IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 _______________________________________________________________________________________ Volume: 03 Issue: 10 | Oct-2014, Available @ http://www.ijret.org 61 ASSESSMENT OF CYCLIC TRIAXIAL BEHAVIOR OF SHIWALIK SANDSTONE Sana Zafar 1 , K.S.Rao 2 1 Assistant Professor (Adhoc), Civil Engg, Dept, M.M.M.U.T, Gorakhpur, U.P, India-273010 2 Professor, Civil Engg, Dept, IIT Delhi, India-110016 Abstract The mechanical properties of rock under dynamic conditions are of great importance in which the fatigue strength of rock plays a vital role. This study represents the effect of variable frequency on dynamic properties of Shiwalik Sandstone. Shiwalik sandstone samples were collected from the powerhouse location of UJH Multipurpose Project, Jammu and Kashmir . “Prediction of fatigue life of Shiwalik Sandstone under varying frequency” was done by conducting Cyclic Load test in Uniaxial and Triaxial condition. Cyclic testing was done at three frequencies i.e. 1Hz, 2Hz and 3Hz[2] and at two confining pressures of 5 and 7 MPa[6]. The S-N curve[4] were plotted at different frequencies in uniaxial condition as well as in triaxial condition to explain the fatigue behaviour of soft rock (Shiwalik Sandstone) It has been observed that loading frequency as well as confining pressure has a significant effect on the fatigue life of the rock. As the frequency increases from 1 Hz to 3 Hz the fatigue stress increases. And in triaxial condition as the confinement increases from 5 MPa to 7MPa the number of cycles at failure increases. Keywords: Fatigue life, Shiwalik sandstone, Cyclic load test, Amplitude, Frequency, Base load, Waveform --------------------------------------------------------------------***------------------------------------------------------------------ 1. INTRODUCTION The mechanical behavior of rock subjected to cyclic loading is important for rock engineering design and construction like drilling and blasting, underground openings, support assessment, resource and waste deposition, working of big machineries, explosions, earthquakes pavements etc. Cyclic loading causes deterioration of rock strength which leads to fatigue failure of rocks and this type of loading causes the failure of the underground structures at a lower fatigue strength. Deterioration of rock under cyclic loading is termed as Rock Fatigue. The maximum applied stress at which rock can withstand an infinite number of cycles without destruction is termed as Fatigue Stress. The stress level at which the failure takes place is Fatigue Strength and the number of cycles is known as Fatigue life of a rock. [7] Fatigue properties of geologic materials are highly dependent on the rock type and the parameters of the cyclic loading like loading frequency, amplitude etc. [1-2] So the designer of a dynamically loaded structure must have adequate knowledge of the cyclic loading to design a stable structure against fatigue failure. Knowledge of fatigue characteristics could also help the designer to predict the fatigue behavior of the structure and take preventive measures. So proper attention should be focused on the dynamic properties of rocks with the goal of understanding their dynamic mechanical features under different loading conditions. The objective of the study is to analyse the effect of frequency on dynamic properties of Shiwalik Sandstone in cyclic uniaxial loading condition and to study the effect of confining pressure on dynamic properties of Shiwalik Sandstone in cyclic triaxial condition 2. EQUIPMENT AND TEST SCHEME 2.1 Rock Samples The present work deals with laboratory investigation of geotechnical properties and parameters of „Shiwalik Sandstone‟. The samples have been collected from the powerhouse location of UJH Multipurpose Project, Jammu and Kashmir (Fig.1) Fig. 1: Location of samples collection (at Powerhouse, UJH Multipurpose Project, J&K)