What is the maximum tip resistance that can safely be applied to the push-in vibrating wire piezometer during installation? We would like to install several push-in VW piezometers at depths up to 80 feet. During CPT testing at the site, strata with a tip resistance of 30 mpa were encountered. Are these stiffer soils more than the VW piezometer can handle?
Answer: The Push-In Piezometer was designed to be used in very soft soils, especially soils whose structure or hydraulic characteristics would be disturbed by drilling. Normal installation procedures for the push-in piezo are to drill within 2 to 5 feet of the target zone and then push the piezometer to the required elevation. Once the push rod is removed, the soil usually collapses and seals the boring. If it does not, you should fill the boring with a bentonite cement grout.
You can use the cone penetrometer rods to push the piezometer inside an existing cone penetrometer hole. The piezometer does not have the same strength as a cone penetrometer and it will be destroyed if
pushed into medium to hard soils. When pushing the piezometer, you must take piezometer readings to be sure that the pore water pressures created when pushing the cone do not exceed the pressure rating of the piezometer, and you will probably have to push very slowly and stop often to let pressures dissipate before continuing.