Degradation of geotechnical properties of rock masses in engineering time

2001: Degradation of geotechnical properties of rock masses in engineering time : Tg22, Tg23, and Tg3 / by Binod Chapagain. - Enschede : ITC, 2001. - 109 p. ; 30 cm. - ITC-MSc thesis. ABSTRACT, supervisor(s): Huisman, thesis availability: ITC Library

ABSTRACT

Rock masses undergo degradation of their geotechnical properties in time due to weathering and erosion. Knowledge of the degradation of the properties, in particular in engineering time, is useful in the design and construction of safe slopes. Virtually no research has been carried out in this field. It has been decided to establish relationship of geotechnical properties of rock masses with exposure time of slopes and make an inference whether any indication of degradation of these properties is found in engineering time. For this purpose three rock formations were selected from the Falset area of Spain. These rock formations are Tg 22 (Middle Muschelkalk), Tg 23 (Upper Muschelkalk) and Tg 3 (Keuper). The data which was collected by the ITC and TUD students during 1996 – 2000 fieldworks was used in the analysis. The three rock formations were divided into seven geotechnical units. The SSPC system was utilized for the calculation of geotechnical properties, C and ф of the rock masses. The calculated rock mass properties values were plotted against the time of exposure of the slopes. Analysis was done for each geotechnical unit separately. It is found that soft sedimentary rocks such as ‘Red clay’ and ‘Gypsum’ of the Tg 22 and ‘Clay’ of the Tg 3 did not show any sign of degradation of the properties in engineering time. Similarly, the geotechnical units, which are composed of limestones, ‘bedding spacing > 50 cm’ and ‘bedding spacing 10 – 40 cm’ of the Tg 23 did not provide any indication. However, the geotechnical units ‘bedding spacing < 10 cm’ of the Tg 23 and ‘limestone / dolomite’ of the Tg 3 showed indication of reduction of the properties in engineering time. To improve the reliability of the results it is recommended to verify the data going into the field and also collect information from the slopes which were exposed in different times in the past.