Volume instability of expansive soils due to moisture fluctuations is often disastrous, causing severe damages and distortions in the supported structures. It is, therefore, necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements. This can be achieved through chemical stabilization using additives such as lime, cement and fly ash. In this paper, suitability of such additives under various conditions and their mechanisms are reviewed in detail. It is observed that the stabilization process primarily involves hydration, cation exchange, flocculation and pozzolanic reactions. The degree of stabilization is controlled by several factors such as additive type, additive content, soil type, soil mineralogy, curing period, curing temperature, delay in compaction, pH of soil matrix, and molding water content, including presence of nano-silica, organic matter and sulfate compounds. Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction. However, presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones. 

Stabilization of expansive soils using chemical additives: A review

One type of problematic soil in geology and geotechnical engineering recognized as collapsible soils can withstand relatively high pressure in an unsaturated state. The constant stresses because of soil saturation leading to a large volume reduction in the partially saturated condition are a matter of issue for the infrastructures constructed in the regions containing these soil types. As one of the environmentally friendly materials and potential stabilizers, nano-silica can be used to treat collapsible soils. The present study investigates the nano-silica effect on the soil collapse treatment in the Sivand region, Fars Province, Iran. A set of laboratory tests, including grain size analysis, Atterberg limits tests, water content, sand equivalent test, proctor and modified proctor tests, normal and double consolidation tests, were performed to determine the soil sample’s geotechnical characteristics. The consolidation test was then carried out on soil samples without nano-clays, reconstructed with 11% moisture content using static compaction methods to show the increasing nano-silica additive from 1 to %5 will obtain the less collapse index. The tests have also done on samples made using the mixture of soil, and nano-silica indicated the swelling of samples after saturation. Test results have shown that the saturation pressure and nano-silica content have direct and indirect relations with the strain of collapsible soils. The extracted test results are used as a database to develop an efficient model to predict reconstructed samples’ strain. Additionally, the parametric and sensitivity analyses confirm the model output with the test results.

Experimental Investigation of Collapsible Soils Treatment Using Nano-silica in the Sivand Dam Region, Iran

The poor engineering properties of the clay soils can be enhanced by adopting suitable soil stabilizing materials. The current study is focused on clay soils treated with various dosages of nano-silica, sodium silicate and their mix proportions to enhance the strength characteristics. Laboratory investigations were carried out to evaluate the influence of nano-silica and sodium silicate on the strength characteristics of clay soils. The experimental variables used in this study were admixture type, different dosages of admixtures and curing period. Unconfined compressive (UC) strength test was conducted in the laboratory to determine the strength characteristics of treated and untreated clay soil with various admixtures. The tests results revealed that the UC strength and Young’s modulus of clay soil are improved with increasing the nano-silica and sodium silicate content. The inclusion of 6% nano-silica to the clay soil improved the UC strength by 421.99% and Young’s modulus by 515.73%. Further, the experimental results were supported by scanning electron microscopy (SEM) analysis which confirms the presence of large particle packs and densified soil matrix for the soil samples treated with nano-silica. This approach of implementing nano-silica and sodium silicate in clay soils can be used as subbase material in road pavement constructions.

Influence of nano-silica and sodium silicate on the strength characteristics of clay soil

Soil stabilization using nano-additives is one of the trending developments of the decade. Many novel nano-stabilizers were tested by researchers for ground improvement applications. However, the capability of such materials in soil stabilization needs further detailed practical investigations beyond the controlled research environment. On the other hand, many well-proven nano-based stabilizers have constraints like availability, cost, difficulty in implementation method, and the practical feasibility of such usages. Among many well-established additives, nano-silica is one such material that was under research for over a decade and showed promising results for use as a soil stabilizer. Hence, the present work proposes a comprehensive review on characteristics of nano-silica, including its physical nature; its influence on curing methods and ageing, its behavior upon adding with soil and other additive materials in terms of strength improvement, hydraulic conductivity and compressibility; reaction mechanism in various soil and additives and a discussion on the gaps that need to be addressed to transfer this technology to field practices. Literature studies indicate that nano-silica as a sole-additive improved the soil strength and it acted as a strength enhancer for cement, lime and fiber treated soils. Also, nano-silica helps in reducing hydraulic conductivity and compression index of the soil. Further, an analysis on the minimum strength improvement with nano-silica on various types of soils is discussed based on the reported literature. With promising results from the review, further advancements on eco-friendly and cost-effective biogenic production methods would establish nano-silica as a competitive additive in the field of geotechnical engineering.

A review on the Choice of Nano-Silica as Soil Stabilizer

Application of waste eggshell as a source of calcium in bacterial bio-cementation to enhance the engineering characteristics of sand

Experimental investigation on stabilization of clay soil using nano-materials and white cement

In recent years, the method to produce bio-cementation in sand using bacterial calcium carbonate precipitation (BCCP) process has become more popular. The major objective of this research paper is to study the capability of BCCP to enhance the unconfined compressive strength of clayey soils. Two types of bacteria were used to generate calcium carbonate precipitation. The experimental design variables adopted in this study are bacteria types (L. fusiformis and S. pasteurii), soil types (low compressible clay and intermediate compressible clay), types of externally supplied calcium solution (calcium chloride and eggshell solution), molarities of cementing solution (0.25, 0.50, 0.75 and 1.00 M) and curing period (1, 3 and 7 days). The experimental test results showed that the BCCP process significantly improves the unconfined compressive strength (UCS) of both soils. The improvement however varied with bacterial types, soil types, types of externally supplied calcium solution, molarities of cementing solution and curing period. In BCCP treatment, S. pasteurii treated soils give more strength than L. fusiformis because of high urease activity of S. pasteurii in the order 450 U/ml. The maximum improvement ratio was achieved in CL soil (2.51) compared to CI soil (2.26) due to particle sizes. The optimum externally supplied calcium solution and molarity of cementing medium were established as an eggshell solution and 0.50 M, respectively. The images from scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis confirmed the experimental findings.

Performance Study on Stabilization of Fine Grained Clay Soils Using Calcium Source Producing Microbes

The current study presents the laboratory investigation on the use of nano-silica (0.2, 0.4, 0.8 and 1.0%) and polypropylene fiber (0.25, 0.50, 0.75 and 1.0%) in problematic clayey soil to enhance the shear strength and compaction characteristics. From the Transmission electron microscopy (TEM) analysis, it is observed that the diameter of nano-particles used in this study was in the range of 10–20 nm. The nano-particles have a spherical shape and amorphous in nature. Extensive laboratory tests such as the standard Proctor compaction test and unconfined compressive strength test have been conducted on untreated and polypropylene fiber along with nano-silica treated clayey soil. The outcomes showed that the addition of polypropylene fiber in poor soil, increase the maximum dry density and reduce the optimum moisture content of the soil. Whereas, the addition of nano-silica to the clay soil results in reduced maximum dry density and increased optimum moisture content. Unconfined compressive strength of clay soil is increased with the addition of polypropylene fiber and nano-silica to the clay soil. The optimum dosage of polypropylene fiber and nano-silica added to the poor soil was 0.75% and 0.8%, respectively. The Young’s modulus of clay soil was increased with the addition of polypropylene fiber and nano-silica. The microscopic analysis confirmed that C–S–H gel was the main cementitious product, and the inclusion of nano-silica can contribute to a denser packing of soil particles.

P. Kulanthaivel

Papers

Experimental investigation on stabilization of clay soil using nano-materials and white cement

Performance Study on Stabilization of Fine Grained Clay Soils Using Calcium Source Producing Microbes

Influence of nano-silica and sodium silicate on the strength characteristics of clay soil

Application of waste eggshell as a source of calcium in bacterial bio-cementation to enhance the engineering characteristics of sand

Combined effect of nano-silica and randomly distributed fibers on the strength behavior of clay soil