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By Dennis J. Lachel, Lloyd B. Underwood

In recent years a great number of papers have been presented at symposiums and have appeared in the literature relative to geologic prediction for rapid excavation and tunneling. Many of these papers describe research projects now underway to investigate tunnel site selection by remote sensing techniques, seismic holography, electro¬magnetic pulse sounding, optical scanning for structural features, and many other exotic geophysical techniques. While it is possible that this research will produce techniques that may prove to be very useful, it appears for the present at least, and perhaps for another decade, that there still will be no substitute for conventional exploration methods such as coring boring, geologic mapping, studies of existing wells, and proven geophysical techniques. Nevertheless, there is still room for tremendous improvement in the conventional techniques for geologic prediction in tunneling. These include: more rapid and accurately aligned coring borings drilled parallel to the tunnel alignment; improved geophysical surveys both prior and during construction; improved methods for predicting ground¬water inflows and water pressures, both of which can greatly influence the cost of driving tunnels. Geophysical techniques can also be ap¬plied to locate deeply incised glacial troughs or ancient buried stream channels that might cross the tunnel alignment. In the meantime, while some researchers continue their efforts to¬ward a breakthrough in new techniques for geologic prediction, it is recommended that other researchers direct their efforts toward sol¬ving specific problems such as accurately predicting ground-water conditions, determining locations of high geostatic stresses, and locations of major fault and shear zones.

Jan 1, 1997

By Jeff W. Butwell

Mill flotation tailings impounded at the Gooseberry Mine site between 1976 and 1984 were determined to be an economic source of gold and silver. The tailings would be recoverable by standard heap leach technology in conjunction with feed agglomeration. Metal recovery at 85% gold and 75% silver is attained on properly agglomerated (pelletized) tailings that average 85% -75 µm (-200 mesh). The impounded tailings averaged more than 18% moisture (32% moisture maximum at depth) in place behind the storage dam. Therefore, the mining method, mixing and agglomeration technique, and materials handling practice were major considerations in making this operation a financial success. The Gooseberry Tailings Project is located about 35 km (22 miles) east of Sparks, NV. The project is owned by Asamera Minerals (US) Inc. The company's Western Nevada Gold prop¬erty surrounds the Gooseberry Mine by several miles on all sides. Gold and silver mineralization at the Gooseberry Mine is restricted to a narrow calcite-quartz vein. Calcite makes up more than 80% of the vein throughout the mine. The host rock consists of porphyritic andesites and dacites constituting volcanic flows. The rocks are propylitized or silicified to a varying degree. This ore mineralogy, then, also describes the tailings processed by heap leaching. The Gooseberry tailings were auger sampled in 1983 and again in 1987 after a final lift of 109 kt (120,000 st) was deposited in 1983 and 1984. The total volume behind the dam was calculated from planimeter measurements from tailings surface to original area topography.

Jan 1, 1990

The Carlin Trend is North America's premier gold producing district. It is located in northeastern Nevada's Elko and Eureka Counties along a northwest trending belt about 65 km (40 miles) long and 8 km (5 miles) wide (Thorstad, 1989; Jones, 1989). This trend is the worldwide reference site for epithermal, sedimentary rock-hosted microscopic gold deposits. At least 19 deposits have been discovered to date, varying in size from 933 kg to 1.08 kt (30,000 to 35 million contained oz) of gold (Fig. 1). Newmont Gold Co. and its parent, Newmont Mining Corp., jointly constitute the largest mineral right holders in the district. They own or control more than 1000 km'- (386 sq miles) in and around the Carlin Trend and own all or part of 16 out of the 19 mines and prospects identified to date. Since the initiation of Newmont's exploration activities in the Carlin Trend in 1961, 2.24 kt (72 million oz) of cumulative gold resources have been identified. Cumulative production from all mines since the start-up of Newmont's Carlin mine in 1965 to the end of 1989 was about 202 t (6.5 million oz) (Jones, 1989). The incentive of sustained high gold prices and innovation in processing technology resulted in a significant acceleration of gold output over the last few years. Newmont Gold alone produced more than 43.5 t (1.4 million oz) in 1989. That is equal to 22% of the cumulative 1965 to 1988 output, and an almost 200% increase over its 1986 output.

Jan 1, 1991

By Leslie Thompson, Randy Hiebert, Marietta Canty

A paper is presented in which an innovative biological process is described for the treatment of cyanide-, metals-, and nitrate-contaminated mine process water. The technology is capable of detoxifying cyanide and nitrate and immobilizing metals in wastewater from agitation cyanide leaching as well as heap leaching. A pilot-scale demonstration is described in which a pilot plant was constructed to detoxify cyanide and immobilize several metals from a mine process wastestream at a mine in Nevada. The demonstration was performed jointly under the Mine Waste Technology Program (MWTP), which is funded by the U.S. Environmental Protection Agency (EPA) and is jointly administered by the U.S. Department of Energy's (DOE) Western Environmental Technology Office (WETO) and the Superfund Innovative Technology Evaluation (SITE) Demonstration Program under Interagency Agreement Number DW89938513-01-0. MSE Technology Applications, Inc. (MSE) located in Butte, Montana, was the contractor responsible for conducting the project, and Pintail Systems Inc. of Aurora, Colorado, was the technology provider. The pilot-scale unit was field tested at the Echo Bay McCoy/Cove Mine southwest of Battle Mountain, Nevada. The biotreatment process was con­sidered to be very successful in detoxifying cyanide from the mine process water. The process was also determined to be very effective in removing metals. The pH was consistently neutral­ized and nitrates were successfully removed in the mine process water. As a result of conducting these pilot-scale tests, the biotreatment process was concluded to offer an innovative, cost­effective alternative for the treatment of mining wastewaters.

Jan 1, 1998

By Cyril Heever

ROCKS outcropping in Elandsrand's lease area consist of quartzite, shale and lava of the Pretoria group and are underlain first by 1 300 metres of dolomite and then by the Black Reef series. This in turn rests unconformably on Ventersdorp and Witwatersrand rocks and truncates the basal member of the Ventersdorp Super group, the Ventersdorp Contact Reef (VCR), near the northern boundary of the lease. The Ventersdorp Super group is composed of lava and varies in thickness from nil in the north of the lease area to 1 000 metres in the south. The VCR, less than 100 cm thick, dips 210 to the south east and lies between 1 786 and 3 386 metres below datum. The Oberholzer dyke straddles the north-western corner of the property and separates the dewatered Oberholzer compartment, over which most of Elandsrand lies, from the as yet undewatered Turffontein compartment. As so much of the lease area is covered by thick impermeable rocks, the water-bearing capacity of the underlying dolomite was expected to be low. The man-material (MM) and rock hoisting ventilation (RU) shafts were sited well within and above a gravimetrically determined 200-metre 'safe-limit' contour of the northern slope of the Gatsrand. Two pre-cementstion holes were drilled and the cementation rigs were placed within a 15 metre annulus round each shaft to seal any likely water-bearing pockets in the proximity of the excavation during sinking through the first 300 metres of shales and the surface water-table.

Jan 1, 1981

By T. S. Golosinski

Most of the 154 t (170 st) truck fleets that were predominant in large surface mines in the 1970s and 1980s are approaching the end of their economic life. One replacement option considered by mine operators is a change to the 2 18 t (240 st) trucks. A comparison of load capacities between the 1.54 t (170 st) and the 2 18 t (240 st) trucks indicates a large productivity advantage in favor of the 218 t (240 st) trucks. This advantage, however, is often reduced by a number of site-specific factors. Therefore, a careful evaluation is required to define the actual benefit of changing to the large trucks. This article discusses some important factors that have an impact on truck size selection, based on several different studies. 218 t (240 st) trucks The 2 18 t (240 st) rear dump trucks were first introduced for surface mine service almost 10 years ago. However, it is only during the last few years that this equipment has gained acceptance in the surface mining industry. About 250 units were employed in surface mines worldwide at the beginning of 1992, and further purchase commitments are being made. Encouraged by the mining industry’s interest, all major off-highway mining truck manufacturers now offer 218 t (240 st) models (Table 1). At present, the existing 218 t (240 st) truck fleets are dominated by electric drive trucks. However, recent introduction of a 2 18 t (240 st) mechanical drive truck rounds out the development of this truck size.

Jan 1, 1992

By Mark L. Bricker

The Jim Bridger Coal Mine, operated by Bridger Coal Co., is located in Sweetwater County, WY about 56 km (35 miles) northeast of Rock Springs. Bridger Coal is a joint ven¬ture between Nerco Coal Corp, the operator, and Idaho Energy Resources Co. The permit boundary encompasses more than 81 km'- (20,000 acres) on the western side of the Continental Divide. Since the mine began opera¬tions in 1974, it has produced about 82 Mt (90 million st) of coal while moving about 344 hm3 (450 million cu yd) of virgin earth. Annual production averages 4.5 Mt to 6.4 Mt (5 million to 7 million st) of run-of-mine coal. Coal is consumed on-site by the Jim Bridger Power Plant, a 2000-MW generating station. Electricity is transmitted to the Pacific Northwest power grid that includes Oregon, Idaho and northern California. Geology The mine is located on the northeast flank of the Rock Springs uplift. This is a broad, asymmetrical anticlinal feature about 97 km (60 miles) long and 56 km (35 miles) wide with a north-trending axis. This uplift separates the Green River Basin to the west and the Great Divide and Washakie Basins to the east. Precambrian rocks on the apex of the uplift are estimated to be 5200 m (17,000 ft) above the Precambrian rocks in the Green River and Washakie Basins. Normal faults with generally less than 30-m (100-ft) vertical displacement cut through the uplift. The dip of strata on the flanks is generally between 3° and 15°.

Jan 1, 1991

By I. Edgar Odom

Hectorite is a rare magnesium-lithium clay mineral that occurs at many places in the McDermitt caldera of Nevada-Oregon. Commercial development of several high purity deposits began in 1986. The hectorite that was precipitated in a lake environment formed after the collapse of the McDermitt caldera. Hectorite beds and lenses are associated with volcanic sediments, limestones, dolomites, zeolites and locally sandy bentonites. The high purity deposits appear to be associated with hydrothermal areas. The hectorite consists of extremely small, flake-shaped crystals. Calcium (Ca) is the predominant exchangeable ion. Its color ranges from white to light green. Commercial uses include high-brightness, magnesium-aluminum-silicate (MAS) products, organophilic clays, pulp retention and ceramics. The MAS is used as a suspending agent, binder, stabilizer and thixotrope in aqueous solutions for cosmetics, household cleaners, pharmaceuticals and miscellaneous industrial applications. Hectorite-based organophilic clays are used in printing inks and paints. The McDermitt caldera complex is located astride the Nevada-Oregon boundary west of the town of McDermitt, NV (Fig. 1). The structural complex is elliptical in shape, extending about 43 km (27 miles) north-south and 34 km (21 miles) east-west. This area was the site of extensive volcanism during the Miocene (24 to 18 million years). The complex consists of five overlapping calderas with the oldest at the south end of the complex (Rytuba et al., 1979). Each of the vent areas collapsed and is marked by a ring fracture zone. The ring fractures around the outer boundary of the caldera complex are shown in [Fig.1].

Jan 1, 1992

By A. Tsouchlaraki

The physical relief is a variable of utmost significance in the course of the analysis, evaluation, design and management of the visual environment. In this sense, there are cases where it would be desirable to isolate the relief from the other elements making up the visual environment and to investigate its visual value separately. Such cases include the technical works that cause major and permanent alterations to the relief, as well as the works, of which the spatial arrangement depends on the morphology of the ground. Slopes, distances, hypsometric difference values, viewsheds are elements of the relief that affect the visual value of a landscape, but also the ability of a particular landscape to accept and absorb new activities. This paper describes an evaluation and prediction model of the visual value of the landforms. A questionnaire survey takes place in order to investigate the public preference, using a sample of 221 persons in the broader area of Athens. The means used to demonstrate the various forms of reliefs are 32 perspective digital relief images. Following this and in order to investigate the elements of the relief that affect its visual value, 20 quantitative indices were developed and examined so as to select the best ones. Linear prediction models of the visual value were investigated from the previous elements, through a regression process. The applications of the proposed model in physical environment planning are many, such as the prediction of visual impact by arranging works that alter the relief of a region, as it happens in mining, metallurgical and waste disposal sites.

Jan 1, 2005

By Trevor A. Moss

Installation of equipment and structures at mines often requires mine planners to evaluate unique loading and operating conditions. Consideration of these unusual features is required throughout design and construction and into operation. Most planners understand the necessity of employing sound civil, structural and mechanical engineering techniques to design these structures and equipment. However, the influence of geotechnical factors on the overall progress of construction and operation is less appreciated. Mine operators routinely perform exploratory drilling to define ore deposits. These exploration activities can be extensive and often include provisions for assessment of subsurface conditions as they relate to the mining operation - requirements for ground support. All of these factors are important to the economics of the mine and are well justified. Surface facilities are provided to access and service the mine, and they play an important role in the successful development and operation of a project. Headframes, hoist foundations and shaft collars, in particular, are examples of unique installations encountered at underground mine sites. The design and above-surface behavior of these facilities can be analyzed with the usual fundamental engineering practices employed throughout the engineering professions. However, near surface exploration for the purposes of assessing soil and rock conditions for foundations is often given a reduced priority and less consideration. This article provides an outline of the benefits and importance of performing such exploration. References here relate particularly to shaft headframes, hoists and shaft collars. But the issues raised apply equally to other installations of a similar nature, including milling equipment.

Jan 1, 1992

By B. C. Haimson

The Committee on Rapid Excavation of the National Research Council has recognized in its 1968 report the need for "improvement of rock-mechanics techniques for measuring subsurface stress field in deep boreholes and for determining stress distribution in walls of underground excavations". The technique recommended in this paper as being most suitable for both deep hole and tunnel wall stress determination is Hydraulic Fracturing. Using this method stresses are calculated directly from the fluid pressures necessary to initiate and extend a fracture away from a borehole. Stress determination by hydraulic fracturing is rather insensitive to inhomogeneity or anisotropy, is not limited in depth except by the length of the hole, requires simple equipment which is commercially available, and can be carried out by unskilled personnel. The method has been worked out theoretically and extensively tested and verified in the laboratory. A number of field tests in deep holes ranging from 300 to 6300 ft have yielded surprisingly good results. Preliminary underground tests have been very encouraging and most recent measurements in a tunnel complex at the Nevada Test Site yielded stresses that were both consistent and reasonable when compared with the expected directionsand magnitudes. It is recommended that hydraulic fracturing be considered as a method of in-situ stress measurement both in the pre-excavation stage of design and during tunneling.

Jan 1, 1974

By Ching L. Wu, Bolek Chytrowski, Peter Frobenius, Dale Roberts

During the past few years, the first stage of the Waste Isolation Pilot Plant, (WIPP) which consists of an exploratory shaft, a ventilation shaft, shaft stations, access drifts and test rooms, has been under construction. Construction of the first stage is scheduled to be completed in the summer of 1983. The U.S. Department of Energy (DOE) is constructing the WIPP facility to demonstrate the feasibility of disposing of defense-related nuclear waste in the bedded salt deposits of the Delaware Basin near Carlsbad, N.M. The project promises to be a proving ground for underground nuclear waste storage facility design and construction. The completed underground plant will extend over an area of 647,500 m2 (160 acres), and 1,360,500 metric tons (1,500,000 tons) of salt will be excavated. The first stage of the project, the Site and Preliminary Design Validation (SPDV) Program, provides for full-scale construction of the major components of the underground facility. Shaft construction and underground development are described. Rock bolt installation is performed as required for roof control. Geotechnical instrumentation is installed to monitor the behavior of underground openings. Direct observation of the constructed shafts, shaft stations, and underground openings is expected to confirm the adequacy of the underground design and allow full-scale construction of the first U.S. underground nuclear waste storage facility to proceed.

Jan 1, 1983

By Pat DeWilliam

The Yakobi nickel-copper deposit is located essentially at tidewater in the east-central part of Yakobi Island, about 16 1 airline km (100 airline miles) west of Juneau, and can be reached by float plane and boat from Juneau and Sitka. The fishing village of Pelican, population 400, is situated 14.5 km (9 miles) to the east. An unimproved road, approximately 4 km (2.5 miles) long, connects a dock site at Lisianski Strait with the main part of the deposit known as the Basin Area (Fig. I). Other mineral occurrences are known as the Takanis, Flapjack, and Beach Areas. Another smaller nickel-copper deposit is located about 32 km (20 miles) to the south on Western Chichagof Island and is known as the Mirror Harbor nickel-copper deposit. The original discovery of the Yakobi deposit was made by S.H.P. Vevelstad about 1920 and a 47.5-m (156-ft) long adit was driven on the southwest side of the deposit in the Basin Area. The deposit was examined by J.R. Van Fleet of Union Carbide in 1930 and by J.G. Fairchild in September 1931. Stanley and Yates of the International Nickel Co. of Canada (Inco) visited the property in August or September 1937. In 1942, the controlling interest in the deposit, covered by 124 unpatented claims, was said to be held by Vevelstad and associates

Jan 1, 1991

By T. D. Rourke, E. J. Cording, O&apos

INTRODUCTION Detailed investigation of a 60-ft-deep excavation in a mixed profile of sands and stiff clay was performed by the University of Illinois for the Washington Metropolitan Area Transit Authority (METRO). The work was coordinated through DeLeuw, Cather and Co., the General Engineering Consultant of METRO. Instrumentation was concentrated in a portion of braced excavation for the Gallery Place Station near the intersection of 7th and G Street. The early construction date, the 60 ft depth of cut, and the proximity of large buildings formed the basis for selection of this site as the focal point of observation and measurement. A history of lateral and vertical displacement is provided wherein movements which occurred during excavation to the full depth of cut and, subsequently, during station construction and the removal of braces are described in detail. Observations of preloading and the consequent brace loads and wall displacements are described. The effect of temperature change on brace loads is discussed and the measured apparent earth pressure for the 60-ft cut is provided. The paper discusses the relationship of lateral displacements of the cut wall to the construction procedure, and compares the lateral wall displacement with both lateral and vertical movement in the surrounding soil mass. Based on observed movement, the method by which displacement was predicted for a nearby 82-ft-deep excavation is described. The performance of the 82-ft-deep excavation has been summarized elsewhere (2).

Jan 1, 1974

By Philip A. Mattson

INTRODUCTION Engineers involved with rock mechanics know the importance of discontinuities within a rock mass and their effect on its behavior when subjected to loads from structures or construction excavation activities. Various geophysical tools have been developed to provide comparative information on subsurface conditions, such as electrical resistivity, assorted seismic test methods, acoustic tests, etc. While these investigative means have proved invaluable in numerous situations, especially those where site alternatives are being evaluated, they shed little light on the difficult problem of quantifying the rock strength. For that purpose, a laboratory test program of samples obtained in the field is usually undertaken, often in conjunction with a variety of in-situ tests. While standard samples provide sufficient information on the rock properties, questions on the macro-structure of joints, faults, fissures, and their infillings often go unanswered. Presently, attempts are being made to incorporate into rock sampling technology new techniques which are directed towards providing better information on the incidense and orientation of discontinuities. One such device incorporates a scribe knife within the core barrel which scores the sample lengthwise as it is cored. The orientation of the scribe is known, thereby relating the bedding, planes, fractures, etc. to a spatial framework. A second approach, called the Integral Sampling Method, is the subject of this paper. Stated briefly, this method utilizes a grout injection to bond fractured rock to a steel reinforcing bar at the center of the coring. The bar is intended to act as a

Jan 1, 1979

By Changwoo Lee

Under drastically deteriorated situations, diesel equipment was introduced to some of local coal mines, aiming at higher productivity and better safety. To accommodate various diesel equipment in conventionally developed mines, mining system itself had to be modified; much larger trackless haulage ways were excavated. Possible health hazards of diesel not taken into account at the beginning become a serious concern and effective control measures are being searched for. The purpose of this paper is to study the diffusion characteristics of diesel exhaust in local coal mines. One of the parameters affecting dispersion of diesel contaminants is the coefficient of turbulent diffusion. Since CO2 is known to be closely correlated with other contaminants such as CO, NO, NQ, SO2 and RCD, it was chosen as a tracer gas in a series of dispersion experiments. A large diesel passage as well as a conventional track haulage way were the sites for the experiments. Rectangular dispersion pulses were generated for 30 ~60 seconds and CO2 concentrations were recorded at several locations 50~190 m downwind. The diffusion coefficients calculated graphically vary between 0.10~0.48 m2/s at both haulage ways. The results are analyzed to find any correlation with the air velocity and the distance from the disperser. Skobunov's empirical formula is applied to the experimental data for comparison and the relationship between Reynolds number and Ex/Dp/sci0.4 Sc1…

Jan 1, 1995

By W. H. Langer

Natural aggregate is the number one non-energy mineral resource in terms of value and volume and is a necessary commodity for sustainable communities. While aggregate is a non-renewable resource, supplies are nearly inexhaustible on a global scale. Natural aggregates have characteristics that differentiate them from most other mineral commodities: a high number of potential extraction sites, a high volume to value ratio, significantly different set of potential environmental impacts, and regional importance combined with a narrow economic transportation radius. Because of these and other differences, resource management policies for aggregates should differ from ?general? mineral resource policies, even though the end goal is the same for both ? ensuring sustainable resource management. To achieve the goals of sustainable aggregate management each stakeholder ? government, industry, the public, and non-governmental organizations ? will need to accept certain responsibilities, one of the most important of which is to become informed about natural resource issues. Sustainability is about making trade offs among competing objectives, and people disagree about the appropriate balance among the goals of economic prosperity, social equity, and environmental health. One of the primary purposes of mineral indicators is to provide information to decision makers and the public so as to ensure that the public debate about policy choices is grounded in fact. We identify the unique aspects of aggregate resource management and introduce the concepts of sustainable mineral resource management. We then present mineral indicator sets for aggregate resources from Italy, the United Kingdom, and Slovenia to demonstrate that effective mineral indicators should be specific to the resource in question and the public values and objectives.

Jan 1, 2003

By Mike Rhodes, Paul Miller, John W. Neale, Vishal Deeplaul, Barrie Hancock, Tony Pinches

The Beaconsfield underground gold mine is one of only a few new Australian gold projects to come into operation in the current climate of low gold prices. Up to 200,000 tonnes per annum of Tasmania Reef ore will be mined and processed over a minimum eight-year life to a depth of 900 metres below surface. The Tasmania Reef is a gold-bearing quartz-carbonate-sulphide vein occupying an old fault structure which transgresses a series of sedimentary beds. The sulphides are predominantly pyrite with lesser arsenopyrite, and also minor copper as chalcopyrite. Drilling to date below this level clearly indicates that the high-grade orebody is open at depth and that the mine life should be extended significantly over time. Since redevelopment of Beaconsfield mine began in the 1980's, extensive exploration has identified a resource of 1.5 million tonnes within a 450 vertical metre zone beneath the old workings, which extended more than 450 metres below the surface. Installation of an 800 litre per second capacity pump station 180 metres below the surface has been critical in overcoming one of the major hurdles experienced during previous operations in the early 1900's. A multi-stage development program, designed to bring the mine into full production, and incorporating construction of the on-site gold treatment plant incorporating bacterial oxidation, has now been completed. Prior to execution of a detailed engineering design of the Mintek-BacTech bacterial oxidation process, a programme of bacterial oxidation testwork was completed to provide a basis for fixing the process design criteria. A flow diagram of the Beaconsfield treatment plant is shown in Figure l. It comprises:

Jan 1, 2000

By G. Norman Owen, Roger E. Scholl, Tor L. Brekke

INTRODUCTION Underground structures are generally regarded to be safer than surface structures during strong seismic motion, except when crossing a causative fault. Recent studies of observed earthquake damage to tunnels generally support this view, although instances of severe damage and, occasionally, collapse are reported. For proposed underground construction of sensitive structures such as nuclear power plants, liquefied natural gas facilities, and nuclear waste repositories, a verification of the seismic response of underground structures will be required.. This paper discusses the stabilization recommendations used in a study of additional costs required to protect tunnels against ground motion caused by earthquakes and underground nuclear explosions (1). The study is a part of the site investigations for possible construction of a nuclear waste repository. The additional costs estimated in the study are not presented here; only the stabilization measures are presented in the present paper. The tunnels, which would constitute the underground facilities of a possible repository, are assumed to be 5.5 m (18 ft) in diameter and to be located at a depth of 600 m (2,000 ft). Three candidate geological materials are considered: argillite (shale), granite, and tuff. Several peak ground accelerations are used: 0.3g, 0.5g, and 0.7g for earthquakes, and 0.5g, 0.7g, and 1.0g for underground nuclear explosions. Potential damage due only to shaking is considered here. This paper does not discuss problems that result from creep or sudden rupture of intersected faults or from ground failures at portals.

Jan 1, 1979

By Hisakazu Matsushita

1. Introduction This is a report on applications of the earth pressure type balanced shield tunneling projects executed under narrow streets on soft alluvial layers in Japan. Japan is a long island country surrounded by the sea. Steep mountain ranges run along the archipelago and numerous rivers originate from the mountains, leaving only limited areas of flat land along the upper and middle reaches of the streams. The majority of cities in Japan are on soft alluvial layers. Alluvium represents an extremely complex soil formation, sections bordering diluvium being characterized by sharp undulations. Various difficulties are therefore encountered in shield tunneling work undertaken in such ground conditions. Particularly, at work sites lying in an unstable, waterbearing layer with high permeability, shield excavation becomes utterly impossible, hampered by large amounts of underground water as well as land collapsing caused by the water. Even when work can somehow be accomplished by using chemical grouting or by lowering ground water level, which require extra expenses and time, undesirable effects such as ground surface settlement are unavoidable in projects undertaken in the past. The newly developed method allows safe and accurate tunnel excavation at normal speed and without giving any adverse effects on buildings above, even under such unstable ground conditions. An outline of this new method was announced at the "International Tunnel Symposium '78" held in Tokyo, and the method has since been employed in a number of tunneling projects in this country. This report provides further data on the new method with reference to some of those projects, explaining how it allows tunnel excavation with

Jan 1, 1979