a tunnel excavator has a substantially tubular shield having rotatably mounted on one end a motor - driven cutting disk rotatably carrying a multiplicity of roller cutters . the shield is comprised of a head section having front anchors in addition to the cutting disk , an inner section telescopically nested in the head section and constrained to only axial displacement relative to the same , and a tail section having rear anchors and coupled to the inner section for both bending and rolling movements relative to the same . hydraulic push jacks act between the head and tail shield sections for advancing the shield . a pair of hydraulically independent antirolling jacks are connected between the inner and tail shield sections so as to enable the tail shield section , which is anchored during excavation , to bear against the rolling of the head shield section .