Large-size sample sampling device for undisturbed soil at bottom of foundation pit and using method of large-size sample sampling device

The invention provides a large-size sample sampling device for undisturbed soil at the bottom of a foundation pit and a using method of the large-size sample sampling device. The device comprises a sampling box and a bottom cutting frame, wherein an open end is arranged at the lower part of the sampling box; the bottom cutting frame is arranged outside the sampling box, and the bottom end part of the bottom cutting frame is propped against the open end in a sliding manner and is used for closing the open end; U-shaped sliding chutes are formed in two ends of the upper part of the sampling box; supporting strips are arranged at positions, which correspond to the U-shaped sliding chutes, of the upper part of the bottom cutting frame; and the supporting strips are connected with the U-shaped sliding chutes in an inserted manner. According to the device disclosed by the invention, undisturbed soil samples of different depths are obtained by utilizing depth conditions created by foundation pit excavation, the device does not have requirements on independence of the soil samples and is suitable for sampling various sandy soils and clays, particularly soil bodies such as clean sandy soils and soft soils which cannot stand independently.