Geotextile filters have gained extensive applications in geotechnical and geoenvironmental drainage systems. Despite of the abundant research about geotextiles filtering coarse-grained soils, there is little experimental study on the performance of geotextiles filtering fine-grained soils. Since clogging and blinding of geotextiles are more likely to occur in clayey soils, a complex filtration performance of the filters is expected, posing great challenges to the long-term durability of the filtration system. In this research, long-term permeability tests were conducted on silty clay filtrated by three types of nonwoven needle-punched geotextiles. Comprehensive results regarding the permeability evolution, soil retention and clogging behavior were obtained. Interior clogging behavior of the geotextile was checked after the tests by means of scanning electron microscopy. Significant reduction around two orders of magnitude from 10⁻⁸ m/s to 10⁻¹⁰ m/s was observed in the permeability coefficient of the silty clay-geotextile system after 90 days of seepage flow. The influence of filtration opening size of the geotextile was obviously noticed in the initial permeation process, while the thickness played an increasingly important role at the later stage. Geotextile with the larger thickness and smaller filtration opening size had more soil retention and poorer filtration performance. In addition, a theoretical equation relating permeability coefficient and filtration opening size of nonwoven geotextile under clogged condition was proposed.

To avoid serious clogging and loss of drainage capacity, which puts the underground structure at risk of anti-floating failure, the buried drainage filter must be equipped with a nonwoven geotextile layer. In this scenario, nonwoven geotextiles are subjected to normal compressive stress, which can cause changes in geotextile porosity and structure, affecting the filtration behavior of the geotextile filter. In this paper, in order to evaluate the filtration compatibility of the soil–geotextile system, gradient ratio (GR) tests were performed under a hydraulic gradient of 1.0 using a specially designed gradient ratio filtration device capable of applying normal stress. In total four nonwoven geotextiles and two types of soil were used. The results of the gradient ratio filtration tests were discussed in terms of GR values, the permeability of the soil–geotextile system, and the amount of fines retained in geotextiles. It was shown that under a larger normal compressive stress, the GR value would also increase, while the permeability coefficient of the soil–geotextile system decreased. The filtration responses to various soil–geotextile combinations differed under normal compressive stress. A thick nonwoven geotextile with a small filtration opening size exhibited poor filtration performance while benefiting soil retention. Fines retention was influenced by geotextile thickness, soil type, and normal compressive stress magnitude. In addition, for nonwoven geotextiles filter fine-grained soil under normal compressive stress, the test results indicated that anticlogging design criteria should be improved.

Nonwoven geotextiles are commonly utilized as filter materials in drainage and filtration engineering. This study focuses on the clogging phenomenon of the nonwoven geotextile filter wrapping the blind drain in the active anti-floating technology of underground structures. In this paper, the filtration compatibility of clay-nonwoven geotextiles was evaluated using a newly developed gradient ratio test device that can apply normal stress. Two fabrication technics and four specifications of nonwoven geotextiles were used to filter clay, and the geotextiles’ clogging degree was assessed after the test. The influences of normal stresses, hydraulic gradients, and fabrication technics on nonwoven geotextile filtration performance were discussed based on results from a series of gradient ratio tests. Relevant assessment parameters (clogging coefficient, soil retention, and equivalent porosity) were also presented to quantify the clogging degree of nonwoven geotextiles after the test. Furthermore, the clogging process of nonwoven geotextiles filtering clay was initially explored, and the filtration effect of the needle-punched and heat-bonded nonwoven geotextiles was evaluated. The results showed that normal stress had a significant effect on nonwoven geotextile filtration, with needle-punched nonwoven geotextiles having better soil filtration and water permeability. Discussions on nonwoven geotextile applications in specific environments or conditions are also presented.

The utilization of treated dredged sludge as a partial replacement for natural sand and gravel in construction projects offers a promising approach to reducing the exploitation of natural resources. The conventional vacuum preloading (VP) method, while widely used for soft soil improvement, is often associated with prolonged consolidation periods and high energy consumption in its later stages. Conversely, the electroosmosis (EO) technique is effective in enhancing drainage in low-permeability soft clays but is constrained by issues including anode corrosion, high operational costs, and uneven soil reinforcement. This study presents an experimental investigation into an alternating vacuum preloading and electroosmosis method for sludge treatment based on the underlying reinforcement theory. A series of laboratory model tests was conducted using a self-made vacuum–electroosmosis alternating test device. The reinforcement efficiency was assessed through the continuous monitoring of key performance indicators during the tests, including water discharge, surface settlement, electric current, electrode corrosion, and energy consumption. Post-test evaluations of the final soil shear strength and moisture content were also performed. The test results demonstrate that the alternating vacuum–electroosmosis yielded more significant improvement than their synchronous application. Specifically, the alternating vacuum–electroosmosis increased total water discharge by 46.1%, reduced final moisture content by 20.8%, and enhanced shear strength by 35.6% relative to the synchronous mode. Furthermore, an alternating VP-EO mode was found to be particularly advantageous during the electroosmosis phases, facilitating a more stable and sustained dewatering process. In contrast, the application of vacuum preloading alone resulted in inefficient performance during the later stages, coupled with relatively high energy consumption.

The selection of a preferred foundation pit support design involves a rigorous comparative analysis of alternatives against specific performance metrics. When advanced designs incorporate material behaviors not codified in standard specifications, numerical simulation becomes indispensable for capturing the associated performance data. This study establishes a performance evaluation framework predicated on numerical simulations that integrate specialized constitutive models while complying with fundamental design codes. Leveraging a damage plasticity model for accurate material representation, the methodology is demonstrated through a case study of soil-mixing wall support schemes. Six distinct configurations, comprising variations in pile diameter and the spatial layout of embedded H-piles, are assessed using a multi-indicator framework, including shallow soil plastic strain, wall plastic damage, steel displacement, deflection curvature, and ground surface settlement. These indicators, often inaccessible via conventional analytical methods, are quantified through numerical analysis. A systematic comparison of the results facilitates the identification of a preferred design that reconciles engineering economy with safety constraints. The efficacy of the proposed simulation-based comparative assessment approach is further quantitatively consistent with subsequent construction monitoring data. It is noted that the total stress method is adopted throughout the analysis, wherein groundwater effects, including phreatic water, micro-pressurized water, and dewatering, are incorporated implicitly via adjusted soil unit weights rather than explicit pore pressure calculations. This treatment is justified by the relatively short construction duration compared to the consolidation time scale of the soft clay deposits, rendering undrained conditions a reasonable approximation for the serviceability-oriented performance assessment presented herein.