Proceedings of ISSMGE TC101—Advanced Laboratory Testing & Nature Inspired Solutions in Engineering (NISE) Joint Symposium

Clayey soils are always associated with undesirable mechanical properties that limit their direct use as foundation materials without a particular treatment process. Many methods have been developed to improve the mechanical characteristics of the problematic clay soil. Using different types of fibre in ground improvement has generally approved a significant enhancement of the engineering properties of the soil. Silkworms are insects that produce cocoons enriched with durable silk fibres. Although these products are being used in valuable industrial sectors, the waste of such material can be used in alternative fields. This study aims to investigate the contribution of cocoon fibres to the strength and stiffness of kaolinite clay. For that purpose, cocoons have been cut into two different shapes of threads and mixed with a specific amount of clay and water to gain a desired predetermined density. The UCS test was performed on each specimen, and the results were analysed. The results showed that the inclusion of cocoon threads in clay samples has shown a significant improvement in the unconfined compression strength of the mixture. However, it reduces the initial elastic modulus of the soil.

This study is centred around the potential of repurposing agricultural residues in India to partially replace cement. India is the world’s second-largest cement producer, with 537 million metric tonnes (MMT) of annual output at the cost of 149 MMT of carbon dioxide emissions. India is also the second largest producer of rice (124 MMT) and wheat (112.2 MMT), from which ash from incineration of straw and husk can be produced. Potential ash product in a year amount to 3.3 MMT in Uttar Pradesh (north), almost 2 MMT in Punjab (northwest), 1.6 MMT in Madhya Pradesh (central-western), and 1.5 MMT in Haryana (northwestern). Upon some chemical adjustment, ash can be conditioned into an alkali-activator. India is also the world’s second-largest sugarcane producer (413 MMT), generating 4.4 MMT of press mud each year. Maharashtra and Karnataka western states supply 4.4 and 2.5 MMT of press mud. Press mud is an organic calcareous waste with a potential of becoming biogeopolymer binder (for partial replacement of cement) upon activation with an alkali matter. Uttar Pradesh in the north and Tamil Nadu in the south emerge as potential national hubs for a new biogeopolymer production, constituting press mud as calcium-based precursor and ash as alkali-activator. The new binder can be used for stabilisation of expansive, organic, and erodible soils.

The consensus is that by incorporating plant-based additives into the ground stabilisation, the natural capacity of the soil to adapt and respond to environmental stresses can be retained if not enhanced. Plant-based additives potentially enable the soil to exhibit self-healing, self-forming, and self-producing functions, and to re-establish capabilities that are compromised. This study primarily focuses on wastes from rice, wheat, and maize milling and scopes for their use as alkali-activator. It also examines technical and logistical scopes of using a lime-based waste from sugarcane processing as a natural pozzolan (available at 3 to 6 wt.% of total harvested sugarcane biomass). The alkali-activator is a final product of chemically adjusted calcinated husk and straw (at 20 to 25 wt.% of total harvested biomass) and bran (at 1.5 to 2 wt.%). The mixing of the two creates a biogeopolymer that, upon application to certain soils, initiates a binding process. Target Nigerian soils are expansive black cotton and Abakaliki Shale Formation, erodible lateritic soils, and highly organic soft marine clays. The emphasis of this paper is on logistical rather than geomechanical aspects and to this end, geographical distribution of cultivated lands, mills and refineries, so too problematic soils and geohazards, and the average crop cycles and harvest seasons are collated into a database. Findings suggest that Lagos (south), Sokoto and Kano (north), and Minna (centre west) are four potential powerhouses for production of bio-geopolymers.

With growing global interest in sustainability and the necessity of its incorporation into every facet of living, earthen materials continue to attract interest of geotechnical engineers. Due to their widespread serviceability and cost-effectiveness, earth materials have been used for construction for thousands of years. But due to its vulnerability to excessive loading, wetting and implications of earthquakes, the natural soil needs to be stabilized in order to address these problems and guarantee the durability and accessibility of the structure. Unsurprisingly, construction using natural earth (subsoil) is regaining popularity given the increased awareness of the environment. The alternative approach of using earthen materials in construction promotes sustainability in the building sector by reducing the embodied carbon and reliance on calcined materials such as cement.

The main goal of improving natural soils is to make them more resilient to disasters brought on by excessive and abnormal loading, changing climatic conditions, and natural calamities like earthquakes and landslides. It is necessary to enhance the engineering features of clay soils in particular because they are prone to subsidence. Cement, lime, calcium-based stabilizers, fibers, and recycled plastic waste are all widely used binders for enhancing the engineering qualities of clay soils. In this study, glass powder (GP) and silica fume (SF) are combined with clayey soil to test the soil's strength characteristics. Clays are combined with 10, 15, and 20 wt.% glass powder and 10 wt.% silica fume for this purpose, and then cured for up to 7 and 28 days. According to research, a 15% GP and 10% SF mixture yields the best test outcomes. In comparison to the control samples, the compressive strength, flexural strength and direct shear strength of the best design mixture increased by 391%, 385% and 386% respectively.

Soil stabilization, widely used to enhance soil engineering properties, typically involves replacing weak soils incapable of supporting structural loads with stronger ones or fortifying them using mechanical and/or chemical methods. While mechanical compaction at specific moisture levels effectively improves soil properties, it often falls short for weak soils. Lime and cement have long been used as chemical stabilizers. Recent advancements in materials manufacturing have, however, introduced nanomaterials as a promising alternative for significantly improving construction materials. This study explores the use of carbon nanotubes (CNTs), given their exceptional properties, for soil stabilization. Different percentages of CNTs (0.001%, 0.01%, and 0.1%) were integrated into a soil-cement matrix, using TritonX 100 (1% concentration) as a dispersion agent. Several tests, including unconfined compressive strength (UCS), direct shear strength, and water absorption, were conducted to evaluate the stabilized soil's performance. The results demonstrated that an optimum CNT content of 0.01% significantly enhanced the soil's overall properties, with a remarkable 360% increase in UCS observed after 28 days of curing. Cohesion values reached 71.03 kPa at 28 days, marking a 104.5% improvement compared to CNT-free samples. Additionally, samples with 0.001% CNT exhibited excellent water absorption resistance, remaining intact for 72 h with a total absorption value of 8.7%.

Geotechnical design involves a myriad of complexities due to the inherent variability of soil and the necessity to simplify intricate geological conditions for engineering analyses. This review note explores the implications of variability and simplifications in geotechnical design and proposes potential solutions to address these challenges. Variability in soil properties arises from natural geological processes, anthropogenic influences, and spatial heterogeneity. This variability poses uncertainties in geotechnical analyses, leading to potential discrepancies between the predicted and actual performance of engineered structures. The consequences can range from increased construction costs to compromised safety and functionality of projects. To facilitate design calculations, engineers often resort to simplifications such as assuming homogeneous soil behavior or idealized geometries. While these simplifications aid in model development and analysis, they may not capture the true complexity of soil-structure interactions, leading to conservative or inadequate designs. To mitigate the adverse effects of variability and simplifications, a comprehensive approach is required. Tailored laboratory testing campaigns should be prioritized to quantify soil variability using advanced testing techniques. Probabilistic methods and stochastic modeling can account for uncertainties and variability in design parameters, enabling the incorporation of risk analysis into the decision-making process. Furthermore, the development of advanced numerical modeling tools, incorporating geotechnical data from multiple sources, can improve the accuracy of design predictions.

Stability of ground slopes is of paramount importance in geotechnical engineering. Several mitigating methods have been proposed in the literature and applied in practice. In this study, the effect of nano-bio-treated columns, as green cement inclusions, on the stability of a clayey slope is investigated by conducting two centrifuge Ng model tests. Rigid inclusions have been made by using enhanced Microbially Induced Calcite Precipitation (MICP) and 1.5% nano-\(\text {SiO}_2\). Unimproved and improved models were loaded in a beam centrifuge device by increasing centrifugal acceleration. Failure surfaces gradually appeared in the unimproved model after the centrifugal acceleration reached 40 g. By increasing the acceleration to 58 g, at the end of the test, very large deformations were observed. In contrast, the stability of the improved model was maintained without any clear failure surface by the end of the test where the centrifugal acceleration was increased up to 77 g. It indicates the use of new nano-bio cement inclusions can be an effective approach for improving slope stability in clayey soils.

In recent years, the number of monitoring techniques developed for management of natural and engineered ground systems such as slopes, embankments, and retaining walls has significantly in-creased. The current study examines a slope stability problem near Kyrenia Castle, a 7th century castle located in Northern Cyprus. The landslide and accompanying reinforced concrete/stone walls, constructed for rehabilitation purposes, are monitored for a period of two years. The current condition of the site is back-analysed using the finite element method (FEM) as a conventional analysis. To detect changes over time, close-range photogrammetry (CRP) is employed using photographs taken with an unmanned aerial vehicle (UAV) to generate a dense cloud model. The results demonstrate the compatibility of the CRP with FEM, making the technique a viable and efficient option for various engineered and natural ground systems. CRP is proved fast, cost-effective, sustainable, and non-destructive.

The liquefaction phenomenon in saturated granular soil occurs due to the transformation of a soil medium from a solid-like state to a fluid-like state. Such viscous medium transformation occurs due to the generation of excess pore water pressure and resulting in reduced intergranular forces. The weakened intergranular forces subsequently reduce the shear strength characteristics due to loss of effective stress causing large deformations and instabilities. This study addresses the influence of high plastic fines on the flow and non-flow behaviour of sand-containing carbonates located on the shores of Famagusta Bay, Northern Cyprus. Varying proportions of 10, 20, and 30% of plastic fines were incorporated in the carbonate sand and specimens were reconstituted at relative densities of 35 and 70%. Three different types of highly plastic fines, such as silt (MH), clay (CH) and equal proportions of clay and silt (MH-CH), were incorporated into the sand (SP) and were subjected to consolidated undrained triaxial test conditions. The primary analysis of the experimental testing focused on the critical state behaviour by utilising the state parameter and modified state parameter to assess flow or non-flow behaviour.

The concept of “loessification,” introduced by Berg in 1916, describes the transition of non-loess ground to loess ground via weathering. The theory dismisses the aeolian deposition phase in loess cycle, and is heavily centred around pedogenic processes, climate actions and interaction between residual sands/silts and neighbouring soil sequences. The role of loess constituting sand and silt particles, their size and shape, and the effect of these on structures evolving from isotropic consolidation is largely ignored. This paper makes use of scale-dependent porosity indices to explain the role of sand shape in formation of structures through fines migration and isotropic consolidation. Compared to residual sands, deltaic sands are more likely to become collapsible via isotropic consolidation. Overall, the influx of fines restricts the ability of isotropic consolidation to facilitate the loessification. The collapsibility of loess soils is evident through their shift from a state of random loose packing to random close packing. In the case of residual sands, this transition is most prominent at a fines content of 30 wt.% when subjected to confinement levels as low as 100 kPa, and at lower fines content of 20 wt.% under higher confinement levels. Conversely, for deltaic sands, the transition remains unaffected by the degree of confinement and is most marked at a fines content of 30 wt.%.

A programme of consolidated undrained triaxial shear tests is conducted on two residual and deltaic sands of similar size and different shape. Dry pluviation was used to generate an initial random open packing ahead of isotropic consolidation. Overall, both residual and deltaic sands exhibit a non-flow (NF), strain hardening (HS), dilative response. In absence of fines’ fraction, deltaic sands exhibit some levels of softening. It is tempting to attribute this behaviour to the initial random packing because of aeolian deposition (i.e., dry pluviation). There is a threshold fines’ content below which sand dilates (upon undrained straining) and reaches the USS, and above which sand rapidly loses strength (i.e., structurally collapse) and contracts before dilating towards the USS. Confinement level has a control on this threshold fines’ content if sand is angular enough. The thresholds fines content for residual sand varies between 10 to 30 wt.% (confinement depending). For deltaic sands, the threshold fines’ content happens between 10 to 20 wt.% fines’ contents and collapse is far less sudden.