Shield type hydraulic tunnel boring machine

A shield type hydraulic tunnel boring machine having means for detecting an occurrence of excess excavation due to accidental collapse in tunnel face ground apt to occur during tunnel boring works through soft and unstable ground and for further determining the location, shape, scale and the like of such excess excavation occurred is provided. The means comprises optimumly a plurality of ultrasonic wave transmitting and receiving devices disposed as spaced at least along a radial line on the front surface of a substantially disk shaped rotary cutter head of the machine for transmitting ultrasonic waves in forward and upward directions and receiving reflected waves from tunnel face ground wall, a wave transmission and reception controlling means, and a transmission-to-reception time interval detecting means for determining distances from the respective wave transmitting and receiving devices to the ground wall. The wave transmitting and receiving devices include ones oriented in diagonally angled directions with respect to the axial line of the machine shield to cover diagonal upward range in front of the cutter head, detected time interval values of which are further modified depending on the diagonal angles of these devices to determine the heights of the ground wall in the diagonally upward directions. The respective detected values of the plurality of the devices are scanned to determine the location, shape, scale and the like of the excess excavation.