Deep Excavation and Improvement of Passive Earth Reaction in Weathered Chalk: Design with Deep Soil Mixing or Concrete Cross Wall Solutions-PPT Presentation

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The Pont de Sèvres T3A project investigated ways to improve passive earth pressure using deep soil mixing (DSM) and concrete cross-walls.<br /><br />The ground at the site consists of weathered chalk, with a deformation modulus of 15–30 MPa and a limit pressure of 1–2.2 MPa. Five unreinforced concrete cross-walls were installed in front of a sensitive building across the street. Each wall is 1.5 m wide and supports 6.3 m of diaphragm wall.<br /><br />The concrete was specified as C40/50, with compressive and tensile strengths of 25.6 MPa and 1.8 MPa, respectively. The cross-walls were assessed using the Mohr–Coulomb criterion, with cohesion of 3,400 kPa and a friction angle of 60°. For a 6.3 m support height, the linearized Caquot–Kerisel coefficients were Kpγ = 4.1 and Kpc = 3.3.<br /><br />For finite-element analysis, Plaxis 2D could not accept passive-pressure coefficients directly, so the soil was represented using cohesion and friction angle. Parameters were selected to reproduce the same passive earth pressure as the design values: Kpγ = 4.1, Kpc = 3.3, c′ = 2 MPa, and φ′ = 27°.<br /><br />DSM treatment presented an additional challenge because the works extended to 40 m below ground level, where uncertainty in column verticality could affect performance. The DSM layout was imported into Robot Structural Analysis to estimate stiffness and Young’s modulus from the column response.

Keywords

Pont de Sèvres T3A

passive earth pressure

deep soil mixing

concrete cross-walls

weathered chalk

diaphragm wall

Mohr–Coulomb criterion

Caquot–Kerisel coefficients

Plaxis 2D

Robot Structural Analysis