Parametric analysis of tunnel behavior in jointed rock

Madkour, H.

doi:10.1016/j.asej.2012.01.002

Cited by 17 publications

(3 citation statements)

References 6 publications

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“…Jointed rock masses are often found during tunnel excavation; most failures of the tunnel opening during excavation are reported to be related to joints (Ghorbani et al, 2015). Joints commonly occur in sets that are more or less parallel and are regularly spaced (Madkour, 2012). Often, several sets of joints have different directions so that a rock mass is broken up into a blocky structure (Jaeger et al, 2009).…”

Section: Joint Analysismentioning

confidence: 99%

Mechanical properties of selected granitoids along the Karora hydropower project, Besham, Northern Pakistan: Insights from petrography and joint analysis

Khan

et al. 2023

Front. Earth Sci.

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The stability of tunnel site depends upon the deformation behaviors of the surrounding rocks, including joint density, mineral composition, micro cracks, and grain boundaries. The aim of this study was to analyze the mechanical properties of the Besham Complex in Northern Pakistan in terms of petrography and joint analysis. The Besham complex is prone to deformation as it is bounded by the Main Mantle Thrust (MMT) in the north, the Thakot fault (Tf) in the east, and the Swat block in the west. In the study area, the deformation was observed at the mesoscopic scale, while alteration in grains and fractures were determined at a microscopic scale. Detailed petrographic study of the representative samples from each station revealed that the area is dominantly composed of granite, quartz syenite, quartz monzonite, granodiorite, quartz-rich granitoid, monzogranite, alkali feldspar granite, and quartz monzodiorite. Extensive field work was performed to determine the joint volume (JV), in which the number of joints per cubic meter was recorded for each joint set. The rock quality designation (RQD) was calculated through JV analysis. An RQD value <25% suggested that most rocks are very poor quality, while samples with RQD values between 25% and 50% are poor quality. The petrographic analysis revealed that the dominant contents of the rock samples are feldspar (55.6%), quartz (27%), and mica (17.4%). Petrographic control over surface joint volume was established, suggesting that abundant feldspar, coarse grain, anhedral to subhedral grain shape, microcracks, and alteration of minerals provide planes of weakness for joints and thus reduce the RQD value. Therefore, some serious precautions and supporting measurements, such as shotcrete, rock bolts, metal mesh, and steel arch supports, are essential to avoid severe geo-hazards during further excavation.

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Section: Joint Analysismentioning

confidence: 99%

Mechanical properties of selected granitoids along the Karora hydropower project, Besham, Northern Pakistan: Insights from petrography and joint analysis

Khan

et al. 2023

Front. Earth Sci.

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“…They found out that the existing expressions (valid for isotropic rock masses under a uniform state of stress) are applicable only if the plane of transverse isotropy strikes parallel to the tunnel axis; otherwise three-dimensional analyses are necessary. Klopčič and Logar (2014) and Madkour (2012) showed that a large portion of displacements occurs ahead of the tunnel face especially when tunnelling with the dip, but did not consider failure of the rock matrix. Schubert and Mendez (2017) also investigated the influence of the orientation of the schistosity on the tunnel behaviour using the example of the Galgenberg Tunnel.…”

Section: Introductionmentioning

confidence: 99%

On the variability of squeezing behaviour in tunnelling

Mezger¹

2020

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The magnitude of squeezing deformations in tunnelling often varies over short distances, even if there is no obvious change in the construction method, in the depth of cover, in the lithology or rock structure. As long as the reasons for the variability are not known, the tunnelling-induced convergences cannot be predicted with sufficient reliability. Reliable predictions, however, are important for determining the temporary support or the excavation diameter. Otherwise, large-scale tunnel repairs may be necessary, which can cause delay and additional costs due to remedial actions as well as due to the enforced interruption of other operations in progress at the same time. The analysis of different case studies concerning the AlpTransit project shows that the squeezing variability can be traced back to the heterogeneities in the rock mass at different scales as well as the variation of the orientation of the planes of anisotropy (bedding or schistosity) to the tunnel axis. In order to improve safety and economy of tunnel construction in squeezing ground, the influence of these factors on the convergences was determined quantitatively (by means of analytical solutions or numerical modelling), so that they can be used as indicators during construction for the timely identification and prediction of the squeezing behaviour. Particular attention was paid on factors, whose variation, even if small, may affect the convergences sensitively . Based on these quantitative investigations, design aids were developed, which should help the project engineer to estimate and better understand the variability of the squeezing intensity. The squeezing variability also concerns TBM tunnelling: In contrast to conventional tunnelling, shielded TBMs are particularly vulnerable to squeezing due to the very limited space available. Therefore, in order to better deal with the squeezing variability in TBM tunnelling, different (stiff as well as deformable) lining options were discussed.

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“…The jointed rockmass manifests complex mechanical behavior like anisotropy, dilatancy, hysteresis, irreversible strain, and strongly path-dependent stress-strain relationships which is generally associated with the existence of a lot of joints or cracks and their propagation [11]. The joint orientation also play an important role in creating voids and occurrence of permanent deformations.…”

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Analysis and prediction of brittle failure in rock blocks having a circular tunnel under uniaxial compression using acoustic Emission technique: laboratory testing and numerical simulation

2021

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In this research, the failure mechanism and anomalous behavior of intact and jointed rock block having a circular tunnel under compression are studied. This was done by monitoring the progressive failure of a rock tunnel subjected to uniaxial loading. The tests were conducted in sandstone blocks and “Acoustic Emission” (AE) technique was used to identify the crack damage and other failure attributes. Three cases have been considered in the research, i.e. tunnel in the intact rock, with horizontal joints, and with vertical joint sets. Images of progressive failure, acoustic signals, and applied loads were simultaneously recorded during the test. The intact block demonstrates continuous crack generation while the block with horizontal joint set shows a stepwise cracking pattern. In the third case where the vertical joints were employed, the deformation was largely roof failure and joint perpendicular extension was dominant. The AE events show that a sudden drop and then a quiet period of seismic “Ib value” could be considered as the precursors to forecast the rockburst hazard. The paper also compares the results of the physical model test with a 2D finite element model. The compared results show good agreement between the physical and numerical models.

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Parametric analysis of tunnel behavior in jointed rock

Cited by 17 publications

References 6 publications

Mechanical properties of selected granitoids along the Karora hydropower project, Besham, Northern Pakistan: Insights from petrography and joint analysis

Mechanical properties of selected granitoids along the Karora hydropower project, Besham, Northern Pakistan: Insights from petrography and joint analysis

On the variability of squeezing behaviour in tunnelling

Analysis and prediction of brittle failure in rock blocks having a circular tunnel under uniaxial compression using acoustic Emission technique: laboratory testing and numerical simulation

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