Estimating an empirical equation connecting subgrade reaction modulus with cone penetration test for sandy soils

Abdelaziz Ahmed Bohagr Abdelaziz Ahmed Bohagr,Ghassan Ahmed El Gehani Ghassan Ahmed El Gehani,Mustafa M Amami Mustafa M Amami,Mohammed Mahmoud Boudejaja Mohammed Mahmoud Boudejaja

doi:10.30574/gjeta.2021.9.2.0127

Abdelaziz Ahmed Bohagr Abdelaziz Ahmed Bohagr, Ghassan Ahmed El Gehani Ghassan Ahmed El Gehani + Show 2 more

Open Access

https://doi.org/10.30574/gjeta.2021.9.2.0127

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Abstract

In geotechnical engineering, the coefficient of subgrade reaction is regarded as one of the most important parameters used for describing the interaction of soil and structure as well as describing some soil characteristics, subgrade reaction coefficient can be calculated theoretically using many different formulas, laboratory via specific well-known tests, and in site through field plate loading test. On the other hand, the cone penetration test is one of the most frequently used field tests to investigate the soil. The lately carried out researches showed a good relation between the subgrade coefficient and the tip resistance collected from the CPT, but the results obtained from the proposed method are still doubtable. In this paper, fifteen plate load tests and thirty CPTs, already collected for private site investigation project, have been used for finding the best fit equation connecting the subgrade reaction coefficient Ks with the tip resistance qc. The finds of the established equation have been compared extensively with those of other well-known related equations. The results show the ability of the concluded equation to get Ks results in the acceptable range of sandy soils. However, the depth and shape effect on the suggested formula need further investigations since all the plate load tests in this project have been carried out on the soil surface with a 45 cm diameter circular plate.

Highlights

Module of subgrade reaction Ks is one of the most important coefficients used in the structural analysis of the foundations, this coefficient concerns the structural engineering as well as the geotechnical engineering, the main concept of this coefficient is that the soil under the loaded area acts like elastic springs to resist the vertical deformation exerted by the load on the soil
The results show the ability of the concluded equation to get Ks results in the acceptable range of sandy soils
The tip resistance qc readings collected from the Cone penetration test (CPT) is analyzed using computer software (CPTU-ACQ), and the values of qc are plotted against the different values of Ks to estimate the best equation can be used to connect the variables, to check the adequacy of the formula a series of comparisons is made with analytical software's which are (Microsoft Excel) and (Minitab)

Summary

Introduction

Module of subgrade reaction Ks is one of the most important coefficients used in the structural analysis of the foundations, this coefficient concerns the structural engineering as well as the geotechnical engineering, the main concept of this coefficient is that the soil under the loaded area acts like elastic springs to resist the vertical deformation exerted by the load on the soil. This concept transformed to a fundamental module established by Winkler [1] which state that: Ks = σ δ. Several equations were provided depending on some different variables such as the modulus of elasticity of the foundation, the shape, the depth of foundation, and the elastic characteristics of the soil such as the modulus of elasticity and Poisson ratio, these equations are given in Table (1)

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