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Cochin marine clay found along the coastal belt of Kerala pose significant geotechnical challenges due to their high compressibility, low shear strength, and substantial organic content. Lime stabilization, a widely used soil improvement technique, often fails to deliver long-term strength enhancements in such soils because organic matter inhibits pozzolanic reactions and reduces pH over time. Therefore, chemical additives should be introduced while applying lime stabilization in those areas. In this paper, an attempt has been made to examine the effect of NaCl on lime-stabilized Cochin marine clay over an extended period of 120 days unlike previous studies that focused on CaCl₂ or MgCl₂ additives and shorter curing durations. Soil specimens were prepared with 6% lime and varying NaCl concentrations (2.5%, 5%, and 10%) and subjected to unconfined compressive strength (UCS) tests after curing periods of 0, 7, 30, 60, and 120 days. Scanning electron microscopy (SEM) was conducted after 120 days to assess microstructural changes. Results revealed that adding 5% NaCl significantly enhanced strength, achieving over a sevenfold UCS increase after 120 days compared to lime-only treated samples. Cementation improved due to formation of calcium silicate hydrate and calcium aluminate hydrate. NaCl enhanced the ion exchange by increasing the availability of Ca²⁺ ions and reducing clay particle repulsion through double-layer compression. Whereas, excess salt (10%) led to dispersion and reduced long-term strength. The study concludes that sodium chloride, at an optimized concentration, can effectively mitigate the limitations of lime stabilization in coastal areas with organic-rich marine clays.

At present, nearly 100 million tonnes of fly ash is being generated annually in India posing serious health and environmental problems. To control these problems, the most commonly used method is addition of fly ash as a stabilizing agent usually used in combination with soils. In the present study, high-calcium (ASTM Class C—Neyveli fly) and low-calcium (ASTM Class F—Badarpur fly ash) fly ashes in different proportions by weight (10, 20, 40, 60 and 80 %) were added to a highly expansive soil [known as black cotton (BC) soil] from India. Laboratory tests involved determination of physical properties, compaction characteristics and swell potential. The test results show that the consistency limits, compaction characteristics and swelling potential of expansive soil–fly ash mixtures are significantly modified and improved. It is seen that 40 % fly ash content is the optimum quantity to improve the plasticity characteristics of BC soil. The fly ashes exhibit low dry unit weight compared to BC soil. With the addition of fly ash to BC soil the maximum dry unit weight (γ dmax ) of the soil–fly ash mixtures decreases with increase in optimum moisture content (OMC), which can be mainly attributed to the improvement in gradation of the fly ash. It is also observed that 10 % of Neyveli fly ash is the optimum amount required to minimize the swell potential compared to 40 % of Badarpur fly ash. Therefore, the main objective of the study was to study the effect of fly ashes on the physical, compaction, and swelling potential of BC soils, and bulk utilization of industrial waste by-product without adversely affecting the environment.

The engineering behaviour of fine-grained soils is a dominant function of their clay mineralogical composition. Based on their dominant clay mineralogical composition, the natural fine-grained soils may be grouped as montmorillonitic soils, kaolinitic soils and montmorillonitic-kaolinitic soils. This article presents the e-log σ ' behaviour and compression indices of compacted montmorillonitic and kaolinitic soils at salient points along their compaction curves. It is shown that in spite of having almost the same liquid limit and or plastic limit, compacted montmorillonitic and kaolinitic soils exhibit vastly different e-log σ ' behaviour and compression indices, irrespective of the placement conditions. It is illustrated that the compacted montmorillonitic soils exhibit higher compression indices than the compacted kaolinitic soils under any placement condition. The results from the present study are hoped to have practical values while selecting the type of soil and or placement conditions for better performance of geotechnical structures where compaction is preferred to be adopted.

River sand is a naturally occurring conventional construction material, which has good frictional properties. Due to a steep rise in the construction activities all over the world, natural sand resources are getting depleted. This has favored / forced the construction industry in general and geotechnical engineering practice in particular to go for manufactured sands (M-sands). This necessitates a proper understanding of the frictional characteristics of M–sands. In this technical note, the results from a comparative study of the friction angles of river sand and M-sand with reference to the effect of grain size, grain angularity, dry density and gradation are reported. It is shown that M-sand exhibits higher friction angles than river sand at minimum density levels and river sand exhibits higher friction angles than M-sand at maximum density levels, on average, irrespective of grain size. It is also shown that poorly graded M-sands exhibit higher friction angles than well graded M-sands at minimum density levels, whereas well graded river sands have higher friction angles than poorly graded river sands irrespective of density levels.

Marine clays possess poor engineering properties and need to be improved prior to any construction activities on them. Lime stabilization is a widely adopted method of chemical stabilization for such types of soils. This study analyzes the impact of surcharge loads on the lime stabilization of Cochin marine clay subgrades throughout the curing process. Two processes, namely cementation and consolidation, must be taken into account in the case of lime-stabilized soil cured under surcharge loads and how the structures of stabilized soils change over time, particularly in the early phases of curing when considerable structural changes take place. The strength and deformation properties of lime-stabilized Cochin marine clay that was subjected to surcharge loading during curing were examined. For varying curing period up to 180 days, surcharge loads of 3 kPa, 7 kPa, 10 kPa, 15 kPa and 20 kPa were applied on Cochin marine clay treated with 6% lime. The effect of surcharge loading on California bearing ratio (CBR) and compressibility characteristics was evaluated at different curing periods. It was found that the application of surcharge load during curing improved the CBR and compressibility of samples drastically, with and without lime treatment. Compressibility and settlement of marine clay subgrades were found to decrease and yield stress was increased due to the combined effect of surcharge loading and lime treatment.

Undrained shear strength of a soil at the liquid limit water content can be considered to be around 1.7 kPa according to several researchers. Plasticity index of soils has been defined by one school of thought as a range of water content producing a 100-fold variation in their undrained shear strength. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is 170 kPa. The undrained shear strength-water content relationship has been found to be linear in the log–log plot for a wide range of water contents beginning from around the plastic limit to near the liquid limit. Normalization of undrained shear strength—water content relationship in a log–log plot has led to the conclusion that the water content at the liquid limit and at the plastic limit, obtained by cone penetration, could also be uniquely related. This contradicts the original understanding of Atterberg limits, namely liquid and plastic limits which are two independent parameter not related at all. It is more suitable to call this value of plastic limit from cone method as PL 100 to differentiate it from Casagrande’s plastic limit.

Pre-consolidation stress is a maximum consolidation stress to which the soil mass has been subjected in the past. Many methods are available to determine the value of pre-consolidation stress of an over consolidated soil mass in the field from the laboratory one dimensional consolidation test data. These methods, except the log–log method, have their own in-built limitations and their results are not validated. In the present work, the results from the log–log method have been validated with the actual values of pre-consolidation stress of the soil mass. It has also been shown through a comparative study that the log–log method is user friendly and that it yields conservative values of pre-consolidation stress for undisturbed soils as well as for compacted soils.

Organic matter is an undesirable constituent of the soil. Soils containing organic matter are associated with significant secondary compression and unsatisfactory strength characteristics. The estimation of organic matter in soils is hence a topic of concern for geotechnical engineers. The routine estimation of organic matter is carried out using the loss on ignition method put forward by ASTM and BS codes. The bureau of Indian standards has laid down the method for determining the organic matter present in soils, by the chromic oxidation equivalent of soil organic matter. This method is usually ignored due to the recovery of hazardous chromium whose disposal is dangerous to the environment. However, loss on ignition method also involves serious limitations like uncertainty in ignition time and temperature. This paper presents the results of the study conducted to identify various factors affecting the determination of organic matter using codal procedures. Tests were carried out on artificially prepared organic soils, prepared by mixing kaolinite, bentonite and sand with predetermined percentages of starch. Results have shown that IS code and BS code method I can be adopted when organic content in soils is less than 10%, and sample size is limited to 0.5 g. The loss on ignition method is the most reliable method with an optimum ignition time of 4 h and ignition temperature of 450 °C. The results of analyses performed on artificially prepared organic soils provide an insight into the selection of best method for determining organic matter in soils through an improved scientific perspective.

Determination of compaction characteristics of soils constitutes an essential part of any mechanical ground improvement project. The compaction characteristics vary with the compaction energy used in the process of densification. Standard Proctor compaction test is conducted in the laboratory to determine the compaction characteristics of soils used under normal applications. However, there are many practical situations where soils in the field need to be compacted under compaction energies other than that used in the standard Proctor test. This paper addresses the issue of relating the compaction characteristics of soils with the compaction energy input. The generalized regression equations developed facilitate the user to conduct only standard Proctor compaction test in the laboratory the results of which can be used to predict the compaction characteristics at any required compaction energy level quite satisfactorily.