Untreated Loess Research Articles

Investigation on the Shear Behavior and Mechanism of MICP-Treated Loess Soil

Microbially induced carbonate precipitation (MICP) has been utilized as a new method to improve loess soil strength. In this study, we investigated the influence of the main parameters on the shear strength of MICP-treated loess specimens. Initially, culture media with different formulas and pH values were examined to identify the most efficient medium for loess soil. To explore the shear behavior of MICP-treated loess under general stress levels, unconfined compressive strength (UCS) tests and triaxial tests relevant to the compression strength and vertical loads were performed on MICP-treated loess with different calcium sources, cementation concentrations, and curing periods. Subsequently, calcium chloride was selected as the optimal calcium source based on the ultimate strength of the MICP-treated loess. The effective cementation concentration in the loess soil was between 1.0 and 1.25 M. The ultimate strength of the MICP-treated loess was 3.6 times of the untreated loess. The stress-strain curves indicate that a higher cementing effect can be expected with an increase in the curing period. The formation process of calcium carbonate and the micromorphology of the MICP-treated loess samples were examined using scanning electron microscopy. In this study, we present an environmentally friendly technique for improving loess soil strength.

Geotechnical studies on cemented and untreated Behshahr loess and Amol clay of Iran

There has been little research into the effects of cement on the geotechnical properties of two types of fine-grained soil with roughly the same grain size. The cement percentages used in this investigation were 0, 4, and 8% by dry weight of soil. Compaction features, consolidation characteristics, unconfined compressive strength (UCS), and Atterberg limits were all determined in the laboratory. Furthermore, scanning electron microscopy (SEM) examinations were used to analyze the microstructures of cemented and untreated loess and clay. Notably, the MDD for loess and clay are 1.72 gr/cm3 and 1.57 gr/cm3 at CC = 0%, respectively, and 1.7 gr/cm3 and 1.55 gr/cm3 at CC = 4%. The OMC for loess and clay are 15% and 22% at CC = 0%, respectively, and 17% and 20% at CC = 4%. At CC = 0%, loess and clay have cohesion values of 25 kPa and 28.7 kPa, respectively, and 190 kPa and 140 kPa at CC = 8%. Internal friction degrees for loess and clay are 24 and 29 degrees at CC = 0%, respectively, and 36 and 34 degrees at CC = 8. The consolidation test findings demonstrated that increasing the cement proportion reduced cemented soils’ compressibility. The Plasticity Index (PI) rose as cement concentration increased. However, significant percentages of cement concentration reduced the plasticity index. Furthermore, adding cement agents resulted in significant improvements in elasticity modulus and UCS for both soils. The SEM results indicated that the cement-treated loess was denser and more homogenous than the cement-treated clay sample. Triaxial tests reveal that cement particles improve cohesiveness and internal friction angle.

Splitting tensile strength and microstructure of xanthan gum-treated loess

The tensile strength of loess is closely related to geological disasters. As eco-friendly materials, biopolymers have an excellent strengthening effect on the mechanical properties of soil. The effect of different initial dry densities and xanthan gum (XG) contents on the microstructure and mechanical behavior of XG-treated loess was studied with a series of microscopic tests and splitting tensile tests based on the particle image velocimetry technique. The results show that the XG became concentrated and agglomerated during dehydration, forming bridge links between soil particles and covering their surfaces. The XG-treated loess had a significant concentration of micropores and mesopores, with greater peak pore size distribution values than untreated loess. The specimens’ load–displacement curves with different XG contents and initial dry densities showed strain-softening. The displacement vector field indicated that specimens’ primary cracks were radial–vertical, and the secondary cracks were well-developed. The strain-softening phenomenon was more significant with increased XG content and initial dry density, and the specimens’ splitting tensile strength and brittleness increased. XG treatment gave the soils stronger cementation and a denser structure, helping to increase strength and brittleness. This research provides a scientific basis and practical experience for applying XG in geotechnical engineering.

A Cross-Linked Polymer Soil Stabilizer for Hillslope Conservation on the Loess Plateau

The soil of the Loess Plateau is highly susceptible to erosion due to its distinct loess structure with poor water stability and disintegrates easily. Previous research has focused on improving soil strength without considering stability and ecological performance. Comprehensive improvements may be achieved by cross-linked polymers (CLPs), but their effect on loess structure remains unclear. In the present study, we investigate CLPs as a new organic soil stabilizer to improve soil aggregate stability. To determine the effect of CLPs on the stabilization of loess, a series of indoor tests was conducted to assess unconfined compressive strength, water stability, soil-water characteristics, and plant height. The stabilization mechanism was analyzed by comparing the microstructure, mineral composition, and features of functional groups of loess before and after treatment. The results showed that, compared with untreated loess, the unconfined compressive strength and anti-disintegration property of treated loess were significantly increased. The water retention capacity was improved, and the germination rate and growth of plants were promoted. Microscopic analysis showed that the use of CLPs did form new minerals in the loess or change the functional groups, rather, CLPs improved the microstructure, reduced the total volume of pores, and increased the degree of soil compaction. Field tests showed that the erosion of loess hillsides was effectively controlled by CLPs. Under the same erosive conditions, the slope surface treated with CLPs was more intact than the untreated slope surface. Our findings provide new strategies regarding the application of CLPs as soil stabilizers to control loess erosion and promote vegetation restoration.

Experimental study on improvement design of loess curing in engineering environment

This paper investigated the characteristics of improved loess curing in engineering environment. Loess was divided into silt and silty clay, and lime and lime-fly ash were selected as admixture materials. Direct shear tests and permeability tests were performed to research the rules in strength and permeability. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were performed to analyze the improved mechanism. The conclusions are as follows: (1) compared with results curing in laboratory conditions, the fast change periods of strength and permeability starts later and continues longer time for each improved type when curing in engineering environment. For fast change periods of strength, the remolded compacted loess and 2:8 lime-treated loess are between 14~28 days, 3:7 in 14~90 days, and lime-fly ash-treated loess in 28~180 days. As far as permeability is concerned, the permeability coefficient of lime-treated loess and lime-fly ash-treated loess reaches 10−7cm/s in 90 days and 180 days, respectively. (2) Over the long term, the improvement effect still occurs at a slow rate. From 180 to 1090 days, the strength of lime-treated loess and lime-fly ash-treated loess increased by 13.2~16.5%, and their permeability coefficients decreased by 4~7.7%. (3) The properties of untreated loess have a significant role in strength and permeability, and silt and silty clay own different effect ways. (4) Curing conditions and untreated loess properties results to differences of improved loess in age standard and improvement effect, these effects should be considered in engineering projects.

Determining soil water characteristic curve of lime treated loess using multiscale structure fractal characteristic

Soil–Water characteristic Curve (SWCC) is meant to describe the mechanical behavior of unsaturated soil. The present paper focuses on the internal multi-scale microstructure of Xining untreated loess and lime-treated loess with the use of scanning electron microscopy (SEM) and image processing technique. A new SWCC model was presented based on the fractal dimension of pore size distribution. The SWCC of untreated loess was calculated from fractal dimension and fitted well with curve tested from Fredlund SWCC device. The SWCC of lime-treated loess was then calculated. Two curves of Xining untreated loess and lime-treated loess have been compared and reasons for the difference have also been discussed. The results indicate that the content of large pores in lime-treated loess decreased and the content of micro-pore increased. The bracket pores were changed into cement pores. The pore fractal dimension D of Xining untreated loess is 1.39 and the pore fractal dimension D of Xining lime-treated loess is 1.53. Air-entry value of untreated loess is 12.16 kPa, while lime-treated Loess—35.15 kPa. In transition region, matric suction of lime-treated loess was in the range of 35.15 kPa ~ 4000 kPa, while matric suction of untreated loess—12.16 kPa ~ 2600 kPa. The range of the transition region in lime-treated loess is larger than that in the loess, while in the range of saturation region, the reverse applies. Under the condition of the same matrix suction, the saturation of lime-treated loess is greater than that of untreated loess. In the residual region, the difference of SWCC of soil samples is small.

Dynamic properties and environmental impact of waste red mud-treated loess under adverse conditions

Under the combination of heavy loading and high moisture content, the metastable structure of natural loess can easily lead to uneven settlement and damage the overlying infrastructure. Using traditional binder such as cement has harmful impact on the environment, especially due to resource consumption and carbon emission. This research has identified the feasibility of using red mud waste as a partial replacement of cement for loess subgrade treatment in terms of dynamic properties and environmental impact. The performance of loess treated with a combination of waste red mud (RM) and small amount of cement additive (C) is evaluated by considering the complex engineering geological conditions. The results show that dynamic stress (σd) and moisture content (w) have a more significant influence on the dynamic properties of RMC-treated loess compared with confining pressure (σ3) and loading frequency (f). Higher w shows a remarkable reduction in the dynamic load resistance of treated loess, yet the addition of RMC still can improve the microstructure and water sensitivity of loess. Specifically, the failure dynamic stress (σdf) and the maximum dynamic elastic modulus (Edmax) of the treated loess at higher w are found to be 100% and 400% higher than those of untreated loess respectively. RMC treatment also improved the dynamic cohesive (cd) value from 23.2 to 173.6 kPa compared with untreated loess. In addition, the leaching toxicity and radiation of RMC-treated loess indicate that it does not pose any risk to the groundwater. Finally, revised Monismith model has been developed based on the proposed formula for predicting power index b, which can be capable of describing the long-term deformation stability under cyclic loading.

Effect of pre-dynamic loading on static liquefaction of undisturbed loess

Static liquefaction can make the loess unstable when the shear stress subjected to a monotonic loading exceeds the undrained peak shear strength of undisturbed saturated loess. It is a phenomenon in the failure of soil deposits caused by a sudden increase of pore water pressure accompanied by large deformations and loss of effective stress that can make soils behave like flowing liquids. In general, the static liquefaction is influenced by confining pressure, microstructure and particle size of the undisturbed loess. The composition and particle size of loess are not easy to be changed, but it is not the case for microstructure during the earthquake. A few scholars focused on the characteristics of static liquefaction when the natural loess was disturbed by pre-dynamic loading. The deviator stress, pore pressure, effective confining pressure of undisturbed loess will respond differently to liquefaction if the loess experienced pre-dynamic loading. This study examined static liquefaction phenomenon in saturated undisturbed loess considering the effects of pre-dynamic loading and confining pressure. Pre-dynamic loading tests with different peak ground acceleration (PGA) showed that the cumulative strain is in the range of 0.019–0.189% under the conditions of PGA = 0.15g, PGA = 0.30 g, PGA = 0.40 g, respectively. Undrained static triaxial compression tests at three different confining pressures (100, 150, and 200 kPa) were implemented on undisturbed loess samples. Static liquefaction was observed at confining pressures of 100 kPa and 150 kPa with different pre-dynamic loadings, and the liquefaction potential of the undisturbed loess decreased with the increases of confining pressure. Loess specimens treated with pre-dynamic loading were easier to liquefy than the samples without pre-dynamic loading treatment. Samples treated with pre-dynamic loading exhibited higher excess pore water pressure than those without pre-dynamic loading treatments. Therefore, the internal friction angle and cohesive force were 5.13%∼15.04% and 26.44%∼82.04% lower than untreated loess. It reveals that the normalization between the maximum and the minimum principal stresses can be used to quantify the liquefaction potential of undisturbed loess.

Mechanical properties and micro-mechanism of loess roadbed filling using by-product red mud as a partial alternative

Abstract The disposal of red mud waste has induced critical environmental issue worldwide. While adding red mud waste as a partial alternative in loess subgrade projects can effectively reduce the red mud waste accumulation and engineering cost. Therefore, the feasibility study of red mud waste as loess subgrade filling is in urgent demand. In this study, the mechanical characteristics and micro-mechanism of red mud-treated loess with a small amount of cement additive (RMCL) were analyzed systematically. In order to study the effect of red mud addition on RMCL, tests on the compaction characteristics, strength properties, dynamic behaviors of RMCL were carried. The action mechanism of red mud was also revealed through a series of X-ray diffraction (XRD), light microscope (LM) and scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) test. The results show that the red mud content CR has a significant effect on the unconfined compressive strength (UCS) of RMCL. An appropriate amount of red mud waste can effectively improve the mechanical properties of loess subgrade filling. The optimal CR is approximately 15%–20% for loess roadbed filling in this study. In addition, the UCS of RMCL increases with the increasing curing time, but first increases and then decreases with the increase of CR. Considering the effect of CR and curing time, an empirical Gauss 2D model is strongly proposed to predict the UCS value. A good linear relationship is also observed between the UCS value and the resistivity for RMCL. Moreover, the dynamic elastic modulus of RMCL is four times higher than that of untreated loess. Both dynamic stress and confining pressure have significant effect on the dynamic characteristics of RMCL. Based on the microanalysis of XRD, LM, SEM, and EDS, red mud can promote the generation of more cementitious hydrate such as C-S-H/C-A-S-H and Aft due to its strong alkalinity and hydrolysis. These hydrates, red mud fine particles, and aggregates can adhere to the surface of loess particles or fill inter-granular pores to obtain a more compact and stable soil structure, leading to a significant improvement of mechanical properties. The study provides an effective way to recycle red mud waste as a substitutable filler in loess roadbed, exhibiting environmental and economic benefits.

Influence of Submergence on Stabilization of Loess in Shaanxi Province by Adding Fly Ash

In this study, the influence of fly ash (FA) content (0%, 10%, 20%, and 30%) on the alteration in the physical and mechanical parameters of loess is investigated. The influences of curing time (0, 14, and 28 days) and submergence and non-submergence conditions are analyzed as well. Analysis considers the variation in Atterberg limits (liquid limit, plastic limit, and plasticity index), compaction parameters (optimum moisture content (OMC), and maximum dry density (MDD)), unconfined compressive strength (UCS) stress, UCS strain, California bearing ratio (CBR) value, and swell potential. Results show that the application of FA-stabilized loess (FASL) is effective. Specifically, the MDD decreases and the OMC increases, the UCS stress increases and the UCS strain decreases, the CBR value improves and the swell potential declines, but Atterberg limits are insignificantly changed by the increase in the FA ratio compared with those of untreated loess. The UCS stress and CBR value are improved with the increase in curing time, whereas the UCS strain is negligible. FASL under submergence condition plays an important role in improving the effect of FA on the UCS stress and CBR value compared with that under non-submergence condition. The UCS stress and CBR value are more increased and more decreased than the UCS strain in submerged samples. Therefore, the application of FASL in flood areas is important for obtaining sustainable construction materials and ensuring environmental protection.

Physicochemical and Mechanical Properties of Lime-Treated Loess

This paper studies the changes in physicochemical and mechanical properties of lime-treated loess at different lime contents and curing days. The physical tests were conducted in particle size distribution, Atterberg limits, specific gravity, specific surface area and cation exchange capacity of lime-treated loess, while its chemical tests included electrical conductivity, total dissolved solids, pH, and oxidation reduction potential of extracts from 1:5 soil to water. Finally, the relevant mechanical tests were performed in unconfined compressive strength. The results showed that the physicochemical and mechanical properties of lime-treated loess were altered during hydration and pozzolantic reactions, which caused the formation of aggregation and new cementitious minerals. As a result, the performance of lime-treated loess acquired great improvement compared to that of untreated loess. The improvement can attribute to the first immediate aggregation formation due to flocculation induced by cation exchange, and then the filling between the aggregations or particles due to the formation of new cementitious minerals. In addition, the results indicated that the chemical properties of lime-treated loess are more relatively sensitive to environmental change than their physical and mechanical properties.

Evaluation of the antibacterial activity and treatment of acne with SiO2-ionized loess

SiO2-ionized loess was prepared from the reaction of loess and sodium hydroxide at 1,400°C for 2 h. The antibacterial activity of SiO2-ionized loess against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aerusinosa, and Propionobacterium acnes causing acne was examined by comparing the results against those of untreated loess, and treatment efficacy was examined for treating acne using soap containing SiO2-ionized loess. The minimum inhibitory concentration value of SiO2-ionized loess against S. aureus, P. aerusinosa, B. subtilis, E. coli, and P. acne was 10.0, 10.0, 2.5, 5.0, and 2.5 mg/mL, respectively. However, medium containing untreated loess had no antimicrobial activity. A treatment efficacy test revealed that acne symptoms decreased as the duration of using soap containing SiO2-ionized loess increased.

Effect of SiO2-ionized loess on the treatment of tinea pedis

SiO2-ionized loess was prepared from the reaction of loess and sodium hydroxide at 1,400°C. The antifungal activity of SiO2-ionized loess against Trichophyton tonsurans, causing tinea, was examined by comparing against that of untreated loess. Soap containing SiO2-ionized loess was used for clinical efficacy tests in the evaluation of the treatment of tinea pedis. The mineral components in loess were maintained after the reaction and the content of ignite loss was decreased to 0.64%, compared to loess. The antifungal ratio reached 56.8% on medium containing 2.0% SiO2-ionized loess and 81.1% on medium containing greater than 3.0% SiO2-ionized loess. However, medium containing untreated loess had no antifungal activity. A clinical efficacy test revealed that soap containing the SiO2-ionized loess led to a significant improvement in symptoms, with the efficacy increasing as the duration of treatment increased.

Adsorption and desorption of Am(III) on calcareous soil and its parent material

The adsorption and desorption of Am(III) on a calcareous soil (sierozem) and its parent material (loess) were studied by batch technique. The molarities of the Am(III) aqueous solutions were less than 5 . 10-9 mol/l. High adsorbability was found of Am(III) on the calcareous soil and its parent material. In order to decrease the adsorption and, hence, to investigate the adsorption characteristics properly, stable Eu3+ as hold back carrier and analogue was added to the aqueous solution. The relative contributions of CaCO3, organic matter (OM) to the Am(III) adsorption on calcareous soil and its parent material were investigated. The adsorption and desorption isotherms of Am(III) on untreated soil and loess and the three kinds of treated soils and three kinds of treated loesses to remove CaCO3, OM and both CaCO3 and OM were determined, respectively. It was found that all isotherms were linear, the average distribution coefficients (K-d) for the untreated soil and for the untreated loess were almost equal, while there was an obvious difference between the values of the average distribution coefficients (K-d) for the treated soil and the treated loess to remove CaCO3 or OM. The adsorption-desorption hysteresis on the untreated and treated soils and loesses actually occurred and there was an obvious difference between the hysteresis coefficients on both the corresponding treated soil and loess. It can be concluded that the adsorbability of Am(III) on calcareous soil is similar to that on its parent material, and that the contributions of CaCO3 and OM to the Am(III) adsorption by the untreated soil are different from those by the untreated parent material.

Sorption and desorption of neptunium(V) on loess: batch and column experiments

Summary The sorption and desorption isotherms and the corresponding distribution coefficients (K d, mL/g) of Np(V) for untreated loess and three kinds of treated loesses were determined by using the batch technique at moderate concentrations (∼10-5mol/L) under ambient aerobic conditions in the presence of 0.01mol/L CaCl2. For the treated loesses, selective extraction methods were used to remove CaCO3 and organic matter (OM) from the loess. The isotherms were analyzed with the Freundlich equation. The relative contributions of OM and CaCO3 to the Np(V) sorption on the loess were investigated from the parameters of the Freundlich equation. The effects of adding fulvic acid (FA) from the loess and the carbonate in solution on the sorption of neptunium(V) on the loess were studied. The breakthrough curves (BTCs) and displacement curves (DPCs) of Np(V) on the untreated loess column and on the treated loess columns were determined under ambient aerobic conditions at moderate concentration (1.1×10-4mol/L) in the presence of 0.01mol/L CaCl2. The results of column experiments are in accord with the results of batch experiments. It was found that (1) Np(V) in the loess under the present experimental conditions was relatively mobile and the distribution coefficients were relatively low at moderate concentrations, (2) the sorption/desorption hysteresis of Np(V) on the loess occurs, (3) the sorption of Np(V) on the loess was mainly determined by the clay minerals, (4) the addition of FA or carbonate in the aqueous solutions had an obvious positive effect on the Np(V) sorption on the loess, (5) the retardation of Np(V) migration in the loess at moderate concentrations was inconsiderable.