Stability conditions in an area located NW of Barcelona (Spain) are discussed. Here, several mass movements were observed, mainly affecting weathered Paleozoic slates. Many of these failures involved slopes cut along recent infrastructures: debris flows, wedge and plane failures, generally surficial, occurred more frequently. After a detailed geological and geomorphologic survey, geomechanic characterization was carried out, according to RMR and SMR classifications. This rating gave a prediction of slope behaviour, in fairly good agreement with the real observed one.
Stability numerical analysis was carried out for the main cut slopes, based upon the Limit Equilibrium Method. First of all, the deterministic factor of safety was computed using the mean values of parameters. After that, a simulation technique based upon the Monte Carlo Method was applied in order to obtain factor of safety distributions. The probability of failure was estimated as P(F<1).
Finally, results from deterministic and probabilistic approaches were compared. The effectiveness of different possible remedial measures was highlighted by means of a sensitivity analysis, which showed that the more important parameters in the study area are the geometrical ones (height, slope and failure plane angles). The final technical solutions adopted are briefly outlined. 相似文献
In late 2005 and early 2006, the WTW Operating, LLC (W.T.W. Oil Co., Inc.) #1 Wilson well (T.D. = 5772 ft; 1759.3 m) was drilled
for 1826 ft (556.6 m) into Precambrian basement underlying the Forest City Basin in northeastern Kansas. Approximately 4500
of the 380,000 wells drilled in Kansas penetrate Precambrian basement. Except for two previous wells drilled into the arkoses
and basalts of the 1.1-Ga Midcontinent Rift and another well drilled in 1929 in basement on the Nemaha Uplift east of the
Midcontinent Rift, this well represents the deepest penetration into basement rocks in the state to date. Granite is the typical
lithology observed in wells that penetrate the Precambrian in the northern Midcontinent. Although no cores were taken to definitively
identify lithologies, well cuttings and petrophysical logs indicate that this well encountered basement metamorphic rocks
consisting of schist, gneiss, and amphibolitic gneiss, all cut by aplite dikes.
The well was cased and perforated in the Precambrian, and then acidized. After several days of swabbing operations, the well
produced shows of low-Btu gas, dominated by the non-flammable component gases of nitrogen (20%), carbon dioxide (43%), and
helium (1%). Combustible components include methane (26%), hydrogen (10%), and higher molecular-weight hydrocarbons (1%).
Although Coveney and others [Am. Assoc. Petroleum Geologists Bull., v. 71, no, 1, p. 39–48, 1987] identified H2-rich gas in two wells located close to the Midcontinent Rift in eastern Kansas, this study indicates that high levels of
H2 may be a more widespread phenomenon than previously thought. Unlike previous results, the gases in this study have a significant
component of hydrocarbon gas, as well as H2, N2, and CO2. Although redox reactions between iron-bearing minerals and groundwater are a possible source of H2 in the Precambrian basement rocks, the hydrocarbon gas does not exhibit the characteristics typically associated with proposed
abiogenic hydrocarbon gases from Precambrian Shield sites in Canada, Finland, and South Africa. Compositional and isotopic
signatures for gas from the #1 Wilson well are consistent with a predominantly thermogenic origin, with possible mixing with
a component of microbial gas. Given the geologic history of uplift and rifting this region, and the major fracture systems
present in the basement, this hydrocarbon gas likely migrated from source rocks and reservoirs in the overlying Paleozoic
sediments and is not evidence for abiogenic hydrocarbons generated in situ in the Precambrian basement. 相似文献