Massive sulfate attack to cement-treated railway embankments

Abstract

Two access embankments to a railway bridge, having a maximum height of 18 m, experienced a continuous and severe heave shortly after construction. Vertical displacements reached 120 mm in a 2-year period. The embankments were designed, by including soil–cement-treated transition wedges, to provide an increasingly rigid support as the trains approach the stiff bridge abutments. A grid of 10 m deep jet-grouting columns was also built, with the purpose of stabilising the embankments. Instead, a sustained swelling deformation, which extended to depths of 8–10 m, was activated. The compacted soil was low-plasticity clayey material, with a variable percentage of gypsum. The embankments suffered a massive ettringite–thaumasite attack, which was triggered by the simultaneous presence of cement, clay, sulfates and an external supply of water (rain). The paper describes the field extensometer and inclinometer records, the long-term laboratory tests performed, some mineralogical observations and the reactions leading to the growth of expansive crystals, and presents a model that simulates the measured heave. Forces acting against the bridge, which was seriously damaged, were estimated. Remedial measures include removal of the active upper zone of the embankments, and the construction in stages of slabs supporting the rails and founded on piles built on both sides of the embankments. The case is considered unique because of the magnitude of the reaction developed in the embankments, and its damaging action on the nearby bridge structure.Postprint (published version

Dissolution-precipitation-driven upward migration of a salt crust

“…Salt precipitation in porous media is a phenomenon of great importance in various applications such as soil sciences and hydrology [1,2], archelogy and monument preservation [3][4][5], concrete science [6], and geotechnical engineering [7]. When the precipitation occurs at the surface of a drying porous medium, this process can lead to the formation of a porous salt crust covering the surface [8][9][10][11][12].…”

“…Then, the air layer formation must be explained. This point is very briefly discussed in [15] with the qualitative evocation of the possible role of dissolution-precipitation mechanisms and/or mechanical effects, the latter being suspected in relation with the wellknown fact that crystallization in pores can lead to stress generation [4,5,7,17]. Actually, one must realize that the physics of salt crusts is an unexplored area.…”

Chemo-mechanics of salt damage in stone

“…While this was recognized long ago in geomorphology 1,2 and conservation science [3][4][5][6][7] , it has only recently emerged in concrete science as the most convincing explanation for sulfate attack [8][9][10] and in geotechnical engineering for the floor heave of anhydrite-containing rock formations 11 . In the latter case, the most dramatic situation was a geothermal drilling through anhydrite-bearing rock formations that opened access for water to convert anhydrite to gypsum.…”

Analysis of massive sulphate attack to cement-treated compacted soils

“…The embankments give access to a bridge 196 m long, Pallaressos bridge, and have a maximum height of 18 m in the proximity of the bridge abutments. Structural details of Pallaressos Bridge are described in [5].…”

“…The soil stabilization treatment usually encompasses thin layers of soil; however, massive sulphate attack can also occur when the treatment concerns larger soil masses. This is the case of two railway embankments, Pallaressos embankments, built in Spain and affected by sustained damage ( [5]).…”