A hydraulic measuring head is a calibrated measuring instrument that is used for continuous and discontinuous mechanical cone penetration testing. The force on the mechanical cone is transferred to the surface by means of the inner rods and converted into a hydraulic pressure that is displayed by means of 2 pressure gauges. CPT data are supposed to be recorded manually by the CPT operator while performing the test.
The hydraulic measuring head composes of a fluid-filled measuring body with hydraulic piston, 2 read-out pressure gauges, and an automatic by-pass valve. This valve diverts the hydraulic pressure automatically from the pressure gauge with the low measuring range to the pressure gauge with the high measuring range when the pressure raises and it protects of the smallest of the 2 manometers against too high pressures.
The CPT test can be performed with either a jacket cone or with a friction jacket cone (also called Begemann cone). The jacket cone allows for continuous as well as discontinuous CPT testing. The friction jacket cone allows for discontinuous CPT testing only.
Since the hydraulic measuring heads are also suitable for discontinuous CPT testing, it is provided with a J-slot selector.
The advantages of a hydraulic measuring head are numerous:
- Simple and straightforward measuring tool
- Gives direct feel with what is going on
- Read-out in kN
- Suitable for both continuous and discontinuous mechanical CPT testing