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DESIGN OF THE TECHNOLOGICAL PROCEDURE OF BUILDING THE DRIVEN TUNNEL BY MEANS OF PHYSICAL MODELLING Weiglová Kamila Brno University of Technology, Faculty of Civil Engineering, Department of Geotechnics, Veveří 331/95, 602 00 Brno, Czech Republic Erbenová Alexandra Brno University of Technology, Faculty of Civil Engineering, Department of Geotechnics, Veveří 331/95, 602 00 Brno, Czech Republic SYNOPSIS The article deals with states of stress and deformation to the failure limit state of one Dobrovskeho tunnel tube. Within the physical modelling the whole tunnel profile was sold with thinking over the influence of lining up to the limit state. Further, the technology of driving by vertical segmentation excavation was studied. 1. INTRODUCTION For solving problems at the Institute of Geotechnics connected with the construction of the Dobrovsky tunnel belonging to the Great City Circuit (GCC) in Brno, physical, or scale models were built up solving the strain and stress states up to the failure strength for one tunnel tube. We were given the data input necessary for the formulation of the solution of problems connected with the construction of the Dobrovsky tunnel in models, such as dimensions of the tunnel, geological conditions and the technological procedure of the construction, by the GEOtest Brno, which participated in the construction of the Galleries in the tunnel considered. Within the modelling the following were solved at the Institute of Geotechnics - - The whole profile of the tunnel, considering the lining, the system being loaded up to the failure strength with the formation of shear surfaces. The finding of the stability of the provisional rock pillar (middle pillar) between the galleries during the tunnelling by the vertical division of the purchase including the determination of the optimum length of the area. Examination of the rate of extrusion of the foundation into the footwall up to the deformation strength of the rock pillar. Inversion analysis during the identification of the deformation of models (shear potential) and using the stereophotogrammetric analytical method. The scale models were built up on the basis of dimensional analysis and in accordance with the theory of similarity. The transition from the tunnelling with the full profile to the technology of tunnelling by the vertical division was implemented by the set of physical conceptional models (termed by Geo-Brno A, B, C) and detailed models (denoted by Geo-Brno D1, D2, D3, D4). 2. GEOTECHNICAL DESCRIPTION OF THE MODELLED PLACE AND GENERAL PRINCIPLES Dobrovsky tunnels of the GCC will be an important part of the basic communication system of Brno-City, but they will also be a part of the roadway network of the Czech Republic (1/42) and the international European network (E 461) The tubes in the length of about 1 000 m will be driven, only the sectors near the portal will be sunk. The tunnels will be conducted in parallel in the axial distance of about 80 m. The overall length of the tunnels will be about 1 200 m. Fig. 1 The geological environment consists of cover layers of loess loams and charges. In the lower horizon in places there are water-bearing and sandy terraces. The foundation of the terraces consists of Brno calcareous clays of Neogene (Miocene) age. The clayey massif subsequently also the tunnel tubes proper will be tunnelled. TRANSVERSAL GEOTECHNICAL PROFILE – PALACKEHO AVENUE STATIONING 1.39 KM (TUNNEL I) AND 1.38 KM (TUNNEL II) Fig. 2 Interpolation of the Exploration Probes Explanation: 123456- made-up ground loess loam, light brown, rigid to solid clayey loam, dark brown, rigid clayey loam, dark brown, rigid to solid clay-sandy gravel, and-or sand with gravel with interlayers of clayey loam, water bearing grey clay, rigid Physical models were applied at the stationing 1.380 km (tunnel II), i.e. for the sector with low overburden layers. Determining for the choice of the technological procedure of the construction is the stability of the rocks, both from the viewpoints of labour safety, mechanisation of the working methods and also with respect to the maximum efficiency of the construction performance. For the use of the technology of tunnelling by the vertical division in cohesive soils it was necessary to identify the principles of the New Austrian Tunnelling Method for the full profile (section). That is why in the first phase conception physical models were built (models Geo-Brno A, B, C). The appropriate forecast of the rock stability is, however, very difficult, because a whole number of factors affecting one another must be considered. They are above all: the dimensions of the unlined face of the tunnel, the strength of the rock, its original stress, the size of the stress concentrations brought into the rock by the breaking, the rigidity of the outfit of the tunnel, the “primary state” and, in the case of clays, the effect of time is also very important. From those factors we usually only know the dimensions of the face of the tunnel. For the stability of the face also the orientation and inclination of the rock beds are important. By removing the soil from the working face of the tunnel the face of the tunnel becomes unstable. The unrigged roof loses its natural support and the length of the area is thus prolonged by this unwanted way. That is why the largest risk area is the stability of the face, where at the same time the subsidence of the structure is threatening. For the implementation of the building of the Dobrovsky tunnel the decisive factor is the stability of the face and the quality of the technological proceeding of the construction. The objective of the technological tunnelling in the Geo-Brno models was the determination of the pressures inside the tunnel necessary for maintaining the stability of the face for the different lengths of the area for different values of the defined parameters. From the above it follows that the stability of the face is closely related to the stability of the overlying layers and the stability of the provisional rock pillar (model Geo-Brno D). Since these problems of stability of the Dobrovsky tunnel affect the technological procedure of the construction, respecting the changeability of the properties of rocks in place and time, it was necessary to solve these wide and requiring problems of the stability of the tunnel also by means of experimental modelling, i.e. by physical models Geo-Brno A, B, C, D and on the basis of measurements in situ and the results of physical modelling subsequently optimise the calculation methods. For the solution of stability for all models we started from the theory of limiting states. 3. CONDITIONS OF SOLVING THE TASK BY MODELLING FOR TUNNEL DOBROVSKEHO To maintain the relation between the model and the reality it was necessary to fulfil the following conditions: Geo-Brno models have to be geometrically similar to reality Actions taking place in the Geo-Brno model and in the working have to belong to the same class of actions. The initial and edge (boundary) conditions in the model, expressed in the dimensionless form, have to be numerically identical with dimensionless conditions in the working. The dimensionless arguments of the same name have to be numerically equal in the model and in the working. The following magnitudes (the system of length, mass and time) have the same effect on the state of tension in the rock massif and the deformation of the outfit of the tunnel: V1 V2 V3 V4 V5 V6 V7 V8 V9 volume mass height of overlying beds physicomechanical modulus resistance of rock to failure height of tunnel opening width of tunnel opening driving speed thickness of gunite reaction of outfit 1 1 1 -2 l m t -3 0 -2 -2 0 0 1 1 1 1 0 1 1 0 0 0 0 0 0 0 0 -1 0 Among the magnitude there exists (on the basis of theory) the relation: F(V1, V2, V3, V4, V5, V6, V7, V8, V9) = 0 n=9 In determining the dimensionless products we are interested in solving the system of equations. For the formulation of solving the problems it is necessary to experimentally determine regressive functions of the critical state of tension necessary for maintaining the tunnel Dobrovského with low overlying beds. The critical state of tension depends on the following dimensionless parameters: Pv Pc Pk Pp Ptm Pu ratio thickness of overlying beds to diameter of purchase value of the ratio of volume density of material multiplied by the average of purchase to coherence ratio of length of free purchase (attack) to the diameter of purchase the ratio of the free purchase (drive) to the diameter of the purchase. the ration of the total maximum strain in the axis of the tunnel before the driving to cohesion function of the angle of shear strength 4. MODELLING MATERIÁLS, SCALE OF MODELS, METHODS OF MEASURING THE STATE OF STRAIN AND RESHAPING The choice and procession of equivalent materials for the model of Dobrovsky tunnel is important, because it depends on them to what extent the conditions of similarity will be fulfilled. Equivalent materials have to fulfil the conditions of similarity with the genuine material not only in the basic parameters, such as the volume density, pressure strength, tension and shear, modulus of elasticity, the Poisson number, but it has also to have a similar working diagram. Therefore it was necessary to pay close attention to the choice and selection of the model materials. For solving the stability of the tunnel from EM the law of similarity for the building of the model are fulfilled by granular materials. The scale of the model is chosen according to the smallest part of the structure (in our case it is the thickness of the outfit), which must be feasible. For the Geo-Brno models the Dobrovsky tunnel the scale chosen was 1 : 20. The purpose of the measurement was to find out as exactly as possible the state of tension, reshaping, coworking of the structure of EM and obtaining information about the actual safety of the work of Dobrovsky tunnel. The measurement of the state of stress and reshaping in the physical models Geo-Brno TD carried out by means of the following measuring and methods: Fig. 3 measurement of the state of tension by means of pressure cushions tensometric measuring o mechanical detectors o electromechanical resonance-string tensometers o electromechanical thermometers, core and contact ones o electrical tensometers – miniature detectors geodetic and photogrammetric measurement Scheme of the distribution of mechanical and electrical miniature sensors in the model thermometers Fig. 4 Scheme of the distribution of pressure cushions and electromechanical for Geo-Brno models D1, D2, D3 and D4 5. CONCEPTUAL MODELS In tunnelling with divided cross-sections there arise a number of carrier rings that damage the rock that is why the New Austrian Tunneling Method (NRTM) prefers the method of tunnelling with a full profile. As the first step in solving the Dobrovsky tunnel was the implementation of the so-called conceptual models of Geo-Brno A, B, C., Here the circular outfit was considered with the diameter of 6 m for low overhead layers for three cases: o o o Model A: secured face – variable areas Model B: secured area – non secured face Model C: non secured face – variable areas For the considered models we used a space steel frame “stand” (200 × 200× 200) and in it we formed a frame structure with the dimensions 200 × 80 × 40 cm. The tunnelling proper of the tunnel work was simulated by a circular outfit. During the technological procedure of tunnelling an area of elastic, elastic-plastic deformations and an area of defect were formed. The models were gradually loaded so as to admit the above deformations up to the deformation, i.e. to the formation of shear faces. For the determination of the shear potential in models A, B, C we carefully discovered the shear faces and identified them by means of gypsum castings. The shear faces from the physical models were determined by photogrammetric measurement. The size of the shear face of model A is 0.4165 m2, of model B 0.2585 m2, of model C 0.2077 m2. From the size of the shear faces it is evident that the greatest shear potential is that of model A, when there were secured face – variable areas. GEO-BRNO TD – MODELS A, B, C (FINISHED BUILDING OF MODELS) Fig. 5 PHOTOGRAMMETRIC DETERMINATION OF SHEAR AREAS Fig. 6 Model A after failure Fig. 7 Exposure of the shear area of model A Fig. 8 Gradual filling-in of the shear area of model A with plaster Fig. 9 Plaster casting of the shear area of model A with fitting points DETAIL MODELS (GEO-BRNO TD – D1, D2, D3, D4) We are led to the division of the purchases by different reasons, above all, however, by the fear of the stability of the rock mass. In the replacement of big tunnel profiles by several smaller ones (see D1, D2, D3) we must solve a number of problems, but the basic problem is that of the bearing capacity of the newly formed construction elements. The provisional rock pillars, whose bearing capacity will be decisive for the stability of the newly constructed profile, have the whole area of purchase without the technologically necessary purchase of 124.80 m2, the width of the purchase is 13.75 m2, and the height of the purchase is 11.8 m2. The purchase is vertically divided into two lateral purchases with a Gothic vaulting, whose width is 4.755 m and the purchase in the middle part is 3.475 m wide. In the further phase the gallery will be tunnelled in the calotte, which will connect the two lateral galleries and in the end the cores will be knocked out that can be divided analogously as the lateral galleries and the lower part closes as if the whole ring. The mechanical behaviour of the rock brickwork environment consisting of a great number of elements were followed in models Geo-Brno D, from the beginning of the activity of forces during the vertical division up to the possible loss of bearing capacity of rocks or EM forces to overtake and further transport the forces. If the tunnelling is carried out by the system of vertically ordered partial purchases, then there are formed temporary rock pillars between them. That is the so-called primary state, i.e., the state when only the primary outfit of the underground object is active and/or its partial part of purchases, which means that there should not occur the disturbance of the temporary rock pillar and the face of the underground work TD, which affect each other. In tunnelling of the tunnel by the vertical division of the purchase with a Gothic vault the analysis of the state of tension in the middle pillar is necessary, because the state of tension is decisive for the choice of the technological procedure of building tunnels and it basically affects the stability of these requiring underground objects. ZONING OF THE TUNNEL PROFILE – MODEL D1 Preparation and driving proper of profile D1 Fig. 10 Fig. 11 ZONING OF THE TUNNEL PROFILE – MODEL D2 Fig. 12 Fig. 13 The structure is divided into two lateral purchases with the Gothic vault, which affect the underground construction considerably. In the division of the second purchase with the Gothic vault the load of the first purchase with the Gothic vault increases, as well as the size of the deformation of the rock or EM. The second purchase with the Gothic vault is tunnelled under more difficult conditions, because the original quiet state of tension is increased by the strains that are concentrated in the surroundings of the second of the first profile. It is necessary to look for a geometric shape, such as the thickness of the provisional pillar that would still fulfil the condition that the limiting strength of the rock inside it, under the length of the area, is not exceeded. INSTALATION OF PRESS AREAS AND THEIR GAUGING Fig. 14 Fig. 15 FULFILLMENT APPROACH OF A STAND Fig. 16 Fig. 17 Fig. 18 Fig. 19 GRADUAL SHIFTING OF THE OUTFIT FOR ESTABLISHING SUITABLE LATERAL CONDITIONS FOR JUDGING THE STABILITY OF THE PILLAR Fig. 20 Fig. 21 MODEL D3 – TECHNICAL PROCEDURE OF DRIVING FOR THE DETERMINATION OF PRESSURES NECESSARY FOR MAINTAINING THE STABILITY FOR DIFFERENT LENGTH OF DRIVE Fig. 22 Fig. 23 An appropriate forecast of stability in the pillar is very important, because it is necessary to take into consideration a number of factors affecting each other. They are, e.g., the dimensions of the unlined front, the original tension and the size of the concentration of the state of tension (mainly during the vertical division), the rigidity of the outfit and the effect of time. Therefore it was necessary to investigate the real state of the TD and the behaviour of the rock (EM) and their mutual action. In the technological procedure of the building of TD by vertical division (the state of D1, D2, D3) to the final state of the full profile of D4, in the course of the expansion of the breakout of the calotte, in examining the core of the purchase and breakout for the lower vault conspicuous changes in the state of tension were observed and deformation of the given area. The model Geo-Brno D4 respected special mechanical behaviour of the brick veneer (in the division D1 to the state D4) so that it might fulfil its mission reliably and for the whole time of the technological procedures of the building. The state of tension and the deformation of the model Geo-Brno D4 were exactly determined. Summarising the results of the model Geo-Brno D4, it is evident that the ratio of the forced volume change to the volume change evoked by the mechanism of deformation, determines, besides the condition of deformation, also the critical state of tension. MODEL D4 Fig. 24 Fig. 25 Fig. 26 Fig. 27 The outfit of the tunnel, i.e. gunite and reinforcing elements were replaced for the model, on the basis of similarity, with Plexiglass of the thickness of 3 mm and Novodur of the diameter 1.6 cm. In the model 7 purchases were applied (7 reinforcing elements). Electrical miniature sensors were applied to the middlereinforcing element. Fig. 28 Formation of the shear surfaces for the limiting loading 6. CONCLUSION The analyses of the models Geo-Brno D1, D2, D3 unambiguously determined the increased horizontal and vertical states of tension in the middle pillar. In model tests of Geo-Brno TD the loading of the primary lining (D1, D2) in the middle pillar was 2.8 times higher than that of the external primary lining and the vertical load was 3.9 times higher than the horizontal loading. The above results confirm a great overload of the middle pillar and the technological procedure must respect the length of the area to maximum 95 cm. The tension strength due to the outer loading on models was 0.0151 MPa. On the basis of the dimensional analysis and the method of similarity the limiting value 0.4379 MPa was determined for real models (TD). Physical scale models confirmed the fact that if the technological procedure of building the Dobrovsky tunnel is observed, the technology of tunnelling by the vertical division is applicable. LITERATURE WEIGLOVÁ,K. Conception solution of the effect of technology in building the tunnel Dobrovskeho in Brno. In Sborník 31. konference “Zakládání staveb Brno 2003”, konané v Brně (Proc. of the 31th Conference Foundations Brno 2003), Akademické nakladatelství CERM, 2003, s. 39 – 43, ISBN 80-7204-304-8 WEIGLOVÁ,K. The solution of conceptual problems linked with the construction of a tunnel. In Proc. Computer Methods and Advances in Geomechanics. The University of Arizona Tucson, USA. Rotterdam, AA Balkema, 2001. PROCHÁZKA,P., WEIGLOVÁ,K. Coupled modelling using DSC and TFA models. In Proc. 2nd International Conference on Theoretical, Applied, Computational and Experimental Mechanics (ICTACEM2001). Kharagpur, India Indian Institute of Technology, 2001, pp 12 DESAI,C.S., SALAMI,M.R. A constitutive model and associated testing for soft rock, p. 299 – 307, In: Int. j. rock Mech. Min. Sci. &geomech. abstr., Vol. 24, No 5, 1987 DESAI,C.S., SOMASUNDARAM,S, FRANTZISKONIS,K. A hierarchical approach for constitutive modelling of geologic materials, p. 225 – 257, In International journal for numerical and analytical methods in geomechanics, Vol. 10., 1986 The contribution was elaborated as part of the grant project GA ČR No 103/03/0483.