Author's Personal Copy Finite Elements in Analysis and Design 44 (2008) 525 – 536 www.elsevier.com/locate/ﬁnel Pullout capacity of a reinforced soil in drained and undrained conditions Ahmed Bayoumi a , ∗ , Antonio Bobet b , Junhwan Lee c a CH2M Hill, 2485 Natomas Park Dr, Suite 600, Sacramento, CA 95834, USA b School of Civil Engineering, Purdue University, West Lafayette, IN, USA c School of Civil and Environmental Engineering, Yonsei University, Seoul, South Korea Received 9 April 2007; accepted 5 January 2008 Available online 1 May 2008 Abstract A ﬁnite element model is built to analyse the pullout capacity of a stiff inclusion embedded in a soil matrix under both drained and undrained conditions. The inﬂuence of several parameters, including soil/reinforcement friction and vertical stress, on the pullout capacity of clean and silty sands reinforced with a steel strip is investigated. The ratio of undrained to drained pullout capacities ranges approximately from 0.58 to 0.89 depending on the interface friction coefﬁcient and vertical stress. The most important factor for the pullout capacity in both drained and undrained conditions is the coefﬁcient of friction at the interface. Other parameters such as the relative density of the sand, the overburden pressure, the coefﬁcient of lateral pressure, or the soil model used, have a relatively smaller effect.  2008 Published by Elsevier B.V. Keywords: Reinforced soil; Drained and undrained pullout capacity; Soil/reinforcement friction 1. Introduction The use of mechanically stabilised earth (MSE) retaining walls is a very cost-effective solution, particularly with low strength soils as foundation. MSE walls consist of three com- ponents: the backﬁll, the reinforcing inclusions, and the facing. Reinforcement inclusions include metallic strips, mesh, plastic geotextile or geogrid in the form of strips or sheets; the face of MSE structures is either vertical or sloped and the backﬁll material is typically conﬁned behind a facing [1]. The rein- forcing inclusion provides additional strength and stiffness to the original soil, resisting the bulging and the lateral stresses in the soil mass that are induced by an applied surcharge or self-weight. The pullout capacity of a steel reinforcement embedded in a granular soil matrix depends on a number of factors such as the friction coefﬁcient between the reinforcement and the soil, the applied normal stress at the level of the reinforcement, reinforcement embedment length, and soil properties. The ef- fect of drainage conditions on the pullout capacity is another ∗ Corresponding author. Tel.: +1 916 215 1149. E-mail address: abayoumi@ch2m.com (A. Bayoumi). 0168-874X/$ - see front matter  2008 Published by Elsevier B.V. doi:10.1016/j.ﬁnel.2008.01.009 signiﬁcant factor that is believed to be responsible for the failure of a number of earth-reinforced structures. The failure of Blue Heron road embankment in McCreay County, Kentucky, is an example of the serious consequences of unaccounted drainage conditions. The failure occurred in the MSE wall after a heavy rainfall [2]. Reinforced soil can be considered as a composite system and its performance can be evaluated using experimental (including ﬁeld tests and prototypes) and analytical (including numerical) approaches. Reinforced soil has been the focus of a substan- tial amount of numerical simulations done by a number of re- searchers; although some simplifying assumptions such as 2D plane strain conditions are generally made, the results approx- imate well ﬁeld observations. Adib et al. [3] discussed com- parisons between ﬁeld measurements and ﬁnite element (FE) analyses that were conducted to evaluate the performance of MSE walls and earth embankments. The comparisons consid- ered the location of maximum tension in the reinforcement, dis- tribution of tension along the reinforcement, and distribution of maximum tension in the reinforcement. The results of the FE analyses compared reasonably well with measurements except for the maximum tension in the geogrid. Drainage conditions were not addressed in the analysis.