Physical modeling of tunnel induced displacement in sandy grounds (original) (raw)
Related papers
Ground Movements due to Shallow Tunnels in Soft Ground. II: Analytical Interpretation and Prediction
Journal of Geotechnical and Geoenvironmental Engineering, 2014
This paper considers the practical application of analytical solutions for estimating ground movements caused by shallow tunneling in soft ground using closed-form expressions presented in a companion paper based on linearly elastic and average-dilation models of soil behavior (Pinto and Whittle, 2011). The analytical solutions express two dimensional distributions of ground deformations as functions of three parameters: the uniform convergence and relative ovalization of a circular tunnel cavity, and either the Poisson's ratio or the average dilation angle for elastic and plastic behavior, respectively. This paper shows that the analytical predictions can achieve very good representations of the distribution of far field deformations through a series of case studies in clays and sand. In some cases, the input parameters can be interpreted from a simple calibration to three independent measurements of ground displacements comprising surface settlements above the tunnel centerline and at a reference offset, and the lateral displacement at the springline elevation, recorded by an inclinometer at an offset of one tunnel diameter from the centerline. However, it is generally more reliable to use a least squares fitting method to obtain the model input parameters, using all available extensometer and inclinometer data.
Experimental study of surface failure induced by tunnel construction in sand
Engineering Failure Analysis, 2020
An experimental study was conducted to determine the effects of tunnel construction on ground movements in sand. In this regard, a small-scale three-dimensional model test was developed, and several laboratory model tests were carried out under single gravity in a sand sample with three different relative densities of 30, 50, and 75% and a cover-to-diameter ratio of 3. To simulate the volume loss induced by the tunnel boring machine, the casing method was utilized. In the model tests, an elastic aluminium liner was used as a tunnel supporting system and a pipe casing was utilized to model a tunnel shield. By pulling out the tunnel shield progressively and replacing it with tunnel liner, the soil was allowed to move toward the tunnel and the surface settlements were measured by using linear variable differential transformers. The results show that increasing the value of the relative density of sand reduces the ground movements induced by tunneling. The settlement trough width increased almost linearly with increment of the overburden. Also, the results reveal that in dense sand the ground settlement trough is slightly less than the volume loss. For loose sand, the volume of settlement trough is nearly twice the volume loss. In shallow tunneling and loose sand produces remarkable movement on the ground surface.
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.
Ground Behaviour Around a Tunnel Using Various Soil Models
Electronic Journal of Geotechnical Engineering
Finite Element (FE) analyses are used world widely in geotechnical engineering to obtain the soil displacement caused by tunnelling. The surface settlement induced by tunnelling predicted by FE is known to be wider and shallower than the field measurements particularly for stiff clays with high coefficient of earth pressure at rest, K 0 . It has been recognized that neglecting the non-linearity, anisotropy and three-dimensional effects of the soil model as well as K 0 condition can be the reasons of this discrepancy. Unfortunately, such numerical studies were only limited to the problem in the plane strain condition whereas tunnelling is obviously a three dimensional (3D) problem. This paper compares 3D FE modelling of tunnel constructions in stiff soil of London Clay using non-linear soil model with low and high K 0 regimes. It was found that modelling using isotropic non-linear soil with low value of K 0 gave the best matched-fit data on the observed greenfield surface settlement ...
Ground loss due to circular tunnel deformation in sands
2008
Considerable ground settlement can occur during tunnel construction. Shape of the settlement trough during tunnel deformation closely follows a normal distribution curve. However, most analytical solutions only approximately represent this profile because of the assumption of uniform radial displacement field around the tunnel during its deformation which presumably exists only at shallow depths. For large diameter tunnels and when non-uniform grout pressure is used, tunnel axis is prone to distortion making these solutions unreliable. This paper examines experimental results of tunnel collapse in small-scale centrifuge environment. Tunnel walls were represented by pressurised rubber membrane. Cover to diameter ratio of the tunnel and relative density of the sand were the only variables in the tests. All tests were conducted on the large diameter centrifuge at IIT Bombay. The results show that deformation above the crown and width of settlement trough, both increase near to the ground surface. The results are compared to data available in the literature and relationship between point of inflection and tunnel depth is derived.
The effect of suction on ground surface settlement for a tunnel
E3S Web of Conferences, 2019
This paper addresses the physical modelling of a tunnel for saturated and unsaturated sand as well as tests in dry condition. A series of tests were conducted for a 50 mm diameter tunnel buried 25 mm into a poorly graded fine sand under different normal stresses: 0.78, 1.56, 2.34 and 3.31 kPa. Suction was controlled by means of the hanging column technique (HCT). Particle image velocimetry (PIV) was also utilised to obtain the vector displacement and compared with the results of the physical modelling. The results of the fully saturated sample showed that the sample experienced a sudden spatial collapse above and around the tunnel's crown. In addition, large displacement on top of the tunnel's crown was also observed for the fully dry case. However, the unsaturated sample did not experience any sudden collapse. This was attributed to the effect of the suction contribution on strength.
3D numerical simulations of tunneling induced soil deformations
Journal of Physics: Conference Series, 2021
The accurate prediction of the maximum surface subsidence caused by shallow tunneling in soil environments is a valuable criterion for safe design and operation, especially in urban areas. To investigate the surface subsidence due to tunneling, the simultaneous impact of depth and diameter of the tunnel in both saturated and dry conditions have been investigated using a FLAC3D Finite Difference Method. Six models having different diameters (7 m, 8 m, and 9 m), depths (12 m, 16 m, and 20 m), and face pressures (0.34 MPa, 0.36 MPa, and 0.38 MPa) were developed. A step-by-step excavation process of the tunnel advance was considered in the modeling to account for deformations ahead of the face and the shield’s effect. Results showed that depth and diameter induce a significant effect on the ground surface displacement values and crown displacement values. As face pressure increases, the effect of tunnel depth and diameter on surface and crown displacements decreases, and the effect of s...
1 Ground Movements Due to Shallow Tunnels in Soft Ground: 1. Analytical Solutions
2016
ABSTRACT: This paper presents simplified closed-form analytical solutions that can be used to interpret and predict ground movements caused by shallow tunneling in soft ground conditions. These solutions offer a more comprehensive framework for understanding the distribution of ground movements than widely used empirical functions. Analytical solutions for the displacement field within the ground mass are obtained for two basic modes of deformation corresponding to uniform convergence and ovalization at the wall of a circular tunnel cavity, based on the assumption of linear, elastic soil behavior. Deformation fields based on the superposition of fundamental, singularity solutions are shown to differ only slightly from analyses that consider the physical dimensions of the tunnel cavity, except in the case of very shallow tunnels. The Authors demonstrate a simplified method to account for soil plasticity in the analyses and illustrate closed-form solutions for a three-dimensional tunn...
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