CREEP IN THE MANNENABSTRACT:INTRODUCTION:http://blogs.agu.org/landslideblog/2014/11/04/mount-mannen-rockslide-1/http://www.ngu.no/upload/Publikasjoner/Rapporter/2014/2014_031.pdfhttp://discovery.ucl.ac.uk/18706/1/18706.pdf1.1Mount Mannen is a unstable rock slope 1215 m above Rnningen in the Romsdal Valley located in Norway. It has the potential of creating a rock avalanche of 2-20 million m3 with catastrophic consequences for houses and infrastructure in the valley, in particular as a landslide dam may be formed, including upstream and downstream flooding. The rockslide behaved in unpredictable manner. The bedrock consists of Proterozoic sillimanite-bearing gneisses with inherited structural weaknesses from the tectonic deformation. Specifically, the metamorphic foliation surfaces are prone to be reactivated where favorable orientation occurs in regards to the gravitational forces (Saintot et al. 2011)

1.2 Creep is name applied to slow deformation of solids under small loads acing over long periods of time.

1.2.1 stages of creepCreep in rocks is epressed as a function of strain and time . general form of creep function can be expressed as /Jaeger and Cook 1976/: = 1(t) + v2t + 3 (t)where, is the total creep strain; 1(t) is the primary or transient creep, v2t the secondary or steadystate creep, and 3(t) the tertiary creep or accelerating creep which occurs just prior to failure of the sample. The general form of these three stages is illustrated in Figure 1-1.

Fig 1.1five components of a constant load test in strain time spaceRef: http://maps.unomaha.edu/Maher/GEOL3300/week6/rheology.html

elastic response: immediate and recoverable. primary creep: decelerating strain rate. secondary creep: constant strain rate (viscous behavior). tertiary creep: accelerating strain rate that leads to failure. brittle failure.1.2.2 Empirical creep functions The most common empirical creep functions are the power law: 0 < n < 1 and the logarithmic creep function: = A ln t in which A and B are constants . All empirical creep functions can be shown to be related if they are expressed in terms of creep strain rate 0 M 1Steady state secondary creep corresponds to M = 0 and & = C = constant. If 0 < M < 1, the power law creep function (Equation 1-2) is obtained. M = 1 gives the logarithmic law (Equation 1-3). Values for M less than zero imply tertiary creep.1.2.3 Rheological modelsThe simple rheological creep model is Kelvin model it considers spring and dashpot in parallel , mainly used for modeling primary creep and time recoverable deformation .This model works on time frames of thousands of years for earthly deformation conditions]where s is the stress and t is time. K is the spring constant and h is the dashpot viscosity. Note that the Kelvin model does not include any plasticity: some time after the load has been removed the strain will be fully recovered.