Features of the numerical modeling of the hydrogeological conditions of the soil massive during the excavation of the pit in the Plaxis software complex
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Abstract
The construction of multi-storey civilian buildings, especially in the central districts of cities, is often accompanied by a developed underground part, which requires deep pits. The construction of such pits often leads to a change in the hydrogeological condition at and near the construction site.
This paper presents a comparison of the stress-strain state of the " base - pit enclosure" system, depending on the method of modeling hydrogeological conditions.
The study is divided into two stages: determination of the main features of the Plaxis software complex toolkit for modeling and determining pore water pressures; creating of numerical models and performing calculations. . The first part of the study describes the basic principle of determining stresses in saturated soils, pore pressure calculation types, hydraulic boundary conditions, and types of soil drainage.
In the second part of the study, the numerical models were developed in Plaxis 2D, based on the real object and hydrogeological conditions at the construction site. The two most popular methods for modeling hydrogeological conditions during dry excavation in the pit are described. A step-by-step calculation is performed taking into account the stages of excavation in the pit and dewatering and the construction of retaining structures according to the scheme provided by the design solutions.
The results of the calculations demonstrate the difference in the obtained values of forces and horizontal displacements of the retaining wall for models created using different methods of setting the hydrogeological conditions of the base.
In order to improve the accuracy of calculations and determine the impact of soil permeability, the impact of the stratigraphy of the base was excluded by solving theoretical problems with a homogeneous soil massif composed of clay or sandy soil with groundwater filtration rates in a wide range (kx=ky=0.001...6m/day). Based on the results obtained, it was found that both methods correlate with each other in the case of the presence of poorly filtering soils with a filtration coefficient of k=0.001...0.05 m/day, the calculations demonstrated similarity in the displacements and forces of the retaining wall in such schemes up to 97.9-99.9%. Instead, in the case of soils with high water permeability (k=0.4...6 m/day), the difference in results is up to 56.5%.
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References
Terzaghi K. Theoretical Soil Mechanics, New York, John Wiley & Sons, Inc. – 1943 – 248р.
Bishop, A.W. & Blight, A.K.G. Some aspects of effective stress in saturated and partially saturated soils. Géotechnique, - 1963 - 13: 177-197.
Brinkgreeve, R.B.J., Engin, E., Swolfs, W.M. Plaxis 2D Reference Manual 2018, Tutorial Manual, Reference Manual, Delft University of Technology, The Netherlands. – 2018 – 55-64.
Galavi V. Groundwater flow, fully coupled flow deformation and undrained analyses in Plaxis 2D and 3D; Internal Report, Delft, Plaxis. – 2010.
Gouw Dr, Tjie-Liong. Common Mistakes on the Application of Plaxis 2D in Analyzing Excavation Problems. 9. – 2014. - 8291-8311.
Gouw, Tjie-Liong. Deep Excavation Failures, Can They Be Prvented. Proc. International Symposium on Sustainable Geosynthetics and Green Technology for Climate. – 2012. – 342-357.
Terzaghi K., (1943) Theoretical Soil Mechanics, New York, John Wiley & Sons, Inc. 248.
Bishop, A.W. & Blight, A.K.G. (1963). “Some aspects of effective stress in saturated and partially saturated soils”. Géotechnique, 13: 177-197.
Brinkgreeve, R.B.J., Engin, E., Swolfs, W.M. (2018). Plaxis 2D Reference Manual 2018, Tutorial Manual, Reference Manual, Delft University of Technology, The Netherlands. 55-64.
Galavi V. (2010). Groundwater flow, fully coupled flow deformation and undrained analyses in Plaxis 2D and 3D; Internal Report, Delft, Plaxis.
Gouw Dr, Tjie-Liong. (2014). Common Mistakes on the Application of Plaxis 2D in Analyzing Excavation Problems. 9. 8291-8311.
Gouw, Tjie-Liong. (2012). Deep Excavation Failures, Can They Be Prvented. Proc. International Symposium on Sustainable Geosynthetics and Green Technology for Climate. – 342-357.