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Post-Mining 2005, November 16-17, Nancy, France 1 SOME EXAMPLES OF THE CAVITY FILLING ALONG TRANSPORTATION ROUTES ABOVE ABANDONED ROOM AND PILLAR LIGNITE MINES IN TOKAI REGION SAKAMOTO, Akio1, YAMADA, Noritoshi1, SUGIURA, Kenrou1, KAWAMOTO, Toshikazu2 1 TOBISHIMA CONSTRUCTION COMPANY, Nagoya Branch, Japan.; [email protected]; [email protected]; ,[email protected] 2 NAGOYA UNIVERSITY, Emeritus Professor, Nagoya, Japan. ; [email protected] ABSTRACT: The authors describe the applications of the integrated cavity filling technique to abandoned lignite mines in Tokai region. These abandoned lignite mines were in operation until 1960s and the routes of Tokai By-Pass Expressway and the linear motor car railway line for Aichi Exposition pass over these abandoned mines. Since the size of abandoned mines were much larger than the route of the expressway and the elevated monorail, limited areas relevant to their stability had to be only filled. This article describe the details of cavity filling operations in these two projects, which may be some valuable examples for assessing the methods how to deal problems associated with mine closures in long term. KEYWORDS: Abandoned mine, Lignite, Filling technique, Mitake, Nagakute RESUME : Les auteurs décrivent les applications d’une technique de remblayage des cavités aux mines de lignite abandonnées dans la région de Tokai. Ces mines abandonnées ont été exploitées jusqu'à dans les années 60. L’autoroute et la ligne ferroviaire construites pour accéder à l’Exposition d'Aichi sont ensuite passées à l’aplomb de ces mines abandonnées. La taille des mines abandonnées étaient beaucoup plus grande que l'itinéraire de l'autoroute et du monorail, seuls des secteurs d’extension relativement limitée ont dû être remblayé. Cet article décrit les détails des opérations de remblayage des cavités dans ces deux projets. Ceci peut être considéré comme des exemples instructifs de traitement de problèmes liés aux fermetures de mine dans le long terme. MOTS-CLEFS : Mine abandonnée, Lignite, Technique de remblayage, Mitake, Nagakute 1. Introduction The extraction of lignite using room and pillar mining technique was widespread in Tokai region of Central Japan until 1960s (Figure 1). These mines are abandoned since then and some of these areas have become urbanized. Furthermore, some transportation routes such as Tokai by-pass expressway and Aichi Exposition linear motor car line pass over the abandoned lignite mines. Since the areas of old-mining operations are much larger than those of the routes, it was necessary to fill limited areas required by these respective projects. The authors involved with cavity filling for some time in Tokai region and they have developed their own integrated cavity filling technique (i.e. Sugiura & Yamada, 2003; Sugiura et al., 2005; Sakamoto et al. 2005a, 2005b). This technique was also further advanced to carry out cavity filling operations on limited areas required by a given project. The integrated cavity filling technique for a limited area involves several fundamental steps such as the exploration of dimensions of cavities, establishing the filling plant facilities, building outer-walls and filling of required space and monitoring. All these steps must be performed with due considerations of environmental restrictions and regulations. Post-Mining 2005, November 16-17, Nancy, France 2 In this article, the authors describe two specific examples of cavity filling operations in Tokai region of the Central Japan. The details of these two cavity-filling operations may be some valuable examples for assessing the methods to deal problems associated with mine closures in long term. Figure 1. Lignite deposits in Tokai region and locations of sites. 2. Outline of Limited Area Filling Technique When the filling of abandoned mines is necessary for a limited area, the outerwalls are first constructed and the space between the outerwalls is then filled (Figure 2). The outerwall has higher strength and solidifies much more rapidly. These outerwalls act as barriers for lower strength inner space filling material while it solidifies. All these operations utilize some constructional and environmental monitoring. The constructional monitoring is associated with controlling the filling state of cavities and maintaining the quality of filling while environmental monitoring involves the ground deformations due to filling operations, the variation of characteristics of underground water as well as its levels. Post-Mining 2005, November 16-17, Nancy, France 3 Figure 2. Illustration of actual cavity filling operations of limited areas. 3. Application to Tokai By-Pass Expressway The first example is associated with the cavity filling of abandoned lignite mines in Mitake town and Kani city at an interchange on the route of Tokai By-Pass Expressway. A plan view and geological cross sections are shown in Figure 3. The N-S section coincides with the alignment of the Nagoya-bound Expressway while E-W section is aligned with the local roadway. Figure 4(a) shows an artist illustration of the interchange and filling works. In the same figure, a part of the abandoned lignite mine, which was uncovered, is also shown (Figure 4(b)). One of the challenging problems associated with cavity filling operations is how to determine the exact geometry of cavities to be filled. Although some mining plans submitted to the authorities at the time of mining operations are generally available, these documents do not coincide with actual mining layouts. Furthermore, the geometry may change with partial degradation and collapses of pillars and roof layers. Figure 5 shows the distribution of cavities and pillars beneath the interchange area of the Tokai By-Pass Expressway obtained from sonar exploration method through drillholes, which was carried out as an experimental filling operation. Since a limited area has to be filled, the limited area filling technique is employed. The composition of the filling materials for outerwalls and inner space differ from each other. Thus, their strengths are also different from each other (Table 1). Furthermore, the composition of the filling materials differed depending upon the characteristics of the superstructure. Higher strength filling materials are used beneath the foundations of viaducts of the expressway. Besides clay and sand scums, the amount and type of hardening materials differed according to the required strength characteristics of the filled space in relation to the type of superstructures of the expressway. The diameter of drillholes for grouting was 100mm and the average spacing of the drillholes for grouting was 15m. The volume of experimental filling operation was 2,155m3. However, the total volume of experimental filling operation was 81,000m3Figure 6 shows the areal distribution of outerwall filling and inner space filling at this particular location. Post-Mining 2005, November 16-17, Nancy, France 4 N W E S (a) Plan view (b) Cross sections Figure 3. Geological cross sections at the vicinity of the interchange of Tokai By-Pass Expressway. Post-Mining 2005, November 16-17, Nancy, France 5 (a) Artist illustration of cavity filling and constructed Interchange at Kani City (b) Exposed abandoned lignite mine Figure 4. Tokai Expressway passing through abandoned mines in Mitake-Kani area. Post-Mining 2005, November 16-17, Nancy, France 6 Figure 5. The distribution of pillars and cavities obtained from sonar exploration technique. Table 1. Composition of mixtures of filling materials depending upon superstructures. Beneath Embankment Beneath Viaduct Foundations Materials Low strength (>100kPa) High strength (>400kPa) Outerwall Inner Space Outerwall Inner Space Clay scum (kgf) 360 340 360 360 Sand scum (kgf) 180 170 180 180 Special hardening agent (kgf) 90 100 120 150 Special Sodium Silica (kgf) 48.8 12.2 48.8 24.4 Water (kgf) 724 763 715 725 Post-Mining 2005, November 16-17, Nancy, France 7 Figure 6. Distribution of outerwall and inner space filling. Various Monitoring was carried out for measuring ground tilting, outerwall gradient, filling state and quality control of filling materials and ground water characteristics during the filling work. 4. Application to Aichi Exposition Linear Motor Car Railway Project The second example is associated with the route of Aichi Exposition linear motor car transportation system in Nagakute town of Aichi Prefecture, Japan. The railway passes over Nagakute lignite deposits, which were extracted until 1950s (Figure 7). The railway is elevated through viaducts and the lignite seams dips west. The length of the line having cavities beneath is about 1km and the depth of cavities ranges between 6 and 57m. The average height of the extracted lignite seam was about 1m and tributary area ratio was 65%. Since Aichi Exposition linear motor car route passes through a highly urbanized area, the construction space is very limited. The total volume of grouting was 19000m3 and 990 drillholes (total length of drillholes 35.7km) were bored. The drillholes for outerwall and inner space had to be bored from the central pavement of the existing roadway (Figures 8 and 9). The filling materials Post-Mining 2005, November 16-17, Nancy, France 8 denoted as type A and type B are prepared separately at two plants and they were mixed just before grouting into the drillholes. Their compositions are given in Table 2. The distance between the plants and grouting locations was up to 630m. Figure 7. Geological cross section and locations of viaducts of the monorail and cavities. Table 2. Composition of filling materials (unit kgf/m3). Type A Filling Material (Plant A) Type B Filling Material (Plant B) Filling Required Clay Sand Special Water Special Water Retarder Materials Strength Scum Scum Sodium Hardening (kPa) Silica Agent Outerwalls 400 360 180 48.8 595 120 120 C x 0.5% Inner space 400 360 180 24.4 575 150 150 C x 0.5% Figure 8. Planned layout of drillholes for outerwalls and inner space filling works. Post-Mining 2005, November 16-17, Nancy, France 9 Figure 9.

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