التقييم اللااتلافي لمقاومة تحمل التُرب المحلية تحت الطرق بإستخدام مقاييس فحص الهطول خفيف الوزن

NON-DESTRUCTIVE ASSESSMENT OF BEARING RESISTANCE OF LOCAL SUBGRADE SOILS THROUGH LIGHT WEIGHT DEFLECTOMETER MEASUREMENTS

    In highway and airport pavement design, subgrade strength mostly affected the thickness of pavement layers, California Bearing Ratio (CBR) is one of the simple empirical methods that is commonly used to determine the strength and stiffness of subgrade soil, subbase, and base-course material in airfield and highways pavement system layers. The CBR test is performed originally to determine the thicknesses of flexible pavements layers by using empirical techniques. The test is normally conducted on compacted remolded specimens and may be performed on undisturbed soils or-soils in the field expressed by field, in-place or in-situ CBR test. In-situ CBR test is intended to determine static-properties of-unbound-pavement-layers represented by bearing capacity of subgrade soils without requiring the digging of test pits. However, as the testing procedure of CBR test is laborious and time consuming beside the development in testing techniques, methods are proposed for correlating CBR value with dynamic measurements such as those obtained from Light Weight Deflectometer (LWD).

    In this work, two testing methods were used on three types of subgrade soils: static test method represented by the in-situ CBR to evaluate strength parameters, and dynamic test method which was implemented using LWD device to estimate the dynamic properties of subgrade soils. Three roadway projects were selected at Karbala city to evaluate different subgrade soils. The sites were Al-Meelad district, Al-Fares district, and Al-Rofaee zone at which their soils’ type were classified as A-1-b, A-3, and A-7-6, respectively.

    Statistical analyses were performed to predict the bearing resistance of subgrade soils based on LWD dynamic measurements such as dynamic modulus and surface deflection, in addition to the water content and dry density obtained from field density tests methods. The results of six statistical models for two subgrade groups (i.e., granular soil and clayey soil) indicate that the LWD has a significant potential for compaction quality control and for determining in-situ dynamic moduli of pavement layers during construction and surface deflections. In addition, the results indicate that the dynamic modulus from LWD is well correlated with the bearing ratio for various subgrade soils. Furthermore, basic physical properties from field density tests has significant correlation with CBR value. A comparison between dynamic measurements and physical properties indicate the dynamic modulus is most significant than field density.

    For verifying the statistical models, two under construction sites were selected at Karbala city: Al-Takahe district, and Al-Emam Ali district. The subgrade soil of selected sites was classified according to AASHTO to as A-1-b and A-3 at Al-Takahe district, and Al-Emam Ali district, respectively. The initial results showed the ability to predict bearing resistance of subgrades based on their basic physical properties and dynamic measurement obtained by LWD test device.