Jamal Rostami

Developing new equations for TBM performance prediction in carbonate-argillaceous rocks: a case history of Nowsood water conveyance tunnel

Nowsood water conveyance tunnel is 49 km long and has been designed for transferring 70 m3/s water from Sirvan river southward to Dashte Zahab plain in the west of Iran. This long tunnel has been divided into three sections, namely 1A, 1B and 2. By April 2008, about 5.3 km of the lot 2 of this project, with a total length of 26 km, were excavated by a double-shield TBM. The bored section of tunnel passed through different geological units of three main formations of the Zagross mountain ranges which mainly consist of weak to moderately strong argillaceous-carbonate rocks. This paper will offer an overview of the project, concentrating on the TBM operation, and review the results of the field performance of the machine. Also results of statistical analyses to evaluate correlation of TBM performance parameters with rock mass characteristics will be discussed. The results of machine performance analysis indicated that there are strong relationships between geomechanical parameters and TBM performance parameters in this particular project. In this research some empirical equations and a chart have been developed to estimate TBM performance parameters in similar cases based on common rock mass properties.

Study of Dominant Factors Affecting Cerchar Abrasivity Index

The Cerchar abrasion index is commonly used to represent rock abrasion for estimation of bit life and wear in various mining and tunneling applications. Although the test is simple and fast, there are some discrepancies in the test results related to the equipment used, condition of the rock surface, operator skills, and procedures used in conducting and measuring the wear surface. This paper focuses on the background of the test and examines the influence of various parameters on Cerchar testing including pin hardness, surface condition of specimens, petrographical and geomechanical properties, test speed, applied load, and method of measuring wear surface. Results of Cerchar tests on a set of rock specimens performed at different laboratories are presented to examine repeatability of the tests. In addition, the preliminary results of testing with a new device as a potential alternative testing system for rock abrasivity measurement are discussed.

Continuous Monitoring of Pin Tip Wear and Penetration into Rock Surface Using a New Cerchar Abrasivity Testing Device

Evaluation of rock abrasivity is important when utilizing mechanized excavation in various mining and civil projects in hard rock. This is due to the need for proper selection of the rock cutting tools, estimation of the tool wear, machine downtime for cutter change, and costs. The Cerchar Abrasion Index (CAI) test is one of the simplest and most widely used methods for evaluating rock abrasivity. In this study, a new device for the determination of frictional forces and depth of pin penetration into the rock surface during a Cerchar test is discussed. The measured parameters were used to develop an analytical model for calculation of the size of the wear flat (and hence a continuous measure of CAI as the pin moves over the sample) and pin tip penetration into the rock during the test. Based on this model, continuous curves of CAI changes and pin tip penetration into the rock were plotted. Results of the model were used for introduction of a new parameter describing rock–pin interaction and classification of rock abrasion.

Study of borehole stability of Marcellus shale wells in longwall mining areas

With the widespread drilling of gas wells in Marcellus shale, there are high potentials for wellbore instability problems when wells are located in longwall mining areas, which in many areas such as southwest Pennsylvania, West Virginia, and eastern Ohio are being used for extraction of the coal seam overlaying the gas reserves. The ground deformation, caused by coal mining, could generate large horizontal displacement and complex stress change in subsurface rock. This in turn triggers ground movement which can cause casing failure, and thus interruption in the operation of the well that raises safety and environmental concerns. This could result in shutting down the well for repair, or permanent abandonment. Thus, it is critical to characterize the parameters related to the longwall mining process and to propose a general casing design guideline in such areas. In this paper, numerical modeling was utilized to simulate the complex ground conditions and resulting stresses and strains in longwall mining areas. A casing design spreadsheet was then constructed for design of appropriate selection of casings, based on the results of the numerical modeling. Our results were validated with field practices of wellbore design in southwest Pennsylvania. This paper also provides a methodology for investigating potential ground deformations, resulting stress/strain changes, and wellbore stability issues for oil and gas wells drilled in longwall mining areas in Marcellus shale or similar formations worldwide with active coal mining activities.

Full scale linear cutting experiment to examine conical bit rotation

Conical bits are very common in excavation of soft to medium rocks in a great deal of mining and construction applications. Bit rotation allows the conical bits to maintain their tip shape and allows them to work more efficiently for extended period of time. This paper discusses the importance of bit rotation and the research work of measuring bit rotation and the impact of various parameters on this phenomenon. To find the relevant factors contributing to bit rotation, a few dominant parameters such as bit type, cut spacing, depth of cut, attack angle, and skew angle were considered. The paper described full scale linear cutting tests which were performed at Kennametal rock cutting lab in Latrobe PA. This linear cutting test is a prototype experiment to verify the direct measurement of bit rotation, to evaluate the impact of related parameters before performing rotary cutting tests. This paper offers the review of the linear cutting test results and outlines the observed bit rotation during experiments and their practical implications.

Study of conical bit rotation using full-scale rotary cutting experiments

Conical bits are very common in the excavation of soft to medium rock in many mining and construction applications. These bits are claimed to rotate as they cut the rock, allowing for uniform wear of their tip and body that helps maintain the tip shape, and works efficiently for an extended period of time. This paper will present an extensive study of bit rotation, including full scale cutting tests performed to measure bit rotation using different cutting geometry to evaluate the mechanism and extent of bit rotations relative to the controlling parameters. This includes bit type, depth of cut, cut spacing, skew angle, and sequence of cuts. The testing started with linear cutting tests, which indicated limited to no bit rotation when the bit was fully engaged with rock. As a follow-up study, full-scale rotary cutting tests, the impact of cutting parameters, as well as cutting speeds on bit rotation were studied. Full-scale rotary cutting tests were conducted using a test drum laced with an instrumented bit. Bit rotation was measured under the rotary motion of the cutter-head with several variables. The results of rotary cutting tests showed that bit rotation occurs when the bit enters and exits the rock. The results of rotary cutting tests and the impact of various parameters on measured bit rotation; especially skew angle will be summarized in this paper.

Review of Ground Characterization by Using Instrumented Drills for Underground Mining and Construction

In underground mining, many miners are injured or lose their lives because of roof/pillar instability each year, and this is a persistent safety risk. Characterization of overlying strata is important for the design of safe and cost-effective ground support systems. Entry roof characterization can be performed by geological back-mapping of the ground using various methods such as geophysical logging, borescoping, rock mass rating, and intelligent roof bolt drilling systems. This paper offers a brief review of mine roof characterization methods, followed by an introduction to and discussion of roof characterization methods using instrumented roof bolters. A brief overview of the various instrumentation systems developed for roof bolt drills is presented. The results of the preliminary study and initial testing indicate that, despite recent improvements in the area of ground characterization by instrumented drills, there are still several issues that must be addressed to improve the efficiency and accuracy of existing systems. A summary of suggested improvements is provided.

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.

Evaluation of Granular Soil Abrasivity for Wear on Cutting Tools in Excavation and Tunneling Equipment

AbstractThis paper presents an experimental study of tool wear and abrasivity of granular soils using a testing system specifically designed for the evaluation of wear on earth-moving machines, especially soft ground tunneling applications where the impact of soil abrasion on the operation is significant. In the testing system, a propeller fitted with steel covers of different hardnesses is rotated at 60 rpm in granular soil samples in a chamber under ambient pressures of up to 10 bar. The developed system can quantitatively assess the abrasive characteristics of soils through the measurement of weight loss on the special covers of the propeller, accounting for soil gradation, mineral composition, sphericity and roundness, water content, and tool hardness. Preliminary test results indicate that water content, particle angularity, and relative hardness between the tool and soil have significant impact on tool wear and soil abrasion. For the tests conducted, it is observed that angular sands produce signifi...