Application study of HPT (Helical Probe Test) in sedimentary sand of Bauru Group

Abstract

In Brazilian foundation practice, SPT Test is generally used in the design of pile and shallow foundations. Ranzini (1988) just already suggested supplementing the conventional SPT with measurement of the torque required to turn the split spoon after driving. After this, some Brazilian consultants began to use that new technique. The torque measurement is additional information that improves a traditional in situ test, SPT, which is well-known in foundation practice. New methods based on SPT-T to predict the bearing capacity of piles lead to good correlation with the load test results, for the soils studied. Nevertheless, the SPT-T does not supply information of the first meter, so necessary to shaft foundation and pavement projects. Therefore, Yokel and Mayne (1988) developed and tested the Helical Probe Test, HPT. The equipment consists in a rod with a helical screw and a torquemeter connected in the upper side that read the torque needed to insert the probe. The probe is inserted into the ground by turning it with a little vertical force. The measurements are generally taken each 15cm considering the peak torque. These authors suggested a speedy of 180o each 4 seconds. Peixoto (2001) developed an electric torquemeter and a data acquisition system that permitted to study influence of some factors in torque measurements: the behavior of the torque versus rotation degree shape; the speed test; efficiency considering the length rod and the split spoon. Here, the electric torquemeter is used connected to the analogue torquemeter to turn possible measure the torque continuously and evaluates the shape curve of torque versus rotation degree. It is being used a helical screw with 38,1mm outer diameter, suggested by Yokel and Mayne (1988), comparing with that suggested by the ABNT NBR 6484 (2001), with 56mm outer diameter. This first study is being done in the Sedimentary Sand of Bauru City, inland of São Paulo State, Brazil.