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The logistic function is introduced for modeling the compression curves of reconstituted clays over a wide stress range beginning from the initial void ratio. Three parameters in the model can be determined by the least square method based on the measurements. It is found that the compression curves of reconstituted clays can be interpreted very well by the proposed model. The error in the void ratio between the calculations and the measurements varies within a narrow range of ±3%, based on the databases available from our research team and the independent researchers. The proposed model possesses the merit of continuity and derivability without singularity, compared with the conventional piecewise linear method of interpreting the compression behavior. In this study, a simply empirical way is also suggested for determining the compression curves of reconstituted clays in the case without performing consolidation tests. The three parameters in the model are correlated with two physical indices: the void ratio and the void ratio at the liquid limit. [ABSTRACT FROM AUTHOR]

Desiccation cracking is a common phenomenon for red clay due to alternating wet and dry weathers. The presence of cracks definitely affects the strength of the soil; however, characterizing the development of desiccation cracks inside the soil has been a challenge. The purpose of this study was to propose a method to quantify the volumetric crack rate (VCR) of red clay and investigate the influence of VCR on the unconfined compressive strength (UCS) of red clay. First, the relationship between wave speed and VCR was quantified by a prefabricated crack method to obtain the equivalent VCR (EVCR). Then, the EVCR was compared with the surface crack rate (SCR) to determine the reliability of the method. Finally, unconfined compression tests were carried out to explore the relationship between EVCR and UCS. The results show that the relationship between the prefabricated VCR and wave velocity can be described by a logarithmic equation. The calculated VCR by this equation is linearly correlated to the SCR of red clay, indicating that the logarithmic equation is effective to quantify the VCR of red clay caused by wet and dry cycles. The UCS and residual strength of red clay containing cracks reduce following an exponential function with increasing EVCR. Gray relational analysis showed that the correlation between UCS and EVCR is better than that between UCS and SCR, suggesting that it is more reliable to express the crack rate by EVCR when studying the UCS of red clay. [ABSTRACT FROM AUTHOR]

This study aims at establishing the hydraulic conductivity–effective vertical stress–void ratio interrelations for naturally sedimented clays under one-dimensional condition. The roles of soil structure developed during the depositional and the post-depositional processes in both the relationships of hydraulic conductivity versus effective vertical stress and void ratio versus effective vertical stress are investigated. It is found that the soil structure effect on the hydraulic conductivity–effective vertical stress curves can be attributed to that on the compression curves. The effect of initially deposited state on the hydraulic conductivity is also linked with that on the void ratio for naturally sedimented clays under the same values of effective vertical stress. The investigations indicate that the interrelation between hydraulic conductivity and compressibility is independent of initial state. That is, the hydraulic conductivity–void ratio relationship of naturally sedimented clays is independent of soil structure and initial state. Such a relationship is found to be a function of void ratio at liquid limit. Consequently, the hydraulic conductivity can be estimated based on the hydraulic conductivity–void ratio database established for naturally sedimented clays with a wide spectrum of void ratio at liquid limit. An empirical way of determining hydraulic conductivity is also proposed for naturally sedimented clays. A series of one-dimensional incremental load consolidation and hydraulic conductivity tests were performed. These data together with those compiled from the literature are used for investigating the accuracy of the suggested methods of determining hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Silty clay is a common embankment material whose moisture increases over time due to soil–atmosphere interactions and climate changes. The objective of this study is to investigate the unsaturated shear strength and microstructural evolution of compacted silty clay on wetting paths. Suction-controlled triaxial tests, scanning electron microscopy (SEM) observations, and mercury intrusion porosimetry (MIP) tests were performed on compacted silty clay specimens at various matric suctions and net confining pressures. The results show that both the matric suction and the net confining pressure have positive effects on the unsaturated shear strength of compacted silty clay. Nevertheless, they tend to cause different failure forms of the specimens, indicating distinct mechanisms behind their contributions to the soil shear strength on wetting paths. A change in matric suction does not lead to obvious evolution of clay particle orientation, but an increase in net confining pressure causes a weaker preferential orientation of clay particles. The shape of pore size distribution curves is slightly affected by the matric suction on wetting paths, while an increase in net confining pressure obviously reduces the proportion of large pores. The brittle failure of compacted silty clay appears due to the presence of open microcracks at high matric suctions. [ABSTRACT FROM AUTHOR]

To investigate the disintegration characteristics of the carbonaceous rocks in Guangxi Province, the typical carbonaceous rocks in the section exposed by the Hechi-Baise Expressway were investigated in this study. First, based on their mineral compositions and contents, the carbonaceous rocks were divided into four types: carbonate chert, carbonaceous argillaceous limestone, carbonaceous illite clay mudstone, and carbonaceous illite clay shale. Then, through indoor wet-dry cyclic disintegration test, the disintegration characteristics of the four types of rocks were studied. The test results showed the following: (1) the disintegration residues of the carbonate chert and the carbonaceous argillaceous limestone decrease linearly as the number of wetting-drying cycles increases. (2) The disintegration index of the carbonaceous illite clay mudstone and the carbonaceous illite clay shale decreases exponentially as the number of wetting-drying cycles increases. (3) As the number of wetting-drying cycles increases, the disintegration index curves of the carbonaceous illite clay mudstone and the carbonaceous illite clay shale samples gradually become stable until the disintegration of the samples is completed. (4) The disintegration of carbonaceous rocks is mainly affected by the clay content, followed by the structural form, but it cannot be ignored. [ABSTRACT FROM AUTHOR]

Isotropically and anisotropically consolidated undrained triaxial compression shear tests are conducted on 87 specimens of eight kinds of clays reconstituted over a wide spectrum of initial water contents. These data in conjunction with those of 55 specimens previously published by the authors and their research team are used to investigate the shear strength–compressibility interrelation for reconstituted clays. The effects of the initial void ratio and the consolidation stress path on both the consolidated undrained shear strength–consolidation effective stress relationship and the compression curves in terms of the void ratio against the consolidation effective stress are investigated. It is found that the consolidated undrained shear strength–void ratio relationship is independent of the initial void ratio and the consolidation stress path, and a quantitative expression is proposed for determining the relationship as a function of the void ratio at the liquid limit. Meanwhile, the compression curves of reconstituted clays at different values of the initial void ratio and the void ratio at the liquid limit from different consolidation stress path tests can be normalised into a unique line with the application of the intrinsic compression framework. Accordingly, a quantitative expression can be established to determine the relationship between the consolidated undrained shear strength and the effective consolidation stress. The validity and accuracy of the proposed equations are discussed based on data from independent researchers and from the research team. [ABSTRACT FROM AUTHOR]

To determine the moisture contents of unsaturated clay embankments in southern China considering the stress state, 753 moisture data of three existing embankments for about 20 years were measured, and six frequency domain reflectometry sensors were installed in a widened embankment in southern China to monitor the moisture content. The soil water characteristic curve (SWCC) and stress-dependent soil water characteristic curves (SDSWCCs) were determined in the laboratory using a pressure plate apparatus and a stress-dependent parametric equation was established. The finite element model of a typical unsaturated clay embankment in southern China considering the SWCC and SDSWCCs was created. Then, the variation of the moisture contents of the clay embankment was simulated. The results show that the vertical stress has an obvious effect on the moisture distribution in embankments, especially the positions inside embankments where the vertical stress is large and cannot be neglected. The finite element model considering the SDSWCCs, therefore, should be selected when analyzing the moisture filed of embankments in southern China. For the existing clay embankments in southern China, their moisture contents gradually increase from the optimum moisture content to equilibrium values, which is close to the plastic limit and increases by 99% of the optimum moisture content. In addition, the resilient modulus values at different locations of the embankment and that of the whole embankment are reduced by 55 to 62%. And the safety factor of the slope obviously decreases, and its reduction is greater than 60%. [ABSTRACT FROM AUTHOR]

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A series of one-dimensional incremental load consolidation–hydraulic conductivity tests was performed on reconstituted clays. Based on these tests, together with the test data compiled from the literature, the quantitative interrelation between the variation of hydraulic conductivity in the vertical direction with void ratio and the compression behaviour is established. It is found that the hydraulic conductivity in the vertical direction can be expressed as a function of void index, initial void ratio and void ratio at the liquid limit. The effects of initial void ratio and void index on hydraulic conductivity in the vertical direction for a given clay with a given void ratio at the liquid limit can be comprehensively attributed to the effect of void ratio on hydraulic conductivity in the vertical direction. These two findings introduce the point that the hydraulic conductivity in the vertical direction is a function of void ratio and void ratio at the liquid limit. Empirical equations are proposed to determine the hydraulic conductivity in the vertical direction using void ratio and void ratio at the liquid limit or using effective vertical stress, initial void ratio and void ratio at the liquid limit. These two empirical equations are correlated based on the concept of intrinsic compression. [ABSTRACT FROM AUTHOR]

The settlement behavior of soft natural clays under a 14-year embankment load is investigated by obtaining the high-quality undisturbed samples of soft natural clays beneath a constructed embankment. It is found that the conditional way of determining the settlement by combining the layerwise summation method of calculating settlement, the Osterberg method of determining the embankment load-induced stress in subsoil, and the compression parameters determined from high-quality undisturbed samples overestimates the settlement, compared with the field observations. The key cause is that the Osterberg method overestimates the vertical superimposed stress in this case. The modified method of determining the vertical stress in subsoil suggested by the authors is adopted for improving the accuracy of vertical superimposed stress calculated. The balance among errors in the settlement calculation model, determination of vertical superimposed stress induced by embankment loads, and measurement of compression parameters are also discussed. [ABSTRACT FROM AUTHOR]

The virgin compression of reconstituted clays is essential for assessing soil structure developed during geological processes as a reference to compare with that of natural clays. It is well observed experimentally that compression behavior of reconstituted clays is greatly affected by initial water contents. However, the quantitative description of virgin compression seldom includes initial water content effects. In this study, a new quantitative description is proposed for describing initial water content effects on virgin compression of reconstituted clays. The proposed general compression model is then used to predict the compression behavior of 24 types of clays over 90 tests covering a wide range of stress levels. An overall good agreement between the predicted and measured compression curves suggests that the proposed model provides a useful means to estimate the virgin compression of clays reconstituted at various initial water contents. This work can then be taken as a useful reference with enabling the initial water content of reconstituted clays equal to the natural water content of natural clays for evaluating soil structure. [ABSTRACT FROM AUTHOR]

Degrees of consolidation can be determined by two different methods using deformation and excess pore pressure variations for reconstituted and natural clays in laboratory tests and engineering practice. Theoretically, the relationship between the degrees of consolidation determined using the two methods should be unique. However, this study finds the experimental results from fifteen one-dimensional incremental load consolidation tests on five kinds of natural clays deviated from the theoretical line. The experimental relationships correlating the degrees of consolidation determined by the two methods are also found not unique, instead, consisting of a cluster of curves depending on different step stress increments. Two key causes are found to be responsible for the substantial discrepancy between experimental and theoretical results: (1) the nonlinear development of deformation during the dissipation of excess pore pressure; (2) the degree of consolidation determined by excess pore pressure measurements lower than 100% when the degree of consolidation determined based on the deformation-time curve becomes 100%. It is also found that the experimental relationships correlating the degrees of consolidation determined by the two methods are significantly affected by the values of degree of consolidation with excess pore pressure dissipation at 100% of consolidation degree with deformation observations. [ABSTRACT FROM AUTHOR]

Dredging activities in China produce a great deal of clay suspensions which are generally pumped into yards as filling materials to form reclaimed lands. Understanding the settlement behavior of clay suspensions during settling process is essential in engineering practice for meeting the design requirement on the storage capacity of reclaimed yards. To this end, this study performed 25 types of sedimentation tests on the clay suspensions with different liquid limits, initial water contents, and initial heights using different sizes of sediment columns. The experimental results indicate that the settlement–time curves of clay suspensions can be classified into three stages. It is found that the first stage can be ignored, and the sedimentation can be attributed to the second stage termed as settling stage in practice. Hyperbolic model is proposed for describing the settlement–time relationship during the settling stage, and a quantitative method of determining the settlement at the end of the settling stage is suggested. The changing trends of the settlement and the time at the completion of sedimentation are investigated with considering the effects of liquid limit, initial water content, and initial height. [ABSTRACT FROM AUTHOR]

It has been well recognized that pore fluid salinity significantly affects physical and mechanical properties of clays. However, how to correlate the pore fluid salinity effects on mechanical behaviour with physicochemical variations induced by pore fluid salinity changes is still pending. This study investigates the changes in liquid limit, oxide compositions and compressibility with pore fluid salinity, based on experimental data obtained from reconstituted specimens of two marine clays in China. It is found that oxide compositions vary little with the change in pore fluid salinity, indicating that no chemical reaction occurs during pore salt changing for the investigated clays. Such a finding means that the pore fluid salinity effects on compression behaviour of reconstituted clays can be attributed to the variations in physical properties. For the investigated marine clays with illite as predominant clay mineral, the void ratio at liquid limit is the crucial physical index of assessing the pore fluid salinity effects on the compression behaviour. The intrinsic compression concept is also introduced to compare the compression behaviour of reconstituted clays with and without pore salt. A quantitative approach is proposed to assess the pore fluid salinity effects on the compression behaviour of marine clays reconstituted at different initial water contents. [ABSTRACT FROM AUTHOR]

It is often recognized that organic matter contained in natural clays and dredged clays is detriment to the engineering properties by increasing their compressibility. This study takes humic acid as an example to illustrate that organic matter may decrease the compressibility of reconstituted clays with a wide spectrum of predominant clay minerals: kaolinite, illite and smectite, based on experimental results from thirty types of one dimensional incremental load consolidation tests. It is found that the main factors of influencing the compression behaviour of reconstituted clays with humic acid are initial void ratio and void ratio at liquid limit. The difference in compression curves between reconstituted clays with and without humic acid can be attributed to humic acid effects on particle density and liquid limit of clays. The humic acid effect on the compressibility of smectite-dominant reconstituted clays is found to be much more sensitive than that for kaolinite- and illite-dominant reconstituted clays. A quantitative approach is also suggested to assess the compression behaviour of kaolinite- and illite-dominant reconstituted clays with humic acid using intrinsic compression concept. [ABSTRACT FROM AUTHOR]

Isotropically consolidated undrained triaxial compression shear tests were performed on three reconstituted clays to investigate the effects of initial water contents on the pore pressure behaviour. The test results show that during undrained shearing the excess pore pressure normalised by isotropic consolidation pressure has a linear relationship with the effective stress ratio under a given initial water content, and the slope of the linear relationship changes with initial water contents for a given reconstituted clay. The pore pressure coefficient at failure also varies with initial water contents, ranging from .5 to .96 for the reconstituted clays investigated. By comparing the pore pressure response induced by shear stress, the mechanism of decrease in undrained strength with an increase in initial water content is identified from higher shear-induced pore pressure. Finally, a simple equation is also proposed to link the slope of linear relationship between normalized pore pressure and effective stress ratio with undrained strength and effective friction angle. [ABSTRACT FROM AUTHOR]

Understanding the compression behaviour of dredged clays is essential for their effective use with drainage. Measuring consolidation parameters of dredged clays at high initial water contents is a time-consuming and tough work. The research team has accumulated the database of 110 one dimensional incremental load consolidation tests for dredged clays. Based on this database, this study proposes a simple method of determining virgin compression of dredged clays using three physical parameters which can be easily measured. The compression curves of dredged clays can be divided into the pre-yield and the post-yield zones. Basic equations are suggested for describing the compression behaviour of the two zones. The associated parameters are correlated with the initial void ratio and the void ratio at liquid limit. The predicted compression curves are compared with the measured ones with the accumulated database and the independent data available from literature. The error of the void ratios predicted is found to vary within 10% compared with the measured ones. In engineering practice, the work in this study can be applied instead of the time-consuming and tough experiments to simply estimate the compression behaviour of dredged clays. [ABSTRACT FROM AUTHOR]

Six natural clays with a predominant clay mineral of illite and two pure clay minerals (kaolinite and smectite) were mixed with organic matter to prepare 64 samples of organic clays containing different organic compounds at different contents. The organic compounds are classified into two categories (insoluble and soluble in water) for studying their effects on physical properties of organic clays investigated. When original clays are mixed with organic material insoluble in water, the particle size distributions and the particle densities of organic clays can be approximately determined pro ratio of each component. Adding humic acid into original clays causes little aggregate or disperse action on solid particles. The Atterberg limits of organic clays containing organic matter insoluble in water vary with organic content in a nonlinear fashion, and its changing rate depends on the liquid limits of original clays. On the other hand, when original clays are mixed with organic compounds soluble in water, dissolved organic matter in pore water should be taken into account for measuring their Atterberg's limits. Atterberg's limits of organic clays containing organic matter soluble in water are greatly affected by the predominant clay mineral of original clays. For the original clays with a predominant clay mineral of illite and kaolinite, liquid limit increases with the increase in organic content, but contrary changing fashion is found for smectite. [ABSTRACT FROM AUTHOR]

Incremental load one-dimensional consolidation tests were performed on dredged clays with and without ageing to investigate their time-dependent compression behaviour. The dredged clays investigated had a wide spectrum of liquid limits within 55.6% to 100% and a predominant clay mineral of illite. It is found that vertical yield stresses develop notably during ageing. The developed vertical yield stresses vary within the range of 1.2 to 1.8 times the specifically assigned vertical effective stress under which ageing is allowed for 15 to 105 days. But the corresponding ageing volumetric strains are small, varying within the range of 0.6% to 3.4% with most being less than 2%. The test results obtained also allow proposing an empirical equation of assessing vertical yield stress. The changing law of vertical yield stress with stress level for ageing, ageing time, soil properties is investigated based on the empirical equation. Moreover, it is found that the structural resistance of dredged clays developed during ageing for a period of consolidation time up to 105 days is weak compared with the sedimentation compression line of natural clays developed during long geological ageing. But the compression curves of dredged clays with ageing converge slowly to the intrinsic compression line over a wide range of stresses, like natural clays subjected to the effect of soil structure developed during long depositional and post-depositional processes. [ABSTRACT FROM AUTHOR]

The undrained secant deformation modulus E u is an important parameter to quantitatively estimate the undrained settlement of soft clays. A series of isotropically consolidated undrained triaxial compression shear tests were carried out on four reconstituted clays and two naturally sedimented clays to evaluate the effects of the initial water content w 0 , liquid limit w L , and soil structure on E u. The test results showed that the variation in E u with deviator stress was significantly affected by w 0 and w L for reconstituted clays. The normalized modulus E u /(p ′)0.9 linearly decreased with increasing w 0 / w L. This linear relation at a lower w L lies above that at a higher w L. These observations suggest that the soil with lower plasticity and lower initial water content possessed higher values of E u. As the deviator stress increased, the effect of w 0 and w L on E u gradually vanished. It is also evidenced that the value of E u for naturally sedimented clays depended on the soil structure. The soil structure clearly enhanced the E u in the preyield regime in comparison with the corresponding reconstituted clay. Once the soil structure was damaged with increasing consolidation stress in the postyield regime, a significant reduction in E u was observed with a lower value than that of reconstituted clays. The difference in E u / S u between naturally sedimented and reconstituted clays gradually decreased with increasing deviator stress. This implies that the effect of the soil structure on E u diminished at higher deviator stress levels. • The variation of undrained modulus E u with initial water content is proposed. • The normalized modulus E u /(p ')0.9 is linearly correlated to w 0 / w L. • The degradation of E u for natural clay due to loss of soil structure is observed. • The influence of soil structure on E u vanishes at higher deviator stress level. [ABSTRACT FROM AUTHOR]

Red clay, an easily cracking lateritic soil, is extensively distributed in southern China. Cracked red clay slopes often show shallow failures under rainfall, which is challenging to reproduce by finite element methods. This study aims to examine how desiccation cracks and vegetation affect the shallow stability of a red clay cut slope during rainfall. Numerical models of the slope are created using ABAQUS, and an effective approach is proposed to simulate the distribution of desiccation cracks. The reliability of the numerical models and approaches is validated against field surveys. Parametric analysis is then conducted to investigate the influences of rainfall parameters, crack parameters and vegetation parameters on the slope stability. The results demonstrate that the presence of desiccation cracks can cause shallow failure and greatly reduce the factor of safety of the slope. This indicates that control of crack development is important to maintain slope safety. Moreover, the stability of cracked slopes can be obviously improved by vegetation with roots longer than 0.5 m. A tap root system appears to perform better than a fibrous root system. However, shallow-rooted vegetation may also contribute to the shallow stability of the slope by restraining the formation of desiccation cracks. [ABSTRACT FROM AUTHOR]

The hydraulic conductivity of naturally sedimented and reconstituted clays is often interpreted using the settlement–time curves measured from consolidation tests. Understanding the accuracy of the interpreted hydraulic conductivity is essential in geological and geotechnical engineering. To the best knowledge of the authors, such a work has been little reported up to now. This study aims at investigating the errors of the interpreted hydraulic conductivity via the comparison between the interpreted values and the measurements. The ratios of the interpreted values of hydraulic conductivity over the measurements are examined based on the data from the consolidation–hydraulic conductivity tests performed in this study in conjunction with those published by our research team. The investigated clays cover wide geological origins and depositional states. The geological origins and depositional states are linked with the errors of the interpreted hydraulic conductivity for understanding the roles of these factors in the uncertainty of the interpreted hydraulic conductivity. The causes responsible for the discrepancy in hydraulic conductivity between the interpretations and the measurements are identified. The probability distribution of the errors of the interpreted hydraulic conductivity is also investigated. • Investigating accuracy of hydraulic conductivity interpreted from consolidation test • Identifying cause responsible for error of interpreted hydraulic conductivity • Investigating role of geological origin and depositional state in hydraulic conductivity • Identifying uncertainty of error of interpreted hydraulic conductivity • Investigating probability distribution of error of interpreted hydraulic conductivity [ABSTRACT FROM AUTHOR]