Estimation of Adjacent Building Settlement During Drilling of Urban Tunnels

Transcription

1 Estimation of Adjacent Building During Drilling of Urban Tunnels Shahram Pourakbar 1, Mohammad Azadi 2, Bujang B. K. Huat 1, Afshin Asadi 1 1 Department of Civil Engineering, University Putra Malaysia (UPM), Selangor, Malaysia 2 Qazvin Branch, Islamic Azad University, Qazvin, Iran ABSTRACT Recent urbanization developments in big cities with limited available land for construction, have led the public transportation systems to go underground areas. The occurrences of unexpected damages due to wrong predictions on the behavior of the tunnel lining, the surrounding soil and the improper designing of the tunnel emphasizes the importance of the study and in addition the prediction of possible changes in form throughout the tunnel excavation. Studying the rate of a structure's settlement designed within the vicinity of these tunnels is therefore of great importance. In this paper, employing the Finite Element Method (FEM), optimizing settlement of the structure is considered throughout tunnel excavating. What have to be carefully considered are the horizontal distances between the tunnel and buildings with different stories, the diameter of the tunnel, and the relation between the settlements of buildings in any given direction. In addition, the vertical distance between tunnel and buildings is a crucial issue taken into account in this research. The result of this research can be useful to optimize the construction and implementation of underground structures. KEYWORDS: Tunnels; Finite Element Method; ; Adjacent building INTRODUCTION With the rapid increase in urbanism, there is now a scarcity of available land in large cities resulting in the inevitable implementation of underground lines and the construction of underground metro tunnels in large cities [1, 2]. Such activities undoubtedly face several challenges due to the lack of enough space for locating workshops, constructing shafts and monitoring the local traffic via urban installations among many different problems [3]. The ranges of problems resulting from tunnel drilling include settlement due to the excavation and damaging effects on the surface structures. The prediction and mitigation of different possible damages caused by construction-induced ground movements represents a serious challenge in the design of tunnels. This is a particularly significant problem for shallow tunnels excavated in soft soils, where expensive remedial measures like compensation grouting or structural underpinning must be considered prior to construction [4]. The drilling is mechanized and then applying the pressure on to the face could reduce half of such settlement. Thus, measuring the number of settlements in underground drillings and comparing them with the permissible settlement levels for the surface structures are of critical importance [1, 5, 6]

2 Vol. 19 [2014], Bund. B 470 Several approaches have been used to predict ground deformations related to tunneling. There are three methods, namely, finite-element technique, numerical technique, and empirical technique, that are commonly employed to estimate the ground deformations resulting from tunneling. The choice of technique depends on the complexity of the problem. These strategies also are subject to some significant limitations; initial, in their applicability to totally different ground conditions and construction technique, and second, within the restricted data they provide regarding the horizontal movements and subsurface settlements. Therefore, a correct analytical technique is essential for more accurate estimation of tunneling-induced ground movements [5, 7, 8]. One of the most significant problems in the planning of underground structures is to ensure that the conditions and design oddity planned to utilize the most effective technique of stability analysis should be economical in varied aspects of simplicity while at the same time the results should be sufficiently correct in respect of reliability [9]. However, there has not been much research done to develop a method that can accurately determine predictability of ground deformations. According to the description of tunneling effects on the surroundings, a necessary parameter is studied in this research is the structure settlement on top of the excavated tunnel caused by tunnel boring machine (TBM). The numerous modes for adjacent buildings and the tunnel itself are assumed and the results are estimated and analyzed. MODELING In this paper, the idea is that the tunnel is drilled by a tunnel boring machine and subsequently followed by an installation lining. In this technique, more than the required amount of soil is removed (more than the final diameter) for the tunnel and then the lining runs over that [9]. In this technique reacquired currency tension will occur. This study is designed to evaluate structure settlement caused by drilling a tunnel. In this regard, different diameters of the tunnel, the horizontal and also vertical distances between the tunnel and buildings with their number of stories are modeled. In addition, the soil layering variations in several models should be noted. Assessment of modeling Plaxis is a finite element advanced software used for analyzing the stabilities and also deformations evident in geotectonic engineering projects. This software simulates the effect of rock or soil surroundings, a tunnel drilling project, and studies the interaction between a tunneling method and the surrounding environment. This software permits a simulated modeling of tunnels with a circular section through the TBM drilling technique, and tunnels with compound sections that have arches of various radii through NATM tunnel drilling technique or some other method of tunnel drilling. In modeling cases done by finite element software, a particular geometry being used in such a modeling ought to be selected optimally to prevent possible undesired effects that might emerge when there is a wrong or unsuitable selection of dimensions. As earlier mentioned, the settlement of a structure due to drilling has been studied in this research and every element influencing such a settlement has been considered. Therefore, in the basic model the geometric section utilized for the modeling includes a width of 70 meters and a depth of 35 meters. The tectonic specification of the model is in such a way that there are two soil layers present. In the basic model there is no subterranean water evident and also the soil material is drained. The behavioral model of the soil material is the Columbus's Solution, the settlement of which been examined at point A and also point B. The analysis of the created model is done through different phases. At the primary phase, the tensions within the soil are noted when the structure is established, examined without excavating a

3 Vol. 19 [2014], Bund. B 471 tunnel. In the subsequent phase, the model is analyzed with the tunnel considered. It is significant to note that the place changes ought to be set at zero in the earlier phase as the analysis of this model is for the purpose of evaluating the place change in the structures during the drilling process. Furthermore, it is assumed that while drilling the tunnel, there has passed a lot of time when the establishment of the structure thus it has come to its final place modification limit before the drilling time. In the final part, the analysis is completed by assuming the performance of final lining. The assessed place changes during this part are added to the ones in the previous phase to provide a picture of all such changes occur throughout the tunnel route. Figure 1 represents a network of components in one of amongst the created models. This figure shows that the elements are generated when being meshed five times. Figure 2 shows the situation of the structure and also the tunnel within the initial modeling as connected to the surface of the ground and also the schematic figure at points A and B in the basic model. It is significant to note that point B is at the right and point A on the left side of the lowest balance of the building. Tables 1 to 4 summarize the specifications of the soil layers, the final covering of the tunnel's properties, variations in settlement with changes in tunnel diameter, and specification of surface structures respectively. Figure 1: Elements network in the provided models

4 Vol. 19 [2014], Bund. B 472 Figure 2: A schematic view for considering points A and B Table 1: Soil layers characteristics Layer Type of soil Thickness (m) Coherence (KN/m 2 ) Friction angle Poisson coefficient Specific gravity (KN/m 3 ) Elasticity modulus (KN/m 2 ) 1 Fill clay Table 2: Mechanical parameters of the tunnel lining Explanation Poisson s ratio Normal stiffness ( kn/m ) Elasticity modulus ( kn/m 2 ) Lining tunnel s thickness (30cm) RESULTS ASSESSMENT Comparison of building settlement due to changes in horizontal distance between building and tunnel In this section, the model tunnel is located at different horizontal distances from the adjacent structure and the diameter can increase. Meanwhile, the changes in the diameter of the tunnel assessed

5 Vol. 19 [2014], Bund. B 473 in the final settlement can be summarized. Consequently, in this provided model, various diameters between 4 and 6 m are factored in. The data in Table 3 and Figure 3 demonstrate the increasing horizontal distance of the tunnel to structure versus final structure settlement. In addition, Figure 4 illustrates settlement changes along with tunnel different diameters at both points A and B. In the created models in this case, the simultaneous influence of variation in the tunnel diameter and various placements in the tunnel under the structure has been considered. As Figure 3 shows, increases in the settlement in at point A can be seen. It can also be observed that while the horizontal distance of structure and the tunnel is very significant, the increase in settlement at both points A and B is reduced dramatically. As the horizontal distance increases up to 6 meters and the establishing of the tunnel is right under point A, the settlement at point A increases considerably as the thickness of the soil under the tunnel decreases whereas swelling at point B markedly increases. Also, it is worth mentioning that as the tunnel diameter changes, the settlement at point A increases sharply, as shown in Figure 4. Table 3: The variation in the final settlement of the building under the influence of diameter increase in the tunnel s different placements Diameter (m) Horizontal distance between structure and tunnel (m) A (mm) B (mm)

6 Vol. 19 [2014], Bund. B 474 Figure 3: Increasing horizontal distance of tunnel to structure versus final structure's settlement (Tunnel diameter 6 m) Figure 4: Changes in settlement at point A and point B with variation in tunnel diameter (Tunnel located under structure) Figures 5 to 7 show the variation in bending moment and shear force as the tunnel diameter changes, and the percentage of bending moment as the tunnel diameter changes respectively.

7 Vol. 19 [2014], Bund. B E E E E E Tunnel diameter (m) Bendind moment changes Figure 5: Changes in bending moment as the tunnel diameter changes Figure 6: The variation in shear force as the tunnel diameter change 3.0% % 2.0% 1.5% 1.0% 0.5% 0.0% Percentage of bending moment changes Tunnel diameter (m) Figure 7: The percentage of bending moment as the tunnel diameter changes Comparison of the building settlement due to stories variations with increasing tunnel diameter Figure 8 illustrates one of the provided models for a two-storied building and Figure 9 shows a comparing of the increasing diameter and the settlement at point A, below the two, four and six-storied buildings.

8 Vol. 19 [2014], Bund. B 476 Table 4: Characteristics of surface buildings EA (kn/m) EI (kn m 2 /m) ʋ w (kn/m/m) d (m) Figure 8: with an increase in horizontal distance considering a diameter of 6m and vertical distance of 6m (Building with two stories) Figure 9: Comparison of the stories changing and structure 's settlement at point A(at the lowest balance of the building and on the left side- with increasing the tunnel diameter

9 Vol. 19 [2014], Bund. B 477 Comparison of the building settlement due to variation in the vertical distance between structure and tunnel Variation in the vertical distance between structure and tunnel have been considered in two paths ( Figures 10 and 11). In path 1 ( Figure10), tunnel exactly is located under the building and with increasing vertical distance from the center of tunnel to surface, settlement changes can be seen as shown in Table 5 and variation is plotted in Figure 12. As expected, with increasing vertical distance from the building, it can be noted that the settlement is reduced. In path 2, tunnel has been constructed 3 m under the building and with increasing vertical distance between structure and tunnel, settlement can be summarized as shown in Table 6 and Figure 12. Figure 10: Path 1: Tunnel is located below the building Figure 11: Path 2: Tunnel is located 9 m apart from the built Table 5: with an increase in vertical distance considering a diameter of 6m(path 1) Vertical distance between structure and tunnel (m) A (mm) B (mm)

10 Vol. 19 [2014], Bund. B 478 Table 6: with an increase in vertical distance considering a diameter of 6m(path 2) Vertical distance between structure and tunnel (m) A (mm) B (mm) Figure 12: due to vertical changes between tunnel and adjacent structures at point A in two different paths It is evident from Figure 12, at point A,the range of settlement changes in path 1, when the tunnel is exactly excavated under the building is more than that of path 2, When the tunnel is located 9 m from the structure. CONCLUSION This paper presented a numerical study of the interaction between adjacent building and tunneling in urban areas. Various simulations were done using a Finite element technique which takes into

11 Vol. 19 [2014], Bund. B 479 consideration the presence of the building during tunneling. According to the results, the building evidently has a direct relation to the tunnel diameter. Also, it can be noted that an increase in the tunnel diameter directly affects the extent of settlement. As the horizontal distance increases 2.4 meters and the establishment of the tunnel is toward the left side of the building, settlement increases considerably due to the decrease in the thickness of the soil under the tunnel. At the point (at the lowest balance of the building and on the left side) where the tunnel is nearest to it, there is considerable settlement increase as the thickness of the soil under the tunnel decreases whereas swelling at the opposite point (at the lowest balance of the building and on the right side ) markedly increases. The point which is located far from the tunnel has a settlement of almost zero level when the tunnel is far away at the distance of D, and thereby more displacement of the tunnel does not have any effects on the settlement at this point. REFERENCES [1] Mroueh, H. and I. Shahrour, A full 3-D finite element analysis of tunneling adjacent structures interaction. Computers and Geotechnics, (3): p [2] Mirhabibi, A. and A. Soroush, Effects of building three-dimensional modeling type on twin tunneling-induced ground settlement. Tunnelling and underground space technology, : p [3] Meguid, M., et al., Physical modeling of tunnels in soft ground: A review. Tunnelling and underground space technology, (2): p [4] Yang, J., B. Liu, and M. Wang, Modeling of tunneling-induced ground surface movements using stochastic medium theory. Tunnelling and underground space technology, (2): p [5] Loganathan, N. and H. Poulos, Analytical prediction for tunneling-induced ground movements in clays. Journal of Geotechnical and Geoenvironmental Engineering, (9): p [6] Chou, W.-I. and A. Bobet, Predictions of ground deformations in shallow tunnels in clay. Tunnelling and underground space technology, (1): p [7] Ding, L., et al., Wavelet Analysis for tunneling-induced ground settlement based on a stochastic model. Tunnelling and underground space technology, (5): p [8] Liu, H., et al., Effects of tunnelling on existing support systems of perpendicularly crossing tunnels. Computers and Geotechnics, (5): p [9] Azadi, M., S. Pourakbar, and A. Kashfi, Assessment of optimum settlement of structure adjacent urban tunnel by using neural network methods. Tunnelling and underground space technology, : p , EJGE