The object of this paper is to describe the construction and operation of a triaxial apparatus for testing soils containing material passing the 3-in. sieve size. Also, the presentation of a few typical results obtained on various types of soil will be made. The development of this type of equipment was accelerated, late in 1948, by the specific need for investigating the shear strength characteristics of foundation material for the Corps of Engineers' Folsom Project in California. This soil varied from gravel to clayey sandy gravel. Since, in general, the amount of clay present was of a significant amount, it was necessary to determine the shear resistance of the minus 3-in. portion of the material, in order to bring out the effect of the very plastic fines on the relatively high shearing resistance of the gravel. A second, and equally important, need for equipment of this magnitude was the testing of gravel without plastic fines under conditions of high lateral pressure. It was, therefore, necessary to devise equipment which would accommodate material of this size. No attempt was made to revolutionize the present equipment generally used in testing by triaxial methods the shear characteristics of soil; rather, an effort was made to adapt current ideas to new equipment capable of testing large soil specimens. Wherever possible, standard stock items were used in preference to prefabricating special parts, so that the unit could be made with a minimum of expense. Where commercial products are referred to by name in this paper, it is only for the purpose of clearer description. Competitive products can, in most cases, be satisfactorily substituted.