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"The first 90 years of the last century generated a considerable volume of technical literature on the subject of grinding mill power and its prediction. It is therefore surprising that during this time there were no published models for predicting grinding mill power draw which were validated using a wide range of comprehensive industrial scale data.Notwithstanding this lack of data, the majority of models placed limited emphasis on the internal dynamics of mills and relied on simple assumptions which considered the charge to take up a fixed position and shape.Laboratory based studies (Liddell, 1986), and industrial data (Morrell, 1993), showed that these assumptions did not hold over a wide range of operating conditions, and brought into doubt the ability of the (then) existing models to accurately predict grinding mill power draw. Furthermore no model treated AG,SAG and ball mills as a single class of devices whose power draw could be predicted with the same equations.Through a detailed investigation of the charge dynamics, coupled with a large data base of industrial mill power draws, this situation was rectified by the end of the century, by which time a model had been developed and validated, which accurately predicted the power draw of all wet tumbling mills. This paper describes this model and reviews some of the earlier attempts at mill power modelling.INTRODUCTIONThe early 1900?s saw the beginnings of published papers which tackled the problem of what influenced the power draw of tumbling mills and what equations (models) were suitable for predicting power draw. This interest continued for the rest of the 20th century and the literature contains many papers that attempted to satisfactorily answer these questions. A common and disappointing theme in the majority of them, however, is the distinct lack of suitable experimentally derived power draw data. This deficiency consequently limited the practical application of many of the attempts at modelling mill power draw. Prior to the early 1990?s some limited data on the power draw of grinding mills in the literature can be found, but as Harris et al (1985) remarked they are ?... too frequently unusable simply because one or more essential variables have been omitted?. The absence of published results, from vigorous experimental testing of the various models, has resulted in a general lack of evaluation of the validity of assumptions and hypotheses that such models contain. Harris et al (1985) however, did make some efforts in attempting to evaluate the performance of various power prediction equations and in so doing further developed a semi-empirical one of their own. However, in using manufacturers? published data, which themselves were undoubtedly generated by proprietary equations of unproven validity, they probably succeeded in generating little more than a consensus of the various errors in these models."

Jan 1, 2003

"The first 90 years of the last century generated a considerable volume of technical literature on the subject of grinding mill power and its prediction. It is therefore surprising that during this time there were no published models for predicting grinding mill power draw which were validated using a wide range of comprehensive industrial scale data.Notwithstanding this lack of data, the majority of models placed limited emphasis on the internal dynamics of mills and relied on simple assumptions which considered the charge to take up a fixed position and shape.Laboratory based studies (Liddell, 1986), and industrial data (Morrell, 1993), showed that these assumptions did not hold over a wide range of operating conditions, and brought into doubt the ability of the (then) existing models to accurately predict grinding mill power draw. Furthermore no model treated AG,SAG and ball mills as a single class of devices whose power draw could be predicted with the same equations.Through a detailed investigation of the charge dynamics, coupled with a large data base of industrial mill power draws, this situation was rectified by the end of the century, by which time a model had been developed and validated, which accurately predicted the power draw of all wet tumbling mills. This paper describes this model and reviews some of the earlier attempts at mill power modelling."

Jan 1, 2003

By Bernardo Siqueira

This paper presents a unique stirred milling technology, Outotec HIGmill™, a modern, flexible and energy efficient grinding solution for fine and ultra fine grinding being tested in an industrial scale level. The test was performed at an iron ore pellet producing plant in Sweden (for confidentiality reasons, it will be referred to only as “the client”) where a pilot HIGmill™ unit (HIG25) was installed parallel to a conventional regrind circuit to compare its performance to the existing ball mill. By using a continuous test run procedure and evaluating the parameters of F80, P80, mill shaft rotation speed and power drawn it was determined its grinding capabilities, operational flexibility and energy efficiency. Outotec HIGmill™ outperformed the existing ball mill in the plant proving its capabilities to grinding finer, with steeper particle size distribution (PSD) and much higher energy efficiency. The tests performed showed that, with further refining of its operation, it is capable of consistently deliver the required PSD with up to 30% higher grinding efficiency.

Aug 16, 2017

By Alex Doll, Derek Barratt

"There is a number of comminution tests commonly used in the mining industry. Many of the tests are used for a particular grinding model or mill sizing program and are incompatible with other tests of different models. This paper provides an overview of the commonly used grinding and crushing tests, which models (or practitioners) use a particular combination of tests and draws some relationships between the incompatible tests based on the DJB Consultants Inc. database of projects.Case studies will demonstrate similarities and differences between major mining districts with some comments about homogeneous and heterogeneous behaviour within the grindability results.INTRODUCTIONThere are a number of bench-scale grindability tests in use for sizing and predicting throughput for grinding circuits. Part of the reason for this variety is there are a number of different grinding models in use in the Industry, and those models operate using incompatible test results as input (Doll and Barratt, 2008).By using the database of testwork in the DJB Consultants, Inc. (DJB) Millpower 2000 database (see Table 1), some of the more commonly used tests are compared and relationships will be drawn."

Jan 1, 2011

By T. Hackett

Western underground coal reserves are tremendous, but recovery in western seams can be poor because of mining problems caused by deep cover, geologic anomalies, and thick seams. For instance, many seams contain a rock parting too thick to be extracted economically with the coal. This forces the operator to mine the coal above or below the parting. Subsequently, the rock pressures induced by mining make the part left difficult or impossible to extract by standard mining methods. Because upper and lower parts of the seam are frequently of minable thickness, the presence of rock partings can result in a significant loss of coal. Given a longwall recovery of 60 pct and equal thickness for the two parts of the seam, overall recovery is reduced to less than 30 pct if one part only is mined. The coal left in place is unavailable to meet the nation's energy needs, or to produce revenues for coal companies or government. [ ] Multi-slice longwall mining has the potential to recover the portion of split seams that are now left in the mine. Using superimposed standard longwalls with chain pillars, overall recovery could be doubled, depending on panel and pillar widths. Using a combination of advancing and retreating longwalls in descending slices, overall recovery could be improved to more than 80 pct. Because of the potential for improved recovery, the Bureau of Mines is analyzing the ground control factors affecting multi-slice longwall under western mining conditions and is conducting field trials at a planned multi-slice operation.

Jan 1, 1987

By R. Karl Zipf, Christopher Mark

Highwall mining continues to grow in importance as a coal production method from U.S. surface mines. It may account for as much as 4% of the total U.S. coal production, according to one recent estimate. Analysis of Mine Safety and Health Administration (MSHA) accident and injury statistics shows that, overall, highwall mining has maintained an admirable safety record. Its fatality and injury rates are comparable to those for other surface mining methods, and are significantly lower than those for underground mining. No mining method is risk free, however. Highwall mining injuries have been associated with handling materials, slips and falls, machinery, powered haulage, and other types of incidents. But perhaps the greatest risk, to both personnel and equipment, is from ground control. The two most significant ground control hazards are rock falls from the highwall and equipment entrapment underground. Highwall Stability Ensuring highwall stability through proper ground control engineering is of paramount importance to safe highwall mining operations. The only fatality to occur during the last five years at a highwall mining operation was due to highwall collapse. There have also been numerous near-misses, several of which have involved extensive damage to equipment. In the central Appalachians, where the majority of highwall mining occurs in the U.S., hillseams are the most prominent geologic structures that affect highwall stability. Hillseams (or mountain cracks) are near vertical fractures in the rock that are formed in response to natural weathering and erosion of hillsides. They extend hundreds of feet down from the surface. They typically run parallel to the hillside, but they can also extend across narrow points or ridge lines. The hazard arises when rock slabs that form along the hillseams detach and fall away from the highwall face (See Figure 1). [ ] Unfortunately, it is impossible to control the location of hillseams or reliably detect their presence within a highwall. There are, however, a number of measures that can be taken to minimize the risk of failure associated with hillseams: Planning-Most operators choose to skip those areas of the highwall where a prominent hillseam daylights (See Figure 2). Existence of such areas is known for several weeks in advance of highwall mining; therefore, planning engineers can adjust the layout of highwall mining panels to locate barrier pillars within areas of questionable highwall stability. [ ] Inspection and monitoring-Daily inspection of the benches above the active highwall mining area is a prudent precautionary measure. A crack in a bench immediately above a highwall miner is shown in Figure 3. Simple displacement monitors may be useful for detecting movement along cracks that may precede a significant life-threatening failure. New tools, such as slope monitoring radar, may also prove useful in detecting motion of the rock slopes above active highwall mining operations. Good blasting practice-Most surface coal miners in the central Appalachians use pre-splitting and the familiar halfbarrels are routinely seen throughout the pits. Shorter delays along the face and longer delays between rows can direct more of the blast force parallel to the face, potentially doing less damage to the wall rock. In addition to pre-splitting, decreasing the burden, spacing and charge weight in drill holes close to the highwall will also decrease damage to the wall rock. Decreasing the highwall slope angle-Decreasing the highwall slope angle from 90° (vertical) to 70°-80°, especially in areas of known hillseam concentration, could eliminate the hillseam hazard (See Figure 4). Angled highwalls are routinely employed in many Midwestern surface mines and in some

In the last four years, 2007~2010, 9 out of 24 metal/nonmetal underground mine fatalities were caused by ground fall across United States of America (Mine Safety & Health Administration, MSHA). To reduce or eliminate incidents/accidents caused by ground fall, this paper clarified how to design and select ground support based on different ground conditions, how to use mine ground support standards, what geotechnical engineers and underground operators should do to keep mine production free of ground failures.

Jan 1, 2012

By Christopher Mark

After the United States and Australia, South Africa has the largest. modern underground coal mining industry in the world. Historically, South Africa has been the cradle of many innovations in ground control, particularly in the area of pillar design. Today, South African mines are grappling with many of the same issues faced by their U.S. counterparts, including safety during pillar retreat operations, selecting the proper roof support, and maintaining long-term pillar stability. The author recently visited seven underground mines in the Mpumalanga, Free State, and KwaZulu-Natal provinces. Mining methods included longwall, room-and-pillar with continuous miners, and drill-and-blast. The mines represented a cross-section of geology and ground support practices. At each mine evaluations were made of the Coal Mine Roof Rating (CMRR), roof support practices, pillar design methods, and general ground control experience. The coal seams observed were generally thick (2-5 m), the depths of cover moderate (less than 200 m), and the roof rocks relatively strong (CMRR greater than 45). Unfortunately, the South African roof fall fatality rate is approximately three times greater than in U.S., perhaps in part because roof bolts seem to be more widely spaced in most South African mines. Roof bolting equipment was generally outdated, and the quality of bolt installation was a major concern. Pillar design, on the other hand, is quite advanced, and pillar failures are rare. Several novel partial pillaring techniques are employed, including "checkerboard" mining in which every other pillar is removed, 3-cut systems, and high-extraction mining where engineered final stumps are left by design. The paper also offers observations on ground control management techniques (including recently introduced Codes of Practice), the role of the mine inspectorate, and the status of the research community.

Jan 1, 1999

By William J. Conrad, Ryan J. Molka, Erik C. Westman

"In order to study pillar and overburden response to retreat mining, a ground control program was conducted at a Central Appalachian mine. The program consisted of several monitoring methods including a seismic monitoring system, borehole pressure cells in the pillars, and time-lapse photogrammetry of the pillar ribs. Two parallel geophone arrays were installed, one on each side of the panel with the sensors mounted 3m (IO ft) into the roof. A total of fourteen geophones recorded more than 5,000 events during the panel retreat. A MIDAS datalogger was used to record pressure from borehole pressure cells (BPCs) located in two adjacent pillars that were not mined during retreat. A series of photographs were taken of the pillars that had the BPCs as the face approached so that deformation of the entire rib could be monitored using photogrammetry.Results showed that pillar stability and cave development were as expected. The BPCs showed an increase in loading when the face was 115 m (380 ft) inby and a clear onset of the forward abutment at 30 m (100 ft). The photogrammetry results displayed pillar deformation corresponding to the increased loading. The microseismic monitoring results showed the overburden caving inby the face, again as expected. The significance of these results lies in two points, I) we can quantify the safe manner in which this mine is conducting retreating operations, and 2) we can use volumetric technologies (photogrammetry and microseismic) to monitor entire volumes of the mine in addition to the traditional point-location geotechnical measurements (BPCs).INTRODUCTION AND BACKGROUNDExcavation of underground openings is a difficult job in a challenging environment. The rigor of the process is compounded by the lack of a method that allows quantification of changes within the rock mass as excavation progresses. Statistics kept by the Department of Labor, Mine Safety and Health Administration show that 16% of fatalities and lost time incidents in the underground mining industry are due to unexpected rock mass failure (MSHA, 2015). A recent example is the Crandall Canyon, Utah, coal mine accident caused by the vertical collapse of a longwall coal mine on August 6, 2007 (Dreger, Ford, Walter, 2008)."

Jan 1, 2016

By Todd Minoski, Matthew McElhinney, Mark Mazzella, Morgan Sears, Craig Compton

The National Institute for Occupational Safety and Health (NIOSH) is staffed with Engineers, Geologists, and Field Technicians conducting a variety of ground control research. The mission of the ground control teams within the Mine Systems Safety Branch (MSSB) is to eliminate ground failures leading to mineworker injuries and fatalities. Advancing the science behind ground control relies heavily on conducting mutually beneficial research at participating mines which is detailed in specific references throughout the paper. The ground control teams have several types of field instruments at their disposal to measure the ground response in underground mines. These include borehole pressure cells (BPCs), vibrating wire stress meters (VWs), hollow inclusion cells (Hi-Cells), roof and rib extensometers, load cells, and convergence meters. These instruments are used to measure changes in pressure, strain, and displacement within the underground environment. Instrumentation data is collected automatically using intrinsically safe or MSHA permissible dataloggers if required. Information is transmitted to the dataloggers using approved cable to distances of 200–1,000 ft. depending on the type of datalogger being used. Once mining is completed, the dataloggers are retrieved and brought to the surface, providing in-mine data to mine management and engineers for the conditions currently being encountered in a particular mine. This data, in conjunction with geologic data and stress mapping, can be used to validate numerical models. The practical application of these models is extremely important for mine management and engineers, particularly when faced with more challenging mine environments. Insight gained from applying these models can be used to make better engineering-based judgments for areas that will be mined in the future. The impact of such applications can result in a reduction of ground-fall accidents and injuries as well as generally safer working conditions.

Feb 1, 2024

By Jinwang Zhang, Zhaohui Wang, Jiachen Wang

"Thick coal seams (seam height larger than 3.5 m) account for a large portion of the proven coal reserves of China, and underground thick coal seam mining provides about 50% of the Chinese annual coal production. Such seams are mainly mined using the longwall top-coal caving (LTCC) method. For safe and successful mining, a number of analyses on the stability of surrounding rocks in the LTCC face area have been extensively performed, and certain research achievements have been made. This paper introduces the main findings on rock pressure occurrence in the LTCC face during the last few decades and presents face and roof stability control techniques. INTRODUCTIONUnderground thick coal seams in China provide 1.8 billion tons of coal every year, which accounts for approximately 50% of the total Chinese annual coal production and 25% of the world, indicating that thick coal seams stand an important position in Chinese coal mining industry (Wang, 2005). Before the 1980s, thick coal seams were mined mainly by using the multiple-slice mining method. With the improvement of mining techniques and equipment in last two decades, longwall top-coal caving (LTCC) and high-seam, single-cut longwall are employed for thick coal seam extraction, offering advantages over multiple slicing from entry excavation and production perspectives (Wang, 2013).. The primary author of this paper introduced the most popular thick coal seam mining methods in China at the 30th ICGCM (Wang, 2015). This paper presents the stability of surrounding rocks in face area and ground control techniques for mining thick coal seams. For traditional longwall faces (seam height less than 3.5 m), the well-developed VoussoirVoussoir beam theory has been successfully used to analyze the movement of overlaying strata, which indicates that ground control techniques have become mature for this mining system. In such faces, the four-leg support with loading capacity of 4000–8000 kN is considered adequate for safe and successful mining. These faces normally have an annual yield of 1–2 million tons (Wang, 2007). For thick coal seams, however, the traditional support becomes inadequate and the ground control problem change to be more difficult and complex. Thus, development of large-scale mining equipment and ground control techniques for enlarged mined-out space and entries have been recognized as the most basic technical problems in mining thick coal seams."

Jan 1, 2017

By S. Bhattacharyya

"Coal bearing rocks are low in strength and have geological discontinuities and moisture sensitivity. Roof and rib falls have been a major cause of fatalities in underground coal mines. Mine engineers design ground control plans for regulatory approvals. A number of tools are available from the National Institute for Occupational Safety and Health to design and assess these plans. Quite often there is not enough geotechnical input information available and databases are used. The Appalachian coalfields have extensive scientific studies to provide reliable regional inputs. Coal mines in the western United States and Canada have different geological and geotechnical conditions, and less available data. Use of inappropriate inputs in the tools like Analysis of Retreat Mining Pillar Stability, Analysis of Longwall Pillar Stability, and Analysis of Roof Bolt Systems may result in unsafe designs or over conservative designs. The tools are convenient but thorough understanding of the inputs, calibration with local test results, and operating experience are important for effective designs. The current paper contains examples of difficulties faced during mine planning using the above tools. INTRODUCTION Sedimentary rocks hosting coal are low in strength. Scientific studies have placed the uniaxial compressive strength (UCS), triaxial strength, tensile strength, and shear strength of sandstone, shale, siltstone, and claystone in lower range of strength among engineering materials (1). Coal bearing rocks are most often weakened by the presence of faults, folds, slickensides, bedding planes, fractures, and other geological discontinuities. The host rocks and coal are often moisture sensitive. The geological discontinuities allow water to enter the strata from surface and underground sources. This combination of low strength, structural weakness, and presence of water results in difficult ground control situations for the coal mines. Roof (2) and rib falls have been a major cause of fatalities in the U.S. coal mines. Modern underground coal mines necessitate wide entries to accommodate large production equipment. The gate roads, section entries, and the mains entries of a highly productive coal mine are as wide as twenty feet (6.1 m). The actual intersection width is nearly thirty feet (9.1 m). Adequate ground control is a key to maintain safe production in such mines. Mine engineers and their consultants routinely submit ground control plans to the regulatory authorities. While working out the necessary roof control system the mine engineers are required to demonstrate the adequacy of the proposed system. There are multiple ways to demonstrate this. Some engineers use traditional load calculation approach of roof bolts (3). Some engineers use numerical methods. Yet a large number of professionals resort to a suite of ground control design software offered by National Institute for Occupational Safety and Health (NIOSH) commonly referred to as “NIOSH Ground Control Toolbar.” These software tools are free and easy to download from NIOSH website. The software included in this package are: Analysis of Longwall Pillar Stability (ALPS), Analysis of Retreat Mining Pillar Stability (ARMPS), Coal Mine Roof Rating (CMRR), Analysis of Roof Bolt Systems (ARBS), Analysis of Horizontal Stress Effects in Mining (AHSM), Analysis of Multiple Seam Stability (AMSS), Analysis of Retreat Mining Pillar Stability - Highwall Mining (ARMPS-HWM). These tools are relatively simple to install and use in planning and designing coal mines and prospective coal mines. They accept a number of geotechnical inputs which are collected from either an existing mining operation or from exploratory boreholes. In the absence of necessary input parameters, the programs use default values which are drawn from databases of geotechnical properties built by NIOSH."

Jan 1, 2015

By Paul C. Schmall, John F. Donohoe, Arthur B. Corwin, Derek Maishman

Ground freezing was utilized to provide complete stability of the excavation face and complete groundwater cut-off for the jacking of the three tunnel boxes for the Interstate 90 / Interstate 93 approach to the Fort Point Channel crossing. Through a wide range of geological conditions and large buried obstructions, the freezing provided complete stability of the face so that a 11.5 m (38 ft) high free standing vertical face could be mined without the need for any additional face support. Obstructions were incorporated into the massive frozen ground matrix, and held in place so that they could be excavated with a minimum of disturbance. The freezing provided an absolute groundwater cut-off, and permitted the work to be done without disturbance to the active rail system immediately above. With the use of instrumentation such as borehole thermocouples, the effectiveness of the freezing was guaranteed and the jacking proceeded with complete confidence and assurance of the ground conditions ahead.

Jan 1, 2001

By Andrew Chegwidden, Tara Wilk

Shaft 18B-1 is the second shaft to be constructed as a part of contract C547A along the New York City water supply system Tunnel No. 3. More complex than Shaft 17B-1, this site has an additional 30 m (100 ft) of overburden for a total excavation depth of approximately 78 m (256 ft) through water-bearing overburden soil and 145 m (475 feet) of gneiss bedrock to connect to the underlying Water Tunnel No. 3. round freeing was specied as the method to provide temporary earth support and ground water control for the overburden material. An extensive supplemental geotechnical investigation (SGI) and frozen soil testing program was performed to develop the design of a temporary ground freezing system, consisting of over 7,315 m (24,000 ft or 4.5 miles) of drilling for the installation of 95 freeze pipes. At the start of shaft excavation, the upper sandy silts strata was found to have an unprecedented low thermal conductivity, leaving the frozen soil face approximately 0.6 to 1 m (2–3 ft) behind the cutline. The ground freezing earth support needed to be augmented with ring beams and liner plates to support this soil face and allow for the excavation to proceed and be completed safely.

Jun 23, 2024

By P. C. Schmall

Ground freezing has been used for the sinking of deep mine shafts for more than 140 years. While advances in refrigeration technology have refined the overall freezing operation, the basic ground freezing concept remains the same. This paper presents an overview of the ground freezing process and the unique advantages that ground freezing brings to shaft construction. Design and construction considerations, including instrumentation and monitoring, are discussed. Case studies are presented to illustrate ground freezing applications for mine shaft installation.

Jan 1, 2010

By Paul C. Schmall, Arthur B. Corwin, Hugh S. Lacy, Derek Maishman

For reasons of hydraulic design and constructability, water supply tunnel systems are often located relatively deep, in competent rock. Where the rock lies below a thick cover of water bearing soils, artificial ground freezing offers a low risk, cost-effective method of constructing access shafts. Several examples, in Kansas City, MO and in Brooklyn and Queens, NY, illustrate the use of freezing to provide structural support and ground water exclusion. In the case histories presented, the shafts range from 6m to 12m (20 to 40 ft) in diameter and soils vary from clays to boulder beds with depths in excess of 73m (240 ft) to competent bedrock. Where tunnels for infrastructure are designed to be driven in rock, vertical access may encounter a considerable thickness of overburden soils with groundwater. In such cases, shaft sinking problems are analogous to those confronted by mining engineers over 100 years ago. At that time, newly developed refrigeration machines were set to freeze the ground water and stabilize running sands. Although modern technology has refined our efforts, the basic features of the ground freezing to be described here are the same as those used in the last century. Vertical holes drilled on a circle surrounding the shaft site are equipped with leak-free steelpipes through which a refrigerated brine is circulated. In this manner, a frozen cylinder, seated in rock, is formed when the earth freezes between adjacent pipes. Shaft excavations take place inside a self-supporting, ground-water excluding structure. For mines, no better method of sinking production shafts through deepwater-bearing ground has yet been established. Indeed, major deposits of coal, potash, and salt would have remained inaccessible to this day were it not for the continued use of artificial ground freezing. If mine shaft freezing became relatively commonplace, early applications to civil engineering were few. Mussche and Waddington (1946) mention only five projects between 1892 and 1935; three of these relate to subway or vehicular tunnels in Paris, Antwerp, and (the most extensive) at five locations of the Moscow Metropolitan Railway development. In the United States, the method was used to spectacular effect in 1936, freezing about 3,000 cubic yards of silt to stop a slide

Jan 1, 1999

By Gregory T. Ziegler

A complex soil profile and high water table, together with a below-grade active subway tunnel, an above-ground elevated railway line, and the heavily travelled Northern Boulevard all passing above the tunnel alignment, combined to make mining of New York?s Northern Boulevard Crossing what is widely considered to be the most challenging portion of the multi-billion-dollar East Side Access project. The Northern Boulevard Crossing is a vital link in this project which, when completed, will connect the Long Island Railroad to Grand Central Terminal in Manhattan. How the sequential excavation method (SEM) tunneling was successfully accomplished, despite the obstacles, was a textbook exercise in practical innovation coupled with close cooperation between the owner, the construction manager, Hatch Mott MacDonald, the designer, Parsons Brinckerhoff, the contractor, Schiavone-Kiewit, and spe-cialty geotechnical contractor, Moretrench.

Sep 1, 2013

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 Noreen Tarac, Pablo Forgoso, Philipp Schober

A multiple use storage facility building is being developed in the Philippines on a peninsula that was reclaimed in the 1990s without any soil treatment. The subsoil now consists of loose to medium dense silty sand underlain by a soft to medium stiff clay. A liquefaction assessment by analytical methods have shown that the loose to medium dense silty sand yields a high potential for liquefaction and lateral spreading during pthe design level seismic event. To mitigate the risk of liquefaction and lateral spreading, as well as assure the slope stability of the shoreline, a solution utilizing a combination of ground improvement techniques by means of a Mixed-In-Place (MIPTM) Lattice Grid Wall and Stone Columns was developed and successfully executed. For the detailed seismic design, a Finite Element 3D analysis was undertaken to simulate static and dynamic actions on the buttress wall. The liquefaction assessment and settlement calculation were carried out based on analytical design approaches. For the execution of the Lattice Grid Wall, the Mixed-In-Place (MIPTM) method developed by BAUER Spezialtiefbau GmbH was applied. The stone columns were installed using the Wet Top Feed method.

Sep 8, 2021

By Sunil S. Basarkar, Vinothkumar S

Ground Improvement Techniques serves to improve various engineering properties for supporting various foundations. These may be undertaken either by conventional or advanced methods. The Controlled Modulus Column (CMC), also known as Rigid Inclusion is a soil improvement technique to reduce the total and differential settlement by using semi-rigid soil reinforcement columns. The CMC technique can be executed by displacement or non-displacement methods. It does not aim to bypass the compressive layer or to install a pile that will directly support the entire load from the structure. Principle of the technique is to introduce a load transfer platform between the head of the column and structure and transform a uniform load into soil. Initially, the structural load transmitted into the soil generate the settlement greater than CMC piles. When the settlement between the soil and column became equal at neutral point, maximum structural load shall be balanced by the positive friction and tip resistance to stabilize the foundation without exceeding the allowable settlement limit. This paper describes the behaviour of soil reinforcement with CMC column and their installation process with reference to a project at the Dry Bulk Terminal Port, San Pedro- Abidjan (Western Africa). Methodology of CMC, requirements of Ground Improvement, arrangements and outcome of this method are presented in this paper.

Sep 1, 2022