Optimizing Multiagent, Multi-Injected Swell Modifier

Pavements founded in expansive soils undergo distress because of alternate swelling and shrinkage with respect to the changes in the moisture content. While variation in soil moisture content is inevitable over the life of a pavement, the performance of expansive sub-grades can be improved by adopting suitable measures. Cohesive non-swelling soil cushion is among the several techniques available to mitigate the problems associated with expansive clays. Since this technique has a few limitations, an alternative has been tried by providing a cushion of industrial waste, stabilized with lime. Granulated blast furnace slag and fly ash are the by-products of steel plants and thermal power plants respectively; whose disposal poses a problem. They can be used effectively as cushioning materials in place of sand or CNS. Detailed laboratory studies have been carried out, using these materials for cushioning over expansive clay beds. Lime-stabilized ground granulated blast furnace slag or fly ash, in the form of a cushion, has been placed over an expansive soil bed and the resulting heave measured. In both cases considerable reduction in heave was noticed in the expansive clay beds. CBR tests were also conducted on the cushion-soil system. Their results indicate a significant increase in the soaked CBR value. This investigation points to the utility of these two waste materials for use in sub-bases of flexible pavements.

Laboratory investigations on the swelling behavior of composite expansive clays stabilized with shallow and deep clay-cement mixing methods

Expansive soil is the most predominant geologic hazard which shows a large amount of shrinkage and swelling with changes in their moisture content. This study investigates the macro-mechanical and micro-structural behaviours of dredged natural expansive clay from coal mining treated with ordinary Portland cement or hydrated lime addition. The stabilised expansive soil aims for possible reuse as pavement materials. Mechanical testing determined geotechnical engineering properties, including free swelling potential, California bearing ratio, unconfined compressive strength, resilient modulus, and shear wave velocity. The microstructures of treated soils are observed by scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy to understand the behaviour of the expansive clay blended with cement and lime. Test results confirmed that cement and lime are effective agents for improving the swelling behaviour and other engineering properties of natural expansive clay. In general, chemical treatments reduce the swelling and increase the strength and modulus of expansive clay, subjected to chemical content and curing time. Scanning electron microscopy analysis can observe the increase in formation of particle clusters with curing period, and x-ray diffraction patterns display hydration and pozzolanic products from chemical particles. The correlations of mechanical properties and microstructures for chemical stabilised expansive clay are recommended.

Expansive clays exhibit high potential for volume change because of changes in soil moisture. It is estimated that the annual cost of damage to facilities built on expansive clay in the United States exceeds $9 billion. Because of the physico-chemical nature of expansive clay behavior, the use of chemical agents to improve their behavior is common. The research reported involved development of a viable method to simulate injection of chemical agents into soils and evaluation of the results. The agents included in this study were lime, a potassium based agent and a group of what are called ionic agents. The clay utilized was weathered from the Eagle Ford Shale formation in north central Texas. An injection treated layer of the clay, using one of the differing chemical agents, was placed between a relatively wet layer and relatively dry layer of untreated clay, to test each chemical's affects on moisture movements. The sealed cylinders were allowed to have what moisture movements during a fifteen week period. The cylinders were opened and the soil layers tested for water content, dry unit weight, soil suction, and swell potential. Cylinders of untreated clay, constructed in the same way, but not injected were also analyzed. The injection process developed is believed to have simulated field injections well. The results of moisture movement, soil suction, and swelling potential provided insight into how these chemical agents can affect moisture movements and soil behavior when injected in this clay.

Volume change behaviour of expansive clays has been one of the leading causes of damage to civil infrastructures worldwide. Contributing factors that lead to failures relate to changes in water content within the soil. Variations of water content can vary significantly based on an area’s climate regime. Trinidad has two seasons, the dry season (January to June) and the wet season (July to December). This variation leads to volume changes of expansive clay, where they exist mainly within the central and south regions of Trinidad. These areas are densely populated by residential and commercial buildings, which can be susceptible to damages from unsaturated expansive clays. The Soil Water Characteristic Curve (SWCC) for expansive clays is critical to estimate their unsaturated properties for the analysis of water flow movement. This study investigates the SWCCs for two expansive clay soil types in Trinidad. A WP4-T (Water Potential Measurement) is used to measure soil suction. The shrinkage curve (SC) test is conducted to consider the volume change of soil. The Fredlund and Xing (1994) SWCC equation and Fredlund and Zhang (2013) SC equation are used to fit the measured data. The SWCCs in terms of gravimetric and volumetric water contents and degree of saturation are compared. It is found that the normalised degree of saturation SWCC can provide a better display of the SWCC and estimation of the air-entry value.

The stabilisation of expansive clay subgrades using recycled glass (RG) was proposed, as a sustainable ground improvement technique. Previous studies mainly focused on using RG powder with contents up to 10%, while the current study utilised sand-size particles and up to 40% RG content. Physical properties, compressibility, strength characteristics, and long-term climatic effects on the volumetric behaviour of stabilised clay were investigated. Volumetric responses of stabilised clay were analysed through a constitutive model developed for environmentally stabilised clay. The experimental results revealed that the plasticity of mixtures decreased by 30% as RG content increased to 40%. By using larger RG particles, the strength and bearing capacity increased by about 45% and 130% with the addition of 25% RG. However, adding about 6% of glass powder was sufficient to increase the strength and bearing capacity to about 100% and 200%, respectively. The swell-shrink results suggested that the maximum swelling was achieved in the second cycle in which the clay classification was converted from medium to high expansive clay. The experimental results were also compared and discussed with corresponding data collected from the literature. The outcomes of this study advance the prediction and understanding of the mechanical behaviour of RG-stabilised clay.

Changes in the chemistry of the pore fluid are known to have an impact on the hydro-mechanical behaviour of clays. Experimental evidence collected in recent decades has led to the formulation of constitutive chemo-mechanical models for expansive soils used in engineering practice for the containment of pollution, such as bentonite. Less attention has been paid to modelling the chemo-mechanical behaviour of non-expansive clays, which are less frequently used for geoenvironmental applications, but equally exposed to chemical changes. Key differences between the impact of salinity on the fabric of expansive and non-expansive clays are pointed out. At the macroscopic scale, an increase in salinity causes a translation of the normal compression line of non-expansive clays to higher void ratios, which in some cases is also accompanied by an increase in compressibility. The opposite occurs for expansive clays. Such experimental evidence provides the basis for a chemo-mechanical model formulated in the frame of elasto-plasticity with generalised hardening, whose yield surface expands with pore fluid concentration. The model is validated against experimental results, both original and from the literature. Simulation results compare very well with those of tests performed on reconstituted, compacted and intact samples.

Social awareness aims to increase practical skills, such as sustainable development, which seeks to increase the use of different types of waste in construction activities. Although insufficient attention is sometimes given to these actions, it is essential to spread information regarding new studies in the field of waste recycling, which encourages and promotes waste use. Reusing and recycling construction waste in the creation of buildings and infrastructure are fundamental strategies to achieving sustainability in the construction and engineering sectors. In this context, the concept of waste would no longer exist, as waste would become a material resource. Therefore, this study analyses the behaviours of two unbound mixed recycled aggregates (MRA) in the structural layers of an unpaved rural road with low traffic (category T43). The sections were built on inappropriate soil (A-7-6) with a high degree of free swelling. The experimental road consisted of three sections: the first was made with natural aggregates (NA) that were used as a control, the second was composed of MRA in the subbase and NA in the base, and the third section was completely composed of MRA. The materials were characterised in the laboratory. The behaviours of the structural layers in the experimental road were determined by controlling compaction (“in situ” density and moisture) and measuring the deflections and load capacity (deflectometer) during the 18 months after construction. The results show that the sections made with recycled aggregates meet the technical specifications required by General Technical Specifications for Road and Bridge Works (PG-3). Therefore, the water-soluble sulphate content and Los Angeles abrasion coefficient limits can be increased for recycled aggregates without compromising the quality of this type of road with low traffic. To the best of our knowledge, this is the first study regarding the use of unbound MRA made from construction and demolition waste (CDW) in the construction of an unpaved rural road with low traffic on an expansive clay subgrade.

Expansive clay in semiarid area behaves features of typical unsaturated soil, which is sensitive to climate and moisture, appears multi-fissures, deterioration of mechanical performances with the change of moisture. Consequently, to ensure the rational design of foundation treatment, and safe operation, research on moisture migration mechanism of expansive clays is of great significance. Herein, test models of mixed water migration and vaporous water migration were presented to investigate the mechanism. Series of tests, in which the moisture content in left soil column was same as 24%, and in right soil column was 0%, 6%, 12% and 18% respectively, were conducted under constant temperature. It is concluded that the moisture content changed with increase of migration time in both migration models, and the migration behaves nonlinear when the initial water content increase up to 6% for mixed water migration model and 12% for vaporous water migration model. But the migration characteristic of mixed water and vaporous water were different. The initial 30 days the change of moisture water was larger in mixed migration model, however in vaporous water migration model within 60 to 90 days was larger. These results will provide a basis for reveal evolution mechanism of engineering behaviors of unsaturated expansive clays.

Expansive soils pose significant geotechnical challenges due to their time-dependent swelling behaviour, which can cause severe infrastructure damage. The ability to predict swell potential accurately is vital for effective designs and risk mitigation. This study combines constitutive modelling with machine learning to enhance the predictive capability of swell behaviour in expansive clays. The constitutive swell model introduced by Liu et al. was evaluated by experimental one-dimensional swell tests, demonstrating its ability to accurately predict time-dependent swelling behaviour under varying surcharge pressures (SPs). A data-driven decision tree (DT) framework was created to relate key swelling parameters of Liu et al. model to fundamental soil index properties such as moisture content, SP, and plasticity index to improve predictive accuracy. Based on these measurable index properties, the model successfully captured the final swell potential of clay samples. Independent validation using literature datasets demonstrated high accuracy, with R2 > 0.97 for predicting final swell potential. The proposed DT framework provides geotechnical engineers with a practical tool to assess final swell potential based on fundamental soil index properties, aiding in better infrastructure design and mitigating the risks associated with shrink-swell behaviour.

Exploring the impact of aquaculture sludge on the swell-shrink behavior of expansive clays

Centrifuge model studies on desiccation cracking behaviour of fiber-reinforced expansive clay

Clayey soils which are expansive will swell and can cause lifting of buildings or other structures through the ingress of high moisture. Conversely, during evaporation, it will shrink and can result in building settlement. The vertical cylindrical cells reinforced with geogrid are referred as geopiles in which expansive soil is compacted at 95% optimum moisture content in rigid tank. This research work presents the heave behavior of expansive clay through the provision of geogrid encased with different materials, viz. fine sand, coarse and gravel. We studied that the heave behavior of expansive clay is by using single, two and four geopiles of same diameter filled with above said materials. The results indicated that heave decreased with increasing diameter particles size of the fill materials. The comparisons between unreinforced clay and reinforced clay using geogrid were analyzed.

Results of study of stresses induced in pipes buried in field in expansive clay and exposed to seasonal changes, as well as irrigation; asbestos cement pipes were tested to determine stresses at various sections; measurements of soil moisture changes and soil movements; high stresses resulted in pipe through inequalities in lateral and vertical swelling behavior of clay; these stresses could be greater than those caused by internal pressure.

Biocompatible electroactive hydrogels with bidirectional pH-responsive bending are important for the creation of biomedical actuators. This study developed chitosan/carboxymethylcellulose (CS/CMC) semi-interpenetrating networks (SIPNs) with different volume ratios, which were crosslinked with glutaraldehyde. The swelling and bending behaviors of SPINs were systematically characterized as a function of the pH of the solution and the magnitude of the applied electric field. The hydrogels exhibited pH-dependent bidirectional actuation, with the maximum swelling of 4.67–6.00 at pH ≈ 3.9 and minimum swelling of 1.58–2.53 at pH ≈ 5.7. The SPINs with CS/CMC = 1:1 composition achieved the highest bending angle of 77° at pH ≈ 5.7, while cathodic bending up to an angle of −13.7° was observed in basic conditions. The electromechanical response was significantly enhanced by decreasing the electrode distance and increasing the applied voltage. The observed correlation between the composition, swelling behavior, and bending performance was explained in terms of the electrostatic interactions between NH3+ and COO− groups present in the CS/CMC mixtures. These findings provided novel insight into the ongoing efforts for the development of non-toxic electroactive hydrogels with tailored electromechanical bending behavior necessary for use as artificial muscles and biomedical actuators.