Trench wall grab apparatus for producing a trench in the ground, having: - a support device and - a trench wall grab which is mounted on the support device so as to be substantially vertically adjustable, wherein the trench wall grab has a grab frame at the lower end of which there are arranged two grab buckets which are adjustable by means of an actuating device between an open position for receiving ground material and a closed position for conveying away received ground material out of the trench, - wherein there is provided a determination device which is configured to determine an actual quantity of ground material which has been received by the grab buckets in the closed position, - wherein there is provided a control unit which communicates with the determination device and in which a target quantity of ground material to be received by the trench wall grab is stored, and - wherein the control unit is configured to compare the detected actual quantity with the stored target quantity and to output a signal for repetition of a grab operation if the detected actual quantity differs from the stored target quantity, characterised in that for the repetition of a grab operation, the control unit is configured automatically to lift the trench wall grab to a specifiable height above a bottom of the trench by means of a lifting device and to lower it into the ground again from the specifiable height with the grab buckets open, and in that the control unit makes the specifiable height to which the trench wall grab is lifted again dependent upon the detected actual quantity and/or upon the penetration depth in the preceding grab operation. - a support device and - a trench wall grab which is mounted on the support device so as to be substantially vertically adjustable, wherein the trench wall grab has a grab frame at the lower end of which there are arranged two grab buckets which are adjustable by means of an actuating device between an open position for receiving ground material and a closed position for conveying away received ground material out of the trench, - wherein there is provided a determination device which is configured to determine an actual quantity of ground material which has been received by the grab buckets in the closed position, - wherein there is provided a control unit which communicates with the determination device and in which a target quantity of ground material to be received by the trench wall grab is stored, and - wherein the control unit is configured to compare the detected actual quantity with the stored target quantity and to output a signal for repetition of a grab operation if the detected actual quantity differs from the stored target quantity, for the repetition of a grab operation, the control unit is configured automatically to lift the trench wall grab to a specifiable height above a bottom of the trench by means of a lifting device and to lower it into the ground again from the specifiable height with the grab buckets open, and in that the control unit makes the specifiable height to which the trench wall grab is lifted again dependent upon the detected actual quantity and/or upon the penetration depth in the preceding grab operation.