Geotextiles and Geomembranes最新文献

Hydraulic conductivity tests were conducted on six bentonite-polymer (B–P) geosynthetic clay liners (GCLs) to investigate the effect of the slow cation exchange process and polymer elution on the long-term hydraulic conductivity of B–P GCLs. Tests were conducted up to 1458 days and as many as 443 pore volumes of flows (PVFs). Three B–P GCLs consist of linear polymer whereas the other three have crosslinked polymer. One sodium geosynthetic clay liner (Na–B GCL) was used as a control. Hydraulic conductivities (K₆₇₆₆) of B–P GCLs (5.4 × 10⁻¹² m/s to 3.7 × 10⁻¹¹ m/s) per ASTM D6766 were approximately 2-3 orders of magnitude lower than that of Na–B GCL (2.3 × 10⁻⁹ m/s to 3.5 × 10⁻⁹ m/s). Tests were continued after hydraulic and chemical equilibrium to investigate the long-term hydraulic conductivity of GCLs. Hydraulic conductivities of GCLs had an increasing trend after hydraulic and chemical equilibrium. The ratio of K_L/K₆₇₆₆ for B–P GCLs was 3.5–14.7, whereas ratio of K_L/K₆₇₆₆ for Na–B GCLs was 1.0–1.7. Total organic carbon (TOC) tests results confirmed that polymer elution occurred during the entire permeation process. The higher ratio of K_L/K₆₇₆₆ for B–P GCLs was attributed to the effect of polymer elution.

Results from seven years of electrical leak location methods applied to geomembrane-lined ponds to locate leaks are presented. Inspections were conducted on 195 projects designed with single (n = 74), double (n = 120), or triple (n = 1) liners. These projects are located in the U.S.A. (n = 159), Canada (n = 30), and Mexico (n = 11). All inspections were conducted on full ponds, which resulted in the detection and repair of 1230 leaks during the study period across an analyzed area of 322 ha. From 2015 to 2021, the average was 14 leaks/ha, with values ranging from 0 to 689 leaks/ha. The results reveal that larger inspected areas (greater than 2 ha) tend to have fewer leaks. 63% of projects had up to 5 leaks/ha. 15% of projects had more than 20 leaks/ha. The results of this study could influence landfill designers, operators, and environmental agencies in defining new practices for designing and operating geomembrane-lined ponds.

Designing geosynthetics for asphalt overlay is challenging due to the diversity of paving composites and paving geogrids available on the market. Challenges remains on the ideal product and tack coat to avoid debonding failure and to increase bonding quality. This research evaluates interface shear strength properties of geosynthetic-asphalt concrete specimens using seven geosynthetic interlayers tested under different tack coat rates based on asphalt retention of geosynthetics. Leutner shear tests were conducted on laboratory-prepared asphalt concrete specimens under different interface combinations. Index asphalt retention of paving geosynthetics depended on various parameters including geosynthetics type, geotextile backing, thickness and coating. The study suggests 100% of asphalt retention of the composite as design tack rate for paving geocomposites and paving geogrid composites with permanent porous fabric backing, while 220% asphalt retention as tack coat rate is suggested for geogrids. The optimum tack coat for reinforcement composites with light fabric backing falls between the optimum tack coat rates for composites and grids. The study also showed that the interface shear bond is a complex property and is not necessarily related to the fabric backing being permanent or temporary, the mass of the fabric backing, and the geosynthetics coating type and bitumen content individually.

This paper presents a comprehensive three-dimensional numerical investigation of horizontal square anchors embedded in geogrid-reinforced sand. Prior experimental studies have demonstrated notable enhancements in anchor uplift capacity when placed below geogrid reinforcement in soil. However, these results are limited to small anchor plates tested in laboratory conditions with over-reinforced sand. In contrast, this study focuses on large field-scale anchors and explores the influence of anchor width, embedment depth, reinforcement size, stiffness, and tensile strength on uplift capacity. The findings reveal that the optimal size for geogrid reinforcement is three times the anchor width. A diminishing improvement in uplift capacity with increasing anchor width was observed. Additionally, deeper anchor embedment reduces the uplift capacity improvement in geogrid-reinforced sand. The geogrid reinforcement is found to be more efficient in the case of shallow anchors placed in loose sand. The major contribution of this paper lies in the response analysis of large anchors and providing a better understanding of the uplift mechanism in geogrid-reinforced sand.

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, K_d ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses.

A new type of small, dry-filled geotextile tubes is introduced, that, in a stacked formation, can be used as dike cores. Dikes made out of these tubes consist of great potential regarding more resilient flood protection. The geotextile protects the fill from erosion, enabling steeper slopes along with reduced material and less land consumption. The behavior and potential failure mechanisms of such dikes were investigated first by literature research and second by full-scale hydraulic model tests under systematic variation of tube number, number of textile layers, filling ratio, and fill material. The tubes were exposed to the loads of seepage and overflow. Most relevant failure mechanisms were seepage-induced sagging, lateral displacement, and overturning of the upper tube due to overflow. During seepage, the tube height was reduced by up to 22.8 % due to sagging. Overflow led to a lateral displacement of up to 13 cm and, at overflow heights of 23.1 cm and 26.8 cm, to overturning of the upper tube. The present results give new insights into the behavior of innovatively constructed geotextile tubes under hydraulic loads and serve as basis for the development of design rules.

To enhance the mechanical properties and stability of desert railway embankments, the utilization of geogrids has proven to be an effective measure. The article conducted field tests and discrete element simulations to thoroughly examine the static performance of embankments reinforced with geogrids. The study systematically explored the macroscopic and microscopic characteristics of the geogrid-reinforced embankment under static loading. Various factors were investigated, including the horizontal laying arrangements and depth to the top layer of the geogrid, as well as key design parameters such as the number of geogrid layers, geogrid width, and vertical spacing between geogrid layers. The findings indicate a progressive enhancement in the ultimate bearing capacity of the embankment with an increase in both the number of geogrid layers and the geogrid width. Conversely, there is a decrease in ultimate bearing capacity as the depth to the top layer increases. In comparison to unreinforced embankments, reinforced embankments exhibit a reduced contact anisotropy, signifying that the geogrid effectively disperses static loads, resulting in a more uniform contact distribution. The geogrid restrains both displacement and rotation of the aeolian sand, and this restraining effect progressively strengthens with an increase in the number of geogrid layers or the geogrid width. The research findings can serve as a reference for the design and application of aeolian sand railway embankments.

The anisotropic effective stiffness matrix (ESM) of the unit cell (UC) of a geocell layer with different laying modes (denoted by θ), which cannot be measured directly by conventional tests but can be obtained by the mathematical homogenization method (MHM) on the UC of the geocell layer, is needed in simulation and design of geocell reinforced embankment. The components of the ESM are divided into two independent parts based on whether they depend on θ. Compared with the direct numerical simulation (DNS), the homogenized numerical simulation (HNS) of the embankment with the ESM reduced the calculation cost, and the settlement loading curves were in good agreement with the test curves. By analyzing the results of HNS, it was found that (1) the vertical stress diffusion effect is independent on θ, (2) the membrane effect is dependent on θ, and (3) two aspects of the lateral resistance effect were verified.

To improve the defects of low electroosmosis efficiency in the later stage and high energy consumption of conventional vacuum preloading combined with electroosmosis, the vacuum preloading-stepped electroosmosis method (VP-SEO) with prefabricated horizontal drain (PHD) was proposed for dredged sludge in this paper. In the test, waste concrete fine aggregate was used as the horizontal drainage cushion to alleviate the clogging of the PHD. The results showed that compared to vacuum preloading combined with electroosmosis (VP-EO), more drainage channels throughout the soil were produced after VP-SEO treatment, and VP-SEO could maintain a higher drainage efficiency in the later stage of treatment with improved final drainage and consolidation. The sludge treated by VP-SEO showed a significant increase in vane shear strength and a reduction in water content. Furthermore, the water loss and shrinkage of the soil surface after VP-SEO treatment were more uniform than that of VP-EO treatment, and the electroosmotic energy consumption and anode erosion were also lower. This study provides an effective improvement scheme for solidifying sludge with a high water content by conventional vacuum preloading combined with electroosmosis method.

Prefabricated horizontal drains and vacuum preloading have advantages in the consolidation of ultra-soft dredged sludge and soils for maintenance dredging, reclamation, and ground improvement in coastal regions. While laboratory tests and field trial projects have been reported, a convenient analysis and design method is still unavailable. This study proposes a new simple method for the settlement analysis of soft soils considering horizontal drains, vacuum preloading, creep, and large-strain effects. A unified equation is constructed to account for various layouts of horizontal drains in consolidation. A new explicit method is developed to consider the large-strain deformation with the nonlinear evolution of permeability and compressibility of ultra-soft soils under vacuum preloading. The viscous compression is taken into account using a simplified Hypothesis B method. The proposed solution also facilitates convenient consideration of multiple layers of soils and drains subjected to staged loading. The proposed method is examined by a series of physical model tests with different horizontal drain dimensions. Finally, the method is applied in the analysis of two well-documented field cases in Hong Kong and Japan, which confirms its effectiveness and accuracy.