力对体应变发展具有抑制作用,表明浅层土体更容易产生压缩变形。

原状黄土土-水特征曲线与湿陷性的相关性

为了研究原状黄土土-水特征曲线与黄土湿陷性之间的联系,在陕西西安长安区取地表以下30 m范围内的原状黄土土样,进行基本物理指标试验和湿陷性试验。对不同典型地层的黄土-古土壤试样进行土水特征曲线试验,通过电镜扫描从微观角度分析。研究结果表明:大孔隙的数量与饱和体积含水率呈正相关;中孔隙的数目与过渡区斜率的大小呈正相关,孔隙数目越多土体失水速度越快;微小孔隙的数目和土的塑性指数影响残余含水率的大小。对于不同深度土层,饱和体积含水率和过渡区斜率与土层的湿陷系数呈正相关;塑性指数接近土层的湿陷系数对残余体积含水率的影响不明显;古土壤层的SWCC与湿陷系数之间存在与黄土层相同的正相关性。文章从非饱和土力学的方向去研究黄土的湿陷性,为湿陷性的研究提供一种新的研究角度。

Colloid-facilitated release of polybrominated diphenyl ethers at an e-waste recycling site: evidence from undisturbed soil core leaching experiments

Polybrominated diphenyl ethers (PBDEs), a class of persistent organic pollutants, have been frequently detected in soil at e-waste recycling sites. However, the key factors controlling the transport of PBDEs from surface soil to the vadose zone and groundwater are unclear. Here, colloid-enhanced leaching of PBDEs from undisturbed soil cores collected at an e-waste recycling site in Tianjin, China, is reported. Spatially heterogeneous release of colloids and PBDEs was observed in all the tested soil cores under chemical and hydrodynamic perturbations, indicating the presence of preferential flow paths. Colloid concentration in the effluent significantly increased as ionic strength decreased (from 10 to 0.01 mmol/L), probably due to the stronger electrostatic repulsion between colloidal particles and the soil matrix at lower ionic strength. In contrast, colloid mobilization was not significantly affected by the changes in pH of the influent (from 4.0 to 10.0) and flow rate (from a Darcy velocity of 1.5 to 6.0 cm/h). The concentrations of 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether (BDE-209), the predominant PBDE congener at the site, detected in the leachate (ranging from 1.09 to 3.43 ng/L) were much lower than previously reported results from packed column leaching tests, and were positively correlated with colloid concentrations. This indicates that remobilization of colloids at e-waste recycling sites can promote the leaching and downward migration of PBDEs from surface soil. The findings highlight the potential risk of surface soil PBDE contamination to groundwater quality and call for further understanding of colloid-facilitated transport for predicting the fate of PBDEs at e-waste recycling sites.

干湿循环作用下原状黄土渗透性及其对土-水特征曲线的影响

为评估干湿循环作用对原状黄土水力特性的劣化效应,对甘肃Q 3黄土进行了4组不同干湿循环路径下的饱和渗透试验与土-水特征测试,分析土体饱和渗透系数和土-水特征曲线随干湿循环次数、循环幅度和下限含水率的变化规律。结果表明:原状黄土饱和渗透系数劣化度与干湿循环次数间关系可采用双曲线函数进行描述,6次循环后劣化度变化趋于稳定;土体饱和渗透系数劣化度随循环幅度增大而线性增大,随下限含水率增大而线性减小。V-G模型对干湿循环下黄土的土-水特征曲线拟合效果良好,模型参数θs、α、n变化幅度较小,而参数θr随循环次数增加呈指数下降趋势。依据试验结果建立了考虑干湿循环3参数的饱和渗透系数劣化模型与土-水特征曲线模型,并对土体非饱和渗透系数进行了预测分析。

武汉长江Ⅰ级阶地原状土样获取技术研究

本文分析了原状土样获取的技术标准现状和行业现状,研究了钻进方式、取样工具选取的适宜性综合分析、土样的封装及运输。对比试验研究表明,在武汉长江Ⅰ级阶地粘土层段采用锤击钻进配合使用敞口薄壁取土器,在砂土层采用锤击和回转组合钻进配合使用内置环刀取土器,辅以胶盖自封和胶带密封,取得的原状样品在现场质量评测、室内样品制备性和试验性方面均有比较良好的表现,基于此套方法获取的原状样原始结构受扰动较小,土的原始结构力保持良好。

大功率汽轮机故障工况下高调阀控制方式切换性能研究

无扰切换是当前主流大型汽轮机阀门管理实现的一个重要功能,目前的大部分无扰切换研究工作都集中在设备正常状态的无扰切换实现方法上,尤其是起机并网时的无扰切换实现。为了研究火电机组灵活性,本文以多台600 MW级别机组为研究对象,针对机组存在的阀门管理缺陷进行故障诊断并实施优化改造,使机组安全顺利地投运了顺序阀配汽方式。然后,在此基础上进行了2类非正常运行工况下的无扰切换试验研究,探讨了机组故障状态下的无扰切换快速反应能力和设备故障对无扰切换的影响。试验结果表明:进行阀门管理优化不仅能够提高机组应对故障的反应能力,而且还能够降低机组切换控制系统对辅机等设备故障的敏感性。这对提高机组故障状态下的安全稳定性具有一定的借鉴意义。