1. Before hammering, enough clay and water must be added into the casing, and then the clay slurry must be added at the same time of impact to ensure the feasibility of clay slurry wall protection.
2. In the process of drilling, add water in time to adjust the mud specific gravity: ≤ 1.25; viscosity: 18-20s; sand content: ≤ 6%.
3. Fixed interface and final hole acceptance. During the drilling process, according to the geotechnical engineering investigation report, when entering the moderately weathered tuff, the technician of the construction unit shall check the rock sample, and then report it to the supervisor and Party A to determine the interface and check the final hole. During the acceptance, take out the samples from the drilling slag, find out the rock samples and fill in the labels such as rock depth and sampling time. After the labels are filled in, bag them for retention.
4. The percussion drill shall be aimed at the center of the pile casing, the deviation shall be no more than ± 20 mm, the low hammer shall be started to compact, the hammer height shall be 0.4-0.6 m, and the clay mud shall be added in time to protect the wall, so that the wall of the hole is squeezed and compacted, and the speed shall be accelerated and the stroke shall be increased until the hole depth reaches 3-4 m below the pile casing, and the hammer shall be increased to 1.5-2.0 m or above, and the normal continuous impact shall be conducted.
5. In the process of drilling, the verticality of the hole should be checked every 1-2m. If deviation is found, drilling shall be stopped immediately and measures shall be taken to correct it. In order to maintain good hole shape, low hammer and intermittent impact should be used to pass through the variable layer and the part prone to deflection.