In large and medium-sized construction projects, where administrative office complexes, shopping centers, housing complexes or industrial buildings are built, it is very common to require very strong, light structures that are resistant to fire or earthquake risks. These structures are in turn supported by underground foundations that provide sustainability to the structure of the building under construction. But what dimensions should these foundations have? how deep in the soil or subsoil? and what diameter should they have? what equipment is necessary for these boreholes? Here we will try to address a little about foundation drilling and risks.

1.- What is foundation drilling?

Foundation drilling is when you and your crew use a drill rig or auger to drill large, deep holes in the ground; the operator will then insert a structure into these holes to build the foundation for a construction project. Typically, these boreholes are drilled deep below the earth’s surface to obtain maximum bearing capacity. Large buildings and structures need adequate support and stability, which is why the boreholes must be so deep. The bedrock underneath can be used for additional support.

This type of drilling can be done for new projects or pre-existing foundations. However, this practice is mainly used for new projects. Foundation drilling is not as simple as it sounds. Many people, including the rig operator, project manager and site engineers, must coordinate to complete this project successfully.

2.- How does foundation drilling work?

Foundation drilling involves using large drilling rigs to bore deep holes into the ground, which are then filled with concrete or other materials to create a stable base for large structures like buildings and bridges, essentially anchoring the foundation by extending deep into the earth to reach solid bedrock for maximum load-bearing capacity; this process typically utilizes an auger drill with a helical screw blade to remove soil while drilling, and may require casing systems to stabilize the borehole during operation depending on soil conditions. This work has any risks above all when you unknow existing underground services.  And what kind buried services has; public or private services.

3.- Diameter and depth of foundation drilling

The diameter of foundation drilling can range from as small as a few inches for micropyles to several feet for large, drilled shafts, while the depth can vary from tens of feet to over 300 feet depending on the project and soil conditions; typical diameters might be between 12 to 48 inches, with depths ranging from 10 to 150 feet depending on the drilling method and equipment used.

In any case, these variables will always be considered basic to determine the diameter and depth of the foundation”

• Type of soil
• Location of the project
• Design: Weight to be supported; depending on the height and use of the building to be built

4.- Steps – Steps in foundation drilling

• Site preparation: Identifying the location of the holes and marking the drilling points.
• Carry out a location of the possible buried services, in the area to be drilled, our company is a specialist in this service.
• Drilling: Using the auger drill to bore the hole to the desired depth, removing soil continuously.
• Casing installation (if needed): Lowering a casing pipe into the hole to stabilize the walls.
• Concrete placement: Pumping concrete into the hole to fill it and create the foundation pile.
• Removal of the drill rig: Once the concrete is set, the drilling rig is moved to the next location.

5.- Impact Force of foundation drilling in the Subsoil

The impact force of foundation drilling in the subsoil depends on several factors, including the drilling method, soil type, drill bit size, and drilling speed. Here’s a breakdown of key considerations:

a. Drilling Method

              •            Rotary Drilling (e.g., auger drilling): Applies torsional force rather than direct impact.

              •            Percussion Drilling (e.g., DTH hammer, cable tool drilling): Delivers repeated impact forces to break through hard formations.

              •            Vibratory Drilling (e.g., sonic drilling): Uses high-frequency vibrations to reduce friction and penetration resistance.

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b. Soil and Subsoil Conditions

              •            Loose Soils (sand, silt, clay): Lower resistance, less impact force required.

              •            Dense Soils (compacted clay, gravel): Higher resistance, moderate impact force needed.

              •            Rocky Subsoil: Requires significant impact force, often with percussion or DTH drilling.

c. Drilling Equipment & Parameters

              •            Bit Weight and Diameter: Larger bits require more force.

              •            Rotational Speed: Higher speeds reduce penetration resistance but increase wear.

              •            Drilling Fluid or Air Pressure: Helps to reduce resistance and remove cuttings.

2. Estimating Impact Force

For percussion-based drilling, impact force can be estimated using:

                         F = m . a  ; a = v / t —-> F = m . v / t

where:

              •            F  = impact force (N)

              •             m = mass of the hammer or drill bit (kg)

              •             v = velocity of impact (m/s)

              •             t = time duration of impact (s)

For example, if a 500 kg hammer strikes at 5 m/s with an impact duration of 0.05 s:

Conclusion

As you can see, the weights, forces, and speeds of these machines are considerable, which makes the risks many and, in some cases, can lead to loss of materials, increased costs and time in projects and even personal injuries, or in the worst case, loss of human lives. Therefore, in good risk management in construction projects where the policy is the mitigation or elimination of high-risk factors, work planning with the contracting of utility locating service, or private utility for utility marking      

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