Loose, semi-solid and solid rock

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The geology divided rocks by its strength in loose rock e and hard rock e. The engineering and building geology also knows even half bedrock e. In the specific case, the assessment and determination of the relevant structural soil class (1–7) is carried out by experts who are familiar with soil mechanics . The technical discipline that deals primarily with the behavior of solid rock is rock mechanics .

Loose rock

Cones of coarse sand

Loose rock (soil classes 1–5) is a non-solidified pile of aggregates , the aggregate parts of which have no solid cohesion, i.e. little grain binding. The spaces in between are filled with air or water . It has a very low shear strength , and slopes or embankments to its stability is relatively well with the friction angle describe. In addition, loose rock can be divided into non-cohesive (grain binding only through friction), cohesive (particle adhesion mainly through cohesion , e.g. through clay minerals ) and organic (cohesion through matting of organic fibers ).

According to Maidl's definition (see literature and web links ), loose rock is a mixture without any mineral bond. It can be a mixture of minerals , rock fragments and organic material or consist solely of one of these components. It is possible to break down the mineral components according to grain size . Another feature is the predominantly point contact of the partial bodies. Loose rock basically consists of several phases or states of aggregation (solid-liquid, solid-gaseous or solid-liquid-gaseous), the ratio of which is often shown in a triangular three-phase diagram.

The main types of loose rock are - from coarse to fine:

In some loose rock, such as older sand or gravel banks , the rock grains can be slightly cemented together , as long as this is not yet a property that determines the strength .

From loose rock there are also some celestial bodies , in particular sun distant asteroid and most of comet nuclei . In the case of the former, the consistency roughly corresponds to a slightly solidified conglomerate. Comet cores, on the other hand, are a mixture of the ice of various frozen gases, so-called " star dust ", and pieces of rock made of meteorite- like material.

Solid rock


Solid rock (soil classes 6–7), the everyday language calls them “stone”, “ natural stone ” or “ rock ”, are mechanically resistant rocks whose structure and deformability correspond to those of solids . With an increase in pressure / temperature or through mountain water , the gaps (pores) in loose rock are reduced and filled ( cemented ) with deposits such as calcite and silica , clay minerals and iron oxides , so that a loose material such as calcareous sand, sandy gravel, lime sludge or Clay hard rock such as sand-lime brick , conglomerate and breccia , lime sinter , limestone or clay slate can arise. This process is described as diagenesis in rock science and consists of compaction (pressing) and cementation (supply of binding agent).

In addition to sedimentary rocks (sedimentary rocks, often diagenetically solidified loose rock), solid rocks also include the other two rock classes magmatites (solidified rocks : plutonites , volcanic rocks , dike rocks ) and metamorphic rocks (transformation rocks : e.g. gneisses ). They are called natural stone in construction.

If the compressive strength of solid rock is greater than about 100 N / mm² (1,000 kg / cm²), the corresponding soil class exceeds the value of 6. The hardness and shear strength of these rocks depend on the internal structure, including the grain size, fissures and Foliation . Measured in terms of the mean compressive strength, sandstone sometimes exceeds this limit at 200-3,000 kg / cm², while limestone and dolomite (300-1,800) are less common, while granite and gneiss range up to around 2,500 kg / cm². The most mechanically resistant rock found in the upper crust of the earth is fine-grain basalt (up to over 5,000 kg / cm²).

Semi-solid rock


Semi-solid rock (soil class 6) lies between loose and solid rock. They have compressive strengths below 80  N / mm² (800 kg / cm²). To detonate such rocks, an amount of explosives of around 150–200 g / m³ is required. The typical mechanical properties of semi-solid rock can on the one hand be due to advanced diagenesis of loose rock, on the other hand to advanced weathering , relatively strong fissures or the special material properties (mineral stock) of solid rock.

Examples of semi-solid rock are weak to medium-grade diagenetic clay stones (e.g. " oil shale "), chalk , limestone marl , some plasters , limestone tuffs , travertines and volcanic tuffs . Heavily weathered marbles or dolomites can also be included.

Literature and web links