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Rock strength and elastic behavior are important for foundations such as spread footings resting on rock and drilled shafts socketed into rock. In addition to traditional rock quality information; stiffness and failure parameters are helpful for design. MnDOT has previously used a low-capacity load frame for routine rock testing but this apparatus does not generate sufficient force for testing hard rock. The report provides a comprehensive suite of results from 134 specimens tested under uniaxial compression and 33 specimens tested under triaxial compression on a wide variety of rock; including hard rock; which frequently is of interest for high-capacity foundation systems. Thus; an economic benefit is realized if the strength of the rock is measured; as opposed to correlated with an index parameter; due to the potential to reduce foundation size and construction time. Information from the testing was used to expand the MnDOT database of rock properties and allow for improved designs based on accurate measurements of Young's modulus; uniaxial compressive strength; and friction angle.

A steel pipe-pile section; filled with concrete; was instrumented and tested under axial load. Two types of strain gages; resistive and vibrating wire; were mounted to the steel-pipe pile and checked by determining the known Young's modulus of steel Es. The steel section was filled with concrete and a resistive embedment gage was placed in the concrete during the filling process to measure axial strain of the concrete. The axial load - axial strain responses of the steel (area As) and concrete (area Ac) were evaluated. The stiffening of concrete; related to curing; was also studied. Assuming the boundary condition of uniform axial displacement; i.e.; equal axial strain in the steel and concrete; (Sf (Bzs = (Sf (Bzc = (Sf (Bz; the sum of the forces carried by the two materials; Fs + Fc; where Fs = (Sf (Bz * Es * As and Fc = (Sf (Bz * Ec * Ac; provides a reasonable estimate - within 3% - of the pile force. For the particular specimen studied (12 in. ID; 0.25 in. wall thickness); the stiffness of the composite section of steel and concrete was about three times larger compared to the steel section without concrete. Further; the concrete carried about 70% of the load; but the axial stress in the concrete; at an applied force of 150;000 lb; was less than 20% of the compressive strength of the concrete.