Search

Geotechnical testing serves to assess the strength and stiffness of in-situ soils, for purposes such as informing foundation design. Despite its importance, time constraints, financial considerations, and site-specific limitations often restrict testing to isolated locations with limited horizontal resolution. Therefore, this paper presents a novel hybrid generative deep learning model designed to approximate soil properties across sites based on sparsely sampled geotechnical data. The model uses geological subsurface samples derived from random field theory as 'a priori' data for a conditional variational auto-encoder (CVAE) model. By doing so, it attempts to map the relationship between in-situ data and the corresponding spatial coordinates, as well as the inherent link between in-situ data and spatial distribution. Then, in the post-processing phase, a Kriging model interpolates minor discrepancies between the measured and predicted values. To demonstrate its practical application, this paper focuses on cone penetration testing (CPT) as the geotechnical test method. The model's development is thoroughly discussed, followed by the validation using in-situ data and an analysis conducted with synthetic data. It is shown that the uncertainty associated with CVAE-Kriging depends upon both the distance from the sample point and the site's inherent complexity. The proposed methodology not only offers refined subsurface modeling but also expands the understanding of uncertainty in geotechnical testing. Practically, it can assist geotechnical engineers with insights during the survey phase. • A hybrid deep generative method for geological subsurface modeling is proposed. • Substantial 'prior' information is incorporated to guide subsurface modeling. • Validation is performed using multiple non-stationary cases and various methods. • The CVAE's uncertainty correlates with the complexity inherent to the site itself. [ABSTRACT FROM AUTHOR]

In this paper, a series of suction-controlled triaxial tests were conducted to investigate the hydromechanical behaviour of an unsaturated kaolin mixture. The studied variables included the mean net stress, suction, and initial dry density. The suction was controlled over a wide range – in the span of 0–390 MPa using the axis translation method and the vapour equilibrium technique, aiming to holistically study the mechanical response of unsaturated soils. The discussion focused on the critical state behaviour and dilatancy characteristics of the tested soil. The experimental results indicate that the ductility of the soil decreases and shifts towards brittleness with increasing suctions. The critical state stress ratio (M a) of the soil exhibits a significant increase with suction, and this increase becomes more pronounced with higher initial dry density. Conversely, the impact of suction on the critical state line in the specific volume-mean net stress plane (v -ln p net plane) diminishes with higher initial dry density. Furthermore, suction notably influences the stress-dilatancy relationship of kaolin mixtures, while the effect of confining pressure appears to be marginal. The influence of suction on the stress-dilatancy relationship primarily stems from its impact on the critical stress ratio (M a), which can be normalized by dividing the stress ratio by the critical state stress ratio. Lastly, the stress-dilatancy equation of the modified Cam-clay model is extended to capture the effect of suction on the dilatancy characteristics of unsaturated soils. • The mechanism of suction-induced over-consolidation is analysed. • As suction increases over a wide range, the critical state stress ratio (M a) notably rises. • The impact of suction on dilatancy is a result of its influence on M a. • The suction-induced friction angle is unaffected by initial dry density. [ABSTRACT FROM AUTHOR]

In this paper the use of ER measurements in soils in the context of biocementation, is investigated considering its use as an indicator of treatment efficiency measured trough the presence of biocement, or to provide information about the presence of chemical by-products during or after final washing operations. The electrical resistivity of a slightly biocemented sand was analyzed on a laboratory scale test conceived to reproduce field measurements conditions such as varying degrees of saturation and the presence of chemical by-products in the pore fluid. The results confirmed that, independently from the degree of saturation, the nature of the pore fluid was the parameter that affected most the electrical resistivity measurements, and the presence of calcium carbonate affecting soil structure was detected only after removal of the treatment by-products by a complete final soil washing using water. From a practical point of view this non-destructive technique is more adequate to be used mainly at the end of the treatment, to check that complete soil washing has occurred, rather than checking the presence of bio-cement specially if the amount precipitated is not very high as it was the case of the tests performed. • During the biocementation process by-products are generated (ammonium & chlorides). • By-products must be removed from the soil to ensure environmental sustainability. • ER measurements allow checking that all by-products were removed from the soil. • When removed, is possible to detect the effect of biocement on ER measurements. [ABSTRACT FROM AUTHOR]

Classical clustering (CC) normally divides a database into a predetermined number of fixed clusters before assigning each target site into one of these clusters to build a quasi-local model. Because the range of target sites is much larger than the range of clusters, it is possible that the identified cluster contains database sites that are weakly correlated to some assigned target sites, especially when these target sites are located near the cluster boundaries. The existence of weakly correlated sites in the cluster may make the quasi-local model less effective in predicting soil properties at the target site. This paper proposes a Tailored Clustering Enabled Regionalization (TCER) framework that can minimize the inference uncertainty at a target site. It mainly consists of two parts: (1) a site similarity measure to quantify the similarity between database sites and the target site and (2) a novel tailored clustering (TC) approach to identify the optimal cluster (called quasi-regional cluster) of database sites with the highest site similarity measures. In comparison to the traditional TC, the novel TC does not require users to specify a site similarity threshold that divides database sites into those within the cluster and those outside the cluster. Finally, a hierarchical Bayesian model is applied to the quasi-regional cluster (rather than the entire database) to infer geotechnical/geological properties at the target site. The capability of TCER is verified using synthetic and real examples. It is shown that the proposed TCER is computationally efficient and can reduce inference uncertainty. • An inter-dataset similarity measure is modified to make it suitable for comparing the similarity between two sites. • A novel clustering approach is proposed for identifying a cluster that is highly correlated to the target site. • A tailored clustering enabled regionalization framework is proposed for reducing inference uncertainty of a target site. [ABSTRACT FROM AUTHOR]

In geotechnical engineering, an appreciation of local geological conditions from similar sites is beneficial and can support informed decision-making during site characterization. This practice is known as "site recognition", which necessitates a rational quantification of site similarity. This paper proposes a data-driven method to quantify the similarity between two cross-sections based on the spatial variability of one soil property from a spectral perspective. Bayesian compressive sensing (BCS) is first used to obtain the discrete cosine transform (DCT) spectrum for a cross-section. Then DCT-based auto-correlation function (ACF) is calculated based on the obtained DCT spectrum using a set of newly derived ACF calculation equations. The cross-sectional similarity is subsequently reformulated as the cosine similarity of DCT-based ACFs between cross-sections. In contrast to the existing methods, the proposed method explicitly takes soil property spatial variability into account in an innovative way. The challenges of sparse investigation data, non-stationary and anisotropic spatial variability, and inconsistent spatial dimensions of different cross-sections are tackled effectively. Both numerical examples and real data examples from New Zealand are provided for illustration. Results show that the proposed method can rationally quantify cross-sectional similarity and associated statistical uncertainty from sparse investigation data. The proposed method advances data-driven site characterization, a core application area in data-centric geotechnics. • A novel method is proposed for quantifying 2D cross-sectional similarity of soil property spatial variability • An efficient formulation of 2D auto-correlation function is derived for a unified representation of 2D spatial variability • The challenges of sparse investigation data, non-stationarity, and inconsistent cross-sectional dimensions are tackled • The proposed method facilitates the quasi-regional clustering of geotechnical data [ABSTRACT FROM AUTHOR]

The ink-bottle effect, resulting from the non-uniformity of pore structure, plays a significant role in the hydraulic behaviour of soils. In this paper, a series of laboratory tests including standard mercury intrusion porosimetry (MIP), intrusion-extrusion cyclic MIP (IEC-MIP), and scanning electron microscopy (SEM) were conducted on two soils (a Nanyang expansive clay and a Kaolin mixture) to examine the evolution pattern of ink-bottle effect in soils with different initial void ratios. To evaluate the impact of such evolution on the soil-water retention behaviour, the axis translation and vapour equilibrium techniques were utilised to measure the water retention curve of the tested soils (SWRC). A key part of the analysis involved a separation between pore bodies (or ink-bottle pores) and pore throats to facilitate a more thorough examination of the pore structure. The test results indicated that the reduction in soil volume during compression is mainly attributed to the reduction in pore body size, whereas the pore throat size remains relatively constant. Therefore, the ink-bottle effect would weaken with a decreasing initial void ratio, which will reduce the hysteresis potential of soils, manifesting as a contraction of the SWRC hysteresis loop. Additionally, under a fixed void ratio but with decreasing pore size, the ink-bottle effect will also weaken, which will reduce the distance between the drying and wetting curves with increasing matric suction. Finally, the mechanisms regarding how the evolution of ink-bottle effect during soil deformation influences water retention hysteresis were addressed. • Soil-water retention curves (SWRCs) of two soils under wetting-drying cycles were measured. • The ink-bottle effect was investigated using the intrusion-extrusion cyclic MIP test. • The weakening of the ink-bottle effect occurs as the initial void ratio of soils decreases. • Mechanisms for the contraction of SWRC hysteresis loop as the ink-bottle effect weakens are revealed. [ABSTRACT FROM AUTHOR]

Accurately predicting slope reliability under a rainfall/rainstorm event is an important prerequisite for preventing rainfall-induced landslide hazards. However, the predicted probability of slope failure under the rainfall/rainstorm event is often larger than the observed frequency of slope instability. The spatial variability of multiple soil parameters was rarely accounted for. To address this issue, this paper proposes an efficient sequential probabilistic back analyses approach for learning multiple spatially varying soil parameters using Bayesian Updating with Subset simulation (BUS) method. Two survival records of a real slope in India (i.e., the slope stays stable before the rainfall and the slope keeps stable after a 57-day weak rainfall) are successively used in the sequential probabilistic back analyses of soil parameters. The results indicate that the proposed sequential probabilistic back analyses approach can effectively update the distributions of multiple spatially variable soil parameters by the fusion of slope survival records. More accurate statistics of soil parameters can be obtained when additional slope survival records are used in the probabilistic back analyses. Furthermore, two slope failure records under a 3-day heavy rainfall event and a rainfall event ranging from May 1, 2016 to June 30, 2016 in Chibo, India are, respectively, used to predict the slope reliability and further validate the effectiveness of the proposed approach. The predicted probabilities of slope failure under the target rainfall events are well consistent with the actual observation frequency. The proposed approach can provide a powerful and versatile tool for determining the statistics of soil parameters and early warning of landslide hazards under the future rainfall events. • An efficient back analysis approach is proposed for learning multiple spatially variable soil parameters under rainfall. • The BUS method and surrogate models greatly facilitate the sequential probabilistic back analyses of soil parameters. • A real unsaturated slope is investigated to illustrate the effectiveness of the proposed approach. • The proposed approach can effectively update the distributions of soil parameters and slope reliability prediction. • The using of field observations can reduce the uncertainties of soil parameters and enhance the slope reliability prediction. [ABSTRACT FROM AUTHOR]

The Authors have presented an interesting paper (Hrubesova et al., 2020), which aims (in part) to validate the Moharjerani (1999) calibration approach for establishing the 80 g/30° fall-cone penetration depth equating to the liquid limit by the Casagrande percussion-cup approach, determined according to the British Standard. In this paper, the Discussers present some clarifications on, and state various observations regarding, the approaches adopted in the Hrubesova et al. (2020) investigation, as well as the Moharjerani (1999) calibration approach employed therein. The Discussers also present a description of some relevant literature not covered in the Authors' paper (Hrubesova et al. 2020) aimed at making further clarifications on this important area of geotechnical practice. • In present global context, percussion-cup and fall-cone generally considered equally valid for liquid limit (LL) determination • Fall cone (FC) approach generally has superior repeatability and reproducibility • Recommended to consistently redefine LL uniquely as water content at which universal FC penetrates specified depth into remoulded specimen • Plastic limit (plastic/brittle boundary) condition uniquely established using standard thread-rolling method • Any agreement between water contents of plastic limit (PL) and PL 100 for a given fine-grained soil essentially coincidental [ABSTRACT FROM AUTHOR]

The fate of reservoir landslides is mainly dictated by the mechanical behavior of soil in the sliding zone. This soil may be altered under changing environmental conditions of both physical and chemical nature. In this paper, we present a laboratory study on the changing soil properties under complex physicochemical interactions. The soil specimens are subjected to 1, 2, 3, 5, 7, and 10 wetting-drying cycles. The soil strength is determined by triaxial tests. These tests are performed with three types of pore water, namely, acidic groundwater (AGW), normal groundwater (NGW), and distilled water (DW). The deterioration of soil strength, the change in soil microstructure and mineral composition are observed and correlated. Interesting findings for reservoir landslides are drawn: acidic underground water considerably damages the soil microstructure and deteriorates the shear strength compared to normal underground water, while distilled water causes minimal disaggregation. A three-stage micromechanism associated with four physicochemical interactions is revealed, providing insights into microstructure damage and mineral transformation. • Combined effect of physicochemical interaction on the shear strength of sliding zone soil. • Microstructure evolution of sliding zone soil by five classified pores. • Variations in minerals and cations signify potential chemical interactions between soil and water. • Four types of physicochemical interactions in the evolution process of sliding zone soil. • Three-stage evolutionary mechanism for soil deterioration. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop an easy procedure to diagnose the cyclic behavior of fine-grained soils, leading to liquefaction. There are approaches to this problem with reference to liquid limit (w L), plasticity index (PI), clay content, (C%), in-situ water content compared to the liquid limit (w n /w L), average grain size (D 50), and liquidity index (I L). Previous research has indicated that fine-grained soils defined as "sand-like" are prone to liquefaction. There is consensus that liquefiable silty soils have "sand like" characteristics. In the transition from sandy to clayey, it is generally accepted that it would be appropriate to make a judgment by making use of mechanical testing and that clayey soils do not liquefy. This paper presents the results of dynamic triaxial shear testing (CTX), where excess pore water pressures and axial strains are evaluated compared to the physical properties to reach the threshold for cyclic failure. Samples of undisturbed soil procured from different locations of the city of Adapazarı, Turkey, were subjected to CTX testing. The results were interpreted in the light of the physical properties to arrive at a judgment of cyclic failure. Being able to identify a liquefaction prone fine grained soil by merely measuring a few physical properties without resorting to arduous cyclic testing would be an advantage to the practising engineer. This however necessitates the elimination of the ' gray zone' for which most researchers recommended the use of cyclic testing. The main finding of this study is that samples reaching double strain amplitude (DSA) of <5% in the CTX test contain no sand and have a clay content of 20% or more. An attempt to establish a relationship between sensitivity to cyclic loading and physical properties is also made. • Seismic liquefaction in fine-grained fluvial soil. • Relationships between physical properties and cyclic triaxial test results of fine-grained soils. • Revision in the limit values of physical properties of soils for evaluation of liquefiability. [ABSTRACT FROM AUTHOR]

Soft soils show noticeable creep, damage and transversely isotropic properties. An incremental three-dimensional Nishihara model is proposed to present the stress-strain relationship of soft soils in this paper. The Drucker-Prager yield criterion of the transversely isotropic media, the transversely isotropic flexibility matrix, and the damage law to Nishihara's constitutive model are applied to construct the transversely isotropic viscoelastic-viscoplastic damage constitutive equation of the soil. Afterwards, the constitutive model is implemented by applying a stress return mapping algorithm. We verified the proposed model by comparing the results calculated by ABAQUS with triaxial compression experimental data from Hong Kong marine deposits (HKMD) and Shanghai soft clay. Finally, based on the proposed model, we present several numerical examples to investigate the influences of damage parameters on the time-dependent behaviors of saturated soft clay. • Soft soils show noticeable creep, damage and transversely isotropic properties. • An incremental 3-D Nishihara model is proposed to present the stress-strain relationship of soft soils. • A transversely isotropic viscoelastic-viscoplastic damage constitutive equation is constructed. • Influences of damage parameters on the time-dependent behaviors of soft soils are investigated. [ABSTRACT FROM AUTHOR]

For the deformation and evaluation of reservoir accumulative landslide, it is of great significance to study the strength characteristics of slip zone soils under rainfall and reservoir operation. In this paper, slip zone soils from Tongjiaping landslide in the Three Gorges Reservoir area is taken as the research case, and the self-developed seepage device matching with the ring-shear test is designed and manufactured. Then, the shear strength of slip zone soils under different seepage-shear conditions is studied to reveal the strength evolution law of riverside landslide. Eventually, the creep characteristics of slip zone soils are described by the Burger model. The experimental results indicate that: (1) the weakening effect of slip zone soils will be induced by the increase of seepage cycles, change amount of seepage pressure, initial and constant seepage pressure, which decrease the residual strength of slip zone soils. (2) When the seepage cycles are <15, the weakening of residual strength of slip zone soils is not obvious. While when the cycles reach 20, the residual strength of soil samples decreases rapidly. (3) The Burger model, which connected the Maxwell model and Kelvin model in series can appropriately reflect the creep characteristics of slip zone soils of Tongjiaping landslide. The research results reveal the weakening law of mechanical strength of slip zone soils under seepage cycles, which provides a basis for the mechanism of accumulative landslide under the fluctuation of reservoir level. • The soil sample seepage device matching with the ring-shear test is designed and manufactured. • Shear strength of slip zone soils under different seepage-shear conditions is carried out. • Creep characteristics of slip zone soils are described by the Burger model. [ABSTRACT FROM AUTHOR]

Moraine soils are widely distributed in the Qinghai-Tibet Plateau. With increased global warming, moraine soil-related geohazards have become increasingly common, posing a serious threat to the infrastructure (e.g., the Sichuan–Tibet Railway) and inhabitants of this region. This paper aims to investigate the mechanical behavior of ice-rich moraine soil in the Tianmo Valley by conducting a series of triaxial constant strain rate (CSR) and coupled thermomechanical (CTM) tests on artificially moraine soil containing different ice forms (crushed ice and block ice). The results show that in general, compared to moraine soil containing crushed ice, moraine soil with block ice has a higher peak strength, a similar internal frictional angle and a considerably larger cohesive strength. The stress–strain curve of the soil containing crushed ice shows a strain-hardening form, while that of the soil containing block ice is represented by a strain-softening model similar to that of dense soil. In the CTM tests, it is revealed that the rising temperature could cause a sharp increase in strain and lead to sample failure, even when the axial load is far below the material's peak strength. A comparison between samples with different ice forms reveal that the soil containing crushed ice is more sensitive to temperature change. The tests demonstrate that the ice form has a significant influence on the mechanical behavior of moraine soil, and the temperature rise can result in a dramatic decrease in soil strength. Therefore, efforts should be made to detect the occurrence form of buried ice and the changes in the environmental temperature as well as the stress state of moraine soil slopes in situ. • The strength of the moraine soil containing block ice is higher than that of the soil containing crushed ice. • The stress-strain curve of the soil containing crushed ice shows a strain-hardening form. • The stress-strain curve of the soil containing block ice is represented by a strain-softening model. • The mechanical behaviors of samples containing crushed ice are more sensitive to temperature rise than that of block ice. • A stress threshold value exists when the temperature rise acts as a dominant role affecting the deformation of moraine soil. [ABSTRACT FROM AUTHOR]

Most soil-water characteristic curve (SWCC) models contain more than three parameters, but these parameters typically do not have a distinct geometric or physical meaning, or the parameters used are inaccurate because of their high reliance on inverse parameter estimation methods. This phenomenon greatly limits the application of SWCC in the study of mechanical and hydraulic properties of unsaturated soils. To explore the nature of SWCC, this paper reexamines the role of the parameters in the two most commonly used SWCC models from the perspective of the relationship between capillary and adsorbed water. A new and flexible SWCC model (named the MVF model) with four parameters is proposed, which can separate the two different regions by physical constraints on the residual saturation S r and residual suction ψ r. Ten published experimental data sets are compiled to evaluate the performance of the MVF model by comparing it with both the existing models and the experimental data. The MVF model shows excellent performance in terms of goodness of fit, and the fitting parameters are provided with a clear geometric meaning, which helps to establish the connection between the basic properties of the soil and the SWCC. This study consolidates the application and reliable determination of SWCC in estimating the mechanical and hydraulic properties of unsaturated soils. • The relationship of capillary and adsorbed water and the role of the fitting parameters for FX and VG models are reviewed. • A flexible modified SWCC model with four fitting parameters based on FX and VG model is proposed. • The physical constraints from residual suction and residual saturation are employed in this study to reduce the uncertainty of the parameters. • The parameters in the proposed model can better capture the features of the SWCC. • A flexible variation on the mathematical form of the model can be applied to bimodal soils. [ABSTRACT FROM AUTHOR]

The salinization of agricultural soil is a common issue of concern. However, the coupling relationship between soil chemical properties and mechanical behavior has been largely ignored. A constant water content triaxial test was conducted by controlling suction on unsaturated agricultural soils collected from paddy fields. The soil samples were diluted with different salt solutions (a distilled water, a sodium chloride (NaCl) solution and a calcium chloride (CaCl 2) solution) to investigate the influence of salinity on the mechanical behavior of soils. The pore water pressure of silt loam was significantly influenced by the pore water salinity, while the pore water pressure of silty clay was significantly influenced by the net normal stress. The results showed that the salt type and concentration significantly affected the cohesion value of silt loam. An empirical constitutive model that incorporated osmotic suction was presented in this paper to explain and quantify the effect of pore water salinity on the shear strength of silt loam. Osmotic suction was considered an independent stress variable in the constitutive model, unlike the salt type and concentration. The Barcelona unsaturated constitutive model explained how the pore water salinity affected the mechanical behavior of agricultural silt loam. With an increase in the osmotic suction in silt loam, the yield surface expanded to both sides of the original ellipses, resulting in an increase in cohesion. The constitutive framework considering osmotic suction provides an improved prediction of the mechanical behavior of agricultural soil under natural conditions subjected to salinization/desalinization. This framework can be implemented in a stabilization plan when the soil and salt are involved in agricultural activities. • A modified unsaturated triaxial test to obtain detailed mechanical behavior of agricultural soils • Investigated the influence of soil pore water salinity on the mechanical behavior of agricultural soil. • Soil pore water salinity had a higher influence on silt loam than silt clay. • The osmotic suction should be considered as an independent stress variable in the constitutive framework. [ABSTRACT FROM AUTHOR]

The technique of carbonated stabilization is an innovative method to improve the engineering performance of soft soils. However, the improvement in the engineering performance of stabilized soils with carbonized steel slag has not been studied. In addition, the effect of clay minerals on carbonation parameters and D-W cycle performance remains unknown. To this end, in this paper, three types of synthetic soils containing different clay minerals were prepared to be stabilized by carbonated steel slag. The strength performance and microstructural evolution of carbonated steel slag stabilized soils were investigated by drying-wetting (D-W) cycle tests, unconfined compression strength (UCS) tests, X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM). The results showed that the compressive strength after and resistance to D-W cycles of carbonated steel slag stabilized soils were significantly improved due to carbonation treatment. The presence of clay minerals in stabilized soils led to the high values of optimum moisture content for carbonation (C-OMC). The C-OMC value of stabilized soils containing montmorillonite was higher than that of stabilized soils containing kaolinite. Montmorillonite had a higher negative effect on the D-W cycle performance of soils compared to kaolinite. This fact could be reflected by the fluctuation of UCS and mass change ratio (R m). The main carbonation product by three types of carbonated steel slag stabilized soils was calcite, which remained stable after D-W cycles. After carbonation for 18 h, the generated calcite and carbonation degrees for three types of stabilized soils were obtained. In the microstructures of carbonated steel slag stabilized soils, the spindle-like clusters of the generated calcite appeared, which adhered to the surface of mineral particles. The aggregated degrees of the generated calcite in stabilized soils containing clay minerals tended to decrease after D-W cycles. In this work, a new type of carbonated steel slag stabilized soil was studied. The results indicated that the effect of clay minerals on the engineering characteristics of soil should be considered. • Carbonated steel slag is used to stabilize three types of artificial soils. • Influence of clay minerals on performance and microstructure of carbonated steel slag stabilized soils is investigated. • The existence of clay minerals leads to increasing values of the optimum moisture content for carbonation. • The main carbonation product is calcite which remains to be stable after drying and wetting cycles. [ABSTRACT FROM AUTHOR]

Enzyme-induced carbonate precipitation (EICP) is a potential method to improve the mechanical properties of granular soil. The one-phase premixed percolation method using purified urease enzyme is widely adopted for in-situ EICP treatment currently, but it is expensive and uses a relatively large amount of urease. This paper proposes a multiple-phase method consisting of a percolation of premixed soybean crude urease and cementation solution followed by several percolations of cementation solution in one cycle of biocementation. The utilizing rate of urease was increased by at least four times for the production of precipitated carbonate compared with the one-phase method. The proposed method also weakened the clogging of carbonate precipitation, thus bringing out a relatively uniform EICP treatment. After four cycles of biocementation (each cycle included five applications of cementation solution), the unconfined compressive strength of EICP-treated ASTM C778-graded sand exceeded 10 MPa with a CaCO 3 content of ~20%. • Soybean crude urease was employed to catalyze CaCO 3 precipitation via EICP. • A multiple-phase EICP method was proposed for soil improvement. • The proposed method could significantly improve utilization efficiency of urease. • A relatively uniform CaCO 3 precipitation was obtained in EICP-treated sand. • The UCS of EICP-treated sand exceeded 10 MPa with a CaCO 3 content of ~20%. [ABSTRACT FROM AUTHOR]

The evolution of sliding zone soil originating from a muddy interlayer in the Three Gorges Reservoir (TGR) in China is accompanied by an increase in clay content, and the subsequent changes in its mechanical properties control the initiation or reactivation of large-scale bedrock landslides. In this paper, using sliding zone soil samples from the Xingfusi landslide in the Wanzhou area, two groups of remolded saturated specimens were prepared with clay contents of 25.0% and 12.5%. Direct shear creep tests and a series of ring shear tests were carried out to investigate the shear behaviors of the specimens with different clay contents. On this basis, the effect of clay content on the evolution of landslides was discussed. The results show that (1) during the long-term creep process before landslide initiation, the shear creep modulus of sliding zone soil in steady creep state significantly decreases with an increase in clay content, which results in the increase in cumulative creep displacement. (2) The increase in clay content in sliding zone soil will lead to a reduction in peak shear strength and residual frictional resistance. In the drained shearing on saturated sliding zone soil with a high clay content, the excess pore-water pressure on the sliding surface cannot dissipate as rapidly due to the small permeability of sliding zone soil with a high clay content, which may favor postfailure movement. (3) With an increase in shear displacement rate, the residual strength first shows a weak "negative shear rate effect" and then shows a significant "positive shear rate effect". However, with an increase in clay content, the initial shear rate for the residual strength showing a "positive rate effect" will decrease. (4) Sliding zone soil with a high clay content generally does not exhibit strength recovery, while sliding zone soil with a low clay content clearly recovers its peak residual strength due to volume change of the shear zone caused by secondary compression after a long period of reconsolidation. In this case, a greater external load or reduction in effective normal stress needs to be applied to reactivate the landslide. • An increase in clay content of sliding zone soil results in the increase in cumulative creep displacement. • High clay content decreases the initial shear rate for the residual strength showing a "positive rate effect". • The effect of clay content on the strength recovery of sliding zone soil was revealed. • The effect of clay content on the whole evolution of landslides was explained. [ABSTRACT FROM AUTHOR]

There is a growing interest in the geomechanical behaviour of low performing soils strengthened with alkali-activated materials, which have been promoted as low-carbon-footprint binders. This paper focuses on the performance of a sandy clay stabilised with NaOH-activated blast furnace slag after short (28 days) and long (90 days) curing periods. Triaxial compression experiments were conducted at a range of mean effective stresses (41 to 600 kPa) and overconsolidation ratios (1 to 12.2). The experimental data was used to calibrate a kinematic hardening constitutive model and the ability of the model to capture the behaviour of artificially stabilised sandy clay was investigated. Triaxial results carried out on the stabilised soil at both curing periods showed a behaviour resembling that observed for cement-mixed clays. The model, which had never been tested in artificially stabilised soils, successfully predicted the smooth elastoplastic transition observed on the non-stabilised soil specimens and the peak/residual shear strains and strain-softening behaviour after peak strengths in its stabilised state after 28 and 90 curing days. • Predicting the triaxial compression behaviour of a sandy clay stabilised with an alkali-activated binder. • Stress-strain behaviour typical of artificially cemented clays with conventional binders. • A kinematic hardening model was applied to predict the stress-strain behaviour. • The impact of the alkali-activated binder on the stress-strain behaviour was well captured by the model. • Typical shear failure cracks with approximately 45° slope or vertical cracks were observed on the stabilised specimens. [ABSTRACT FROM AUTHOR]

Transitional soils mixed with terrestrial silicate and marine carbonate deposits are commonly found in coastal regions, which have special geological and geotechnical characteristics. This study examines the engineering properties of the compressibility and crushing characteristics of this type of transitional silicate‑carbonate soils. Scanning Electron Micrograph, X-ray fluorescence and laboratory tests were first conducted to identify the physical and mechanical properties of the pure silicate and carbonate soil samples adopted in this study. A total of 54 one dimensional compression tests were carried out for soil samples mixed with varying portion of silicate and carbonate sands by applying increasing loading level, where particle size distribution was obtained post each test to quantify particle breakage. The soil deformation is found to comprise two components that are caused by inter-particle rearrangement and particle breakage. The test results show that particle breakage tends to play a dominant role on the deformation with increasing content of carbonate sand and load level. The series of laboratory tests and the associated interpretations in this paper are expected to provide an improved understanding of the compressibility and crushing characteristics of transitional sediments mixed with silicate and carbonate sands. An equation was proposed to establish the relationship between particle breakage and crushing work, which provides a predictive assessment of particle breakage for transitional soils accounting for varying portion of silicate and carbonate sands. • The microscopic characteristics of silicate and carbonate sands were identified. • The compression behaviors of transitional silicate-carbonate soils were examined. • Soil deformation is divided into inter-particle rearrangement and particle breakage. • Particle breakage of transitional soils were analyzed through gradation evolution. • An equation is proposed for the assessment of breakage of transitional soils. [ABSTRACT FROM AUTHOR]

In geological engineering, the unsaturation and non-uniformity of soil have significant influence on slope stability. However, they were common neglected in published literature. Based on the three-dimensional (3D) rotational failure mechanism, this paper introduces a method that combines the gravity increase method and the upper bound theorem, to evaluate the factor of safety (FS) of 3D stepped slope in non-uniform and unsaturated soils. The soil cohesion increases linearly with depth, and three nonlinear unsaturated shear strength models are adopted in this study. After the calculations of internal energy dissipation rate and external work rate, the analytical formula of FS is derived, and the lowest FS value is obtained through optimization. To prove the validity of the proposed method, the present results are compared with previously published solutions. A parametric study is carried out, and the influences of a number of factors on FS are discussed. For non-uniform and unsaturated soils, the new formula for calculating the FS of 3D two-stage slopes is presented for practical use in geological engineering. • New formula for calculating the FS of 3D two-stage slopes is derived. • GIM is introduced to evaluate FS of 3D stepped slopes in inhomogeneous and unsaturated soils. • Validity of the analytical solutions obtained in this study is verified. [ABSTRACT FROM AUTHOR]