Rohola Hasanpour

Impact of Overcut on Interaction Between Shield and Ground in the Tunneling with a Double-shield TBM

Double-shield TBMs (DS-TBM) are among the most technically sophisticated excavation machines in use by tunneling industry. The use of shields around the TBM allows the machine to pass through weak grounds and adverse geological conditions. However, there are limitations in applicability for DS-TBM in some ground conditions where large deformations are anticipated. The presence of the shield limits access to the tunnel walls for observation of ground conditions. This means limited possibilities of observing and analyzing ground conditions to avoid certain problems. Similarly, the presence of the shield does not allow the intrusion of the ground into the tunnel envelope, which is the main objective of using a shielded machine in the first place, yet it also creates the possibility of ground pressing against the shield. In such conditions, TBM may get stuck (including shield jamming and cutterhead blocking) in complicated geological structures, especially under high ground cover or in weak rocks, where large convergences are expected. This could cause major delays and impose a heavy and expensive burden on the tunneling operation. Some of the issues related to application of DS-TBMs in squeezing ground have been discussed in Hasanpour (2014) and Hasanpour et al. (2014a, b) and some possible scenarios and concepts for mitigating the related problems are offered. There are several performance parameters that should be considered with high accuracy at the design stage of a TBM for preventing machine entrapments. Size of the annular space or gap between ground and shields (created by overcut), length and diameter of shields, thrust force and torque, and machine advance rate are the most important performance parameters in tunneling by a shielded TBM. However, selecting the correct overcut, compared to other performance parameters, has a significant impact on preventing shield jamming. Selecting an appropriate or optimum value for overcut at the design stage of DS-TBM tunnel and implementing the predetermined overcut is the easiest way to address machine jamming, with the possibility of adjustment along the tunnel by using movable gage cutters. The adjustments can be directly related to ground properties and optimized to reduce the risk of machine jamming, while minimizing both the amount of material that is excavated and hauled out of the tunnel and the amount of grout that is placed behind the segments. For preventing the shield seizure, increasing the annular gap between the rock and shield is often utilized at the machine design stage. This feature can be included in the design of the cutterhead to accommodate a given overcut as a base design, and as needed, the excavated diameter of the tunnel, and hence the gap above the shield can be increased to react to bad ground where large convergences are & Rohola Hasanpour roha93@gmail.com

Impact of Advance Rate on Entrapment Risk of a Double-Shielded TBM in Squeezing Ground

Shielded tunnel boring machines (TBMs) can get stuck in squeezing ground due to excessive tunnel convergence under high in situ stress. This typically coincides with extended machine stoppages, when the ground has sufficient time to undergo substantial displacements. Excessive convergence of the ground beyond the designated overboring means ground pressure against the shield and high shield frictional resistance that, in some cases, cannot be overcome by the TBM thrust system. This leads to machine entrapment in the ground, which causes significant delays and requires labor-intensive and risky operations of manual excavation to release the machine. To evaluate the impact of the time factor on the possibility of machine entrapment, a comprehensive 3D finite difference simulation of a double-shielded TBM in squeezing ground was performed. The modeling allowed for observation of the impact of the tunnel advance rate on the possibility of machine entrapment in squeezing ground. For this purpose, the model included rock mass properties related to creep in severe squeezing conditions. This paper offers an overview of the modeling results for a given set of rock mass and TBM parameters, as well as lining characteristics, including the magnitude of displacement and contact forces on shields and ground pressure on segmental lining versus time for different advance rates.

DEM modeling of a monowire cutting system

Monowire block cutting machines can be used for natural stone block squaring and slab cutting operations. The plants where the cutting operations are performed demand high product quality with minimum operational costs. The major parameters affecting the economy of the operation are the energy consumed and the wear induced on the diamond beads during the cutting operation. An efficient cutting operation can only be maintained by selecting proper cutting parameters. Therefore, cutting parameters should be clearly understood. Experimental studies and numerical modeling methods are significant in terms of identifying the energy consumption occurring during natural stone cutting with monowire. Experimental studies and numerical modeling using discrete element method were performed on Afyon White Marble. Experimental studies have been performed by using a specially designed, fully automatic monowire cutting machine, and numerical analyses were carried out by commercially available software called three-dimensional particle flow code (PFC3D). A discrete element model for the cutting operation was developed, and various numerical models were performed for different peripheral speeds and cutting speeds, while, at the same time, the actual cutting operations were being carried out in the laboratory. Finally, the data obtained from the experimental works were compared with the data from numerical modeling. A comparison indicates that the frictional energy values obtained by means of numerical modeling are in good agreement with the results of the laboratory measurements. This study clearly put forward the influences of effective parameters on monowire cutting operations in natural stone industry. Furthermore, it filled an important space in the literature about the use of monowire block squaring machines.

Estimating major elemental oxides of an andesite quarry using compositional kriging

Abstract Andesite blocks with specific mechanical properties for facing and building stones should be chosen from fresh ones. These blocks can be recognised through major elemental oxides analysis. The number of samples that can be taken and analysed is limited. Then, major elemental oxides should be estimated at unsampled locations. In this study, block compositional kriging which satisfies constraints of the compositional data and generates estimations with a minimum prediction error variances was used. The estimated blocks were classified as exploitable and unexploitable regarding major elemental oxides’ thresholds of the fresh andesite obtained from petrography and mineralogy studies.

Analysis of Roof Caving Characteristics at a Coal Mine by Using Full Scale 3D Numerical Modeling

Regular and efficient caving of roof strata behind is essential in maintaining a trouble free operation in underground longwall mining when especially mined area is left for caving. As the face advances, roof strata should be regularly caved forming a goaf as homogenous as possible. In case of having an uncaved roof behind the coal face, load on the face increases dramatically leading to serious fall of roof conditions. Therefore it is of paramout importance to have the roof regularly caved behind a longwall face. This paper presents the problems encountered at a coal mine in Turkey due to high face pressures and subsequent flow of roof at the face roof junction. The height of the fully mechanised longwall face is 4.5 m. Sliding of face coal and later the fall of roof strata in front of the shields created serious stability and safety problems in the mine. Stopes opened in the roof had to be filled by usign forepoling, foam and concrete. This rescue operation had to be completed securely before starting of the cutting operation at the longwall face. Obviously rate of production of the longwall face has been severly declined during this period. There were a couple of reasons for having such a difficult condition in the mine. The longwall panel was located near to a syncline axis leading to high tectonic stresses. There were lots of small faults through the working face. Longwall face was extremely loaded by a very strong limestone layer having a thickness of up to 80 m located at 120 m above the coal seam. Although the strata between the limestone layer and the coal seam has a readily caving characteristics, the limestone caved at long intervals causing high face pressures due to its cantilever beam effect. Moreover during caving of the limestone, severe dynamic loads are experienced in the vicinity of longwall face deteriorating stability conditions. Therefore it was decided to model the effect of limestone layer’s behaviour by means of numerical modelling. A full scale model was created in accordance with all geometrical conditions and operational parameters by using FLAC3D software. The face advance is also simulated on the model. Stress and deformation state of the coal face, surrounding rock and especially the problematic limestone layer are analysed. To solve the problem, a blasting pattern is selected to weaken the limestone layer by using drill holes opened from the surface. This paper presents the numerical modelling results in relation to selection of the best blasthole geometry to decrease loading on the face and hence maintain a safe, efficient and stable longwall operation.