Quantifying Soil Moisture Reduction by Wicking Geotextile to Minimize Pavement Distresses

Excessive moisture in pavement foundations including base courses and subgrade is one of the major causes for pavement distresses, which often pose safety risks to vehicles and drivers and increase the cost for maintenance and reconstruction. Moisture can weaken pavement foundations and become a source for freeze-thaw problems in cold regions, which accelerate the deterioration of pavements with time. Therefore, pavement drainage is critical to pavement performance. Typical drainage systems are effective for saturated soils but become less effective or ineffective for unsaturated soils. Wicking geotextile that contains deep-grooved fibers can generate suction when in contact with water and reduce moisture in unsaturated soils. However, the effectiveness of the wicking geotextile in reducing moisture depends on several factors including the percent of fines in soils. So far, no simple test method is available to evaluate the effectiveness of the geotextile in reducing moisture in soils including those with fines and no fine content limit has been established for the wicking geotextile to be effective. The proposed research is to develop a simple soil box test to quantify the effectiveness of the wicking geotextile in reducing moisture in sands at different fine contents and distances from the geotextile as compared with the conventional geotextiles. The soil box tests will first determine field capacities of silty sands at different fine contents and then evaluate moisture reduction by geotextiles by measuring moisture contents at different distances from the geotextile location at different times. These tests will determine the amount of moisture reduction and the distance of influence, and the fine content limit for the geotextile to be effective. The objective of this research is to develop a simple test method to quantify soil moisture reduction by geotextile and provide guidance for its use in sands with fines.

All infrastructures are built on earth, which consists of soils and rocks. Excessive moisture in pavement foundations including base courses and subgrade soil is one of the major causes for pavement distresses, which often pose safety risks to vehicles and drivers and increase the cost for maintenance and reconstruction. Moisture can weaken pavement foundations and become a source for freeze-thaw problems in cold regions, which accelerate the deterioration of pavements with time (Zhang et al., 2014). Therefore, pavement drainage is critical to pavement performance. Geotextile (factory-made fabric product) has been used in soils to remove water. Conventional geotextiles contain large voids and can drain water out of soils when they are saturated, but become ineffective for unsaturated soils. Recently, a wicking geotextile has become available in the market. This product employs deep-grooved nylon fibers to increase surface areas and create suction when they are in contact with water. The wicking geotextile can remove water from both saturated and unsaturated soils due to its unique surface topography (Zhang et al., 2014; Guo et al., 2021). However, its water removal ability may be limited when the suction in the geotextile is close to or lower than that in the soil such as in case soil contains fine particles. In other words, the effectiveness of the wicking geotextile in reducing moisture depends on the percent of fines in soils and the distance from the geotextile location. Figure 1 shows the wicking geotextile transports and discharges water mostly through evaporation at the edges in the field. Before the installation of the geotextile in the field, its effectiveness of removing moisture from the soil, especially with a fine content should be evaluated. Unfortunately, so far, no simple test method is available to evaluate the effectiveness of the geotextile in reducing moisture at different distances in soils including those with fines. In addition, no fine content limit has been established for the wicking geotextile to be effective. Therefore, there is an urgent need for developing a simple test method to quantify the effectiveness of the wicking geotextile in reducing moisture in soils at different fines and distances from the geotextile as compared with the conventional geotextiles.

"Unfortunately, so far, no simple test method is available to evaluate the effectiveness of the geotextile in reducing moisture at different distances in soils including those with fines. In addition, no fine content limit has been established for the wicking geotextile to be effective. Therefore, there is an urgent need for developing a simple test method to quantify the effectiveness of the wicking geotextile in reducing moisture in soils at different fines and distances from the geotextile as compared with the conventional geotextiles. Task 4: Perform soil moisture reduction tests to quantify the moisture reduction for silty sands at different fine contents without geotextile, with a conventional woven geotextile, and with a wicking geotextile at different time periods (3, 7, 14, and 28 days) under typical temperature and relative humidity levels in a control room. Task 5: Reduce and analyze all the test data including but not limited to: (1) contact angles for geotextiles, (2) gradations, compaction curves, and shear strengths of silty sands at different fine contents, (3) field capacity profiles of silty sands at different fine contents, (4) moisture reduction profiles of silty sands at different fine contents and time periods, (5) influence distances of geotextile in silty sands at different fine contents, and (6) fine content limit for the effectiveness of geotextile. Task 6: Prepare a research report to summarize all the test data, results, findings, and make recommendations for future applications of the simple test method and the fine content limit. A written report will be submitted to MATC in Microsoft Office Word format."

This research is expected to develop a simple test method for quantifying moisture reduction in soils with fines by a geotextile and determine a fine content limit for the effectiveness of the geotextile in soil moisture reduction. These results are expected to ensure the improved performance of pavements thus minimizing pavement distresses, prolonging pavement life, reducing maintenance and reconstruction cost, and improving the safety of roads.

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