In the tunnel construction, shotcrete is the necessary construction content often involved in initial support and secondary lining,its quality has a significant impact on the durability of tunnel construction . Luoyang Gentong has compiled a number of technical measures that cannot be ignored in the construction of shotcrete. Let's see below together:

Mix ratio design

1.The ratio of shotcrete and cement is between 1:4 and 1:4.5, and the amount of cement is reasonably controlled so as not to affect the initial strength growth rate and shrinkage.

2.The sand ratio of the mixture is between 45% and 55% to prevent blockage of the bone path.

3.Adjusting the water-cement ratio to 0.4~0.5 to ensure the strength of the shotcrete and increase the rebound loss.

4.Reasonable addition of concrete accelerator,can not cause late strength loss due to the pursuit of early strength.

Construction preparations

1. Check the pipeline and joints to ensure that the air duct does not leak air, the water pipe does not leak water, and install one valve joint every 40~50m.

2. Buried shotcrete thickness inspection mark，and record its exposed length；At the same time, pull the line, level with the wooden bar while spraying, control the flatness of the spray surface and compact the concrete.

3. Examine the excavation section and make up the undercut site; reinforce the bad geological section in advance and set sufficient illumination at the spray surface.

Maintenance measures

1. After the concrete thickness is qualified, t flattening the concrete plane after initial setting.It is strictly forbidden to destroy the bond between the internal structure of fresh concrete and the base layer.

2. The last layer of concrete is finally condensed for 2 hours and then watered for not less than 14 days.

3. Water retention and maintenance is required when the temperature is below 5 °C

Concrete thickness inspection

1. Check the thickness of the shotcrete，drilling to check the thickness of the reinforcement layer within 8 hours after the end of the injection； If the thickness of the sprayed layer is insufficient, it shall be refilled in time.

2. Reinforcement layer thickness error is -5~+8mm

 Concrete strength testing

1. Cutting or drilling crack-free concrete specimens from the site

2. Controlling the discreteness of compressive strength test values of test specimens to ensure the rationality of the data

3. Perform appearance inspection to eliminate empty drums and cracked parts

Dust control measures

1. Select spray air pressure by experiment to control the spray force

2. Mix the shot evenly to reduce the amount of rebound and dust

3. Take two times of tidal spray to reduce rebound

4. Strictly control the amount of accelerator