Errors in documenting the subsoil and their impact on the investment implementation: Case study

Improper recognition of the subsoil is the most common cause of problems in the implementation of construction projects and construction facilities failures. Most often, their direct cause is the mismatch of the scope of geotechnical diagnosis to the appropriate geotechnical category, or substantive errors, including incomplete or incorrect interpretation in the creation of a geological-engineering model and often overlooked hydrogeological conditions. In many cases, insufficient recognition and documentation of geotechnical and/or geological and engineering conditions leads to damage and construction failures, delays in consider construction, and the increase of the investment budget. That’s why, in order to avoid the above, particular attention should be paid to proper geotechnical and geological-engineering documentation at the design and construction stages. The selected example of the investment analyzed errors in the geological-engineering documentation, which mainly concerned the lack of recognition of locally occurring organic soils, the incorrectly determined location of the groundwater table and the degree of compaction of non-cohesive soils, and numerous errors of calculated values of soil uplift pressure. The detection of the errors presented in the paper made it possible to select the correct technology for the construction of the sanitary sewage system and to increase the thickness of the horizontal shutter made of jet grouting columns in the area of the excavation. In addition, the article discusses the principles of proper calculation of limit states and subsoil testing, which have a significant impact on the implementation of planned investments.

Determination of deformation properties of soils as input parameters for calculation

When designing the foundations of any building structure, it is important to know not only the load of the structure, but also the deformation characteristics of the subsoil. Their underestimation leads to incorrect design of the foundations or even to failures, the reparation of which requires considerable financial costs. The real values of the deformation soil properties gained from the geotechnical investigation often do not match the tabulated values used in the design. In this contribution, actual and tabular values of selected soil properties in the bedrock in the locality of Kosicka kotlina are compared. Simple buildings designed according to the 1st geotechnical category are in the described location predominantly based on Neogene clay of intermediate plasticity class F6 and less on clays class F8. These are soils sensitive to changes in their natural moisture – they swell when exposed to water, thus become unstable. It is therefore important to use the most accurate values in the calculation of the foundations. The analysis of 130 measured values confirmed that 52% of the all measured values are outside the indicative table data. The use of inaccurate input values can bring a risk and threat to safety, reliability and proper use of any construction. It is therefore necessary to carry out the appropriate geotechnical investigation of soils for all types of buildings.