Flanged or Direct-buried Lighting Poles: Which to Choose

Flange connection on a foundation

The shaft is fixed to the foundation through a flange connection. Anchor bolts on an embedded plate are cast into the foundation in advance; the pole’s base flange is then fitted onto these bolts and tightened with nuts. The foundation itself is made separately, before the pole is installed. It can be monolithic, on shell piles, or a ready-made block.

Direct burial in the ground

The shaft is lowered into a prepared pit of the required depth and concrete is poured around the lower part of the pole. There is no separate foundation and no flange connection. This method is used mostly for shorter poles, and where the soil accepts such installation without a separate calculation of the base.

Comparing the two methods

The final choice of method is confirmed by a calculation for the specific soil, pole height and loads — send us the input data and we will advise the optimal option.

What we choose

We make poles for both fixing methods. Which one to use is agreed with you at the technical specification stage and depends on the pole height, the soil on site and the project requirements. For more on the foundations themselves, see the article Lighting Pole Foundations: Types, Construction, Calculation.

Example: how much of the shaft ends up in the ground

On a flanged pole the whole shaft stands above the foundation. On a pole set in the ground, the shaft length equals the height h plus the embedment depth e (for a pole without a bracket, with the luminaire at the top of the shaft). EN 40-2 uses the same sum for its straightness tolerance (see our summary of the standard).

For 8 m and 10 m poles the summary gives three options for e; we take two of each. The share of the shaft below ground is 13–16%. That part is hidden, and corrosion usually starts at ground level and just below it (see Wear and Corrosion of Metal Poles).

Share = e ÷ (h + e). The depth is set by the soil and the calculation; the figures are a guide from the EN 40-2 summary, not the parameters of our poles.

What is checked during installation and in service

Example: a street with 21 poles

A street 480 m long, with UMO-8 poles on one side of the street at a 24 m spacing (three heights, the lower limit of the rule in Distance Between Street Lighting Poles). 480 ÷ 24 = 20 spans, i.e. 21 poles including both end poles. What this means for each method:

• flange connection: 21 foundations, each with an embedded anchor cage (anchor bolts on an embedded plate). If the cage has four M24 anchors, as in FPO-1000-1 (see Foundation Anchor Cages), that is 21 × 4 = 84 anchors, and their nuts are tightened and checked;
• direct burial: 21 pits with concrete poured around the shaft, no anchor cages and no nuts, but a longer shaft. With a conventional e = 1.2 m (for reference, per EN 40-2), shafts standing 8 m above ground would total 21 × 9.2 = 193.2 m against 21 × 8 = 168 m, i.e. 25.2 m more.

What is worth comparing is the full cost of the site, including foundations, not the price of one pole.

Checklist before you order

• the soil and groundwater level are known (geotechnical survey report): they decide whether direct burial is enough;
• the height, number and area of luminaires and the wind region are known (Wind Regions of Ukraine), because the moment at the base depends on them;
• the fixing method has been agreed and written into the technical specification: poles for direct burial have no flange, so changing the method later means reworking the pole base;
• the lower edge of the hatch will be at least 300 mm above the ground (for reference, per EN 40-2; this is not a statement that our poles conform), so the foundation top level has been agreed;
• the schedule leaves time for the concrete to gain strength: the pole is set on a foundation that has reached at least 50% of the design strength.

What goes into the foundation with flanged mounting

A flange with four holes is welded to the bottom of the shaft, and under it lies an anchor cage with anchors set in the concrete. The flange size, the hole spacing and the anchor diameter have to match, so the cage is chosen by the series and height of the pole.

The cage mark encodes the height in millimetres and the variant number: FPO-1000-1 is 1,000 mm high. Cages are made of S245/S345 steel and supplied uncoated.

Data from the pole cards and from the article on FPO, FPM and FKM anchor cages. A pole for direct burial has neither a flange nor an anchor cage.

Waterproofing a shaft set in the ground

The most vulnerable part of such a shaft is hidden underground. The technical requirements call for bitumen varnish or another coating agreed with the customer on the root part. Waterproofing is not part of the supply of poles and foundations, so it has to be provided for separately.

So when you compare costs, put the longer shaft (see the example above) and the waterproofing on the direct-burial side. The flanged option has a foundation with an anchor cage instead.

Hinged version

On request we make the pole in a hinged version with a hinged foundation anchor cage. Such (mobile) poles consist of a fixed part and a movable part, and the movable part rotates freely on a hinge unit. In the order, state whether the pole is stationary or mobile, with a hinge unit.