When the stone of the porch is hard and stable (I ~ II fence), and the terrain is steep, and there is no drainage requirement, the porch can only be reinforced with a ring frame to reduce dripping after rain.
(2) End wall (straight line) doors and column doors
1. End-wall portal: It is suitable for areas with open terrain and stable rocks (Grade II ~ III surrounding rocks), and consists of end wall, portal top and drainage ditch. The function of the end wall is to resist the longitudinal thrust of the mountain, support the upward slope of the cave and maintain its stability. The drainage ditch at the top of the portal is used to collect the surface water flowing down the slope and then walk away.
2. Pillar portal: When the local potential is steep (grade IV surrounding rock), the uphill slope is easy to slide, and the wing wall cannot be set due to geological or topographical conditions, two (or four) large-section pillar piers can be set in the end wall to increase the stability of the end wall.
(3) wing wall portal and ear wall portal
1. Wing wall type (splayed wall) portal: When the portal is poor in geology (surrounding rock above Grade IV) and the longitudinal thrust of the mountain is large, wing walls can be set on one or both sides of the end wall type portal. The wing wall can resist the longitudinal thrust of the mountain and increase the anti-sliding and anti-overturning ability of the portal. Both sides protect the cutting slope and play the role of retaining wall. The top surface of the wing wall is consistent with the uphill extension surface, and a ditch is arranged on it to lead the surface water collected by the ditch at the top of the portal to the cutting groove for drainage.
2. Ear-wall portal: This portal structure has a good effect on upward slope drainage, slope water collection, and preventing the tunnel from peeling against the wind, which can greatly reduce the slope erosion. The hole is spacious, the structural style is beautiful, and it is convenient to deal with the hole with inconsistent slope.
(4) stepped entrance
When the entrance is located in the hillside area, and the slope on one side of the entrance is high, in order to improve the starting point of the slope on the backer side and reduce the slope height, the top of the end wall is changed into a gradually rising step form to adapt to the terrain characteristics, reduce the number of masonry and excavation of the entrance, and beautify the entrance.
(5) Inclined portal
In order to shorten the length of the tunnel and reduce the amount of excavation, when the tunnel entrance line intersects the ground contour line obliquely, the entrance with parallel contour lines and straight lines can be adopted.
(6) Protruding entrance
1. Bamboo cut hole: When the hole is a loose accumulation layer, it is usually necessary to avoid large brushing and sloping. Generally, it is appropriate to extend the open-cut tunnel to restore the original terrain. At this point, you can use the bamboo cutting portal.
2. Bell mouth tunnel: For high-speed railway tunnels, in order to slow down the aerodynamic effect of high-speed trains, single-track tunnels are generally equipped with bell mouth tunnel buffer sections, which are also used as tunnel openings.
(7) sunshade cave door
When it is necessary to build a shade shed outside the cave, its entrance usually extends far away. Shading structures can be divided into open and closed types.