Bored Pile Recommendation for Solar Panel Structures

The excavated pile foundation is one of the best recommendations for creating a foundation for ground and carport structures manufactured by SSM do Brasil, a company operating in the market of metallic structures for photovoltaic panels.

The company seeks, through its engineering sector in partnership with the new product development sector, to provide specialized assistance to each project, studying the technical and technological options available on the market.

Regarding the foundation, we are based on the technical knowledge of our engineers, regulatory technical concepts as well as feedback from integrator and installer customers.

Among the main advantages of this type of foundation construction are:

• Good mobility of excavation equipment;
• Allows adequate quality control and production speed that optimizes the work schedule;
• Enables checking sampling of the excavated soil, comparing it with the SPT survey;
• Offers absence of vibration and can be carried out close to the boundary without damaging neighboring buildings;
• Allows a safe assessment of the pile's load capacity, through sizing based on analysis of the SPT type percussion test;
• It can be used for both shallow (direct) and deep (indirect) foundations;
• It has the possibility of manual drilling using a shell auger (excavator) or mechanical excavation with mobile equipment on wheels or tracks or mixed excavation;
• Resists high loads (up to 100 KN);
• It can be carried out in sloping locations that do not have a water level (water table);
• Optimizes the overall work schedule;
• It stands out with a lower final cost compared to other types of foundation.

Lease/excavation

The first step would be to locate the pile using a template according to the project. Before starting the excavation, it is recommended to make a template with a square and axis lines and carry out the location using a center plumb. Finally, it is prudent to place a wooden picket in the center (axis) of the stake.

The second step would be to excavate with an excavator until reaching a depth of one meter and continue excavation with a manual or mechanical shell type auger up to the design elevation.

Drilling is done with a short auger coupled to a rod to the depth specified in the project, and the characteristics of the soil must be confirmed by comparison with the nearest drilling. When specified in the project, the bottom of the drilling must be fitted with a socket.

There is no standard depth for foundations of soil and carport plants, attention must be paid to the design considerations in details and notes, which can vary the diameter from ø25 to ø 40cm and depth from 100 cm to 500 cm, even in the same project.

Concreting

Concreting must be done on the same day as drilling or within a maximum of 24 hours, using a funnel that is at least 1,5 meters long. The purpose of this funnel is to guide the flow of concrete.

Concrete intended for the foundation must follow the preparation conditions established in NBR 12655. Mixes made in a concrete plant or in a concrete mixer truck must follow the provisions of NBR 7212.

The materials used in the manufacture of concrete, such as Portland cement, aggregates, water and additives, must comply with the respective specific Brazilian standards. Pay special attention to the type of cement.

The receipt and acceptance of concrete must be carried out according to the procedures described in NBR 12655, with special attention to the Compression Test and Consistency Test.

Armor Placement

The piles not subject to traction or considerable flexion only have starting/connection by means of the metal pillar in “C” profile (according to structure design specification – isopleth), with no structural function, placed immediately after concreting at a standard depth of 600 mm on the pile, which can vary from 400 mm to 700 mm underground, depending on the irregularity of the terrain, as defined specifically for the project by the calculating engineer. It is important to pay attention to the measurement of the first hole in the structure pillar to fix the scissors with a standard measurement of 800 mm for the lower end.

In the case of piles subjected to tensile, horizontal or moment efforts, the designed reinforcement must be placed in the hole before concreting, with stirrups, leaving the starting reinforcement above the ground, as defined in the foundation project.

It is recommended to turn the tip of the reinforcement with a minimum of 10 cm so that it is inside the crowning block (in the case of a carport) or in the square base in the diameter of the pile (in the case of a solo plant). It is recommended to use a circular plastic spacer to meet the coverage provided for in the project.

Preparation of the pile head and connection with the crown block

To connect the pile with the capping block, the level of razing and the length of the stops (starts) defined in the project must be observed. The section of the pile above the razing level must be demolished.

The resulting section must be flat and perpendicular to the pile axis and the demolition operation must be carried out in such a way as not to cause damage. If there is inadequate concrete below the razing level, the section must be demolished and restored. The material to be used in the restoration must have a resistance no lower than that of the concrete in the pile.

In the case of a starting length shorter than the design, a splice must be carried out by overlapping or overlapping and welding, according to the procedure described in NBR 6118.

Execution Records

In the work log, or similar document, the following information must be recorded:

• General identifications: work, location, name of operator, executor, contractor;
• Date of execution;
• Identification of the pile: diameter, name or number according to the Foundation Project;
• Drilling length;
• Armor length;
• Lease deviation (if any);
• Average concrete consumption per pile, based on the volume of concrete in the concrete mixer truck; • Drilling characteristics (manual/mechanical);
• Start and end time of drilling;
• Start and end time of concreting;
• Frame positioning;
• Relevant observations;
• Name and signature of the executor, supervisor and final contractor.

Recommendations

• Piles spaced less than three x diameters of the drill pile must be carried out at intervals of more than 12 hours;
• At least 1% of the piles, and at least one per project, must be exposed below the razing level to check their integrity and shaft quality;
• It is recommended that the excavated pile is always carried out above the water table level to avoid the risk of strangulation of the shaft;
• Due to the increasing effort as the excavation progresses, at least two people are recommended to carry out the work.
• It is very important to pile and clean the bottom of the excavated piles to ensure tip resistance.

Visual example

The opinions and information expressed are the sole responsibility of the author and do not necessarily represent the official position of the author. Canal Solar.