The NSR-10 places each building unit in a low, medium, high or special category according to its number of levels and its loads, and that category sets the minimum number of borings and their depth (Title H, tables H.3.1-1 and H.3.2-1). A house of up to 3 levels requires at least 3 borings 6 m deep; a building of 4 to 10 levels, 4 borings 15 m deep.
The four categories
Low: up to 3 levels, or column loads below 800 kN. Medium: 4 to 10 levels, or between 801 and 4,000 kN. High: 11 to 20 levels, or between 4,001 and 8,000 kN. Special: more than 20 levels, or more than 8,000 kN. Levels include basements, roof terraces and mechanical floors, and the less favorable category governs (H.3.1.1).
Minimum borings
Low: 3 borings 6 m deep. Medium: 4 borings 15 m deep. High: 4 borings 25 m deep. Special: 5 borings 30 m deep (table H.3.2-1). At least half must recover samples, taken every meter in the first 5 m, and at least half must fall within the building footprint (H.3.2.4).
The depth also depends on the foundation
At least 50% of the borings must reach the depth in the table, measured from the bottom of the excavation, and also the depth the foundation requires: 2.5 times the width of the largest footing, 1.5 times the width of a mat, or the length of the longest pile plus four diameters. For excavations, at least 1.5 times their depth, and 2 times in type E and F soils (H.3.2.5).
Why it matters for the structural design
The geotechnical study gives the bearing capacity, the expected settlement and the soil profile that amplifies the earthquake. A study with fewer borings than required can be rejected by the curaduría or by the independent reviewer, and a well-done study allows more economical foundations. In Barranquilla, it is also worth knowing whether there are expansive clays.
Source: NSR-10, Title H, chapter H.3.
Frequently asked questions
How many borings does a house need?
For a low-category building of up to 3 levels, the NSR-10 requires at least 3 borings 6 m deep (table H.3.2-1).
And a 10-story building?
4 to 10 levels is the medium category: at least 4 borings 15 m deep, or deeper if the foundation requires it.
