ABSTRACT: Contrasting geophysical, rock mechanics and rock engineering experience in basalts, caused by either exceedingly low or extremely high stress are described, from projects in the USA and Brazil. The first involves a nuclear waste characterization project in Hanford basalts in the USA, and the second describes, in much more detail, stress-fracturing problems in numerous large tunnels at the 1450 MW Ita hydroelectric project in SE Brazil's basalts. Particular phenomena that were noted, include linear stress-strain loading curves when columnar basalt is loaded horizontally, and a k 0 value reaching about 20–25 at Ita HEP.

ABSTRACT: El Hierro island, 0,2 million years old, is the youngest of the Canary Islands. Since it was recognized UNESCO Biosphere Reserve in 2000, the road infrastructure to be planned has to cause a minimum impact on the landscape of the island. This applies to El Verodal Tunnel to be built in the NW side of the island. Due not only to orography but also to administrative constraints, site studies are scarce. Moreover, the implementation of the existing rock mass classifications for volcanic rocks makes the design of the tunnel harder due to the great variability shown by these materials.

ABSTRACT: An economical and environmentally-friendly solution to stabilize jointed vertical rock slopes in works of improvement and cross section widening of a local road section in Gran Canaria Island (Spain) is presented in this paper. Due to the mountainous relief of this territory, this road cross over an extremely narrow section between two deep cliffs with vertical rock slopes on jointed phonolitic ignimbrites. The structural solution involves the construction of traditional gravity retaining walls with passive fully-grouted steel bar anchorages within its foundation. The rock mass nailing under the foundation of the retaining walls and even the adjacent rock slopes is also designed. This system combines traditional constructions of high simplicity with modern techniques of rock reinforcement.

ABSTRACT: Given the conditions found along the entire expressway that connects the city of Machico and the village of Caniçal, on the Madeira Island, specifically the topography, the urban occupation and the highly unfavorable geological-geotechnical conditions, characterized by the existence of slope deposits of significant depth with very poor resistance characteristics, different solutions had to be used for the retaining structures, specifically gravity walls, reinforced earth retaining walls with jet-grouting foundation, anchored pile walls and soil nailed walls and slopes.

ABSTRACT: This work presents a back-analysis of a tunnel section based on measured convergences values. The tunnel, located in La Palma Island, was excavated in basaltic pyroclastics. The analysis used FLAC 2D and shows the excavation and supporting of the tunnel along with other phases during construction. With this analysis we aimed to obtain realistic values of the geotechnical parameters of pyroclastics. However, its accuracy depends on a great number of variables. Finally, modulus of deformation and parameters C M and Φ M of pyroclastic were estimated. These estimated values are not the only possible solution given the available data, but they represent realistic values in the authors'opinion.

ABSTRACT: Chillida's visionary artwork to create a large Space in the Tindaya Mountain represents a big technical challenge. On the one hand, dimensions of the span and flat profile of the cavern roof are unique in underground engineering. On the other hand, the transmission of the artist's idea and the realization of an aesthetic concept combining art, technique and nature in a natural way will require an innovative support solution.

ABSTRACT: The Socorridos pumping station and water storage tunnel are located at Madeira Island, Portugal, and are part of a system conceived to reutilize the water flow from the Socorridos hydroelectric plant. This facility includes an underground cavern with 26 m high, 12 m wide and 44 m length, and a tunnel 1250 m long with a storage capacity of 40,000 m 3 . The rock mass at the site is of volcanic origin with most of the excavation performed in a mass of volcanic breccia and basalts but with consolidated alluvia recent deposits located in the roof arch of the cavern. A description of the main characteristics of the project is presented and the results predicted by the design are compared with the values given by the instrumentation.

ABSTRACT: Convergence-confinement is one of the most popular methods that is applied for analyzing the interaction of a circular opening in rock masses. It is assumed that circular tunnel excavated in a continuous, homogeneous, isotropic, initially elastic rock mass subjected to a hydrostatic stress p 0 . Selecting appropriate failure criteria is very important in the analysis since it affects on plastic zone and on the resulted displacement and stress field around the opening. Some closed-form solutions have suggested for the ground reaction curve, although they are driven based on elastic-perfectly plastic or elastic-brittle-plastic models of rock mass behavior. Brown et al. (1983) proposed a stepwise procedure based on Hoek-Brown criterion to solve stress and displacement around the circular opening for elastic-strain softening model of rock mass behavior. A similar stepwise procedure was extracted in this study for Mohr-Coulomb criterion. Finally a sensitive analysis was implemented for Mohr-Coulomb and Hoek-Brown criteria in respect to their parameters. By comparison of the relative displacement caused by changing strength parameters in Hoek-Brown and Mohr-Coulomb criteria, it can be concluded that Mohr-Coulomb criterion is more sensitive in respect of variation of strength parameters of rock mass than Hoek-Brown.

ABSTRACT: In the last two decades a new fundamental road network was undertaken at Madeira Island. Due to the vigorous relief of the Island, the great heterogeneity, the structural and lithological complexity of volcanic rock formations and to the land occupation, tunnels became dominant and a large spectrum of innovative structural tunnel solutions were developed. The objective of this paper is to give a global vision of the importance of this group of infrastructures, focusing in the new fundamental road network evolution and construction of road tunnels at the island and in the conception and design aspects, along with the description of the geological-geotechnical conditions, primary and secondary lining, phased construction and monitoring.

ABSTRACT: This paper presents the work done to recovey the historical Fuente Santa spring, well known at Middle Age due to its miraculous medical effects. The spring was buried by San Antonio volcano eruption in 1677, with debris, cinders and lava flows. A gallery was recently excavated under extreme and difficult natural conditions, a total lack of stability with granular materials involved. The direction of the axis of the gallery was initially unkown.

ABSTRACT: Due to the existing conditionings for the implantation of the different areas that comprise Cabo Girão Tourist Resort, at Madeira Island, namely the vigorous relief and the geological-geotechnical conditions, it was necessary to conceive an important group of retaining structures, using different solutions, varying from gravity and semi-gravity cyclopean concrete structures to reinforced concrete walls and soil nailed walls or nailed slopes. This paper presents the conception of the project in its different stages and the main activities developed under the scope of the special technical assistance provided during the execution phase.

ABSTRACT: The Machico-Caniçal Expressway, 8 km in length, is part of the Madeira Island's new development program, which connects Funchal city to Caniçal village via a continuous expressway along the island's southern coast. This expressway crosses an extremely mountainous region affected by the existence of two very heterogeneous geological volcanic complexes, generally covered by unstable slope deposits or by thick alluvial deposits, leading to the construction of a wide range of civil engineering Works. This paper presents the main aspects related with the design and construction of six double tunnels along the referred expressway, as well as a number of safety aspects related to these tunnels.