Abstract: Based on orthogonal test, the softening mudstone interlayer effected by three factors, i.e. temperature, brine density and immersion time, is studied. The extremum difference analysis and variance analysis are respectively applied to analyzing the results of the test. Any two factors are the binary liner regression; the relative importance ratio according to the standardized regression coefficients for the uniaxial compressive strength and elastic modulus of mudstone interlayer is used to build judgment matrix; analytic hierarchy process is used to calculate weights of various factors. The results show that the temperature and the immersion time play a decisive role on the softening process of mudstone interlayer; and the weights of analytic hierarchy process are more than 98%. The greatest influencing factor is immersion time whose weight is about 80%. The change of brine density has hardly any effect; therefore it can be neglected in the practical project. With the immersion time extending and the temperature increasing, the cracks in mudstone interlayer are gradually intruded into solution; meanwhile, the uniaxial compressive strength and elastic modulus show a decreasing trend. In view of the insignificant role the brine density plays in the whole experiment, only temperature and immersion time are taken into consideration to establish the equations.

Key words: mudstone interlayer, orthogonal test, uniaxial compressive strength, elastic modulus, analytic hierarchy process