Effect of Moisture Content on Subgrade Soils Resilient Modulus for Predicting Pavement Rutting

Abstract

The subgrade soil stiffness, which depends on the in-situ moisture content and soil index characteristics, is a key factor in pavement rutting. Due to variations in the compaction process used during construction and seasonal changes, the subgrade soil moisture content may deviate from the desired condition. The resilient modulus (MR), an important parameter of the Mechanistic-Empirical (M-E) pavement design process, is used to specify the subgrade soil stiffness. Repeated load triaxial tests, which can be challenging and time-consuming to execute, are often used to determine MR. As a result, correlations between MR and more accessible stiffness metrics and index qualities are frequently used. California bearing ratio (CBR) and repeated load triaxial tests were carried out in this investigation. Soil specimens were fabricated at moisture levels that were both above and below the optimum moisture content (wopt). The results of the two tests were correlated, and statistical models were created to correlate the parameters of the generalized constitutive resilient modulus model with the characteristics of the soil index. Additionally, utilizing the MR found for subgrade soils compacted at wopt and ±2%wopt, pavement rutting was analyzed for three base layer types. The results demonstrated that a laboratory-measured MR (MR(Lab)) decreases as the moisture content increases. Specimens compacted at −2%wopt showed higher MR(Lab) than specimens compacted at wopt. Specimens compacted at +2%wopt showed lower MR(Lab) than specimens compacted at wopt. Results also indicated that the MR(Lab) predicted higher pavement rutting compared to field measured MR (MR(Lab)). If a stabilized aggregate foundation layer was employed instead of an untreated granular base, subgrade soil moisture condition showed a significant impact on rutting.

An Updated Cyclic CBR Test with Realistic Stress Values under the Plunger for Resilient Modulus Calculation

“…It is known from previous studies that M r values obtained from the cyclic triaxial test are in a lower interval than those obtained from the standard cyclic CBR test. In [16,21,23,33], the modulus values obtained from the cyclic triaxial test are in the intervals 20-90 MPa, 40-110 MPa, 55-80 MPa, and 56-159 MPa, respectively. All these results are fully comparable with the results in this paper.…”

“…The method has been tested and used by a number of authors [15,16,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Although the influence of the state of stress on the modulus has been correctly mentioned in some papers, and some studies have even been performed under an intuitively lower loading force not set up according to the standard CBR test [25,29], the question of the magnitude of the stress under the plunger has been overlooked.…”

Effect of the Field-Stress State on the Subgrade Resilient Modulus for Pavement Rutting and IRI

“…Predicting flexible pavement performance is highly dependent on the accuracy of the M R value. Islam and Gassman (2023) [28] found that the laboratory-measured M R obtained using the stress state in NCHRP-285 predicted higher rutting than the M R back calculated from FWD testing and PMED v2.6.2.2 default values. The rutting predicted from the laboratory-measured M R exceeded the field-measured distress but was below the design threshold.…”

“…The RLTT test is commonly used to measure the resilient modulus of subgrade soils in the laboratory [12][13][14][15][16][17][18]. This test is designed to simulate the stress induced by traffic loading through a series of cyclic deviator stresses applied to the specimen at different confining pressures [13].…”

A Numerical Simulation of Moisture Reduction in Fine Soil Subgrade with Wicking Geotextiles

“…However, during actual service, precipitation infiltration and capillary rise may cause the subgrade moisture content to reach an equilibrium humidity higher than the optimal moisture content, leading to the degradation of subgrade support performance [5,6], further resulting in a decline in the pavement's service life. Rahman et al [7,8] revealed that specimens compacted at +2%w opt showed a lower modulus than specimens compacted at w opt . The soil moisture condition significantly influenced the subgrade modulus and the resulting subgrade rutting, which led to the severe degradation of road service performance.…”