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By N. Ripepi

"The Langmuir model has been widely used for the coal-methane sorption process via an isothermal test. However, even though the temperature-dependent Langmuir model were recognized theoretically and experimentally, the quantitative relationship between the Langmuir’s constants (a & b) and temperature have not been clarified and confirmed by lab test data. This paper collects 158 methane-coal sorption data under different temperatures, which apply the Langmuir model to consider the relationship between Langmuir’s constants (a & b) and temperature (see APPENDIX I). Even though the Langmuir model cannot be used to show the physical state of methane adsorption on coal, it is widely used because of its simplicity and the reasonable explanation of its parameters (a & b). The results from these published isothermal tests confirm that 1) there is no consistent relationship between Langmuir’s constant-a and temperature; 2) the Langmuir model is a temperature-dependent model, and the temperature-dependent feature is mainly shown by the relationship between Langmuir’s constant-b and temperature; 3) The relationship between Langmuir’s constant-b and temperature can be described by both the exponential and linear relationship with dried coal. This paper provides a database for temperature-dependent Langmuir’s model, which can be used for reservoir simulation of coalbed methane reservoir, coal seam degasification modeling for underground coal mines considering the heating effect induced by geotherm and heat injection (via hot water, hot steam, ultrasonic, etc.). INTRODUCTION The isothermal test for gas sorption on coal is one of the fundamental tests in Coalbed Methane (CBM) recovery fields, such as underground coal mine methane degasification, CBM gas-in-place estimation, and carbon dioxide sequestration in un-minable coal seams. Generally, two methods, volumetric and gravimetric, are employed to obtain isothermal data (Bush, A. & Gensterblum, Y., 2012). Based on these two approaches, a series of commercial and self-assembled instruments are built and several calculation methods are used to obtain isothermal data (Bush, A. & Gensterblum, Y., 2012, Gasparik, K., 2014; Goodman, A. L., et al, 2004; Zhang, L., et al, 2013). In the post-processing stage, many models are provided to analyze isothermal data in order to understand the storage mechanism of gas in coal. Common models include the Langmuir model (and its extended forms), the pore-filling model, multilayer adsorption model (BET), and the Gibbs’ model. Among these models, the Langmuir model is the most widely used for its simplicity and functionality. The Langmuir model is expressed as follows:"

Jan 1, 2016

By Craig Hartley

? A helper stands beside a continuous miner as the operator is at the controls. The operator means to push the stop button but hits the drum rotation start button by mistake. The drum begins to turn and the bits catch the helper's clothing. He is thrown violently to the ground and suffers multiple contusions. ? A farmer's wife helplessly watches her husband drawn into the claws of farm machinery while she frantically and unsucessfully searches for the control to stop the machine. ? A mechanic on the night shift replaces plugs in the lubrication systems of all three engines of an airliner following routine maintenance. In doing so', he fails to notice that "0" ring seals have not been mounted on the plugs. A few hours later, as the fully loaded airliner is cruising high over the ocean, oil pressure on one engine drops precipitously. The pilots quickly shut down the engine and turn for home. Almost immediately, the two remaining engines lose their oil and fail.

Jan 1, 1983

By Basar Arioglu, Mustafa Tanriverdi, Seok Jae Seo

"INTRODUCTION Istanbul is a unique megalopolis connecting two continents. Population growth and economic development require permanent solutions and continuous investments on the transportation infrastructure. While the average population growth rate in Turkey is around 1.3% per annum, Istanbul is growing at an even faster rate of more than 1.5%. Even more striking is the fact that car ownership in Istanbul is increasing 5% a year, which is four times faster than the population growth. Although Istanbul Metropolitan Municipality (IMM) has worked persistently to improve the quantity and quality of the public transportation system in the city through, in particular, extending the available rail system network, the need for extra roads has always fallen behind demand. To make things worse, Istanbul is divided by the Bosphorus Strait, the large waterway connecting the Black Sea to the north and Marmara Sea to the south, which leads to the Mediterranean. This waterway is crossed via two suspension bridges, the Bosphorus Bridge built in 1973 and the Fatih Sultan Mehmet Bridge built in 1988. Current daily traffic across the bridges is around 450,000 vehicles per day. Ever increasing cross-Bosphorus traffic demands require other routes to be in place a soon as possible. While a third bridge farther north is currently under construction, yet another tunnel crossing is coming to the end of construction and is planned to be in service by December 2016. Being implemented under a Build-Operate-Transfer (BOT) model, Istanbul Strait Road Tunnel Project (ISRTP, the Project) has been under the spotlight not only because of its distinctive technical characteristics but also because of its robust business model, exacting financial and legal arrangements, diverse stakeholders and challenging organizational management structure. The following paragraphs offer an overall view of the Project from inception to where it stands now and extend to the imminent operational phase, touching lightly on all major aspects of this challenging journey."

Jan 1, 2016

By Joseph Sopko, Xavier Lacourse-Dontigny

For the REM (Réseau Express Métropolitain) project, a 2500 m tunnel was built using a tunnel boring machine (TBM) under the Montreal Pierre Elliott Trudeau Airport (ADM). Although the geology under the Montreal Airport (ADM) would have been suitable for an excavation with a hard rock machine, the rst section reuired an earth pressure balance (EPB) TBM due to the soft soil located under wetlands. After excavating 280 m, the TBM was blocked in a transition zone of unconsolidated, water-bearing soils directly above the underlying bedrock. A free air intervention was not possible due to these geological conditions. After several failed attempts to create a slurry cake for hyperbaric interventions, a ground freezing system was designed and implemented, incorporating angled pipes drilled from outside the wetlands to directly in front of the cutterhead. This paper discusses the engineering reuired to form a frozen, water-tight zone in front of the cutterhead using liuid nitrogen. It also describes the complex method of replacing the disc cutters while holding the ground freezing system active in a manner protecting the health and safety of the workers.

Jun 23, 2024

By Richard W. Patton

With the advent of the Clean Air Act and the installation of flue gas desulfurization (FGD) equipment (scrubbers) on coal fired power plants, the management of solid wastes has taken on added importance. Aside from the large amounts of fly ash and bottom ash usually generated, large quantities of liquids in the form of scrubber sludge are also produced. These wastes must be disposed of within the constraints of land and water quality regulations. This paper describes the practices adopted by the electric utility industry in denting with this problem, including methods of generation and treatment, quantities and characteristics of the materials, and transportation and disposal practices. The paper also briefly describes final product characteristics and several applications for commercial utilization and land reclamation.

Jan 1, 1983

By M. R. Shahan, W. R. Reed, P. Zhang, J. P. Rider

Roof bolter operators may be exposed to high respirable dust concentrations on continuous miner sections with blowing face ventilation when bolting is performed downwind of the continuous miner. One solution to reduce the high respirable dust concentrations is to use a canopy air curtain (CAC) to deliver clean air from a filtered blower fan directly to the bolter operators under the canopies. The influence of CAC installation in the airflow and dust dispersion around the location of the roof bolter operator can be evaluated by using computational fluid dynamics (CFD). This study, performed by the National Institute for Occupational Safety and Health (NIOSH), considers two scenarios: (1) a roof bolting machine in the center of the entry for installation of the fifth row of bolts from the face, and (2) a roof bolting machine positioned close to the face for the installation of the last row of bolts. In both scenarios, the bolting machine is placed in an environment which contains 6.0 mg/m3 of respirable dust and is ventilated by a blowing curtain with 3,000 cfm (1.42 m3/s) of air. This environment is used to simulate the roof bolter machine operating downstream of a continuous mining machine. Two operation positions are simulated at the same bolting location: dual drill heads in the inward position for two inside bolts; and dual drill heads in the outward position for two outside bolts. The influence of the CAC on airflows and dust dispersion is evaluated with the CAC operating at 250 cfm (0.12 m3/s). INTRODUCTION Roof bolting machines are used to drill bolt holes into the roof of an underground mine at specified patterns and to install roof bolts to secure the roof from falling. At times, the roof bolting machine is also used to install rib bolts; however, only the roof bolting operation was considered in this simulation. Though the roof bolting operation drastically improved the safety of miners from roof falls, some roof bolter operators are experiencing health problems associated with respirable dust. Based on recent statistics [1], following a low point in the late 1990s where the prevalence of coal workers’ pneumoconiosis (CWP) in miners with 25 years or more tenure was approximately 5%, CWP now exceeds 10% for miners with 25 years or more of tenure. In central Appalachia (Kentucky, Virginia, West Virginia), 20.6% of long-tenured miners have CWP and 4.5% have progressive massive fibrosis, the most severe form of CWP. CWP, also known as black lung, is an occupational respiratory disease that has no cure and can ultimately be fatal. The only way to prevent the incidence of black lung is to eliminate miners’ exposure to respirable coal mine dust. Current U.S. regulations require that the overall respirable dust concentration to be 1.5 mg/m3 or less for a full-shift sampling if respirable quartz is not present; otherwise, the standard is 10 divided by the percent quartz (not to exceed the 1.5 mg/m3 respirable dust standard) [2, 3].

Jan 1, 2019

By Clark D. Harrison

This paper compares the ash slagging potential of Illinois No. 6 Seam coal: as raw coal; as commercially cleaned coal processed in a baum-jig plant; and as coal cleaned to a reduced ash specification at the Electric Power Research Institute's Coal Cleaning Test Facility. The comparison is based on: ? ASTM ash fusibility data ? A slagging index ? Gravity fractionation analyses of critical mineral matter compounds ? Comparative pilot combustion tests. The first three grounds of comparison are laboratory data; and the final comparison involves burning approximately 15 tons of each coal at CONOCO's 1.5 MBtu/hr (440 KW) test combustor. The evidence of these .four comparisons indicates that lowering the ash specification of coal before combustion can significantly improve the ash slagging characteristics of Illinois 90. 6 Seam coal.

Jan 1, 1984

By Charles L. Allie

In June, 1980, Reserve Mining Company completed a 370 million dollar construction project which included process modifications required to reduce the silica content from nine to five percent by weight and increase the iron con- tent of Reserve's pellets from 62.5 to 65.8 percent by weight (dry basis); process modifications and additions required to implement "best available technology" water quality controls; and installation of "best available technology" air emission controls. The new process began operation on June 24, 1980 and is being optimized to meet design objectives. Dry cobbing, fine screening and flotation additions to the concentrating process have reduced the silica content of Reserve's pellet from nine percent to five percent by weight. The process reclaims and reuses all process waters, stores all tailings in a zero discharge tailings basin and meets all air emission standards.

Jan 1, 1980

By Erika Moonin, Jim Nickerson, Claudio Cimiotti, Roberto Bono

"In response to the severe drought on the Colorado River basin and in order to preserve existing water capacity to the Las Vegas Valley, the Southern Nevada Water Authority contracted a new deep-water intake (Intake No. 3) located in Lake Mead. The current project (Contract No. 070F-01-C1) includes 5 km (3 miles) of tunnel with very difficult geological conditions and a 200- m (650-ft) deep shaft and marine works. This paper will present the current status of the design-build contract being constructed by Vegas Tunnel Constructors and the challenges and problems faced and the innovative solutions developed to handle the difficult conditions encountered during tunneling with up to 15 bars of pressure.ProjectbackgroundThe Las Vegas Valley receives the majority of its water from Lake Mead, which is located approximately 30 km (20 miles) east of the Las Vegas, NV metropolitan area. Due to the severe drought that has hit the southwest region of the United States, the water level in Lake Mead has receded from its high water level of 372 m (1,221 ft) above mean sea level (amsl) to a low of 330 m (1,076 ft) amsl in June 2015. Should the lake level continue to fall, at elevation 320 m (1,050 ft) amsl, the current water intakes will not be able to draw enough water to meet the needs of the local area. The risk of losing water capacity has prompted the construction of a new deeper intake. Not only is the new Intake No. 3 situated at a lower elevation in the lake at 262 m (860 ft) amsl, the new Intake No. 3 is also located to draw better quality (Fig. 1).Project challengesThe project has had several difficult challenges to overcome:• The work consisted of a 1.2 kt (1,300 st) structure constructed on a barge and lowered 100 m (330 ft) into Lake Mead anchored with 9,200 m3 (12,200 cu yd) of tremie concrete.• The drill-and-blast starter tunnel was impacted by three inflow events, resulting in a one-year project delay.• One of the main challenges was selecting the tunnel boring machine (TBM) and excavating the tunnel with expected hydraulic head pressure of as much as 17 bar (16 bar was the highest pressure recorded during the drive), crossing faulted areas, low rock cover and the risk of tunnel instability due to direct connection with the lake.• Extensive pre-excavation grouting with a constant head pressure ranging from 12 bar to 15 bar.• Structural repair of the cutterhead in difficult hydrogeological conditions [water inflow of approx. 800 m3/hr (4,000 gpm)].• Complete repair of the cascade sealing system for the main bearing and two replacements of the pinion bearings.• The TBM approach to the intake structure."

Jan 1, 2015

By Stephen C. Tadolini, Colton Cook, Cody Hildreth, Frederick Cybulski

"Broken and jointed ground is extremely hazardous and requires unique stabilization techniques to protect worker and critical entries. Bolting techniques, even the most advanced with pre-load to create roof compression, can leave large gaps of unconfined and separated roof. This roof can also be susceptible to water inflows which only exacerbate the support problem. These types of conditions existed on long term development main entry accessing several future longwall panels. The geotechnical assessment identified well-defined jointing systems that also permitted water to flow between the roof separations, which “lubricated” the roof material and minimized any frictional advantages. Chemical injection of a Polyurethane material, Minova Carbopur WS, was placed beyond the bolted horizon to move the water to the rib lines and reinforce the fractured and broken roof. The injection material permitted the effective use of bolting patterns and helped ensure long-term stability of these critical entries. The paper describes the evaluation techniques, design patterns, basis for chemical selection and application, and results and recommendations.BACKGROUNDThe injection of mine and underground civil structures using polyurethane (PUR) has been ongoing for over 50 years. The applications in mining have included gate road stabilizations, longwall set-up and tear-down entries, and simple consolidation of coal mine roofs. PURs have also been used for roof stabilization during longwall shield recoveries. Polyurethane injection was initially developed by the Bergbau-Forshung GmbH, a German coal mine research institute, in the early 1960s (Jankowski, 1972). The product became a standard stabilization method in Germany after its commercial introduction in 1971 (Knoblauch, 1994), and was successfully manufactured at the Minova Essen, Germany location for over 50 years. With the recent closing of the German underground mines, that manufacturing facility has been closed and moved to Katowice, Poland, where production continues today Injection products are also being successfully manufactured by Minova in Australia and the United States.Polyurethane injection in underground coal mines is used in difficult ground conditions in fractured immediate and main roofs. It is also common as a rock stabilization remedy to prevent longwall face caving during shield removal. As presented in the case study, polyurethane was applied to minimize the inflow of water from beneath a stream channel while providing reinforcement and consolidation of the fractured roof that had lost confinement. Polyurethane is a two-component system (Part A and Part B) that is injected into a borehole and can chemically bond to the rock, not relying on friction or mechanical interlock to provide support. The material is injected under pressure, coupled with a low viscosity and small particle size; it flows into roof fractures and separations, which are the paths of least resistance. New developments in low viscosity PUR materials allows penetration of cracks as tight as 0.002 inch (0.05 mm) wide. This also allows for the closures of extremely small cracks to minimize the inflow of water, even if the water is under pressure. Combinations of designed expansion properties and low viscosities make the materials ideal for minimizing and stopping flows of water from underground structures."

Jan 1, 2019

By Liangguo Kang

Coal, as one of the vital sources of energy in China, has raised widespread concerns regarding its safety issues amidst the country’s economic growth driven by coal. To address this concern, this study employed the Kuznets curve, multiple linear regression, and data envelopment analysis models to investigate the impact of Chinese coal economic development on coal mine deaths from 1992 to 2021. The findings revealed a clear correlation between the Chinese coal economy and coal mine deaths. Specifically, per capita coal output, the death rate per million coal tons, and the death rate per hundred thousand persons exhibited positive, negative, and negative correlations, respectively, with the growth of coal income over the past three decades. Moreover, when the coal workers and coal output factors remained unchanged, the income of coal demonstrated a negative correlation with future changes in coal mine deaths. Notably, with three decades of coal economy development, substantial improvements in coal mine safety have been observed in China. Consequently, this research provides valuable insights for formulating safety measures and policies in coal mines across different economic levels, as well as a useful framework for assessing safety development in the coal industry.

Jan 20, 2024

By W. R. Reed, Y. Zheng

A recent study conducted by the National Institute for Occupational Safety and Health (NIOSH) evaluated the roof bolter canopy air curtain (CAC) systemin a blowing face ventilation system, demonstrating its effectiveness and illustrating the CAC protection zones. This study evaluates the roof bolter machine CAC while operating in an exhausting face ventilation system. This study considers two similar locations to allow comparison with the previous blowing face ventilation (Zheng et al., Min Metal Explor 36(6):1115–1126, (2019)) study: (1) a roof bolter machine bolting the roof at 20 ft (6.1 m) from the face and (2) a roof bolting machine bolting at 4 ft (1.2 m) from the face. The environment introduces 6.0 mg/m3 of respirable dust to represent the roof boltingmachine operating downstreamof the continuous miner. However, the exhausting face ventilation uses an exhaust curtain with 9000 cfm (4.25 m3/s) of air. Two roof bolter machine working positions are simulated with the use of dual drill heads in the inward position for two inside bolts and in the outward position for two outside bolts. The influence of the CAC on airflows and dust dispersion is evaluated with the CAC operating at 250 cfm (0.12 m3/s) with dust reductions ranging from 39.5 to 82.8%. When the roof bolter machine operated close to the face, increasing CAC airflow was required for adequate protection since the dust reductions can be as low as 39.5%. Additional CAC airflows of 350 cfm(0.17 m3/s) and 450 cfm(0.21 m3/s) were evaluated and demonstrated that dust reductions increased to 59.7% (350 cfm) and 72.0% (450 cfm) for the worst location where the roof bolter operators located.

Aug 26, 2020

By B. Kolonja

This paper considers simulation of truck dispatching system designs using maximum expected production of the truck-shovel system as the measure of performance. Two methods are utilized, multiple comparisons with the best (MCB) and the combination of MCB and the variance reduction technique known as common random numbers (CRN). These two techniques are compared via simulation experiments. The results show that the combined procedure of MCB with CRN is the superior tool to reduce the total number of replications needed to ensure the specified probability of correct selection over the finite number of designing systems. In this case study, MCB with CRN reduces the variance by 29% and the number of required replications by 48%. Also, the MCB with CRN procedure narrowed the confidence interval by 18%.

Jan 1, 1994

By Harold J. Schock

The cases of no auxiliary ventilation and ventilation with tubing were mathematically modeled, using a turbulent dispersion model. The scooptram that is used to load is modeled as a variable-speed, variable-strength source of pollutants moving in and out of the dead-ended drift. Model predictions are compared to experimental measurements. A parametric analysis was performed to determine the effect of exhaust pipe location and time spent out of the drift, as well as to determine if a relationship existed between CO2 and NO levels. It was concluded from this analysis that when modeling a load-haul-dump cycle, it is necessary to use a model that has the capability of predicting changes in source strength as well as source location. It was also determined that four relevant factors include effective heading height, apparent longitudinal diffusion coefficient, transverse concentration gradient at the face, and average dispersion width of the exhaust jet. As these factors change with heading geometry and ventilation configuration, they were determined experimentally, Carbon dioxide was used as a tracer to calibrate the model; since, knowing the fuel flow rate, it is possible to calculate CO2 production. The above four factors in the computer model were calculated using a regression analysis, comparing predicted local concentrations to measured local concentrations. The model was then verified after this calibration process using additional experimental results. With the calibrated model, it is possible to predict pollutant concentrations at any location in the heading using an engine map and the previously calculated flow field. A parametric analysis shows that the exhaust pipe location can have a significant impact on operator exposure to exhaust gases. It was also shown that NO concentration varies directly with C02 levels. Predictions using the dynamic model are contrasted with constant source strength (pollutant flow rate) results. An analysis of these predictions for computing time-weighted average NO shows the dynamic model predictions of operator exposure to this pollutant to be less than one-half of the value predicted using a constant source model.

Jan 1, 1981

By D. Duvris

The main objective of this work was to quantitatively investigate exhaust emission levels relative to maintenance (service) intervals during the operation of diesel-powered equipment at an underground bauxite mine in Greece. Such emissions depend on a great number of parameters, including the type of engine (technology) and its tuning, the type of work performed (as related to the engine workload), the suggested maintenance intervals, the altitude, the temperature and humidity of the atmosphere in the underground mine, the properties of the fuel and the operator's training and experience levels. The necessary ventilation quantities were calculated based on exhaust gas-concentration measurements and site-specific relationships between pollutants and adjusted air-quality indices. Diagrams comparing the necessary and recommended airflow for several equipment groups, featuring two engine types and different maintenance intervals, are presented.

Jan 1, 2000

By Dan Norrgran

In recent years, a great deal of attention has been focused on developing mill liners to increase wear resistance, improve grinding efficiency and reduce energy consumption in milling applications. The installation of an appropriate mill liner is critical as it affects the overall cost and product quality. A mill liner has two specific functions. The first is to protect the mill shell and mill ends from direct contact with the abrasive grinding media (in this case, the liner serves as a wear surface). The second function is to transport the grinding media, creating energy for size reduction. The liner acts as a lifter, mechanically transporting and cascading the grinding media. The mill lining is a major cost in the milling operation. The costs associated with the mill lining include the capital cost of the lining, downtime required to replace the worn liner and the labor for installation. Generally, in hard rock mining, the life of a mill liner in secondary ball mills is 12 to 24 months.

Jan 1, 2009

By K. V. Raj

In the mining industry, computational fluid dynamics (CFD) modeling is used extensively to simulate air flow in underground mines. CFD modeling of pollutant transport in open-pit mines is relatively new. Modeling the actual pit geometry of an open-pit mine and the open domain is complex. The complexity is primarily due to the faceted geometry of an open-pit mine with its numerous associated sharp features. Important issues that are not considered carefully at the geometry level are generally propagated to the subsequent processes. Several challenges and pitfalls are encountered in modeling pollutant transport in open-pit mines. These challenges and pitfalls are related to the geometry, meshing, boundary conditions, and turbulence modeling parameterization. An appropriate mesh selection is critical. A detail discussion of the meshing of the domain of an open-pit mine is presented in this paper. The selection of an appropriate turbulence model, such as kappa-epsilon (?-e), large eddy simulation (LES), Reynolds stress model (RSM), etc., to obtain the best possible solution is equally significant. This paper discusses the various challenges in modeling the pollutant transport process in an open pit and some of the approaches adopted to address these challenges.

Feb 27, 2013

By T. Payne

Underground heat issues are mainly focused on the detrimental effects to a workers health. However, working in hot, humid conditions has other negative effects. Studies have shown that safety, productivity, workforce morale and operating cost are also worsened in these conditions. The human body has several mechanisms for rejecting heat and remaining cool. However, once the air temperature exceeds about 34°C, the only effective mechanism is by evaporation of sweat from the skin. This is assisted by acclimatisation which is the human body?s enhanced ability to combat extended exposure to heat. The body has to remain well hydrated when working in heat as even small degrees of dehydration cause significant decreases in the ability to work in heat. There are two ways in which heat load can be reduced: Through use of refrigeration/vent/cooling to reduce thermal stress on workers; Reduce the contribution that heat sources have to underground heat load (e.g. reduce idle time, fleet size, etc). Some of the sources of underground heat have the potential to be more manageable than others. Geothermal heat and heat from autocompression will be found in all mining situations in varying degrees depending on geothermal gradient and surface temperature, however, the use of equipment and blasting may be streamlined to reduce the underground heat load. It is through a combination of the available options that most mines will successfully control their heat related problems. Mt Isa, which has been a focus for heat related study in Australia, has successfully implemented protocols for working in heat. Through combining these with the installation of a surface bulk air cooling plant, Mt Isa has consistently reduced the incidence of heat illness. This is likely to be the most cost effective method of reducing heat load for deep mines in Australia. Shallower mines which may only occasionally encounter hot conditions should consider more portable cooling options. This study will review the heat issues in underground Australian metalliferous mines.

Jan 1, 2009

By Christopher B. Kapes

To reduce concentrate dewatering and drying costs, the Concentrator Division at Phelps Dodge Morenci, Inc. investigated available filtration technologies. Numerous methods were explored, including: drum, disk, belt, pressure, hyperbaric, and ceramic media filtration. An economic evaluation of the individual filtration technologies indicated the advantages of ceramic media filtration for Morenci concentrates. This paper discusses the technological development culminating in the first full scale application of ceramic media disk filters in North America. Low moisture contents are obtained at high production rates and greatly reduced operating costs.

Jan 1, 1994

By Ingo Ossenbühl, Wolfgang Dolsak, Vojtech Gall, Axel G. Nitschke

"Yielding support systems for application in underground construction have a long history, primarily in mining. Typical examples are tunnels subject to loading conditions that lead to overstressing of the newly installed support or existing tunnel structures in active fault zones. Recent applications for tunnel rehabilitation projects unveiled the capabilities and flexibility of combined yielding support systems presented in this paper. Frequently, the main requirements for tunnel rehabilitation applications are a fast, safe, and simple installation along with the need for flexibility with regards to existing tunnel geometries. A combined support system consisting of steel sets with yielding connections and special groutable hoses has proven to be an efficient support measure providing a multitude of advantages compared to conventional rehabilitation approaches. The presented yielding support system provides an immediate and active support, while it allows for controlled yielding upon experiencing loads beyond its support capacity. INTRODUCTION The excavation of underground spaces leads to redistribution in the existing stress regime. This load redistribution goes along with deformations in the surrounding rock mass. Magnitude and duration of these deformations depend on the tunnel’s depth and geological conditions, but also on the installed support system. Modern civil tunneling infrastructure has generally an envisioned service life of about 120 years. Conventional tunneling provides typically a dual support system, split into the initial (or primary) and final (or secondary) lining. A typical design principle in civil tunneling is to let the vast majority of deformations acting on the initial lining cease, before the final lining is installed. Based on this approach, the loading on the final lining is significantly reduced and signs of overstressing, such as cracking of the lining, are typically limited to the initial lining. However, special cases in swelling and squeezing ground require different approaches, including yielding support systems."

Jan 1, 2016