A new concept for interpretation of building-excavation interaction in 3D conditions

https://doi.org/10.1016/j.tust.2020.103757Get rights and content

Highlights

  • Building location WRT Potential Failure Surface, PFS, impacts excavation interaction.

  • Excavation deflection IL due to building surcharge resembles ground surface profile.

  • Eq. beam plus basements must be modeled to study the building-excavation interaction.

  • Excavation corner effect can be interpreted based on PFS position WRT the corner.

Abstract

This 3D numerical study presents the factors affecting displacements and rotations induced by deep excavation in the vicinity of a tall building with an emphasis on the building parameters. An accurate model of a 31.2 m deep excavation with an adjacent 12-story building was used to validate the numerical modeling. Plane strain analysis of the excavation-induced deformations using building surcharge method proved the inadequacy of the surcharge method regardless of the building stiffness. Although the results of the equivalent beam method and the building structural method was in general conformity with each other, modeling structural details of the building showed better capability in capturing even local interactions of the building and the excavation. Parametric study in 3D conditions investigated effects of the buildings position and dimensions on displacement interaction by examining the development of a potential failure surface (PFS). The results showed that the building’s position and dimensions relative to the PFS as well as the building proximity to the excavation corner play decisive roles on determination of the excavation induced displacements/rotations and should be considered in the design of the excavation support system near buildings.

Introduction

The development of theoretical and empirical knowledge about impacts of deep excavations and tunneling on adjacent buildings as well as underground structures such as tunnels (Zhang et al., 2013, Klar and Elkayam, 2010), piles (Zhang et al., 2019a, Zhang et al., 2019b, Zhang et al., 2019c, Franza et al., 2017) and lifeline facilities such as buried pipelines (Hasanpour et al., 2020a, Hasanpour et al., 2020b) has been enhanced with an increase in the construction of need-based underground spaces in both structural and geotechnical engineering..

Soil specifications (Zhao et al., 2019), excavation geometry, dimensions and topographic conditions of the site and its surrounding (Zhang et al., 2019a, Zhang et al., 2019b, Zhang et al., 2019c), types of support of excavation systems and their properties (Elshafie et al., 2013), excavation-induced groundwater drawdown (Goh et al., 2020, Zhang et al., 2018) and executive procedures (Chen et al., 2018, Kim and Finno, 2019) as well as dimensions and properties of the adjacent building (Cording et al., 2010, Son and Cording, 2007, Son and Cording, 2011, Goh and Mair, 2011) and its position with respect to the excavation (Goh and Mair, 2014, Castaldo et al., 2013) are important factors affecting building-excavation interaction.

Because investigation of these factors is beyond the scope of one study, some of the factors which are common for a specific region have been assumed to be constant. For example, Bangkok has a high groundwater level and a soft clayey soil layer; thus, diaphragm walls are commonly used to support deep excavations (Chheng and Likitlersuang, 2018, Khoshnevisan et al., 2017). Tehran, however, is developed on higher strength cementitious soils; thus, soil nailing and anchorage, sometimes in combination with piles, are commonly adopted as supports of deep excavations. Thus, in the studies which deal with building-related parameters, the soil specifications, excavation support systems and the excavation geometry and dimensions are generally assumed to be constant.

The studies have investigated the effects of building-related factors on the grounds of the building weight and stiffness. In order to simultaneously analyze the excavation and adjacent building, building modeling methods such as the equivalent elastic beam method (Basmaji et al., 2019, Namazi and Mohamad, 2013, Mirhabibi and Soroush, 2012), exerting of building weight onto flexible bedding (building surcharge method), and the building structural modeling (Cai et al., 2017) have been used.

Goh and Mair (2014) used the equivalent beam method and proposed building modification factors applicable for determination of the effect of the adjacent excavation on deflection and strain of the building. They employed 2D numerical models of weightless framed buildings with mat and spread footings on the crest of a strutted excavation in soft clay. They also used the equivalent simple beam method to represent the bending stiffness of the building frame. Neither the weight nor position of the building in relation to the potential failure surface (PFS) of the excavation were taken into account.

Son and Cording (2007) modeled a building near an excavation and showed that openings such as doors and windows of masonry buildings significantly reduces their shear stiffness compared to their bending stiffness. They suggested that a 30% increase in the wall opening ratio results in a 45% to 61% reduction in shear stiffness of the equivalent wall.

Despite the popularity of the equivalent beam and the building surcharge methods as building models (Basmaji et al., 2019, Namazi and Mohamad, 2013, Mirhabibi and Soroush, 2012), there are serious doubts about their adequacy. Using an equivalent surface beam in building-twin tunneling interaction overestimates the stiffness of the building and leads to less settlements (even in comparison with 3D simulations) of the building during tunneling (Mirhabibi and Soroush, 2013, Mirhabibi and Soroush, 2020). Thus, generally speaking, these approaches are not recommended to be used in numerical modeling of the building-excavation interaction. Empirical methods for estimation of excavation-induced deformations can be employed only in combination with numerical modeling. The application of a free-field settlement curve of an excavation to an adjacent building is commonly adopted as an empirical method for damage level estimation of buildings, but is not adequate under all circumstances (Laefer et al., 2009).

In order to evaluate the effect of some geometrical parameters, such as the width of a building or excavation or the corner effect on the induced deformations, only 3D models should be used. Three-dimensional numerical analyses are essential for special geometries such as narrow excavations (Yang et al., 2020) or estimation of forces of structural elements of the excavation support system (e.g. strut forces) (Zhang et al., 2019a, Zhang et al., 2019b, Zhang et al., 2019c). Some studies have been carried out to convert plane-strain analyses results to 3D analyses results; however, they cannot be generalized to all cases (Wang et al., 2019, Fuentes and Devriendt, 2010).

Excavation-induced deformations of an adjacent building in a real project, that are represented in the forms of horizontal displacement, settlement, rotation, internal strain and cracking, are generally monitored to determine the building damage level (Namazi and Mohamad, 2013). The building deformations are induced by the deformations of the ground surface, which are a consequence of the strains inside the soil body behind the excavation. Most of the strains, mainly shear strains, are accumulated in a band which is called potential failure surface (PFS). Thus, the location of PFS and its extension throughout the soil (which forms potential failure wedge, PFW) affects the induced deformations of the overlying building. A lack of consideration of the effect of the adjacent building position with respect to the PFS is noticeable in the literature.

This study presents the numerical modeling of a staged excavation along with its adjacent building using PLAXIS 3D 2017 software. The numerical modeling approach was verified, in both plane-strain and 3D conditions, based on monitoring data from a deep excavation adjacent to a building in north of Tehran. The selected case study features a 3D geometry which may provide the possibility of better investigation of the building-excavation interaction (Houhou et al., 2019, Russo et al., 2019) for a building close to the excavation corner.

A parametric study was conducted using plane-strain modeling by which the sensitivity of excavation-induced displacements to three types of building modelling methods, for different building dimensions and positions, was investigated. The main section of the paper presents results of a comprehensive 3D-modeling parametric study, which adopts the real geometry and properties of the building. The parametric study was carried out by varying building length (B), width (L) and position (e). Changes in excavation displacements and building rotations are studied, and the most important factors affecting the building-excavation interaction in 3D modeling are introduced.

Section snippets

Characteristics of case study

The case study used to validate the numerical modeling was a 31.2 m deep urban excavation with an adjacent 12-story concrete building on the west side of the excavation (Fig. 1(a)). As shown in Fig. 1(b), the building has the length (B) and width (L) of 30 m, embedment depth of 4.5 m and is located 15 m away from the excavation corner and 4.5 m from the excavation edge. The building has a 1.5 m thick mat foundation, frames with 6 m spans and a floor height of 3 m. The building retaining walls

Numerical modeling

The numerical modeling was based on the finite element method adopted in PLAXIS 3D 2017. A 6 m wide slice model, including two consecutive piles of SOE, (with plane-strain conditions as depicted in Fig. 2(a)) as well as a fully 3D model (Fig. 2(b)) were used for the numerical analysis of the building-excavation interaction. Although the slice model is geometrically 3D, it responds like a plane strain model and yields similar results of 2D analyses. Moreover, some elements such as anchors and

Results of parametric study

The effects of the stiffness, weight and position of the building relative to the excavation on the building-excavation interaction were examined by both the slice and 3D models and were explained on the basis of the building location with respect to the potential failure surface (PFS) inside the soil. The building stiffness and weight were varied by adopting different combinations of B and L. The maximum horizontal displacement of the excavation edge at the midpoint of the crest (i.e. at the

Conclusions

The present study investigated the interaction of a deep excavation and an adjacent building with an emphasis on the location and dimensions of the building. The numerical modeling procedure for building-excavation interaction was verified by plane-strain slice and 3D modeling of an actual excavation and its adjacent 12-story building in PLAXIS 3D 2017 software. Twenty seven plane-strain models and thirty six 3D models were analyzed to investigate the effects of the building modeling method as

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CRediT authorship contribution statement

Arman Maddah: Methodology, Software, Formal analysis, Investigation, Writing - original draft, Visualization. Abbas Soroush: Conceptualization, Supervision, Project administration. Roozbeh Shafipour: Validation, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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