Screw piles can be installed (driven) by any means capable of developing and applying sufficient torque to the pile head. The preferred method of driving screw piles is via hydraulic power.
Small construction equipment, such as bobcats, tractors or even tracks are readily adaptable to utilize a hydraulic power rate. Reddi-Walk
and Leveling Services currently uses a small farm tractor with a three-point hitch and power takeoff for hydraulics, modified with the necessary hydraulic pumps, reservoirs, controls and motors. As modified, this tractor weighs 800 lbs., has a 6´ minimum vertical clearance and a 3´10" minimum horizontal clearance.
Generally, installation in cohesive, non-granular soils is accomplished by drilling a pilot hole to stab the pile. The diameter and depth of the pilot hole various with the soil conditions encountered at the
site and the linked of the screw pile to be installed. Recommended pilot hole depths and diameters are for 10´, 20´, and 30´ screw pile lengths are listed below in Table 1, Table 2, and Table 3, respectively.
Table 1 - Recommended Pilot Hole Depth & Diameter for 10´ Screw Pile in Cohesive Soils
Soil Conditions
Pilot Diameter
Pilot Depth
Remarks
Loose/Organic
6"
3´0"
Medium Stiff Clay
6"
6´8"
Stiff / Very Stiff Clay
6"
10´0"
Water Lubricant
Table 2 - Recommended Pilot Hole Depth & Diameter for 20´ Screw Pile in Cohesive Soils
Soil Conditions
Pilot Diameter
Pilot Depth
Remarks
Loose/Organic
6"
10´0"
Medium Stiff Clay
6"
15´0"
Stiff / Very Stiff Clay
6"
20´0"
Water Lubricant
Table 3 - Recommended Pilot Hole Depth & Diameter for 30´ Screw Pile in Cohesive Soils
Soil Conditions
Pilot Diameter
Pilot Depth
Remarks
Loose/Organic
6"
15´0"
Medium Stiff Clay
6"
20´0"
Stiff / Very Stiff Clay
6"
25´0"
Water Lubricant
To properly determine the appropriate driving parameters at a site, it may be necessary to drill a full-depth hole to reveal existing soil conditions. At least one test pilot whole should be performed before
prior to installing screw piles to verify existing soil conditions. Where unusual soil conditions exist or are expected to vary widely, additional test holes should be considered. Proper pilot hole size
and depth are essential to ease of installation and prevention of over-driving stresses to the pile.
Screw piles can also be installed in granular materials, using a technique of modulation of the applied driving torque and use of a hold-back cable. Alternately driving the screw pile and restraining it via the
hold-back cable effectively "walks" the pile into the granular material without over stress or breakage.
