Daniela Oliveira

Mixed face conditions are well known to present some of the most challenging environments for tunnel drives with closed shields, being extremely demanding for both the tunnellers and the machines (Thewes 2004). They arise when two materials with totally different behavior are present at the face. Some examples are the contact between a strong limestone and a weak shale (eg. Ottawa), a transported soil covering an eroded bedrock surface (eg. Kuala Lumpur, Vancouver), and stiff clay or till interfacing cohesionless sand or gravel. The underlying competent rock or stiff soil may have paleo-topography (valleys and hills) making predictive engineering and alignment selection challenging for a tunnel. In this case, however, the transition between the two materials will be well defined. A variant of mixed face conditions is the transitional face where there is a zone of composite rock or rock/soil with mixed components of variable strength and integrity. Such an environment would be a saprolitic interface between granitic bedrock and the in situ residual soils above, denominated changing ground, where the transition is not well defined (eg. Singapore, Brazil). Both of these types of ground conditions present known and often unexpected issues to mechanized tunnelling. A failure to anticipate these challenges in a project can result in tunnel delays, spiralling costs and ultimately temporary shutdown, leading most of the time to unnecessary claims. Common problems include: inability to maintain face pressure; ground loss; settlements; sinkholes; slow rates of advance; rapid tool wear; damage to tools, mixing arms and other parts of the TBM; frequent and long interventions; clogging; blow-outs. These challenges will be discussed with reference to projects in Brazil, Malaysia and Singapore. The paper addresses several questions related to the appropriateness of face stability, settlement and ground loss mechanisms, TBM selection, conditioning agents and other issues and potential solutions.

OLIVEIRA, D. G. G. de. Optical televiewer in boreholes – methodological proposal for implementation and application in underground work. 2015. 187 f. Dissertação (Mestrado) – Instituto de Geociências, Universidade de São Paulo, São Paulo, 2015.
The rock mass characterization is an essential step in engineering geology, providing the possibility of performance prediction of this massive due to numerous requests of any work to be done. In the case of urban underground works, such as subway lines, for example, geological and geotechnical characterization of rock masses is critical for identifying geological conditions linked to its stability, being effective in determining the geotechnical parameters that influence the design of massive excavation, whether by the conventional method (NATM), or mechanized, using tunneling boring machines (TBM).
Structural features such as foliation planes, folds, faults and fracture systems deserve special attention as they are associated with weakness zones in addition to all the geomechanical characteristics of the massif. In urbanized areas, such as São Paulo Metropolitan Region (RMSP), geological, geomorphological and occupation hinders exposure and identification of these features on the surface. In this context, new techniques have been developed to facilitate access to the above features. Among these new techniques is the optical televiewer (OPTV, OTV), which aim to obtain 360° images of the borehole walls, providing what might be considered a virtual core of a borehole.
The optical televiewer has been a technology introduced in Brazil since 2001, but only recently has been published in ABGE  Borehole Manual (2013), however, there are no specifications on the acquisition methodology, interpretation and application possibilities. This paper presents suggestions for the acquisition of these images, their interpretation and suggestions of applications in engineering works, taking as an example the design in projects of underground works of the São Paulo Metro.
In the specific case of urban underground excavations ground knowledge is essential, since its construction is an activity to be developed within the urban context, which could cause significant interference with the community, resulting in a high risk to neighboring population. Added to this is the fact that a little-known mass can result in oversized contention, increasing the cost of the work or undersized, increasing its risk.
As mentioned in ISRM (1978), as the descriptions of rock masses and discontinuities become more complete and unified, it will be feasible to design engineering structures in rock reducing the costs and increasing the reliability of the interpretation and extrapolation of the results.

Keywords: Optical televiewer, geological-geotechnical investigation, rock massif characterization, urban underground excavations.

The present paper introduces the main geological and geotechnical aspects of Line 4: Stretch South from Rio de Janeiro Metro system. Crossing several geological scenarios, from very good rock to soils formed in transitional environment, the stretch will be excavated with Tunneling Boring Machine (TBM) with a diameter greater than 10 meters. Having as main reference more than 250 boreholes, the present paper discusses and introduces the main aspects from geological units, as well as geological geotechnical cross sections developed to the detailed design. From the different materials that will be excavated by the TBM, the two types of gneisses (Augen and Kinzigitic) and the compact to very compact sand are the most representative.

New technologies have been continuosly developed to help in rock mass investigation, contributing to increase the understanding of the geological and geotechnical characteristics. In the case of São Paulo Metro (like in other major cities) the urbanization conditions jeopardize the access to outcrops, which preclude obtaining precise information of in situ rocks and its discontinuities. One alternative to overcome such problem is the use of borehole televiewer logging that reproduces a “virtual borehole core”, and provides important information on the geomechanical characteristics of the rock mass, since it provides structural data that helps in the geological and geotechnical model understanding.
This paper presents an evolution on the proposal presented by Oliveira et al., 2012, taking into account the experience acquired on the analysis and description of several boreholes televiewer logs in projects of the São Paulo Metro. Therefore, a technical specification is proposed in order to establish the technical requirements for the application of the boreholes televiewer technique and presents a methodology to describe the geologic-geotechnical features presented in the logging.