Undrained stability of unsupported conical slopes in two-layered clays
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TECHNICAL PAPER
Undrained stability of unsupported conical slopes in two‑layered clays Wittawat Yodsomjai1 · Suraparb Keawsawasvong1 · Chanachai Thongchom1 · Jintara Lawongkerd1,2 Received: 1 July 2020 / Accepted: 24 September 2020 © Springer Nature Switzerland AG 2020
Abstract A conical slope is widely used in many constructions of in situ piles, piers, footings, mat foundations, raft foundations, energy storages, or water tanks since this unsupported excavation is much cheaper than an excavation with supports. This paper presents new plasticity solutions for undrained stability of unsupported conical slopes in two-layered clays by using axisymmetric finite element limit analysis. Four parametric studies were performed on the slope height ratio, the slope inclination angle, the thickness ratio of two-layered clay, and the strength ratio of two-layered clay, where the stability factor of this problem is investigated. In all the cases, the exact stability factors are accurately bracketed by lower and upper bound solutions within 1%. The design charts for estimating the stability of conical slopes in two-layered clays are proposed. Three failure mechanisms, i.e., toe, based, and face failures are observed and discussed in the paper. The predicted failure mechanisms of the unsupported conical slopes in two-layered clays are presented in order to portray the impact of all considered dimensionless parameters. Keywords Limit analysis · Slope stability · Conical slope · Unsupported excavation · Layered soil · Undrained stability
Introduction A conical slope is an unsupported excavation with an inclined slope angle. It can be generally found in many constructions of in situ piles, piers, footings, mat foundations, raft foundations, energy storages, or water tanks because this construction technique is cheaper than those of supported excavations (e.g., sheet pile walls, pile walls, diaphragm walls). This excavation technique is also used in an open-pit mining, where an example of a conical excavation is shown in Fig. 1 [37]. In addition to planar slopes under plane strain condition (e.g., [1, 6, 7, 17, 27, 28, 39] or three-dimensional slopes in Cartesian coordinate (e.g., [4, 18–21, 29], conical slopes are commonly under axisymmetric condition. The accurate stability prediction of the conical slope is a necessity for several construction projects when this technique
* Suraparb Keawsawasvong [email protected] 1
Department of Civil Engineering, Thammasat School of Engineering, Thammasat University, Pathumthani 12120, Thailand
Applied Mechanics and Structures Research Unit, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand
2
is used during the process of excavation from the ground surface to the final depth of excavation. Without the consideration of an inclined angle of an unsupported excavation, the early studies by Britto and Kusakabe [2], Pastor and Turgeman [30], Griffiths and Koutsabeloulis [5], and Lyamin and Sloan [24] presented some stability
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