The construction of underground structures is playing a relevant role in modern society. As a result of noticeable tunnel boring machine (TBM) evolution, mechanized excavation methods are gaining increased market shares. TBM driven tunnels are generally used in combination with precast concrete segments as the main support system for reducing or minimizing surface disturbances during construction and to fulfill the project requirements with regards to quality, construction times, budget and safety. Within this framework optimization approaches strongly focused on these process parameters, rather than the general structural performance of the segments. However, improving the performance by using conventional reinforcement, High Performance Fiber Reinforced Concretes (HPFRCs) or a combination of such enables a possible reduction of the lining thickness or the amount of reinforcement. To this aim, this paper presents a new hybrid solution for precast tunnel segments with a reduced thickness, which leads to new perspectives in reducing the total amount of concrete, in decreasing the volume of disposal materials from the boring process as well as to minimize the TBM size. A parametric numerical study is developed for evaluating the effectiveness of proposed hybrid solution. The latter is based on high strength reinforced concrete in combination with HPFRC at the longitudinal joints, whose geometric configuration is properly modified to maximize the segment's bearing capacity.
This contribution presents a new tester for tunnel lining segments in the final serviceability load stage. It aims to concentrate the resources of testing laboratories on a single segment capturing most of the real conditions present in real tunnels. Its variability is presented, that is, the geometrical and mechanical configurations it can adapt to. Its performance is validated by means of a prototype test on a conventionally reinforced tunnel lining segment. Horizontal and vertical loads are applied simultaneously to simulate similar loading conditions as in real tunnels. To this end, three hydraulic cylinders are coupled, so that forces up to 5 MN in both directions can be applied. The external loads are introduced radially in a semi‐distributed manner at eight different points of the segment extrados. The kinematics recorded show a proper load distribution on the specimen. Moreover, it brings into light its weak spot, that is, the longitudinal joint.
Lasteinleitungsstellen von Tunneln aus Tübbings sind lokal hoch beansprucht. Insbesondere betrifft dies die Ansatzpunkte der Vorschubpressen und die Längsfugen als Kontaktstellen zwischen den einzelnen Segmenten in Ringrichtung. Gewöhnlich dominiert die Teilflächenpressung der Längsfuge die Dimensionierung des ganzen Tübbings; abseits davon wird er jedoch nicht voll ausgenutzt. Im Beitrag werden zwei Lösungskonzepte vorgestellt. Eines verstärkt die Tragfähigkeit der Längsfugen im Bereich der Lasteinleitung durch hochfesten Beton und hybride Bewehrung aus Stabstahl und Stahlfasern. Übrige Tübbingteile werden weiterhin in Normalbeton ausgeführt. Darauf abgestimmt erfolgt die Betonage; stehend und hybrid. Alternativ werden Tübbings aus durchgehend hochfestem Beton mit Aussparungen entwickelt. Entsprechende Entwürfe werden im Großmaßstab im Labor umgesetzt und hinsichtlich ihrer Tragfähigkeit geprüft. Sie liegt bei beiden mit ca. 75 % bzw. 86 % deutlich über derjenigen eines herkömmlichen Referenztübbings. Auch hinsichtlich der CO2‐Äquivalente zeigen sich Einsparpotenziale von ca. 35 %. Zudem verringert die geringere notwendige Tübbingdicke den Ausbruchquerschnitt, was Kostenvorteile bringt.
Tunnels in unfavorable ground conditions are exposed to high internal stresses due to localized loading at the outer face. Addition of extra layers of compressible material as a countermeasure needs more material and greater excavation volumes which is in conflict to the global goals of CO2 reduction. Thus, two alternative types of segments with higher bearing capacities are proposed that allow for lining thickness reduction. They are derived from multi‐load topology optimization considering relevant load cases during construction and in service. The first design incorporates centered recesses that maximize segmental stiffness. The second shifts the recesses to the outer face increasing their potential to absorb deformation. Two prototypes of each type are fabricated from high performance steel fiber reinforced concrete. Experiments show that a concrete reduction of up to 55.2% is achieved with respect to a conventional design. The volume savings give space for layers of radially compressible material.
In this chapter, important research results for the development of a robust and damage-tolerant multimaterial tunnel lining are presented. This includes the production, design and optimization of fiber-reinforced hybrid segmental lining systems based on numerical models and experimental investigations under tunneling loads. In addition, novel tail void grouting materials are developed and optimized regarding their infiltration and hardening behavior while taking the interaction with the surrounding ground into account. In order to expand the applicability of mechanized tunneling regarding soils characterized by significant swelling potential due to water uptake by clay minerals, a deformable segmental lining system is presented. The risk of damage due to high localized loads is reduced by the integration of additional radial protective layers on the lining segments and a compressible annular gap grout, which protect the tunnel structure by undergoing high deformations after reaching a certain yielding load. However, the deformability of such support systems affects the distribution of the stresses around the tunnel which governs the magnitude and buildup of the swelling pressure in the soil. Therefore, the development of damage tolerant lining systems requires a material and structural design which ensures an optimal soil-structure interaction through a synergy of computational and experimental techniques.
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