Search Documents

By L. P. Weber

During the years 1983-1987, a research programme, jointly performed by the steel producers ARBED, British Steel Corporation, Peine-Salzgitter, Unimetal, and co-sponsored by the European Community for Steel and Coal (ECSC), has been carried out on steel H-piles of different shapes. The initial aim of the testing programme has been the improvement of bearing capacity, both in sandy and clayey soils. At two test sites, standard H-beams are compared to H-piles with different types of laggings or to H-piles grouted both under low and high pressure. In this paper and in view of the open european market in 1992, the H-pile capacities and their corresponding allowable loads, determined from codes, recommendations and computation procedures in use in Belgium/Luxembourg (B/L), France (F), Federal Republic of Germany (G), and the United Kingdom (UK) as well as their evaluation from dynamic CAPWAP and Case methods are compared to the static capacities measured in-situ. In addition, procedures for estimating the load/movement behaviour of H-piles from CPT, pressuremeter, and CAPWAP are compared to the measured curves.

Jan 1, 1991

By Clyde E. Williams

[As a results of work conducted during the past three years, the Northwest Experiment Station of the Bureau of Mines, in cooperation with the University of Washington at Seattle, Washington, has developed a process for the production of sponge iron. Commercial operation of this process in a 3 to 4-ton scale has been so satisfactory that its use on a large scale (20 to 100 tons per day) can be safely considered. Description of Process. The process consists in passing a mixture of iron ore and coal through a rotating kiln heated at one end to a temperature sufficient to convert iron oxide to metallic iron, discharging, cooling, and separating the sponge iron from the residual coke and silicious material on a magnetic separator. Both the coal and the ore should be crushed to peso as 6-meth scream, tans producing particles finer then 1/12 of an inch. Seventy-five parts of coal or other carbonaceous material arc charged with every 100 parts of ore), This large amount of coal is required in order to supply sufficient carbon to maintain a strongly reducing atmosphere in the charge, but may be reduced to about 65 parts per 100 parts of ore by recovering and using tae carbon that remains in the discharge product. Large-scale operation and refinements in furnace design should lower this ratio to perhaps 56 or 60 parts of coal to 100 parts of ore.]

Jan 1, 1924

By Zachary Q. Maassen

The purpose of this paper is to highlight the environmental benefits of properly managing slurry waste as it is generated on site. The following projects will be used to illustrate the importance of proper onsite waste management. Project: Jet Grout Backflow Dewatering The goal was to dewater the backflow directly onsite to produce a dry, solid waste and reusable water. The backflow spoil was pumped directly to the dewatering system as it was generated. Utilizing mechanical separation equipment and flocculation polymer the waste volume was reduced by 44%. Due to the site footprint and high volumes, slurry waste removal and onsite processing were the only two feasible options. Onsite dewatering proved to be the environmentally beneficial option as it eliminated the need for slurry waste hauling and disposal. The benefits of utilizing a dewatering system are listed below: Project: Soil Mixing Spoil Recycling for Slurry Wall Construction In this application the spoils generated contain bentonite mud, cement mixture and organic ground soils. The goal of this project was to process the backflow mixture to recover reusable bentonite mud and separate the soil as a dry, stackable waste product. The treatment system replaced the traditional method of vacuum truck extraction and facility disposal. The environmental benefits of properly handling the backflow is a decrease in fresh water usage, bentonite additive reduction, and the reduction of CO2 emissions. The paper will consist of a project scope, technical equipment and process description, environmental impact reduction calculations and lessons learned for each project.

Jan 1, 2018

By Vern Pfannenstiel

Jan 1, 2005

By Kelly E. G

NZ Steel's flushing slag typically contains 1.2 per cent V203. Extraction of vanadium from powdered slag using a salt (NaCI or Na2CO3) roast/leach process was investigated. With NaCl, optimum extraction conditions were a charge containing 10 per cent NaCI, roasting in air at 875°C for 4 hours, followed by leaching in dilute H2SO4. Extractions were typically 30-50 per cent. NaCI roasting did not chemically attack the slag; the phase transformations that occurred were due to high temperature oxidation. Slag particle size had a significant effect on extraction.Optimum conditions for extracting vanadium by Na2C03 roasting were 20 per cent Na2CO3 in the charge and roasting in air for 3-4 hours at 850-875°C followed by water leaching.Na2CO3 roasting involved chemical attack that resulted in the formation of perovskite (CaTiO3) and carnegieite (NaAISiO4).The extent of vanadium extraction depended on the amount of Na2CO3 added and the original slag SiO2 content.Compared to the separate roasting treatments, simultaneous treatment with NaCI and Na2CO3 gave lower vanadium extraction, while requiring considerably higher roasting times and temperatures.

Jan 1, 1982

By W. Scheetz

The Brewer Gold Mine is an open-pit, heap leach operation that processes about 122 kt/m (135,000 stpm). The mine is operated by Brewer Gold Inc., a subsidiary of Westmont Mining Inc., and is located near Jefferson, SC, about 80 km (50 miles) southeast of Charlotte, NC and 80 km (50 miles) northeast of Columbia, SC (Fig. 1). All of the ore to date has been produced from a breccia body of hydrothermal origin and a related smaller body of fault-controlled ore, known as the B-6. Reserves at the time the mine commenced production were 4.6 Mt (5.1 million st) grading 1.4 g/t (0.042 oz per st) gold. History Although some reports of a pre-Revolution War shaft at the Brewer are in the literature (Lieber, 1856, Nitze and Wilkens, 1897), gold was first produced in earnest from the Brewer Mine in 1828. Production occurred primarily from placer deposits south of the present mine workings. Lieber noted in 1856 that “every branch, gulch, ravine or even declivity of the main hill has been washed and rewashed.”

Jan 1, 1991

By J. R. Long, R. S. Dean, F. S. Wartman, E. T. Hayes

The production of titanium in I5-lb. lots and with a purity sufficient to be consolidated into ductile metal, as described in a previous paper,' has provided adequate material for a study of the physical properties of titanium and a more thorough examination of its working qualities. Data on the physical properties reported in that paper were obtained on metal fabricated by a fixed procedure, standardized for the purpose of control of the reduction, and are representative only of material fabricated under those conditions. There are many possible variables in the working schedule, which will have significant effects on the properties of the finished material; and since the previous working methods were not necessarily the best, an investigation of the fabrication of titanium by other methods was undertaken. In this work the consolidation of the powder by pressing and sintering was conducted essentially as outlined in the report cited' and all efforts were centered on fabrication methods for those powders and the proper- ties produced by them. Hardness, density, microstructure, and tensile properties were determined at various stages in the working and annealing; and resistivity measurements were made on a few bars and drawn wire. Consolidation of the PowdeR The screen analysis of the available titanium powder is given in Table I. No attempt was made to alter the size distribution from that noted because this powder, although coarse by normal powder-metallurgy standards, produced acceptable compacts suitable for the present work. Because of their large specific surface, finer powders are more contaminated by oxygen and produce harder compacts, which are difficult to work. The powder as produced is soft, compresses in a normal fashion, and exhibits very little tendency to adhere to the die surfaces. Unlike aluminum and magnesium powders, it can be readily pressed without the use of die lubricants. When compacted at 50 tons per

Jan 1, 1946

By J. R. Long, E. T. Hayes, R. S. Dean, F. S. Wartman

The production of titanium in I5-lb. lots and with a purity sufficient to be consolidated into ductile metal, as described in a previous paper,' has provided adequate material for a study of the physical properties of titanium and a more thorough examination of its working qualities. Data on the physical properties reported in that paper were obtained on metal fabricated by a fixed procedure, standardized for the purpose of control of the reduction, and are representative only of material fabricated under those conditions. There are many possible variables in the working schedule, which will have significant effects on the properties of the finished material; and since the previous working methods were not necessarily the best, an investigation of the fabrication of titanium by other methods was undertaken. In this work the consolidation of the powder by pressing and sintering was conducted essentially as outlined in the report cited' and all efforts were centered on fabrication methods for those powders and the proper- ties produced by them. Hardness, density, microstructure, and tensile properties were determined at various stages in the working and annealing; and resistivity measurements were made on a few bars and drawn wire. Consolidation of the PowdeR The screen analysis of the available titanium powder is given in Table I. No attempt was made to alter the size distribution from that noted because this powder, although coarse by normal powder-metallurgy standards, produced acceptable compacts suitable for the present work. Because of their large specific surface, finer powders are more contaminated by oxygen and produce harder compacts, which are difficult to work. The powder as produced is soft, compresses in a normal fashion, and exhibits very little tendency to adhere to the die surfaces. Unlike aluminum and magnesium powders, it can be readily pressed without the use of die lubricants. When compacted at 50 tons per

Jan 1, 1946

By Sebastian Lobo-Guerrero

Welcome to DFI45! our first on-line annual meeting. We cannot deny the severe impacts that the COVID19 pandemic is having in our industry and our lives. We extend our support to all of our members that have been impacted in many different ways. But through the middle of this difficult and challenging times, our beloved annual conference emerges, trying to re-unite our industry and remind us why we love what we do so much. DFI45 was not originally planned to be delivered virtually, but as our world changed, we adapted. Adversity became an opportunity to re-invent our annual conference. Thanks to the vision of our Organizing Committee, we saw the amazing new possibilities and DFI45 is today a reality. Our theme for this year is People + Purpose + Passion. This theme was decided before the COVID 19 pandemic started, but today it is more relevant than ever before. We are a group of very diverse people at DFI. Our organization includes Contractors, Consultants, Suppliers, and Academics just to name a few sub-groups. But we all have a common purpose and try to find common ground. We are all extremely passionate about what we do, and this excitement is really what makes this organization what it is today. This conference celebrates this passion as you can see in our three main Keynote Sessions. On a local scale, we want to go back and remember the contribution of our industry to our beloved National Monuments in Washington D.C. On a national scale, we want to explore and recap the development of Government Guidelines and Specifications that became the world standards. And finally, we want to close the conference with a session celebrating the family legacy and share amazing stories of families with multiple generations working in our industry. Besides our Keynote Lectures, the conference is full of exciting content such as several case histories, experimental research in deep foundations, applications of new technologies, business aspects and risk management considerations for deep foundations, just to list a few. We also have our now traditional events such as the Hal Hunt Lecture, Awards Reception, DFI Educational Trust 5K Fundraiser, etc. For the first time, all this content will be delivered using different virtual formats, including on-demand presentations, plenary sessions, interactive chat rooms, etc. We are excited about these possibilities. To conclude, we need to recognize the people that against all odds made this conference a reality. First our sponsors, they adapted to the most abrupt change never thought before, and they always stayed there with us, providing unconditional support. Without them no conference is possible. Next, our Organizing Committee that re-invented the concept of an annual conference and found new and exciting ways to make this happen! Our Technical Program Committee led by our Technical Program Chairs, Jennifer Nicks and Gregg Piazza, showed us that nothing is impossible. And last, but not least, the amazing DFI staff that make dreams reality. It has been an honor to serve as the Conference Chair for DFI45. It is an experience that will stay with me for the rest of my career. Conference Chair: Sebastian Lobo Guerrero, Ph.D., P.E. American Geotechnical and Environmental Services (A.G.E.S.)

Oct 27, 2020

By S. Hardcastle

Various controlled and ambient tests were undertaken to evaluate the performance of a variety of digital heat stress monitors, psychrometers and simpler temperature/relative humidity data loggers that measure, or determine, such parameters as: dry-bulb, natural wet-bulb, psychrometric wet-bulb and globe temperatures. In this comparison, funded by the Deep Mining Research Consortium, it has been found that all the instruments can competently measure dry-bulb temperature but the accuracy of other sensors could introduce significant uncertainty. For example the quality of relative humidity sensors and failure to correct for the barometric pressure difference in deep mines, directly impacts upon the calculation of psychrometric wet-bulb. The comparison has shown that the response of dry-bulb and globe temperature sensors can vary widely under different radiant heat conditions; however this would be negligible in most mines. Of more concern is the differing performance of the natural-wet bulb sensors especially at low relative humidity and low air velocity. Furthermore, from these tests and the currently available theory it was not possible to determine if any of the natural-wet bulb instruments measured that value correctly or validate any relationship between psychrometric and natural wet-bulb temperature at low air speeds where their difference is greatest. Consequently the uninformed use of some of the commercially available environmental heat stress monitors or derivations from other instruments could provide erroneous results affecting the work load category that can be accommodated or the rest ratio regime required.

Jan 1, 2009

By P. M. Lin

A subsidence monitoring program over a longwall panel was established (1) to explore the impacts of dynamic subsidence on the ground surface and structures and (2) to correlate the movements between the structures and their corresponding points on the ground. The program consisted of a transverse line survey and a series of survey points around the structures on the ground surface and their corresponding survey points on the exterior walls of the structures. The vertical displacement of each point can be expressed as: where Si is subsidence at i point; Sif is the final subsidence at i point; F is face location in terms of distance from the i point and SD is seam depth. The development of subsidence can be divided into five stages. Damage to the structures starts at the beginning of the second stage, The maximum damage developed in the middle of the third stage. The relationship of the vertical displacement between ground surface and structures can be expressed as: G = aH + b where G is ground displacement, H is structures displacement, and a and b are constants. The relationship is linear. However, the strain is non-linear and more complicated because of the interaction of the ground surface and structure.

Jan 1, 1989

Similarities and Dissimilarities in Florida Phosphate Ore Types - Surface and Bulk Property Analysis of the Flotation Feed, Concentrate and Tails

Sep 13, 2010

By J. G. van der Watt

Due to increasing concerns of global rare earth element shortfalls in the near future, possible alternative sources of rare earth elements have recently become of economic interest. One such alternative is decanting acid mine water originating primarily from abandoned old mines in the Witwatersrand region of the Republic of South Africa. In this study, a novel way of rare earth element removal from the acid mine drainage was employed, making use of bentonite clay, which has very good adsorbent properties, as a rare earth element carrier material. The process can be economically viable only, if the elements can be selectively removed from the bentonite clay carrier material so as to yield reusable clay. Acid leaching was proposed to liberate the adsorbed rare earth elements from the bentonite clay. Accordingly, acid leaching experiments were performed to study the desorption of three commonly-found rare earth elements, namely neodymium, samarium, and dysprosium, from bentonite clay in the presence of sulphuric and hydrochloric acid. It was established that the three rare earth element species could be selectively removed as a group from iron, magnesium, and manganese metals through the careful manipulation of the pH. An investigation into the kinetic aspects of the rare earth element desorption process from the bentonite clay was also undertaken. The applicability of various kinetic models such as zero-order, pseudo first-order, pseudo second-order, elovich, parabolic diffusion, and power function were tested to describe the time-dependent desorption of rare earth elements from bentonite clay. It was determined that the pseudo second-order kinetic model represented the dissolution processes for neodymium, samarium, and dysprosium from bentonite clay the most accurately.

Jan 1, 2012

By Sachihiko Tokunaga, Hirofumi Taguchi, Kenji Maruyama, Hidenori Takahashi, Yoshiyuki Morikawa

"Abstract The present study proposed a new liquefaction countermeasure to improve sandy ground and conducted a trial execution. The new method is a floating-type and lattice-shaped cement treatment method, where cement-treated soil is not fixed to a non-liquefiable stratum. A fixed structure such as treated soil should be formed at the side of the floating-type treated soil to reduce its lateral displacement. In the study, one-dimensional dynamic response analyses were first conducted to confirm the mechanism of the new method. Then, a series of centrifuge model tests were performed to demonstrate the effect under a stress condition at the prototype scale. The analyses and model tests confirmed the effect of the liquefaction countermeasure. Finally, trial executions were carried out to confirm high-quality vertical execution.INTRODUCTIONLiquefaction induced by an earthquake generates sand boiling and ground settlement. Other problems have also been reported, including a decrease in bearing capacity and an increase in the horizontal earth pressure against retaining walls. To prevent these problems caused by liquefaction of the ground, various countermeasures have been proposed, such as cement deep mixing and high-pressure jet mixing methods. These methods have the big advantage of being applicable to ground that contains soil with a fine-grain fraction. Furthermore, the unnecessary displacement caused by the construction can be reduced. In Japan, a lattice-shaped cement-treatment method has frequently been used at many construction sites to prevent liquefaction, where cement-treated piles are intersected to form a lattice, as shown in Fig. 1. The lattice-shaped walls can reduce the shear stress generated by an earthquake, restricting the liquefaction at that location. However, the construction cost of the cement treatment is relatively high compared to other methods such as the sand compaction pile (SCP) method, and needs to be reduced. In particular, the cost of the high-pressure jet mixing method, which can be applied to the liquefiable ground under existing structures, is significantly high. Therefore, decreasing the total volume of the cement treatment is necessary to reduce the construction cost."

Jan 1, 2014

By Yoshinori Iwasaki, Shosei Serata, Yutaka Mochida

A new comprehensive insitu instrumentation technique named this RCC Method has been developed for rapid assessment and improvement of the structural stability of underground openings. When applied to tunnel construction, the degree of present and prospective safety of underground openings can be determined in quantitative terms within 10 to 20 minutes of microcreep observation. When applied to mining, roofs and floors can be stabilized by controlling the stress conditions. This stress control method has eliminated the need for intensive roof bolting and extensive floor renewal in all cases where it was applied. Use of this technique is illustrated by field examples from the Seikan Undersea Tunnel of Japan and deep potash mining in Canada. NEW INSTRUMENTATION TECHNIQUE: THE RCC METHOD Failure problems in underground excavation usually arise in weak non-elastic grounds where conventional rock mechanics theories of elasticity are not only useless but also misleading. Presently, discontinuity planes in the ground are being considered a factor in assessing these failure problems, and while this development is interesting academically, it is not of much use in actual excavation work, where it is nearly impossible to identify and quantize all existing planes of discontinuity. Even if such an extraordinary task could be accomplished at an underground excavation site, effective use of the data would be difficult and impractical for rapid excavation work, with the possible exception of rare cases of ideally elastic ground.

Jan 1, 1976

By C. E. Hales

In an effort to improve efficiencies and reduce costs, AngloGold has embarked on a process to develop and deliver consistent, high quality, tailings based support or construction products to stopes and tunnels on request. A three-phase approach of product conceptualisation, design and delivery has been adopted. To date a substantial amount of laboratory development has taken place with promising results, indicating that the project aims are achievable. Dans un effort pour améliorer le rendement et réduire les coûts, AngloGold s’est embarqué dans une opération qui vise à développer et fournir aux chantiers d’extraction et tunnels, sur demande, des produits de construction ou de support basés sur rejets qui sont réguliers et de haute qualité. Une méthode à trois volets a été adoptée : conception, création et livraison. A ce jour, un développement important en laboratoire s’est produit, avec des résultats pleins de promesses, qui semblent indiquer que les buts du projet peuvent être atteints. In der Bemühung, die Effizienz zu steigern und Kosten zu verringern, hat AngloGold begonnen ein Verfahren zu entwickeln welches auf Anfrage konsistent hochqualitative auf Haufwerk basierender Unterstützung oder Bauprodukte für Abbaustellen und Tunnels entwickelt und liefert Eine Dreiphasenplan zur Produktkonzeptualisierung, Design und Lieferung wurde adoptiert. Bis jetzt hat eine substantielle Anzahl an Laborentwicklung mit vielversprechenden Resultaten stattgefunden und aufgezeigt, daß die Projektziele erreichbar sind.

Jan 1, 2003

By Jackson R. Pressley, M L. Hopkins, R E. Danell, N T. Moxon, Andrew Bowman

Efficient and cost effective blasting is achieved by closely matching the explosive energy to the strength of the material in which it is being used. Although there are many empirical relationships wich approximate this situation complete the blast optimization can only be achieved by quantitatively assessing explosive/rock interactions and explosive performance. The performance of an explosive is essentially governed by its velocity of detonation or the rate at which the detonation wave travels through the explosive column.

Jan 1, 1991

By C. G. Hunkin

In situ, or in-place leaching is concerned with the extraction of metals from natural mineral disseminations without removal from their geologic location which, in many cases, amounts to the reversal of the deposition process accompanied by a presumed increase in velocity of the processes, if the project is to be profitable. Solution mining processes involve removal of minerals such as sulfur, common salt, and potash, generally leaving cavernous voids, in contrast to in situ leaching which term is applied to the selective dissolution of a mineral from its gangue without sensible disturbance of the formation. Where such a process can be operated, the advantages are manifold and have been so recognized by miners from the earliest days of mining. Recent technological developments have encouraged a reassessment of the status of in situ leaching, and it now appears possible to extend the application of the method from a few isolated special situations to many uranium and copper deposits. Anaconda's interest in the techniques stems from long experience with vat and heap leaching, 'dump leaching, and natural leach activities associated with several established mines. Increasing activity through-out the industry has been noted, particularly in leaching low grade pillars and the peripheral zones of operating mines, often by the introduction of leach solutions via boreholes drilled from surface. Reactivation of dormant mines] using similar techniques has been successful. Over the long term, environmental improvement activity will lead to excess sulfuric acid production, even to a disposal problem. The cost of leach solutions and reagents must be reexamined in this light. The mineral industry now classifies as uneconomic deposits of readily soluole minerals whose potential value, on a per acre basis, may De several times that of many currently profitable oil field reser-

Jan 1, 1971

By D. -H. Park, G. -j. Kim, Y. -J. Park, C. -S. Hong, S. -Y. Choo

To evaluate the quantitative tunnel behavior influenced by characteristics of discontinuity, this pa-per executes the parametric study using 2 and 3-dimensional DEM analysis. First of all, this study finds that displacement and the stress of shortcrete are proportioned to frequency of joint and rockbolt axial force is adversely proportioned too. Secondly, it is found that the most sensitive in-put parameter used in Barton-Bandis(BB) model is residual friction angle. Finally, when joint sets are encountered at tunnel excavation face, to identify the most critical joint orientation is very crucial for a stability of tunnel. La thèse a pour but d’étudier les influences sur la stabilité du tunnel, au niveau du réseau de la discontinuité et de la valeur de sa nature aquis par le projet récemment exécuté en vue de mener à l’analyse quantitative de cette stabilité, en appliquant chaque différent paramètre comme la fréquence de diaclase, la constante de résistance des modèles de Barton-Bandis(BB) ainsi que la relation entre le sens d’excavation du tunnel et le réseau de diaclase en 3 dimensions. En fait, cette étude nous a montré que la fréquence de diaclase s’accroît proportionnellement au déplacement et à la contrainte du béton projeté. L’angle de friction résiduel s’est montré le plus sensible à la stabilité du tunnel parmi les modèles de BB. Aussi à travers l’analyse à 3 dimensions, il s’est vérifié que si l’angle de pente du groupe de diaclase est horizontal entre l’axe du tunnel et la direction, il donne une influence importante sur le comportement du tunnel. En particulier, l’influence était la plus importante sur un fond rocheux dont la diaclase horizontale est grande. Um das quantitative Verhalten des Tunnels zu bewerten, eroertert dieses Papier eine parametrische Studie mit Hilfe der DEM Analyse. Auch wird hier eine zweidimensionale Analyse von Ver-bindungen verschiedener Frequenzen in der Gesteinsmasse, eine sensitive Analyse von allen der im Barton-Bandis-Modell (BB) genutzten Parameter und eine Dreidimensional-Analyse mit ver-schiedenen dreidimensionalen geometrischen Veteilungen von Verbindungen ausgefuehrt. Erstens: Die Studie findet heraus, dass Vedraengung und Druck im Shortcrete proportional zur Frequenz von Verbindungen und Axialkraft der Steinbolzen antiproportinal ist. Zweitens: Es wird herausge-funden, dass die am meisten Sensitiven der im BB-Modell angewendeten Eingaben die am Ende uebriggebliebenen Reibungswinkel sind. Und schliesslich wird herausgefunden, dass wenn Ver-bindungsteile an der Tunnelaushoelungsoberflaeche ausgemacht werden, fuer die Tunnelstabiltaet die Identifikation der meist kritischen Verbindungsorientierung sehr bedeutungsvoll.

Jan 1, 2003

By the courtesy of Metropolitana Milanese (Milan Underground), roost of the delegates visited on April 12, 1991 the tunnel of "PORTA VENEZIA" STATION of MILANO RAILWAY LINK. The "PORTA VENEZIA" STATION will be the most important in the link and it will he also the largest underground project of the whole railway transport network in Lomhardy. The particular conditions of the soil and the collocation of site in the center of Milano have required new technologies and the technical solution applied to this job is called "Cellular Arch Method" by its designer Prof. P. Lunardi. Our sincere thanks go to Prof. P. Lunardi and Eng. E.M. Pizzarotti of Rocksoil, Milano who have kindly furnished us a technical description of this method. Eng. Pizzarotti was the guide during the visit and gave all the technical explanations to the delegates. THE "VENEZIA" STATION IN THE 2PB SECTION OF THE RAILWAY LINK The excavation of cavities in loose ground, exceeding a certain dimension and at shallow depth, is not feasible using traditional methods: in fact it is not possible to consolidate the ground around the cavity in such a way that homogeneity and resistance is sufficiently guaranteed.

Jan 1, 1994