1. Laboratory investigations and full-scale observations showed the weak strength and high deformability of diatomaceous clays. The full-scale observations showed in connection with this that in the case of short cuts for the given tunnel section these clays remain stable for 24–36 h. Thus, it was possible to drive the tunnel in short two-meter cuts without bracing with the construction of 2-m-long concrete lining rings. 2. Full-scale measurments of the earth pressure with dynamometric sections showed that the distribution of the pressure in the diatomaceous clays is close to uniform over the tunnel contour. 3. The magnitude of the active pressure under the given geologic conditions is many times smaller than in a calculation for a hydrostatic stress field on the basis of the weight of a earth column above the tunnel.