Showing papers on "Expansive clay published in 1998"

Mechanical behaviour of unsaturated highly expansive clays

Abstract: This thesis concerns the mechanical behaviour of unsaturated highly expansive clays. Given the high cost of damage to buildings, structures and roads caused by unexpected ground movements associated with unsaturated highly expansive clays and the increasing use of compacted expansive clays for engineered barriers for environmental protection and other purposes, it was considered important to investigate the behaviour of these materials. Previous researchers had reported the occurrence of substantial irreversible components of either wetting-induced swelling or drying-induced shrinkage during cycles of wetting and drying performed on unsaturated highly expansive clays containing active clay mineral such as montmorillonite. This form of irreversible behaviour cannot be represented by existing elasto-plastic models for unsaturated non-expansive clays. It had therefore been suggested that the behaviour of unsaturated highly expansive clays was fundamentally different to that of unsaturated non-expansive clays, and that the constitutive models developed for unsaturated non-expansive clays were inappropriate. The behaviour of an unsaturated highly expansive compacted bentonite/kaolin mix under isotropic stress states has been studied in a programme of controlled-suction tests incorporating isotropic loading and unloading at constant suction and cycles of wetting and drying (variation of suction) performed either under constant load or at constant volume. A smaller series of tests was also performed on unsaturated compacted samples of non-expansive pure kaolin. Either net shrinkage or net swelling occurred over a wetting/drying cycle for samples of the same soil, depending upon the compaction pressure. Irreversible shrinkage or swelling occurred during subsequent wetting/drying cycles, not just during the first cycle. Net shrinkage during a wetting/drying cycle was sometimes accompanied by a distinct change of stiffness (a yield point) during the appropriate drying path, but at other times was not. Yield points were never observed during both drying and wetting stages of a cycle. Net shrinkage or swelling during a wetting/drying cycle was always accompanied by a substantial net change of degree of saturation Sr during the cycle (termed hydraulic hysteresis). Experimental evidence showed that there is no fundamental difference between the mechanical behaviours of unsaturated highly expansive soils and unsaturated non-expansive soils. The experimental results suggested that unified modelling for both unsaturated highly expansive soils and unsaturated non-expansive soils is desirable. A new constitutive modelling framework is therefore proposed. In the modelling framework new forms of stress variables, with conjugate strain increment parameters, are used for the first time. Results from theoretical analysis of the influence of suction on inter-particle forces are used in developing the modelling framework. The influence of hydraulic hysteresis on stress strain behaviour is included in the framework, which has been developed in such a way that the otherwise difficult, transition between saturated and unsaturated conditions can be modelled in a relatively straightforward fashion. In the new modelling framework, both net shrinkage and net swelling during wetting/drying cycles, can be explained.

Model for the simulation of swelling-pressure measurements on expansive soils

Abstract: Numerous laboratory swelling tests have been reported for the measurement of swelling pressure and the amount of swell of an expansive soil. These test methods generally involve the use of a conven...

Geomembranes and the control of expansive soils in construction

Abstract: The author of this book states that expansive soils have caused more than $10 billion in damage in the U.S. alone. Geomembranes are increasingly being used as moisture barriers to control expansive soils. This reference work on geomembranes provides detailed information on preconstruction testing and assessment, techniques for combating soil expansion, and protection against groundwater pollution from landfills. Detailed case studies are also included.

Laboratory and field studies of response of structures to heave of expansive clay

Abstract: Laboratory and field studies are presented concerning the interaction that takes place between expansive soils and structures. A model floating slab and fixed slab were constructed on a highly expansive soil contained in a stainless steel box, which was also used to obtain large, undisturbed soil samples and used as a part of the laboratory experiment. A controlled heave test was conducted to investigate the effect of heave rate on swelling pressure. In the field, an instrumented, reinforced concrete structure and an in situ test were carried out to investigate heave movement, structure—expansive soil interaction and structural damage, while the ground was artificially wetted through vertical sand drains. The field and laboratory tests were compared with the results of the conventional oedometer test. The swelling pressure obtained from the constant volume test, in which the volume of the specimen was kept constant throughout the test, almost coincides with the average pressure predicted from the braced f...

Geomembranes and the Control of Expansive Soils

Abstract: The geomembrane is a member of the family of geosynthetics. It is a manmade fabric, a hydrocarbon compound treated to generally provide a substantially waterproof material. Geomembranes have been used to create a barrier to minimize moisture changes in expansive soils. These moisture changes cause volumetric changes in the swelling and shrinking clays and shales. Expansive soils are found on all the earth's continents with the exception of the polar ones. These soils have been identified in forty of the fifty United States. Damage estimates to transportation facilities, homes, and businesses exceed $10 billion annually in the United States. Case studies using geomembranes examine primarily Texas highways. The work of Wyoming Department of Transportation on more than fifty highway projects is reported. In these and other states the geomembrane barriers have been used horizontally and vertically, often both ways. Mention is made of highway treatment in Israel and railroad lines in China. The past and current impact of the expansive soils on buildings are considered in Australia and the United States. Durability results indicate the geomembrane will last decades. Geomembrane costs have decreased and placement rates have increased. The geomembrane moisture barrier generally can decrease damages caused by expansive soils.

Quantifying Properties and Variability of Expansive Soils in Selected Map Units

Abstract: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Dedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Table of

Stabilization of Expansive Clays in Oman

Abstract: Swelling of expansive soils and the associated movement of foundations cause serious distress to many structures. With the existing expansive clays in Oman, many buildings have shown severe damages resulting in considerably high maintenance costs. To avoid such damages prior to construction, expansive clays may be stabilized. This paper reports the findings of an experimental investigation to reduce swelling properties of clays. For this reason a potentially expansive soil from Al-Khod was selected. Several economical stabilization techniques were applied. These include remolding the soil with different proportions of sand, lime and cement and finally using different proportions of salt in the pore fluid. All techniques were found effective in reducing the expansive behavior of the tested soil to various degrees, except salt which showed an increase in swelling potential. Furthermore, this study indicated that lime addition is best suited to improve the swelling behavior of the selected soil.

Structure and hydrocollapse behaviour of loess

Abstract: Loess has a metastable structure and undergoes structural hydrocollapse when loaded and wetted, leading to subsidence and damage of overlying structures, which presents enormous engineering problems in many countries in the world. This problem is a focus of much research on both the nature of the phenomenon and the means. of overcoming its negative consequences. However, there remains a need for fundamental experimental and theoretical studies aimed at understanding the many uncertainties involved in the hydrocollapse phenomenon. An experimental programme has been conducted to study the fundamental nature of the hydrocollapse phenomenon in loess, and the primary features of the metastable structure controlling it. High quality disc-shaped specimens were prepared from natural undisturbed, very soft and slightly cemented loess soils using two simple devices which were designed and manufactured in the laboratory. Artificial loess materials were prepared by mixing pure silt particles of different geometrical characteristics (crushed sand, ballotini glass balls) with various clay types (kaolinite, bentonite) to produce mixes with different clay/silt ratios. Soil specimens of metastable structure were created from natural and model loess materials using the air-fall technique, which allowed full control over the critical variables. The index properties of the materials were determined experimentally, together with their geometrical characteristics from scanning electron microscope (SEM) studies. The compressibility characteristics and hydrocollapse behaviour were measured via one-dimensional (oedometer) compression tests. Two testing methods were used: the single oedometer test and the double oedometer test. The results indicated that the experimental approach used in this research can be used successfully to investigate the hydrocollapse problem of loess deposits. The small-clay loess model was constructed and examined. The results proved that this model is valid. The collapse behaviour of reconstituted and undisturbed loess specimens prepared from the same material was qualitatively similar, although the reconstituted materials exhibited greater collapsibility, particularly under low normal effective stresses. Specimens prepared from pure silt revealed very little collapse in spite of relatively high initial voids ratios (e ≤ 0.9). The existence of bonding materials, such as clay minerals at the points of particle contact, is thus apparently essential for hydrocollapse to occur. Specimens prepared from pure silt-bentonite mixtures exhibited low hydrocollapse values in comparison with those for pure silt-kaolinite mixtures. It was observed that there is an optimum clay mineral content for maximum hydrocollapse and it depends on the type of clay mineral and the level of applied stress. Higher values of hydrocollapse were obtained with smooth, spherical glass balls as the silt fraction, thus confirming that the geometrical properties of the silt particles also have a significant effect on the hydrocollapse behaviour of loess deposits. The position and distribution (mixing method) of clay particles inside the soil structure were equally found to have a significant effect on the hydrocollapse behaviour. The index properties of Libyan loess were found to be very similar to those of other loess deposits world-wide. The Tripoli loess can be classified as silty loess with high susceptibility to structural hydrocollapse in the same manner as other better known loess deposits in the world.

Coupled analysis of a backfill hydration test

Abstract: SUMMARY BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flowdeformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the ‘in situ’ experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identification of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal. ( 1998 by John Wiley & Sons, Ltd.

The geotechnical properties and behaviour of a pro-glacial lake clay, and its cementitious stabilization

Abstract: The Tees Laminated Clay forms a continuous deposit around the Tees estuary in north east England and was deposited in a proglacial lake which occupied the Teesside area during late Devensian times, disappearing about 13 000 years ago. It overlies till, with which it has a sharp contact and reaches a maximum thickness in parts of central Middlesbrough of just over 9 m. The laminations consist of alternating thin layers of clay and silt, and represent seasonal increments of sediment. Kaolinite and illite, with lesser amounts of chlorite, dominate the mineral composition. Quartz tends to account for less than 35%. The notable carbonate content may be diagenetic in origin. The birefringence ratio of the clay minerals indicates a medium degree of particle orientation which suggests a partially flocculated fabric.

Optimizing multiagent, multi-injected swell modifier

Abstract: 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 optim...

Quantitative Analysis of Clay Minerals Using X-Ray Diffraction Technique. Part 1

Abstract: Qualitative and quantitative analysis of clay minerals are important in the evaluation of the swelling potential of expansive soils A relatively simple method for the quantification of clay minerals of Al-Khod (Northern Oman) using an X-ray diffraction method is described in detail in this paper. The method is based on the additions of known internal standards to the clay sample. The clay investigated in this study contained montmorillonite, palygorskite, illtte and kaolinite. Internal standards of these minerals were mixed with the clay at different proportions and intensities of reflected peak areas were measured. It was found that the peak areas intensities relate linearly with additions of different proportions of standards. From these intensities, the clay minerals present in the clay of Al-khod were estimated.

Control of shrinkage and swelling of expansive soils

Abstract: Fly ashes are used to improve the properties of expansive soils. The paper brings out the effect of two different fly ashes containig different lime contents on shrinkage and swelling behaviour of expansive Indian Black cotton soil. Since the specific gravities of the fly ashes are considerably different,Void ratio at shrinkage limit and % of swelling are used to describe the shrinkage and swell behaviour of soils. Both fly ashes increase the shrinkage void ratio and decrease the % swell of the soil. While high lime fly ash is more effective in increasing the shrinkage void ratio, low lime flyash is more effective in reducing the swelling. Lime content which causes floculation of soil particle, is responsible for the differences.

Soil movement and water potentials in trees growing in expansive clay soils

Abstract: Summary An experiment on four Eucalyptus maculata street trees growing in expansive clay soil in Melbourne, Australia, was conducted to investigate the relationships between soil water content and soil vertical movement, z, and soil water content and leaf water potential measured just prior to dawn Ψd. Consequently a relationship was developed which showed z linearly decreased as Ψd decreased. These results highlight the possibility that measurements of Ψd can be used to predict critical levels of z known to be associated with building damage.

A unique model for the sand and clay behavior

Abstract: Since more complex and ambitious works are built and since more powerful calculation tools are used for their dimensioning, finer behavior laws are required. The aim is to adjust the most representative models to the labor and in situ tests in order to evaluate a growing number of parameters.