Predicting the swelling behaviour of expansive soils using decision tree framework

Controlling the swelling and shrinkage deformation of expansive soil is essential for the design of earth structures surrounded by expansive soils. Swelling and shrinkage deformation could induce severe damages (i.e. cracks and/or distortion) to infrastructures – for example, embankments, pavements and pipelines. In this study, a series of laboratory tests and a field trial on expansive soils in Huai’an, China were conducted to investigate their shrinkage–swelling cycle characteristics. A technology combining quicklime stabilisation and surcharge pressure was proposed to limit the shrinkage–swelling deformation of Huai’an expansive soil in a highway embankment project. The experimental and field test results show that (a) the swelling potential of Huai’an expansive soil increased with an increase in the number of drying–wetting cycles without surcharge pressure; (b) the swelling potential decreased with an increase in the magnitude of surcharge pressure; (c) the addition of quicklime to Huai’an expansive soil combined with surcharge pressure could reduce the swelling potential significantly; and (d) the shear strength of expansive soil samples decreased as the number of drying–wetting cycles increased. The measured settlement from the field test indicated that the proposed technique can reduce the swelling potential and control the heaving of Huai’an expansive soil effectively.

Expansive soils experience volumetric changes due to water content changes. These volumetric changes cause swell and shrink movement in soils, which in turn will inflict severe damage to structures built above them. A Proper understanding of how the expansive soil behaves during the wetting/drying process is essential for assessing the mitigation action of expansive soil hazard and design suitable foundation. The structures that build above expansive soil bed are susceptible to heave and to withstand swell pressure, thus the swell pressure must be considered in the design. This study focuses on swelling properties of two expansive clay from Ngawi, East Java and Wates, Yogyakarta. Laboratory test on disturbed samples is used to identified and to measured swelling properties. A series of swelling test was performed under constant soil dry density. The influence of initial water content and surcharge pressure on swelling properties (i.e swell percent and swell pressure) of compacted samples were investigated. The swelling properties test used ASTM standard 4546-03 method B. It was found that the lower initial water content the higher the swell percent, but the swell pressure seems not to be affected by initial water content. At the same initial water content, swell percent decrease with the increase of surcharge pressure, but swell pressure remains unchanged.

This study focuses on the advancements of characterization of unsaturated expansive soils which would allow better prediction of its swelling and mechanical behaviours. The paper has been divided into three parts. Firstly, a novel model is developed by considering two micro-soil parameters, soil-specific surface area and internal pore size distribution, to predict the natural swelling in expansive clayey soils. The model was validated by comparing the predictions with experimental results for eight soils. Secondly, the paper deals with the diffused-double-layer (DDL) theory-related electrostatic forces from individual clay minerals of expansive soils and their influence on soil swelling. A DDL-based model was also developed, which was validated for swell prediction for fourteen expansive soils. A good correlation was observed for both models when the results were compared with experimental results. Finally, the paper demonstrated the use of vapour pressure technique to control suction beyond 5 MPa for performing suction-controlled repeated load triaxial (RLT) test at high suction state. This novel technique mitigates the limitation of axis-translation technique for maintaining suction till the air-entry-value (AEV) of the ceramic disk. These new models and unsaturated laboratory testing techniques would aid in better characterization of expansive soils in their unsaturated state. This would also provide accurate prediction of swell and stiffness behaviours of soils, thereby reducing the uncertainties in the design of civil infrastructure built on expansive soils.KeywordsUnsaturated soilsSwellingExpansive soilsResilient modulusHigh-suction state

The aim of this study was to highlight the effects of entering duplicated or overlapping data from published studies using the same data registries into a meta-analysis, including its identification and management using a novel structured framework. Secondary analysis of data from a proportional meta-analysis of 30-day cumulative incidence of venous thromboembolic events (VTE) after metabolic and bariatric surgery was performed. Sensitivity analysis was conducted a) including all studies regardless of duplication (uncorrected sample) and b) comparing it to a corrected sample of studies. We developed a decision tree framework to identify duplicated data from prospective studies and data registries. We demonstrated that biasing from duplicated data, primarily from data registries, underestimated the incidence of VTE in the literature by 0.15% of the patient population (an erroneous difference equivalent to 22.06% of total VTE). This error persisted at 8.16% of total VTE when limiting to studies using a primarily laparoscopic approach. The decision tree framework used a comparison of the data source (country and hospital or registry), sampling time frame (dates/years of included data) and inclusion characteristics (included procedures/diagnoses or inclusion criteria) to identify potentially duplicated data. Inter-rater reliability was excellent (κ=1.00, P<.001), although only 17.86% of studies coded as containing data duplication were verified by the authors while the remaining studies could not be verified. Lastly, we identified a strong lack of diversity in the geographical origins of the data from the included studies. We demonstrated that inadvertently including duplicated data in a meta-analysis can result in substantially inaccurate pooled estimates. We outlined a comprehensive decision tree framework that future researchers can apply to assist with decision making when identifying and managing duplicated data, including that from prospective trials and data registries or other publicly accessible datasets. We explored the effects of entering duplicated or overlapping data from published studies using the same data registries into a meta-analysis; and developed a decision tree framework to identify such duplicated data from prospective studies and data registries. We analyzed data of 30-day incidence of venous thromboembolic events after metabolic and bariatric surgery. We demonstrated that including duplicated data, mainly from data registries, in a meta-analysis can result in substantially inaccurate pooled estimates, underestimating the incidence of total venous thromboembolic events by 22.06%. We also found a lack of diversity in the geographical origins of the data. The decision tree compared data source (country and hospital/registry), sampling time frame (dates/years of included data) and inclusion characteristics (inclusion criteria/procedures/diagnoses) to identify potentially duplicated data. Future researchers can apply the framework to make decisions when identifying and managing duplicated data from data registries or other publicly accessible datasets.

As evident from many studies, mineralogical composition dominantly governs the behavior of expansive soils. Among several minerals, the influence of montmorillonite on swelling behavior is extensively investigated. However, studies focusing on montmorillonite quantification and deriving its exact influence on consistency and swelling behavior are scarce. With this in mind, expansive soil samples were collected from different regions in India and characterized for montmorillonite content (MMC). Based on the obtained results, relationships for MMC versus swelling and consistency property were developed. Interpretation of results reveals a distinct nature of natural expansive soils (NES) and mineral-rich bentonite soils (BS). It has been found MMC in NES is largely confined to 44%, while the same for BS is as high as 90% was reported. Similarly, liquid limit of < 100% and plasticity index of < 60% for NES and greater than these percentages for BS was identified has a benchmark for distinguishing between these soils. Furthermore, an increase in swelling potential, liquid limit, and plasticity index and a decrease in shrinkage limit and shrinkage index with an increase in MMC are found from the correlations. The analysis of results besides demonstrably confirming the marked influence of MMC also warranted the necessity to probe the presence of mixed layer minerals and their role on swelling and consistency behavior of expansive soils. The results presented in the study can help to decide suitable technique or additive to alter the behavior of expansive soils.KeywordsExpansive soilMontmorillonite contentSwelling behaviorMixed layer mineralsConsistency limits

Disintegration and decomposition of sedimentary materials and igneous/metamorphic rocks in arid and semi-arid plateaus form expansive soils. The parent materials of expansive soils are 5.3 million years (basic igneous rocks) to > 570 million years (basement complex rocks) old. Developing an index property to estimate the fraction of primary minerals that decompose to clay is important as expansive clays drive their moisture-related volume changes. Data of 119 expansive soils from Nigeria, Tanzania, Ethiopia, Sudan, India, Australia, Oman, Chad Basin, Morocco, Kenya, and Zambia are analyzed to develop an index property termed decomposition ratio (Dr) to quantify the fraction of primary minerals that decompose into expansive clay. The sand+silt fractions represent the undecomposed primary mineral content, while the clay fraction represents the fraction of primary minerals that decomposed completely. Expansive soils from India, Sudan and Tanzania are characterized by median Dr values of 0.52–0.74; expansive soils from Ethiopia, Nigeria, Australia, Ghana, Chad Basin, Morocco, Zambia, and Kenya are characterized by median Dr values of 1.02–1.43. Dr values < unity imply that < 50% of primary minerals have decomposed into clay. Analysis of Dr data indicated that clay formation tends towards equilibrium when weathering of parent material depletes their primary mineral contents to 35%. Normalizing liquid limit with Dr regulates variations in liquid limit of expansive soils with similar clay content but formed under different conditions.

To investigate the soil structure and mechanical behavior of an unsaturated expansive clay soil, triaxial and mercury intrusion tests have been performed and are presented in this paper. Also an optical test system was developed for studying the internal structure evolution of the unsaturated expansive soil during shear-loading tests. The research results show a linear relationship between the cohesion intercept and the degree of saturation of the unsaturated clay for the test data. For the tested soil, the pore-size distribution curves were found to be bimodal. The measurement results from mercury intrusion tests confirm that the micropores of Guangxi expansive soils of this study remain constant, and that the macropores vary with the dry density of soil samples. Comparing the volumetric strain curves with the soil particle area curves, some correlation and dependence on the macropore variation of soil samples during shear-loading tests can be shown to exist.Key words: soil structure, mechanical behavior, unsaturated soil, mercury intrusion, expansive clay.

Many relevant studies on lime stabilization have been done with regard to swell-shrink behaviour of expansive soils. Sequential lime mixing technique was also proven to be effective in limiting the swell shrink behaviour. But, strength and deformation are generally the most important parameters in assessing the effect of soil stabilization in pavement and other geotechnical practices. Therefore, the impact of these modification techniques has to be studied in terms of unconfined compressive strength of lime-treated soft clays. Such studies would definitely imbibe confidence in the practitioners to take up these advanced stabilization techniques which would in turn make our designs more robust and safer. In this regard, the current investigation is taken up to examine the efficiency of lime precipitation technique by sequential mixing of sodium hydroxide (NaOH) and calcium chloride (CaCl2). The lime precipitated in expansive soil is likely to change the basic properties by short term modification reaction and long term pozzolanic reactions between soil and lime. In expansive soils, Initial Consumption of Lime (ICL) was established based on the experiment proposed by Eades and Grimm. All the laboratory tests were done by maintaining these moisture and compaction conditions. Lime precipitation was employed on the mixes and its time dependent impact on physico-chemical behaviour of expansive soil and formation of various cementation products were studied. The study discusses the effect of these reactions on Particle size, Unconfined Compressive Strength (UCS) and California baring ratio (CBR). The soil-lime modification reactions had significant impact on the index properties and Particle size of the expansive soil. Due to strong short time modification reactions and long term pozzolanic reactions, a notable increase in the CBR and UCS values of the expansive soil was observed

Proceedings of geotechnical sessions at the 2001 Annual Civil Engineering Conference, held in Houston, Texas, October 10-13, 2001. Sponsored by the Shallow Foundation and Soil Properties Committee of the Geo-Institute of ASCE. This Geotechnical Special Publication contains 14 papers that discuss the effects of trees and moisture movements on various lightly loaded foundations on expansive clays. Papers review current state of the practice in foundation design, maintenance, and remediation as it relates to vegetative effects and expansive clays on foundations. Topics include: tree root damage to buildings; predicting volume changes in expansive soils resulting from environmental factors including vegetation; drought; expansive clay soil problems and solutions throughout the world; soil-structure interaction; field test program to obtain geotechnical properties; depth of wetting and active zone in expansive soils; slabs on expansive clay with vegetation considerations; volume change coefficient of expansive clay; in-situ modification of active clays for shallow foundation remediation; cracking of pavement due to drying shrinkage; soil suction measurements; and data base on under-slab moisture contents in Texas.

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

Swelling and collapse behavior of unsaturated expansive subgrades stabilized with recycled glass

Interactions of expansive clay soils with transportation facilities have caused billions of dollars of damage. In the process of determining agents and methodologies to overcome expansive clay behavior, multiple injections of chemical agents into the subgrade to modify clay behavior are most promising. A study was conducted to optimize a potassium-rich solution of four parts. The modifying solution has been injected into expansive clay subgrades with success since the early 1970s. A laboratory methodology was developed to inject specimens multiple times and to conduct swell tests. Screening tests were conducted to evaluate linear effects that each of the four constituents had on swell response through interpretation of a factorial design. Analysis of replicated tests, randomly arranged in blocks, revealed that one constituent had no effect on swell behavior. A central composite experimental design then was used to optimize the remaining constituents. The resulting response surface equation led to an optimal combination for swell abatement, confirmed during short- and long-term verification testing. The optimal blend of constituents was determined to reduce swell from 7.2 percent to 0.84 percent under injection situations simulating the field, and it was found to improve the reduction in swell by 2.6 percent compared with the original blend. In addition, XRD confirmed that modification of clay occurred. This study was unique in its use of laboratory simulation of multiple field injections and in its use of statistical analysis to minimize the number of tests needed to ensure confidence in the optimization sought.

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.

The hydro-mechanical behavior of unsaturated soil, particularly expansive soil, is influenced significantly by cyclic wetting and drying. Understanding the soil parameters is crucial when evaluating the performance of infrastructures constructed on expansive clay. As a result of extreme rainfall events, highway slopes containing highly expansive Yazoo clay in Mississippi, U.S., become vulnerable to volume change. The phenomenon creates perched water zones within the slopes and poses a risk of slope failure. The soil-water characteristic curve (SWCC) defines the relationship between water content and soil suction, which can be obtained from different laboratory procedures. However, conventional laboratory methods have some limitations. To address this, various analytical and predictive models have been developed, but they can only offer estimates based on soil characteristics and lack seasonal variations occurring in field conditions. Studying seasonal SWCC through field measurements can help understand soil responses to changing moisture conditions. The current study utilized field data from six highway slopes in Mississippi and classified the data into different seasons: spring, summer, and fall. After obtaining van Genuchten parameters from the fitted curve for each season, the finite element method was applied to evaluate the parameters for accurate numerical analysis of infrastructures containing expansive clay. The study observed the variations in flow parameters with seasonal change that cannot be achieved when data from only one season is considered. The findings underscore the importance of field instrumentation data for developing SWCC and the significance of seasonal flow parameters in infrastructure design.

Construction on weak expansive soils is challenging due to their low bearing capacity and high-volume susceptibility under moisture fluctuation. The uplift pressure from expansive clay can induce significant swelling pressure on foundations, but on the other hand, shrinkage of clay can result in substantial foundation settlement during dry seasons. This differential movement of the foundation can distress the superstructure of a building, resulting in serviceable and ultimate limit state failures. The current approach to dealing with foundations in expansive clay soils is to construct a rigid slab that can withstand the anticipated movement or a pier-type approach using engineering design principles or a normal-type slab based on the fill being placed under controlled conditions. We introduce a capping layer under the foundation to control moisture fluctuation and increase the bearing capacity of the foundation using a recycled glass-based stabilization approach. A prototype foundation was constructed in the laboratory using an optimum stabilization mix design that was derived using glass and other sustainable additives. Slab movements and soil conditions were monitored over a 6 month period under simulated dry/wetting moisture fluctuations and operational loads. Results revealed that the performance of the foundation under controlled conditions was outperformed by the capping layered foundation during service loadings including seasonal moisture fluctuation. The outcomes from this research will have a significant impact on improving foundation performance in expansive soils, as well as proposing a sustainable foundation construction process using recycled glass waste.