A snow-plough blade group having a variable snow removing surface and comprising: a first snow-removing blade; a second snow-removing blade; a first support bearing the first snow-removing blade and the second snow-removing blade; the second snow-removing blade being mobile with respect to the first support between a first position, in which the first snow-removing blade and the second snow-removing blade identify a first snow-removing surface, and a second position in which the first snow-removing blade and the second snow-removing blade identify a second snow-removing surface which is larger than the first snow-removing surface; a second support which is hinged to the first support and can be borne by a work vehicle; a first hydraulic cylinder which is connected between the first support and the second support for orientating the first support with respect to the second support; characterized by further comprising: a discharge of liquid in overpressure; bypass valve means which connect the first hydraulic cylinder with the discharge of liquid in overpressure; said bypass valve means being configured such that, when the pressure of the liquid contained in the first hydraulic cylinder exceeds a threshold pressure value, due to a lateral impact on the second snow-removing blade, the bypass valve means place the first hydraulic cylinder in liquid communication with the discharge of liquid in overpressure, thus modifying the orientation of the first support, of the first snow-removing blade and of the second snow-removing blade with respect to the second support, for absorbing lateral impacts; a sensor which detects a position assumed by the second snow-removing blade with respect to the first support; the bypass valve means varying the threshold pressure value according to the sensor reading. a first snow-removing blade; a second snow-removing blade; a first support bearing the first snow-removing blade and the second snow-removing blade; the second snow-removing blade being mobile with respect to the first support between a first position, in which the first snow-removing blade and the second snow-removing blade identify a first snow-removing surface, and a second position in which the first snow-removing blade and the second snow-removing blade identify a second snow-removing surface which is larger than the first snow-removing surface; a second support which is hinged to the first support and can be borne by a work vehicle; a first hydraulic cylinder which is connected between the first support and the second support for orientating the first support with respect to the second support; characterized by further comprising: a discharge of liquid in overpressure; bypass valve means which connect the first hydraulic cylinder with the discharge of liquid in overpressure; said bypass valve means being configured such that, when the pressure of the liquid contained in the first hydraulic cylinder exceeds a threshold pressure value, due to a lateral impact on the second snow-removing blade, the bypass valve means place the first hydraulic cylinder in liquid communication with the discharge of liquid in overpressure, thus modifying the orientation of the first support, of the first snow-removing blade and of the second snow-removing blade with respect to the second support, for absorbing lateral impacts; a sensor which detects a position assumed by the second snow-removing blade with respect to the first support; the bypass valve means varying the threshold pressure value according to the sensor reading. a discharge of liquid in overpressure; bypass valve means which connect the first hydraulic cylinder with the discharge of liquid in overpressure; said bypass valve means being configured such that, when the pressure of the liquid contained in the first hydraulic cylinder exceeds a threshold pressure value, due to a lateral impact on the second snow-removing blade, the bypass valve means place the first hydraulic cylinder in liquid communication with the discharge of liquid in overpressure, thus modifying the orientation of the first support, of the first snow-removing blade and of the second snow-removing blade with respect to the second support, for absorbing lateral impacts; a sensor which detects a position assumed by the second snow-removing blade with respect to the first support; the bypass valve means varying the threshold pressure value according to the sensor reading.