Ground Response due to Buried Structure Construction Process (original) (raw)
Related papers
Tunnel excavation disturbs the initial stresses balance and causes stresses redistribution in soil around it. It is significant to study the characteristic of displacements of soil surrounding around tunnel with and without lining. The finite element analysis is used world widely in tunnelling to obtain the soil displacements caused by tunnel excavation. Based on numerical simulation method, the vertical displacements of soil surrounding around Baghdad metro at Baghdad city center, under Al-Tairan Square, are predicted in this paper using the commercially available finite element package, Abaqus 2016. Aseries of actual tunnelling processare simulated by using a fully coupled three dimensional stress-pore pressure finite element model to realistically capture the mechanical and hydrological interaction between the tunnelling and ground water. The vertical displacements of soil surrounding around Baghdad metro passing under Al-Tairan Square are computed through the time periods of three sequential simulation steps. These steps are named as the excavation, linings installation, and consolidation steps. It is found that maximum vertical displacement occurs at the crown to the downward with value equal to 28.5 m approximately after linings installation immediately. Also highlighted is the importance of the stress-pore pressure coupled analysis in the numerical prediction tunnel behaviour.
One of the most widely risks in tunnelling in urban regions is the excavation under urbanized constructions. The loads of these constructions are considered as surcharge loads applied at the ground surface. Existing of such surcharge loads leads to increase the stresses and to change all field variables in medium during and after tunnel construction. It is significant to predict the ground settlements and the displacements of soil surrounding around tunnel at sites where buildings, rivers, etc. exist or may be existed in the future. In this paper, movement of soil around Baghdad metro are predicted at location, its coordinates are 443954.463 m for X and 3688861.836 m for Y, in which buildings with medium heights are found basing on numerical simulation method. The commercially available finite element package, Abaqus 2016, is used to simulate Baghdad metro at this location. A series of actual tunnel process is simulated using a fully coupled three dimensional stress-pore pressure finite element model to realistically capture the mechanical and hydrological interaction between tunnelling and ground water. Then, the vertical displacements of soil surrounding around Baghdad metro at that location are computed through the time periods of three sequential simulation steps. These steps are named as the excavation, linings installation, and consolidation steps. It is found that maximum vertical displacement occurs at the crown to the downward with value equal to 3.8 m approximately after linings installation immediately. Practical implications of the findings from this study are also discussed.
Numerical Analyses of Soil Deformations Around Deep Excavations
2013
In this study, the deep excavation of Cincin Station located along the Bağcılar-Otogar metro line which is currently under construction in Istanbul is modeled numerically. The excavation (depth 32.5 m) of the station is carried out with a surrounding slurry trench diaphragm wall and top-down construction method. The six slabs of the station building and the foundation mat are used as support elements. Lateral soil displacements are measured with inclinometers placed in the wall and nearby soil layers. The results of numerical analysis using soil profile and geotechnical parameters obtained from conventional field and laboratory tests and measured lateral displacements are compared. Then using the same soil model, soil displacements expected to occur if some other alternative excavation support systems were used is investigated. As alternative support systems use of steel pipes as internal bracing and a piled wall with pre-stressed tie-backs are considered. The calculated soil displacements for different support systems are compared with each other and the measured values. The effects of certain design parameters such as the rigidity of internal bracing elements, the pile diameters and the pre-stressing level of tie-backs are investigated through numerical analysis.
Tunnelling and Underground Space Technology, 1999
This paper pn,.sents an evaluation of the settlement prediction techniques used to estimate the surface settlements associated with the construction of the Greater Cairo Metro Line 2. The construction of the Cairo Metro involved I~he construction of cut-and-cover underground stations and bored tunneling. A typical underground station was executed using top-down construction technique. The twenty two meters excavation was carried inside a watertight box with 50-m-deep diaphragm walls to form the sides and a 7m thick groutedplug at the bottom. Tunneling was performed using a slurry shield tunnel boring machine, TBM, having an internal diameter of 9.48 m. This analysis is the first step in uiew of enhancing the procedures of settlement prediction and appraising potential damages to overlying structures and utilities for the future construction of the twin road tunnels in the historical urban environment of AI Azhar area and If7~an El I~alily market in Cairo.
MATEC Web of Conferences
Soil displacements due to unsupported deep excavation may cause severe damages to the nearby structures and foundations systems. Such excavations affect the state of stresses and displacements field of the surrounding soil. In this study, the soil displacements at five observation points were continuously monitored for23 days, which was the time period of excavation of about 7 m deep open tunnel. The reference points were installed on the ground surface at horizontal distance ranging from 1.25 to 3.25 m from tunnel excavation edge. The construction work was related to the project of developing the Army Channel/ Zeyouna section in the Eastern part of Baghdad City. The field observations indicate upward vertical displacement and outward lateral displacements during the first 10 days when the excavation depth was within 4 m. After that, the displacement trend was generally reversed. The displacement values were within 12 mm and vary from one observation point to another depending on the lateral distance of each point from excavation edge. The finite element package PLAXIS 3D was used to simulate the problem after obtaining the required soil parameters by an extensive site investigation. The analysis results in general, compare well with the field observations in terms of soil displacements at the reference points, especially during the first 10 days. This finding may reveal the reliability of the analysis results at other locations in the surrounding soil.
Ground deformation mechanism due to deep excavation in sand: 3D numerical modelling
In densely built areas, development of underground transportation system often involves excavations for basement construction and cut-and-cover tunnels which are sometimes inevitable to be constructed adjacent to existing structure. Inadequate support systems have always been major concern as excessive ground movement induced during excavation could damage to neighbouring structure. A detailed parametric analysis of the ground deformation mechanism due to excavation with different depths in sand with different densities (D r =30%, 50%, 70% and 90%) is presented. 3D finite element analyses were carried out using a hypoplastic model, which considers strain-dependent and path-dependent soil stiffness. The computed results have revealed that the maximum settlement decreased substantially when the excavation is carried out in the sand with higher relative density. This is because of reason that sand with higher relative density possesses higher stiffness. Moreover, the depth of the maximum settlement of the wall decreases as the sand become denser. The ground movement flow is towards excavation in retained side of the excavation. On the other hand the soil heave was induced below the formation level at excavation side. The maximum strain level of 2.4% was induced around the diaphragm wall.
Characterizing Surface Ground Settlement Induced by Underground Tunnel Excavation
2016
The construction of underground tunnel, without a proper mitigation and proper design, a catastrophic event may be happen due to ground sedimentation. In the view of the issue of ground movement, it is possible to predict the ground sedimentation by plotting a Gaussian graph perpendicular alongside the direction of tunnel construction. The information obtained in the qualitative and quantitative data can be used to solve the geotechnical problems. This is to provide enough and reliable information to evaluate the performance of the structure and also the characteristics of the soil. The study is based at the location of Greater Kuala Lumpur (KL) and Selangor, specifically from Sungai Buloh Station, then across to KL and will end at Taman Desa Seroja Station for in total of 51km and 31 stations
INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING
A criterion proposed by Instituto de Ingeniería, UNAM (II-UNAM) to perform ground-lining interaction analyses for tunnels, when these are formed by segmented rings and double lining, is described. The criterion can be introduced in the "hybrid" analysis method, which is an iterative procedure between geotechnical and structural numerical modeling, where the convergence in terms of diametrical displacements between both types of modeling allows determining the effective stiffness of the tunnel [1]. The criterion allows calculating loads and mechanical elements for the tunnel lining and checking serviceability limits corresponding to constructive or operative aspects. It is useful in the design stages, for revisions of tunnels that are under construction or for existing tunnels affected by new engineering works. In this paper, it is applied to check the interference of a new deep foundation with an existing tunnel.
2020
The current study is aimed at investigating the basic soil behavior involved in a TBM-EPB excavation and the capability of the Modify Cam Clay (MCC) model is verified for the analysis of the soil settlement in cohesive soils. Tunnel excavation in urban areas can engender considerable ground movements, which is known as one of the complicated issues that may have negative effects on the extant structures. In this paper, the construction of the second line of the Mashhad metro is considered as a case study. Each section of the ground was modeled by two constitutive models, namely MCC and Mohr-Coulomb (MC). Afterwards, the results of numerical analyses and monitoring data were compared with each other. In addition, real parameters of soil, such as volume loss and the inflection point, were obtained via empirical approaches verified by tunnel monitoring. Numerical modeling was performed by FLAC3D software. Based on the transverse and longitudinal sections settlement, the MCC model showe...
Tunnelling and Underground Space Technology, 2006
Understanding, and hence predicting, the ground displacements associated with multiple tunnel constructions in soft ground (soil rather than rock) is particularly important in urban areas. It has been shown by a number of previous authors that the effect of previously strained soil above the first tunnel has an effect on the ground displacements observed above subsequent tunnels constructed in close proximity to the first. This paper describes the design, development and preliminary test results for a purpose built test tank for modelling, at approximately 1/50 scale, multiple tunnels constructed in soft clay. The tank is 1.80m long, 0.60m wide and 0.45m high (this height is doubled when the consolidation section of the tank is added). The soil is consolidated from slurry to a prescribed strength by specifying the moisture content. A water bag arrangement is used to maintain a surcharge at the soil surface after consolidation in order to produce a realistic over-consolidation ratio. The tunnels (0.08m diameter) are constructed using an augering technique, with a shield and lining arrangement that allows a consistent 'volume loss' to be produced during construction. The tank has side faces made of clear Perspex, which enables the movement of the soil close to these faces to be observed. The soil displacements are recorded using digital cameras and analysed by computer. The paper describes some of the promising initial test data and the trends observed.