Shah, Syed Samran Ali (2024) Developing and Designing Sustainable Nature-based Solutions (NBS) for Mitigating Landslips. Doctoral thesis, University of West London.

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Abstract

In the UK, geohazards like landslides and soil erosion have a major negative influence on the economy and public safety. Traditional cement-based slope stabilisation is costly and harmful for the environment. Although nature-based solutions, such as vegetation and biopolymers, provide affordable substitutes, there are still issues determining how reliable and successful they will be in the long term for wide usage in slope stability assessments. This research aimed to develop, design, and evaluate the impact of plant-derived biopolymers and vegetation on soil and slope stability. The PhD research was structured into three distinct phases.
Phase 1 focused on the effects of controlled wetting and drying cycles (wd) on the
hydromechanical properties of clay and silty sand soils and their implications for the performance of typical flood embankments. Volumetric changes were monitored throughout
the wd cycles. Parameters measured included the soil water characteristic curve (SWCC), saturated hydraulic conductivity (ksat), effective cohesion (c′), and effective angle of internal friction (ϕ′) at both 1 and 10 wd cycles. The results indicated that the ten wd cycles reduced
saturated moisture content and produced a flatter SWCC compared to the single cycle for clayey soil. Additionally, ksat was significantly higher after ten cycles than after one for clayey soil, while no significant differences were observed in both SWCC and ksat for silty sand soil
across cycles. The effective angle of internal friction (ϕ′) for clayey soil decreased from 28.5 to 20.1 as the wd cycles increased from one to ten, while the effective cohesion (c′) remained constant at 10 kN/m². In contrast, for silty sand soil, ϕ′ increased from 34.6 to 37.5 with the increase in wetting and drying cycles, with c′ remaining constant at 1 kN/m². Numerical modelling of transient water flow, coupled with slope stability analysis, highlighted that the
performance of flood embankments depends on the soil's hydromechanical properties and the duration of flooding. These findings underscore the necessity for proactive measures to mitigate landslide risks in regions subject to frequent wetting and drying cycles for clayey soil, thereby ensuring the safety and resilience of slopes and associated infrastructure.
Phase 2 of the research investigated the effects of biopolymers derived from chia and basil seeds on the hydromechanical characteristics of clayey and silty sand soils under conditions of one and ten wetting and drying cycles at two different temperatures (25°C and 40°C).
Volumetric changes and water drop penetration time (WDPT) were assessed from one to ten cycles after each cycle. The SWCC, ksat, c' and ϕ' were measured after both 1 and 10 wd cycles.
The findings demonstrated that the application of biopolymers significantly increased soil stability and strength, particularly in clayey soil, where marked improvements in effective cohesion and angle of internal friction were observed. The basil seed-based biopolymer
outperformed the chia seed-based variant. Similar enhancements were noted in silty sand soils treated with these biopolymers, particularly in the effective angle of internal friction. Both seed-based biopolymers increased soil water repellency and retention regardless of soil type.
These results underscore the capacity of chia and basil seed-based biopolymers to enhance soil strength, presenting a nature based and environmentally friendly strategy for proactive landslide risk mitigation in areas experiencing frequent wd cycles, thus ensuring the resilience
and safety of slopes and related infrastructure.
In the third phase, the ability of Bermuda grass (Cynodon dactylon) to enhance the stability of clay and silty sand soils at varying depths was examined. Consolidated drained (CD) direct shear tests were conducted on soil samples with and without grass reinforcement at depths of 0–10 cm, 10–20 cm, and 40–50 cm to evaluate the impact of grassroots on soil stability. The roots of Bermuda grass markedly improved soil shear strength and, thus, stability, further
demonstrating the potential of vegetation in slope stabilisation practices. X-ray computed tomography was employed to conduct a detailed scan of soil columns with and without Bermuda grass. This analysis aimed to quantify the root systems present and assess theirinfluence on soil pore structure.
Overall, the study highlighted how NBS, such as vegetation and seed-derived biopolymers, can improve soil stability in climate change scenarios, resulting in more resilient infrastructure in areas vulnerable to erosion and landslides.

Item Type:	Thesis (Doctoral)
Identifier:	10.36828/thesis/13414
Subjects:	Construction and engineering > Civil and environmental engineering
Depositing User:	Marc Forster
Date Deposited:	02 Apr 2025 09:46
Last Modified:	02 Apr 2025 10:00
URI:	https://repository.uwl.ac.uk/id/eprint/13414

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