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Enhancing the dynamic properties of expansive soils using cementitious materials has attracted the attention of many researchers over the past few decades. Supplementary cementitious materials (SCMs) can be used as partial substitutes for cement owing to their pozzolanic activity that further improves the mechanical performance of cement-stabilized soils upon curing. In this study, the effect of cement and zeolite incorporation on the mechanical behavior of expansive clay was quantified using the pressure wave velocity (Vp) indicator obtained from ultrasonic pulse velocity tests performed at different curing times. Furthermore, a polynomial model was developed to establish the relationship between Vp and zeolite replacement levels at specific curing times and cement contents. The results show that a polynomial function captured the decreasing trend of Vp upon the increase in zeolite at curing times below 14 days. Additionally, the developed equation explained the upward trend of Vp owing to the pozzolanic activity of zeolite at later curing times with an accuracy of over 92%. The coefficients of the polynomial model also increased with the increment of the cement percentage which conformed to the consecutive rise in Vp. Ultimately, the polynomial coefficients were expressed in terms of cement content and curing time using the Volterra series. Using this model, the optimum percentage of cement replaced with zeolite (Zopt), the efficiency of using Zopt instead of cement, and the percentage of zeolite replacement to achieve equivalent Vp of cemented clay samples (ZC) were estimated. The findings of this study contribute to promoting geotechnical sustainability by replacing cement with zeolite that has a considerably lower environmental footprint. Clay is a type of soil that can be found in many construction projects. For instance, many roads and buildings' foundations are constructed on clay soils. To ensure the necessary strength of the clay under the main structure, the soil should often be stabilized using adhesive construction materials such as cement. Interestingly, a portion of the cement could be replaced with other minerals not only to improve engineering performance but also to promote sustainability by lowering cement consumption. In this study, the effect of zeolite as a partial replacement for cement on the strength of clay soils was experimentally evaluated. The effect of various design parameters, such as cement replacement level and curing time, on the stability of clays was investigated using an advanced technique called the ultrasonic pulse velocity (UPV) test. Furthermore, a simple mathematical model was proposed based on the experimental results to help engineers design the stabilization plan and timely decide about the next steps of the construction process. [ABSTRACT FROM AUTHOR]

New ways to apply sustainable materials, such as biomass components, are essential for reducing dependence on fossil fuels. This work investigated the engineering properties of unsaturated expansive subgrade soils stabilized by bio-based energy coproducts containing lignin. Lignin is a waste by-product of the paper and pulp industry that is frequently burned. Highway subgrade could consume lignin as an environmentally benign, low-cost, and energy-efficient chemical substance for soil stabilization. Swell and shrink behavior of expansive subgrade soils complicates highway construction and causes damage to existing highways. However, research on the hydromechanical properties and volume change behavior of lignin-stabilized expansive soil is limited, and better insight is required into its unsaturated behavior for safe and economical pavement design practices. In this research, a series of geotechnical laboratory tests were conducted to characterize expansive subgrade soils treated with lignin by determining the Atterberg limits, compaction and consolidation behaviors, swelling characteristics, and water retention properties. The mechanisms influencing the changes in engineering properties of lignin-treated expansive soils were further investigated using soil pH, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The study shows that the optimal lignin content contributed to an acceptable degree of soil stabilization. The lignin-based cementing material effectively bonds soil particles together and fills pores, thereby preventing water infiltration into the soil and reducing the swell–shrink potential of stabilized soils. [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 low bearing capacity of expansive soils often results in serviceability issues and premature failures of infrastructure built upon them. Various studies have demonstrated the use of different soil treatment methods using mechanical or chemical approaches to stabilize the weak ground as a precaution. Most of the reported studies are limited to either lab-based investigations or field monitoring works without the scientific connection between theory and translation. This study aims to verify the field application of a novel soil stabilization method by conducting laboratory-controlled experiments and field performance testing as verification. Enzyme–based soil stabilization was adopted for in-situ clay soil in combination with ordinary portland cement as a sustainable stabilization approach. Soil samples were collected at different regions from the field to evaluate the effectiveness and the mechanism of soil stabilization in the field by the means of replicating stabilization at the laboratory scale using identical mixing proportions of the additives. The mechanical behavior of stabilized soil was assessed through the unconfined compression strength and California bearing ratio test methods. In addition, the changes in the chemical composition of the soil due to the additives were evaluated through the X-ray diffraction testing technique and microporosity test using 2D images translated to 3D profiles from X-ray micro CT tomography. The efficacy of field stabilization was evaluated by conducting the falling weight deflectometer test in the stabilized site. Results from the study are useful to understand the efficacy of field soil stabilization and enhance the reliability of enzyme–based stabilization in practice. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate expansive soil stabilization using different additives. Twenty soil mixtures consisting of 10%, 20%, 25%, and 30% zeolitic tuff (ZT) with 2%, 4%, and 6% lime in various combinations were used to stabilize the soil for pavement subbase application. A comprehensive test program, including Atterberg's limits, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), resilient modulus, and permanent deformation, was performed on natural and stabilized soil specimens. Scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX) was used to confirm the study findings. Adding ZT increases the availability of the silica and alumina needed for the pozzolanic reaction; test results revealed that adding ZT increases the maximum dry unit weight, CBR, UCS, resilient modulus, decreases plasticity, and permanent deformation. As such, ZT can improve the physical and mechanical properties of lime-stabilized soil as a pavement's subgrade and subbase layers. [ABSTRACT FROM AUTHOR]

This study investigated the different geotechnical characteristics of soil stabilization with the addition of lime and rice husk ash (RHA) in varying amounts (3%, 5%, 7%, and 9% lime, and 4%, 8%, 12%, and 16% RHA). A series of compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), pH, and X-ray diffraction (XRD) tests were performed in the laboratory to assess the impact of the considered admixtures on the stabilized soil parameters. This study also proposes the successful integration of an artificial neural network (ANN) and a Gaussian process regression (GPR) with the experimental UCS observations. The lime concentration, RHA concentration, and curing period were considered as the input parameters, and UCS was considered as the response. The proposed framework was extended to analyze the compressive behavior of treated soil on the minuscule level. Such coupled machine learning-based experimental investigation can provide deep insight into the soil behavior which otherwise would have remained unexplored due to the prohibitive nature of performing laboratory experiments on a large scale. The findings demonstrated the effectiveness of RHA in addition to lime in stabilizing the considered expansive soil. With the addition of lime and RHA mix, the UCS and CBR values of the treated soil increased significantly. [ABSTRACT FROM AUTHOR]

Singapore has a relatively high water table. When liquefied natural gas (LNG) storage systems are built in soils below the water table in Singapore, the engineering properties of the surrounding soils could be improved through cement stabilization. Due to the extremely low temperature (T) of LNG (approximately −162°C), the effect of ultralow T on the physical and mechanical properties of cement-stabilized soil in case of accidental LNG leakage should be investigated. However, existing studies on cement-stabilized soils are limited to T above −20°C. Therefore, in this study laboratory experiments to quantify volumetric expansion, unconfined compressive strength (UCS), and Young's modulus (E) of cement-stabilized soils at −40°C, −80°C, and −120°C were conducted. The experimental results indicated that the stabilized soils' volumetric expansion reached ≤2.6% at −120°C. The UCS and E of the stabilized soils increased from 0.9 to 27.6 MPa and from 99.8 to 2,669 MPa, respectively, and the T decreased from 24°C to −120°C. In summary, the ultralow T induced limited volumetric expansion (<3%) for cement-stabilized soil and significantly increased its strength and E, which indicated that cement soil stabilization could be beneficial for underground LNG storage systems in Singapore when exposed to accidental LNG leakage. [ABSTRACT FROM AUTHOR]

Efficient utilization of problematic soils such as soft clay by imparting additional strength using various stabilization techniques is done to improve soil properties. The application of nanomaterials in the area of soil stabilization has great potential to create a stiff skeleton, especially when blended with cementitious materials. Using the response surface method, this study focused on studying the effects of single and blended cementitious systems, comprising cement (0% to 20%), slag (0% to 20%), and nanosilica (0% to 2.4%), on the properties of soft clay in wet conditions [water-to-soil ratio (w/s) of 53% to 87%]. The mechanical [California bearing ratio (CBR), unconfined compressive strength up to 91 days] and durability (freezing-thawing durability factor) properties of stabilized clay were investigated, and the bulk trends were corroborated by thermogravimetry and microscopy analyses. Based on statistical analysis, incremental addition of cement, slag, and nanosilica led to the systematic increase in the properties of soft clay, albeit to different extents and with different mechanisms. At the low w/s (53%), superior mechanical and durability properties were obtained for soft clay stabilized with the ternary binder comprising cement, slag, and nanosilica. Numerical optimization showed that stabilizing this weak type of soft/expansive clay is possible, but the results (proportions, performance, cost) varied based on the target design criteria and application. [ABSTRACT FROM AUTHOR]

Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [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]

Many techniques, most notably soil stabilization, have been developed to enhance soil characteristics due to the growing trend of constructing structures on clayey soils. Therefore, it is imperative that researchers address clay-related issues utilizing geotechnical engineering achievements. This study evaluated the effect of volcanic ash (tuff) as a natural pozzolan on the improvement of cement performance in the clay stabilization. Various compositions of cement (0%–6% by dry mass) and tuff (0%–20% by dry mass) were added to clay and cured for 7 and 28 days. Then a set of tests, including modified Proctor, Atterberg limits, electrical conductivity (EC), pH, unconstrained compressive strength (UCS), California bearing ratio (CBR), wet-dry durability, and scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses, were performed on the untreated and treated samples. The secant modulus (E50) was measured to evaluate the stiffness of the specimens. The data showed that the incorporation of tuff into the studied cement-stabilized clay considerably enhanced the mixture mechanical properties and substantially reduced the plasticity index of the samples. After a 28-day period, the samples containing 6% cement and 15% tuff, as the optimum mixture, had increases of the UCS and CBR values of approximately twice those containing 6% cement. Moreover, the inclusion of tuff into the cement–soil blends increased the durability of the samples. According to the SEM and XRD analysis, the addition of tuff to the samples containing cement caused the formation of more cementitious compounds and fully changed the soil structure. The findings indicate that the use of tuff can lead to improved cement performance in the stabilization process. [ABSTRACT FROM AUTHOR]

3 represents the application of Eq. (4) with HT ht . For this, they established as criteria HT ht for the subbase and 2,100 kPa for the bases. Notation I The following symbols are used in this paper: i HT ht unconfined compressive strength; HT ht coefficient of determination; and HT ht porosity-to-volumetric cement index. [Extracted from the article]

This paper compares experimental results on the stabilization of clayey dredged material (DM) using quicklime (QL), hydrated lime (HL), portland cement (PC), and Class F fly ash (FA). The DM was a clay, high-plasticity soil, dredged from the US Army Corps of Engineers Port Arthur (USACEPA) facility along the Neches River located in Orange and Jefferson Counties, Texas. The soil consists of a large proportion of clay (66%), has high moisture limits (plasticity index: PI = 52 and liquid limit: LL = 80), and is characterized as a fat clay with silt. Physical properties of the untreated DM, such as unconfined compressive strength (UCS), consistency limits, and compaction behavior, were determined. Stabilizing reagents were mixed in various percentages by dry weight of DM. Results indicate that 12% QL, 6% HL, 6% PC, and 7.5% Class F FA by dry soil weight must be used to meet a minimum benchmark criterion of a PI value below 35, which was established based on Texas Department of Transportation (TxDOT) specifications. Standard compaction tests were carried out in accordance common standards with ASTM D698 to determine the optimum moisture content (OMC) for all mixtures. Stabilized mixtures were prepared at the corresponding OMC, and unconfined compressive tests were run according to common standards. Tests results were compared with the relevant literature, and a linear regression model was developed to predict the PI reduction as a function of initial PI, LL, and stabilizer type and content with good accuracy (R2 = 0.86). Overall, tests showed that stabilization of clayey DM using lime products, PC, or FA significantly improved the DM physical properties, which could then potentially be used as a local fill construction material that is cost-effective and environmentally friendly and reduces the overall use of cement products. [ABSTRACT FROM AUTHOR]

Shallow slope failures are common in highway embankments in the north Texas region and pose significant maintenance problems for the Texas Department of Transportation (TxDOT). As a cost-effective alternative, recycled plastic pins (RPPs) can be utilized to stabilize slopes and prevent shallow slope failures. RPPs are fabricated from recycled plastic and waste materials (i.e., polymers, sawdust, and fly ash). It is a lightweight material and less susceptible to chemical and biological degradation than alternative reinforcing elements. RPPs are driven into the slope face, which provides additional resistance along the slip surface, increasing the factor of safety against shallow slope failure. The current study presents a field demonstration project of a highway slope reinforced with RPPs. The slope was located on the southbound side of U.S. Highway 287, near the St. Paul overpass in Midlothian, Texas. Surficial movement had taken place in the slope, resulting in cracks along the shoulder near the bridge abutment. Three 15.25-m (50-ft) sections over the cracked portion were reinforced using RPPs. In addition, two 15.25-m (50-ft) unreinforced control sections were provided between the reinforced sections to compare the performance. The northbound side of the slope was not reinforced and was also considered the control slope. After installation of the RPPs, the performance of the slope was monitored by using instrumented RPPs, inclinometers and a topographic survey. The performance monitoring results indicated that all of the reinforced sections were performing better than the control sections on the southbound slope. Two locations on the northbound control slope failed during the monitoring period. RPPs provided support and resisted failure of the southbound slope. Moreover, the RPP spacing at the crest played an important role in resisting the displacement. [ABSTRACT FROM AUTHOR]

Reinforcing soil with fibers is a useful method for improving the strength and settlement response of soil. The soil and fiber characteristics and their interaction are some of the major factors affecting the strength of reinforced soil. The fibers are usually randomly distributed in the soil, and their orientation has a significant effect on the behavior of the reinforced soil. In the paper, a study of the effect of anisotropic distribution of fibers on the stress-strain response is presented. Based on the concept of the modified Cam clay model, an analytical model was formulated for the fiber-reinforced soil, and the effect of fiber orientation on the stress-strain behavior of soil was studied in detail. The results show that, as the inclination of fibers with the horizontal plane increased, the contribution of fibers in improving the strength of fiber-reinforced soil decreased. The effect of fibers is maximum when they are in the direction of extension, and vice versa. [ABSTRACT FROM AUTHOR]