Currently, several expressways in the Taklimakan Desert have adopted or plan to adopt geosynthetic-reinforced soil (GRS) retaining walls as embankments. However, the annual temperature variation in this desert environment reaches up to 60 degrees C, representing an environment with typical extreme temperature variations. To investigate the deformation characteristics of aeolian sand GRS retaining walls under these temperature variations, three sets of model tests were conducted under different loading conditions, and changes in the geogrid strain, horizontal facing displacement, and horizontal earth pressure behind the wall under cyclic temperature conditions were examined. The results show that cyclic temperature variations have a limited effect on the internal temperature field of aeolian sand-reinforced soil retaining walls away from the boundaries. The expansion and contraction characteristics of the modular blocks, geogrids, and aeolian sand under temperature changes cause thermal cycles to affect the horizontal facing displacement, geogrid strain, and horizontal earth pressure behind the wall, with all exhibiting regular fluctuations in response to ambient temperature. Owing to the restraint of horizontal displacement at the wall toe and the relatively high overall stiffness of the facing, the measured geogrid tensile loads are lower than the values calculated using the AASHTO/FHWA simplified method and the simplified stiffness method.
Expansive soils cause significant pavement distress due to seasonal swell-shrink behavior induced by moisture fluctuations. Unlike previous studies that focused on monotonic swelling, the present work evaluates long-term pavement response under repeated swell-shrink cycles simulating seasonal wetting-drying conditions. Accordingly, mitigation of swell-shrink deformation through modifications in pavement thickness and the use of geosynthetic reinforcement is investigated. Two pavement configurations with prepared subgrades of 250 mm and 500 mm thickness, placed above the existing subgrade, were evaluated under repeated uplift loading-unloading cycles applied through a circular plate over nine cycles to simulate differential swelling and shrinkage, inducing a maximum subgrade heave of 12.5 mm. A woven polyester geotextile (200 kN/m) and a biaxial polyester geogrid (200 kN/m) were installed at the interface between the existing subgrade and prepared subgrade layer. The results demonstrate that geosynthetic reinforcement enhances swell pressure resilience by restricting upward soil movement and redistributing swelling-induced stresses within the pavement system. The improvement was most pronounced in the thinner pavement section, where resilience increased by about 17%-18% during the first cycle and up to 20%-28% after repeated swell-shrink cycles.
Conventional vacuum preloading is widely used for dredged slurry treatment, but vacuum pressure loss often leads to inadequate bottom consolidation and uneven reinforcement. This study proposes a vacuum preloading method with top-bottom drainage and investigates its consolidation performance and the influence of time ratio (i.e. bottom-to-top vacuum application time) via laboratory model tests. Overall, the proposed method achieves better consolidation than conventional vacuum preloading, with higher drainage, larger settlement, lower post-treatment water content and improved vane shear strength of dredged slurry. Time ratio greatly affects consolidation efficiency, and the optimal ratio is 1:1. At this ratio, the proposed method raises the average vane shear strength by 14.4% and reduces post-treatment water content by 6.0% compared with conventional vacuum preloading. Results demonstrate that top-bottom drainage vacuum preloading enhances vacuum pressure uniformity, promotes water discharge, and achieves more effective and uniform consolidation of dredged slurry.
The paper describes a case of using geogrid-reinforced pile-supported (GRPS) embankments to control the differential settlement of bridge approaches. The results showed when the embankment height increased to 2.4 times the clear pile spacing, the soil arching effect fully developed. When the pile spacing increased from 2.5 m to 3 m, the weakening of the soil arching effect led to a 20% increase in the maximum subsoil displacement. Next, the influence of moving vehicle loads on the soil arch was studied using a three-dimensional finite element model of GRPS embankments. The study found that under moving vehicle load, the maximum vertical displacement at the bottom of the embankment increased by 6% to 9% compared with the static load. The maximum tensile force of the geogrid increased by 18% to 26% compared with the static load. Lastly, the influence of dynamic load parameters on the soil arching effect of GRPS embankments was analyzed. The results showed that changing from the half-sine load type to the sine load type increased the maximum vertical stress at the bottom of the embankment by 6%. The study also found that the vehicle wheel load was the most sensitive to the influence of geogrid tension.
The gradation characteristics of the granular subbase () layers play a crucial role in highway subsurface drainage. This study investigates the gradation effects on in-plane permeability of layers (kGSB) with and without drainage geocomposites (). Large-scale permeameter experiments were performed, using 12 different gradations and two types of GCs (Biaxial Geonet Geocomposite, and Triaxial Geonet Geocomposite, ) under standard traffic load. Densely-graded materials exhibited a lower in-plane permeability (kGSB similar to 5 m/day), which increased by ten-fold and 15-fold with and embedment, respectively. Openly-graded materials (kGSB > 750 m/day) showed a 18% and 35% enhancement with the embedment of and TGG, respectively. Traffic loading caused a 15% reduction in in-plane permeability. A suitability chart based on the time-to-drain approach was developed to ensure effective subsurface drainage. Furthermore, globally applicable condition-based empirical models, considering subbase gradations proposed by various transportation agencies, were proposed to estimate the permeability of GSBs with and without GCs. The findings highlighted that the GCs significantly enhanced permeability, particularly of densely graded materials. Additionally, a design example is presented to illustrate the effectiveness of highway subsurface drainage with installation.
