Influence of Geological Conditions on Design and Construction of Tunnel by AK JHA (original) (raw)
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Control of rock joint parameters on deformation of tunnel opening
Journal of Rock Mechanics and Geotechnical Engineering, 2016
Tunneling in complex rock mass conditions is a challenging task, especially in the Himalayan terrain, where a number of unpredicted conditions are reported. Rock joint parameters such as persistence, spacing and shear strength are the factors which significantly modify the working environments in the vicinity of the openings. Therefore, a detailed tunnel stability assessment is critically important based on the field data collection on the excavated tunnel's face. In this context, intact as well as rock mass strength and deformation modulus is obtained from laboratory tests for each rock type encountered in the study area. Finite element method (FEM) is used for stability analysis purpose by parametrically varying rock joint persistence, spacing and shear strength parameters, until the condition of overbreak is reached. Another case of marginally stable condition is also obtained based on the same parameters. The results show that stability of tunnels is highly influenced by these parameters and the size of overbreak is controlled by joint persistence and spacing. Garnetiferous schist and slate characterized using high persistence show the development of large plastic zones but small block size, depending upon joint spacing; whereas low persistence, low spacing and low shear strength in marble and quartzite create rock block fall condition.
Bulletin of Engineering Geology and the Environment, 2018
A methodology for designing a tunnel support system according to the actual ground conditions and the critical behaviour types is analysed in this paper. The methodology is justified with the principles of the New Austrian Tunnelling Method that incorporates the top heading and bench method. The role of the geological material and its implication in tunnel design, reinforced with advances in site investigation methods, cannot be based solely on the development of the geotechnical classification systems and the consequent quantification of the rock masses. Support requirements for rock masses with equal classification ratings can be different. The procedure presented in this study cannot bypass the geological and/or in situ characteristics dictating or influencing the tunnel behaviour compared with a standardised classification that could miss the specifics and particularities of and around a tunnel section. The step-by-step procedure is applied in a tunnel excavated in tectonically disturbed heterogeneous flysch sediments in Serbia. The complex structure of these materials, resulting from their depositional and tectonic history that includes severe faulting and folding, presents a challenge to geologists and engineers. The possible ground types are evaluated, and then, combined with the factors of the tunnel geometry, the primary stress condition, and the water conditions, several behaviour types are considered. These classified behaviour types, followed by the suitable mechanical properties that are required for effective tunnel engineering design, are the basis for the numerical design of the appropriate primary support measures to achieve stable tunnel conditions. The twin-tube, two-lane highway tunnel was successfully constructed without significant problems.
Engineering Geology and Tunnels
Tunnel Engineering - Selected Topics
Currently, knowledge and understanding of the role of geological material and its implication in tunnel design is reinforced with advances in site investigation methods, the development of geotechnical classification systems and the consequent quantification of rock masses. However, the contribution of engineering geological information in tunnelling cannot be simply presented solely by a rock mass classification value. What is presented in this chapter is that the first step is not to start performing numerous calculations but to define the potential failure mechanisms. After defining the failure mechanism that is most critical, selection of the suitable design parameters is undertaken. This is then followed by the analysis and performance of the temporary support system based on a more realistic model. The specific failure mechanism is controlled and contained by the support system. A tunnel engineer must early assess all the critical engineering geological characteristics of the rock mass and the relevant mode of failure, for the specific factors of influence, and then decide either he or she will rely on a rock mass classification value to characterise all the site-specific conditions. Experiences from the tunnel behaviour of rock masses in different geological environments in Alpine mountain ridges are presented in this chapter.
The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exponential distribution function has less effect on the tunnel stability compared to the two other distribution functions.
Tunnel Evaluation in Crocker Formation by Geological Strength Index (Gsi) System: A Case Study
Geological Behavior, 2018
This study was conducted to determine the value of Geological Strength Index (GSI), to predict rock mass properties, very unfavourable discontinuities combination and tunnel support pressure for rock bolts or shotcrete and to determine the suitability of GSI for a tunnel in Crocker Formation. Engineering geological mapping and discontinuity survey was done along the tunnel face as well as rock sampling. GSI values and the disturbance factor were obtained from field observation on the tunnel face. Point load and dry density test was conducted to determine the Uniaxial Compressive Strength (UCS) and unit weight, respectively. The rock mass properties, kinematic analysis and limit equilibrium analysis was used to determine the factor of safety (F.O.S) and pressure to stabilise the tunnel. The rock mass was characterised by 94.88 MPa UCS, 0.024 MN/m3 unit weight, widely space and high persistency. The GSI value is 50 with 0.8 disturbance factor. The cohesion, friction angle and tensile strength are 3.671 MPa, 25.20° and 0.056 MPa respectively. The friction angle was reduced by 5° due to lower shear strength of bedding plane. There are eight possibilities of discontinuities combinations on tunnel crown that have F.O.S lower than 2 and combination of joints 2, 4 and 6 has the maximum wedge volume of 28.37 m3. The maximum support pressure of rock bolts or shotcrete for F.O.S of 2 at the tunnel crown is 0.04 MN. The high F.O.S value may have been due to the overestimation of friction angle and cohesion of discontinuity plane. Then, this study shows that GSI system is unsuitable for the tunnel in study area which behave as anisotropic and structurally controls rock mass, but if needed, the values of rock mass properties, discontinuities combination and support pressure can be used for tunnel design.
Scientific Research and Essays, 2011
In this paper, a detailed geomechanical investigation of rock masses of North Water Convey Tunnel (NWCT) and its stability analysis has been carried out. The NWCT is located in the north of Iran and is to be constructed in-order to convey water for agriculture purposes. The main instability in the tunnel is joints and faults. The rocks mass encountered in the tunnel route are made of argillaceous, sandstone and shale. The tunnel has been divided into two parts, lot1 and lot2 having a length of 14 km and 26 km respectively. It is proposed to be constructed by telescopic shield method using a tunnel boring machine (TBM). In this study, the most suitable methods are utilized for the stability analysis and design of support of the tunnel. For the empirical investigation, the rock mass were classified based on RMR, Q, RSR, GSI and Rmi systems. The geomechanical properties of the rock mass were determined from the laboratory and field investigations. The results obtained from the analysis show that the tunnel is highly unstable due to the presence of a fault and hence strong supports are need in these regions. The support system used is concrete lining, as the tunnel in used for water conveyance. The tunnel alignment in lot1 is divided into 12 lithology types as; LI-SH1, LI-SH2, LI-SH3, LI-SH4, LI1, LI2, LI3, LI4, LI5, SI, CZ and FZ regions. Similarly, the tunnel alignment in lot2 is divided into 21 lithology types as; SH-ML1, SH-ML2, SH-ML3, MLI-SH1, ML-SH2, ML-SH3, ML-SH4, ML-SH5, SH-LS1, SH-LS2, SH-LS3, SH-LS4, LI2, LI3, LI4, LI5, LI6, LI-MA, LI-SH, CZ, FZ regions. A stability analysis is a necessity as during the tunneling instabilities, such as the presence of a shear zones, may cause an obstruction and delaying of TBM progressing rate. Key words: Tunnel boring, stability analysis, rock mass classification system, empirical and numerical methods, support pressure. w r n a J J RQD Q J J SRF = × × (1) This classification system includes six parameters of rock quality as following: 1. Rock quality designation (RQD) 2. The number of joint sets ( n J ) 3. The joint surface roughness ( r J ) 4. The degree of joint weathering and alteration ( a J ) 5. Joint water reduction factor ( w J )
TO STUDY(CASE) THE PRODUCTIVITY OF ROCK SUPPORTS IN TUNNELING PROJECTS
For underground projects and works throughout the world tunnels are very significant. Diverse geological conditions are observed during tunneling works. During tunneling rock mass alongside the tunnel becomes unstable due to blasting, benching and other methods of tunneling. This unstable rock mass is to be stabilized for effective working and long life of tunnel. Controlling and recording of such process is very important during the excavation in underground works. Tunneling works also consume the major cost of underground projects as well as immense time is consumed during tunneling and rock mass stabilization including reworks.Rock supports being a vital part underground projects and also foremost contributor to expenditure and time, is one of the region where effort desired to be done. The installation of tunnel rock support systems is usually not planned because of strange conditions of rock can be observed
THE 1ST INTERNATIONAL CONFERENCE ON INNOVATIONS FOR COMPUTING, ENGINEERING AND MATERIALS, 2021: ICEM, 2021, 2021
In the practical construction of underground excavations, the groundwater level in the surrounding rock masses can fluctuate due to water accumulation (reservoirs), water abstraction and, in particular, due to the consequences of climate change. This fluctuation causes changes in the geomechanical state of the rock mass and effects on the support structure. This phenomenon and its effects must be predicted in order to get appropriate suggestion for the design and construction measures. The article presents some simulation results that analyse the redistribution of geomechanical processes in the jointed rock mass around a tunnel with and without support as well as the rule of the changes of the internal forces in the support structure when the groundwater level changes by using UDEC.