Tunnel design: including tunnel route selection, longitudinal section design, cross section design, auxiliary tunnel design, etc.
Route selection: Select the location and length of the tunnel according to the line standard, topography, geology and other conditions. Various schemes should be compared when selecting the line. For long tunnels, auxiliary tunnels and operational ventilation should be considered. The location of drilling holes should be selected according to geological conditions. Consider the stability of slope and uphill to avoid collapse.
Longitudinal section design: the longitudinal slope along the tunnel center line should obey the limited slope of the line design. Because of the high humidity in the tunnel, the adhesion coefficient between wheel and rail decreases and the air resistance of the train increases, so the longitudinal slope of long tunnel should be reduced. Longitudinal slopes are mostly single slopes and herringbone slopes. Single slope is beneficial to win elevation, and herringbone slope is convenient for construction drainage and ballast. In order to facilitate drainage, the minimum longitudinal slope is generally 2 ‰ ~ 3 ‰. Section design: the section of the tunnel, that is, the inner contour of the lining, is made according to the limit of not invading the tunnel building. China tunnel construction gauge is divided into two types: steam diesel locomotive traction section and electric locomotive traction section, which are divided into single-line section and double-line section respectively. The inner contour of the lining usually consists of a single central circle or three central circles and an arch formed by straight or curved side walls. Add inverted arch in weak geological area. The inner contour area above the rail surface of single-track tunnel is about 27 ~ 32 square meters, and that of double-track tunnel is about 58 ~ 67 square meters. In curved sections, due to factors such as the inclination of ultra-high external rail vehicles, the section should be appropriately enlarged. The height of the inner contour of electrified railway tunnel should be increased because of hanging catenary. The overall dimensions used in China, the United States and the Soviet Union are as follows: the height of single-track tunnel is about 6.6 ~ 7.0 meters, and the width is about 4.9 ~ 5.6 meters; The height of the double-track tunnel is about 7.2 ~ 8.0m, and the width is about 8.8 ~10.6m. When building two single-track tunnels on the double-track railway, the influence of stratum pressure distribution should be considered in the line spacing. The rock tunnel is about 20 ~ 25m, and the soil tunnel should be widened appropriately.
Auxiliary tunnel design: There are four kinds of auxiliary tunnels: inclined shaft, vertical shaft, parallel pilot tunnel and horizontal tunnel. Inclined shaft is an inclined main tunnel dug in a favorable place on the mountain near the center line. The inclination angle of inclined shaft is generally between18 ~ 27, and it is lifted by hoist. Inclined shafts are generally rectangular in cross section, with an area of about 8 ~ 14 square meters. The shaft is a vertical excavation tunnel near the center line of the top of the mountain, leading to the main tunnel. Its plane position can be on the center line of the railway or on one side of the center line (about 20 meters away from the center line). The shaft section is mostly circular, and the inner diameter is about 4.5 ~ 6.0 meters. The parallel pilot tunnel is a small parallel tunnel excavated at a distance of 17 ~ 25m from the tunnel center line, which is connected with the tunnel through an inclined channel and can also be used as the pilot tunnel of Line 2 in the future. Since China adopted parallel pilot tunnels in the construction of liangfengya railway tunnel of 1957 Sichuan-Guizhou Railway, about 80% of 58 tunnels with a length of more than 3 kilometers have been built with parallel pilot tunnels. Transverse tunnel is a small cross-section tunnel opened on the favorable terrain near the valley side of mountain tunnel. In addition, the tunnel design also includes the entrance design, excavation method and lining type selection.
Tunnel penetration control survey: Tunnel survey is to ensure that the deviation between the center line and the elevation measured at the tunnel penetration surface does not exceed the specified limit.
Center line plane control: In the past, triangulation was used for long tunnels, and traverse method was used for short tunnels to control center line deviation. Since 1950s, traverse method has been used to control the tunnel penetration error in the tunnel survey with the length of 1km in China. The appearance and development of photoelectric rangefinder solved the difficulty of ranging. The main and auxiliary closed traverse method is adopted inside and outside the mountain tunnel, that is, the angle is measured on the main traverse, the distance is measured by photoelectric rangefinder, and only the angle is measured on the auxiliary traverse. A polygon composed of major and minor wires can only adjust its angle, but not its length. In this way, the main guidance line method is simpler and more practical than the triangle method and more reliable than the single wire method. The main and auxiliary closed traverse method is adopted as the central line plane control of Dayaoshan double-track tunnel in China. Before measuring the tunnel centerline, the deviation value after the opening of the tunnel in the future should be considered. According to the length and plane shape of the tunnel, the measuring points and the positions of the expected through points are arranged on the topographic map first, and the necessary dimensions are measured on the plane map, and then the necessary accuracy of the measuring angle and distance is calculated according to the tolerance specified in the specification, and then the measurement is carried out. This process is called measuring design or tunnel penetration error. The limit error of tunnel centerline penetration prediction below 4 km is100 mm; The limit error of 4 ~ 8 km tunnel centerline penetration is150 mm.
Elevation control: ordinary level can be used for short tunnels, and precision level can be used for long tunnels to ensure the required accuracy. The limit error of elevation penetration is 50 mm, and the tunnel excavation methods are divided into cut and cover method and underground excavation method. Open excavation method is mostly used for shallow buried tunnels or urban railway tunnels, and underground excavation method is mostly used for mountain railway tunnels. According to the size and location of excavation section, there are local excavation method and full-face excavation method. Drilling and blasting method is the most widely used in stony rock strata, and direct tunneling by roadheader is gradually popularized. Shield method is widely used in soft geology.
Tunnel investigation: determine the location, construction method, lining type and support mode of the tunnel, and investigate the technical scheme of the tunnel, that is, the topography, geological conditions, groundwater distribution and water source and other hydrological conditions within the range. In the process of tunnel survey and excavation, it is necessary to understand the classification of surrounding rock. Tunnel excavation will affect the stability of rock mass around the tunnel. Classification of surrounding rocks refers to the comprehensive strength of surrounding rocks in turn. 1975 Technical Specification for Surrounding Rock of China Railway Tunnel Project is divided into 6 blocks. On the classification of rocks, before the 1970s, the classification methods such as field commander and Pullman rock were widely used. Various classification systems widely used in the world and recommended by the International Society of Rock Mechanics since 1970s are used by Barton. In addition, Japan uses elastic wave velocity as a classification. The determination of surrounding rock types of tunnel engineering provides a basis for reasonable design and smooth construction.
Tunnel design: including longitudinal design of tunnel line, cross-sectional design, auxiliary tunnel design, etc.
Route: Select the location and length of the tunnel according to the standard, route topography and geological conditions. The route should be a comparison of various schemes. For long tunnels, auxiliary tunnels and operating ventilation settings should be considered. The location of the hole must be selected according to the geological conditions. Consider the slope and its stability range to prevent landslide.
Longitudinal design: the design limit slope along the tunnel centerline to the longitudinal slope line. Because of the high humidity, the adhesion coefficient between wheel and rail in the tunnel decreases, while the air resistance of the train increases, so the vertical slope should be reduced in the long tunnel. The shape of longitudinal slope is mostly single slope and herringbone, the elevation of single slope is for contending for slope, and herringbone is for construction drainage and slope ballast removal. In order to facilitate drainage, the minimum value of longitudinal slope is generally 2 ‰ ~ 3 ‰. Cross-section design: the outline of tunnel lining, that is, crossing into the tunnel construction, is to gauge and work. China tunnel structure is divided into two types: steam locomotive and diesel locomotive traction section and electric locomotive traction section, which are divided into single section and double section respectively. Generally speaking, the outline of lining consists of a single circular arch or a three-center circular arch and a straight or curved wall. Add a positive arch to the soft geological area. The contour area of inner rail surface of single-track tunnel is about 27 ~ 32 square meters, and that of double-track tunnel is about 58 ~ 67 square meters. Due to the factors such as the height inclination of rail vehicles in curved sections, the section should be appropriately enlarged. Overhead contact system of electrified railway tunnel should be improved and paid attention to. The size outline adopted by the United States and Susan countries is as follows: the height of single-track tunnel is about 6.6 ~ 7.0 m, and the width is about 4.9 ~ 5.6 m; The height of the double-track tunnel is about 7.2 ~ 8.0m, and the width is about 8.8 ~10.6m. Two single-track tunnels are built on the double-track railway, and the distance between the lines must consider the distribution of stratum pressure on the rock tunnel, about 20 ~ 25m, and the soil tunnel should be widened appropriately.
Auxiliary tunnel design: There are four types of auxiliary tunnels: shaft, auxiliary shaft, tunnel pit, parallel shaft and horizontal hole. The vantage point leaning near the center line of the mountain range is digging holes in the tunnel. The inclination angle is generally between18 and 27, and the hoisting room is lifted. The inclined section is generally rectangular, with an area of about 8- 14 square meters. The hole dug on the top of the mountain near the center line of the shaft perpendicular to the tunnel is the hole. Its plane position is at the center line of the railway or about 20 meters away from the center line). Most of the shafts are circular in cross section, and the inner diameter is about 4.5 ~ 6.0 m. The parallel tunnel pit is a parallel tunnel excavated at a distance of 25 m from the center line of 17 tunnel, which is very small with the oblique passage of the tunnel and can also be connected with the second line drift to be expanded in the future. 1957—— The self-built Liangfeng Railway Tunnel in China adopts parallel L-shaped cutter pits, with three stone pillars in one length. About 80% of the tunnels over 58km have built parallel cutter pits. The tunnel is a small cross-section tunnel built on the open terrain of the waterfront near the river ditch of the mountain tunnel. In addition, the tunnel also includes the design of east gate, the design of excavation method and the selection of lining type.
Tunnel penetration control survey: Tunnel penetration is to ensure that the deviation of survey and elevation survey lines at the tunnel penetration surface does not exceed the specified limit.
Center line plane control: Before triangulation for long tunnels, traverse method is often used to control center line deviation for short tunnels. Since the 1990' s, China has adopted traverse method to measure the tunnel length over 65438±0km, which can also control the tunnel penetration error. The appearance and development of photoelectric rangefinder has solved the difficulty of distance. All the main and auxiliary tunnels in mountain tunnels are closed by traverse method, that is, the angle is measured on the traverse network and the distance is measured by photoelectric rangefinder, and the auxiliary traverse only measures the angle but not the distance. A polygon composed of minor lines is uneven only by the length difference of angle adjustment. Therefore, the main and auxiliary traverse method is simpler and more practical than the triangulation method and more reliable than the single traverse method. The data of China main line tunnel takes double lines as the auxiliary closed midline plane to control the midline measurement of the tunnel, so it is necessary to consider the deviation value before the tunnel is completed in the future. According to the length and shape of the adit working face, the position of the measuring point and the leading through point are arranged on the topographic map, and the necessary size and quantity on the plan are predicted, and then the accuracy of the measuring angle and quantity is calculated according to the tolerance specified in the specification, and then the necessary survey is carried out. This process is called measurement design or tunnel breakthrough error, and the limit error of the expected line breakthrough of a 4 km tunnel is+100 mm; The tolerance of 4-8km tunnel passing through the central line is+150mm.
Elevation control: ordinary level is used in short tunnels and precision level is used in long tunnels, which can ensure the accuracy required by the application. The error of elevation exceeding the limit is+50 mm Tunnel excavation methods are divided into cut and cover method and underground excavation method. Open-cut method is mostly used for shallow-buried tunnels or urban railway tunnels, while cut and cover is mostly used for mountain railway tunnels. According to the section size and excavation position, the excavation method and the whole section are divided. In the rock drilling and blasting method of rock drill, the most widely used tunneling machine is gradually popularized. Shield excavation is more common in loose geology.