Pile Design and Construction Practice, Fifth edition

44 Types of pile

The ‘Soilex’system, developed in Sweden, uses the patented expander body to form an
enlarged bulb to displace and compact the soil. The expander body consists of a thin folded
sheet metal tube which, after insertion into the soil, is inflated by injecting concrete or grout
under controlled pressure to form a bulb 5 to10 times the original diameter. Installation may
be by conventional drilling, driving, jacking or vibration methods or placement in a pre-
formed hole, the pile shaft geometry above the bulb being determined by the method of
installation. The tube dimensions before expansion range from 70 to 110 mm square up to
3 m long which following inflation provides end-bearing areas of 0.12 to 0.5 m^2. In
Borgasund, Sweden, fifty-seven 11 m long Soilex piles using a 110 mm expander body
welded to 168 mm diameter thick wall tube were installed by a vibrator in a predrilled hole
in medium dense sand below new railway bridge abutments. Approximately 0.5 m^3 of con-
crete was used to inflate the expander body to form an 800 mm diameter bulb producing a
pile which had an estimated ultimate load capacity of 1100 kN, limited by the strength of the
concrete-infilled steel shaft. The system is also useful for underpinning where short piles are
appropriate and as tension ground anchors; in all cases the spacing of piles is critical to
avoid interference.

Uniform

section

Tapered

section

203 mm (8)

tip diameter

Figure 2.22Union Monotube pile (Union Metal Manufacturing Co.).