Rock Load Estimation for Underground Structures

Two equations are proposed for the estimation of rock loads on underground structures. The first equation is an equation for the equivalent rock load on shallow underground caverns based on the rock tunneling quality index and the scaled crown span at the given cavern location. The second equation proposes a method for estimating the horizontal stress ratio in the rock zone for cut and cover subway stations based on the jointing patterns of the rock at the site. The actual rock loads on both types of structures can range from zero to very high based on the localized geotechnical conditions. Good practice in the design of underground structures requires that equations for rock loads can effectively determine a close estimate of the rock load based on the limited geotechnical data often available.