Open cut and dark cut are two different underground construction methods, which play an important role in urban construction and infrastructure construction. Below I will introduce the characteristics and application scenarios of these two methods in detail.

　　1. Open cut method

　　Open cut method, also known as foundation pit method, refers to the underground construction method of first digging the ground, building lining in the open air, and then covering and backfilling. Open cut method is generally suitable for shallow buried tunnels, with the advantages of simple, fast, economical construction technology and good stress conditions of the main structure. But its disadvantages are also obvious, such as long traffic blocking time, noise and vibration. The construction process of open cut method generally includes foundation pit dewatering, slope reinforcement and foundation pit earthwork.

　　1.1 Features:

　　- Simple construction: no complex support system is required, and the construction process is relatively intuitive.

　　- Low cost: Compared with dark cut method, the construction equipment and technical requirements of open cut method are not high, so the cost is lower.

　　- Large impact range: The construction process will have a greater impact on ground traffic and the surrounding environment.

　　- Strong applicability: Suitable for areas with good geological conditions and low groundwater levels.

　　1.2 Application scenarios:

　　- Municipal pipeline laying, such as water supply, drainage, gas pipelines, etc.

　　- Shallow underground space development, such as underground shopping malls, parking lots, etc.

　　- Basic engineering construction, such as foundation excavation of bridges and buildings.

　　2. Concealed excavation method

　　Concealed excavation methods generally include drilling and blasting (mining) method, shield method, pipe jacking method, etc. Among them, the drilling and blasting method is a method of excavating rocks by drilling, charging, and blasting, and is mostly used in tunnel construction. The shield method is a fully mechanized construction method in the construction of concealed excavation. It is to push the shield machine into the ground, support the surrounding rock with the shield shell and pipe segments to prevent collapse into the tunnel, and use a cutting device to excavate the soil in front of the excavation face, transport it out of the cave through the excavation machinery, and pressurize it at the rear with a jack, and assemble prefabricated concrete pipe segments to form a mechanized construction method of tunnel structure. The pipe jacking method is a trenchless construction method that uses a jacking device to push the tool pipe or tunnel boring machine from the working pit through the soil layer to the receiving pit and lift it up. At the same time, the pipeline following the tool pipe or tunnel boring machine is buried between the two pits.

　　2.1 Features:

　　- Small impact on the ground: The impact on ground traffic and surrounding buildings during construction is small.

　　- High technical requirements: Professional tunnel boring machines and complex support systems are required.

　　- High cost: Due to the particularity of technology and equipment, the cost of the dark excavation method is usually higher than that of the open excavation method.

　　- Wide applicability: Applicable to various geological conditions, including soft soil, hard rock, etc.

　　2.2 Application scenarios:

　　- Metro tunnel construction, such as tunnel construction of urban rail transit.

　　- Construction of long-distance water and gas transmission tunnels.

　　- Tunnel projects of highways and railways crossing mountains or cities.

　　Open excavation and dark excavation have their own advantages. Which method to choose depends on the specific needs of the project, geological conditions, cost budget and consideration of the impact on the surrounding environment. In actual projects, these two methods are sometimes used in combination to achieve the best construction effect.