Effect of soil moisture content on the bearing capacity of small bored piles in the unsaturated soil of Maringá, Paraná, Brazil

Verônica Ricken Marques,Ewerton Guelssi,Antonio Belincanta,Jorge Luis Almada Augusto,Mary-Antonette Beroya-Eitner,Hauke Zachert,T.M.P De Campos,M.M.A Mascarenha,F.A.M Marinho,G.F.N Gitirana

doi:10.1051/matecconf/202133703006

Abstract

In this study, the influence of soil moisture on the bearing capacity of piles founded in an unsaturated clay soil was investigated. The soil studied, composing the upper soil layer in Maringá, Brazil, is lateritic, has degree of saturation between 37% and 70% and has collapsible behaviour when wet. The bearing capacity was determined by full-scale load tests following the Brazilian Standard for Static Load Test. Two pile lengths, 4 m and 8 m, were considered. To analyse the influence of soil moisture, two tests were performed for each pile length: one in soil in its natural moisture content and another in pre-moistened soil. Results show that for both pile lengths, an increase in water content caused a significant reduction in bearing capacity, which is attributed to the decrease in the matric suction of the soil. This is confirmed by the results of the initial evaluation made on the variation of matric suction and its contribution to the bearing capacity with changes in water content. In summary, this study confirms that the pile bearing capacity in unsaturated soil is dependent on soil water content, highlighting the fact that the approach of assuming full saturation condition in the evaluation of the pile bearing capacity in such soil may give erroneous results. Moreover, this study demonstrate that the empirical methods most commonly used in Brazil for pile bearing capacity determination, the Décourt & Quaresma and Aoki & Velloso methods, are overly conservative when applied to the Maringá soil.

Highlights

Earliest theoretical methods for determining pile bearing capacity are based on saturated soil parameters, e.g. Terzaghi [1], Vésic [2]
Most of these methods are empiricallybased that relate Standard Penetration Test (SPT) and/or Cone Penetration Test (CPT) results with the bearing capacity of the piles obtained from field tests
Where ‫ܣ‬௕ and ‫ܣ‬௦ are, respectively, the base and lateral pile area in m2; ‫ ܥ‬is a coefficient for the base resistance that varies with soil type and given in kPa; ܰ௕ is the average of the SPT N-values taken at depths immediately above and below the pile base; ܰ௦ is the average of the Nvalues along the pile shaft; and ߙ‫ כ‬and ߚ‫ כ‬are coefficients that depend on the type of pile and soil, respectively

Summary

Introduction

Earliest theoretical methods for determining pile bearing capacity are based on saturated soil parameters, e.g. Terzaghi [1], Vésic [2]. The said methods are considered complex and generally applicable only to purely clay or sand soils. They are generally not used in the country (Cintra and Aoki [3]). Many Brazilian workers have tried to develop alternative methods that are more suitable for use in the country Most of these methods are empiricallybased that relate Standard Penetration Test (SPT) and/or Cone Penetration Test (CPT) results with the bearing capacity of the piles obtained from field tests. The most commonly used are those proposed by Décourt & Quaresma [4], which Décourt [5] later modified, and by Aoki & Velloso [6]

Objectives

Methods

Results