M. A. C. de Sá, J. de D. G. dos S. Junior, D. V. S. Resck, E. A. B. Ferreira, and C. A. B. Franz, “A dynamic minipenetrometer for assessment of soil mechanical resistance in undisturbed soil samples”, PAB, vol. 42, no. 11, pp. 1659–1662, Nov. 2007.