Rocks – Something you need to know

Rotary piling is inseparable from rock and soil. Different geological conditions and different rock types require the selection of different drilling tools. Only by choosing the appropriate type of drilling tools can you get twice the result with half the effort. Let’s learn a little bit about rocks.

Rock types include igneous rocks, sedimentary rocks, and metamorphic rocks. Igneous rocks such as granite and basalt, sedimentary rocks such as sandstone and mudstone, and metamorphic rocks such as phyllite and schist.

Ⅰ.The origin of rock

1. Causes and changes

All geology is caused by rock weathering, transportation, deposition and metamorphism. Rocks melt and become magma. Magma invades the earth's crust or erupts to the ground where it cools and turns into igneous rock. Igneous rocks become sediments through weathering, transport and deposition. Sediments are compacted and cemented to form sedimentary rocks. Igneous and sedimentary rocks become metamorphic rocks under the action of high temperature and pressure. Finally, igneous rocks, metamorphic rocks, and sedimentary rocks melt again under the action of various factors to form magmatic rocks.

2. Internal and external effects

（1）Internal forces: Plate subduction, thermal convection, radioactivity and other factors produce melting and form magma. The magma invades the earth's crust and erupts to the surface. After solidification and cooling, it becomes igneous rock.

（2）External force: External force and solar energy are the main factors, and gravity participates in the driven process. In form, they are respectively represented by the role of the sea, the role of oceans and lakes, the role of rivers and groundwater, and the role of glaciers and gravity. In the process, it is manifested in the process of elegance, erosion, transportation and sedimentation.

Ⅱ. Classification of rock

Molten magma invades the earth's crust or erupts from the surface, and condenses to form igneous rocks. Sedimentary rocks are formed through weathering, transportation, deposition, compaction, and cementation. Metamorphic rocks are formed through high temperature and pressure.

Igneous rock is a rock formed by the condensation of high-temperature molten magma on the surface or underground. It is also called igneous rock or volcanic rock. Magmatism can be divided into intrusion and intrusive rocks (including shenchengyan and epigenetic rocks); magma extrusion and volcanic rocks (including lava, extrusive rocks and pyroclastic rocks).

Igneous rocks are formed when molten rock, known as magma, cools and solidifies. This process can occur within the Earth's crust or at the surface. When magma cools within the crust, it forms intrusive igneous rocks, such as granite, that are typically large and massive. On the other hand, when magma cools at the surface, it forms extrusive igneous rocks, such as basalt, that are typically smaller and have a more limited range of textures and mineralogy. Igneous rocks are composed of minerals that crystallize from a molten state and can range from highly vesicular to dense and crystalline in texture.

Sedimentary rocks are formed through the accumulation and cementation of sediments, which can include fragments of preexisting rocks, minerals, and organic matter. These sediments are typically transported by water, wind, or ice and deposited in layers or strata. Sedimentary rocks can be further classified based on the origin of their sediments, such as detrital or chemical sediments. Detrital sedimentary rocks are formed from the accumulation of fragments of preexisting rocks, while chemical sedimentary rocks are formed through the precipitation of minerals from solution. Sedimentary rocks range from clastic to carbonate in composition and often have a layered or stratified structure.

Metamorphic rocks are formed through the transformation of preexisting igneous, sedimentary, or metamorphic rocks under high temperature and pressure conditions within the Earth's crust. These conditions cause changes in the texture and mineralogy of the rock, resulting in unique characteristics such as foliation, banding, and recrystallization. Metamorphic rocks are classified based on their origin and the temperature and pressure conditions under which they formed. For example, regional metamorphic rocks, such as slate and schist, formed under high-pressure conditions over a large area, while contact metamorphic rocks, such as hornfels, formed under high-temperature conditions near igneous intrusions. Metamorphic rocks range from foliated to nonfoliated in texture and often have a banded or layered structure.

Ⅲ. Weathering

1. Rocks are broken, loosened, and disintegrated under the action of solar radiation, atmosphere, wind, water, and organisms. The effect that causes the above phenomena is called weathering.
2.  According to the degree of weathering, it can be divided into: light weathering, moderate weathering, strong weathering, and full weathering.
3. The characteristics of rocks after reaching the relevant degree of weathering are as follows:

• Fully weathered: generally in the form of sand and debris, with a strength ranging from 260kPa to 350kPa.
• Strong weathering: Generally in the form of fragments, the intensity ranges from 350kPa to 750kPa.
• Weathering: The core is short or columnar, with a strength between 20MPa and 80MPa.
• Light weathering: The rock cracks are slightly developed, the structure is basically unchanged, and the strength is between 50MPa-240MPa.

Rotary drilling rigs are easy to drill into fully weathered rocks; drilling in strongly weathered rocks is difficult.