Development of a New In Situ Testing Probe Combining CPT and VST

In situ testing refers to testing geotechnical properties in the natural state of geotechnical soil. Its primary means include cone penetration testing (CPT), free fall penetration testing (FFT), vane shear testing (VST), and so on, each of which corresponds to measuring different mechanical parameters. This article develops a new type of in situ testing probe combining CPT and VST to comprehensively measure multiple mechanical parameters of submarine soils. The probe has the following characteristics. It contains a CPT component and a VST component, which can simultaneously measure several soil mechanical parameters—cone-tip resistance, sidewall friction, pore water pressure, and shear stress. The above parameters can reflect most of the geotechnical properties. The internal design of the CPT component “three-cylinder” type pressure sensors, of which the cone-tip resistance sensor has the characteristics of high sensitivity and extensive measuring range, solves the problem of measuring the soft and hard soil layers with one probe. The error of the sensor’s full scale is within 0.3%. A noncontact torque sensor is designed inside the VST component, and the relationship between torque and shear stress is modeled and analyzed. Ultrasonic wireless transmission is used inside the probe, avoiding the problems of machining difficulties and lead wires caused by transmission lines.