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Sand dunes: Highly mobile and unstable surfaces
Published in P.G. Fookes, R.H.G. Parry, Engineering Characteristics of Arid Soils, 2020
Dunes are built of mineral sand or sand-sized aggregates of clays, salts or ice. Quartz sand (the commonest material) generally remains loose. Carbonate sand, which is locally common, can also accumulate in loose anchored and mobile dunes, but may eventually cohere to as “aeolianite” (Gardner 1983; Gardner and McLaren 1993).
Consolidation of Soft Sandstones Used in Historical Constructions. Application to a Case Study
Published in International Journal of Architectural Heritage, 2022
Fernando F. S. Pinho, Pedro C. Lamas, Gonçalo C. Teotónio
The Fort was built on a raised sandstone platform overlooking the sea, Figure 2a. The building, having a square plan, two bulwarks at the SE and SW corners and two polygonal batteries facing the ocean was classified as a “Portuguese Property of Public Interest” in 1957. It is surrounded by a moat cut into the sandstone, Figure 2b and c, which in turn is protected by walls, which are much degraded in some places, Figure 2d. The Fort was originally built with existing stone, initially the remnants of a previously ruined fortification, and then with stones extracted from a quarry located a few tens of meters to the south, Figure 2e. This very porous sandstone is the product of cementation and compaction of wind-accumulated sands, creating a rock mass with a well-defined stratification (aeolianite) and whose fundamental constituents are, according to Carvalho and Romariz (1973), calcium carbonate (about 79.4%), sandy terrigenous debris (19.5%) and clay (0.9%). The first fraction came from the dissolution of calcite, from the existing shells and later precipitated among the sand dune grains (mainly of quartz and quartzite), a process responsible for the cementation degree of the dunes, making it possible to use the aeolianite as a building material. An initial approach to determining the physical properties of this stone, involving laboratory tests on samples taken nearby, found it to be poorly compacted, highly porous and easily disaggregated (Lamas, Sokolová, and Galhano 2016). Tests related to the presence of water revealed a material that is easily infiltrated by water which means that, in the rainy season, besides reducing the already weakened strength properties, it allows easy penetration of salts into the pores.