in order to define the features of design of foundations on the sandstones, it is necessary to know their properties and characteristics. To sedimentary deposits of the black sea basin include Sands, limestones, clays, sandstones, mudstones, coarse-grained rocks of Neogene and Quaternary age. The rock in places out on the day surface are often subjected to processes of weathering, become fractured, split into separate fragments. Often, if surface layers are durable sandstones, the formation of distinct protrusions in the terrain.
Sandstone called clastic rock in which the particles are cemented by cement of different compositions. They are formed during weathering of rocks followed by precipitation periodogram water and air flows. During migration is the sorting of particles by size and density. Subsequently, the particles are held together by the cement. After the destruction of sediments by processes of weathering and migration remain the most durable, solid particles (mainly quartz particles). The sandstones are composed of feldspars, micas, glauconite, various debris and minor impurities. The cement composition may be siliceous, calcareous, argillaceous, ferruginous and complex.
the Sandstones are divided by the mineralogical composition of the particles on monomineral and polymineral (consist of two or more minerals). For example, quartz sandstones are composed of quartz. Polymineral sandstones consist of quartz and feldspars, quartz and micas. Grauwacke called a durable Sandstone of different composition (mainly the products of weathering of volcanic precipitation of intermediate and basic composition). They have a lot of fragments of the destroyed rocks. They cement consists of finely grained particles of destroyed material. Tuffaceous Sandstone consists of material of volcanic origin.
durable High physical-mechanical indicators have sandstones with siliceous cement, the worst – clay. Sandstones with clay cement crumbling from frost and moisture, resistant from water. Calcareous cement boil in hydrochloric acid. On sestavit, clay cement there are traces of knife. Siliceous cement has good toughness and durable.
the composition of the sandstones can be identified by color, and knowing the composition and degree of weathering – you can judge the strength of the monoliths. Sandstones with a high content of quartz have a bright or grayish color. Greenish shade gives glauconite. The iron hydroxides give color to a rusty, reddish, brown color. Organic matter give the cement a dark or dark-brownish color. In fact, the sandstones are sand, which was subsequently stsementirovannyj. Cement was formed or as a result of loss of minerals from the water during the circulation along the sandy rock. Or later, after the formation of precipitation as a result of penetration of water through the system cracks. In such cases, the Sandstone occurs locally in the places of fracture.
Calcareous cement is formed in the sandstones, formed in the sea. Ferruginous cement is of continental origin.
Physical and mechanical properties of Sandstone depend on the mineral composition of cement, Sandstone composition, and porosity. Sandstones with clay cement is not resistant to temperature changes, sandstones with calcareous cement exposed to the effects of aqueous solutions of different chemical composition. Maximum strength possess sandstones with siliceous and ferruginous cement, the compressive strength over 200 megapascal. In sandstones with clay cement – not more than two megapascals. More influence on the properties of sandstones is played by the size and uniformity components of the beans. Fine-grained rocks have a compressive strength of about 120 megapascals, medium-grained 90. The older rocks erode cement, porosity is increased – this leads to a reduction in the strength of the breed.
the Most diverse composition of Sandstone and of cement requires the carrying out of works - geotechnical investigation of Sandstone in the field and laboratory. Sandstones with clay cement is tested in the laboratory by soaking. In the process of weathering of these sandstones may occur deformation of buildings and structures, may occur landslides. Special attention should be paid to the examination of Sandstone weathering. Also the strength of the soil decreases, when the sandstones beds are intercalated with the siltstones. In the fractured sandstones and sandstones with a weak cement often circulating groundwater. The porosity of sandstones can reach up to 25%.
the Degree of weathering of rock is determined by comparing the density of the weathered sample with the density newaverage sample. If there are severely weathered or softened rocky soils it is necessary to determine the bearing capacity using static tests.
the geotechnical report should contain information about lithology, information about dangerous natural processes on the hydrogeological conditions, the shape of the dip, on the state of soils.
the construction of the Foundation upon the solid rock the soils can be performed with a minimum depth of backfill. When calculating the depth to take into account properties of the soil, stratification, water table, loads from buildings and structures, climatic factors.
OOO "GUILD ENGINEERING" will perform all necessary geotechnical studies on sandstones in the time convenient for You efficiently and promptly.