Numerisk modellering av støp bak stuff på E16 Wøyen - Bjørum

Det er i denne rapporten sett på hvilke deformasjoner og spenninger en støp bak stuff på E16 Wøyen - Bjørum under Bjørumbekken vil bli utsatt for. Det er ved bruk av numerisk modellering i programmet Phase2 laget plot for deformasjoner og spenninger ved to ulike kvaliteter på berget. Beregningene viser at en slik støp vil ta opp minimalt med deformasjoner og spenninger. Det bør måles deformasjoner i den nåværende sikringskonstruksjonen for å verifisere at deformasjonene i berget har avtatt slik som forutsatt i beregningene

A Hybrid Methodology of Rock Support Design for Poor Ground Conditions in Hard Rock Tunnelling

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Design of Rock Support in Hard and Layered Rock Masses Using a Hybrid Method: A Study Based on the Construction of the New Skarvberg Tunnel, Norway

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Applicability of Reinforced Ribs om Sprayed Concrete in Sections of Poor Quality and Swelling Rock Mass

When excavating tunnels, reinforcement and support is required depending on the quality of the rock mass. In good quality rock mass, simple reinforcement such as sprayed concrete and rock bolts is usually adequate as support. In areas with very weak rock mass and unfavourable stresses, more comprehensive support methods need to be applied to avoid large deformations in the rock mass. In Norwegian hard rock tunnelling, the geology is characterised mostly by hard rock intersected by weakness zones that often contain swelling minerals. The common rock support in such weakness zones is rebar reinforced ribs of sprayed concrete (RRS) combined with rock bolts and reinforced sprayed concrete between the ribs. This practice is mostly based on experience and the scientific basis to support the practise and its best application is limited. The main objective of this thesis was to explore deformations in sections of weak rock in hard rock tunnels, with the purpose of developing a better understanding of the use of RRS in tunnelling. A special focus have been placed on how swelling minerals may affect the system. This has been achieved by performing full-scale in-situ monitoring, laboratory testing, numerical modelling and collection and systemization of existing data. Field monitoring of RRS in Norwegian road tunnels has shown only small deformations in the rock mass and no substantial strain in the rebar of the RRS. When evaluating the field measurements based on numerical modelling, it has been found that the RRS have not been subjected to any load, and hence have had no load-bearing function. By comparing data from a parameter study based on numerical modelling with data extracted from The Norwegian Public Roads Administration (NPRA) tunnel data base, it was discovered that that RRS has been applied in tunnels where the conditions probably would not require load-bearing support. In the literature, a convergence of 1% is suggested as the limit for the rock to require load-bearing support. This implies that there is an interval where the need for rock support exceeds bolts and sprayed concrete, but where load-bearing support is too extensive. To explore how swelling minerals may affect the support construction, reconstituted cores of swelling gouge have been tested triaxially. The registered deformation was found to be dominated by creep in the material and no swelling was observed during the saturation of the initially dry specimens. This implies that swelling was insignificant compared to other deformation processes, but as the deformation rate increased during saturation, it may have accelerated the creep process. Oedometer testing on the swelling gouge with different initial water contents was conducted on the fraction < 20 µm. The behaviour of the material suggests that one could find the water content for where the intracrystalline swelling ends and the osmotic swelling begins. This is important since the rock stress in many cases exceeds the osmotic swelling stress, while it will not exceed the intracrystalline swelling stress. Related to in-situ gouge, one may thus be able to predict whether the material will swell if exposed to water or if the rock stress may force water out, making it shrink. The oedometer testing also showed that the swelling pressure was dependent on the density of the material. The results described above imply that the current design of the RRS is in most cases over-dimensioned and that a leaner design, which is not load-bearing, is probably sufficient for most cases. Earlier, reinforced but unarched RRS was used, which require less material (steel, concrete) compared to the load-bearing arched RRS used today. By performing surveillance of the deformations based on total stations, the use of unarched RRS could be safely implemented, first at a project level and later, when having more data, on a systematic level. As part of implementing such a leaner RRS, it is important that effort is also devoted to characterizing the weakness zones and identifying the most important parameters of their deformability

Main aspects of deformation and rock support in Norwegian road tunnels

The general geology of Norway makes most of its tunnels to be constructed mainly in strong rock intersected by weakness zones of different sizes and characteristics. The Norwegian support tradition is, to the largest degree as possible, to reinforce the rock to make it self-bearing. In weak rock, this reinforcement has been accomplished by using bolts, sprayed concrete and ribs of reinforced concrete (RRS). RRS are normally designed with 6 rebars mounted on brackets that are attached to rock bolts with a center to center distance of 1.5 m covered in sprayed concrete. The spacing between the RRS in the tunnel direction is usually 1 to 3 m. In recent years, the application of RRS has gradually changed from following the blasted tunnel profile that formed unarched RRS that reinforced the rock to using RRS with an arched design that supports the rock. Following this development was an increase in the use of materials, as the amount of sprayed concrete used is now considerably larger and the rebar diameter changed from 16 to 20 mm. This change has also caused an abrupt increase in the support measures used for decreasing rock quality, from simple reinforcement by bolts and sprayed concrete to load-bearing arches. The authors believe that a more gradual transition is logical and this article will discuss and evaluate the current Norwegian support strategy by reviewing international theory, performing parameter analysis and presenting data from current and previous Norwegian road tunnels, with a focus on rock mass quality and deformations. It is concluded that arched RRS is not necessary for all cases where it is used today, and that evaluation of the need for load bearing arched RRS should be based on deformation considerations. Norwegian conditions comprise the basis for the discussion, but the problem at hand is also of general interest for hard rock tunnelling conditions.Main aspects of deformation and rock support in Norwegian road tunnelspublishedVersio

Analysis of the stabilising effect of ribs of reinforced sprayed concrete(RRS) in the Løren road tunnel

The Løren tunnel is a road tunnel at Ring road 3 in Oslo, Norway. The tunnel has a length of 915 m in rock, has two tubes with three lanes and breakdown fields, and was first opened in 2013. For rock support in the case of weak rock masses, ribs of reinforced sprayed concrete (RRS) were used. The scope of this article is to present and analyse the results of a measurement programme carried out on three of these ribs. This is done by focusing on deformations in the rock and the support function of the ribs due to these deformations. The instrumented RRS had strain meters installed in the reinforcement and the concrete. From the surface above the RRS, multipoint borehole extensometers were placed to survey the soil and rock mass deformations caused by tunnel advancement. In addition, 2D and 3D rock stress measurements and rock property testing were conducted. The measurements and numerical modelling show that the deformations are too small to cause a considerable load on the installed support construction and that the 2D stress measurements seem to best fit the in-situ stress conditions. The rock mass quality in the area of this study is on the verge of where one usually starts using reinforced ribs. It is concluded that the RRS are not required because of deformations in the rock but, rather, because of the need to lock blocks, increase the friction in joints and prevent movement in larger filled joints. For this purpose, the RRS should probably be designed differently to get the most out of the materials used

Main aspects of deformation and rock support in Norwegian road tunnels

The general geology of Norway makes most of its tunnels to be constructed mainly in strong rock intersected by weakness zones of different sizes and characteristics. The Norwegian support tradition is, to the largest degree as possible, to reinforce the rock to make it self-bearing. In weak rock, this reinforcement has been accomplished by using bolts, sprayed concrete and ribs of reinforced concrete (RRS). RRS are normally designed with 6 rebars mounted on brackets that are attached to rock bolts with a center to center distance of 1.5 m covered in sprayed concrete. The spacing between the RRS in the tunnel direction is usually 1 to 3 m. In recent years, the application of RRS has gradually changed from following the blasted tunnel profile that formed unarched RRS that reinforced the rock to using RRS with an arched design that supports the rock. Following this development was an increase in the use of materials, as the amount of sprayed concrete used is now considerably larger and the rebar diameter changed from 16 to 20 mm. This change has also caused an abrupt increase in the support measures used for decreasing rock quality, from simple reinforcement by bolts and sprayed concrete to load-bearing arches. The authors believe that a more gradual transition is logical and this article will discuss and evaluate the current Norwegian support strategy by reviewing international theory, performing parameter analysis and presenting data from current and previous Norwegian road tunnels, with a focus on rock mass quality and deformations. It is concluded that arched RRS is not necessary for all cases where it is used today, and that evaluation of the need for load bearing arched RRS should be based on deformation considerations. Norwegian conditions comprise the basis for the discussion, but the problem at hand is also of general interest for hard rock tunnelling conditions

Pull-out and critical embedment length of grouted rebar rock bolts - mechanisms when approaching and reaching the ultimate load

Rock bolts are one of the main measures used to reinforce unstable blocks in a rock mass. The embedment length of fully grouted bolts in the stable and competent rock stratum behind the unstable rock blocks is an important parameter in determining overall bolt length. It is required that the bolt section in the stable stratum must be longer than the critical embedment length to ensure the bolt will not slip when loaded. Several series of pull tests were carried out on fully grouted rebar bolts to evaluate the pull-out mechanics of the bolts. Bolt specimens with different embedment lengths and water/cement ratios were installed in either a concrete block of one cubic meter or in steel cylinders. Load displacement was recorded during testing. For some of the bolts loaded beyond the yield load, permanent plastic steel deformation was also recorded. Based on the test results, three types of failure mechanisms were identified, corresponding to three loading conditions: (1) pull-out below the yield strength of the bolt steel; (2) pull-out between the yield and ultimate loads, that is, during strain hardening of the steel; and (3) steel failure at the ultimate load. For failure mechanisms 2 and 3, it was found that the critical embedment length of the bolt included three components: an elastic deformation length, a plastic deformation length and a completely debonded length due to the formation of a failure cone at the borehole collar

Experimental triaxial testing of swelling gouge materials

Adequate rock support in weakness zones that may contain swelling minerals poses one of the main challenges of excavating tunnels in hard rock conditions. Deformations under such conditions are influenced by several factors, including the properties of the rock mass, rock stress and the possible swelling potential of the minerals. Thus, dimensioning rock support may be challenging. To increase the knowledge regarding the processes behind deformations in areas of swelling gouge material, an experimental triaxial laboratory test of such material was performed. The main objective was to investigate whether the material might exert pressure under typical in situ stress conditions, or whether other processes might be dominant. In addition, the possible elastic and strength properties of such material were investigated. The testing was performed on reconstituted cores with material from four different locations in eastern Norway. The material was dried and then pressed into cores using a compactor. The triaxial testing consisted of four successive phases: pre-stressing 1; water addition under constant strain; pre-stressing 2 and failure. The results indicate that factors other than swelling pressure are the main causes of tunnel deformation, as no build-up of swelling pressure was observed during the water addition phase. Initially, the E-modulus and strength properties of the samples were very low, which can cause large, immediate deformations in situ. In addition, creep and possibly a reduction in the Emodulus during water addition seemed to cause time-dependent deformation