Tang, Chuanjin
(2024)
Tunnelling effects on capped piles and masonry buildings with shallow strip foundations.
PhD thesis, University of Nottingham.
Abstract
The increasing demand for infrastructure space in urban areas presents enormous prospects and challenges for the expansion and utilisation of underground spaces. Tunnels are a common way to utilise underground space, yet tunnel excavations are often situated close to existing underground and surface structures (such as piles, strip foundations, and masonry buildings) and bring potential risks to these structures. Therefore, it is important to understand soil-structure interaction mechanisms in tunnelling scenarios to provide a reference for designing new tunnels near deep pile foundations or under masonry buildings with shallow strip foundations. Nevertheless, due to the complexity of actual engineering projects, few studies have accurately investigated the comprehensive tunnel-soil-pile interaction (TSPI) and tunnel-soil-masonry building interaction with shallow strip foundation (TSBI) problems.
This thesis focused on three main areas to provide insights into TSPI and TSBI problems: (1) mechanisms of tunnelling under capped non-displacement piles (TSPI), (2) development of new approaches for studying tunnelling under masonry walls with shallow strip foundations (TSBI), and (3) TSBI mechanisms involving different types of masonry walls and material parameters. This study used geotechnical centrifuge testing as the primary method to simulate the tunnelling process under foundations in dense sand. In particular, based on the previous method for studying tunnel-pile-elastic framed building interaction problems developed at the University of Nottingham Centre for Geomechanics (NCG), an advanced coupled centrifuge-numerical modelling (CCNM) approach was developed (regarding the study of (2)). In the new CCNM approach, the displacements of a strip foundation affected by tunnelling measured in the centrifuge model are transferred to an Abaqus numerical model of a masonry wall, which predicts changes in structural loads within the wall and then feeds back the updated loads to the strip foundation in the centrifuge model. This iterative process continues between the centrifuge and numerical models until the system reaches stability. The new CCNM method combines the advantages of centrifuge models (providing soil stress/deformation data) with those of numerical models (capturing structural details along with associated load distributions and deformations) and achieves the use of non-linear materials and a continuous interface between physical and numerical domains in hybrid testing.
The study of (1) tunnelling under capped non-displacement piles (TSPI) focuses on the effect of a pile cap (representative also of a raft or grade beam) in contact with the soil surface on load transfer mechanisms. Experiments included loading tests to ascertain the foundation capacity and load-displacement response in the presence/absence of an underlying model tunnel. Individual `reference' pile response is compared for cases with and without a pile cap, including pile displacements and load distributions between the head, shaft, and base; the case of `friction' piles with a compressible base is also considered. Results show that uncapped piles with relatively large service loads experience `geotechnical failure' (i.e. large settlements or a significant increase in settlement rate with tunnel volume loss) to mobilise base or shaft resistance, while pile caps can effectively prevent geotechnical failure.
The study of (2) tunnelling under masonry walls with shallow strip foundations (TSBI) verifies that the CCNM approach can effectively achieve load redistribution within masonry walls during tunnelling and its applicability in scenarios with different relative wall-to-tunnel positions. The CCNM test results, when compared with `conventional' test outcomes where wall loads remain constant during tunnelling, highlight the importance of wall stress redistribution in risk assessments. The function of load redistribution is also well demonstrated in eccentric cases, where the location of tensile damage shifts from the lower part of the wall to the upper part (near the middle of sagging/hogging regions) when the wall-to-tunnel eccentricity e/L increases from 0 to 1/2. The bays nearest the tunnel centreline exhibit more bending behaviour with equivalent plastic strain areas (PEEQ) reducing with e/L, while bays above inflection points or further away from the tunnel show mixed bending and shear response with PEEQ for bays further away tending to increase with e/L.
The study of (3) TSBI mechanisms with different types of masonry walls and material parameters reveals the role of wall structural characteristics and material properties in TSBI problems by CCNM tests on tunnelling under standard masonry walls (with different heights and openings) and non-standard walls (with varying Young's modulus and density within a two-storey masonry wall with openings). The results show that high bending stiffness and low self-weight cause a dispersed distribution and horizontal connections (i.e. wall length direction) of tension damage areas within the walls and similar maximum bay angular distortions, while low bending stiffness and high self-weight result in a concentrated distribution and vertical connections (i.e. wall height direction) of tension damage areas and higher maximum bay angular distortions. No gaps exist between the foundation and the surface, and more flexible or lighter walls produce greater differential settlements. This part also explores the impact of the existing walls on soil movements during tunnelling.
In short, this thesis makes innovative contributions to, in tunnel excavation scenarios, the load transfer mechanisms of cap piles, the testing approach for the response of masonry walls with shallow strip foundations, and the deformation and damage mechanisms of masonry walls.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Marshall, Alec
Heron, Charles |
| Keywords: |
tunnel, pile, pile cap, strip foundation, masonry wall, centrifuge modelling, Abaqus, hybrid modelling |
| Subjects: |
T Technology > TA Engineering (General). Civil engineering (General) > TA 630 Structural engineering (General) |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering > Department of Civil Engineering |
| Item ID: |
79937 |
| Depositing User: |
Tang, Chuanjin
|
| Date Deposited: |
10 Dec 2024 04:40 |
| Last Modified: |
10 Dec 2024 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/79937 |
Actions (Archive Staff Only)
 |
Edit View |
Tools
Tools
