The portable Soil Test Probe provides a new dimension. This instrument, portable and operable by one person, will provide reproducible numerical data related to resistance of the soil to flow under load. It may be used in soils up to the consistency of hard pan, to any depth below the surface and without the need to make an excavation or otherwise disturb the soil.

The probe shown consists of a head on a square shaft with a number of extensions, all of which may be coupled together. A ratchet wrench with a torque measuring handle is used to install, remove or take readings. Corner marks at one-foot intervals provide means to determine the depth below the surface when a reading is taken.

The hub of the probe head is forced into the ground by application of torque acting on the blade of the probe. Thus the torque required to turn the probe is proportional to the resistance of the soil to penetration of the hub. It is this property of soil which is of interest in making an anchor selection in determining the bearing strength – especially for end bearing screw foundations or footings.

Probe readings can be related back to the general soil classifications to determine anchor holding capacities (see Soil Classification data above)

For end bearing foundation work, the bearing strength of the soil may be calculated directly from the probe reading.

This heavy duty probe will withstand torque to 1800 lb inches (200 Nm) on the scale, so it will not penetrate packed gravel, shale or rock. Thus, for foundation work, other means such as augering will be required to determine the thickness of the hard strata. When the hard strata is penetrated, the probe can be used to evaluate the quality of an underlying softer soil.

As is the case with any instrument, the value of the data taken with the probe will be no better than the care used in conducting the tests. It is best to average the results of several tests in the same area for, even within a few feet, some variances will be found.

The main requirement during probe testing is to ensure the probe advances a full pitch before readings are taken. This is accomplished by application of heavier down pressure on one handle of the wrench while the probe is being screwed into the ground.

When extensive probing is to be done, speed can be increased by using ½”, heavy duty drill motor with reversing switch to install and to remove the probe. Readings are taken while the motor is at rest by engaging the shaft with a crow’s foot wrench on the torque handle.