Analysis of the Working Performance of a Back-to-Back Geosynthetic-Reinforced Soil Wall

Back-to-back geosynthetic-reinforced soil walls (BBGRSWs) are commonly used in embankments approaching bridges and narrow spaces. However, the available literature and design guidelines for BBGRSWs are limited. The aims of this research were to develop a greater understanding of the working performance of BBGRSWs and to optimize the design method of a BBGRSW to ensure the cost-efficiency as well as the stability of the structure. On the basis of a monitored BBGRSW structure located in China, we established a numerical model. The parameters of the materials used in the actual project were determined through triaxial and tensile tests. The numerical results were compared with the measured results in the field to verify the correctness of the selected parameters. Two parameters were investigated by the FEM method: the reinforcement length and the arrangement. The FEM analysis indicated that post-construction deformations such as displacement and settlement could be reduced by reinforcing the same layer on both sides. Longer reinforcements were needed to achieve the same performance if the reinforcements were cross-arranged. Thus, BBGRSWs can have a superior performance if the reinforcements are connected in the middle from both sides. Even with longer reinforcements, the safety factor of the wall with a cross-arranged reinforcement was smaller than that with same-layered reinforcements.

Subsurface organic amendment with plastic film mulching reinforced soil organic carbon through altering saline soil aggregate structure and regulating fungal community

The combination of plastic film mulching and subsurface organic amendment is a novel strategy for saline soil amelioration and utilization in China. However, how the strategy affect soil organic carbon (SOC) contents directly and indirectly (physical protection and microbiological regulation) were still not-documented. Therefore, four treatments, i.e., no amendment with and without plastic film mulching, subsurface (10-30 cm soil depth) organic amendment with and without plastic film mulching, were arranged and sampled after three-year filed experiment. Compared with no amendment with and without plastic film mulching, subsurface organic amendment increased the SOC content in the 0-40 cm soil depth by 70% and 90%, respectively. Plastic film mulching decreased SOC by 16% without organic amendment. Subsurface organic amendment transformed the dominant aggregation particles from <0.053 mm to 0.25-2 mm, indicating that both direct carbon input and indirect physical protection contributed to SOC increment. Conversely, SOC decreased with plastic film mulching due to the 14% lower fungal diversity compared with soil without plastic film mulching, was supported by the positive path coefficient from fungal diversity to SOC. Therefore, the combination of plastic film mulching and subsurface organic amendment increased SOC by 61% by direct carbon input and indirect physical protection and microbial regulation. In conclusion, subsurface organic amendment with plastic film mulching reinforced soil organic carbon increment through altering saline soil aggregate structure and regulating fungal community, and confirmed it is a feasible way to increase SOC for saline soil amelioration.

Modelling of stress transfer in root-reinforced soils informed by four-dimensional X-ray computed tomography and digital volume correlation data

Vegetation enhances soil shearing resistance through water uptake and root reinforcement. Analytical models for soils reinforced with roots rely on input parameters that are difficult to measure, leading to widely varying predictions of behaviour. The opaque heterogeneous nature of rooted soils results in complex soil–root interaction mechanisms that cannot easily be quantified. The authors measured, for the first time, the shear resistance and deformations of fallow, willow-rooted and gorse-rooted soils during direct shear using X-ray computed tomography and digital volume correlation. Both species caused an increase in shear zone thickness, both initially and as shear progressed. Shear zone thickness peaked at up to 35 mm, often close to the thickest roots and towards the centre of the column. Root extension during shear was 10–30% less than the tri-linear root profile assumed in a Waldron-type model, owing to root curvature. Root analogues used to explore the root–soil interface behaviour suggested that root lateral branches play an important role in anchoring the roots. The Waldron-type model was modified to incorporate non-uniform shear zone thickness and growth, and accurately predicted the observed, up to sevenfold, increase in shear resistance of root-reinforced soil.