Understanding the Impact of Lime Stabilization on Expansive Soil for Grounding and Analysis Adopting LIBS
Stabilization of soil for grounding purposes has been performed by adding different wt% of lime. Electrical breakdown measurements under lightning impulse voltage showed a reduction in breakdown voltage and the time to breakdown with increment in the lime content in the soil. These parameters also increased with curing period for all concentrations of lime of stabilized soil samples. The results show that pH and electrical conductivity of the expansive soil increase as the lime content increases, but decrease with increasing the curing period. Mineralogical and micro-structural analysis has been made by means of X-ray diffraction (XRD) studies and by scanning electron microscope (SEM) analysis. The axial strength obtained from unconfined compressive strength (UCS) analysis, the plasma temperature and the electron number density calculated from Laser Induced Breakdown Spectroscopy (LIBS) data tend to increase with increment in lime content as well as the curing period of the lime stabilized soil. Using univariate analysis, the normalized intensity ratio of Ca II peaks from LIBS spectral data are correlated with lime content in the soil samples at various curing periods. The partial least squares regression (PLSR) technique is successful in determining the soil parameters with the help of LIBS spectral data, at different curing periods with an R2 value greater than 0.95 and the percentage RMSE value smaller than 4%.
Effect of short-term sulphate contamination on lime-stabilized expansive soil
Lime stabilization is an age-old technique for controlling the swell-shrink characteristics of the expansive soil. However, the presence of sulphate in the expansive soils renders the lime stabilization ineffective due to the formation of detrimental compounds–ettringite and thaumasite. The formation of these detrimental compounds can be counteracted by treatment with low-calcium or non-calcium based stabilizers. However, there is a possibility of sulphate contamination post lime stabilization through external sources. Therefore, the present study brings out the effect of short-term sulphate contamination on lime-stabilized expansive soil using sodium sulphate solution. To achieve this objective, the lime-stabilized expansive soil was cured for 1, 7 and 28 days, and subsequently mixed with sulphate solutions of 5000–20,000 ppm concentration and allowed to equilibrate for 1 day. The experimental results showed that the sulphate contamination had a significant effect on the soil structure, physico-chemical and index properties of lime-stabilized soil. The mechanism governing the deterioration of the stabilized soil depended on the curing period of lime-stabilized soil prior to contamination with sulphate. Short-term sulphate contamination of lime-stabilized soil cured for 1 and 7 days resulted in highly flocculated structure, whereas the lime-stabilized soil cured for 28 days resulted in the formation of ettringite. This is evidenced with the aid of Scanning Electron Microscopy (SEM) images, X-ray diffraction (XRD) and Energy Dispersive X-Ray Analysis (EDAX). It can be concluded from this study that the ettringite formation occurs even after the formation of pozzolanic compounds in lime-stabilized soil.
Effect of Pore Fluid on Cyclic Behaviour of Reconstituted Marine Clay
The effect of pore fluid chemistry on the cyclic behaviour of fine grained soil is studied by performing strain controlled undrained cyclic triaxial tests on reconstituted marine clay with 0.4 M sodium chloride solution and distilled water. Specimens using different pore fluids were prepared by slurry consolidation method at vertical stress of 50 kPa. The influence of physico-chemical factors on the cyclic behaviour of reconstituted marine clay was brought out by studying the effect of number of cycles on the cyclic shear modulus degradation of clay. The effective confining pressure was taken as 150 kPa, loading frequency as 1 Hz, number of loading cycles as 100, and the strain range is kept in between 0.3% to 1%. The experimental results show that, with 0.4 M sodium chloride solution as the pore fluid, the shear modulus increases at lower strain range. The variation of damping ratio with the cyclic shear strain was also brought out in this study.
Combined effects of wet-dry cycles and interacting fluid on desiccation cracks and hydraulic conductivity of compacted clay
Compacted clays are used as barriers in landfills mainly due to their low hydraulic conductivity and self healing properties. These clays are subjected to moisture fluctuations and simultaneously exposed to leachates. Besides swelling, the shrinkage and cracks developed during drying get altered due to their exposure to contaminants and control their hydraulic behaviour. Therefore, this paper quantifies the volumetric behaviour and cracks pattern of compacted clay exposed to salt solutions during wet-dry cycles using X-ray computed tomography (XCT) imaging experiments. The results showed that the cracks volume of clay specimen interacted with 4 M NaCl solution is significantly greater than the specimens interacted with distilled water (DW) and 0.4 M NaCl solution at the end of drying cycles. XCT and digital camera imaging experiments showed that the cracks did not develop at same locations in specimen interacted with DW, indicating the self healing property of clay. However, the development of cracks at same locations in specimen interacted with 4 M NaCl solution indicates the complete deterioration of self healing property of clay. This resulted in significantly higher hydraulic conductivity of compacted specimen interacted with 4 M NaCl solution than the specimens interacted with DW and 0.4 M NaCl solution at the end of different wetting cycles.
Distress of an industrial building constructed on an expansive soil: A case study from India
This paper presents a case study of a two-storey building in Oragadam, near Chennai (India), which has undergone distress due to the presence of expansive soil. Undulations in the floors, cracks in partition walls and non-uniform heave in the pavement are some of the failure patterns noticed in and around the structure. Undisturbed soil samples were collected from the site to identify the cause of distress. From the field inspection and laboratory testing it was found that the use of unsuitable fill material (expansive soil) followed by the ingress of excess water from the garden and improper planning of the location of the rainwater-harvesting system were the causes of the initiation of distress in the building.
Effect of Physico-Chemical Interactions and Cyclic Wet–Dry Process on Behaviour of Compacted Expansive Soils
Physico-chemical interactions and alternate wetting and drying process have marked influence on the swell–shrink and hydraulic behaviour of compacted expansive soils used in various engineering applications. The microstructural, shrinkage cracks pattern and hydraulic behaviour of compacted expansive soils get altered due to the interactions with leachates and cyclic wet–dry process. Therefore, the effect of concentration of leachates and cyclic wetting–drying process on the swell–shrink, shrinkage cracks, microstructural and hydraulic behaviour of compacted expansive soil is studied in this theme lecture paper. The shrinkage cracks developed in clay specimen during a drying cycle were quantified using the X-ray computed tomography images and vernier caliper height measurement. And the same method was used to quantify the cracks in desiccated specimens interacted with different concentrations of interacting fluid. Scanning electron microscope and mercury intrusion porosimeter studies were carried out to understand the microstructure of salt solution-interacted specimens. The influence of physico-chemical interactions and cyclic wet–dry process on the self-healing capacity of compacted expansive soil specimens was brought out by carrying out hydraulic conductivity tests.
Influence of Footing Size on Reinforcement Geometrical Parameters
The load-bearing capacity of the reinforced sand bed depends on the optimum geometrical parameters of the reinforcement layer. This paper presents the effect of the size of the footing (D) on optimum geometrical parameters of the reinforcement, that is, placement depth of the first reinforcement layer (u) and the vertical spacing between the reinforcement layers (h). The jute geotextile reinforcement layer was used for the present model tests. All model tests were conducted using 50 mm diameter circular footing in a steel tank having an inner dimension of 450 mm × 450 mm × 350 mm. In each test, sand was placed at a relative density (Rd) of 70%. Finally, the present test results are compared with the plate load tests of jute geotextile reinforced sand beds using footing diameter (D) 150 mm. The size variation factor for two different diameters (D) of footings is 3. The test results show that the values of optimum geometrical parameters of the reinforcement are not much varying with the respective size of the footing (D). In comparison, the variation with the respective size of the footing is relatively higher for optimum vertical spacing of the reinforcement (h) than the optimum placement depth of the first reinforcement layer (u).
A rapid method of determination of swell potential and swell pressure of expansive soils using constant rate of strain apparatus
Swell potential and pressure of expansive soils are conventionally determined using an oedometer apparatus. The specimens are commonly saturated by submerging in water under a seating pressure. Generally, the test takes a long time, as the saturation process is slow. This article presents an improved saturation method by back pressure application in a constant rate of strain (CRS) loading apparatus. Controlled strain loading (CSL) was adopted to bring back the swollen specimens to their initial thickness instead of conventional incremental loading. It is observed that the time taken to complete the test is 7 to 13 times faster compared to the conventional method. When compared to the conventional method, the swell potential and pressure values obtained with the back pressure saturation were found to be higher by about 19 % to 34 % and 6 % to 28 %, respectively. The reason for these higher values is attributed to the attainment of greater saturation using the back pressure saturation technique.
Evaluating Soil Shrinkage Behavior Using Digital Image Analysis Process
In this paper, the shrinkage behavior of silty clay soil widely found in Warangal is characterized under free evaporation condition over a wide range of suction. As a part of the research evaluation, a comprehensive laboratory test program was framed and conducted on the samples collected from Warangal. Slurries of soil samples were subjected to desaturation by evaporation, and the change in the sample dimension was captured with camera still images and Vernier caliper. The captured images were processed and used for quantifying the overall volume change. The shrinkage behavior was represented as soil shrinkage curve (SSC), and the curve exhibited three zones. The proportional or normal shrinkage was dominant with volume of water lost from the pores equaling the volume change in the sample. The structural and residual shrinkage phase indicated the loss of water from both inter- and intra-aggregate pore spaces with gradual increase in time. The study showed the existence of bimodal porosity in low plasticity soil and also discusses the reliable efficiency of the proposed experimental procedure to study the shrinkage behavior of soils with low plasticity.
Effect of hydraulic gradient on swell and hydraulic response of desiccated expansive soil–an experimental study
Desiccation cracks in compacted clay liners act as preferential flow paths and affect the hydraulic response during initial stage of wetting. This paper investigates the effect of initial hydraulic gradient on swell, infiltration and hydraulic conductivity during wetting of desiccated expansive soil specimens in oedometric-infiltrometer test set-up. The experimental results on the desiccated specimens demonstrated that the rate of swelling and the infiltration rates in the initial outflow region through the annular gap and permeation outflow region through the swollen soil matrix increased with the increase in hydraulic gradient, whereas the time for reoccurrence of outflow and the establishment of steady state condition decreased. The outflow infiltration rates of the desiccated specimens subjected to initial hydraulic gradients (i) of 2, 5 and 20 reduced from 1.56 × 10−3, 4.83 × 10−3 and 6.57 × 10−2 cm/s, respectively, in the initial outflow region to about 6.65 × 10−6 cm/s (under i= 20) in the permeation outflow region due to the swelling of the desiccated expansive soil. The minimum possible initial hydraulic gradient that can be adopted on desiccated expansive soil specimens during infiltration testing was found to be 2 without considering the infiltration driven by soil suction.