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By H. H. Hughes, J. G. Dunn, P. G. Fernandez, H. G. Linge

Dissolved Arsenic (As) is stabilised primarily as As(III) and As(V) and enters ground water streams from sources such as the increasing metallurgical processing of As - containing ores [1]. As(III) is more toxic than As(V) and is less effectively removed from solution by oxide precipitation. Even for dilute As(III) solutions, skin contact or ingestion can cause dermatitis or cancer and there are stringent effluent control standards in place for As containing effluent from mining operations [2]. Chemtronics (Perth, Australia) has manufactured a compact digital voltamme­ter, based on anodic stripping voltammetry (ASV) and suitable for use in the laboratory or field. In this paper we demonstrate the utility of this equipment for measuring As(III) concentration with a detection limit of ca. 10 ppb.

Jan 1, 1995

By John W. Greene

ennec?tt's Bameys Canyon Mine personnel developed an mnovahve process to extract gold from a small (1.8 million tons) sulfide ore zone in an oxidized ore body located at the Bameys Canyon Mine. This approach consists of extracting the sulfides from the ore via flotation, shipping the concentrate to Kennecott's new smelter, and mixing the flotation tailings with the oxide ore, agglomerating the mixture, and stacking the resultin tailings/oxide ore combination on the heaps. Conventional heap leaching technology is utilized to recover the gold from the mixed materials. Overall, the total gold recovery from the sulfide ore is esti­mated to be 90%. This approximation is based on a smelter gold recovery of 98% from the concentrate and an 88% recovery from the tailings during heap leaching

Jan 1, 1996

By H. G. Linge

The Australian gold industry currently contributes some $4bpa to the national economy [l]. Some 40% of the total gold is produced in the region centred on Kalgoorlie known as the Eastern Goldfields of Western Australia. This region is the largest single centre of production with an output of some 100 tpa of gold [2]. In the Eastern Goldfields, refractory arseno­pyritic gold ore is an increasingly significant source of gold, feeding several operations utilizing bio-oxidation as the pre­carbon in pulp/leach (CIP/L) treatment process [1]. This paper desribes an alternative pre-CIP/L treatment option for use in the Eastern Goldfields based on the chlorination of arsenopyrite by chlor-alkali technology [3] using the salt resources available from saline water present in abundance in the region.

Jan 1, 1995

By G. D. Ritson

Gold surveys were sent to 21 gold operations around the world. Eleven different surveys were sent, each targeting a dif­ferent unit operation used commonly in gold processing. On a monthly basis the individual reports were returned to the opera­tions. Empirical data collected during the surveys has con­tributed to more effective engineering design. Graphical rela­tionships established have been used by the operations to "benchmark" performance against the industry and identify areas of possible improvement. This paper presents some of the findings related to the fol­lowing four surveys that investigated parameters specifically relating to carbon processing. Rescan Gold Survey GO 1 - Carbon Management practices Rescan Gold Survey 003 - Carbon Stripping Rescan Gold Survey 006 - Carbon Loading Isotherms Rescan Gold Survey 007 - Screening A final report documenting all the surveys will be compiled

Jan 1, 1998

By D. W. Hill

By seeking to define the social and political parameters of both established and potential uses of the underground, this paper will attempt to formulate and state the problem posed in the realms of public choice for obtaining more rapid development and more beneficial use of the underground environments. Essentially, the paper will pursue the following outline: 1. Established policies and established uses of the underground 2. Potential uses of the underground for social benefit 3. Constraints on development and policy a. Psychological constraints b. R & D plus physical constraints c. Economic constraints d. Public choice and policy contraints (both governmental and non-governmental) e. Legal and other structural constraints 4. Defining the problem from the social standpoint 5. Suggestions for surmounting the constraints and meeting the problem: some hypotheses for the future.

Jan 1, 1974

By John E. Urosek, Mark L. Mott, Gary E. Smith

One function of Mine Safety and Health Administration (MSHA), Pittsburgh Health Technology Center's Ventilation Division is to provide assistance to MSHA enforcement and industry personnel for maintaining adequate fresh air to all areas of an underground mine. In fulfilling this objective, total mine venti1ation pressure-air quantity distribution on investigations are conducted to measure the air pressures and quantities necessary to describe and analyze the existing ventilation systems. Various ventilation parameters are calculated from these measured pressures and quantities. Some of these parameters are: pressure drop in intake and return airways, air leakage, percentages of air reaching active sections, average regulator drops, and fan pressures. The purpose of this paper is to present and compare values of ventilation parameters calculated from investigations at twenty underground coal mines.

Jan 1, 1987

By J. Girard-Dwyer, T. Camm

Direct costs such as medical, legal, administrative, and worker’s compensation costs, property damage, lost earnings, and lost benefits are typically used to compute the economic impacts of occupational injuries. However, there are also a number of less obvious, indirect costs that substantially contribute to the overall loss costs. In fact, for every $1 of direct costs an estimated $3 to $5 of indirect costs are also incurred. This paper presents a systems approach that incorporates engineering, economics, psychology, and sociology in order to evaluate the total value of investments in safety. By studying the interrelated system comprised of the injured worker, their family and coworkers, as well as the organizational structure that was the setting for the incident, a methodology can be developed that will more accurately capture the true costs of mine injuries.

Jan 1, 2004

By S. J. Porter, M. T. McRae

The Melbourne City Link project includes two three-lane highway tunnels, 1.6 and 3.4km long, respectively, which are both approximately 16 meters wide and 9 meters high. The tunnels will be excavated through interbedded, moderately to highly jointed siltstones and sandstones of the Silurian Age Melbourne Mudstone formation over the major parts of their lengths. The strength of the intact rock varies from less than 5 MPa to greater than 70 MPa. Based on the available information regarding the performance of large span tunnels in weak rock, it was considered that the commonly applied empirical design guidelines for tunnel support, based on rock mass classification systems, should be augmented by more explicit design methods. The support design was, therefore, validated by analytical procedures, including numerical analyses, which are described in this paper.

Jan 1, 1997

By Ahmet Gursoy

Maryland, will be the widest vehicular tunnel ever built by the trench tube method. Careful coordination and planning were required to meet the tight and fast design and construction schedules. During the preliminary design, traditional design drawings were bypassed in favor of 25 preliminary design reports representing major work breakdown structures (tasks). For each task, alternative design solutions were examined and analyzed by means of trade-off studies on the basis of engineering, constructibility, and economic considerations, thus providing an overall conceptual value engineering approach for the entire project. So far, total value engineering proposed by the contractor for Contract I I (largest contract of the project at $245 million) is less than 1.5 percent of the contract value. This is an important indication of the success of the design phase planning.

Jan 1, 1983

By C. E. Schmidt

Homestake crushing and grinding, practice-was completely revised during the period of 1951-1953. During the conversion, both crushing plants at the head frames the Ross and the Yates, were changes at each plant involved replacing the two 8K gyratories with a rebuilt, The flow sheet single thirty inch gyratory for primary crushing to four inch. The gyratory discharges to a seven foot Symons standard cone crusher set at 1-1/8 inch opening. The cone discharge goes to Tyrock screens fed by vibrating feeders. Screen openings, are l/2 inch by 5 inches: at the Ross. Plant, and 3/8 inch by 5; inches at the Yates. Screen oversize goes to a seven foot Symons cone brusher converted to the short head type; the crusher setting is 5/16 inch. Crusher, discharge; is closed circuited with the Tyrock screens, The above crushing installation delivers a minus 5/8 inch rod mill feed to the mill bins. The crushing revision eliminated the-180 heavy South African type stamps, which had previously reduced the 2 inch crushing plant product to a minus 5/8 inch feed for the 10 rod mills, and 8 ball and pebble.; mills, other revisions in the mill flow sheet, resulted in 3 identical units of about 1350 tons per day, capacity per unit, Each unit consists of an open, circuit 6 foot by 12 foot rod mill, fed from two 24 in by 48 inch vibrating feeders of the four feeders available per unit. A gathering belt delivers the ore discharge of the feeders to the Transportoweigher, which in turn discharge s, into the rod; mill feed spout. Rod Mill discharge is the feed for the 9 foot by 11 foot ball mill, The ball mill is closed circuited with a 16 foot by 30 foot Dorr Classifier. The Homestake make amalgamator, for coarse gold recovery in the ball mill circuit, made' necessary a 36 inch spiral conveyor between the classifier rake discharge and, the combination drum and double scoop feeder on the ball mill See Figure l - the flow sheet of the two stage grinding units.

Jan 1, 1958

By E. Watkins, V. Gangrade, P. Zhang, J. Addis, D. W. H. Su, T. Minoski, C. Hollerich, M. Van Dyke, S. Schatzel, H. Dougherty

"This paper presents the results of a comprehensive study conducted by the Centers for Disease Control (CDC), National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Mining Research Division (PMRD) to evaluate the effects of longwall-induced subsurface deformations and permeability changes on shale gas well integrity and safety under shallow cover. NIOSH researchers selected a study site over a southwestern Pennsylvania coal mine, which extracts 1,500-ft-wide longwall faces under 482 feet of cover. One in-place inclinometer well and three permeability monitoring wells were drilled and installed over a 125-ft by 275-ft centers abutment pillar. In addition to the inclinometer well and monitoring wells, surface subsidence measurements and underground coal pillar pressure measurements were conducted as the first 1,500-ft-wide longwall panel on the south side of the abutment pillar mined by the site.A number of FLAC3D finite difference simulations (Itasca Consulting, 2017) were conducted to estimate surface subsidence, coal pillar pressure increases, and horizontal displacements in the in-place inclinometer (IPI) monitoring well. Comparisons of the FLAC3D finite difference simulation results and the surface, subsurface, and underground instrumentation results show that the measured IPI casing deformations are in reasonable agreement with those predicted by the FLAC3D models, and that the measured surface subsidence and underground pillar pressure are in excellent agreement with those predicted by the 3D models. Measured permeability changes were incorporated into a preliminary calculation to evaluate the effect of a hypothetical shale gas well leak on longwall ventilation. Results from this 2018 research clearly indicate that under shallow cover, the measured horizontal displacements within the abutment pillar are at least one order of magnitude higher than those measured in a 2017 study under deep cover and slightly higher than those measured in a 2014 study under medium cover. This research represents a very important step and initiative in utilizing the knowledge and science obtained from mining research to improve miner and public safety as well as the safety and health of the workers in the oil and gas industries"

Jan 1, 2019

By David Newman

Multiple seam underground coal mining is ubiquitous in Appalachia. Many coal properties have from two to ten or more economically mineable coal seams. Because of the ability to penetrate 600-feet to 1,000-feet or deeper into the mountainside leaving panels of web pillars separated by barrier pillars, highwall mining is a hybrid between surface and underground mining. As a result, many of the ground control problems commonly associated with multiple seam underground mining exist with multiple seam highwall mining. These include: i) multiple seam interaction between web and barrier pillars in superjacent mines, ii) subsidence and caving propagating to overlying seams and mines, iii) pooled water and the potential for inundation resulting from a breakthrough between an active highwall mine and abandoned underground mines in the same or superjacent seams, iv) the presence of overlying or underlying mine workings where pillar columnization in the active mine is not possible, and v) the question of whether to mine ?top-down? or ?bottom-up.? Case histories are presented from southeast Ohio where the Middle Kittanning No. 6 and Lower Kittanning No. 5 seams are successfully highwall mined with 20-feet to 40-feet of largely shale interburden. A highwall miner was caught in a highwall collapse in the Middle Kittanning No. 6 seam when it was overmining auger workings in the Lower Kittanning No. 5 seam. Multiple seam interaction caused by the overmining transferred overburden stress onto the Lower Kittanning No. 5 seam. The overburden concentrated through web pillars initiated auger web pillar failure, resulting in roof collapse and subsidence in the Lower Kittanning No. 5 seam that propagated up to the Middle Kittanning No. 6 seam. A second case history involves multiple seam highwall mining in southeast Kentucky. The A3 Rider, A3, B2, and C1 seams are being highwall mined around abandoned underground mines in the A3 and B2 seams and augering in the A3 Rider. Because of spoil storage constraints for the surface contour mines, the highwall miner follows the active pits in each seam so a standard sequence of ?top-down? or ?bottom-up mining does not exist.

Jan 1, 2009

By Francis F. Pitard

The presence of elements, minerals, or chemical compounds in materials at very low concentrations is becoming a constantly increasing concern for several segments of the Industry. Some trace elements or chemical compounds may be considered as hazardous, some are simply considered as undesirable In complex processes where they could be constantly recycled and end up as the major factor of decreasing quality for some valuable products. In some other cases, the presence of a trace element or mineral may be highly desirable because of its economical value: precious metals are falling into this category, they probably were the first trace elements to draw our attention. Tremendous quantity of money is spent for analysis at the trace level, also the analytical "tool" has been considerably improved during recent years, but still the sampling aspect of the problem remains obscur for many, and because of it, large quantity of analytical efforts become meaningless. Not only the absence of sampling strategies is badly affecting the representativeness of a large majority of samples, but furthermore for the same reasons, many laboratories are failing In their endeavor to prepare reliable standard reference materials. The reason of this failure has its roots in the unability to estimate effectively the sampling characteristics of the element, mineral, or compound of interest, not to mention the unability to perform precise and accurate complete analysis, so essential for the instrumental analyst (1). In this paper a strategy to perform a better sampling operation is recommended. SELECTION OF A PROBABILISTIC APPROACH AS SOON AS PRACTICALLY POSSIBLE It Is essential to differentiate probabilistic sampling from non-probabilistic sampling. As Illustrated in Figure 1, the sampling operation Is a selection process which could be performed In two different ways: I. A probabilistic selection process according to which all elements of a lot of material to be sampled are submitted to the selection with a same probability of being selected. 2. A non-probabilistic selection process according to which all elements of a lot of material to be sampled are submitted to the selection with different probabilities of being selected.

Jan 1, 1986

By John R. Buzek

Thickeners are simply large tanks, usually circular in shape, which are designed to allow settling of solids and to operate with continuous overflow of clear water and underflow of thick pulp. The dimensions of the thickener are usually such that dewatering of very fine pulps may be accomplished while still 1 overflowing clear water. Some thickeners such as the Genter, Hardinge and Hydrotator types combine thickening with filtering2 while others such as the Dorr type are pure thickenersl,2,3. A schematic diagram of the traction type Dorr thickener is shown in Figure 1. This type is appropriate for tanks over 15 m (50 ft) in diameter. This tank employs a rotating raking mechanism which moves the settled material toward the central discharge. For this and other thickeners, it is common to have a shallow conical tank bottom in order to conform to the geometry of the raking mechanism, and it is often desirable to elevate the tank for ease of access to the product. When the tank does not rest on the ground, the forces resisted by the cone are large, and thick plates must be employed. The fabrication of these tanks requires temporary supports in order to erect the cone. A flat-bottomed tank could also be used because the settled material would soon form a hardened conical surface. However, because of the presence of large bending forces, even larger plate thicknesses are required than for the conical bottom. Significant cost savings often can be realized by the use of a scalloped-bottomed tank such as the one partially shown in Figure 2. The particular scalloped bottom discussed in this paper (and shown in the Figure) employs radial beams forming the outline of the cone-shaped bottom. These beams are supported directly by columns. Cone segments are hung between adjacent beams. The exact geometry of these segments depends upon the cone angle and radius, the number of radial beams, and their inclination. The geometry is chosen to satisfy certain clearance restraints and to utilize the material as efficiently as possible. The resulting thickness of these segments is significantly less than that of the

Jan 1, 1977

By Robert Walker

The win theme of this session is Unique Material Handing Systems. The theme was selected because of two major factors. 1. Accomplishments of unique character manage to attract interest regardless of their age. 2. There is much to be learned from pioneering efforts of the past as they are the stepping stones to technological development. Thus, 2-1/2 years after completion, the engineering feat of Oroville Dam still looms large let us take a close look at this project to see what made it unique. To begin with, it established a number of firsts: At 770 feet it was the highest earth fill dam in the world. At $121 million dollars, it was the largest ever United States construction project (Civil). At 80 million cubic yards it had the largest earth volume of any dam in the world. The extensive use of belt conveyors for this application had never before been tried. The use of a high capacity bucket wheel-excavator with shiftable belt conveyors had never before been utilized as a con¬tractor's tool. The principal of the "integral train" was applied most effectively whereby up to 220,000 tons of material-was transported daily some 14 miles. To achieve optimum economics a number of technical breakthroughs were necessary. The suppliers of major commercial components worked hand-in-hand with system engineers to develop new machinery necessary for the highly mobile characteristics of the systems, viz., single pulley drives delivering 2000 horsepower, 1000 horsepower right-angle shaft-mounted reducers, across the line starting of 1000 horsepower squirrel cage motors, 10 miles of steel chord conveyor belts with belt tensions up to 150,000 pounds, aircraft-type disc brakes, hydraulic take-ups, train loading at a rate of 25,000 tons per hour, automatic train indexing for rotary dumping at 10,000 tons per hour, roll-over car dumping without uncoupling cars, shifting 7500 ft. long conveyors up to 300 feet laterally without disassembly. These are some of the superlatives that have made the Oroville Dam project unique. The measure of its success is demonstrated by the results.

Jan 1, 1970

By Terry Owen

Not since 1917 has a foreign company developed a standalone, grass roots gold mine in Russia. With Russia's political changes of the late 1980s, development of mineral prospects once again beckons foreign investors. Cyprus Amax's interest in Russia began before the mid-1991 breakup of the former Soviet Union. In 1990, Cyprus Amax began searching for such an opportunity. Early this year, production will begin at the Kubaka gold project located in the Russian Far East, near the Arctic Circle. The Kubaka project is a 1.75-kt/d (1,930-stpd) open-pit operation that will produce more than 9.3 t/a (300,000 oz/year) of gold. Identifying Russian mining opportunities In late 1990, the first Cyprus Amax people travelled to Russia. The trip was to determine the potential for western firms to develop profitable mines. This encouraging visit suggested that Cyprus Amax focus on the Russian Far East with its mineral riches and its easier access to the United States. The company's initial efforts thus focused on working with the Soviet Union's Northeast Geologic Expedition, the then government agency for exploration and geology in Russia's Far East. After the breakup of the Soviet Union, Cyprus Amax continued working with the same people, but they now represented new independent, nongovernmental entities. For three years, Cyprus Amax investigated numerous deposits. This resulted in the identification of two properties of significant interest, one of which was Kubaka. Location Kubaka is located in the Northern Evensk District of the Magadan Oblast in the Russian Far East. This is an area east of Siberia. The project is situated in a mountainous area of the Kolyma Range, about 300 km (985 miles) south of the Arctic Circle. It is 285 km (180 miles) north of the fishing village of Evensk and 380 km (235 miles) northeast of the silver-mining town Omsukchan. The site is 950 km (590 miles) northeast of the regional capital city of Magadan. Magadan, the political and economic center of the Oblast, has a population of about 150,000 people. It is served by a year-round deep-water port (with icebreaker assist) and an international airport with service to Moscow and Anchorage, AK. Access to the Magadan region

Jan 1, 1997

By Andrew Thomson, Peter Wright

"A section of a London Underground expanded segmental lined tunnel constructed in the 1970’s progressively deteriorated after 2001, with extensive radial joint spalling and mid-segment cracking. As part of the PPP contract Tube Lines Ltd and their partners carried out various analyses of the tunnel, including analysis of laser scans of the tunnel, geotechnical testing through the tunnel walls, geotechnical desk studies, real-time monitoring and even full-scale segment testing. This paper discusses the behaviour of the tunnel lining in this setting, the causes of failure and the lessons that can be learnt from this rare example of a tunnel which was progressively failing in service. It is finally noted that a replacement tunnel lining was installed during night-time possessions and completed in 2015. INTRODUCTION In 2003, Tube Lines Ltd. was established under a Public-Private Partnership (PPP) scheme to provide maintenance services and upgrade projects for London Underground (LU). The Deep Tube Tunnel Knowledge and Inspection Programme comprised the assessment of all tunnels, shafts and other underground structures. This included a number of lengths of tunnel constructed using segmental concrete linings. First used by LU in the 1960s, the savings both in cost and speed of construction led to concrete linings replacing cast iron for new tunnel construction in all but a few cases. During the initial scoping phase of this programme, inspections identified potential issues with the expanded concrete segmental linings on the Jubilee line. The inspections found a number of segments with surface spalling (Figure 1a), which did not appear on the post-construction defect records. These were generally relatively shallow, up to 40mm deep, spread over a wide area of segment. These were different to spalls caused by handling damage, which are typically localised at segment corners. Subsequent inspections over the following years identified an increasing number of segments with these types of spalls as well as an increased incidence of longitudinal mid-segment cracking (Figure 1b). The increasing occurrence of these defects was hypothesised to be caused by tensile stresses developing in the vicinity of the joint."

Jan 1, 2016

By J. Reyher, R. Bratton, G. Luttrell, B. Li

"Flotation is regarded as the best available method of upgrading minerals and coal fines. However, its efficiency deteriorates rapidly with decreasing particle size. Further, ultrafine concentrates are difficult to be dewatered economically, forcing companies to discard part of the ultrafine materials to impoundments. To overcome these problems, a new method of separating and simultaneously dewatering ultrafine particles has been developed. Following extensive laboratory-scale test work, the process, known as hydrophobic-hydrophilic separation (HHS), has been tested successfully in continuous operations at proof-of-concept (POC)- and pilot-scale tests. The results show that the HHS process is capable of producing high quality clean coal with high recoveries and low moistures. INTRODUCTION Coal preparation plants are designed with up to four parallel processing circuits for treating coarse (> 12 mm), intermediate (12x1 mm) small (1x0.15 mm), and fine (<0.15 mm) particles. The plus 0.15 mm fractions can be effectively cleaned efficiently with gravity separation methods (Wills, 2006). At present, the only commercially viable option for cleaning the finest fraction is froth flotation (Yoon et al., 1999). In flotation, air is dispersed in the form of small air bubbles in a tank in which coal fines are suspended. The small air bubbles selectively collect the hydrophobic coal particles and float to the surface, forming a froth phase which overflows into a launder. As is well known, ultrafine coal particles of less than 30-50 µm are difficult to be collected by the air bubbles, resulting in low recoveries. Furthermore, fine particle flotation suffers from low carrying capacities and poor selectivity due to entrainment problems. (Bethell et al., 2005; Luttrell et al., 2014). In addition, the froth products containing ultrafine coal are difficult to dewater. Mechanical dewatering in general becomes inefficient with decreasing particle size due to small cake porosity and high surface area, resulting in high moistures (Hucko et al., 1988). The cost often becomes prohibitive with particles of smaller than ~45 µm (Bethell et al., 2005). Moreover, the high-moisture products are difficult to handle and incur high shipping costs and lower thermal efficiencies (Honaker et al., 2013)"

Jan 1, 2016

By David G. Chedgy

Noise control is an important consideration in the design and operation of coal preparation plants. It is essential to understand and control noise sources to provide a safe environment for operating personnel. The average noise exposure levels in a typical coal preparation plant generally range between 95 and 100 db. An operator should not be exposed to noise levels of this magnitude for more than 4 and 2 hr, respectively, according to MSHA (Mine Safety and Health Administration) regulations. The major noise sources in a coal preparation plant include noise from impacting the inside surfaces of steel chutes, vibrating screens, coal crushers, pumps, motors, fans, and blowers. The magnitude of noise varies considerably from one situation to another. NOISE EXPOSURE IN COAL PREPARATION PLANTS Noise regulations established by the Occupational Safety and Health administration (OSHA) are accepted by MSHA relative to caal preparation plants. Fig. 14-43 shows a graph of the time of noise exposure in hours per day to which a worker can be exposed for each A-weighted sound level. According to this graph, a worker is permitted to spend 8 hr in a 90-db noise environment, but that time must be halved when the A-weighted sound level increases 5 db. The noise dosage a worker receives is determined by the ratio of the length of time the worker spends in a particular noise environment divided by the length of time he is permitted to spend in that environment. If the worker is exposed to several different sound levels, his total dosage would be the sum of each of the individual dosages. The equation for determining the dosage is: where C is the actual duration of exposure at a given steady state noise level and T is the noise exposure limit for the level present during the time C According to MSHA regulations, the dosage, D, should not exceed one (1) for any worker for a full day of work. As an example of typical plant noise levels, vibratory screens and crushers emanate noise levels in excess of 90 db at a distance of 3 ft (0.9 m) with no material flow. With material flow, noise level increases 1 to 10 db depending

Jan 1, 1991

By Richard Giffen, Boris CARO VARGAS, Terrence Carroll

"This paper takes an in-depth look at the $72 million design-build Norris Cut project, which includes the replacement of an existing 54-inch waste water sewer main to Fisher Island under the Norris Cut Channel. Tunneling through one of the country’s most unpredictable geologies created unique challenges in both the design and construction phases of the project. The paper presents the geotechnical and structural design considerations for the 100-foot deep secant piled TBM launch shaft in the highly permeable Fort Thompson formation limestone and sands. The structural design effort also included the design of the tremie slab, thrust wall and design of the largely unreinforced launch shaft to resist asymmetric loading from partial ground freezing. The retrieval shaft was designed as a deep soil mixed shaft and is thought to be the deepest soil-mixed shaft in Miami. From a construction perspective, this paper discusses the unique challenges of building two shafts with two different techniques and will compare some of the constructability aspects, costs and equipment schedule-considerations related to the use of two separate techniques. INTRODUCTION Nicholson Construction Company (NCC) was awarded a $72.1 million Design-Build contract to replace an existing force main from the Virginia Key Central District Wastewater Treatment Plant (CDWWTP) under the Norris Cut Channel to Fisher Island. The location of the project is shown in Figure 1. The project involves replacing an existing 54-inch diameter pre-stressed concrete sewer force main with a 60-inch diameter fiberglass force main. Arup USA, Inc. (Arup) is the lead designer for Nicholson on this design-build project. Arup is providing design services for the TBM launch and retrieval shafts, segmental tunnel lining, the fiberglass pipe, and the horizontal directional drill component. Miami-Dade Water and Sewer Department currently owns and operates the existing 54-inch sanitary force main that transmits sewage collected from Miami Beach and Fisher Island to the CDWWTP for treatment and disposal. The existing force main was subject to a condition assessment in December 2011 which revealed structural deficiencies in the pre-stressed concrete pipeline."

Jan 1, 2016