Road Design And Construction On Low Bearing Capacity Soils Using Piling Method: Experience Of SLLC “Latvian State Roads”

The road system in Latvia has evolved over time to a complex network of physical structures that include roads, bridges and overpasses, however, in large it consists of narrow roads of local significance that follow the existing topography and consist of thin foundation and pavement layers. In-depth geotechnical research of road sections before construction has only been carried out in recent decades, thereby with a certain regularity SLLC “Latvian State Roads” has to deal with low bearing capacity soils under the road foundation. As the recent experience shows, there are sections of roads that in the past were constructed on peat. In 2018 during the reconstruction works of the regional road P32 Augšlīgatne – Skrīveri a low bearing capacity soil under the road foundation was determined. An additional in-depth geotechnical research showed a bog section with a peat layer at a depth of 10m in a 320 metres long section. Although at that point it was possible to continue the work using simple soil stabilization methods, there were concerns about the longevity of the investment. To stabilize the road foundation, a combination of gravel columns and unreinforced concrete pile columns was used. A total of 952 columns were constructed. The aim of this paper is to share technical information and our good practice of road design and construction on low bearing capacity soils using piling method, and it gives a summary of field observations, geotechnical research, design considerations and risk management assessments that were carried out in this specific case. The positive outcome of this case led to a number of future projects where similar methods for load bearing capacity improvement were planned and used.