Soil with weak bearing capacity, like peat and organic grounds, is widespread in Latvia. During the geotechnical investigation for road reconstruction projects, in many cases the discovered soils with low physical-mechanical properties are located below the existing road structure. It is a challenge for a road design engineer to find a way how to ensure road loadbearing capacity and prevent the occurrence of various deformations. Various methods and technologies for ground structure reinforcement and stabilization are being developed worldwide. During design of road structures, it is important to analyse the geotechnical situation and to identify the main reasons why deformations could occur in the ground layers under the road structure. Each of the developed technologies for weak and unstable soil reinforcement, stabilization is designed to solve a specific problem. Inaccurately and carelessly identifying the causes of problems, road deformations can affect the performance of the recently designed road and even make the existing problem worse. The aim of this paper is to show the soil strengthening methods used in Latvia and to analyse the benefits and disadvantages of these methods.

In the last few years as the road construction budget has been decreasing in Latvia, the number of road construction reinforcement design and construction objects has been increasing. At the beginning of the project development of the existing road condition is assessed, taking into account various pavement evaluation criteria and it is determined on which road sections it is possible to reinforce the pavement and where full construction is required. The road pavement structure in Latvia is developed using “Recommendations for road design. Pavement” and inaccurately defining the bearing capacity of the existing foundation can significantly affect the service life of the designed structure. During the construction of the road, establishing that the bearing capacity of the existing foundation is lower than specified in the project incurs additional costs for the customer. Project changes are made, and special solutions are provided in order to achieve the bearing capacity on the mineral material layers defined in the project. One of the most accurate ways to determine the bearing capacity of existing road structural layers is the static plate test. However, the results of this test are also not 100% accurate and any of them may give unreasonable results due to various influencing factors. The aim of this work is to analyze the results of static plate test by determining the most important factors that affect the obtained load-bearing capacity values, identify biased/erroneous test results, and determine which results reflect the residual load-bearing capacity of the existing road structure.

In the last few years as the budget for the road sector has been decreasing in Latvia, the number of road pavement structure reinforcement projects has been increasing. In order to ensure the long-term viability of the road it is necessary to assess the load-bearing capacity of the existing road structure and the subgrade. During the geotechnical research, the load-bearing capacity of the existing base layers is assessed using static plate test. However, the accuracy of the results is strongly influenced by the thickness of the existing asphalt layer and the size of the dismantled asphalt area. In order to determine the load-bearing capacity of the existing road base in the deeper layers, the engineer performs a subjective experience-based interpretation that is not based on mathematical calculations. With the development of geotechnical survey equipment and engineers’ understanding of the bearing capacity of the subgrade, it is also possible to use other field research methods, such as probing and interpretation of their data. Various software’s for soil calculations have been developed worldwide. With the help of software’s, it is possible to evaluate the properties of soil layers, predict deformations and develop reinforcement solutions, however, the obtained results do not reflect the basic bearing capacity, which is expressed in MPa units. It is planned to develop a Finite Element Method simulation of static plate test based on the values of the soil layer parameters obtained from the interpretations of the probe data and to compare the results with the static plate test performed on site. The aim of the study is to determine whether the load-bearing capacity of the existing base can be accurately determined by finite element calculations - a simulation of a static plate test based on the physical-mechanical properties of the soil determined during the geotechnical survey.

Road design is a complex, time-consuming, and very responsible process. To develop a high-quality and viable road project, it is very important to start with an accurate geological survey in order to define the best road layout. Moreover, the geotechnical characterisation of foundation soils and construction materials as well as the analysis and assessment of geotechnical works are mandatory. Laboratory and in situ investigations are complementary and should be carried out by defining a cost-effective investigation campaign. Most often, Dynamic Cone Penetrometer (DCP) or Cone (static) Penetration Test (CPT) are performed because they are economic and quick. In addition, it is also possible to perform the Marchetti Dilatometer Test (DMT). From the obtained test results, the data are interpreted by determining the properties of the soil layers. Although all probing methods are similar, each of them gives slightly different results. The aim of this study is to analyse and compare the results of the probing test, to determine the difference between the obtained data and to find out how the obtained results affect the development of constructive solutions from the safety and economic point of view.