A new approach for estimating the transverse surface settlement curve for twin tunnels in shallow and soft soils (original) (raw)
Related papers
Investigation of ground surface settlement in twin tunnels driven with EPBM in urban area
Arabian Journal of Geosciences, 2014
Nowadays, with the increasing population of large cities, the need to expand public transportation, especially metro systems, is greatly increasing in urban areas. Therefore, excavation of new tunnels near the existing ones or other excavations located nearby has become inevitable. Excavation of such tunnels in urban areas should be done by considering the effects of these tunnels on buildings and other urban structures. Significant factors affecting interaction between tunnels, as well as the characteristics of surface settlement, are the existence of mixed ground (soil-rock) at tunnel faces or fault zones in the direction of tunnel excavation which have not been clearly investigated by researchers. These parameters have a great effect on the amount of maximum surface settlement and shape of surface settlement curve. Although several studies aim to analyse the interaction between newly excavated and existing tunnels and its effects on surface settlements, this subject certainly needs further investigation. This study mainly focuses on the effects of the interaction between twin tunnels mainly opened in fault zones and mixed ground on the basis of surface settlement measurements by using Earth Pressure Balance Machine (EPBM). Both numerical and empirical methods are used in this study. Observed data are used to test the validity of the results obtained from three-dimensional numerical modelling. The results from numerical methods were in good agreement with the real data. The results of this study reveal that the amount of maximum surface settlement and shape of surface settlement curve are strongly related to spacing between tunnels, fault zone thickness and type of tunnel face material. The interaction factor is almost zero when spacing is larger than 4D (D is tunnel diameter). Independent of fault zone thickness, the effects of the fault on longitudinal surface settlement continue 25 m from both sides of the fault centre.
Effects of important factors on surface settlement prediction for metro tunnel excavated by EPB
Tunnelling and Underground Space Technology, 2013
Due to population growth, people demand more and more transportation services, there can be no doubt that the requirement for tunnels will also grow. Mechanized excavations using EPB have been successfully applied, especially in urban environments where there is less surface space available, over the past twenty years. Because of excavation speed and less hazardous working environments, use of the Earth Pressure Balance Machine (EPB) is a more popular method in metro, railway and road tunnels in urban areas. Control of surface settlement is very important when tunnels are excavated in urban areas or beneath important structures. This research mainly discusses effects of important properties like tunnel depth, overburden pressure, tunnel dimension and face pressure using empirical, theoretical and numerical methods used to control surface settlement. Results of these methods are compared with observation data.
A new equation for estimating the maximum surface settlement above tunnels excavated in soft ground
Environmental Earth Sciences, 2013
Nowadays, due to urbanization and population increase, need for metro tunnels, has been considerably increased in urban areas. Common characterization of urban area tunnels is that they are excavated in very shallow depths and soft ground. In such excavations, main challenge for tunneling is low bearing capacity and easy deformation characteristic of the ground. Tunnel face instability and the potential surface settlement are the most hazardous factors that should be considered in all tunneling methods applied in urban areas. Incorrect estimation of the maximum surface settlement value can lead to irreparable damages to the buildings and other nearby structures. There are several published relationships concerned with field measurements and analytical solutions to estimate the amount of the maximum surface settlement value due to tunneling. These relationships are not precise for calculating the aimed values. Therefore, providing accurate equations for estimation of these values is certainly useful. First purpose of this study is to determine the effective parameters such as geotechnical factors (cohesion, internal friction angle, density, Young's modulus and Poisson's ratio), and engineering factors (tunnel depth, tunnel diameter and face support pressure) on the maximum surface settlement value. In this study, three metro project constructions namely Istanbul, Tehran, Mashhad in the Middle East were chosen. FLAC3D (Itasca Consulting Group 2002) was used for detailed numerical analysis. The second aim is to present better equations in estimating the maximum surface settlement-based actual data set from several tunnel projects and numerical modeling. The results from the new estimation equation are compared with results of empirical and field observations. The maximum surface settlement values obtained from the new equation have good agreement with the actual results for three different metro case studies.
Indian Geotechnical Journal, 2019
This paper describes the effect of basement excavation and foundation loading on tunnel in sand. Typical tunnel geometry of Delhi Metro and soil conditions in part of Delhi (Yamuna Sand) are considered for modelling. The construction sequences of tunnel excavations, basement footing with retaining wall and the loading on footing have been numerically simulated using plane strain assumption in PLAXIS 2D. Basement foundation, retaining wall, sheet pile and support struts are modelled simulating the construction sequence that is normally adopted in practice. The soil is assumed as elastic-perfectly plastic material, and its failure is governed by Mohr-Coulomb criterion. The tunnel lining, footing, sheet pile, wall and struts are assumed as linear elastic materials. The loading on the footing is modelled in several stages simulating different numbers of storeys for studying the effect of basement excavation and structure/foundation loading. The results indicate that the response of tunnel lining is significantly affected by various stages of basement excavation and foundation loading. Based on the several response parameters of tunnel lining, it is concluded that the critical distance between the tunnel edge and basement footing is found as 2.5 times the tunnel diameter within which the basement excavation and foundation loading have shown significant influence on tunnel response.
Surface settlement predictions for Istanbul Metro tunnels excavated by EPB-TBM
Environmental Earth Sciences, 2011
In this study, short-term surface settlements are predicted for twin tunnels, which are to be excavated in the chainage of 0 + 850 to 0 + 900 m between the Esenler and Kirazlı stations of the Istanbul Metro line, which is 4 km in length. The total length of the excavation line is 21.2 km between Esenler and Basaksehir. Tunnels are excavated by employing two earth pressure balance (EPB) tunnel boring machines (TBMs) that have twin tubes of 6.5 m diameter and with 14 m distance from center to center. The TBM in the right tube follows about 100 m behind the other tube. Segmental lining of 1.4 m length is currently employed as the final support. Settlement predictions are performed with finite element method by using Plaxis finite element program. Excavation, ground support and face support steps in FEM analyses are simulated as applied in the field. Predictions are performed for a typical geological zone, which is considered as critical in terms of surface settlement. Geology in the study area is composed of fill, very stiff clay, dense sand, very dense sand and hard clay, respectively, starting from the surface. In addition to finite element modeling, the surface settlements are also predicted by using semi-theoretical (semi-empirical) and analytical methods. The results indicate that the FE model predicts well the short-term surface settlements for a given volume loss value. The results of semi-theoretical and analytical methods are found to be in good agreement with the FE model. The results of predictions are compared and verified by field measurements. It is suggested that grouting of the excavation void should be performed as fast as possible after excavation of a section as a precaution against surface settlements during excavation. Face pressure of the TBMs should be closely monitored and adjusted for different zones.
Journal of Civil Engineering and Materials Application, 2019
Tunnel excavation on soil lands may leads to horizontal and vertical displacements around the tunnel. The displacements can reach the ground surface and cause damages to existing structures on the ground. Hence it is so important to estimate the ground settlement induced by excavation, particularly in urban environments. In this study, the effect of longitudinal distance between two tunnel faces on ground surface settlement is examined during the excavation of twin tunnels. Accordingly, the ground settlement is measured for the states where the distance between tunnel faces is 0D, 0.5D, 1D, 1.5D and 2D. The most important results suggest that creating a longitudinal distance (lagging) between the faces of twin tunnels during excavation operations causes changes in surface ground settlement. The maximum surface ground settlement along the width and length of tunnels decreases as the distance between two tunnel faces increases.
Stage 1 metro construction for the city of Izmir, which has the third highest population in Turkey, has been successfully completed. It included a 2.75 km tunnel excavated by tunnel-boring machine (TBM) using the earth pressure balance (EPB) method in soft ground conditions with shallow overburden. This paper revisits the surface settlement values predicted by the empirical approach, adds numerical analysis, describes the geotechnical instrumentation for field performance and then compares the observed deformations with empirically and numerically predicted ground deformations. INTRODUCTION With a population of 3.5 million, Izmir is the third biggest metropolis and one of the most historically significant cities in Turkey. The total length of planned rail transport in the Izmir Bay area is 45 km, according to the transportation master plan. The Yapi Merkezi – AdTranz Consortium has successfully completed Stage 1 of metro construction for Izmir Metropolitan under a design-and-build t...
Numerical modeling of shallow tunnels : analysis of the surface settlements
2020
The analysis of shallow tunnels is necessarily related to the study of the excavation influence on the ground surface. As the excavation proceeds, surface settlements are expected to be generated, forming the socalled settlement basin. Thereby, its correct evaluation is important since these movements could create disturbances in surrounding structures. Estimation of tunneling-induced ground movements can be done by analytical, empirical, and numerical methods and, currently, the best assessment of tunneling process consists of finite element modeling. The current paper presents a numerical model elaborated in the software ANSYS with the aim to evaluate the surface settlements induced by tunneling. The 3D finite element model concerns soil and lining elements, using the activation and deactivation tool to simulate the excavation and lining placement. To perform the analysis, the soil mass was represented by a plastic model using the Drucker Prager criterion and the concrete lining is considered elastic. Five reported cases of real tunnels (Heathrow Express, Green Park, Barcelona Subway, Brasília Subway, and São Paulo Paraíso tunnels) are simulated to validate the model with analytical and experimental solutions.
Surface subsidence induced by twin subway tunnelling in soft ground conditions in Istanbul
Bulletin of Engineering Geology and the Environment, 2011
Unlike the symmetrical surface settlement trough of a single tunnel which can be described using the Gaussian function, surface settlement over twin tunnels can be symmetric with respect to the mid-point between two tunnels or asymmetric. The paper reports the settlement troughs which developed when earth pressure balance (EPB) machines were used to excavate twin tunnels at shallow depth in the soft ground conditions beneath a developed part of Istanbul. An attempt is made to evaluate the effects of different factors on the surface subsidence. Detailed monitoring was undertaken when one tunnel was advanced ahead of the other and when only one tunnel was being driven. It was found that the shapes of the subsidence troughs over the two tunnels were different and varied with the excavation of the second/subsequent tunnel. It is concluded that changes in the subsidence trough are related to disturbance in the geo-material when an excavation is advanced ahead, as well as the nature and thickness of the overburden. Keywords Soft ground Á Subsidence Á Surface monitoring Á Twin tunnels Résumé La cuvette symétrique de tassement au-dessus d'un tunnel peut être décrite par une fonction gaussienne, mais le tassement au-dessus d'un bi-tube peut être symétrique par rapport au point médian entre les deux tubes ou asymétrique. L'article présente les cuvettes de tassement qui se sont développées quand un tunnelier à pression de terre (EPB) a été utilisé pour creuser deux tubes à faible profondeur dans des conditions de sols mous sous une partie de la ville d'Istanbul. Une tentative est faite pour évaluer les effets de différents facteurs sur le tassement de surface. Une instrumentation de précision a été mise en oeuvre lorsque l'un des tubes était en avance par rapport à l'autre et lorsque seulement un tube était foré. On a trouvé que les formes des cuvettes de tassement au-dessus de deux tubes étaient différentes et se modifiaient avec le creusement du deuxième tube. On a conclu que les modifications de la cuvette de tassement résultent d'une part des déformations des matériaux géologiques lorsqu'une excavation prend de l'avance sur l'autre et d'autre part de la nature et de l'épaisseur du recouvrement. Mots clés Sol mou Á Tassement Á Instrumentation de surface Á Bi-tube
Estimation of Surface Settlements Troughs Due to Subway Station Construction in Claystone
Biosciences, Biotechnology Research Asia, 2015
The article is focused on the issues of predicting the earth surface deformation in building underground structures with complex spatial configuration in restrained urban conditions. Attention is mainly paid to the development of a method for predicting deformations of the earth surface caused by building subway stations, based on numerical modeling. The issues of developing numerical models of complex spatial underground structures have been considered, with regard to the construction sequence. A geomechanical model of predicting deformations in construction of underground structures in claystonelike clays, described as a non-linear transversely isotropic medium, has been proposed. Detailed analysis of the results of the monitoring of the earth surface settlement has been made in the construction of the "Obvodny Kanal" subway station in St. Petersburg (Russia). For the construction of the "Obvodny Kanal" subway station, calculation was made in order to determine the deformation of the earth surface. Substantiation of the reliability of the proposed method of predicting deformations of the earth surface is made based on comparing the monitoring results to a numerical simulation.