Search

As a common natural phenomenon in clayey soil, drought-induced desiccation cracks impose danger to soil structures by degrading soil mechanical strength and hydraulic properties. In this study, through a series of field tests, we evaluated the effect of microbially induced calcite precipitation (MICP) technology on the suppression of desiccation cracks in field clayey soil and examined the impacts of MICP treatment methods (two-phase and one-phase methods) and cementation solution (CS) concentrations (0.5 and 1.0 M) on soil desiccation cracking behaviors and soil microstructure variation. The results revealed that MICP is capable of suppressing desiccation cracks in field soil. The surface crack ratio, average crack width, total crack length, and average crack depth decreased with the increase of treatment cycles and CS concentration. The two-phase MICP method performed better on soil crack suppression than the one-phase MICP method. Further CaCO3 distribution and soil microstructure characterizations indicated that the CaCO3 crystals generated by the MICP process contributed dominantly to the soil crack suppression by filling crack space, bonding soil particles, and reducing soil water evaporation. This study demonstrates that MICP is expected to serve as an eco-friendly and sustainable technology for soil desiccation crack suppression at the field scale. [ABSTRACT FROM AUTHOR]

Pore-size distribution (PSD) of soil is a fundamental property that determines flows of water, heat, chemicals, and electricity and controls distributions of stress and deformation. PSD can be intrinsically related to the soil–water retention curve (SWRC), which is a constitutive relationship describing how the soil skeleton retains pore water via adsorption and capillarity. A general framework to quantify soil's PSD is proposed by first fitting an analytical SWRC model to experimental water retention curves that explicitly separate the SWRC into an adsorptive SWRC and a capillary SWRC. The PSD is then estimated at incremental steps by combining the capillary SWRC and the conventional Young–Laplace equation relating capillary pressure to pore size. Cumulative and density PSD curves for 11 soils covering a wide spectrum of soil types are determined and compared with the PSD functions independently measured using mercury intrusion porosimetry (MIP). Good agreement is observed in the estimated pore size range, distribution pattern, and peak position determined from the two different methods. Differences observed in the methods are attributed to differences inherent in the use of wetting and nonwetting fluids to probe the pore space. The SWRC-based method generally characterizes pore sizes ranging from 100 to 0.02 μm with a major peak located within a pore diameter range of 1–10 μm. As the clay content increases, a secondary peak becomes evident at smaller pore sizes (about 0.01–0.1 μm), where the bimodal pattern reflects the dual-porosity microstructure commonly observed for clayey soils. For soils containing swelling clays, PSD can change substantially with variation in water content; thus, the water-based method is more appropriate than MIP for applications to geotechnical engineering practice. [ABSTRACT FROM AUTHOR]

Interactions between adjacent piled-raft foundations may induce additional settlement and cause the tilt of the structure. This case study investigates the long-term performance of a large piled-raft foundation system supporting high and heavy alumina solution storage tanks based on field measurements and three-dimensional (3D) numerical simulations. To properly consider the interactions among rafts, piles, and soils; the elastoplastic behavior of clayey and sandy soils; and the consolidation behavior of soil after construction, a 3D finite-difference code was utilized for the numerical modeling. Two undrained mechanical analyses were conducted to simulate the installation of foundations/tanks and the filling of alumina solution into the tanks, while two coupled hydromechanical analyses were performed to model the period between the two undrained stages and the stage after tank filling, respectively. The predictive capability of the numerical model was checked by comparing the simulation results first with single pile load test data and then with in situ settlement measurements at different locations of the piled-raft foundations. The long-term behavior of the piled-raft foundations was further investigated by analyzing various aspects including the axial force variation along the pile at different locations, the time-settlement relation at monitoring locations, the vertical effective stress increment and displacement of soil, and the differential settlement between monitoring locations. Based on the simulations, the tilt of the platform was mainly due to the superposition of additional stresses near the centerline of the two rows of piled-raft foundations. Finally, parametric studies were conducted to investigate the interactions among the piled-raft foundations at different pile length configurations. The results show that by properly increasing the length of the piles near the centerline of the two rows of piled-raft foundations, the differential settlement of the platforms can be mitigated. [ABSTRACT FROM AUTHOR]

Monopiles, which have been most extensively used in the offshore wind industries, are usually subject to threats from local scour. The effects of local scour on the bearing capacity of monopiles have been studied based on deterministic soil properties and local scour dimensions. However, the properties of the seabed soil and the dimensions of the local scour both have uncertainty. In this study, a new nonstationary random field model, which can better simulate the nonstationary characteristics of the seabed clayey soil and result in a safer probabilistic design of foundations, is proposed to characterize the spatial variability of the seabed clayey soil. Then, the effects of the spatial variability of the seabed clayey soil and the uncertainty of the local scour depth on the bearing capacity of monopiles are investigated under both uniaxial loading and vertical-horizontal-moment (VHM) combined loading using the random finite-element method combined with kriging metamodeling technique and Monte Carlo simulation. The undrained shear strength of the seabed clayey soil was simulated with a lognormally distributed nonstationary random field, and the local scour depth was treated as a uniform random variable. The negative correlation between them was also considered. The results show that the factor of safety required for the local scoured seabed decreased from 3.3 to 2.6 as the negative correlation was enhanced, greater than or equal to that [factor of safety (FS)=2.6 ] for the intact seabed. The procedure of analyzing the design failure envelop of a monopile in spatially variable clayey soil with a local scour proposed in this study can provide a reference for geotechnical engineers. [ABSTRACT FROM AUTHOR]

In the literature, the influence of spatial variability of the undrained shear strength of foundation soils on the bearing capacity of footings is limited to footings seated directly on the foundation. This is an unlikely arrangement in practice. This paper revisits the footing problem by considering a thin granular layer between a strip footing and soft foundation soil using analytical and stochastic numerical modeling. The analyses are extended to the case of a geosynthetic-reinforced granular layer and to the idealized case of no granular layer. The study shows that the probability that the ultimate bearing capacity for the footing is smaller than the deterministic design value is greater for all three scenarios with randomly uniform clay soil than for the same soil with isotropic or anisotropic spatial variability of strength at practical levels of reliability index β (e.g., β≥3.09 for a permanent footing). The reason for this outcome, which may appear counterintuitive, is explained. Design charts are provided to estimate the deterministic design bearing capacity of a rigid strip footing required to meet a range of target reliability index for the three footing scenarios examined in this study. [ABSTRACT FROM AUTHOR]

Temperature significantly affects the mechanical properties of geomaterials, particularly the creep behavior of soft clayey soils. Thus, an appropriate constitutive model to describe the time-dependent stress-strain behavior of clayey soils at various temperatures is necessary. This study performed temperature-controlled oedometer tests on two clayey soils: Hong Kong marine deposit (HKMD) and kaolinite clay (kaolin). The thermally-induced strain and creep strain rates under different temperature paths were investigated and discussed. A novel one-dimensional (1D) thermal elastic viscoplastic (TEVP) model was developed based on an existing 1D elasto viscoplastic (EVP) model. In the proposed model, the viscoplastic strain rate of soils can be described using three state variables: effective stress, strain, and temperature. The proposed model can be conveniently implemented in creep analysis with the equivalent time concept. The prediction results of the TEVP model were consistent with the experimental data for HKMD and kaolin. [ABSTRACT FROM AUTHOR]

A soil water unit weight of 9.8 kN/m3 has been universally considered to quantify soil volumetric phase properties such as void ratio and degree of saturation, but has been found to greatly vary depending on soil type and the volume scale with which it is defined. Recent experimental and theoretical evidence has indicated that the unit weight of soil water can be significantly greater than 9.8 kN/m3 for clayey soils when gravimetric water content is less than 30%. A soil water unit weight as high as 18.8 kN/m3 is evident for some expansive soils at low water content. The significance of abnormally high water unit weight in quantifying soil phase volumes, saturation, and void ratio was experimentally assessed for various clayey soils and theoretically interpreted as a function of water content and soil type. For clayey soils with low liquid limit, average soil water unit weight can be as high as 12.5 kN/m3 for gravimetric water content less than 10%. This leads to an overestimation of liquid-phase saturation and void ratio by as much as 8% if a soil water unit weight of 9.8 kN/m3 is used. For clayey soil with a high liquid limit, the average soil water unit weight can be as high as 18.8 kN/m3 for water content less than 18%, leading to overestimation of liquid-phase saturation by as much as 36% and void ratio by as much as 20% if 9.8 kN/m3 is used. Charts were developed to estimate average soil water unit weight as a function of soil specific surface area and water content, and as a function of liquid limit and water content. The commonly used value of 9.8 kN/m3 for water unit weight can lead to significant errors in estimating phase volumes, void ratio, and saturation for clayey soils. [ABSTRACT FROM AUTHOR]

The performance of the novel fish anchor has been assessed through field tests. The tests were carried out at three different locations in the Swan River, Perth. The water depths were 2.91–4.73 m. The riverbed soils consisted of clay (Location 1), silty clay (Location 2) and silt (Location 3). The anchor was installed in the riverbed by dropping first through an air column followed by a water column, and finally striking the riverbed at an impact velocity of 10.4 (Location 1), 11.43 (Location 2), 11.72 (Location 3) m/s. The anchor tip embedment depth in the riverbed was measured at 1–2.5 times the anchor length. For similar impact velocity, the tip embedment depth in clay was 1.56–1.68 and 2–2.1 times of that in silty clay and silt, respectively. The capacity was found to reduce with loading angle at the padeye to the horizontal. The ultimate capacity was 1.5–2.6 times the weight of the anchor submerged in water for loading angle 90°, which increased to 8.2–15.6 times the weight for θ0=∼16°. The fish anchor dove, as opposed to pull out of the riverbed, for loading angles ≤37–47° , resulting in nonelliptical failure envelopes, which have been expressed mathematically. [ABSTRACT FROM AUTHOR]

Several widely used field methods for estimating postliquefaction ground deformation are based on the laboratory data from one series of cyclic simple shear tests performed on one uniform clean sand reconstituted to three relative densities. It is not clear if the trends of this one data set are applicable to other clean sands, nonplastic silty sands, and nonplastic silts. A database of 579 test results on postliquefaction volumetric strain, including 299 test results that relate maximum shear strain to the factor of safety against liquefaction triggering, was compiled and used to examine trends for these soils. The database includes postcyclic test data on 10 clean sands, 2 gravels, 3 silty sands, 5 silts, and 3 clayey soils. The enlarged cyclic testing database was used to develop models that estimate postliquefaction volumetric strain and maximum shear strain as a function of soil type, state, and seismic demand. The models are applicable to uniform nonplastic soil. The state parameter was used in addition to relative density and void ratio to characterize the state of the soil. Correlations between these parameters enable the full data set to inform the models. [ABSTRACT FROM AUTHOR]

The drying phenomenon in clays is a multiphysical process accompanied by alterations in the thermal, hydraulic, and mechanical states of the multiphase system. Reversible and irreversible characteristics of shrinkage deformation have been observed experimentally in clayey soils for different ranges of moisture contents. The kinematics of drying due to evaporation and drying-induced shrinkage can be studied by utilizing a coupled thermo-hydro-mechanical (THM) model. An accurate evaluation of drying-induced shrinkage is needed to investigate the thermal cracking and damage of geomaterials. In this study, we developed a thermoporoelastoplastic constitutive framework assuming a non-associative plastic flow rule that can accurately model the transversely isotropic behavior of stiff natural clays in unsaturated conditions. All material parameters used in the non-associative transversely isotropic constitutive model were calibrated based on experimental observations of Boom clay. Then, the capability of the model was assessed by analyzing the convective drying experiment on natural Boom clay. The comparison of the numerical and experimental results confirms the plausibility of the hypotheses made in this study. The results show that the first stage of evaporation ends rapidly and the falling rate period (second stage of evaporation) is the dominant evaporation mechanism due to the intrinsic hydraulic properties of Boom clay and the high evaporative demand of the environment. The developed model reasonably captures the anisotropic elastic and plastic deformations of the clayey soil during the transient drying process. Numerical results demonstrate that drying shrinkage induces a 30% reduction in porosity in which approximately 82% of the total volumetric deformation in drying-induced shrinkage is irrecoverable (i.e., plastic). Moreover, the results indicate that most of the plastic deformation occurs in the first couple of hours of the drying process, when the soil's unsaturated condition is in a funicular state (i.e., where capillary pressure is dominant). Finally, the last section of this paper is devoted to a sensitivity analysis of the THM behavior of Boom clay with respect to its elastic and plastic strength. The parametric study shows approximately 10% more reduction in the final surface shrinkage when the difference between the slopes of the drying-induced compression line and the swelling line (i.e., λ−κ) is doubled. [ABSTRACT FROM AUTHOR]

2(e and g)] to random particle distribution [ HT ht , Fig. The HT ht curves in Fig. In this case, some issues regarding the calculation of HT ht should be clarified. 1(a) presents the variations of thixotropic strength ratio HT ht with time for different types of clay. [Extracted from the article]

In this study, the suction induced by stress release was investigated by measuring the suction of instantaneously unloaded MX80 bentonite specimens after wetting in an oedometer either under different vertical stresses or under a constant-volume condition. Swell-consolidation tests were also performed, and the results were compared with those of specimens wetted under different vertical stresses or a constant-volume condition. The microstructure of the unloaded specimens was investigated using mercury intrusion porosimetry (MIP). The water content and void ratio as well as the degree of saturation of specimens were also determined. Results showed that in the case of limited water exchange between macropores and micropores during stress release, the change in suction was equal to that of stress (−ds/dσv=1). By contrast, with water exchange between macropores and micropores, soil swelling occurred, and the variation of suction was higher than that of stress (−ds/dσv>1). A method was proposed allowing such water exchange between macropores and micropores to be determined (−ds/dσv−modified=1 , where σv−modified is the modified stress considering water exchange), evidencing the macropore drying due to stress release. Comparison of results from MX80 bentonite and other clayey soils showed that when the nonclay (grains such as quartz, calcite, and so on) fraction (NCF) was lower than 35% by mass, NCF had an insignificant effect on −ds/dσv−modified (equal to 1). By contrast, in the case of higher NCF (>35%), −ds/dσv−modified became lower than 1, and the higher the NCF, the lower the −ds/dσv−modified value. These findings provide useful information for better understanding the mechanism involved at the microstructure level in the stress/suction coupling during stress release in clayey soils. [ABSTRACT FROM AUTHOR]

Pore-water pressure in soil is caused by three physically distinguishable sources: ambient (environmental) pressure, surface tension–induced capillary pressure, and the soil's electromagnetic potential–induced adsorptive pressure. The former two form the conventional concept of pore-water pressure, which is considered a constant within a soil-water-air representative elementary volume and can be directly measured by piezometer (under saturated and compressive states) or tensiometer (under unsaturated and tensile states). The third one can be called adsorption-induced pore-water pressure and is localized within a certain distance to the particle surface of soil or intercrystalline surface of swelling clay. The adsorption-induced pore-water pressure is always compressive and dictates the water phase transition in soil by altering water's freezing point, density, and viscosity, among other physical properties. A framework of quantifying the adsorption-induced pore-water distribution via the measured soil water isotherm is presented for any soil type under any given water content. It is demonstrated that the adsorption-induced pore-water pressure can be up to 1.6 GPa in the first few layers of hydration, but will diminish to zero at a distance equivalent to the gravimetric water content >1% for sandy soil and greater than a few percent for silty soil. In clayey soil, the adsorption-induced pore-water pressure can sustain tens of megapascals even at much farther distance, equivalent to ∼30% water content. In expansive clay, the adsorption-induced pore-water pressure inside the crystalline lamellae can exceed 800 MPa. The soil water density functions of a silty soil and a bentonite clay predicted by the proposed framework matched well with that measured independently from the conventional consolidation testing, validating the framework to determine the spatial distribution of the adsorption-induced pore-water pressure in soil. [ABSTRACT FROM AUTHOR]

2 of the original paper" and that "For soils and rocks under undrained condition, HT ht has been proven theoretically to be equal to 0.5 when the Skempton ([22]) HT ht parameter is equal to 1 at fully saturated conditions." For instance, for very stiff clays at high confining pressures, the theoretical HT ht value may barely exceed 0.9 even at fully saturated conditions. The Skempton HT ht parameter depends on both the degree of saturation and the stiffness of the soil skeleton. 1, HT ht is more affected by changes in degree of saturation and confining pressure at small strain conditions compared to large strain conditions (e.g., [10]). [Extracted from the article]

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) (OCR=1 , 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations. [ABSTRACT FROM AUTHOR]

Desiccation cracking in clayey soil, which may lead to soil erosion, geotechnical engineering accidents, or even environmental pollution, is a serious problem nowadays. This research proposed a multifield coupling discrete-element model of clayey soil, in which each element represented a certain volume of soil. Meanwhile, the uneven distribution and transfer of moisture were also achieved. By establishing the relationships between water content and element radius, Young's modulus, and tensile strength, respectively, the model coupled the moisture field with the stress field. Through a discrete-element simulation of desiccation cracking in a thin clay layer, the gradual development of crack network was successfully reproduced, and the proposed model was validated. The uneven moisture distribution in the numerical specimen indicates that cracks can intensify evaporation by increasing the area of soil-air interface. Layer thickness, evaporation intensity, soil-base interaction, and compressive strength are proved to have significant impacts on crack pattern by influencing the equilibrium between desiccation shrinking and cracking. This research provides a new means to study the mechanism of desiccation cracking under multifield coupling effects. [ABSTRACT FROM AUTHOR]

To estimate the cyclic shear-induced ground settlement of clay layers, cyclic simple shear tests were carried out on three normally consolidated clays with different plasticity. The pore water pressure accumulation during cyclic shear and the settlement at the postcyclic recompression stage were measured in tests with unidirectional and two-directional shearing, with different phase shifts between the shear strains applied in the two orthogonal directions and a wide range of shear strain amplitudes. All tests were performed with 200 cycles. In conclusion, firstly, the discrepancies of the pore water pressure accumulation and postcyclic settlement between unidirectional and two-directional cyclic shear were quantified, and the effects of cyclic shear direction on these properties were then described by the total length of strain path. Secondly, a method for estimating the cyclic shear-induced pore water pressure accumulation and postcyclic settlement of clayey soils with different plasticities was then developed considering the effect of cyclic shear direction. [ABSTRACT FROM AUTHOR]

Because the original paper is not about the Millennium Tower case history, this argument has no direct relevance to the subject of the paper. We made no such inferences in the paper and refer interested readers to the case history paper for analysis of the degree to which consolidation was completed at different points in time in the Millennium Tower case study. While the Millennium Tower case history analysis provided the motivation and financial support for the broader study within which the testing program was undertaken, the paper under discussion does not present the case study, which was explained in its introduction. Both discussions lament that the paper did not present analyses of the Millennium Tower case history. [Extracted from the article]

Desiccation cracking in clayey soils occurs when they lose moisture, leading to an increase in their compressibility and hydraulic conductivity and hence a significant reduction of soil strength. The prediction of desiccation cracking in soils is challenging due to the lack of insights into the complex coupled hydromechanical process at the grain scale. In this paper, a new hybrid discrete-continuum numerical framework, capable of capturing hydromechanical behavior of soil at both grain-scale and macroscale, is proposed for predicting desiccation cracking in clayey soil. In this framework, a soil layer is represented by an assembly of discrete element method (DEM) particles, where each occupies an equivalent continuum space and carries physical properties governing unsaturated flow. These particles move freely in the computational space following the DEM, and their contact network and the continuum mixture theory are used to model the unsaturated flow. The dependence of particle-to-particle contact behavior on water content is represented by a cohesive-frictional contact model, whose material properties are governed by the water content. In parallel with the theoretical development is a series of experiments on three-dimensional (3D) soil desiccation cracking to determine essential properties and provide data for the validation of mechanical and physical behavior. Very good agreement in both physical behavior (e.g., evolution of water content) and mechanical behavior (e.g., occurrence and development of cracks, and distribution of compressive and tensile strains) demonstrates that the proposed framework is capable of capturing the hydromechanical behavior of soil during desiccation. The capability of the proposed framework facilitates numerical experiments for insights into the hydromechanical behavior of unsaturated soils that have not been possible before. [ABSTRACT FROM AUTHOR]

Recent research on the topic of pile base resistance has demonstrated that the guidelines provided by existing design manuals and codes are rather conservative in the case of clayey soils under undrained conditions. With the aim of investigating this topic more rigorously, a computationally intensive study was carried out to quantify the effect of the soil rigidity index on the response of pile base resistance. A precise assessment of the results led to the formulation of hyperbolic relationships that capture the development of the base resistance as a function of settlement. The relationships were implemented in a beam column analysis and validated against a full axisymmetric numerical analysis and also with respect to field data from a pile test performed using an Osterberg cell near the pile base. The validation process demonstrated the usefulness of the method and recommendations arising with respect to mobilization of the pile base resistance. This study should, therefore, assist in the development of more scientifically based guidelines for pile design that balance safety and economy. [ABSTRACT FROM AUTHOR]

In the case of roadways, although numerous observations have confirmed that environmental longitudinal cracks induced by expansive clay subgrades often develop at the edge of a roadway, the actual location of such cracks may occur at locations within the roadway. These moisture pathways further contribute to moisture increase in the underlying expansive clay subgrade, ultimately triggering additional longitudinal cracks and uneven roadway deformations. Moisture sensors in the subgrade of a FM2 test section: (a) layout of horizontal moisture sensor array; and (b) moisture content isochrones. [Extracted from the article]

The soil freezing curve (SFC) is a fundamental constitutive relationship between liquid water content and temperature under subzero (0°C or 273.15 K) conditions. SFC governs mechanical and hydrologic behavior of soil in freezing and thawing environments. The state-of-the-art SFC paradigms have been established empirically based on the capillary pressure-based Clapeyron equation. Two practical challenges prevent the rigorous use of the capillary pressure-based Clapeyron equation for realistic prediction of the SFC: (1) unable to use the governing pressure (intermolecular water pressure) for defining water phase change; and (2) unable to account for variations in latent heat of fusion and water density. A new paradigm based on soil sorptive potential (SSP) to predict the SFC from the soil water retention curve is developed, directly using the intermolecular water pressure distribution and pure water phase diagram in lieu of capillary pressure and the Clapeyron equation. The latest theory of SSP is used to quantify intermolecular water pressure distribution. Experimental validation demonstrates that the proposed paradigm yields excellent matches to the experimental SFC data for different soil types, and is a significant improvement over the predictions by the capillary pressure-based Clapeyron equation paradigm. The proposed paradigm reveals that the SFCs for various soils below 273.15 K (0°C) are mostly dominated by adsorptive water. Furthermore, the proposed paradigm can fully explain the practically encountered phenomenon that the SFC for soils with high clay content depends on the initial water content, whereas it does not for sandy soils. Practical significance of the new paradigm in geotechnical engineering problems is demonstrated through predicting soil moisture profiles under freezing and thawing, and permafrost environments. [ABSTRACT FROM AUTHOR]

Soil suction–based analyses are paramount to proper design of foundations in expansive soils, yet availability of field soil suction profiles from direct measurement is limited. A method was developed, using directly measured suction profiles obtained from sites across the US, by which routine geotechnical tests can be used to estimate soil suction to expand the database for estimation of field suction profiles. Herein, the expanded database is used to develop best-estimate clay soil suction envelopes for boundary conditions associated with covered or uncovered ground surface subjected to natural climatic surface flux. Where appropriate for site conditions, the proposed soil suction profile envelopes can be used with any suction-based heave/shrinkage analysis. Key features of the field suction envelopes, consistent with current popular approaches, include climate-dependent estimates for equilibrium suction at depth, depth to equilibrium (stable) suction, and variation in soil suction at the ground surface. Comparisons to existing soil suction envelope recommendations are made. Finally, a limited number of cases of developed/irrigated sites are presented for comparison to soil suction profiles obtained for natural climatic surface flux conditions. [ABSTRACT FROM AUTHOR]

This paper describes key research on expansive soils and the methods employed to characterize them; fallacies in the current characterization of expansive soils are also explained. Novel swell characterization models that account for hydro, chemical, and mechanical behaviors of soils are introduced and used to demonstrate in case studies to improve expansive soil stabilization practices. The first two case studies present the results of expansive soils stabilized by incorporating clay mineralogy and soluble soil sulfate measurements. An innovative design method for successful stabilization of expansive soil is introduced in the first case study, which incorporated both basic clay mineralogy and unsaturated soil behaviors as well as performance-based durability studies. Sulfate soil stabilization works on medium-to-high sulfate soils, including rigorous laboratory and field validation studies, are presented in the second case study. The third case study, which involves a steep earthen embankment built with expansive clayey soils and experiencing recurring surficial slope failures and maintenance issues, is also discussed. Forensic studies explaining the causes of slope failures and their mitigation methods are also included. All case studies reveal the need for detailed data about soil chemistry, including clay mineralogy and sulfate studies, to improve the current field stabilization and infrastructure design on expansive soils. The last section summarizes recent innovations for better health monitoring and management of civil infrastructure built on expansive soils using unmanned aerial vehicle platforms and visualization tools, which will be valuable for validating the application of new materials, designs, and construction processes. [ABSTRACT FROM AUTHOR]

Consolidation parameters are required to support the disposal management of soft soils or mine tailings. The estimation of these parameters from simple correlations using easily measured properties can be advantageous, and considerable work has been done on this topic. This paper proposes two innovations that advance this work: (1) hydraulic conductivity–void ratio (k-e) estimation can be substantially improved by using a single measured value at a high-void ratio, and (2) the compressibility curve itself can be a useful predictor of k-e. Using these findings, general equations are derived that describe k-e using a power law, where the power is either 4 or 5. Examining 79 k-e data sets from clays, clayey tailings, and dredged materials, 94% of all predicted k values are within an order of magnitude of measured k-e values. This level of accuracy, coupled with the advantage of anchoring the k-e function by a measured value at a high-void ratio, is shown to result in robust predictions of settlement in large strain consolidation analyses. [ABSTRACT FROM AUTHOR]

A complete understanding of soil–water interactions and the corresponding mechanical behavior of unsaturated soils requires differentiating adsorptive and capillary components of water retention and dominant water uptake mechanisms. Water vapor sorption (WVS) isotherms have historically been used to quantify the water uptake behavior of clayey soils and to determine related mineral surface properties, such as specific surface area and cation exchange capacity. This paper introduces the WVS kinetics curve as a new measure for gaining additional insights into the WVS behavior of clays. The sorption rate calculated from WVS kinetics curves scales with the cation heat of hydration at low relative humidity (RH<10%), indicating that cation hydration is the first mechanism for water uptake by dry clays. Sorption rates up to 25% RH are related to monolayer adsorption and specific surface area (SSA). A distinct relationship is proposed to relate SSA to the sorption rate normalized with predominant cation valence. [ABSTRACT FROM AUTHOR]

Design of flexible pavements over fine-grained soils requires determination of subgrade resilient modulus over a wide range of degree of saturation and suction for different soils. A novel experimental setup was developed by integrating a cyclic triaxial apparatus with capability to control suction using axis-translation and automated vapor pressure control to the specimen gas phase. System performance was evaluated through repeated load triaxial (RLT) tests for suction ranging from 0 kPa at saturation to 600 MPa at drier conditions. Replicate tests performed on a silty soil and a high-plasticity clayey soil indicated excellent repeatability. Resilient modulus of the materials is essentially unaffected with drying at low-suction range near the air-entry value and the optimum moisture content condition. This property then increases rapidly with subsequent drying until reaching a residual state after which the rate of increase in resilient modulus with respect to suction decreases to a low value. Limitations of a recent prediction model in capturing this trend demonstrated the need to determine resilient moduli over a wider range of suction for developing robust resilient moduli prediction model. [ABSTRACT FROM AUTHOR]

This paper presents a closure to "Full-Scale Field Studies to Evaluate Deep Soil Mixing in Stabilizing Expansive Soils" by Anand J. Puppala, Raja S. Madhyannapu, and Soheil Nazarain. https://doi.org/10.1061/(ASCE)GT.1943-5606.0002647. The discusser pointed out that the presence of alkalines and acids in the soil or groundwater could influence the performance of deep soil mixing based on lime and cement stabilizers. [Extracted from the article]

This paper presents a discussion of "Full-Scale Field Studies to Evaluate Deep Soil Mixing in Stabilizing Expansive Soils" by Anand J. Puppala, Raja S. Madhyannapu, and Soheil Nazarain. https://doi.org/10.1061/(ASCE)GT.1943-5606.0002647. The authors utilized the deep soil mixing (DSM) technology to modify a heavily overconsolidated swelling clay soil in situ to determine the efficacy of the DSM treatment of expansive soils and presented the results obtained from the instrumented full-scale field tests undertaken. [Extracted from the article]

As discussed by Been and Jefferies, normally consolidated soil specimens with the same HT ht exhibit similar consolidation stress-normalized stress-strain-strength behavior (i.e., similar stress paths and critical state shear strengths). Consider a soil specimen at the preshearing effective vertical stress, HT ht , after unloading from a maximum effective vertical stress, HT ht . [Extracted from the article]

Theoretical curves for different values of HT ht , 0.6, 0.8, and 1.0 are superimposed on the graph and can be seen to encapsulate the data. Yet, even without these separate curves, Wroth ([14]) noted that the parameter HT ht would track well with I ' i alone according to CSSM, and recommended the approximation HT ht (5) Graph: Fig. [Extracted from the article]

Long-term ground movements occur after tunnel construction in clayey soils due to dissipation of excess pore pressure generated during construction and a new seepage state that depends on the drainage conditions of the tunnel. A methodology was proposed in the past to evaluate the long-term surface settlements for tunnels in London clay. This paper extends the previous work by proposing a new method to estimate both consolidation-induced vertical and horizontal displacements, as well as consolidation-induced peak horizontal strains. In this method, a new relative soil-lining permeability index, which was modified from the earlier work, is proposed by assuming a radial seepage flow into a tunnel. Using this index along with tunnel geometry and soil properties, a series of equations was derived to better facilitate the calculation of the long-term ground displacements and strains compared to the normalized charts adopted in the previous evaluation method. The applicability of the proposed method is tested against two case histories in London. [ABSTRACT FROM AUTHOR]

Inferences were also drawn from the results of tests done on normally consolidated Wenzhou soft clay ([1]), and Guo et al. ([2]) for comparison of the behavior of the two types of clay soil. In their paper, the authors have reported on the research findings of a stiff overconsolidated clay (Gault clay) from the UK subjected to undrained cyclic loading undertaken in a hollow cylindrical apparatus (HCA). For the Second Conclusion The test results for the stiff overconsolidated Gault clay were presented and discussed by the authors in relation to comparisons between the CT and CHCA test results, permanent strain accumulation, resilient stress-strain response, and pore pressure observations. [Extracted from the article]

A full-flow ball penetrometer is now routinely used in centrifuge testing for characterizing single-layer clay, silt, sand, and stratified soil samples. The behavior of the standard ball penetrometer (including the shaft) used in the field, penetrating through single and two-layer uniform clays, has recently been investigated. However, the ball penetrometers used in centrifuge testing has either a similar or higher area ratio (of the shaft to the ball) and significantly greater equivalent prototype diameter compared with the standard one used in the field. The thickness of the soil layers, however, are scaled accurately mimicking strength profiles in the field, leading to lower relative thickness of the soil layers. Large deformation finite element (LDFE) analyses were, therefore, carried out for the centrifuge ball penetrometers to investigate its performance in characterization of single- and double-layer clays. The results were validated against plasticity solutions and other previously published finite element (FE) results prior to undertaking a detailed parametric study, exploring a range of normalized soil properties and layer thickness. Three commonly used centrifuge balls were studied. For single-layer uniform clay, the area ratio of shaft to ball was shown to have significant influence on the deep bearing factors and the critical penetration depth of attaining that factor. For two-layer uniform clays, the undrained shear strength of the top layer was mostly underestimated because of the lower thickness of that layer relative to the centrifuge ball diameter. In addition, the shear strength of the bottom layer was mostly overestimated because of trapping of stiff clay at the base of the ball, advancing in stiff-over-soft clay deposits. To interpret a reference undrained strength profile, taking into account the scale effects of the penetrometer relative to layer thickness, a framework has been proposed accounting for these effects, with the LDFE data used to calibrate the framework. [ABSTRACT FROM AUTHOR]

This paper presents a case history of the successful application of observational method to instruction microtunneling with successive pipe-jacking. The microtunneling project is the construction of four parallel pipes under Guan River in Jiangsu, China. Four parallel tunnels with external diameter of 4,160 mm and horizontally spaced at 4.8 m apart were jacked over 450 m in cemented silty clay and sand by two slurry-balance microtunnel boring machines (MTBM) at a depth of 4.6 m under the river bed. Since the overburden soil is very thin, proper control of tunneling operations was of utmost importance for maintaining the stability of the river bed. In order to optimize the operation parameters prior to construction under the river bed, a field trial was conducted, which included measurement of ground surface settlement, subsurface settlement, and lateral displacement of the subsurface soils, as well as excess pore water pressure and earth pressure. The relationship between ground response and construction operation parameters is summarized. Appropriate operation parameters were applied during tunneling under Guan River. Although tunneling and pipe jacking under the river was successfully carried out, a difficulty was encountered when the MTBM reached the opposite bank and large settlements were observed. This paper discusses the technical issues faced and lessons learnt from interpretation of the monitoring data collected. [ABSTRACT FROM AUTHOR]

The interdependency of microsoil fabric-related properties and swell/shrink behavior of expansive soils needs to be identified to achieve a more thorough and accurate prediction of heave of expansive soils. In a recent research study, two microsize-related properties of a soil-pore size distribution and specific surface area-were identified and examined in an effort to address their synergistic effects on swelling behavior of soils. To study this aspect in detail, eight natural expansive clayey soils from known expansive soil regions were sampled and studied by using two test methods: conventional one-dimensional vertical swell tests and novel three-dimensional volumetric swell strain tests. Microinternal structural details, including pore void distribution, were obtained from mercury intrusion porosimetry (MIP) studies on compacted soil specimens. Specific surface area (SSA) details of the same soils were determined using the chemical ethylene glycol monoethyl ether (EGME) method. Attempts were made to predict macroswell properties, using both pore and surface area properties. Modeling analyses and results showed that the swelling behavior of the clays was dependent on a newly introduced parameter that accounted for both clay mineralogy constituents and internal pore distribution of the soils. The new swell property models showed accurate predictions of measured swell strains of the present soils, depicting the importance of including mineralogy and pore fabric details in a given soil. [ABSTRACT FROM AUTHOR]

Cyclic hollow cylinder torsional tests were performed in undrained conditions on 12 compacted clay specimens collected from two types of dams (an earth-core rock-filled dam and an earth-zone dam) in Thailand. The cyclic degradation, cyclic pore water pressure generation, and volumetric cyclic threshold shear strain were studied via multistage strain-controlled tests. The testing program encompassed five overconsolidation ratios (OCRs), 1, 1.5, 2, 3.5, and 4, where six to eight cyclic strain-controlled stages were applied in each test with frequency f = 2 Hz. The results reveal that the volumetric threshold shear strain amplitude of these compacted clays ranged between approximately 0.009 and 0.025% and generally increased substantially with the plasticity index (PI). The cyclic pore water pressures normalized by σc′ are consistently lower than previous ones using other types of clays tested with other types of devices at comparable cyclic shear strain amplitudes. The cyclic degradation and cyclic pore water pressure in compacted clay are significantly affected by the OCR. [ABSTRACT FROM AUTHOR]

Ground movements observed during foundation installation and basement construction of a residential 53-story RC tower are presented. The One Museum Park West building is located in Chicago, Illinois, and was developed using a combination of bottom-up methods, used for the construction of a central concrete core of the building, and top-down methods to build five levels of basements. The excavation extended 13-15 m below grade and was made through soft to medium-stiff clays. The building was supported by drilled shafts and a perimeter wall formed by secant piles that transitioned to tangent piles below the bottom of the cut. The system was laterally braced with RC floor slabs structurally connected to the secant pile walls and the RC core. Field performance data were collected by means of settlement points and inclinometers located close to the walls on two sides of the excavation. The construction sequence and attendant ground movements during each main activity are summarized. As much as 160 mm of settlement was recorded in the adjacent streets throughout construction. Wall and foundation installation accounted for approximately 35% of the total settlements during construction, whereas top-down construction of the basement resulted in approximately 40% of the total settlements. These data emphasize the importance of considering all construction activities when making predictions of ground movements adjacent to deep supported excavations. [ABSTRACT FROM AUTHOR]

Compensation grouting is often employed as a mitigation technique to reduce the settlements induced by tunneling. The efficiency of compensation grouting, defined as the ratio of the volume of heave induced at the ground surface to the volume of injected grout, is strongly dependent on grout properties, injection characteristics, and soil properties. In clayey soils, site observations and laboratory tests show high values of compensation efficiency immediately after injection. However, the efficiency can decrease with time if positive excess pore-water pressures develop in the soil during the injection process. Conversely, in sandy soils, a loss of volume occurs because of pressure filtration of the grout during and soon after the injection process, which reduces the compensation efficiency. This paper describes an analytical model that can be used to evaluate the volume loss produced by pressure filtration of cement-bentonite grouts as a function of soil, grout, and injection parameters. The magnitude of pressure filtration is evaluated as the grout efficiency, which is given by the ratio of the volumes of the final grout body to the injected grout. Results show that the grout efficiency increases with decreasing soil permeability and with increasing grout bentonite content. The result of a grout injection test on a silty soil is back-analyzed using this approach in which the grout efficiency is first evaluated through the proposed filtration model and then used to calibrate a numerical simulation of the test. The good agreement between experimental data and computed results shows that prediction of the efficiency of compensation grouting can be improved using the proposed approach. [ABSTRACT FROM AUTHOR]

Das and Deb ([5]) argued that the stress concentration ratio (SCR) increased as the modular ratio (the elastic modulus of support pile and soft soil, i.e., HT ht ) increased. The HT ht was derived about 10,000 from the original Table 1, and the monitored SCR reached a maximum value of 6.6 at the end of embankment construction shown in Fig. In practice, HT ht could be calculated using the HT ht method ([9]; [12]), the HT ht method (the effective stress method, [17], [15], [16]), or the HT ht method ([13]). [Extracted from the article]

Because of its large size ( in plan), the 17.85- to 25.89-m-deep foundation pit of the 492-m-high Shanghai World Finance Center building was excavated by the central-island technique, i.e., bottom-up construction of the central cylindrical shaft first and then top-down construction of the peripheral rectangular pit. As part of the comprehensive study on the characteristics of this large-scale foundation pit, this study mainly focuses on the behaviors of the peripheral pit via the following investigated items: (1) lateral wall deflections; (2) vertical wall movements; (3) lateral ground movements; (4) axial forces in the cast floor slabs and braced struts; (5) lateral earth pressures on both sides of retaining walls; (6) variation of pore pressures along depth and deep artesian water levels; (7) ground settlements; (8) subsurface settlements; (9) basal heaves; (10) vertical column movements; and (11) column stresses. To explore the potential effects of pit sizes on the excavation behaviors, field data from another 33 top-down excavations in Shanghai were also included for comparison. The comprehensive comparisons show that in addition to the well-known factors (e.g., excavation depths, supporting system stiffness, and factor of safety against basal heave), pit sizes in plan played a key role in determination of the pit behaviors. The large-scale pits with the areas in plan of experienced wall deflections and ground settlements three to five times those of regular building basement and metro station excavations with the sizes in plan no more than , and the corresponding influence zones behind the large-sized pits were also much wider. Different from the braced struts that just carried the load because of soil removal in the proximity, the floor slabs sustained the load induced by exposure of the entire retaining wall along the depth. For the top-down excavations in Shanghai soft clay, the lateral earth pressure envelopes behind the retaining walls were trapezoidal, but their magnitudes were significantly smaller than those predicted by the methods available in the literature, and the corresponding peak values occurred at a greater depth. The influence zones of basal heave caused by soil removal (stress relief) extended much deeper below the excavation bases than those assumed in the conventional slip circle basal stability models. [ABSTRACT FROM AUTHOR]

A large amount of field and experimental data has been devoted to rectangular excavations thus far. In contrast, very few data were available for cylindrical excavations, especially those with large diameters in thick soft clay deposits. Via a comprehensive instrumentation program on a unpropped (self-supported) cylindrical excavation constructed by the bottom-up method in Shanghai soft clay, the characteristics of this large-sized circular excavation were extensively investigated. This cylindrical shaft was a part of a large-scale deep foundation pit excavated by the central-island technique. The investigated items included (1) lateral wall deflections, (2) vertical wall movements, (3) lateral ground movements, (4) ground settlements, (5) subsurface settlements, (6) basal heaves, (7) vertical column movements, (8) column stresses, and (9) variation of pore pressures along depth and artesian water levels. Analysis of the field data indicates that discharging of the deep artesian water was one of the key factors affecting the excavation behaviors. The influence zone of basal heave caused by soil removal (stress relief) reached very deep soil layers, far beyond the depths reported in literature. Column movement and stress were shown to be reliable indicators of the relative movement between basal soils, diaphragm walls, and interior columns. Finally, the comparisons of this study with other bottom-up excavations in Shanghai, including 11 cylindrical excavations, 92 building basement excavations, and eight metro station excavations, demonstrate that self-supported (unpropped) cylindrical excavations had much stronger capabilities of resisting deformation than both multipropped regular basement excavations (in terms of deformation magnitudes) and long and narrow metro station excavations (in terms of scale of influence zones). For cylindrical shafts, their diameters, and not wall penetration ratios, played a dominant role in the determination of excavation behaviors. However, when the shaft diameter reached 90 m or more, the advantage of cylindrical shafts over rectangular pits in constraining wall deflection was no longer obvious. [ABSTRACT FROM AUTHOR]

The stress-strain behavior of clayey soil is time dependent. Laboratory study and constitutive modeling of the time-dependent stress-strain behavior are needed to understand the soil behavior and analyze displacements of reclamation works and foundations on clayey soils. The stress relaxation, as one of the significant time-dependent phenomena in clayey soils, has been observed and examined in excavations and constructions, such as the short-term change in lateral earth pressure after installation of a supporting system. In this study, Hong Kong marine deposits (HKMDs), which are clayey soils, and a sand-mixed bentonite (SMB) soil were investigated in relaxation tests. Relaxations were performed in both the loading stage and the unloading stage. This paper is focused on the testing study and modeling of the time-dependent relaxation behavior of clayey soils. Relaxation tests were carried out to measure the changes of the effective stress with time in one-dimensional (1D) straining condition. A new 1D elastic visco-plastic model considering swelling (1D EVPS) was used to simulate the relaxation tests. Analytical solutions from the 1D EVPS constitutive equations were obtained for relaxation tests. All parameters in this 1D EVPS model were obtained from a conventional oedometer test. The analytical solutions from the 1D EVPS model were used to simulate the relaxation behavior and compare with test data. Good agreement between the simulated curve and the measured data were found. [ABSTRACT FROM AUTHOR]

This technical note assesses the widely accepted Thompson's equation used to approximate design resilient modulus () for lime-stabilized soils from the results of unconfined compressive strength () testing. There is limited evidence in the literature to support Thompson's equation relating and for lime-stabilized soils, and other studies have suggested that the relationship provides an excessively conservative approximation for design , specifically above . Laboratory and testing was performed on multiple specimens of three lime-stabilized soils. These data reveal that Thompson's equation provides a lower-bound estimate of from and that Little's recommended relationship provides a more reasonable match to the data. This study also illustrated a lack of a clear correlation between and . [ABSTRACT FROM AUTHOR]

To fully implement seismic performance-based design for geotechnical structures, it is necessary to be able to correctly identify relevant earthquake records for the site in question in conjunction with advanced constitutive models that can accurately predict soil deformation resulting from these dynamic actions. In this paper, a numerical study is conducted to assess the seismic response of an earth dam using different approaches ranging from simple regression models to advanced numerical analyses. A kinematic hardening constitutive model is used to describe the mechanical behavior of the involved clayey soils. Five ground motions are chosen based on an existing hazard assessment to determine the relevant peak ground acceleration and frequency content at the dam site. Two design levels are considered in the evaluation of the seismic response of the earth dam. A comparison in terms of permanent accumulated displacements during the shaking obtained by the different approaches is presented highlighting their limitations and advantages. [ABSTRACT FROM AUTHOR]

Skirted gravity base foundations and suction caisson foundations are considered as viable alternatives to monopile foundations for offshore wind turbines. While recent work has focused on the monotonic moment-rotation response for shallow foundations, the cyclic response and the accumulation of rotation over the life of the turbine must also be addressed. This paper presents cyclic loading tests where approximately 10,000 cycles, with different loading characteristics, were applied to a model shallow foundation (a caisson) in loose sand. On the basis of these tests, a framework for assessing the accumulated angular rotation because of cycling was developed. The settlement and cyclic stiffness response of the caisson were also assessed. It was found, not unexpectedly, that the accumulated settlement of the caisson increased with the number of cycles and cyclic amplitude. It was also found that a cyclic loading regime intermediate between one-way and full two-way cycling produced the largest rotations. The cyclic stiffness was relatively unaffected by the number of cycles. Using an appropriate scaling technique, the proposed framework was used to predict the long-term accumulated angular rotation, for an example, the field-scale monocaisson structure. [ABSTRACT FROM AUTHOR]

Contamination of soils by polychlorobiphenyls (PCBs) is of environmental concern because of their toxicity, persistence, hydrophobic nature, and slow biodegradation potential. Among the PCB remedial technologies, direct oxidation by persulfate is considered to have great potential to be both simple and rapid. However, to produce faster reaction rates, persulfate is often activated using heat, metal chelates, hydrogen peroxide, or high pH. Furthermore, delivery of persulfate in low permeability clayey soils is difficult. Integrating electrokinetic remediation with persulfate has the potential to overcome such difficulties because the applied electric potential can facilitate the delivery of persulfate in low permeability soils as well as activate oxidizing radicals and simultaneously induce oxidative/reductive reactions directly in the soil. This study investigates the potential for in situ oxidation of PCBs in low permeability soils using persulfate as an oxidant and also evaluates the benefits of integrating oxidation with electrokinetic remediation. Several series of laboratory batch and bench-scale electrokinetic experiments were conducted using kaolin, a representative clayey soil, spiked with 50 mg/kg of 2,2′,3,5′ tetrachlorobiphenyl (PCB 44), a representative PCB. Persulfate oxidation activators [elevated temperature (45°C) and high pH (at the cathode)] were investigated to maximize the PCB degradation. In addition, the effect of oxidant dosage on PCB degradation was investigated. The electrokinetically enhanced temperature-only activated persulfate oxidation test resulted in better PCB 44 remediation (77.9%) than the temperature and high-pH activated persulfate oxidation (76.2%) in a 7-day period. The optimal dosage for effective remediation was 30% Na-persulfate (76.2%) because a 20% concentration of the oxidant yielded a lower rate of degradation (55.2%) of PCB 44. The results are encouraging for the use of electrokinetically enhanced persulfate oxidation for the effective remediation of PCBs in soils. [ABSTRACT FROM AUTHOR]

Rapid load pile testing (RLT) techniques such as Statnamic were developed as an alternative to more frequently adopted static and dynamic tests. The existing unloading point method (UPM) for deriving equivalent static load-settlement behavior from rapid load tests seems to be adequate in coarse-grained soils but may result in poor prediction in clays and silts. To address these shortcomings, the UPM has been improved to reflect soil type, and new analysis techniques have been developed. To test the performance of the improved UPM and new analysis techniques, pile tests from two clay sites were analyzed. The first case study site was underlain by very to extremely high-plasticity Quaternary London clay, and the second site was underlain by low- to intermediate-plasticity matrix dominant glacial till. The best predictions of static equivalent load-settlement behavior for very-high-plasticity clay were obtained from a new analysis technique that incorporated a soil-specific rate effect parameter (selected on the basis of the clays' plasticity index) that varied with pile settlement. In general, the UPM performed better for tests undertaken in the low- to intermediate-plasticity glacial till, as there is greater experience of RLT in these soils. The results of the study suggest that the development of analysis techniques would benefit greatly from tests in a wider variety of soil types. On the basis of the findings of this study, improvements to the UPM and Schmuker techniques are presented, which include pile settlement-dependent variation of the damping and rate effect parameters. [ABSTRACT FROM AUTHOR]

The methylene blue (MB) stain test was used to determine the efficiency of lime modification of clay soils and to define the percentage of lime required to reach the stabilization field. Montmorillonite and kaolinite, mixed in variable proportions with quartz sand, were treated with differing percentages of lime, and the MB test was performed on both untreated and treated soils. Results show that the test can determine whether a soil is prone to efficient modification, follows the evolution of clay minerals in the lime modification field, and it also determines the quantity of lime necessary to enter the stabilization field. X-ray powder diffraction, thermal analyses, and electron microscopy observations of the montmorillonite-richer sample showed its crystal chemical evolution in the modification field. Mineralogical results match the outcome of the MB test, defining the same lime percentage for best modification (4%) and confirming that the test can be used for preliminary and ongoing analyses of lime treatment. [ABSTRACT FROM AUTHOR]