Periodic Reporting for period 1 - BALANCE (Biopolymer combine with vegetAtion soiL treAtmeNt for stabilisation of transport infrastruCture Earthworks)
Période du rapport: 2023-01-01 au 2025-12-31
Safe, efficient and secure transport infrastructure is a fundamental requirement to facilitate and encourage the movement of goods and people throughout not only the EU but the whole world. The performance of these networks is critically dependent on the function of cutting and embankment slopes. Many of these transport earthworks in Europe were constructed over 100 years ago, and not designed to today’s vehicle speed, frequency and weather conditions. The long-term intensive dynamic loads generated from the moving vehicles combine with the severe wet-dry weather conditions induced by the Climate Change, increase the likelihood of transport infrastructure earthwork failures, lead to costly disruption of road and rail journeys, with risk to life and property. EU’s leading position in achieving the 2030 goal for sustainable development emphasises the urgency to develop a low-carbon, and sustainable engineering solution that not only can increase resilience and protect vital transport earthworks, but also to reduce the impact on the ecosystems and restore the soil organic carbon loss caused by human activities. The conventional engineering orientated solution alone is insufficient to solve the problem. Therefore, this fellowship leverages traditional soil mechanics with soil science through new insightful numerical modelling, UQ analysis, laboratory and field tests to advance the slope bioengineering method (SBM) by utilizing biopolymer and vegetation together for the reinforcement. This technique is an aesthetically-pleasing, environmentally- and ecologically-friendly alternative to the traditional "hard" engineering methods, which provides additional environmental and societal benefits of carbon fixation, enhanced biodiversity and ecosystem restoration within the built environment. The knowledge and tools from this project will be potentially utilized in other areas, e.g. river bank, sand dunes, flood embankments management, and agricultural and amenity systems.
The effects of six different biopolymers – xanthan gum, sodium alginate, cationic guar gum, chitosan, agar gum, and carrageenan – on the fundamental physical properties, compressibility, permeability, and shear strength of clay were thoroughly investigated. Simultaneously, the study delved into the durability of the modified clay under drying-wetting cycles, aiming to assess its prospective applications in practical engineering contexts. The work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far of this research are summarized as follows:
Analysis of Biopolymer Influence: The research extensively analyzed the impact of various biopolymers on the fundamental physical and chemical properties of clay. This involved a detailed examination of the biopolymer dosage's effects on the boundary water content, pH value, and specific gravity of the modified clay.
Study on Shear Strength, Compressibility, and Permeability: The study meticulously explored the undrained shear strength, compressibility, and permeability of biopolymer-modified clay. The influence of biopolymer modification on the undrained shear strength was investigated through a falling cone test. Additionally, employing a one-dimensional consolidation-permeability joint test, the study delved into the biopolymers' impact on the yield stress, compression index, and coefficient of permeability of the clay. The outcomes highlighted an enhancement in undrained shear strength alongside a reduction in the compressibility and permeability of the modified clay.
Microstructural Analysis: The research conducted an in-depth analysis of the biopolymer's effect on the microstructure of clay. This involved utilizing Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) to scrutinize the microstructure and modification mechanism of the biopolymer-modified clay. The findings revealed a decrease in pore diameter and total pore volume in the biopolymer-modified clay.
Durability and Stability Assessment: The study comprehensively assessed the durability and stability of biopolymer-modified clay under drying-wetting cycles. Through a series of drying-wetting cycle tests, the research analyzed crack development and shear strength concerning varying dosages and cycle repetitions. Notably, the results indicated a reduction in the crack rate of modified clay with an increase in the drying-wetting cycle repetitions, coupled with a significant improvement in its shear strength. Furthermore, finite element numerical simulations illustrated a reduction in the displacement of biopolymer-modified slopes, accompanied by an enhancement in the safety factor of the modified slope. These findings provide valuable insights for evaluating the application potential of biopolymers in practical engineering scenarios.
Analysis of Biopolymer Influence: The research extensively analyzed the impact of various biopolymers on the fundamental physical and chemical properties of clay. This involved a detailed examination of the biopolymer dosage's effects on the boundary water content, pH value, and specific gravity of the modified clay.
Study on Shear Strength, Compressibility, and Permeability: The study meticulously explored the undrained shear strength, compressibility, and permeability of biopolymer-modified clay. The influence of biopolymer modification on the undrained shear strength was investigated through a falling cone test. Additionally, employing a one-dimensional consolidation-permeability joint test, the study delved into the biopolymers' impact on the yield stress, compression index, and coefficient of permeability of the clay. The outcomes highlighted an enhancement in undrained shear strength alongside a reduction in the compressibility and permeability of the modified clay.
Microstructural Analysis: The research conducted an in-depth analysis of the biopolymer's effect on the microstructure of clay. This involved utilizing Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) to scrutinize the microstructure and modification mechanism of the biopolymer-modified clay. The findings revealed a decrease in pore diameter and total pore volume in the biopolymer-modified clay.
Durability and Stability Assessment: The study comprehensively assessed the durability and stability of biopolymer-modified clay under drying-wetting cycles. Through a series of drying-wetting cycle tests, the research analyzed crack development and shear strength concerning varying dosages and cycle repetitions. Notably, the results indicated a reduction in the crack rate of modified clay with an increase in the drying-wetting cycle repetitions, coupled with a significant improvement in its shear strength. Furthermore, finite element numerical simulations illustrated a reduction in the displacement of biopolymer-modified slopes, accompanied by an enhancement in the safety factor of the modified slope. These findings provide valuable insights for evaluating the application potential of biopolymers in practical engineering scenarios.
Through the conducted research, several significant conclusions have been drawn:
Clay Polymer Network Formation: The interaction between biopolymers and clay particles results in the formation of a clay polymer network structure. This structure significantly reduces the compressibility of the sludge, with xanthan gum exhibiting the most prominent effect among the polymers utilized in the experiment. As the dosage of biopolymer increases, the structural yield stress of the modified sludge also increases, leading to a reduction in its compressibility.
Effect on Compression Index: The vertical effective stress significantly influences the compression index of the modified sludge. With increasing dosage, the compression index of the modified sludge further escalates. Notably, surpassing a specific threshold dosage (0.5% for xanthan gum, 1% for sodium alginate and cationic guar gum) results in the modified sludge having a higher compression index compared to the remolded sludge.
Impact on Permeability: Biopolymers exert a blocking effect on soil pores, causing a substantial decrease in sludge permeability. The permeability coefficient of the modified sludge diminishes as the biopolymer dosage increases. Xanthan gum, in particular, exhibits a remarkable effect, reducing soil permeability by two orders of magnitude at a dosage of 1.5%.
Pore Size Distribution: The primary pore size distribution of biopolymer-modified sludge ranges from 0.01 to 1 μm. With increasing content, the total pore volume decreases progressively.
These conclusions provide a comprehensive understanding of the properties of biopolymer-modified sludge. Further research endeavors will aim to develop corresponding design specifications based on these findings.
Clay Polymer Network Formation: The interaction between biopolymers and clay particles results in the formation of a clay polymer network structure. This structure significantly reduces the compressibility of the sludge, with xanthan gum exhibiting the most prominent effect among the polymers utilized in the experiment. As the dosage of biopolymer increases, the structural yield stress of the modified sludge also increases, leading to a reduction in its compressibility.
Effect on Compression Index: The vertical effective stress significantly influences the compression index of the modified sludge. With increasing dosage, the compression index of the modified sludge further escalates. Notably, surpassing a specific threshold dosage (0.5% for xanthan gum, 1% for sodium alginate and cationic guar gum) results in the modified sludge having a higher compression index compared to the remolded sludge.
Impact on Permeability: Biopolymers exert a blocking effect on soil pores, causing a substantial decrease in sludge permeability. The permeability coefficient of the modified sludge diminishes as the biopolymer dosage increases. Xanthan gum, in particular, exhibits a remarkable effect, reducing soil permeability by two orders of magnitude at a dosage of 1.5%.
Pore Size Distribution: The primary pore size distribution of biopolymer-modified sludge ranges from 0.01 to 1 μm. With increasing content, the total pore volume decreases progressively.
These conclusions provide a comprehensive understanding of the properties of biopolymer-modified sludge. Further research endeavors will aim to develop corresponding design specifications based on these findings.