Architectural Design
January 15, 2024
A soil survey is one of the most frequently skipped or underestimated steps in construction projects. Yet no structural calculation is truly reliable without understanding the ground beneath a building. The soil that carries all the loads deserves thorough investigation.
What Is a Soil Survey?
A geotechnical soil survey determines the plot's ground conditions, bearing capacity, liquefaction risk and seismic behaviour. In the field phase, boreholes are drilled, soil samples are taken and in-situ tests are performed. Laboratory analysis then completes the work and the findings are compiled into an engineering report that forms the basis of the structural design.
SPT Testing and Boreholes
The Standard Penetration Test (SPT) is the most widely used in-situ test method. A standard hammer drops a fixed weight from a fixed height onto a sample tube; the number of blows needed to advance the tube 30 cm is recorded as the N30 value. A high N30 indicates dense, high-capacity soil. Under TBDY 2018, soil class is determined from these tests and feeds directly into seismic design parameters.
Liquefaction Risk
During an earthquake, loose sand and silt layers with high groundwater can lose their bearing capacity entirely and behave like a liquid. It is most common in filled coastal and riverbank zones and in areas with shallow water tables. Liquefaction probability is identified in the soil survey and addressed through ground improvement or deep pile foundations if needed.
Impact on Foundation Design
Soil survey results directly determine the type of foundation to be used. On competent soils, strip or pad foundations may suffice; on weak or liquefiable ground, raft foundations, piled foundations or ground improvement become mandatory. These decisions must be made at the start of the project; discovering soil problems mid-construction leads to far more costly remediation. At Home Yapı Mühendislik, the soil survey is an integral part of every project we undertake.
Structural Engineering