The purpose of this paper is to present some of the technical and economic aspects related to the construction of an underground reservoir, currently in progress, for the storage of drinking water to supply the cities of Santos and Sao Vicente, located in the State of Sao Paulo, Brazil. Basically two alternatives are analised to solve the water storage problem, to wit: conventional storage of reinforced Concrete and tunnel excavated in rock. The various factors to be considered for each one of the solutio ns are stated and the conc1usion arrived at is tha t the tunnel storage alternative offers greater advantages from a technical as well as an economic point of view. Some aspects related to construction methods used in tunnel excavation works are also delved into. INTRODUCTION The municipalities of Santos and Sao Vicente are communities located on the coast of the State of Sao Paulo, some 70 kilometers away from the city of Sao Paulo, and constitute a sizeable tourist center subject to great population fluctuations. Several alternatives were examined in order to solve the water deficit, one of them being the construction of conventional reinforced concrete reservoirs on hills existing in the target area. However, this solution presented several unfavorable factors, amongst which were the following: limited availability of adequate locations for the construction of reservoirs, varying from 40 to 50 meters above sea level, near the consumer centers and with not too steep topography; areas subject to instability where several land slides have already occured, which would consequently require slope stabilization of great cost. Given these difficulties, another unconventional solution was examined which has seldom been used in Brazil, to wit. the storage of water in tunnels excavated in rock. This alternative presents some very significant advantages, amongst which the following can be pointed out: the project is situated on Sta. Tereza hill which has a geological formation which lends itself to exacavation, as well as being located in between the two consumer centers; the portal areas are situated in uninhabited locales, which makes expropriation much easier; The number of reservoirs is reduced to only one, however this one has a large storage capacity; consequently both operational and maintenance costs are cut down; there will be a reduction of the number of areas which must be expropriated, as well as less earthmoving, fewer access roads, less slope stabilization and a shorter extension of inlet, outlet and discharge pipe lines which must be installed; greater operational flexibility will be obtained with the interconnection of the Santos and Sao Vicente water systems, thereby increasing the dependability of the overa 11 system; there will be minimal disturbance of the nature of the hill, thus avoiding appreciable alterations in the ecological balance of the existing ecosystem; - the cost of carrying out the job will be much lower than that of a conventional solution.

The largest sewage treatment plant in Norway is being constructed underground at Bjerkås, 30 km south of Oslo. The plant will serve 300 000 persons and is designed to treat a dry weather flow of 3.0 m3/s. The main reason for the subsurface location is environmental. The plant is being placed in 11 parallel caverns of 16 m span with 12 m wide pillars between. The rocks in the area are Cambro-Silurian shale and nodular limestone. The conditions revealed by excavation were very similar to those predicted from the combined results of surface mapping, drill core analyses and seismic measurements The support is systematic bolting and shotcrete, partly mesh reinforced. Some injection work has been undertaken to prevent inflow of water. The rock mass underlying an industrial area nearby is fed by water through several boreholes to prevent lowering of the ground water table in the overlying clay. INTRODUCTION Norway has long traditions of building underground. Our hydro-electric projects make up the corner stone of Norwegian expertise regarding major subsurface constructions. This technology has been converted into use for several other purposes: air raid shelters combined with sport arenas, subway systems, oil storages, general storage and public utility facilities such as water and sewage treatment plants. Although representing a rather unique feature it was not out of the ordinary when the communities of Oslo, Bærum and Asker in 1976 decided to go ahead and build a large regional sewerage facility consisting of 40 km full-face bored tunnels and a mechanical/chemical treatment plant excavated into the hill of Bjerkås in Asker, 30 km southwest of Oslo - adjacent to Oslofjord (Fig.l). During the early surveys - and the preliminary reports - several alternatives were considered - also surface locations. The main reason for choosing the subsurface alternative was of an environmental nature. A surface plant was considered less expensive. However, the difference was eventually considerably less than originally expected. The Bjerkås area was finally chosen for the plant mainly because of political considerations. The rocks were estimated to be of poorer quality here than at the other possible localities, but Bjerkås was already an established industrial area with few private homes. GEOLOGY The project is situated in the geological formation called the Oslo Graben. The bedrock at Bjerkås consists of sedimentary rocks of Cambro-Silurian age, mainly shale and limestone, cut by some Permian dykes. The Bjerkås area is a hill about 70 m high. Due to limitations of space the orientation could not be chosen in the most favorable direction and the minimum rock cover is approx. 15 m. Geological mapping showed that the northern slope of the hill consisted of nodular limestone, in the southern slope there was shale. Seismic refraction measurements showed velocities of about 5000 m/s in the nodular limestone and 2500 - 4000 m/s in the shale. Some crushed zones gave 2000 - 3000 mis, the same as a near surface weathered zone of about 10 m thickness.

This lecture is demonstrating a new technique of supporting a shaft bulge-out used the first time when constructing shaft bulge-out of coal mine General Blumenthal in Germany. It differs from convential design by a step by step supporting of the newly exposed rock face by shotcrete, supporting rings, and rock bolt anchoring fixed to the rock throughout by GD-Topac anchoring system. INTRODUCTION The coal mining enterprise General Blumenthal in Germany intends to drive a 6.5 m diameter tunnel between two shafts. It is foreseen due course that a full face tunneling machine shall commence the drive in the shaft number 8 at a depth of about 1000 m. In preparation of the scheme the shaft had to be widened from 7.6 m diameter to 15 m. Further requirements are two wing-like excavations necessary, projecting 17 m laterally from the bulge-out on opposite sides. The central portion of the configuration is 21 m high, whereas the recesses have a threshold height of 13 m. In the vertical direction the total alteration of the original shaft measures 31.5 m overall. About 4800 cubic meters of rock had to be removed. The sprayed concrete lining of the exposed rock covers an area of 1700 square meters approximately. THE NEW DESIGN CONCEPT The Department for Construction Methods and Construction Management of the Ruhr- University Bochum was commissioned to proceed with the consulting engineering work for the scheme which is perhaps the first of its kind. It differs from the conventional design concept through the stipulation that the newly exposed rock face should be lined with step by step sequences of sprayed concrete support rings and anchor supports. Traditionally there would have been first the drilling and blasting programme to ensure that the new shaft bulge-out has the correct shape. Then either brick lining or steel arches and concrete panels would be built in as necessary. The new concept, by contrast, is a noteworthy break of the local mining traditions. SINGLE SHELL SUPPORT SYSTEM As a result of technical consultations with the Local Mining Authority a single shell lining system was approved. This decision was favorably influenced by the outcome of an investigation programme for this depth and previous mining operations on similar conditions which had shown that the rock was strong and had resisted convergence movements. The approved shaft bulge-out support construction, by contrast, has now been installed in the form of a single shell lining of 200 to 250 mm thick shotcrete. It has steel bar reinforcements, cut and bent on site. At the transition edges between the shaft bulge and the lateral extensions the reinforced concrete thickness has been doubled to 400 mm and attached to the rock at intervals of 1 m by means of 5 m long anchors. The other anchors of the support system are 3.5 m long and have been installed in a pattern of one anchor per square meter due to the safety regulations of the Mining Authorities.