Tunnel surveying
The tunnel surveying is a branch of engineering geodesy and is responsible for the geometrical and metrological issues in tunnel construction .
The use of modern measuring technology is playing an increasingly important role in tunnel surveying. New sensors increase the accuracy and replace conventional, personnel-intensive measurement concepts. The interaction of planning, basic surveying and construction-accompanying measurements is crucial for smooth tunneling , especially in tunnel construction . Only by linking targeted measuring, evaluation and adjustment methods is an efficient construction- building monitoring to implement. The measurement results must be available on the construction site as quickly and transparently as possible so that they can be used together with the other facts, e.g. B. from engineering geological studies to enable effective action on the construction site at all times.
planning phase
In the planning phase, the required map material should be compiled in close cooperation with all the specialist disciplines involved in the project and, if necessary, through targeted compaction measurements, e.g. B. in the area of planned exploratory bores or tunnels can be added. In addition to the conventional map material, aerial photos , from which orthophoto plans are generated, and possibly remote sensing data , e.g. B. SPOT or Landsat with a resolution of 10 to 30 m, from which a digital elevation model can be derived. The breakthrough error to be achieved is an important parameter for planning the entire measurement concept. It ultimately forms the basis for the further procedure of measurement and the instruments to be used.
From a geodetic point of view, the breakdown error can be defined as the predicted theoretical standard deviation of the breakdown point in the longitudinal and transverse direction. The breakdown error, applied to the breakdown location, is derived from the relative error ellipses of the last polygon points in both directions of advance. Models describe complex issues using mathematical methods. Due to the fact that reality can only be represented in a simplified manner by the models, the a priori measurement accuracies are usually applied too pessimistically.
In the case of a basic network, especially in railway tunnel construction, the difficulties arise during the planning stage that when choosing the reference frame, the basic network must not be deformed due to the fitting, i.e. H. it must be tension-free. This fact has to be taken into account in the planning phase. The connection with the higher-level networks is realized by fielding the basic network on the fixed points of the higher-level network in the sense of a Helmert transformation .
In the course of broad international cooperation, especially in large projects such as tunnel construction, the advantages of quality management are very dominant, especially in project control. The points of documentation, design control, contracts, etc. are regulated by standards (e.g. summarized in the DIN EN ISO 9000 family). Companies that form a working group and are certified according to the above standard can work together without extensive additional coordination. The project becomes transparent, i. H. Can be interpreted in a uniform manner for every worker on a construction site. There are new possibilities, also in terms of security controls, which are very important on large construction sites.
Geodetic basics
The basic measurement in tunnel construction is essentially about the construction of a tension-free special network for the transmission of the planned tunnel axis to the site. Increasingly, however, these special networks are also required as a starting point for the control measurements to be carried out during the construction phase and the geotechnical measurements. A special network for tunnel construction generally consists of two portal networks. These are linked together in a larger measurement campaign and connected to higher-level points. Such a concept was presented in (Kahmen et al., 1998) for setting out high-speed roads. Since the portal networks (see illustration) should be available for staking out and monitoring tasks during the entire construction phase and, if possible, beyond, the question of permanent marking arose. Only pillar points are therefore suitable for this task. The higher costs compared to other types of marking are justified, however, by the high level of stability and the compulsory centering that is essential for marking out the tunnel. Another advantage of a pillar network is the possibility that this network can serve as a basis for deformation measurements over a longer period of time and with sufficient stability. For the creation of networks for deformation analysis, reference is made to (Niemeier, 1985).
The concept described above is mostly implemented today through ( satellite-based measurement ) of the special network with supplementary terrestrial measurements in the portal areas and a portal-connecting leveling . In most cases it is crucial not only to create a tension-free special network for engineering and geodetic tasks , but also to transfer this network into a network specified by the client without any major voltages.
Construction-accompanying survey
The construction-accompanying measurements include all underground geodetic measurements and their evaluations. In addition to the daily, freely stationed routine measurements for positioning and checking the directional lasers, this also included station controls and measurements for stabilizing and continuing the underground reference network. Using the associated reflector system for the deformation measurements, the construction site survey can also carry out the main checks that regularly occur to update the tunnel polygon and support the direction of advance. In most cases, independent main control measurements are required by the client and also supported by the contractor. Other instruments and software products should be used consciously.
Propulsion control
Against the background of the greatest possible profile accuracy, both in the excavation and in the outer shell geometry ( shotcrete ), both conventional directional lasers and automatic motor laser systems can be installed in the drives to display the excavation line. Both systems are available for the position-determining process and the manual setting of the expansion sheets.
Profile measurements
Cross profile recordings are part of the daily routine measurements when driving using the shotcrete method . Thanks to the constant controls, it is possible to react quickly to identified under or over profiles and in many cases, greater damage can be limited by measures. In the interval between the length of the cut, both the support arches and the second shotcrete layer are checked with geodetic measurements and documented using suitable software. With this standard method, a reflector is guided in the center of a firmly defined spacer disc along the shotcrete shell and determined trigonometrically by polar measurement. By reshaping on the route and gradient, a reliable statement can be made about the remaining over or under profile in relation to the respective target geometry. This conventional method has the advantage of quick availability of the results, but the disadvantage of only selective control in a rough grid (sample).
Geotechnical measurements in tunnel construction
The geotechnical measurements are used to record three-dimensional displacements of the tunnel construction through optical-trigonometric measurement of retro prisms in the absolute system. The method allows the total station to be stationed freely and, when using a motorized instrument, offers a safe and practical measuring process. The position coordinates are determined by recording at least four connection points that can be regarded as stable. The accuracy of the target point coordinates therefore depends largely on the accuracy of the station position coordinates.
Deformation measurements
On the basis of the stable portal pillar networks, the high-precision underground reference networks for 3D deformation detection in the tunnel drives develop in the course of the advancing tunneling. The freely stationed measurements - based on a large number of already calmed points in the rear section - provide millimeter-accurate documentation of the deformation process in the tunneling area. The measurements can be carried out with a servo tachymeter and corresponding point signaling in the form of bireflex targets on the tunnel outer shell. In a downstream EDP processing, the results of the geotechnical measurements are immediately fed to a static stability calculation, which ultimately includes a classification (so-called trigger lines) of the measurement cross-sections in three alarm limits.
Measurements above ground
Settlement observation of the surface with precision leveling complement the geotechnical measuring program. The results of the settlement measurements, shown in transverse profiles (settlement troughs) and longitudinal profiles, are an important tool for assessing the advance settlement, especially in the abutment areas close to the surface. This factor cannot be determined by underground deformation measurements, because the zero measurement is only made with the shotcrete lining.
literature
- M. Schäfer, G. Weithe: Surveying solutions on the construction sites North Downs Tunnel and Bridge Medway Crossing - high-speed line from London to the Eurotunnel. In: Bauingenieur , June 2004, pp. 280–286
- Prof. Dr.-Ing. em. Bertold Witte, Professorship for Geodesy, Institute for Geodesy and Geoinformation: " Surveying long tunnels from antiquity to the 20th century - using the Eupalinos tunnel , the Gotthard railway tunnel and the English Channel tunnel ...", Géomatique Suisse 11/2015, Pp. 448-453
Individual evidence
- ↑ J. Krüger: Setting out nets, especially for setting out tunnels. In: Hans Pelzer (Ed.): Geodetic Networks in State and Engineer Survey II , 1985, pp. 507-526.
- ↑ S. Elmaghraby: installation and optimization of tunnel networks with breakdown results of some schematic examples. In: Scientific work in the field of surveying at the University of Hanover , No. 162, dissertation, 1989.
- ^ H. Kahmen et al .: A modular concept for setting out high-speed roads. In: Der Vermessungsingenieur , 4/1998, pp. 115–121
- ^ W. Niemeier: installation of surveillance networks. In: Hans Pelzer : Geodetic Networks in State and Engineering Surveying II , 1985, pp. 527–558
- ↑ G. Weithe: London Heathrow Airport: Innovative measurement concept with the luggage tunnel. In: Der Vermessungsingenieur , 5/1996, pp. 204–209.