Search

Ground improvement using a joint technology combined with in situ shallow stabilization of soft clay and soil–cement column-reinforced foundations is an effective technique for the treatment of soft soil foundations. This paper presents a methodology to study the performances of a new joint composite foundation under embankments with an emphasis on the load transfer in the stabilized layer. The deformations of the columns, the surrounding soil, and the overlying stabilized layer are compatible by applying the stress continuity and volume settlement continuity at the bottom of the stabilized layer. Two assumptions of the stabilized layer were considered: a perfectly rigid situation and a deformable one. The corresponding uniform vertical strain between the columns and the surrounding soils in the case of a rigid stabilized layer and the load transfer in the embankment, a stabilized layer, and a column-reinforced foundation in the case of a deformable stabilized layer were analyzed. The settlement and stress concentration ratios of the column-reinforced foundation were evaluated through a parameter study. To give full play to the bearing function of the columns under working conditions in this paper, a reasonable stabilized depth was assumed to be 1.8–2.5 m. [ABSTRACT FROM AUTHOR]

Cement stabilized clay (CSC) from dredged sediment or sludge is receiving increasing attention for its use as construction material. In this paper, seven CSC mixture samples were tested to investigate the effect of constituent proportion parameters and curing time (T) on strength characteristics. Results illustrate that clay-water/cement ratio (W/C) is significantly related to the unconfined compression strength ( q u ) of CSC. This relationship can be expressed by power function with a great degree of accuracy. After fitting and modeling the test data, two experiential formula models for the characterization of CSC strength are developed, which contain multiple parameters without other variable coefficients or parameters. Finally, methods derived from two experiential formulas to estimate the CSC strength under various parameter variables are proposed, and the prediction accuracy evaluation of derivation data and validation data are analyzed. Relationship of CSC strength and clay-water/cement ratio can be expressed by a power function. Strength coefficients are modeled with the moisture content of clay and the curing time. Prediction model are developed to estimate CSC strength under various parameters without variable coefficients. Estimation results correspond well with the actual measured strength. [ABSTRACT FROM AUTHOR]

This paper presents a study of the mechanical properties of a synthetic transparent clay to be used in physical geotechnical models. The manufacturing processes of a synthetic transparent clay consisting of Carbopol polymers, NaOH powder, and distilled water were briefly introduced. The transparency of the synthetic transparent clay influenced by the sample thickness and the mixture of Carbopol materials was assessed by the modulation transfer function (MTF) method. For the synthetic transparent clay with the 0.75% Carbopol material mixture, the clear visible depth was approximately 30–40 cm. The geotechnical properties of the clay with this mixture were measured in detail. The permeability (permeability test) and thermal conductivity (thermal conductivity test) of the synthetic transparent clay with a specific U10 mixture were 5.3 × 10−7 cm/s and 0.62–0.72 W · M−1 · K−1, respectively. These analyses demonstrated that synthetic transparent clay exhibits macroscopic geotechnical properties comparable to those of very soft clay and could be used to simulate submarine landslides. [ABSTRACT FROM AUTHOR]

In order to reduce the foundation settlement, conserve resources, and be environmental-friendly while increasing the use of soil resources, an artificial crust layer formed by in situ stabilization is proposed to combine with prestressed pipe piles over soft ground in road construction. In this study, a centrifuge test and two-dimensional coupled-consolidation finite-element analyses are conducted to simulate the construction of an embankment. And a two-dimensional parametric study is conducted to study the performance indicated by maximum long-term settlement, excess pore water, and tensile stress under various conditions. The results of the centrifuge test clearly show that the measured settlement, excess pore water, and tensile stress are in good agreement with the calculated results. In addition, the key factors of pile spacing and thickness and strength of the crust have an influence on the maximum settlement, stress of the foundation, and tensile stress of the crust using the two-dimensional coupled-consolidation finite-element analyses. And the stress transfer regular of the foundation is analyzed under various conditions. Moreover, the failure of the crust contained tensile cracking and shearing failure and the thickness of the pile that pierced the crust are also affected by the key factors. [ABSTRACT FROM AUTHOR]

Soil solidification technology can create an artificial hard shell on a soft soil surface but the type and proportion of the curing agent, the construction technology, and the strengthening depth have large influences on the strengthening effect and engineering cost. This study introduces a new technology of soil solidification whereby an artificial hard shell layer is used as a new method to improve the soft ground. For the in-situ solidification technology, the soil and curing agent are mixed well by using a strong stirring machine so that the soil is strengthened rapidly and forms a hard crust. We introduce the key technology of the in-situ soil solidification method and determine the in-situ crust carrying capacity. The indoor experiment on the curing agent proportions is validated with field tests and a vane shear test, static penetration test, and plate loading test are used to evaluate the reinforcement effect. The experimental results show that the in-situ curing technology of dredged fill processing markedly reduced the reinforcement depth range of the soil water content, improved the physical and mechanical indices, and increased the bearing capacity and strength of the artificial hard shell layer, thereby fully meeting the requirements for the bearing capacity of construction machinery. [ABSTRACT FROM AUTHOR]

Red clay is widely distributed in Zhejiang Province, China. Rain-induced shallow landslides easily occur on red clay slopes due to the reduction in shear strength caused by rainwater infiltration. The aim of this paper was to study the soil–water characteristic of red clay and its application on analyzing the stability of red clay slope. A series of field tests at different depths of red clay slope were carried out to monitor the variations of water content and matric suction under typical climate conditions. The results showed that the distribution of water content in red clay slope is complex because of long-term wetting–drying cycles. The water content within shallow layer is sensitive to external environment, and the response time of the water content is related to rainfall intensity. It is also observed that the soil water characteristic curve (SWCC) varies at different depths. The SWCCs of red clay can be fitted by linear function. The SWCCs from laboratory tests illustrated that saturated water content is more than 40%. Most of the SWCCs obtained at the depth of 90 cm are within the hysteresis loops of the SWCCs from laboratory test. The short-term rainfall has less effect on the stability of the slope, but the stability continuously decreases after the rain stops. The SWCCs obtained from laboratory were applied to analyze slope stability. Considering the influence of cracks, the computed results are close to field data. The study has a certain directive significance to the design of red clay slopes. [ABSTRACT FROM AUTHOR]

• The feasibility of using anhydrous sodium metasilicate as a geopolymer activator for soil stabilization had been verified. • The strengths of stabilized clay samples activated by a conventional activator and the ASM activator had been compared. • The effects of modulus ratio, content of activators, GGBS on the strengths of stabilized clay samples were evaluated. • The two-stage process of dissolution ofASM powder in geopolymer-stabilized clay was verified by the 29Si MAS-NMR results. This paper presents recent research on the use of anhydrous sodium metasilicate (ASM) powder as the alkaline activator of a one-part geopolymer binder for use in soil stabilization, to enhance the strength properties of soft clay. Geotechnical, mineralogical and microstructural tests were used to determine the performance of the geopolymer binder when mixed into an artificial soft clay. Comparison with the strength development of geopolymer-stabilized clay samples activated by a conventional sodium hydroxide activator and the ASM activator had been made. The effects of modulus ratio (SiO 2 /Na 2 O), content of the activators, as well as the GGBS content, water content, and curing time on the strength development of the geopolymer-stabilized clay samples were evaluated. The results indicate that the ASM powder alone is suitable as an alkaline activator to generate a one-part geopolymer binder for soil stabilization based on its high 28-d strength (4.2 MPa) and its modulus ratio, which was in the optimal range (0.9–1.2). The microstructural analyses confirm the influence of the two-stage dissolution process of the hydrated amorphous alkali metal silicate powders on the strength development of the ASM-powder clay samples and the formation of the geopolymer gels. This study demonstrates that the ASM powder can be used to substitute for sodium hydroxide in generating a geopolymer binder, which can lead to more practical applications for geopolymer in soil stabilization. [ABSTRACT FROM AUTHOR]

• Converting clay to building materials using hydrothermal solidification technology. • The effects of curing conditions, initial dry density and alkaline environment on physical–mechanical parameters were observed. • NaOH solution promoted the conversion of C-S-H gel into Al-substituted tobermorite. • The pore size distribution was determined by combined low-field NMR and MIP. Waste clay was converted into non-sintered building materials by hydrothermal solidification technology to improve resource utilization. The effects of curing time, curing temperature, initial dry density and alkaline environment on the strength development of the hydrothermally solidified clay-slaked lime mixtures were evaluated by compressive strength tests, and the microstructural evolution and solidification mechanism were analyzed by X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (NMR). The generated calcium silicate hydrate (C-S-H), katoite, and Al-substituted tobermorite filling pores and cementing mineral particles were the main factors responsible for the improved strength and compactness of the material. The C-S-H gel was transformed into Al-substituted tobermorite crystals in the presence of 4 mol/L NaOH solution, which greatly increased the compressive strength to 45.3 MPa. The transverse relaxation time (T 2) distribution was transformed into a pore size distribution curve by combined mercury injection porosimetry (MIP) and NMR, which can effectively characterize the evolution of the pore structure. The synthesis conditions determined the type and quantity of hydrothermal products that affect the pore size distribution and microstructure, thereby exhibiting changes in structural and mechanical properties on the macroscale. [ABSTRACT FROM AUTHOR]

Hydrothermal solidification technology can transform waste clay into high-strength building materials with lower energy consumption. Few machine learning methods have been applied to strength prediction of hydrothermally solidified materials, whose mechanical properties differ from those of conventional cement-based materials by virtue of the production method. In this study, six machine learning methods, random forest (RF), gated recurrent unit (GRU), k-nearest neighbors (KNN), back-propagation neuron network (BPNN), extreme gradient boosting (XGBoost) and gaussian process regression (GPR), were used to develop the compressive strength prediction models of hydrothermally solidified clay. These methods can efficiently predict the compressive strength without time-consuming and costly tests and guide the optimization of the mix proportions, thus facilitating the application of hydrothermally solidified clay. For this purpose, 140 experimental data obtained from hydrothermally solidified clay with different Ca(OH) 2 content, dry density, moisture content, curing time and curing temperature were used to proposed the prediction models. In the modeling process, these five effective variable parameters were considered as the modeling input parameters. The performance of these models was compared by correlation coefficient (R2), mean absolute error (MAE) and root mean square error (RMSE). The validity of these models was confirmed by the K-fold cross-validation method, and the influence weight of each input parameter on the prediction results was characterized by sensitivity analysis. The results demonstrated that the GPR model provided the best prediction with an R2 value of 0.989. In the sensitivity analysis, curing time had the greatest influence on the predicted results, followed by dry density, Ca(OH) 2 content, curing temperature and water content. Comprehensively considering the cost, energy consumption and compressive strength, the applicable mix proportion of hydrothermally solidified clay includes Ca(OH) 2 content (not less than 16.64%), moisture content (10%), curing temperature (not less than 87.35 °C), curing time (18 h) and dry density (1.9 g/cm3). [Display omitted] • RF, GRU, KNN, BPNN, XGBoost and GPR were used to predict the compressive strength of hydrothermally solidified clay. • GPR showed the best and most stable predictive performance with good generalization. • Curing time had the greatest influence on the predictions, followed by dry density and Ca(OH) 2 content. • Machine learning can provide reference for the optimization of the mix proportions of hydrothermally solidified clay. [ABSTRACT FROM AUTHOR]