Tunnel–framed building interaction: comparison between raft and separate footing foundations

Abstract

This paper investigates the influence of the foundation configuration (raft or separate footings) on tunnel-soil-framed building interaction using geotechnical centrifuge testing. Tunnelling-induced soil movements and deformation fields, framed building displacements, and structure shear distortions (with associated modification factors) are illustrated. Framed building stiffness and footing bearing capacity are also evaluated experimentally. Results show that the foundation configuration plays an important role in determining the ground response to tunnelling, affecting soil displacement fields as well as the distribution of soil shear and volumetric strains. In particular, foundation settlements and differential horizontal displacements are larger for separate footings compared to raft foundations. The effects of building width, weight, and eccentricity (with respect to the tunnel) on foundation settlements and structural distortions is quantified for separate footings and contrasted against results for raft foundations. The modification factor of the maximum building shear distortion is linked to the relative soil-building shear stiffness; interestingly, for buildings with similar values of relative stiffness, the level of shear distortion within framed buildings is lower for separate footings than rafts.

Role of Footing Embedment on Tunnel–Foundation Interaction

“…Figure3presents contours of normalized ground horizontal ( / ) and vertical ( / ) displacements, along with engineering shear and volumetric strains of the soil at a tunnel volume loss of , = 2.0%. In general, the greenfield results (fromXu et al (2020b)) show: a chimney-like displacement pattern, as expected for the relatively low value of /(Marshall et al, 2012; …”

“…Each story has the same height ℎ =38.1 mm , thus giving a total building height of 79.4 mm. The plane-strain tunneling model described in Xu et al (2020b) was used, with a flexible membrane model tunnel (diameter = 90 mm), a strongbox with a transparent acrylic front wall, and a tunnel volume loss control system. A fine-grained dry silica sand (Leighton Buzzard Fraction E) was used, with minimum and maximum void ratios of 0.65 and 1.01 (Zhao, 2008;Lanzano et al, 2016).…”

“…The modification factors are plotted against relative stiffness in Figure 5 for , = 0.5, 1.0 and 2.0%. proposed by Xu et al (2020b), which were based on centrifuge test data for frames with footings on the ground surface, i.e. = 0.…”

“…Prediction of tunneling-induced structural distortions and damage is a necessary stage of urban tunneling projects. When considering a building founded on shallow foundations, it is generally assumed that the foundations rest directly on the surface, both in numerical (Goh and Mair, 2014;Fu et al, 2018) and experimental (Ritter, 2017;Xu et al, 2020b) studies. However, in reality, shallow foundations are usually buried at a certain depth.…”

Tunneling-Induced Deformation of Bare Frame Structures on Sand: Numerical Study of Building Deformations

“…For the frames, Table 1 provides details of the considered configurations and Figure 2 shows the layout with an illustration of relevant parameters. In this paper, frames are labeled following Xu et al (2020b) as FxtybzL or FxtybzS: x is the number of stories, y the thickness of structural elements at centrifuge model scale, z is the number of bays, while L and S stands for long and short building, respectively. Tunnel volume losses up to 3% were considered, 7Boldini et al…”