Using the laboratory-modeling method developed at the All-Russian Scientific-Research Institute of Engineering Physics, group explosions for the creation of long trenches (canals) are investigated. The minimum canal cross section and its other dimensions are obtained as a function of the basis parameters of the explosion. Conditions for the creation of canals with minimum fluctuation of the profile over the trench length are found, criteria of economic efficiency are derived, and a method is given for choosing the explosion parameters so as to create a canal of specified cross section with minimum expenditure of explosives. The results of the model experiments are compared with the trench dimensions in the Baggi (USA) and T-II (Russia) nuclear explosions.