The influence of the hardening mechanism on the results of the calculation of pit fences in the conditions of St. Petersburg

Introduction. The study is devoted to the issues of modelling and calculating the process of excavation in the conditions of the city of St. Petersburg, where weak clay soils of various genesis are widespread. The relevance of the topic under consideration is due to the need to improve the accuracy and reliability of calculations of soil foundations in conditions of dense urban development. It is especially important to take into account the specific properties of weak clay soils, such as their undrained behaviour and, mainly, shear deformation. The paper focuses on the mechanism of shear hardening, which is critically important for predicting plastic deformations of clay soils in the pre-limit loading stage.

Materials and methods. The main provisions of the nonlinear mathematical model previously proposed by the authors describing the behaviour of weak clay deposits based on the shear hardening mechanism are presented. The untrained behaviour is described on the basis of the modified theory of instantaneous strength by Yu.K. Solovyov, taking into account the formation of excessive pore pressures under deviatory loading in a plane stress-strain state. The model was numerically implemented in a specialized software package developed by the authors that implements the finite element method based on the displacement method.

Results. As part of the study, a numerical calculation was carried out for the development of a pit protected by a cantilever tongue-and-groove fence in conditions of dense urban development in the Central District of St. Petersburg. The paper also provides a detailed comparison of the results of numerical calculations with data from geotechnical monitoring, including measurements of deformations of the tongue-and-groove fencing of the excavation and foundations of the surrounding buildings.

Conclusions. Based on this study, conclusions are drawn about the predictive capabilities of models with a shear hardening mechanism for pit calculations in conditions of weak clay soils. Recommendations are given on the further development of the proposed model, including improvements in taking into account the effect of unloading the base and changes in stiffness parameters during deformation.

1. Fadeev A.B. The finite element method in geomechanics. Moscow, Nedra, 1987; 221. (rus.).

2. Koljukaev I.S. Numerical solution of the problem of the stress-strain state of a slope in an elastic and elastoplastic formulation. Series “Construction” : collection of articles by master's and postgraduate students. 2023; 1(6):439-451. (rus.).

3. Polunin V.M., Kolyukayev I.S., Korablev D.S., Paskacheva D.A. Implementation of an ideal elastoplastic soil model in the deformation domain. Geotechnics. 2023; 15(3):26-42. DOI: 10.25296/2221-5514-2023-15-3-26-42 (rus.).

4. Ulitsky V.M., Shashkin A.G., Shashkin K.G., Shashkin V.A. The basics of joint calculations of buildings and foundations. St. Petersburg, Institute of “Geo-reconstruction”, 2014; 328. (rus.).

5. Schanz T., Vermeer P.A., Bonnier P.G. The hardening soil model: Formulation and verification. Beyond 2000 in Computational Geotechnics. 1999; 16.

6. Mangushev R.A., Penkov D.V. Comparison of the results of numerical calculations using modern soil models (Hardening Soil, Hardening Soil Small and Generalized Hardening Soil) with the geotechnical monitoring results. Bulletin of Civil Engineers. 2021; 85(2):85-93. DOI: 10.23968/1999-5571-2021-18-2-85-93 (rus.).

7. Mussa A., Salah M., Salah L.M. Practical use of advanced constitutive laws in finite element analysis of underground structures. Scientific Papers — Journal of Civil Engineering. 2022; 17(1):1-14. DOI: 10.2478/sspjce-2022-0015

8. Sharafutdinov R.F. Regulatory provisions for determining parameters of nonlinear mechanical behaviour in hardening soil models. Construction and Geotechnics. 2023; 14(1):29-42. DOI: 10.15593/2224-9826/2023.1.03 (rus.).

9. Roscoe K., Schofield A., Wroth C. On the Yielding of Soils. Geotechnique. 1958; 8(1):22-53. DOI: 10.1680/geot.1958.8.1.22

10. Burland J.B. The yielding and dilation of clay. Geotechnique. 1965; 15(2):211-214. DOI: 10.1680/geot.1965.15.2.211

11. Mangushev R., Bashmakov I., Paskacheva D., Kvashuk A. Mathematical modelling of undrained behaviour of soils. International Journal for Computational Civil and Structural Engineering. 2023; 19(1). DOI: 10.22337/2587-9618-2023-19-1-97-111

12. Grimstad G., Andresen L., Jostad H.P. NGI-ADP. Anisotropic shear strength model for clay. International Journal for Numerical and Analytical Methods in Geomechanics. 2012; 36(4):483-497. DOI: 10.1002/nag.1016

13. Langford J., Karlsrud K., Bengtsson E., Hof C., Oscarsson R. Comparison between predicted and measured performance of a deep excavation in soft clay in Gothenburg, Sweden. Geotechnical Aspects of Underground Construction in Soft Ground. 2021. DOI: 10.1201/9780429321559-11

14. Ter-Martirosyan A.Z., Ermoshina L.Y., Anzhelo G.O. Viscosity of Clayey Soils: Experimental Studies. Applied Sciences. 2024; 14(14):5974. DOI: 10.3390/app14145974

15. Ter-Martirosyan A.Z., Manukyan A., Ermoshina L.Y. Experience of determining the parameters of the elastoviscoplastic soil model. E3S Web of Conferences. 2021; 263(16):02051. DOI: 10.1051/e3sconf/202126302051

16. Nieto-Leal A., Kaliakin V.N. Additional Insight into Generalized Bounding Surface Model for Saturated Cohesive Soils. International Journal of Geomechanics. 2021; 21(6). DOI: 10.1061/(ASCE)GM.1943-5622.0002012

17. Kaliakin V.N., Anantanasakul P. Behaviour and modelling of silt-clay transition soils. Smart Geotechnics for Smart Societies. CRC Press, 2023; 253-268. DOI: 10.1201/9781003299127-22

18. Shashkin A.G. Viscoelastic-plastic model of clay soil behaviour. Urban Development and Geotechnical Construction. 2011; 2:1-32. (rus.).

19. Solovyov Yu.I., Karaulov A.M., Vaganov P.S. The theory of instantaneous strength and its application in calculations of stability of consolidating soil masses. Design and research of the foundations of hydraulic structures : materials of the conference and the meeting on hydraulic engineering. Leningrad, Energy, 1980; 104-105. (rus.).

20. Kondner R.L. Hyperbolic stress-strain response: cohesive soils. Journal of the Soil Mechanics and Foundations Division. 1963; 89(1):115-143. DOI:10.1016/0022-4898(64)90153-3

21. Botkin A.I. The strength of loose and brittle materials. News of the Research Institute of Hydraulic Engineering. 1940; 26:205-236. (rus.).

22. Paramonov V.N. The finite element method for solving nonlinear geotechnical problems. St. Petersburg, Geo-reconstruction, 2012. (rus.).

23. Geuzaine C., Remacle J.F. Gmsh: A 3-D finite element mesh generator with built-in pre-and post-processing facilities. International Journal for Numerical Methods in Engineering. 2009; 79(11):1309-1331.

24. Zhusupbekov A.Zh., Ulitsky V.M., Diakonov I.P., Nikolaeva M.V. Obtaining physical and mechanical characteristics of limnoglacial deposits of St. Petersburg for a mathematical model of the soil. Bulletin of Civil Engineers. 2023; 97(2):44-55. DOI: 10.23968/1999-5571-2023-20-2-44-55. (rus.).