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Plate anchors have great advantages that are useful in deep or ultradeep water mooring systems. The keying behaviors have a deep effect on the embedment loss and pullout capacity of strip plate anchors. In this paper, the effect of soil remolding on the keying behaviors of strip plate anchors is studied by large deformation finite-element (LDFE) analysis. First, the LDFE results are compared with centrifugal test results, theoretical solutions, and LDFE data from previous literature, showing good agreement. Then, a series of LDFE cases is studied to investigate the effects of the padeye offset, load eccentricity, soil sensitivity, and initial embedment depth on the embedment loss and pullout capacity of plate anchors during the keying process. The LDFE results show that different load eccentricity corresponds to different soil failure mechanisms, and both padeye offset and soil remolding will reduce the pullout capacity of plate anchors. Finally, an equivalent soil strength is introduced considering rate effect and soil remolding of clay. A combined factor and an equivalent ultimate pullout capacity are used to estimate the ultimate embedment loss and pullout capacity of strip plate anchors in uniform clay, respectively. [ABSTRACT FROM AUTHOR]

Stratum cavity collapse induced by water and sand leakage in a subway tunnel is a sudden urban geological disaster, which can cause serious casualties and economic losses. In response to the hazards of stratum cavity collapse induced by water and sand leakage around subway tunnels, a set of visual test devices with variable hole diameters were designed to simulate the stratum cavity collapse induced by water and sand leakage under comprehensive consideration of the size of the cavity diameter, clay thickness, clay strength, and so on. Based on pressure arch theory and unified strength theory, a critical calculation formula was established for stratum cavity collapse under two modes, of tensile shear and shear failure. Furthermore, the accuracy of the theoretical calculation formula was verified by experiment. The results show that the critical radius increases with the increase of clay strength and decreases with the increase of buried depth and friction angle. Clay soil is more prone to shear failure at the arch foot under the same conditions. The larger the soil sand mix ratio and the cavity diameter, the smaller the critical water pressure of soil collapse. The thicker the soil layer, the greater the critical water pressure. The theoretical analysis method has a clear physical meaning and the theoretical results agree well with the test results. The research results are of great significance for the warning of and prevention of such urban geological disasters. [ABSTRACT FROM AUTHOR]

The piezocone penetration test (CPTu) is a common geotechnical field test to evaluate soil properties. In interpreting the CPTu field measurements, soil drainage conditions are mostly considered completely drained or undrained; however, partial drainage conditions govern for such soils as silts or clayey sand mixtures. Previous studies show that neglecting partial drainage conditions causes incorrect estimation of soil geotechnical parameters. Most studies have been conducted using calibration chambers and centrifuge tests on clayey soils. Due to the complications in modeling the piezocone test, few numerical studies have been performed under partially drained conditions, especially on coarse-grained soils. Among the challenges of numerical modeling of CPTu, one can mention the difficulty of modeling soil structure in large strain mode and soil–water interaction behavior. In this paper, piezocone penetration tests were modeled using the advanced hypoplastic constitutive model and finite-element method. The behavior of Firoozkooh sandy soil under different drainage conditions and relative densities was analyzed. Then, the effect of cone penetration on the surrounding soils was discussed. It was shown that drainage conditions and the soil relative densities significantly affected the trend of variations in excess pore-water pressure (EPWP) generated around the piezocone. [ABSTRACT FROM AUTHOR]

Earth pressure balance (EPB) shield tunneling in coastal silty clay strata often faces the problems of clogging on the screw conveyor or the belt conveyor due to lumps of clay soils formed because of the large cohesion of clay particles. Soil conditioning using common foaming agents is not enough to alleviate the problem. Therefore, the novel dispersed foaming agent was studied in this work using performance and orthogonal compound tests. The foam microstructure was observed using an electron microscope to analyze the evolution mechanism of bubbles for different additives. Both laboratory and in situ tests were carried out to assess the effectiveness of the novel dispersed foaming agents. The testing results showed that 50 vol.% is an optimum foaming injection ratio to improve rheological properties and undrained shear strength of silty clay to avoid the unnecessary waste of conditioning materials. The half-life time (T1/2) and foam expansion ratio (FER) of novel foaming agents using the formation ionic solution as the solvent increased due to existing hydrophilic polar groups based on undisturbed soil samples taken from a Xiamen Metro construction site. It was shown that acids, alkalis, and salt ions had little effect on the FER and T1/2 of foaming agents (Foams A and B) using the macromolecular dispersant. The variations in the plasticity index were similar to those of the liquid limit for the muck conditioned using dispersed foaming agents with sodium citrate, sodium bicarbonate, and sodium chloride at a concentration of 0.1 wt%. Sodium bicarbonate had the most significant impact on the foaming agents' anticlay effect. Compared with commercial and house-made foaming agents of the Fuzhou Metro project, the muck was effectively conditioned by Foams A and B based on the slump and temperature values. In addition, the average cutter-head torque was reduced by about 250 kN·m. The amount of foaming agents used was reduced by about 18.6% and 12.9% on average in the two testing sites, respectively. [ABSTRACT FROM AUTHOR]

In addition to creating environmental threats, the leakage and entrance of chemical fertilizers into soil, which is possible in various ways, dramatically changes the physical and mechanical properties of soil. Furthermore, clay soils in the vicinity of monoammonium phosphate (MAP) contamination show substantially negative behavior, thus, improving the engineering geological factors of soil has become a huge challenge for engineers. Extensive programs such as triaxial compression test, consolidation test, compaction test, Atterberg limits, and collapse tests, in addition to X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were performed on samples containing 10%–30% MAP over 7 days, 1, and 3 months. The mentioned trend was repeated when 0.5%–3% nano A (Al2O3 in alpha phase), nano F (Fe2O3 in alpha phase), and AF in form of a nanohybrid were added to soil which had been contaminated by MAP. Gained reports demonstrated significant declines in maximum dry density, plasticity index, and shear strength of contaminated soil when compared with natural soil. Conversely, increases in liquid limit, plastic limit, consolidation settlement, as well as soil collapse index were observed. Furthermore, a decrease in the amount of minerals in the XRD results and the formation of a flocculated structure in the SEM images in MAP-contaminated soil are evident. According to microstructural analysis, adding nano A, nano F, and AF nanohybrid as an improvement phase caused remediation of the soil structure and created cementation bonds between soil particles, thereby increasing the maximum dry density and soil shear strength, and decreasing the consolidation settlement and soil collapse index. Therefore, the use of AF as an efficient additive to remediate physical and mechanical properties of soils that have been contaminated with MAP, and to decrease the geological hazards of these kinds of contamination is recommended. [ABSTRACT FROM AUTHOR]

In this paper, a constitutive model is presented to model the behavior of various soils (sand and clay) in different loading conditions and the minimum required parameters are obtained. Although some practical features (concepts) of the bounding surface framework and modified Cam-Clay have been employed in its formulations, the model is developed mainly based on the generalized plasticity framework. Moreover, some concepts such as dilatancy relation and loading history surface are redefined. Finally, the proposed constitutive model is evaluated using the experimental data related to two different sandy soils and three different clays under different loading conditions. Finally, it is concluded that the proposed constitutive model can easily be calibrated for various clayey and sandy soils. It can depict different behavioral aspects of these soils under different monotonic and cyclic loading conditions. [ABSTRACT FROM AUTHOR]

In nature, expansive soil is generally in a state of swelling during rainfall, and its soil–water characteristic curve (SWCC) exhibits a three-dimensional space shape under the action of an increasing void ratio. In this study, expansive soil from Hefei, China, was used. SWCC and hygroscopic tests were performed. A three-dimensional hygroscopic swelling mathematical model of the dry density–void ratio–saturation degree was constructed based on the volume change behavior of expansive soils resulting from the hygroscopic test. In addition, depending on the variation in suction with the saturation degree of expansive soil under different values of dry densities, an SWCC mathematical model considering the swelling effect was constructed. The three-dimensional surface model of the hygroscopic swelling of the expansive soil was steeper in the lower saturation degree area. As the saturation degree increased, the three-dimensional surface gradually became flat. The SWCC model of the expansive soil under the action of swelling in a three-dimensional space is an S-shaped surface. The model exhibited dynamic changes in the suction and saturation degrees as the dry density of the soil decreased continuously. The model comprehensively revealed the hydraulic and swelling properties of expansive soil. [ABSTRACT FROM AUTHOR]

Expansive soils are extremely susceptible to swelling and shrinkage associated with seasonal changes in their moisture content. This can cause serious damage to structures constructed on expansive soils. Stabilization using additives is widely used to mitigate the concerns of expansive soils by controlling the changes in volume, thereby increasing the strength and durability of the soils. Multistabilizers, including a low percentage of conventional additives with nonconventional additives, can reduce the costs of stabilization. The performance of the stabilized soil can be enhanced by admixture optimization to ascertain that the agent's ratios are quite adequate to meet the optimal levels of modification. Unfortunately, despite the development of advanced techniques for investigating the stabilization of expansive soil, limited studies are devoted to the optimization of admixture to soils. Hence, in this research, an approach based on rough set theory, a mathematical data mining approach, is presented for multiagent optimization for efficient treatment of expansive soils. The multiadditives used in this study are almond shell ash (ASA), volcanic rock dust (VRD), and portland cement (PC). The differential free swell test, the California bearing ratio test, and the unconfined compressive strength test were applied for assessing the characteristics of the stabilized soil specimens. The obtained results and the confirmatory tests demonstrated that a combination of 20% ASA and 20% VRD with 8% PC provides the optimum results in the properties of expansive soil. The microstructural analysis denoted an enhanced modification of the soil engineering properties. The outcomes of this research confirm that the rough set optimization procedure is highly suitable for application in multiagent optimization for the efficient treatment of expansive soils. [ABSTRACT FROM AUTHOR]

The deep soil mixing (DSM) method is used to improve the mechanical and/or hydraulic properties of soils. The DSM method refers to an in situ mixing of soil, water, and hydraulic binder without excavation. After describing the specific microstructure of DSM materials compared with soils or concrete, four porosity–permeability analytical models from literature and based on microstructural parameters (i.e., porosity and pore-size distribution derived from mercury intrusion porosimetry) were applied to predict the water permeability (K) of soil–cement mixtures. After comparing the estimated permeabilities (Kest) with the experimental measurements of such a parameter (Kexp) using a triaxial cell, an indicator parameter A (=Kest/Kexp) was proposed to evaluate the ability of each model to fit the water circulation in DSM material. By calculating the average ratio 〈A〉 from the 24 materials in the studied database, three of the four applied models satisfactorily estimated the water permeability of the studied DSM materials. To reach an 〈A〉 value closer to 1, an extension of the Aït-Mokhtar's model, initially developed for cementitious mortars, was proposed by considering the specificities of the DSM materials. If previous models used only the contribution of nanopores less than 100 nm to the water flow, the extended model considered the contribution of all pore populations in the permeability calculation. Such an approach resulted in a significant improvement in the matching between the calculated and measured permeabilities. [ABSTRACT FROM AUTHOR]

A method for an a priori estimation of the frost heave ratio for clayey soils, considering the degree of their water saturation upon a closed system of freezing, is proposed. The proposed approach involves the introduction of a new parameter in the mechanics of frozen soils, namely, the frost heave index of clayey soils, which characterizes the degree of frost heaving of soil relative to the maximum height of the frost heave of soil that is fully saturated with water. An introduced parameter is used in the final formula to estimate the frost heave ratio of clayey soils. Laboratory experiments were performed to determine the height of frost heaving of clayey soils with a variation in their moisture and porosity to verify the proposed approach. A comparison of the experimental and calculated results showed a suitable convergence sufficient for the practical use of the formula to determine the frost heave ratio in a closed system of freezing. An example of a calculation to justify antiheaving measures using the proposed estimation of the frost heave ratio is given. [ABSTRACT FROM AUTHOR]

Cement composite soil is a more stabilized method in expansive soil foundation projects, but it is essential to find an ecofriendly modification material to reduce the content of cement and its pollution for the environment. A series of unconsolidated–undrained (UU) triaxial tests were conducted to investigate the modification effect of graphene oxide (GO) on cement-stabilized expansive soil (CS), and the contents of GO were 0.05%, 0.1%, 0.15%, and 0.2%, respectively. The test results show that (1) the deviatoric stress–strain curves of CS gradually change from a weakly softening type to a strongly softening one after adding GO. (2) The compressive strength, shear strength, and toughness of GO-modified cement-stabilized expansive soil are better than CS, and the optimal GO content is 0.05%. (3) Microscopic tests show that GO can promote the hydration reaction of cement and reduce the internal pores of CS. Consequently, the mechanical properties and microstructure of CS can be significantly improved after adding GO, and it is feasible to replace a part of the cement with GO in expansive soil foundation projects. [ABSTRACT FROM AUTHOR]

This paper presents an iterative horizontal method of slices (iterative HMS) for the global stability analysis of a slurry trench in layered cohesive-frictional soils. The iterative HMS differs from existing HMS models in terms of the assumptions on interslice forces. Preceding HMS techniques postulate that normal interslice forces can be evaluated from overburden pressures, which can lead to the violation of failure criteria along interslice boundaries. The iterative HMS ensures that a limit equilibrium system is established without violating the failure criterion throughout the entire soil mass. This is achieved by iteratively adjusting interslice forces by means of enforcing the failure criterion for the aforementioned problematic slice boundaries violating the failure conditions. The performance of the iterative HMS is evaluated in example problems of a slurry trench in uniform clayey soils and cohesive-frictional strata. The results are compared against solutions obtained using finite-element limit analysis (FELA) and a shear strength reduction FEM (SSRFEM). This comparative analysis shows that the adjustment in interslice forces is important for reasonably assessing trench stability conditions. A parametric analysis is performed by using the iterative HMS to show under what trench construction parameters the adjustment of interslice forces cannot be neglected in the stability analysis of a slurry trench. [ABSTRACT FROM AUTHOR]

Soils above the groundwater table and near the ground surface are often partially saturated, and the changes in the degree of saturation and matric suction caused by infiltration may have substantial effects on the stability of geotechnical systems. This work evaluates the significant effect of transient flow on the ultimate bearing capacity of strip footings founded on unsaturated soils under the simultaneous actions of vertical and horizontal loads and moment using the lower-bound theorems of the finite-element limit analysis and the incorporation of second-order cone programming. The unified effective stress theory is incorporated into the soil yield function to model the partially saturated state, and the closed-form solution for one-dimensional transient flow is adopted so as to evaluate the tempo-spatial variations of suction stress. For both sand and clay underlying soils, it is found that the increase of infiltration time leads to a notable decrease of the size of the normalized failure envelopes for either obliquely or eccentrically loaded shallow foundations. The impact of transient flow on the ultimate bearing capacity of surface footings is also observed to be greater for clay soils as compared with sand deposits due to the significant contribution of higher induced suction stress. [ABSTRACT FROM AUTHOR]

Clay–sand mixtures are deposited worldwide, such as naturally sedimentary soils and dredged clays in human activities. These mixtures usually have a fine fraction above the transitional fine content, and the compressibility is dominated by clay matrix and affected by sand fraction. In this paper, an explicit equivalent compression curve is proposed for clay–sand mixtures. This is done by directly incorporating the equivalent void ratio into the intrinsic compression model of the clay matrix. The roles of initial and evolving soil structure developed during the compression process are described by a structural variable, which can be directly computed from the experimental data. Experimental data compiled from various literature are used for evaluating the accuracy of the suggested model. They indicate that the proposed relationship of stress versus equivalent void ratio is simple yet effective to evaluate the compressibility of clay–sand mixtures with a wide spectrum of sand fraction. The model is also practically useful for estimating the compressibility of other gap-graded soils, such as clay–gravel mixtures. The proposed stress versus equivalent void-ratio equation is an elementary function and can be readily implemented into general elastoplastic models. [ABSTRACT FROM AUTHOR]

This paper discusses the second-order reliability-based design optimization (SORBDO) of unsaturated finite slopes. An efficient search algorithm is proposed to locate the most probable slip surfaces using the Morgenstern–Price method of slices. The variability of fitting parameters of the soil water characteristic curve (SWCC) and shear strength parameters have been taken into account for evaluating the reliability of unsaturated finite slopes. Six unsaturated shear strength (USS) models are considered for the analysis of unsaturated soils. The most conservative model for the optimum design of finite slopes is recommended. Moreover, the results indicate that the mean and standard deviation of the fitting parameters of SWCC have a significant effect on the critical centers, critical slip surfaces, and reliability index of the unsaturated finite slopes. The results demonstrate a significant change in the critical centers associated with critical slip surfaces due to the change in the mean and coefficient of variation of the fitting parameters of SWCC. Statistical analysis of the experimental data shows that a positive correlation exists between fitting parameters of SWCC related to air entry value (af) and residual water content (mf). Negative correlations are found between the fitting parameters of SWCC related to air entry value (af) and slope (nf). Similarly, the SWCC fitting parameters related to residual water content (mf) and slope (nf) have negative correlations for clayey soils. It is observed that the correlated value of the reliability index is overestimated with reference to the uncorrelated value for clayey soil slopes. The proposed design charts are beneficial for engineers and practitioners for the sustainable design of unsaturated finite slopes. Overall, the developed rigorous SORBDO framework offers a more rational approach for assessing critical failure surfaces and critical centers, considering the interdependency of random variables. [ABSTRACT FROM AUTHOR]

In this paper, the compressive and tensile ultimate bearing capacity of helical piles, in the load range required for designing 63-kV transmission towers, are studied by conducting analytical and numerical investigations. In this light, an explicit easy-to-use analytical framework was developed by considering the unsaturated soil condition that was validated against experimental records. Also, finite-element models were constructed for fully saturated and fully dry soil conditions. Then, to validate the analytical and numerical solutions in fully saturated and fully dry soil conditions, three compressive and one tensile field tests were carried out, and the results were compared quantitatively with analytical and numerical calculations. Comparative studies showed that the analytical, numerical, and experimental results have a high level of conformity. In accordance with the load ranges of transmission towers, analytical parametric studies were conducted for different geometrical aspects of the helical piles in different soils. Also, for two typical unsaturated sand and clay soils, the ultimate load of helical piles was calculated versus matric suction. Moreover, a vast numerical parametric study was performed to investigate the role of the geometrical aspects of helical piles and soil characteristics on the load-transfer mechanism and ultimate bearing-capacity values for helical piles driven in sandy and undrained saturated clayey soils. Results showed that the maximum load capacity of helical piles occurred in a matric suction less than that of a fully dry soil. In addition, the soil type and the geometrical aspects of the helical pile were shown to have significant effects on the load–displacement behavior and ultimate bearing-capacity values. [ABSTRACT FROM AUTHOR]

The undrained shear strength (su) and overconsolidation ratio (OCR) of clayey soils are two key parameters that are frequently used in geotechnical engineering practice. In comparison to laboratory tests that are expensive and time-consuming, the fast evaluation of these parameters using the field piezocone penetration test (CPTu) is favorable. The available literature contains a number of correlations that have been suggested by several researchers to estimate the su and OCR from CPTu; however, these correlations were mostly empirical and were constants multiplied by CPTu measurements. In addition, these correlations were site-specific and provided rough estimations of these important parameters. In this paper, the process of a CPTu in clayey soils was modeled via finite-element (FE) formulations, and the predictions for excess pore water pressures (EPWPs) that were generated around the penetrating piezocone were elaborated on and used to develop two new relationships for the estimation of su and OCR from CPTu data. A major advantage of the proposed relationships is that they could be employed using CPTu measurements and no other information from laboratory experiments or calibrations with field benchmarks or reference values may be needed. The utilized simulation procedure and the proposed relationships were compared and validated with the laboratory and field measurements and the existing relationships in the literature. [ABSTRACT FROM AUTHOR]

This paper examines the accuracy of a new elastic–thermoviscoplastic (E-TVP) constitutive model developed based on critical state soil mechanics. The model can be used for simulating the temperature-dependent and strain-rate-dependent behavior of clay soils. The study compares the E-TVP behavior of a single soil element with previously published thermo-mechanical experimental results performed on saturated clay specimens at different temperatures. Suggestions regarding unloading and reloading at constant temperatures as well as thermal consolidation under constant loads are presented. A modification for unloading–reloading adds a new criterion to the volumetric thermoviscoplastic strain rate formulation. A physics-based term is added to the current specific volume of the soil to include the viscous effect induced by temperature change. These modifications improve the convergence of laboratory data and simulated model responses. Comparisons of results from an earlier E-TVP model and the newly improved model provide evidence of improved predictive capabilities. [ABSTRACT FROM AUTHOR]

Excavation causes disturbance to the surrounding soil, affecting the soil's mechanical properties. This study presents a case study to investigate the effect of excavation disturbance on soil properties and pile capacity via in situ tests. A series of multifunctional piezocone tests, multichannel analysis of surface wave tests, and electrical resistivity tomography tests were conducted at three sites of the Taihu tunnel region before and after excavation with different depths. The changes in soil mechanical properties and the pile capacity loss were evaluated using the test results. The results indicated that excavation disturbance decreased the cone tip resistance, sleeve friction, soil resistivity, shear wave velocity, and undrained shear strength. In contrast, the friction ratio and the effective friction angle were not affected. The average cone tip resistance of soils in the excavation disturbance zone was approximately 51%, 46%, and 62% of its initial value at Sites A, B, and C, respectively. The variation in soil properties was only observed within a limited depth below the excavation surface, which is defined as the excavation disturbance zone. The piezocone test successfully identified the depth of the excavation disturbance zone, and the disturbance zone height was approximately 0.42 times the excavation depth. In the disturbance zone, the cone tip resistance and the undrained shear strength of the soil decreased linearly from approximately 90%–0% with increasing depth. Because of excavation disturbance, the axial and lateral capacities of a pile beneath the Taihu tunnel were reduced by about 9% and 50%, respectively. [ABSTRACT FROM AUTHOR]

This study investigates the utilization of alkali-activated granular blast furnace slag (GBFS) and fly ash (FA) for stabilizing rammed earth materials and assessing their mechanical and durability properties. Twenty mixtures were designed using the central composite design (CCD) of response surface methodology (RSM). The clay content of the soil, NaOH molarity, and GBFS to the binder ratio were selected as independent variables. Density, water absorption, 28-day compressive strength, and compressive strength loss after 60 days of exposure to sulfuric acid were measured as responses. Also, the microstructure of the specimens and the effects of the sulfuric acid attack were investigated by SEM and XRD analysis. The results revealed that an increase in the clay content of the soil reduced the compressive strength of specimens. Also, higher content of FA than GBFS in binder led to more acid-resistant specimens for mixtures containing a low amount of kaolin clay. On the other hand, for specimens with a high amount of kaolin clay, a higher proportion of GBFS than FA in binder resulted in more acid-resistant specimens. In addition, an increase in NaOH molarity and GBFS content in the binder was accompanied by an improvement in compressive strength. SEM investigations showed more homogenous and compact reaction products for these mixtures. Finally, a numerical optimization method was implemented to obtain mixtures with the highest compressive strength and minimum compressive strength reduction after acid exposure. [ABSTRACT FROM AUTHOR]

This research paper aims to comprehensively investigate the effectiveness and sensitivity of fiber inclusion on the behavior of a clayey soil subjected to desiccation. A series of laboratory experiments including desiccation shrinkage and cracking tests were performed for both unreinforced and reinforced specimens. Polypropylene fiber was used in this study to reinforce the soil, with different fiber contents (FCs; 0.1%, 0.2%, and 0.3%) and fiber lengths (FLs; 6, 12, and 18 mm). The results showed that the desiccation cracking behavior of the soil was significantly affected by the addition of fibers. Desiccation cracking was found to be reduced effectively with increasing the FC; however, interestingly the effect of varying FL was not significant. In addition, the relevant underlying mechanism is discussed. [ABSTRACT FROM AUTHOR]

This paper presents an analytical three-dimensional rotational mechanism for the limit analysis on the overall stability of slurry trenches in layered cohesive soils. The proposed mechanism differs from the traditional torus mechanism in terms of the assumption on the shapes of cross section. The proposed rotational mechanism can have cross section with arbitrary shapes that are described by a smooth rotation radius function. The factor of safety for the overall stability of slurry trenches is obtained by using the new kinematic mechanism. The performance of the proposed mechanism is evaluated by analyzing the overall stability of trenches in single-layered, uniform and nonuniform clayey soils. The computed results are compared with the solutions given by finite-element limit analysis (FELA), which show that the proposed mechanism can give better solutions than the traditional torus mechanism when the length-to-depth ratio of the trench is relatively small. Based on the proposed mechanism, the stability of slurry trenches in layered undrained clay is investigated. The results show that, for trenches in two-layered undrained clay, the strength ratio between the shallow and deep layers can significantly influence the depth of the collapse mechanism. For trenches in three-layered undrained clay with a weak interlayer, the thickness of the interlayer can greatly affect the modes of failure in terms of global or local instability. [ABSTRACT FROM AUTHOR]

This paper focuses on the effectiveness in the improvement of clay soils of using geopolymers of fly ash (FA), metakaolin (MK), or blast furnace slag, activated by an alkaline solution of sodium hydroxide (NaOH), sodium silicate (Na2SiO3), or a mixture of both. The unconfined compressive strength (UCS) of samples cured for 1, 7, and 28 days was determined, and X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy were performed to record the mechanical, chemical, and mineralogical behaviors of the stabilized soils. The results showed an increase from 149.72 kPa (untreated clay) to 460.06 kPa for the clay soil treated with NaOH after 1 day of hardening. The highest UCS was obtained using a MK-based geopolymer (MKG) at 28 days. Oedometric testing showed a reduction in the swelling potential of the clay soil and a decrease in the swelling pressure from 600 to 300 kPa. It was found that all the tested treatments significantly improved the geotechnical properties of the clay soil. However, the MKG treatment was most effective in terms of increased resistance, while the FA-based geopolymer (FAG) provided better results in terms of reducing swelling. [ABSTRACT FROM AUTHOR]

Soft sensitive clays around a pile shaft experience destructuration during pile installation, excess pore pressure (u) dissipation, and creep after pile installation, but their influence on pile shaft resistance is difficult to assess quantitatively. This paper will present a semianalytical approach to evaluate the shaft resistance setup by considering soil destructuration, consolidation, and creep. Pile installation effects will be captured using the cavity expansion method. The dissipation of u will be modeled using linear radial consolidation theory, and the corresponding radial effective stress increase will be estimated by considering the stress relaxation effects. The changes in soil state after installation will be obtained by solving a system of ordinary differential equations with the initial conditions representing the pile installation effects. The limiting skin friction (τf,i) will be calculated by applying an interface reduction factor to the ultimate shear stress under simple shear conditions. Analysis of the results shows that the shaft resistance increases rapidly during the first few days after installation and continues to increase approximately linearly with the logarithm of time (t) after pore pressure equalization. The initial bonding (χ0) and overconsolidation ratio (OCR) have a marked influence on the time-dependent shaft resistance. [ABSTRACT FROM AUTHOR]

A new analytical method for investigating the stability of unsaturated soil slopes was developed by considering a 3D failure wedge under different steady-state infiltration and evaporation. In this light, the general limit equilibrium approach and concept of effective stress in unsaturated soils were implemented. An extensive parametric study was performed as well, to study the effect of slope geometry, unsaturated soil properties and/or state/material variables, position of groundwater level (GWL), and infiltration and evaporation flow rates on the stability of soil slopes against failure and landslide. In addition, a quantitative comparison was made between the safety factors obtained from the proposed unsaturated 3D analysis and those obtained from two-dimensional (2D) and three-dimensional (3D) classical slope stability analysis. It was revealed that the steady-state infiltration/evaporation has a significant influence on the stability of the silty and clayey soil slopes. In addition, the geometrical aspects of the slope and the hydromechanical parameters of the soil largely affect the safety factor of soil slopes against failure. Results show that the safety factors obtained from unsaturated 3D analyses for the silty and clayey slopes are remarkably different from those obtained from 2D and 3D classical calculations; however, negligible differences were found for the sandy slopes in that respect. In addition, a comparative study was performed on the impact of governing parameters on the safety factors of unsaturated slopes under infiltration and evaporation using an unsaturated 3D column method. It was revealed that infiltration has a pronounced effect on the safety factor compared with that for evaporation and that silty and clayey slopes are more affected by evaporation and infiltration than sandy slopes. In general, this study showed that applying unsaturated soil mechanics concepts to 3D stability analysis not only leads to more precise safety factors against the slope failure and landslide initiation but may also reduce the uncertain conservatism considerations in some practical problems. [ABSTRACT FROM AUTHOR]

This paper analytically investigates the postconstruction load-carrying capacity of a cast-in-place pile in clayey soil. The stress release induced by borehole excavation, the slurry supporting effects, and the dissipation of the negative excess pore-water pressure after construction, all of which have significant effects on the effective stresses of the soil around the pile, are the main concerns of this study, which aim to establish a method to reasonably evaluate the load-carrying capacity of a cast-in-place pile after construction. The stress release due to borehole excavation is modeled by cylindrical cavity contraction theory, which employs a K0-consolidated anisotropic modified Cam-clay (K0-AMCC) model to represent the mechanical behavior of the soil. Considering the dissipation of the negative excess pore pressure, the load-carrying capacity after construction is determined by the total stress method, with consideration of the three-dimensional strength of the soil adjacent to the pile. The proposed method was verified by finite-element (FE) numerical simulations. The results indicate that the soil properties and the factors involved in pile construction, such as the stress release due to borehole excavation, the slurry supporting effects, and the dissipation of negative excess pore-water pressure, have substantial influences on the postconstruction load-carrying capacity of the pile. [ABSTRACT FROM AUTHOR]

Field measurements and laboratory tests were carried out to study the mechanical behaviors of soil in response to earth pressure balance (EPB) shield tunneling in mixed-face conditions, i.e., layers of granite and sand. Specifically, an experimental investigation was carried out using a laboratory-scale model to replicate the EPB tunneling operations in such ground conditions. The effects of the ratio of rock/sand at the tunnel face (Tr/Ts) and the cover-to-diameter ratio (C/D) on the soil pressure in the chamber, ground displacement, and volume loss were examined. The results show that the soil's response to the mixed-face conditions differs significantly from that in the homogenous ground and highly depends on the ratio of rock/sand, especially for relatively shallow tunnels. As the ratio of rock/sand at the tunnel face increased, the pressure gradient in the chamber became more inconsistent. The translated cumulative curve does not always provide a good fit in the mixed-face conditions, particularly in cases when the rock/sand ratios are high. A smaller width of settlement trough has been observed for cases with a large rock/sand ratio compared to that in clay and cohesionless soil. [ABSTRACT FROM AUTHOR]

Soft marine deposits are widely distributed in the coastal region of China. The marine soft clays have high water content and high sensitivity, which shows high compressibility and low strength. The installation of precast piles for wind turbines over soft marine clay will generate high excess pore water pressure (EPWP) with very low dissipation rate, resulting in low bearing capacity and large postconstruction settlement, which will affect long-term stability. This study investigated the generation and dissipation of the EPWP correlated with the change in soil structure during the installation of pile foundations in a project of 100 MW wind-power generation in Lianyungang, Jiangsu, China. The results show that the marine soft clay soils feature strong natural structures based on the intrinsic compression concept. The EPWP decreases with increasing distance from the pile, whose influence reaches a distance of 6 m (about 10 times the pile side length). The structural strength of natural sedimentary clay has a remarkable impact on the generated EPWP. The dissipation rate of the EPWP is very slow in mucky clay with more than half the residual value after 30 days, which is mainly attributed to the sharp decline of consolidation coefficient induced by the disturbance of natural clay soils from pile driving. Moreover, hydraulic fracturing can well explain the dissipation characteristics of the EPWP in clay. This phenomenon is actually an ongoing process especially in marine soft clay soils with a strong cementation effect. [ABSTRACT FROM AUTHOR]

Cement stabilization is a soil improvement technique widely adopted for soft soils. The extent of improvement to the physical properties varies largely with soil type and often requires laborious laboratory tests to ascertain such extent of improvement when soil samples from a source are obtained. To offer a quick estimate of the improved unconfined compressive strength of the composite, it is crucial to develop relationships of the strength with essential parameters of the soil. Furthermore, existing studies mainly focused on cement-stabilized clays with minimal granular content. The influence of commonly encountered sand impurities in actual field condition is much less discussed. In view of these limitations, the current study explores the use of activity number (A), liquid limit (wL) and modified apparent void ratio (ec*) as a proxy to unify the strength development of cement-stabilized soft soils used for land reclamation in the modified Abrams's strength predictive model. Incorporation of A and wL is achieved by introducing a new parameter α. Friction due to geometric proximity between sand particles in the composite is represented by ec*. Results show that the proposed model is able to successfully consider the effect of soil properties in the strength development of soils stabilized with Ordinary Portland cement (CEM I) and Portland blast-furnace cement (CEM III/C) and validated with published literature. The proposed models enable quick check of the design when only mix proportions and index properties are available. They also incorporate the influence of sand content, which is merely considered in existing models. [ABSTRACT FROM AUTHOR]

Very often, geogrid layers are placed as reinforcement within pavement and railway roadbeds without careful consideration of their desirable location of placement. Although the clay subgrade soils utilized in this research paper and those in Saha Roy and Deb ([2]) were different and showed differing engineering characteristics, both provided useful information that is lacking in the published literature. Overall, the author's paper provides very useful practical information for enlightening the thoughts of geotechnical and civil engineer practitioners engaged in the design of both railway roadbed and highway pavement structures underlain by clay subgrades. [Extracted from the article]

This paper presents as a discussion of "Performance Evaluation of a Highway Slope on Expansive Soil in Mississippi" by Mohammad Sadik Khan, Masoud Nobahar, Mike Stroud, Sean Ferguson, and John Ivoke. https://doi.org/10.1061/(ASCE)GM.1943-5622.0002240. Repairs to the failed section of the slope were undertaken a few months following the initial slope construction and were carried out by removing the failed soil and replacing it with a backfill that was less plastic, and therefore, not as swell-prone as the original soil. This approach versus the traditional approach when determining the factor of safety of slopes that used the limit-equilibrium method was considered more appropriate to account for the physical changes within the soil matrix that would occur during its wetting and drying cycles. [Extracted from the article]