Experimental Study on Geocell-Reinforced Bases under Static and Dynamic Loading

Abstract

Geocells are a three-dimensional honeycomb type of geosynthetics used to reinforce weak soils and base courses of roads since the 1970s. However, this technology has been hindered by the lack of a reliable design method. The development of a reliable design method requires in-depth understanding of the geocell reinforcement mechanisms. In this study, laboratory model and full-scale moving wheel tests were conducted on geocell-reinforced granular bases over weak subgrade. Plate loading tests were conducted in the medium-scale and large-scale geotechnical boxes at the University of Kansas and full-scale moving wheel tests were conducted in the accelerated pavement testing facility at Kansas State University. Four types of geocells including one high-density polyethylene (HDPE) and three novel polymeric alloy (NPA) geocells were tested in the medium-scale plate loading tests. The effects of geocell confinement and other influence factors on the behavior of granular bases were studied. One selected type of NPA geocell was used in the large-scale cyclic plate loading tests and the moving wheel tests. The subgrade used in the large-scale plate loading tests was an artificial mix of Kansas River sand and kaolin while A-7-6 clay was used in the moving wheel tests. Four types of infill materials including crushed limestone aggregate (AB-3), quarry waste (QW), Kansas River (KR) sand, and Recycled Asphalt Pavement (RAP) were used as the base courses in this study. More than 50 medium-scale plate loading tests, 12 large-scale cyclic plate loading tests, and 4 moving wheel tests on unpaved road sections were conducted. The road sections were exhumed and examined after all the large-scale cyclic plate loading tests and the moving wheel tests. The benefits of NPA geocell reinforcement were evaluated in terms of the number of wheel passes at 75 mm of rut depth and the vertical stress distribution. The test results were analyzed separately in terms of different test methods. It is shown that geocells placed in a circular shape performed better than those in an elliptical shape. NPA geocells increased the stiffness and ultimate bearing capacity of granular bases by 1.5 to 2.0 times. NPA geocell-reinforced bases had higher stiffness and bearing capacity than HDPE geocell-reinforced bases. NPA geocells significantly reduced permanent deformations of granular bases with the number of cycles or wheel passes and increased stress distribution angles. The existence of geocells made compaction more difficult and it was found that the relative compaction of infill materials in geocells is important for the performance of geocell-reinforced bases. The established design method for the planar geosynthetic reinforcement was modified for the NPA geocell-reinforced bases over weak subgrade and calibrated based on the test results from the large-scale cyclic plate loading tests and the moving wheel tests. The California Bearing Ratios (CBR) of the subgrade and base course, the number loading cycles or wheel passes required for 50 to 75 mm rut, the height of geocell, and the thickness of the base course were the variables used to calibrate this design formula. The design method was used to verify the test results and yielded a good comparison.