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4 Types of Foundations Adopted for 15MW Solar Plant (page 4)

All possible measures taken for water discharge using permeable anti-weed sheets

2016/02/11 17:51
Shinichi Kato, Nikkei BP CleanTech Institute
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Four kinds of foundations used according to area

The plant used four different foundation methods in accordance with the slope and terrain of the area to set up panels (Fig. 5).

Fig. 5: Four kinds of foundations were used in accordance with the shape and terrain of the area. Above are the foundations and their outline by area. (source: top, Daiwa Lease/Daiwa House Industry; bottom, Nikkei BP; bottom, Photos of Type B Daiwa Lease/Daiwa House Industry)

The most basic was the concrete secondary product (precast) foundation for flat areas (Type A). When the area was sloping too much to use this foundation, spiral anchors were added to the small precast foundation for slopes (Type B). Rock anchors were used for side slopes where the ground was sloping even more and both the above methods could not be used (Type C).

The plant was initially planning to use only these three types of foundations. However, some areas, to which the precast foundation for flat areas (Type A) had been applied, were found to slope too much to build the base structure for the foundation. As a result, Daiwa House decided to use a fourth foundation, that is, the steel tube-based pile foundation (Type D), in those areas.

When adopting the pile foundation, there was a challenge concerning the method of driving the piles into the terrain. The conventional excavation method called "earth auger," which excavates bedrock with a special cutting edge at the tip, allowed for no more than two to three piles to be driven a day while the cutting edge of the driving machine easily wore out.

Consequently, Daiwa House adopted a method called "down-the-hole hammer" that crushes bedrock and boulders by striking them with a hammer and driving the pile foundations into the terrain (Fig. 6).

Fig. 6: Adopted method that crushes bedrock and boulders by striking them, solving the challenge of driving in the pile foundations. (source: Daiwa Lease/Daiwa House Industry)

Fig. 7: Panel installation on the side slopes. The panels were fixed with mounting system rails and, then, lifted by cranes for installation. (source: Daiwa Lease/Daiwa House Industry)

On the side slopes, solar panels were set up at the minimum height from the ground. The Daiwa House Group installed the panels, lifting and supporting them with cranes after attaching the solar panels with the rails that had been assembled on the mounting systems in advance on a nearby flat area (Fig. 7).

When working on steep slopes including the side slopes, holding fixtures with ropes were set up using pickets at the top with the aim of securing the safety of the workers (Fig. 8). The holding fixtures were left even after construction was completed and the plant started operation. The fixtures are used to secure the safety of operation and maintenance workers.

Fig. 8: Ropes to secure safety of workers during construction on side slopes and for operation and maintenance (source: top Daiwa Lease/Daiwa House Industry, bottom Nikkei BP)

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