A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering of the Asian Institute of Technology, Bangkok, Thailand

Thesis (M.Eng.) - Asian Institute of Technology, 1978

Three series of unconfined compression tests were carried out on rectangular prismatic specimens (25.0xl2.Sx7.S cm) made out of different combinations of gypsum, cement and sand, which were incorporated with planar artificial flaws to study the effect of number of randomly distributed flaws on strength, effect of length of artificial flaws on strength and initiation and propagation of fractures of rock like materials under unconfined compression conditions. All the specimens were tested for 28 days strength. The results showed an increasing number of artificial flaws with a constant length decreases the compressive strength as well as elastic modulus of rock-like materials. Similar relations were obtained for an increasing length of artificial flaws with a constant number of artificial flaws. Nevertheless, strength and elastic properties of these materials showed unique relationships with the parameter defined as flaw density which depends upon the number and length of incorporated flaws. Experimental results are in very good agreement with predicted values obtained adopting strain energy concept at low artificial flaw densities. However, deviation of predicted values from experimental results were obtained at high flaw densities which is considered to be mainly due to mutual stress interference of the flaws. Experiments carried out on specimens made out of gypsum plaster and neat cement showed initiation of fractures always originated from tips of potential flaws and fracture propagation occurred in the direction of maximum compressive stress.