Use of CPT and DCP based correlations in characterization of subgrade of a highway in Southern Ethiopia Region

Abstract

Background: Necessity of highway infrastructure development has been renowned all over the globe. Key success for highway projects mainly depends on the characterization of subgrade soil intended for thousands of kilometers. In practice, any one of the soil test data may not provide exact characterization of subgrade and at least minimum two tests can be used to develop design values of subgrade for a highway pavement. Also, there is a need to have relationship between two to three soil parameters so as to understand evidently about the soil characteristics and their behavior. Methods: Two test data such as CPT and DCP are utilized to develop statistical correlations for better site characterization. Ordinary least squares and the simple arithmetic mean methods are obtained for scatter plots of data pairs and different trends are fitted to the data. Correlation agreements between CPT and DCP for various combinations are plotted for 40 data sets. Results: Liquid limit values ranged from 22 to 56 %, while plastic limits are ranging in between 16 and 43 %. Plasticity index values are varying from minimum 1 % to maximum of 29 %, indicating low to medium swelling potential. Based on the American Association of State Highways and Transportation Officials soil classification system, soil along the chosen highway alignment includes A-2-4, A-4, A-2-5, A-2-7, A-1(a), A-1(b), A-7-6 and A-6. Similarly, according to Unified Soil Classification System, the dominant soils along the highway stretched are placed into inorganic silts or organic clays (MH or OH), inorganic clays (CL), inorganic silts or organic silts (ML and OL), and combinations of the two (CL-ML). Deliberation of sleeve friction measurements resulted minor improvement in correlations and these may be considered trivial. According to Roberson's chart, the distribution of CPT and DCP data obtained along the highway route encompasses four zones. Zone 4 (i.e., silt mixtures: clayey silt to silty clay), zone 5 (sand mixtures: silty sand to sandy silt), zone 6 (sands: clean sand to silty sand), and zone 8 (very stiff sand to clayey sand), with some scattered data points are located in zone 9 (very stiff, fine-grained). Conclusions: The correlations developed in this study indicates that, CPT (q c + f s) and DCP (q c) correlations are very much enhanced compared to other combinations studied in terms of higher coefficient of correlation and least transformation uncertainty. The CPT and DCP data obtained along the highway route is superimposed in Roberson's chart to characterize the subgrade soil swiftly.

Evolution of Deep Neural Network Architecture Using Particle Swarm Optimization to Improve the Performance in Determining the Friction Angle of Soil

“…First, the water content was not included in this study, as it is believed that the effect was taken into account in the number of SPT blows [47]. Besides, many studies have been successful in finding the relationship between the results of in situ experiments (CPT and SPT) and the Plastic and Liquid Limited humidity [48][49][50][51]. Since the SPT is one of the most commonly used tests in practice to indicate the soil's ability to withstand compression and in situ shear, it is believed to relate to the factors that characterize the ability of the shear strength of the soil.…”

Instrumented Cone Penetrometer for Dense Layer Characterization

“…In recent decades, the advantages of the CPT have been acknowledged, such as its simplicity, repeatability, and accuracy [ 7 , 8 ]. Furthermore, reliable correlations between the CPT and other penetration tests have been observed [ 9 , 10 ]. Despite the usefulness of the large-sized CPT rig for penetration through the dense layers, difficulties may arise in conducting the CPT in dense layers of intermediate geomaterials, such as weathered rock, till, or soils containing considerable gravel content, due to the limited availability of large-sized CPT rigs.…”

Effect of RBI Grade 81 on strength characteristics of clayey subgrade

“…The CBR of highway stratigraphy plays a vital role in the design of flexible pavement [20]. The load-penetration curves of CBR tests for the various dosage of RBI Grade 81 are presented in Fig.…”