Raising of the Mangla Dam in Pakistan submerged about 15,780 acres of land, resulting in the relocation of 8020 inhabitants to a newly developed town named New City. The new site, consisting of 1300 acres, is in the sub-tropical zone and comprises badland topography. The parent soils (Siwalik clay) pose infrastructure serviceability issues, causing immense loss to property. The study aims to improve the properties of Siwalik clay (base soil) using industrial wastes like marble and glass powders (5 to 20%) and polypropylene fibers (0.25 to 1.25%) as modifiers. Laboratory tests including grain size distribution, Atterberg limits, standard Proctor compaction, unconfined compression, indirect tensile strength, swell potential, and California bearing ratio were conducted on the control and modified clay samples. The results showed that unconfined compressive strength (UCS) and swelling strains (SS) were increased by 43% and 8% at 1.57 kPa pressure with 15% replacement of marble powder. However, the addition of the 20% glass powder and 0.5% polypropylene fibers not only improved UCS by 110% and 39%, but also reduced SS by 27% and 86%, respectively. The capital construction cost of 1 km long road with modified subgrade using 15% glass powder was reduced by 16% whereas it increased for marble powder and polypropylene fibers by 22% and 17%, respectively. All modifiers had very low hazard to adjoining aqueous environment. Conclusively, glass powder and polypropylene fibers can be used as environmentally-friendly soil improvement modifiers, leading towards sustainable solutions of the serviceability problems.

The current research has been carried out to investigate the interactive behaviour of soil-geosynthetic interfaces. A cost-effective vertical pullout test (VPT) apparatus was designed for this purpose. A series of laboratory direct shear tests (DSTs) and vertical pullout tests (VPT) were carried out using three types of sands and four different types of geosynthetics. All three sandy samples used in this research were classified as poorly graded sand (SP) as per the Unified Soil Classification System (USCS) with median grain size ranging between 0.39~0.2 mm. The geosynthetics used were three woven and one non-woven with a tensile force of 3.3 kN/m~103.8 kN/m. The direct shear test revealed that geometric properties of geosynthetics have an influence on interface shear resistance. Interface friction angle varies between 29.2~38.3. Vertical pullout (VPT) test results show that the pullout force is in the range of 23.9~31.4. The interface friction angle by both direct and vertical pullout tests is more for coarse-grained soils than for fine-grained soils. Interface friction angles from pullout tests were around 19% smaller than direct shear tests. The interface efficiency ranged from 0.69 to 0.97 for all soils; meanwhile, for non-woven geotextiles, the efficiency values are up to 22% higher as compared to woven geotextiles due to theirtexture. The present research indicates that interface friction parameters can be efficiently determined through the interface of a cost-effective VPT which is also comparable with DST. The reliable values of interface efficiency can be obtained for soil-geosynthetic interfaces which can optimize the design and omits the need forassumed conservative values of friction parameters.

The study aims to evaluate the change in the behavior of sub-base materials being used in road pavements through blending fines of different types in different amounts. Fines are added in aggregate samples as part of gradations proposed by the American Association for State and Highway Transportation Official (AASHTO). Composite samples conforming to AASHTO gradations B and C were prepared by mixing coarse aggregates in varying proportions, ranging from 0 to 15%. Laboratory tests—including aggregate quality tests (abrasion test, flakiness index and elongation Index), physical tests (particle size analysis and specific gravity), and strength test (modified Proctor, California bearing ratio, and permeability test)—were performed on the control as well as the modified samples. It was observed that the material with 0% fines yielded the highest CBR values (greater than 98%) and coefficient of permeability of 4.4 × 10⁻⁴ cm/s. However, with the increasing of the fines up to 15%, a substantial reduction in CBR value up to 10% and coefficient of permeability to 1.62 × 10⁻⁷ cm/s was noticed. Based on these results, the modulus of rigidity (M_R) and the corresponding structural numbers were determined for each layer. Conclusively, the required thickness of the base course was increased from 11 cm for the samples with 0% fines to 24 cm (118%) for the samples with the addition of 15% fines according to the AASHTO Design method.

This research examines the mechanical enhancement of earthen mortar through the combined use of cow dung (CD) and sawdust (SD) as biodegradable stabilisers, aiming to develop a structurally reliable and low-carbon alternative to conventional binders. Stabiliser contents ranging from 2.5% to 10% were incorporated into a locally sourced clayey soil, followed by a comprehensive evaluation of fresh and hardened density, unconfined compressive strength, split-tensile strength, flexural capacity, and derived undrained shear strength. The test results show that the CD-SD blend significantly improves mechanical performance, with compressive strength increasing by approximately 40% at 7.5% stabiliser content and tensile strength, and nearly doubling at 10% addition. Flexural strength exhibited a parallel rise of 68% relative to the untreated mix. These improvements are linked to the formation of cementitious reaction products from cow-dung ash, enhanced particle adhesion, and the micro-reinforcing role of SD fibres, which collectively reduce crack formation and increase the material’s resistance to tensile and bending stresses. Concurrently, fresh and hardened densities decreased by 14–21%, producing a lightweight composite without compromising structural reliability. The findings identify an optimum stabiliser range of 7.5–10%, balancing strength enhancement with desirable density reduction. Overall, the study confirms that CD-SD stabilisation provides a feasible, cost-effective, and environmentally responsible approach for improving earthen mortars, offering substantial potential for sustainable construction in regions where low-carbon and locally available materials are essential.