Appraisal of Bearing Capacity and Modulus of Subgrade Reaction of Refilled Soils

Soil is remoulded, replaced, or improved in place to meet the required engineering properties. Relative compaction is the measure of the resulting engineering improvement. But design engineers need the allowable bearing capacity while the modulus of subgrade reaction is the primary input of modern foundation design software. The current research appraised a correlation between Relative Compaction ( ), Moisture Content ( ), and allowable bearing capacity ( ) and another correlation between , RC, MC, and modulus of subgrade reaction ( ). The test samples were extracted from each trial of the standard proctor test using purpose-built extraction tubes. Allowable bearing capacity has been determined by performing unconfined compression tests on the extracted tubes. The relationships have been established employing statistical analysis. It was noticed that soil samples at the lower moisture content (6-9%) show brittle failure before reaching the allowable strain. The soil samples having a moisture content of 10-14% exhibited shear failure, nearly simultaneous to the allowable strain. The soil samples having higher moisture content undergone a strain of 15% without showing the shear failure. A simple equation has also been appraised to determined Ks involving the three-input variable, i.e., , , and . Moderate correlations have been found to exist between the studied parameters, owing to some other variables' influence. Recommendations for future studies have been drawn to quantify the effect of identified parameters. Doi: 10.28991/cej-2020-03091606 Full Text: PD

Stabilization of a dispersive clayey sand

A few decades ago, Geotechnical Engineers had to face challenges dealing with soils with practically immutable properties, so they had to adapt the infrastructure to the as-is condition of the soil/rock mass. With the development of many ground improvement techniques, soils with undesirable properties could be replaced by one with more adequate properties. Those techniques were boosted into a conjuncture where there is a growing need for the occupation of peripheral zones of cities, where the behaviour of geotechnical materials is usually not as suitable as one of the occupied areas. However, conventional techniques to build in those zones tend to be expensive, turning many projects unfeasible. Thus, many researches have been carried out to understand the behaviour of soil improvement focusing on strength, stiffness, liquefiability, expansibility, collapsibility, and dispersibility properties. Thereby, this research aims to study the improvement effect in a clayey dispersive sand with the addition of lime and fly ash, comparing a commercial (dolomitic) and a byproduct lime (calcitic). Different admixtures were be analyzed varying specific weight, lime, and fly ash content, for a curing period of 28 days. The applied methodology consists of Unconfined Compressive Strength (UCS) tests, Small Strain stiffness tests, and durability tests, all of them conducted at every dosage. The experimental program was developed from full factorial design methods and intended to evaluate the response variables related to many factors and the damage caused by the durability cycles. Results have indicated that a small amount of binder was enough to control the dispersive behaviour of the soil, though, in most cases not to grant durability, and it was found that the lime that leads to higher strength admixtures is not necessarily the one which promotes higher durability. Still, the response variables like strength, small strain stiffness, and loss of mass may be related. Besides that, a dosage methodology was proposed based on the porosity/volumetric binder (and lime) content ratio, and this key dosing parameter could be used in the behaviour prediction of cemented soils even when they undergo rough climate conditions.Há algumas décadas, Engenheiros Geotécnicos tinham que enfrentar desafios lidando com solos de propriedades praticamente imutáveis, tendo que adaptar a infraestrutura à condição natural da massa de solo/rocha. Com o desenvolvimento de diversas técnicas de melhoramento do terreno, as características indesejáveis do solo puderam ser substituídas por outras de melhores propriedades. Essas técnicas ganharam força em uma conjuntura em que há uma necessidade crescente de ocupação das zonas periféricas das cidades, onde materiais geotécnicos são usualmente não tão desejáveis quanto em áreas já ocupadas. No entanto, técnicas convencionais para construir nessas zonas tendem a ser dispendiosas, tornando muitos empreendimentos inviáveis. Portanto, diversas pesquisas tem sido feitas para compreender o comportamento de solos melhorados, principalmente quanto às propriedades de resistência, rigidez, liquefação, expansividade, colapsividade e dispersibilidade. Com isso, esta pesquisa visa ao estudo do efeito de uma areia argilosa dispersiva por meio da adição de cal e cinza volante, comparando-se cais comercial (dolomítica) e de resíduo (calcítica). Foram analisadas diferentes misturas, variando-se o peso específico e o teor de cal e de cinza, para um período de cura de 28 dias. A metodologia aplicada consiste em ensaios de Resistência a Compressão Simples (RCS), rigidez inicial, e ensaios de durabilidade, todos para cada uma das dosagens. O plano experimental foi desenvolvido a partir de um projeto fatorial completo, buscando-se avaliar as variáveis resposta em relação a diferentes fatores e ao dano causado por ciclos de durabilidade. Os resultados indicaram que uma pequena quantidade de reagente foi suficiente para controlar a dispersibilidade do solo, embora não necessariamente para conferir durabilidade a ele, e que a cal que gera misturas mais resistentes nem sempre é a que promove maior ganho de durabilidade. Ainda, variáveis resposta como resistência, rigidez inicial e perda de massa acumulada podem ser relacionadas. Além disso, uma metodologia de dosagem foi proposta baseada na razão porosidade/teor volumétrico de agente cimentante (e cal). Por fim, foi observado que o parâmetro-chave de dosagem poderia ser utilizado inclusive para a previsão do comportamento de solos cimentados quando submetidos a condições climáticas adversas

Trends and Prospects in Geotechnics

The Special Issue book presents some works considered innovative in the field of geotechnics and whose practical application may occur in the near future. This collection of twelve papers, in addition to their scientific merit, addresses some of the current and future challenges in geotechnics. The published papers cover a wide range of emerging topics with a specific focus on the research, design, construction, and performance of geotechnical works. These works are expected to inspire the development of geotechnics, contributing to the future construction of more resilient and sustainable geotechnical structures

Effect of Organic Matter on Swell and Undrained Shear Strength of Treated Soils

This paper presents a laboratory and statistical study on swell and undrained shear strength of cemented organic clays blended with eco-friendly (by-product) cementitious materials such as ground granulated blast slag (GGBS) and cement kiln dust (CKD). The presence of organic matter in soils can be very problematic especially during construction of infrastructures such as roads and foundations. Therefore, experimental and statistical investigations are crucial to further understand the effect of organic matter on swell and strength performance of soils treated with by-product materials (GGBS and CKD). Five artificially synthesised organic clays with 0%, 5%, 10%, 15% and 20% organic matters were mixed with 20% cement during the first phase of mixing. In the second phase, cement content was reduced to 4% and blended with 12% GGBS and 4% CKD respectively. All mixed samples were cured up to 56days and subjected to undrained triaxial test and one-dimensional oedometer swell test. The undrained shear strength of the untreated soils decreases from 22.47kPa to 15.6kPa upon increase in organic matter from 0-20%. While the swell increases from 1.17% to 3.83% for the same range of 0-20% organic matter. The results also show improvement on strength and swell upon addition of 20% cement for all investigated samples. For samples treated with 4% cement and inclusion of 12% GGBS and 4% CKD, the treated soils showed better performance in terms of swell potential due to reduction in plasticity compared to the plasticity of soils treated with 20% cement. Undrained shear strength increases from 632kPa to 804.9kPa and from 549.8kPa to 724.4kPa with reduction in organic matter upon addition of 20% CEM and 4% CEM: 12% GGBS: 4% CKD after 56days. The results obtained show that the inclusion of GGBS and CKD reduced swell and increases undrained shear strength irrespective of the percentage of organic materials due to cementation effect. However, results of the statistical studies show that the presence of organic matter influences the extent of performance of the cement, GGBS and CKD treated soils. <br/

A new approach to modeling the behavior of frozen soils

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordIn this paper a new approach is presented for modeling the behavior of frozen soils. A data-mining technique, Evolutionary Polynomial Regression (EPR), is used for modeling the thermo-mechanical behavior of frozen soils including the effects of confining pressure, strain rate and temperature. EPR enables to create explicit and well-structured equations representing the mechanical and thermal behavior of frozen soil using experimental data. A comprehensive set of triaxial tests were carried out on samples of a frozen soil and the data were used for training and verification of the EPR model. The developed EPR model was also used to simulate the entire stress-strain curve of triaxial tests, the data for which were not used during the training of the EPR model. The results of the EPR model predictions were compared with the actual data and it was shown that the proposed methodology can extract and reproduce the behavior of the frozen soil with a very high accuracy. It was also shown that the EPR model is able to accurately generalize the predictions to unseen cases. A sensitivity analysis revealed that the model developed from raw experimental data is able to extract and effectively represent the underlying mechanics of the behavior of frozen soils. The proposed methodology presents a unified approach to modeling of materials that can also help the user gain a deeper insight into the behavior of the materials. The main advantages of the proposed technique in modeling the complex behavior of frozen soil have been highlighted

SMALL STRAIN BEHAVIOUR OF CEMENT TREATED SINGAPORE MARINE CLAY

Ph.DDOCTOR OF PHILOSOPH

Experimental study on the hydro-mechanical behavior of soils improved using the CSM technology

Deep Mixing Methods (DMMs) can be regarded as constantly evolving technologies for improving soil properties in order to satisfy predefined design requirements. Their applications are very common in geotechnical engineering and, in some cases, they can be conveniently selected instead of more traditional techniques. Despite DMMs are customarily used to strengthen soft soils like peats, clays, and silts, they can also be used very effectively in various subsoil configurations for several purposes, as, for instance, in the case of soil liquefaction prevention or cut-off/retaining walls. Even if soil mixing practice has become very consolidated in geotechnical engineering and numerous researchers in the past have tried to develop predictive equations taking into account the more relevant factors affecting the strength of DM constructions, i.e. influence of binder, soil, mixing and curing conditions, there is still no widely applicable formula for the estimation of the field strength characterized by a reasonable level of accuracy. Predictions are normally based on the mechanical behaviour of laboratory prepared mixtures, which, most of the time, significantly differ from in-situ treated soils due to the specific mixing, curing, and subsoil conditions encountered at the site. Technical standards were recently developed to provide general guidelines for the production of good quality laboratory mixed soil samples. Similarly, other codes concerning the critical deep mixing site construction aspects were introduced in several counties in order to improve the quality assurance and quality control (QA/QC) programmes conceived to verify the treatment effectiveness. However, a direct correlation between laboratory and field mixing performance is still far from being described, probably owing to the lack of a sufficient number of well documented case histories. In this research, a comparison tool between laboratory and field procedures has been tentatively deduced from energetic considerations depending on mixing efforts transferred to the soil to be treated using different devices. This thesis mainly focuses on the results of a comprehensive experimental investigation carried out on treated soil mixtures collected from several worldwide jobsites in which the Cutter Soil Mixing (CSM) technology was used. CSM, launched since 2003, is a recent and efficient system that, besides other DMMs, has the advantage of a high level of process control providing detailed information regarding the in-situ mixing method. The elaboration of these data, which significantly support the usual QA/QC procedures, has been used to define a new easily determinable site parameter closely related to the mixing efficacy, which, in turn, greatly influences the performance attained. As other DM methods, CSM produces some amount of spoil material, which is deemed to contain part of the binder introduced into the soil to activate hydration reactions once combined with both water and minerals in the ground. Since no estimation methods are available to evaluate the binder loss, an approximate amount of binding material is customarily added and mixed with the natural soil, hampering the performance prediction. To remedy this situation, a new formulation has been proposed to estimate the binder loss and to compute a more proper cement content. During the research activity, mechanical, hydraulic, mineralogical, and micro-structural tests were carried out in order to describe in detail the behaviour of the CSM treated material from different points of view and to acquire a reliable picture of the main factors affecting the relevant properties of stabilized soils. The obtained test results allowed to develop a new mathematical model for the evolution of the mechanical strength of granular and cohesive soils treated with the CSM technique as a function of the specific site conditions. The defined procedure has proved to be very effective in the major part of the case histories considered in this work

A study on the effects of lime on the mechanical properties and behaviour of London clay

Lime is commonly used as a stabiliser to improve the engineering properties of soils in particular for roads and pavement foundation. Despite the popularity of the technique, only a limited amount of existing experimental data for lime treated soils from advanced testing is available, in part due to the length of the tests. As lime stabilisation is increasingly used for other engineering applications (e.g. embankments, railway layers, canal linings, earth dams, buildings...etc), advanced testing to describe the mechanical behaviour of the treated soils is required. In this research a comprehensive experimental program was carried out to investigate the engineering properties and behaviour of a lime treated high plasticity clay (London Clay). A number of Unconsolidated Undrained (UU), Consolidated Drained (CD) and Consolidated Undrained (CU) triaxial tests were performed to identify the effect of lime dosage, compaction water content and curing time on the shear strength parameters, stressstrain behaviour, volumetric response and dilation of the treated soil. Moreover the study focused on understanding the mineralogical and physicochemical transformations occurring during the curing stage. Based on a number of additional tests (XRD analysis, pH measurement and other chemical testing) they provided a useful reference for the interpretation of the triaxial test results; in order to support hypotheses made on the evolution of the chemical reactions and the development of cementation bonds. Results from CD tests showed that yield, peak, and ultimate strength were greatly improved by an increase in lime content. London Clay samples treated with lime showed a considerable increase in peak stress ratio ( ) peak q / , particularly at lime addition beyond p' the initial consumption of lime (ICL). An increase in the angle of shearing resistance and cohesion intercept with increasing lime content was observed consistently. The stress– strain behaviour of treated London Clay was observed to be nonlinear with a contractive– dilative response. This response is found to be strongly influenced by lime content and the curing period. An increase in dilation with lime amount as well as a progressive suppression in the dilation by the effective stress increase was also observed. A Critical State Soil Mechanics (CSSM) framework was used to interpret the results. Lime addition, curing time and compaction water content were observed to have an impact on the critical iv state parameters in the compression plane (v − p'). However, the overall critical state line (CSL) in the stress space (q − p') of lime treated London Clay appears to be almost parallel to untreated London Clay CSL at the same M value, but lying above the untreated CSL with a cohesion intercept. Moreover, the domain where the untreated soil subsists was observed to expand with lime addition and further enlarge with an increase in the lime content. These features can be further explored by deriving a suitable constitutive model for predicting the mechanical behaviour of lime treated soils