This paper describes the application of the SRC rockmass classification system to tunnels under high horizontal tectonic stress excavated in weak rocks. The analysis was performed on 25 tunnels in Spain and Italy, for which it was found that much heavier supports than those estimated by the RMR index were required. SRC and RMR indices and other relevant geomechanical data were obtained during the site investigation and construction stages. Data corresponding to in situ stress measurements, analysis of tectonic structures and instability problems arising during construction were used to asses the state of stress.
The relationship between tunnel section convergence and the SRC and RMR indices was also analysed. Support measurements based on SRC and RMR classification were compared with those actually used during construction. These analyses indicate that for most of the tunnels examined, supports estimated using the SRC were much closer to those actually installed than those predicted by the RMR index.
Based on the case histories presented, the factors mainly contributing to deformability and consequently to assessing support measurements were: high horizontal tectonic stress, low strength of rocks, overburden thickness and structural anisotropy related to tunnel axis orientation. According to these factors, the tunnels investigated were classified as three types. Tunnels classed as type I were those of low overburden thickness under high horizontal tectonic stress excavated in low strength rocks. The supports installed for these tunnels were much heavier than those predicted by the RMR index, being more in line with those indicated by the SRC index. The type II tunnels had thick overburdens and showed similar stress and strength conditions to the former. The supports installed were practically those foreseen by the SRC index, appreciably differing with respect to the RMR index. Finally, tunnels included in the type III class were those under low to moderate tectonics stress, irrespective of overburden thickness. These tunnels gave rise to RMR and SRC indices that provided acceptable results. 相似文献
Mudstone experience periodic swell and shrink behavior due to alternate wetting and drying cycles at arid and semi-arid regions
with distinctive seasonal changes. This paper examines the influence of cyclic wetting and drying on swelling strain and swelling
pressure to simulate the behavior of such rocks under heavy structures (such as building foundations) and behind the stiff
support systems (such as concrete linings). Mudstone samples from Bakhtiari formation of Masjed-Soleiman region in south west
of Iran were chosen to perform the laboratory tests. The swelling strain under different dead pressures and also swelling
pressure under oedometeric condition were measured over time. The maximum swelling strain and pressure increased with each
cycle but it had a bound. Increasing the number of wetting and drying cycles reduces the time required to reach ultimate swelling
of mudstone. This is a very important conclusion which helps to determine ultimate swelling behavior in a faster way as opposed
to performing standard swelling tests for very long periods. The laboratory’s results are also in good correspondence with
field measurements. 相似文献
Only few (six) focal mechanism, in CMT Catalog, have been so far known for intraplate shallow events in the Andean chain close to Chile–Argentina state border at latitudes ∼35° S. We add two more mechanisms, depths and moment magnitudes by carefully analyzing full waveforms of weak events recorded by broad-band stations of the Chile Argentina Geophysical Experiment (southern profile). The moment magnitudes of both events (Mw = 3.6 and 3.7) are lower than the duration magnitudes (Md = 4.0 and 4.29) reported by NEIC. The source depth, constrained by waveforms for one of the studied events (5.5–8.5 km) seems to be considerably shallower than the hypocenter depth located by means of arrival times (∼20 km). The waveform analysis was complemented by first-motion polarities which resulted in an uncertainty assessment of the focal mechanism. Event 1 (2001-11-03) has a strike-slip mechanism with a small normal component and almost vertical nodal planes in the north-south and east-west directions. The north-south nodal plane could be related to the Calabozos faults system. Event 2 (2002-02-16) has a strike-slip mechanism with a small thrust component. The latter event (its subhorizontal nodal plane) could be associated with the El Diablo-El Fierro fault system. Dextral strike-slip solutions are consistent with recent studies in the area. 相似文献