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article 18, issue 06

Foundation building with human power: ground screws

Theo Schmidt
December 21, 2009 and March 21, 2011, (last update 7.11.2012)


Foundation laying usually means much back-breaking digging even for small buildings. Ground screws are a much easier method for supporting lightweight buildings and are very suitable for installation with human power. They are also easily removed and reused without using machinery. Historically called screw piles, they enabled the rapid construction of foundations for piers and bridges entirely by human power. They were popular for nearly a century and then somewhat forgotten until recently, reappearing for modern uses such as foundations for photovoltaic arrays.

[Editors' note: While we do cover stationary human power uses in HPeJ, this rather static application may seem "off-topic". It is however a good method for securing bicycle sheds and the like.]


Foundations for buildings or utilities are often made of poured concrete, sometimes reinforced with steel. While these can be readily built using human power, there are disadvantages:

There are alternative types of foundations which are especially suitable for construction using human power:

Ground screws

Ground screws are a relatively recent development combining properties of pile foundations and earth anchors.
Traditional piles are generally used as deep foundations, e.g. the many vertical oak piles the city of Venice is built on. They can support both by transferring surface loads down to solid ground and by friction along the whole length of the pile. Piles are often rammed in or vibrated out using heavy machinery. Smaller piles can be rammed into the ground by human power with large or special hammers. They can often be removed with human power using winches.
Earth anchors are steel rods or wire with helical or expanding anchors at the end or at several places along the length. The former are screwed into the earth using machinery, the latter can be rammed in by human power but are generally not recoverable except by digging or breaking out. They are meant only for tension loads, which can be in any chosen direction including vertically upwards, unlike surface anchors or spikes which must be loaded in a single, mostly horizontal direction.

Figure 1

Figure 1: Archimedes: "Give me a place to stand on and I will move the Earth."

Ground screws may be loaded in compression, tension, and shear. While they may be installed using machinery, even large sizes can be screwed in with human power. As already recognized by Archimedes: "Give me a place to stand on and I will move the Earth." A great advantage is that they can also normally be screwed out again by human power - and reused elsewhere: a semi-mobile foundation. The screwing action also allows adjusting the vertical depth to millimeter-precision.

Figure 2Figure 3

Figure 2: Earthscrews with flange (length of thread 0.5 m,
total lengths 0.8, 1.0 and 1.2 m, diameter of tube 75 mm)

Figure 3: Earthscrews (length of thread 0.4 and 0.5 m,
total lengths 0.8 and 1.0 m)

Several types and many sizes exist. I used three each for supporting a garden house, the flanged ones at the rear and the tubular ones at the front. I bought various sizes, unsure whether I might hit large rocks, but in the end was able to use the long ones everywhere. All six were screwed right in. The front three received extentions in the form of further steel tubes.

Figure 3

Figure 4: Garden house with 2.2 kW photovoltaic roof, total weight about one tonne

Inserting the earth screws is very easy. They screw with little effort into the top soil. A spirit level is used to keep the angle vertical. A short lever is sufficient intially.

Figure 5Figure 6

Figure 5: Earthscrew being inserted. Note magnetic spirit level.

Figure 6: Earthscrew nearly in. Note spring scale and water level (plastic tube).

Our soil is relatively "ordinary", a farm pasture with topsoil/grass, then compact soil resting on a layer of conglomerate, frequent rocks and some clay. After a few turns the thread begins to bite and the torque rises quickly. A magnetic spirit level is used to keep the screw vertical. This is easy as long as both arms can be used with a symetrical lever. Soon a longer lever is required and unless two people are available, torque on a single lever produces a force which tends to misalign the screw vertically. If the lever can be easily transferred to the other side, it is however possible to apply force such that the misalignment is immediately corrected. Careful attention to the spirit level allows a near perfect vertical angle and a lateral precision to better than ± 5 mm. The vertical position can be very precise simply by stopping at exactly the right position. Multiple screws can be be brought to the same height with a long spirit levels, a plastic tube filled with water, or a laser-level.

Figure 7

Figure 7: Torque versus depth. The last peak could be a rock,
some of the screws didn't go over 300 Nm.

Support Capacity

The obtainable loading is of course dependent on the type of soil and on the length of the ground screw. The following table gives some values when ground screws of similar type as in the article are subjected to increasing vertical loads and these measured when the screws have settled 5 mm and 10 mm.

Table 3: Vertical loads at 5 and 10 mm settlement, several soil types and several screw lengths, from (Schulz 2004), Table A8-4

ClayClaySand, looseSand, denseGravel, looseGravel, looseGravel, looseGravel, dense
75 mm 100 mm 150 mm100 mm100 mm80 mm100 mm150 mm100 mm
[mm] [kN] [kN] [kN] [kN] [kN] [kN] [kN] [kN] [kN]
5,0 19.5 3.3 6.29.6  51.0
10,0 8.1 42.0 100.018.8 87.0

Historical Development

[All information in this section from Lutenegger (2011), also the figures in the Public Domain]
Ground screws, or screw-piles as they were then known, were first developed by Irishman Alexander Mitchell from 1833. The first devices were used for mooring ships and loaded only in an upward direction. The screw's thread had little more than a single turn and was screwed into the sea-ground with a temporary shaft later removed.
screw pile drawings
Figure 8: Several forms of screw-piles

Later the shaft became the foundation pile itself and these were used as the foundations of offshore lighthouses. One of the first, the Maplin Sands lighthouse was mounted on nine such iron piles, each about 13 cm diameter and with a screw flange of about 1.35 m diameter. Each screw pile was screwed into the sea ground with eight capstan-like levers of 3-5 m length. Figure 9 shows such an arrangement worked by 32 men. Over 60 lighthouse foundations were built in this or a similar manner in Great Britain and USA.

Drawing of screw pile capstan

Figure 9: Capstan on plattform built on two barges, worked by 32 men.

Later screw-piles were used for pier and bridge foundations. The barge method of installation prived impractical in a seaway and methods were devised to work from land, installing the first screw-piles, building and extending the structure and working from this as it grew. An endless rope was attached to the capstan and this pulled by men and later animals or machines. Dozens of screw-pile piers and bridges were built, some of them famous constructions still in use today.
The screw-pile technology was in use and known well into the 20th century. Then it was forgotten for a while until some years ago German Klaus Krinner developed the form shown at the beginning of this article. These are now used for all sorts of lightweight constructions such as fences and photovoltaic arrays, but also buildings.


Figure 10: Method for extending pier from land, installing screw-piles with capstan worked by endless rope. 


Schulz, H.;  Schick, Peter; Schmid, Jürgen. "Tragfähigkeit und Verschiebungen von Schraubfundamenten der Firma Krinner" Institut für Bodenmechanik und Grundbau, Universität der Bundeswehr München, Neubiberg, 05.03.2004;

Lutenegger, Alan; "Historical Developement of Iron Screw-Pile Foundations: 1836-1900" Int. J. for the History of Eng. & Tech., Vol 81 No. 1. January 2011, pp 108-128

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