Helifix Dixie circular hollow section piles can rapidly provide reliable and economical structural support for both new permanent and temporary buildings. When suitable load-bearing strata is at a deeper level, a piled foundation is likely to be more cost-effective at transferring the superstructure loads than undertaking deep excavations to form traditional foundations.
The Dixie micro-pile foundation system is simply screwed vertically into the ground to provide an efficient means of support. Each pile is topped with an engineered flat top plate, which is either cast into reinforced concrete pile caps/ground beams in traditional new build construction or connected directly to the base of modular or temporary structures.
Dixie micro-piles are ideal for use in situations where speed, vibration, noise, contaminated ground or spoil removal are concerns or where there is restricted access to large plant. They are a technically innovative, proprietary, micro-pile system, making it simple for engineers to specify. Furthermore, they are easy to extract from the ground, once a temporary structure is removed, by simply being 'unscrewed'.
This fully engineered solution consists of 3 components:
Traditional New-build Construction
1. The piles are screwed vertically into the ground using a lightweight hydraulic drive head. The helical lead section is installed first, followed by the necessary number of extension sections to reach load-bearing strata.
2. Each pile is topped with the flat plate bracket.
3. Formwork is created around pile brackets.
4. The piles are cast into reinforced concrete to form foundations and the build process continues as required.
Temporary and Modular Buildings
1. The piles are screwed vertically into the ground at the specified centres to the calculated depth and torque.
2. The flat top bracket is fitted to each pile.
3. The building chassis beams are secured to the top plates and construction continues as required.
The load bearing capacity of a helical pile is dependent on:
a. The strength of the soil – evaluated using standard techniques.
b. The projected area of the helical plates – plate surface area and number.
c. Depth of the plates below ground surface level.
Helical piles should be installed to an estimated depth based on soil investigations to ensure the best load bearing capacity.
The soil behaviour mechanism is assumed to follow the theory that the overall capacity of the helical pile is equal to the sum of the capacity of the individual plates. Any friction contribution along the central shaft is generally ignored. The helical plates are spaced far enough apart to avoid overlapping of individual “pressure bulbs” to obtain the best performance.
The following is Terzaghi’s general bearing capacity equation to determine the ultimate capacity of the soil.
Qult – ultimate capacity of the soil, kN
Ah – projected plate area, m²
c – soil cohesion, kN/m²
q’ – effective overburden pressure, kN/m²
B – footing width (base width), m
γ’ – effective unit weight of the soil, kN/m³
Nc, Nq & Nγ – bearing capacity factors
Having determined the capacity of the helical pile, it is recommended that the centre-to-centre spacing between adjacent piles be no less than five times the diameter of the largest plate.
Once the ultimate capacity of the helical pile has been determined an appropriate safety factor must be applied, generally a minimum of 3, to give an acceptable working capacity.