In-situ soil external friction angle testing device and testing method

The invention discloses an in-situ soil external friction angle testing device and method, and the device comprises a drill rod, a protection cylinder, a connecting cylinder, an expansion film, an expansion film protection layer, a sealing sleeve, a mounting seat, a sensor mounting cylinder, a strain pressure sensor, a drill bit, an annular cutting edge, a positioning sleeve, and an expansion film limiting mechanism. A backflow gap is formed between the drill rod and the protection cylinder and used for mud backflow, an expansion gap is formed between the expansion film and the connecting cylinder and used for providing radial pressure for the soil body, an oil cavity is formed between the lower end face of the sensor mounting cylinder and the installation base, and a deformation gap communicated with the oil cavity is formed between the sensor mounting cylinder and the protection cylinder. The strain type pressure sensor is fixedly installed on the outer vertical face of the sensor mounting cylinder, a mediu