Analysis of Necessity and Feasibility for Ground Improvement in Warm and Ice-Rich Permafrost Regions

Characterized by low bearing capacity and high compressibility, warm and ice-rich frozen soil is a kind of problematic soil, which makes the original frozen ground formed by of that unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. With the design and construction of major projects along the Qinghai-Tibet Engineering Corridor (QTEC), such as expressway and airport runway, it is a great challenge to favor the stability of overlying structures by formulating the proper engineering design principles and developing the valid engineering supporting techniques. The investigations carried out in recent years indicated that warm and ice-rich permafrost foundations were widespread, climate warming was significant, and the stability of existing engineering structures was poor, along the QTEC. When the warm and ice-rich frozen ground is used as the foundation soil, the implementation of ground improvement is an alternative measure to enhance the bearing capacity of foundation soil and eliminate the settlement of structures during operation, in order to guarantee the long-term stability of the structures. Based on the key factors determining the physicomechanical properties of frozen soil, an innovative idea of stabilizing the warm and ice-rich frozen soil based on chemical stabilization is proposed in this study, and then, an in situ ground improvement technique is introduced. This study intends to explore the feasibility of ground improvement in warm and ice-rich permafrost regions along the QTEC based on in situ chemical stabilization and provide the technical support and scientific reference to prevent and mitigate the hazards in the construction of major projects in the future.

Improvement of deltaic lateritic soil using river sand and cement for use as pavement construction material

This study examined the effect of mechanical and chemical improvement on deltaic lateritic soils in Warri East in Delta State, Nigeria. Mechanical stabilization was carried out by adding river sand to the natural soil in various proportions, while chemical stabilization was carried out using cement and a mixture of cement and sand. Compaction and CBR tests were conducted on the natural soil before and after stabilization. From the results obtained, it was seen that the mechanical stabilization method improved the strength properties of the soil making it suitable for use as subbase materials, though not as much as the chemical stabilization method or the mixed method of stabilization. It was concluded that using a combination of cement and sand as a stabilizing agent for deltaic lateritic soils can lead to significant reduction in the amount of cement required for soil stabilization thus saving costs.

Distinct Responses of Rare and Abundant Microbial Taxa to In Situ Chemical Stabilization of Cadmium-Contaminated Soil

Understanding the ecological roles of rare and abundant species in the restoration of soil ecosystem functions is crucial to remediation of heavy metal-polluted soil. Our study assessed the efficiencies of five commonly used soil amendments on recovery of ecosystem multifunctionality and emphasized the relative contributions of rare and abundant microbial communities to ecosystem multifunctionality.

Effect of Sand and Sand-Lime Piles on the Behavior of Expansive Clay Soil

Expansive clay soil causes serious problems to many structures due to its swelling and shrinkage during wet and dry seasons. With the existence of expansive soil in Ahkmim new city, Sohag governorate, Egypt, some light buildings, road pavements, and buried pipelines have shown some damage. To avoid such damage, prior to construction, expansive clay soils should be stabilized. Different methods are available to improve the engineering properties of these soils such as densification, chemical stabilization, reinforcement, and techniques of pore water pressure reduction. The chemical stabilization of clay using lime is one of the widespread methods that can be used to improve the behavior of expansive clay soil. This study aims to investigate the effect of both sand and sand-lime piles on the behavior of expansive clay soil. A series of laboratory tests were carried out using the conventional Oedometer apparatus. Sand piles with different replacement area ratios (RARs) (4.68%, 10.16%, 24.6%, 35.84%, and 56.9%) were used. Also, sand piles stabilized with different percentages of lime (3%, 6%, 9%, 12%, 15%, and 20%) and with a replacement area ratio of 35.84% were used. The experimental results showed there is a significant improvement in reducing the swelling potential of expansive clay soil reinforced with sand or sand-lime piles. This improvement increases with the increase of both replacement area ratio and lime content.

Key-Parameters in Chemical Stabilization of Soils with Multiwall Carbon Nanotubes

Chemical stabilization is one of the most successful techniques that has been applied to improve the geomechanical behavior of soil. Several additives have been studied to be a sustainable alternative to traditional additives (Portland cement and lime) normally associated with high cost and carbon footprint. Nanomaterials are one of the most recent additives proposed. This work is focused on one type of nanomaterial, multiwall carbon nanotubes (MWCNTs) with unique characteristics, applied to chemical stabilization of soils and aiming to identify the key-parameters affecting the stabilization improvement. It was found that a surfactant should be added in order to oppose the natural tendency of MWCNTs to aggregate with the consequent loss of benefits. The surfactant choice is not so dependent on the charge of the surfactant but rather on the balance between the concentration and the hydrodynamic diameter/molecular weight due to their impact on the geomechanical compression behavior. As time evolves from 7 to 28 days, there is a decrease in the geomechanical benefits associated with the presence of MWCNTs explained by the development of the cementitious matrix. MWCNTs applied in a proper concentration and enriched with a specific surfactant type may be a short-time valid alternative to the partial replacement of traditional additives.