Currently there is no consensus on how to account for the lateral earth pressures when designing drilled shaft retaining walls in expansive clay soils. Typically an equivalent fluid pressure is assumed which can range from 40 psf/ft to over 100 psf/ft. The range of assumptions currently in use can cause more than a factor of two difference in the maximum bending moment in the shaft. This range could cause the walls to be over-designed or under-designed. A full-scale test drilled shaft retaining wall was constructed on a site underlain by approximately 50 feet of the expansive Taylor Clay. Analysis of the wall is intended to provide information to be considered in design about the effects of the moisture cycles which cause shrinking and swelling. In order to monitor the moisture changes within the clay, 20 Time Domain Reflectometry (TDR) probes were installed behind the wall. This thesis discusses the monitoring plan, calibration, installation, and initial results from these probes. The objectives of this thesis is to provide information regarding the site conditions and reasons for using TDR probes for this project and to describe the monitoring plan, calibration, installation, and the field performance of the TDR probes and the moisture values that have been seen on the site to date. Previous studies show that difficulties can be expected when using TDR probes in highly plastic clays. Results from this study are typical of these results seen previously. The initial results show that 4 of the 20 probes are recording reasonable waveforms. However, the waveforms cannot be analyzed using conventional methods. This result was because the waveform reflection that indicates the end of the probe cannot be defined due to attenuation of the signal, which is typical of highly conductive soils. Also, the large amount of scatter in the electrical conductivity values does not allow for the moisture content to be correlated to the electrical conductivity. In order to use the TDR probes to measure moisture content at the project site, an alternative method needs to be employed to analyze available waveforms. If another method can be successfully employed for the functional probes, the subsequent step would involve recovering the probes that are not functioning properly in order to get a moisture profile along the full cantilevered height of the wall. Direct moisture measurements should also be taken periodically to provide a moisture profile. / text

Estimating the earth pressures applied on drilled shaft retaining walls in expansive clays is challenging due to the soil's tendency to shrink and swell under cycles of moisture fluctuation. While empirical suggestions do exist, significant uncertainty exists regarding the effect of volumetric changes of the soil on the earth pressures. In order to investigate this uncertainty, a fully instrumented drilled shaft retaining wall named in the honor of Lymon C. Reese, was constructed in the highly expansive clay of the Taylor formation. Inclinometers and optical fiber strain gauges were installed in three instrumented shafts and time domain reflectrometry sensors were placed within the soil to measure changes in the moisture content. Nearly two years of monitoring data have been obtained which are used to estimate the earth pressure distribution at different moisture conditions. Processing of the raw strain data was required to eliminate the effects of tension cracks and other microscale factors that caused significant variation in the results. Good agreement was obtained between the processed strain and inclinometer data as the deflected shapes predicted from both monitoring elements were similar. Finally, the earth pressure distribution for six dates that represent different moisture conditions of the Taylor clay were plotted and the results of the strain gauge and inclinometer analysis were consistent. A p-y analysis was also conducted to estimate the range of earth pressures applied on the wall. A triangular earth pressure diagram was used as external load above the excavation level and the equivalent fluid pressure was evaluated by matching the deflected shapes generated from the inclinometer data to those predicted by the p-y model. The results were compared to the empirical values that TxDOT uses for design of similar type of walls in expansive clay. Finally, the side shear and temperature effects on the lateral response of the wall were quantified. A differential linear thermal model was used to evaluate the temperature effects and a t-z analysis was conducted to account for the side shear applied on the wall due to volumetric changes of the soil. It is recommended that their combined effect be considered in the design. / text

abstract: Expansive soils impose challenges on the design, maintenance and long-term stability of many engineered infrastructure. These soils are composed of different clay minerals that are susceptible to changes in moisture content. Expansive clay soils wreak havoc due to their volume change property and, in many cases, exhibit extreme swelling and shrinking potentials. Understanding what type of minerals and clays react in the presence of water would allow for a more robust design and a better way to mitigate undesirable soil volume change. The relatively quick and widely used method of X-ray Diffraction (XRD) allows identifying the type of minerals present in the soil. As part of this study, three different clays from Colorado, San Antonio Texas, and Anthem Arizona were examined using XRD techniques. Oedometer-type testing was simultaneously preformed in the laboratory to benchmark the behavior of these soils. This analysis allowed performing comparative studies to determining if the XRD technique and interpretation methods currently available could serve as quantitative tools for estimating swell potential through mineral identification. The soils were analyzed using two different software protocols after being subjected to different treatment techniques. Important observations include the formation of Ettringite and Thaumasite, the effect of mixed-layer clays in the interpretation of the data, and the soils being subject to Gypsification. The swelling data obtained from the oedometer-type laboratory testing was compared with predictive swelling functions available from literature. A correlation analysis was attempted in order to find what index properties and mineralogy parameters were most significant to the swelling behavior of the soils. The analysis demonstrated that Gypsification is as important to the swelling potential of the soil as the presence of expansive clays; and it should be considered in the design and construction of structures in expansive soils. Also, the formation of Ettringite and Thaumasite observed during the treatment process validates the evidence of Delayed Ettringite Formation (DEF) reported in the literature. When comparing the measured results with a proposed method from the University of Texas at Arlington (UTA), it was found that the results were somewhat indicative of swell potential but did not explain all causes for expansivity. Finally, it was found that single index properties are not sufficient to estimate the free swell or the swell pressure of expansive soils. In order to have a significant correlation, two or more index properties should be combined when estimating the swell potential. When properties related to the soil mineralogy were correlated with swell potential parameters, the amount of Gypsum present in the soil seems to be as significant to the swell behavior of the soil as the amount of Smectite found. / Dissertation/Thesis / M.S. Civil Engineering 2014

Lateral swelling pressure induced in expansive soils upon wetting can adversely impact the performance and integrity of earthen structures and foundations. The yearly cost associated with damage to structures from expansive clays in the United States is estimated to exceed the loss associated with natural disasters such as earthquakes, floods, and hurricanes. The main objective of this dissertation is to provide new insight into the evolution of lateral swelling pressure in variably saturated expensive soils under infiltration via physical testing. In the first part of this study, a new laboratory-scale testing apparatus was built to measure lateral and vertical swelling pressures under anisotropic conditions. The testing apparatus was used to investigate the effect of compaction level on lateral swelling pressure in an expansive clay collected from central Arkansas. Results show that the higher the compaction, the higher the lateral swelling pressure. In contrast, compaction was found to have an insignificant effect on the vertical swelling pressure at a compaction level of less than 90%. In the second part, the laboratory-scale testing apparatus was employed to test the effects of four additives (lime, lime kiln dust, cement, and cement kiln dust). The results showed that the addition of a high calcium additive could significantly reduce the swelling pressures of expansive clay. The third part of the dissertation involved full-scale testing of lateral pressures in an expansive clay upon infiltration. A heavily instrumented 3-m high masonry wall backfilled with an expansive clay was built and subjected to infiltration. The degree of saturation, pore-water pressure, temperature, suction, and lateral and vertical pressures were monitored at different locations during the test. Results showed that the development of lateral pressure is rapid during initial saturation and levels out as the clay approaches saturation levels. This finding highlights the importance of monitoring lateral pressure over time to accurately predict its behavior. The study also found that lateral pressure develops prior to vertical pressure, depending on the area and restraint.

Expansive clays are located world wide and cause billions of dollars in damage each year. Currently, the expansion is usually estimated using correlations instead of direct testing as direct testing is expensive and often takes over a month to complete. The purpose of this study was to determine if centrifuge technology could be used to characterize expansive clays through direct testing. Testing was performed in an centrifuge permeameter on compacted specimens of Eagle Ford clay. A framework was developed to analyze effective stresses in centrifuge samples and methods were proposed to determine the swell-stress curve of a soil from centrifuge tests. Standard free swell test were also performed for comparison. The swell-stress curve determined by centrifuge testing was found to match with the curve found from free swell tests after correcting for differences in testing procedures. The centrifuge tests were found to be repeatable and required several days for testing rather than weeks. / text

O presente trabalho estuda a viabilidade de utilização da escória de alumínio, que é um rejeito da indústria recicladora de alumínio, atualmente sem valor agregado, como elemento integrante na fabricação de argila expandida. A argila expandida é produzida a partir de argilas que produzam expansão piroplástica, que são utilizadas como agregado leve na fabricação de concreto estrutural e também como artigo decorativo em jardins. Inicialmente foram feitas análises dos materiais de partida, como difração de raios X, microscopia eletrônica de varredura, fluorescência de raios X, análise granulométrica, análise termogravimétrica e análise térmica diferencial da argila. Foram feitas incorporações do rejeito junto à massa de argila, na proporção de 5%, 10%, 15% e 20% em massa. As formulações estudadas foram analisadas quanto à expansão linear, variação de massa, massa específica aparente e absorção de água. Foram feitos também ensaios de lixiviação e solubilização. Os principais resultados obtidos mostraram que é viável o uso da escória de alumínio até aproximadamente 5% em massa, para a produção da argila expandida, com características aceitáveis e dentro das normas vigentes. Palavraschave: reciclagem, escória de alumínio, argila expandida, agregado leve. / The use of industrial waste materials as additives in the manufacture of ceramic product has been attracting a growing interest in the last few years and is becoming common practice. The main purpose of this work is to evaluate the possibility of incorporation of aluminum slag into clay materials. Expansive clays are obtained from a pyroplastic expansion, and are usually employed like lightweight aggregate in structural concrete as ornamental garden products. The characterization of the aluminum slag and clay materials was carried out by Xray fluorescence spectrometry, Xray diffraction, granulometry, differential thermal analysis, thermal gravimetry (DTA and TG) and scanning electron microscopy. The studied compositions contained 5, 10, 15 and 20 weight% of aluminum slag into clay mass. The linear expansion, mass variation, apparent specific mass and water absorption of all compositions were determined. Leaching and solubilization experiments were also performed. The main results show the viabilitiy of using up to 5wt% aluminum slag for producing expansive clays with characteristics within the accepted standards. Keywords: recycling, aluminum slag, expansive clay, lightweight aggregate.

O presente trabalho estuda a viabilidade de utilização da escória de alumínio, que é um rejeito da indústria recicladora de alumínio, atualmente sem valor agregado, como elemento integrante na fabricação de argila expandida. A argila expandida é produzida a partir de argilas que produzam expansão piroplástica, que são utilizadas como agregado leve na fabricação de concreto estrutural e também como artigo decorativo em jardins. Inicialmente foram feitas análises dos materiais de partida, como difração de raios X, microscopia eletrônica de varredura, fluorescência de raios X, análise granulométrica, análise termogravimétrica e análise térmica diferencial da argila. Foram feitas incorporações do rejeito junto à massa de argila, na proporção de 5%, 10%, 15% e 20% em massa. As formulações estudadas foram analisadas quanto à expansão linear, variação de massa, massa específica aparente e absorção de água. Foram feitos também ensaios de lixiviação e solubilização. Os principais resultados obtidos mostraram que é viável o uso da escória de alumínio até aproximadamente 5% em massa, para a produção da argila expandida, com características aceitáveis e dentro das normas vigentes. Palavraschave: reciclagem, escória de alumínio, argila expandida, agregado leve. / The use of industrial waste materials as additives in the manufacture of ceramic product has been attracting a growing interest in the last few years and is becoming common practice. The main purpose of this work is to evaluate the possibility of incorporation of aluminum slag into clay materials. Expansive clays are obtained from a pyroplastic expansion, and are usually employed like lightweight aggregate in structural concrete as ornamental garden products. The characterization of the aluminum slag and clay materials was carried out by Xray fluorescence spectrometry, Xray diffraction, granulometry, differential thermal analysis, thermal gravimetry (DTA and TG) and scanning electron microscopy. The studied compositions contained 5, 10, 15 and 20 weight% of aluminum slag into clay mass. The linear expansion, mass variation, apparent specific mass and water absorption of all compositions were determined. Leaching and solubilization experiments were also performed. The main results show the viabilitiy of using up to 5wt% aluminum slag for producing expansive clays with characteristics within the accepted standards. Keywords: recycling, aluminum slag, expansive clay, lightweight aggregate.

Natural soils in work-sites are sometimes detrimental to the construction of engineering projects. Problematic soils such as soft and expansive soils are a real source of concern to the long-term stability of structures if care is not taken. Expansive soils could generate immense distress due to their volume change in response to a slight change in their water content. On the other hand, soft soils are characterised by their low shear strength and poor workability. In earthwork, replacing these soils is sometimes economically and sustainably unjustifiable in particular if they can be stabilised to improve their behaviour. Several techniques have evolved to enable construction on problematic soils such as reinforcement using fibre and planar layers and piled reinforced embankments. Chemical treatment using, e.g. lime and/or cement is an alternative method to seize the volume change of swelling clays. The use of lime as a binding agent is becoming a popular method due to its abundant availability and cost-effectiveness. When mixed with swelling clays, lime enhances the mechanical properties, workability and reduces sensitivity to absorption and release of water. There is a consensus in the literature about the primary mechanisms, namely cation exchange, flocculation and pozzolanic reaction, which cause the changes in the soil characteristics after adding lime in the presence of water. The dispute is about whether these mechanisms occur in a sequential or synchronous manner. More precisely, the controversy concerns the formation of cementitious compounds in the pozzolanic reaction, whether it starts directly or after the cation exchange and flocculation are completed. The current study aims to monitor the signs of the formation of such compounds using a geotechnical approach. In this context, the effect of delayed compaction, lime content, mineralogy composition, curing time and environmental temperature on the properties of lime-treated clays were investigated. The compaction, swelling and permeability, and unconfind compression strength tests were chosen to evaluate such effect. In general, the results of the geotechnical approach have been characterised by their scattering. The sources of this dispersion are numerous and include sampling methods, pulverisation degree, mixing times and delay of compaction process, a pre-test temperature and humidity, differences in dry unit weight values, and testing methods. Therefore, in the current study, several precautions have been set to reduce the scattering in the results of such tests so that they can be used efficiently to monitor the evolution in the properties that are directly related to the formation and development of cementitious compounds. Four clays with different mineralogy compositions, covering a wide range of liquid limits, were chosen. The mechanical and hydraulic behaviour of such clays that had been treated by various concentrations of lime up to 25% at two ambient temperatures of 20 and 40oC were monitored for various curing times. The results indicated that the timing of the onset of changes in mechanical and hydraulic properties that are related to the formation of cementitious compounds depends on the mineralogy composition of treated clay and ambient temperature. Moreover, at a given temperature, the continuity of such changes in the characteristics of a given lime-treated clay depends on the lime availability.

yes / A comprehensive experimental programme was performed with the focus on assessing the effects of compaction delay and ambient temperature on the physical, mechanical and hydraulic properties of lime treated expansive clays. Specimens were mellowed for a period of 0, 3, 6, 12, 24 and 48 h at two different temperatures of 20°C and 40°C prior to being compacted, tested and/or cured for up to 28 days for evaluating the impacts on long-term strength development. All specimens were prepared with the same dry unit weight of 12.16 kN/m3 and moisture content of 40% except for tests aimed at determining dry unit weight as a function of mellowing period. The results revealed that as the mellowing duration increased the dry unit weight declined remarkably at both temperature within the first 12 h. In addition, higher reduction rate was observed when specimens were mel-lowed at a temperature of 40°C. A 97% reduction in swelling pressure was obtained when the specimens were compacted upon mixing (zero hour mellowing period) and left to cure for 24 h prior to testing. Permeability coefficient of lime treated expansive clays was increased by up to 40 times when compaction was delayed for 24 h or when specimens were mellowed at 40°C. Specimens mellowed at a temperature of 40°C showed rela-tively stable values of permeability coefficient over the measurement period which could be attributable to accelerated pozzolanic reaction. The Unconfined Compressive Strength tests revealed that strength of lime treated expansive clays is significantly affected by compaction delay. An increase of 234% and 282% in the Unconfined Compressive Strength was achieved after 24 h of mixing with no compaction delay at 20°C and 40°C respectively. Gradual long-term gain in strength was observable within the 28 days post mixing but the rate of strength gain becomes slower and independent of temperature after the first 24 h of mixing. The results sug-gested that the four key reaction mechanisms occur concurrently with the first 12–24 h after lime addition recognized as being the most crucial period of time. Damaging the cementitious compounds by delayed com-paction is harmful to strength and restraining of swelling potential of lime treated expansive clays.

Yes / This paper focuses on monitoring the evolution of lime-clay reactions using geotechnical parameters as a function of lime content and environmental temperature. Lime contents of 5, 7, 9, 11 and 13% by dry weight of expansive clay powder were added to prepare lime-clay specimens. The specimens were prepared at the same dry unit weight of 12.16 kN/m3 and moisture content of 40% except for tests aimed at the determination of dry unit weight as a function of mellowing period. Prepared specimens were mellowed or cured at two different ambient temperatures of 20 °C and 40 °C. Results attained from Unconfined Compressive Strength and permeability tests were employed to assess the impact of lime content on the mechanical and hydraulic properties of lime treated expansive clays. The results revealed that at the beginning, the rate of strength gain is remarkably fast for a particular period of time which is dependent on lime content. Furthermore, the strength gain on specimens cured at 40 °C is 8 times higher than that observed on specimens cured at 20 °C which highlights significant effect for the environmental temperature on accelerating the chemical reactions. Reduced dry unit weight due to increased resistance to compactability is observable with increasing lime content and higher environmental temperature. Accelerated pozzolanic reaction at higher environmental temperature resulted in permeability coefficient of specimens mellowed for 24 h at 40 °C to be higher than those mellowed at 20 °C. The results also highlighted that the permeability coefficient would be relatively stable when expansive clays were treated with small amounts of lime e.g. 5%.