Analytical Solution for a Loess Tunnel Based on a Bilinear Strength Criterion
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UNDERGROUND STRUCTURES ANALYTICAL SOLUTION FOR A LOESS TUNNEL BASED ON A BILINEAR STRENGTH CRITERION
UDC 624.19.04^624.131.23 Mingnian Wang, Yucang Dong, and Li Yu* School of Civil Engineering, Southwest Jiaotong University, Chengdu, China, *Corresponding author: [email protected].
The design load of a loessal tunnel is usually calculated using the conventional MohrCoulomb strength criterion, which ignores the structural strength of loess and provides inaccurate calculation results. The present paper therefore proposes a bilinear strength criterion considering the structural strength characteristics of loess determined in a triaxial shear experiment. Then, using the new strength criterion, a new theoretical solution is derived for the stress and displacement of loess in each region separately; the solution is validated by numerical simulation. Lastly, the ground reaction curve and the design load of a tunnel are obtained using the proposed method considering the structural strength of loess. The results obtained using the new method are more reasonable and accurate than the results calculated using the conventional method. The proposed strength criterion and theoretical solution expand the knowledge base of loess engineering and provide guidelines for the design and construction of underground structures in loess ground.
Introduction China has the greatest distribution of loess among countries worldwide [1]. The structural strength of loess is one of most obvious geotechnical characteristics for engineering and affects the constitutive model and strength criterion, resulting in conventional constitutive models and strength criterions poorly describing the characteristics of loess [2-4]. Moreover, the loessal characteristics produce complex stress and displacement variations of the surrounding rock that are different from those of conventional soil when loess is disturbed in engineering projects, such as tunnel excavation. The special variation easily gives rise to instability problems of tunnels [5]. There is therefore an urgent need to propose constitutive models and strength criterions considering loessal characteristics and to describe the special stress and displacement variation of loess, which has already drawn much attention from geotechnical scholars and tunnel engineers. The main proposed constitutive models are the modified Cambridge model introducing a structural parameter and the Duncan-Chang model considering structural potential energy and the elastoplastic damage constitutive model of loess [6-9]. However, the proposed models are limited in terms of engineering application. Moreover, the proposed models introduce a large number of parameters, leading to a time-consuming procedure and a huge volume of soil samples. Additionally, strength effect theory indicates that the selection of a strength criterion for soil has a greater effect on the accuracy of calculation results compared with the case for a constitutive model [10]. Nevertheless, there have been few
Translated from Osnovaniya, Fundame
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