Parallel pilot effect in tunnel?

When the tunnel is near the mountain and river, and the lateral cover is thin, horizontal tunnel can be considered. Usually, horizontal holes are not long and economical, so it is best to use horizontal holes first to increase the working face when the terrain conditions permit.

The mode of transportation can be trackless transportation or rail transportation. Due to the convenience of drainage and downhill transportation of heavy vehicles, when rail transportation is used, the longitudinal slope of the transverse tunnel should be at least 3% downhill, while when trackless transportation is used, it depends on the vehicle situation.

These auxiliary designs are very important in tunnel construction.

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These auxiliary designs are very important in tunnel construction.

These auxiliary designs are very important in tunnel construction.

(1) When the horizontal tunnel is used as the ventilation opening during operation, the cross-sectional size of the horizontal tunnel should be considered in combination with the ventilation requirements and construction needs, and permanent lining should be built (at least within the appropriate length range at both ends).

(2) Sometimes the bridge and tunnel are connected at the entrance of the tunnel, which affects the construction, or the geological conditions are poor, the terrain conditions are unfavorable, the excavation volume is large, and the cutting needs to enter the hole. When it is possible to set a horizontal hole near the entrance of the tunnel, the horizontal hole can be used to enter the hole to avoid the construction interference and enter the hole in advance to speed up the speed.

These auxiliary designs are very important in tunnel construction.

Parallel passage adit

These auxiliary designs are very important in tunnel construction.

A tunnel built in parallel with a tunnel.

These auxiliary designs are very important in tunnel construction.

For long-span tunnels crossing mountains, when auxiliary tunnels such as horizontal tunnels, vertical shafts and inclined shafts cannot be selected due to terrain constraints, mechanical equipment conditions, transportation roads and other conditions, in order to speed up construction and advance geological investigation, parallel pilot tunnel scheme can be adopted.

The role of parallel pilot tunnel in tunnel construction

(1) The parallel pilot tunnel is excavated in advance, and the geological survey is carried out to fully grasp the geological situation ahead;

(2) If the single-line and double-tunnel scheme is adopted, the horizontal pilot tunnel is located in the main tunnel, and the geological survey of the main tunnel can be directly carried out;

(3) If a second-line tunnel is reserved, the parallel pilot tunnel will be expanded into a second-line tunnel;

(4) The parallel pilot tunnel can be connected with the main tunnel through multiple transverse channels, which greatly increases the working face of the main tunnel and speeds up the construction;

⑤ The parallel pilot tunnel and the main tunnel can form a ventilation system, a drainage and precipitation system and a feeding and slagging transportation system;

⑥ Parallel pilot tunnel can divide the work in the tunnel into sections to reduce mutual interference;

⑦ The parallel pilot tunnel can also form a control survey traverse network with the main tunnel, which is more conducive to ensuring the control survey accuracy.

(2) Key points of parallel pilot tunnel design

These auxiliary designs are very important in tunnel construction.

(1) The plane layout of parallel pilot tunnels is as shown in the figure. Generally, it is located at the side where the groundwater flows to the tunnel, so as to use the parallel pilot tunnel to drain water to the main tunnel, but it should also be comprehensively determined in combination with geological conditions and spoil ground. The minimum clear distance between the parallel pilot tunnel and the main tunnel should be determined according to geological conditions, construction methods, pilot tunnel span and other factors. It is best to consider that the two "natural arches" formed by the excavation of the pilot tunnel are not in contact, otherwise it is easy to cause landslides. Generally, the distance between the parallel pilot tunnel and the main tunnel is about 15-30m, such as 20m. The elevation of the bottom of the parallel pilot tunnel should be 0.2- 0.6m lower than the bottom of the tunnel to facilitate the drainage and transportation of the main tunnel. In principle, the longitudinal slope of the parallel pilot tunnel is the same as that of the tunnel, or a 3% downhill slope is set towards the exit.

These auxiliary designs are very important in tunnel construction.

(2) When entering the tunnel for the first time, no transverse passage can be set at an appropriate length (about 500 m), and then a transverse passage can be set at every 120- 180m to facilitate transportation, and a reverse transverse passage can be set at every 3-4 transverse passages to facilitate transportation and shunting operations (as shown in Figure 6-7-7). Considering the stability of surrounding rock and smooth transportation, the plane intersection angle between the horizontal tunnel and the center line of the main tunnel is generally 40-45. If the included angle is too small, the surrounding rock within the included angle will easily collapse, and the length of the horizontal tunnel will also increase. If the included angle is too large, the operating conditions of the transmission line will be poor. The slope of the cross passage is determined by the height difference between the main tunnel and the parallel pilot tunnel.

(3) Whether the parallel pilot tunnel is lined depends on the geological conditions, so it is generally unnecessary to build it. When it is regarded as a permanent ventilation pipe or drainage tunnel, it should be lined.

(3) Key points of parallel pilot tunnel construction

(1) The cross section of the parallel pilot tunnel is small, so it is inconvenient to use construction machinery to walk the tire. Therefore, rail transportation is generally adopted, and construction machinery running along the corresponding rail is equipped.

(2) In order to give full play to the role of parallel pilot tunnel in increasing the working face and predict the geological conditions of the main tunnel passing area in advance, the excavation of parallel pilot tunnel should be greater than the distance between the two transverse passages of the main tunnel, but it should not be too large, so as to reduce the ventilation difficulty and construction difficulty of parallel pilot tunnel.

(3) The main tunnel should be divided into several construction sections, and each operation should be arranged and carried out in coordination, so as to make full use of parallel pilot tunnels as construction passages and minimize mutual interference between work areas. The length of zoning and sectioning shall be calculated and determined in combination with horizontal channel spacing, operation cycle, transportation organization and other factors.

(4) Because the ventilation system, drainage and precipitation system, feeding and ballasted transportation system and control survey traverse network in the tunnel composed of parallel pilot tunnels and main tunnels are very complicated, it should be carefully designed, used and managed to fully embody the advantages of parallel pilot tunnels, reduce mutual interference and speed up the construction.

⑤ In rail transit, parallel pilot tunnels are generally transported in one lane. In order to meet the needs of transportation and shunting, a two-lane bus stop can be set up every 2-3 intersections, and its effective length is generally 50-60 meters. ..

These auxiliary designs are very important in tunnel construction.

Inclined well

These auxiliary designs are very important in tunnel construction.

An inclined tunnel dug above the side of the tunnel and connected to it.

(1) When the buried depth of the tunnel is small, the geological conditions are good, and there are low-lying terrain such as valleys on the tunnel side, the inclined shaft can be used as the auxiliary tunnel.

(2) The length of inclined shaft is generally less than 200m, so as to reduce the engineering cost and ensure the transportation efficiency.

(3) The wellhead position of inclined shaft should not be located in flooded area. In general, the minimum width of the hole position should not be less than 20 m, which is beneficial to the layout of the wellhead position and the discharge and slag discharge. The wellhead site is usually equipped with a downhill slope of not less than 3‰ leading to the outside of the hole to prevent vehicles from slipping into the hole and causing accidents, and is conducive to drainage.

Wellbore should avoid crossing high water content and bad geological areas.

(4) The elevation angle α of inclined shaft mainly considers the length of inclined shaft and the convenience of construction, and generally it should not be greater than 25, and it is not suitable to set variable slope in the shaft. The included angle between the inclined shaft and the center line of the tunnel should not be less than 40, and the horizontal road of 15-25 m should be adopted at the junction with the tunnel to facilitate the transportation operation and ensure the transportation safety.

These auxiliary designs are very important in tunnel construction.

⑤ Plane connection between inclined shaft and main tunnel hole.

Single connection type

Inclined duplex

Orthogonal duplex

These auxiliary designs are very important in tunnel construction.

(6) The hoist is generally used to pull the skip car. Belt transportation or trackless transportation can also be used when the slope is very small. The number of tracks in inclined shaft depends on the number of ballast. When the tunnel size is in a single lane, the general bottom width is 2.6m；; ; When using three tracks and two lanes, the bottom width is 3.4m；; ; In the case of two lanes, the bottom width is 4. 1 m (including sidewalks with a width of 70 cm on one side), and the height is usually not less than 2.6 m ... Among them, single line or three-track double line is commonly used, and 20-30 m four-track double line is set in the middle of the inclined shaft as a wrong lane, which can reduce the cross section and save transportation equipment.

(7) The section size of inclined shaft should also be determined according to the needs of slag transportation, that is, the number of tracks. When an inclined shaft needs to be used as a ventilation pipe, its section size should meet the ventilation requirements.

(8) During the construction period, well-head waterproof and drainage works shall be done to prevent flooding. Lining should be built in the wellhead section to ensure the stability of the wellhead, and support should be strengthened at the bottom of the well. If necessary, the lining should be built. Generally, other parts are only supported at the initial stage without lining, which not only ensures the construction safety, but also reduces the project investment. However, if it is used as a permanent passage, it is necessary to build an inner lining.

These auxiliary designs are very important in tunnel construction.

These auxiliary designs are very important in tunnel construction.

vertical scroll of painting or calligraphy

These auxiliary designs are very important in tunnel construction.

A vertical tunnel dug above and connected to a tunnel.

When the covering layer is thin or the long tunnel in the middle is not thick and there is lifting equipment, and it is necessary to increase the working face during construction, the shaft can be used to increase the working face. The depth of the shaft generally does not exceed150m.