Compacted Lateritic Soil Research Articles

Consolidation Properties of Compacted Lateritic Soil Treated with Rice Husk Ash

One dimensional laboratory consolidation test was conducted on compacted lateritic soils treated with up to 16% rice husk ash (RHA), to assess its consolidation properties. Specimens were prepared at three different moulding water contents (2% dry of optimum, optimum moisture content and 2% wet of optimum) and compacted using the British Standard Light compactive effort. Preliminary tests on soils showed improved index properties with an increase in liquid limit (LL), an increase in plastic limits (PL) with a resulting decrease in plasticity index (PI). Preconsolidation pressure increased with RHA content, it also decreased before increasing with increased moulding water content. Reductions in compression index (Cc) and Swell Index (Cs) with increased RHA content were recorded. Cc and Cs generally decreased before increasing with increased moulding water content. The coefficient of volume compressibility (Mv) decreased and increased with higher RHA content; they were also affected by the soil particle state with increasing pressure. The coefficient of consolidation (Cv) showed no observable trend with increased RHA content but generally increased with higher consolidation pressure on the dry and wet side of optimum compacted states.

Desiccation Induced Shrinkage of Compacted Lateritic Soil Treated with Blast Furnace Slag

A reddish brown lateritic soil treated with up to 15% blast furnace slag was compacted with three compactive efforts, (standard Proctor, West African Standard and modified Proctor) with moulding water contents ranging between 10 and 20% of weight of dry mixture. Compacted samples were extruded and allowed to dry in the laboratory for 30 days with measurements taken every 5 days to monitor volumetric changes due to drying. Four specimens compacted on the wet side of optimum using standard proctor effort; at the various slag treatments after 10 days of drying were subjected to four cycles of drying and three cycles of wetting. The results obtained showed that the changes in mass and volumetric shrinkage were rapid within the first 5 days of drying. These changes were proportional to the moulding water contents and were unaffected by the compactive effort. The volumetric shrinkage strain increased with increasing moulding water content and compactive efforts. As the water content relative to the optimum increased towards the wet side, the volumetric shrinkage strain increased and it decreased towards the dry side. For all compaction energies, the initial degree of saturation increased and regardless of the slag content, the volumetric shrinkage strain increased. As the slag content increased, the initial degree of saturation at which the permissible 4% volumetric shrinkage occurred increased. Slag content had marginal effects on the volumetric shrinkage strain as no clear trend was established. For each slag treatment the volumetric shrinkage strain did not vary significantly with increasing number of drying cycles.

Rate-Dependent Undrained Shear Behaviour Of A Compacted Lateritic Soil

Rate-Dependent Undrained Shear Behaviour Of A Compacted Lateritic Soil

Influence of Soil Suction on Small-Strain Stiffness of Compacted Residual Subgrade Soil

The small-strain stiffness of compacted residual lateritic subgrade soil was determined. A bender element apparatus and the filter paper method were integrated to develop a systematic testing procedure to investigate the influence of matric suction on small-strain stiffness, including small-strain shear wave velocity and small-strain shear modulus, with different wetting paths. Soil specimens were compacted at three moisture contents (optimum moisture content, dry of optimum, and wet of optimum), then wetted to various moisture contents by using an environmental simulation apparatus developed to simulate in-service moisture conditions. Test findings indicate that specimen moisture contents increase gradually and finally attain equilibrium in the wetting process. Suction decreases with increasing moisture content and degree of saturation; consequently, small-strain shear wave velocity and small-strain shear modulus decrease. The specimens compacted at dry of optimum have a much lower small-strain shear wave velocity and small-strain shear modulus than specimens compacted at wet of optimum. Nevertheless, the small-strain shear modulus exhibits higher linearity with matric suction than with moisture content. Results indicate that matric suction is a key parameter for evaluating the dynamic properties of compacted soil.

Desiccation-induced Shrinkage in Compacted Lateritic Soils

Specimens prepared from three lateritic soil samples were subjected to drying under laboratory conditions. Volumetric shrinkage strains were measured at the end of the drying period. Results of this study indicate that, for the lateritic soils tested, volumetric shrinkage strains are influenced by soil composition and compaction conditions. Volumetric shrinkage strain increased with higher compaction water content. The influence of compaction water content on measured volumetric shrinkage strain was more pronounced in specimens with higher fines content. A regression equation was developed from the data to estimate volumetric shrinkage strain given the compaction water content relative to optimum, plasticity index, fines content and compactive effort.

Wave-Based Techniques for Evaluating Elastic Modulus and Poisson’s Ratio of Laboratory Compacted Lateritic Soils

A rapid, low-cost evaluation methodology using the wave-based techniques is proposed in this study in order to determine the design parameters e.g., elastic modulus and Poisson’s ratio of the laboratory compacted lateritic soils. Knowing the elastic wave velocities as measured with the wave propagation technique (i.e., a small-strain non-destructive test) and total mass density of the specimens, the elastic moduli and Poisson’s ratio of the soil specimens can be determined. In addition, the unconfined compression test (i.e., a large-strain destructive test) is also performed on the same specimens under the same unconfined testing condition in order to compare the moduli corresponding to different strain levels. The experimental results showed the potentials and limitations of using impulse signal for the determination of the elastic moduli and Poisson’s ratio for laboratory compacted soil specimens from elastic wave propagation techniques.

Lateritic Soil and Bentonite Mixtures Assessment for Liner Usage Purpose

Among all the constructive elements in waste containment systems, base liner may be the one of greatest concern. In Brazil, the use of compacted lateritic soils for this purpose is widely accepted due to their wide occurrence. While they usually achieve compaction and strength requirements, sometimes they may need some improvement in terms of hydraulic conductivity and reactivity to contaminants. This paper describes a laboratory assessment of two mixtures of a lateritic soil and bentonite for liner usage purpose. Laboratory tests included geotechnical, mineralogical and physicochemical characterization, hydraulic conductivity determination in compacted samples and modified Atterberg Limits and grain-size distribution analysis. These two last tests were intended to evaluate the compatibility between the soil and different chemical solutions. The characterization tests showed that the clay content of the mixtures decreased and the plasticity and activity increased relative to the natural soil sample. The hydraulic conductivity of the compacted mixtures decreased two to four times when compared to the compacted natural soil. The results also have demonstrated that the addition of bentonite in the proportions used in the tests increased the compatibility of the natural soil.

Design of Compacted Lateritic Soil Liners and Covers

Laboratory tests were conducted on three lateritic soil samples to illustrate some pertinent considerations in the design of compacted lateritic soil liners and covers. The three design parameters investigated are hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. Test specimens were compacted at various molding water contents using four compactive efforts. The compaction conditions were shown to have some relationship with soil compaction using either the plasticity modulus or the plasticity product (i.e., clay index). For construction quality assurance purposes, the traditional approach was compared with the modern criterion. Deficiencies associated with the traditional approach for soil liners found in literature also apply to lateritic soils. Overall acceptable zones were constructed on the compaction plane to meet design objectives for hydraulic conductivity, volumetric shrinkage strains, and unconfined compressive strength. The line of optimums was identified as a suitable lower bound for overall acceptable zones of lateritic soils. The volumetric shrinkage strain was also identified as the second most important design parameter for lateritic soils. The shapes of the acceptable zones were affected by the fines contents of the soils.

Statistical Evaluation of the Hydraulic Conductivity of Compacted Lateritic Soil

Abstract This paper examines the variation of hydraulic conductivity of a compacted lateritic soil with molding water content, dry unit weight, and initial degree of saturation under as-compacted conditions. Trends in the hydraulic conductivity versus molding water content relationships are similar to those obtained for nonlateritic, temperate zone soils. Hydraulic conductivity generally decreased as dry unit weight and initial degree of saturation increased. However, for the same values of dry unit weight, specimens compacted on the wet side of optimum water content yielded lower hydraulic conductivities than those compacted on the dry side of optimum water content. For lateritic soil specimens compacted at about 2% or more on the wet side of optimum water content, hydraulic conductivities less than 1 × 10−7 cm/s can be achieved when the dry unit weight is greater than or equal to 16.3 kN/m3 and initial saturation is greater than or equal to 88%. Statistical analysis of the results obtained in this study show that relatively weak relationships exist between hydraulic conductivity and molding water content or dry unit weight. Stronger relationships are obtained when hydraulic conductivity is plotted against initial degree of saturation. It is shown that a more accurate prediction of hydraulic conductivity can be achieved when a multiple regression equation is used to relate degree of saturation and compaction energy to hydraulic conductivity. The British Standard heavy compactive effort offers a wider range of molding water contents within which soils can be compacted to yield low hydraulic conductivity. This range is, however, limited by consideration for long-term desiccation and shear strength.

Reliability-based assessment of compacted lateritic soil liners

The first-order reliability method is employed to assess the suitability of lateritic soils as landfill liner materials based on existing models developed from laboratory and field data. The statistical characteristics of lateritic soil properties were first compared with those from which the regression models were developed. Using regression models for hydraulic conductivity, k, and established distributions for the relevant soil parameters, reliability indices are computed considering hydraulic conductivity to have a normal/log-normal distribution. The results indicate that, for the laboratory-based model, reliability index is sensitive to variability in compactive effort and initial degree of saturation. The choice of distribution of initial degree of saturation affects reliability indices significantly and the energy of the British Standard heavy compaction has the highest reliability indices. On the basis of the reliability indices estimated from the field-based model, three variables, namely: compactor weight, initial saturation and plasticity index are identified as significantly affecting the field geometric mean hydraulic conductivity of lateritic soils. However, the hydraulic conductivity of lateritic soils can be better predicted if the compactor weight, as the most significant parameter, can be modelled as Gumbel-type distribution.

Comparative reliability evaluation of lateritic soils as hydraulic barriers

A numerical investigation to determine the existence or otherwise of congruence between laboratory-based and field-based models for predicting hydraulic conductivity of compacted clay liners has been conducted. The comparisons here are based on values of the reliability index estimated with the use of the two models for cases when hydraulic conductivity is assumed to be normally and lognormally distributed. The laboratory reduced Proctor and modified Proctor compactive efforts were assumed to correspond to the lowest and highest compactor weights (165 kN and 338 kN for sheepsfoot rollers only from literature) respectively. The standard Proctor compactive effort was assumed to correspond to the mean compactor weight of 261.4 kN. Reliability estimates from the laboratory-based model were consistently higher than the corresponding values from the field-based model for each of the variables common to the two models. As laboratory samples usually involve small samples which are often unrepresentative of field situations, it is considered that reliability levels estimated with the use of the field-based model provide more realistic assessment of compacted lateritic soils as hydraulic barriers. Compactor weight of 300 kN and above may be needed for effective compaction of lateritic soil liners. Reliability-based designs of lateritic soil liners should incorporate appropriate probability distribution types for variables in the field-based model.

Hydraulic Conductivity of Compacted Lateritic Soil

Hydraulic conductivity tests were conducted on three samples of lateritic soil obtained from the same borrow area and having a narrow range of fines content. Eighty four specimens were compacted at various molding water contents and then permeated with distilled/de-ionized water in the laboratory. Test results show that hydraulic conductivity of the soils decreased with the increase in dry unit weight and initial saturation, especially at higher fines content. Hydraulic conductivity values less than 1× 10−9 m∕s can be obtained at dry unit weights (wet of optimum) and initial saturations greater than 16.0 kN∕ m3 and 86.0%, respectively, provided a minimum compaction energy equal to the British Standard Light effort is used. The difference in hydraulic conductivity values due to variations in molding water contents and compactive efforts are statistically significant as shown by the two-way analysis of variance tests.

Hydraulic conductivity of compacted lateritic soil with bentonite admixture: S. A. Anderson & B. H. Hee, Environmental & Engineering Geoscience, 1(3), 1995, pp 299–312

Hydraulic conductivity of compacted lateritic soil with bentonite admixture: S. A. Anderson & B. H. Hee, Environmental & Engineering Geoscience, 1(3), 1995, pp 299–312

Unsaturated strength behaviour of compacted lateritic soil: U. Mahalinga-Iyer & D. J. Williams, Geotechnique, 45(2), 1995, pp 317–320

Unsaturated strength behaviour of compacted lateritic soil: U. Mahalinga-Iyer & D. J. Williams, Geotechnique, 45(2), 1995, pp 317–320

Hydraulic Conductivity of Compacted Lateritic Soil with Bentonite Admixture

The hydraulic conductivity of two compacted lateritic soils was evaluated to determine the suitability for use in landfill liners and covers. Flexible wall permeameter tests were performed on natural specimens and specimens with 2.5 percent and 5 percent bentonite admixture, compacted to different degrees of relative compaction and different water contents. The saturated hydraulic conductivity was determined at confining pressures of 10,50, and 100 kPa; the results indicate that it is necessary to either have confining pressure greater than about 50 kPa or some amount of bentonite admixture to achieve a Ksat less than 1 × 10−9 m/s. At 10 kPa confining pressure, 5 percent bentonite is needed to ensure an adequate range of compaction conditions for which Ksat less than 1 × 10−9 m/s can be achieved. Bentonite mixes relatively easily with the lateritic soil, probably because of its fine-aggregated nature, and we foresee little difficulty in mixing at the field-scale. The susceptibility to shrinkage cracking was qualitatively evaluated by testing swell potential in a variety of ways. It does not appear that shrinkage will be a problem for a well designed and constructed liner or cover of lateritic soil with 5 percent or less bentonite admixture.

Unsaturated strength behaviour of compacted lateritic soils

This technical note presents the unsaturated shear strength parameters from two theories for two different compacted lateritic soils. The two theories are: (1) a shear strength equation for unsaturated soils, proposed by Fredlund et al. (1978), using two independent stress state variables, the net normal stress and the matrix suction; and (2) Toll's (1990) proposed framework for unsaturated soil behaviour also incorporating volume change. Tests were conducted on two lateritic soils, developed from basalt and sandstone, which have been used for road pavements in south east Queensland, Australia. The shear strength properties were studied on 200mm high, 100mm diameter compacted specimens. Their classification and compaction properties are tabulated. Values obtained for Fredlund's parameter, for the two soils tested, vary with suction. Values obtained for Toll's parameter, for these soils, are in the same range as his results for Kenya gravel. Suction does not affect the shear strength of an unsaturated soil below degree of saturation 53%-55%.

Some engineering characteristics of a compacted lateritic residual soil

In many parts of the world, particularly in humid tropical regions, residual soils are abundant. In this paper the suitability of a residual lateritic soil as a construction material is investigated, with respect to its strength and compaction characteristics. In comparison with other typical construction fills available in Southeast Asia, compacted lateritic soils produce excellent shear strengths and CBR values. However, the brittleness and tensile cracking of this compacted material become enhanced on the dry side of the optimum moisture content, or if excessive compaction is imparted. Nevertheless, at a moisture content of 2% wetter than the optimum, the tensile mode of failure is suppressed and the lateritic fills become ideally suited for the construction of high embankments and impervious dam cores.

Strength characteristics of some compacted lateritic soils in relation to pavement design : Fekpe, E S K Proc Ninth Regional Conference for Africa on Soil Mechanics and Foundation Engineering, Lagos, September 1987V1, P455–460. Publ Rotterdam: A A Balkema, 1987

Strength characteristics of some compacted lateritic soils in relation to pavement design : Fekpe, E S K Proc Ninth Regional Conference for Africa on Soil Mechanics and Foundation Engineering, Lagos, September 1987V1, P455–460. Publ Rotterdam: A A Balkema, 1987

Compressibility characteristics of a compacted laterite soil : Malomo, S Bull Int Assoc Engng Geol, N24, Dec 1981, P151–154

Compressibility characteristics of a compacted laterite soil : Malomo, S Bull Int Assoc Engng Geol, N24, Dec 1981, P151–154

The compressibility characteristics of a compacted laterite soil

Laterite soils occupy large parts of the tropical regions of the world. They are used, in the compacted state, as bases for roads and air-field pavements, as fills for foundations, embankments and earth dams. Although the response to load with decreasing void ratio (compressibility) is important under the conditions of use, it has not been the subject of considerable study. Engineering studies in laterite soils have been limited to classification, compaction characteristics and sometimes, shear strength.