Geotechnical Engineering Journal of the SEAGS & AGSSEA

Strength and Deformation Characteristics of Bandung Lacustrine Clay Under Consolidated-Undrained True Triaxial Testing

Dedi Apriadi — 2026-07-21

The effect of intermediate and principal stress rotation is commonly ignored in the determination of soil stress deformation behavior under two-dimensionally or plane strain conditions. In actual field conditions, soil receives the load three-dimensionally and undergoes stress rotation to reach a stable condition. Therefore, a stress deformation test considering the effect of the intermediate and principal stress rotation to obtain real soil behavior was conducted. Bandung lacustrine soft clay is formed by the deposition of clay soils in the giant ancient lake which is estimated to have about 200 m depth from the ground surface. Undisturbed soil samples from this soft clay were taken and investigated in the laboratory by using Consolidated-Undrained True Triaxial Test. The experiment shows that effective shear strength (ϕ') increases with increasing stress variation (b) up to 10% in the increment of intermediate principal stress 0.5 times to the major principal stress. Giving load with principal stress rotation changed from 0 (zero) degrees to 90 (ninety) degrees produces a decrease in undrained shear strength (S_u/σ_c) up to 15%. The stiffness modulus and the Skempton A_f parameter also increase with increase in stress variation. The results obtained from this study is considered important to evaluate the suitable soil constitutive model for finite element load-deformation analysis.

Study on Permeability and Triaxial Experiments of Clay under Dry-Wet Cycles and Compaction

Gang Zeng — 2026-07-21

The permeability and mechanical properties of clay are significantly influenced by the seasonal wet-dry cycles and compaction. In this study, laboratory experiments were conducted to investigate the effects of the number of wet-dry cycles and compaction degree on clay behavior. The results indicated that the initial compaction degree had a significant influence on the permeability characteristics of soil specimens subjected to wet-dry cycles. Specifically, the permeability coefficients significantly decreased with increasing compaction degree. The measured permeability coefficients for low, medium, and high-compacted samples were 5.48×10^-8 m/s, 8.33×10^-9 m/s, and 7.29×10^-10 m/s, respectively. After three wet-dry cycles, the permeability coefficients of the low and medium-compacted samples decreased to 1.16×10^-8 m/s and 9.08×10^-9 m/s, whereas that of the high-compacted sample increased to 6.76×10^-9 m/s. A relatively strong linear relationship was observed between the permeability coefficient and the compaction degree on a semi-logarithmic plot. Both cohesion and internal friction angle increased with increasing compaction degree. With a growing number of wet-dry cycles, the failure mode of the specimens gradually transitioned from strain-hardening to strain-softening behavior. The modified Duncan-Chang model showed a relatively good fit for the stress-strain relationship of the sample. This research offers theoretical references and technical support for practical applications in clay-related engineering fields.

Improvement of Load Carrying Capacity of Soil using Jute-Geotextile

Swagata Bisoi — 2026-07-28

A comprehensive study is performed on soil and jute-geotextile to improve the load carrying capacity of subgrade soil. An extensive laboratory experiments are carried out to verify the improvement of load carrying capacity for clay soil. Permeability test, unconfined compressive strength (UCS) test and triaxial test are carried out to verify the behaviour of soil considering geotextile material. The sample behaviour is checked for six cases (Case 1: without considering geotextile material in the soil sample, Case 2: h/2 depth, Case 3: h/3 depth each, Case 4: h/4 depth each, Case 5: h/5 depth each and, Case 6: h/6 depth each, where, h is the height of the soil sample). The result shows that the load carrying capacity increases when the geotextile is taken into account as compared to soil without geotextile. It is to be noted that the load carrying capacity increases for case 2 to case 4 considering jute-geotextile in the soil sample. However, the load carrying capacity decreases for case 5 and case 6, though, more layers of jute-geotextile is considered in the soil sample. Finally, an optimum method is proposed to develop maximum load carrying capacity of soil incorporating jute-geotextile.

Effect of Bio-Polymer on the Properties of Expansive Soil

Sagarika Talukdar — 2026-07-28

The process of modifying soil's properties by adding various admixture and additives is one of the most widely practiced ground improvement methods. The stabilization of expansive soils has been examined both from the aspect of removing their potential for swelling and shrinking, as well as from the standpoint of increasing those mechanical properties of relevance in civil engineering. This study evaluated the performance of biopolymer i.e Guar Gum in enhancing Free swell index, Unconfined compressive strength, Atterberg limit, Consolidation, pH and Conductivity of expansive soils. The varied Guar Gum dosages were maintained by dry soil mass weight. According to the results, when the amount of Guar Gum was raised, the strength of the expansive soil after treatment increased swelling characteristics decreased, Atterberg limit increased, coefficient consolidation decreases, pH increased and conductivity decreased. One of the main advantages of using biopolymers such as guar gum as soil stabilizers is that relatively low amounts of Guar Gum percentage i.e. 0.5% - 1.00% are needed to achieve maximum modification of the geotechnical properties comparable to those obtained with conventional soil stabilizers like cement and lime. This is a significant advantage in terms of cost, resource efficiency, and environmental impact. The practical engineering significance of Guar Gum on the properties of expansive soils lies in its ability to effectively stabilize these soils, enhance their strength, improve their workability, and provide a more sustainable and cost-effective solution for construction projects compared to treatment using traditional materials such chemicals such as cement and lime. Guar gum reduces swelling, mitigates plasticity, making it a valuable tool in addressing the challenges posed by expansive soils. Its environmentally friendly nature and cost-effectiveness further enhance its appeal, particularly in projects that prioritize sustainability. By using guar gum to stabilize expansive soils, engineers can ensure more reliable, durable, and cost-efficient infrastructure and improving the safety and performance of structures. Geo-environmental engineering has given a lot of attention to biopolymers because they offer a carbon neutral substitute and stabilize the soil.

Bio-Enzymatic Treatment of Expansive Black Cotton Soil Using TerraZyme and Fly Ash: Quantifying the Strength–Swelling Trade-off

Utkarsh . — 2026-08-11

Black Cotton Soil (BCS), prevalent across central India, poses severe geotechnical challenges owing to its high plasticity, low bearing capacity, and pronounced swelling behaviour. Fly ash and bio-enzyme stabilizers have each been shown to improve expansive soils, but the two have not previously been optimised sequentially on the same highly expansive soil, and the interaction between them has not been quantified. This study reports a three-phase laboratory programme on a CH black cotton soil (LL = 61%, PI = 38%, FSI = 66.67%). Phase 1 optimised the TerraZyme (TZ) dosage on untreated BCS; Phase 2 added Class-F fly ash (FA) at 10–40% by dry weight to the TZ-optimised soil; Phase 3 measured swelling magnitude and swelling pressure on the three key mixes. The replicate scheme is stated in full in Section 3.6: one specimen per mix per condition for UCS and CBR, and two for the swelling tests. Phase 1 identified 67 ml/m³ as the optimum TerraZyme dosage, raising Day-0 UCS from 117.44 to 838.24 kN/m² (7.1×), Day-7 UCS from 134.38 to 1205.43 kN/m² (9.0×), soaked CBR from 3.28% to 13.87% (4.2×) and unsoaked CBR from 13.42% to 16.24% (+21%), while reducing the plasticity index from 38% to 23%. Phase 2 identified 20% Class-F fly ash as the best-performing addition on strength and plasticity criteria, and Phase 3 confirmed that this mix reduced swelling pressure from 2.40 to 1.35 kg/cm² (−43.8%) and swelling magnitude by 50%. However, the fly ash addition was strongly antagonistic to bearing capacity: relative to the TerraZyme-only optimum the Day-7 UCS fell by 70%, and both the soaked (1.82–2.55%) and the unsoaked (6.37–9.12%) CBR of every TZ + FA mix fell below the corresponding values of the untreated soil. The combined mix is therefore not recommended as a load-bearing pavement subgrade. TerraZyme alone at 67 ml/m³ is the appropriate treatment where bearing capacity governs, whereas the TZ + 20% FA combination is suited only to applications in which volume stability governs and the treated layer is not required to carry traffic loading, such as expansive-soil cover or cushion layers, canal linings and non-structural fills. Quantifying and mechanistically explaining this strength–swelling antagonism, rather than recommending the combined mix, is the principal contribution of this study.

Effect of Backfill Stiffness on Minimising Settlement in Rail Bridge Approaches

Fang Dong — 2026-08-24

Non-uniform settlement at the interface between rigid bridge structures and adjacent embankments is a persistent problem in rail bridge approaches, degrading ride comfort, increasing maintenance costs, and, in severe cases, threatening operational safety. While backfill compressibility is widely recognised as a key contributor to this problem, quantitative guidance on how the elastic modulus of backfill materials governs the magnitude of differential settlement and displacement remains limited. This study addresses this gap using three-dimensional finite element (FE) analysis in Midas GTS NX to systematically investigate the influence of backfill elastic modulus, ranging from 25 MPa to 28,000 MPa, on the settlement and displacement behaviour of a jacked-frame-bridge rail approach. The soil was represented using a modified Mohr–Coulomb constitutive model calibrated with parameters derived from a geotechnical investigation report for a jacked frame bridge project in Shandong, China, while the backfill, subgrade, track and bridge structures were modelled as elastic materials. Static construction-stage analyses were performed to obtain the maximum vertical and horizontal displacements, together with the differential settlement and differential horizontal displacement across four monitoring sections spanning the bridge–embankment interface. The results show that increasing the backfill elastic modulus substantially reduces both differential settlement and maximum displacement, with the greatest improvement occurring within the 0–10,000 MPa range; beyond approximately 15,000 MPa, further increases yield only marginal benefit. The maximum vertical settlement decreased by 10%, the maximum ground heave by approximately 81%, and the differential horizontal displacement across the transition zone approached zero at high modulus values. These findings provide engineers with a quantitative basis for selecting backfill materials that balance mechanical performance against cost, and for identifying the elastic modulus threshold beyond which further material upgrades bring diminishing structural benefit.

A Critical Review on Enhancing Thermal Conductivity of Sandy Soils Using Nano Aluminum Oxide (Al₂O₃) under Different Moisture Conditions

Radhwan Abrahem — 2026-08-28

This review synthesizes up-to-date research on enhancing thermal conductivity in natural sandy soils, a key parameter for improving the utility of Ground Source Heat Pump (GSHP) systems and many geotechnical applications. The review is structured around four key research areas that capture the interdisciplinary context of this research. These areas of study include: the studies, which incorporate mineral and non-mineral synthetic additives into sandy soils to improve thermal connectivity and density with particle contact during loading; the other research area included moisture, which was found to improve thermal connectivity with particle contact, and therefore thermal transfer, when all air voids were filled; there were also studies that investigated the effects of nanomaterials, with a strong emphasis on nano aluminum oxide (Al₂O₃), that focused on mechanical properties for sandy soils, such as; strength, and cohesion. Al₂O₃ improved these properties of sandy soils which were factors indirectly assisting enhanced thermal pathways; and lastly, there are other studies that looked at the applications of Al₂O₃ as a heat transfer medium in nanofluids, and phase change materials (PCMs), which provide consistent improvements in thermal performance and superior thermal management. The challenge is that, while areas of investigation have been explored, substantial gaps remain in our understanding of how nano-Al₂O₃ and moisture variability interact to affect the thermal conductivity of sandy soils, particularly in tropical weather and conditions. This study discusses the gap identified above, addresses its applicability, and identifies potential experiments for future work.