Abstrakt
Sandstone weathering/disintegration is a complex process involving loose material production, rockfall phenom-ena, and creation of picturesque natural sceneries. On historical monuments, they induce damage to building stone.
Here we present a new look on sandstone weathering/recession the central aspect of which is rapid disin-tegration of portions of the rock massif, which are no longer physically connected with the main rock mass, though still in situ. A set of field and laboratory measurements including mechanical (tensile strength, drilling re-sistance) and hydraulic (permeability, surface moisture) methods were applied to compare the properties of the disconnected portions with those of the surrounding rock mass.
Also, physical weathering experiments were per-formed to characterize the effect of confinement on the breakdown rate of several sandstone samples. The pres-ence of disconnected portions is very common in dry climates where they are usually elongated parallel to horizontal surfaces.
In humid temperate climates, however, they are less abundant, being elongated mostly ver-tically. The surfaces of disconnection follow bedding planes, planar elements of other sedimentary structures, and subhorizontal fractures, and stress shadows on subvertical cliff faces.
Weathered surfaces of the disconnected portions show reduced tensile strength and drilling resistance values, a faster capillary water absorption and a higher surface moisture compared to the much less weathered surfaces of the surrounding rock mass. Physical experiments demonstrated that a confinement by the surrounding rock mass may considerably delay the loosen-ing of rock during weathering.
The much faster disintegration rates of the disconnected portions of rock com-pared to their surroundings are explained by the fact that they are not confined and have a larger surface area. The recession rates of sandstone surfaces with disconnected portions are highly variable both in space and time and their genesis can be demonstrated by two suggested conceptual models.