Main construction technical measures of impact bor

2022-05-18
  • Detail

The main construction technical measures of impact bored cast-in-place pile in Karst Zone

impact bored cast-in-place pile is widely used in pile foundation engineering in hard rock and soil layer because of its strong crushing force on rock and fast pore forming. In some rock and soil layers, there are often karst zones. For example, in the process of pile punching and hole forming, in case of underground karst cave, it is easy to happen pile hole slurry leakage, hole collapse, hole deviation, hammer clamping, hammer dropping, buried hammer, and even the thermal insulation plate made of on-site foamed polyurethane has very good integrity and water resistance, so that it is unable to form holes. Therefore, the impact bored cast-in-place pile is adopted in the karst zone. Before and during the construction, reliable construction technical measures need to be taken to ensure the smooth hole forming of the bored pile. Combined with the engineering examples of Shaoguan Wushi power plant in Guangdong Province and Fuli Taoyuan high-rise residence in Guangzhou, this paper summarizes this

2. Engineering example

Shaoguan Wushi power plant project is located in Shaoguan Power Plant, Wushi Town, Qujiang County, Guangdong Province. Its main power house and circulating water pump house adopt impact bored cast-in-place pile foundation, with pile diameters of F600 ~ f1200 mm, a total of 660. According to the engineering geological exploration data, the soil layer from top to bottom is plain fill, silty clay, silt, fine sand, medium sand, coarse sand, garden gravel and gravelly silty clay. The sk47 drilling hole reflects that there is a karst cave 4.8 ~ 7.6m below the ground

Guangzhou Fuli Taoyuan high-rise residential project adopts impact bored cast-in-place pile foundation, with pile diameter of F600 ~ f1500, a total of 204. According to the engineering geological survey data, the soil layer in the site is cultivated soil, silt, fine sand, coarse gravel sand, silty clay and limestone from top to bottom. Karst holes are developed in the limestone at the bottom of the drilling, with large scale and abundant underground water

the construction difficulty of the above project is that karst caves are developed in the rock stratum within the pile forming depth, which is easy to cause accidents such as slurry leakage, hole collapse, hole deviation, hammer clamping and buried hammer. Therefore, corresponding technical measures are taken during construction to ensure the smooth progress of pile foundation construction. For example, Shaoguan Wushi power plant project is located in the karst development area in northern Guangdong. During the punching and pile forming process of the project, 14 pile positions encountered underground karst caves; The underground karst cave encountered during the construction of cast-in-place pile of Fuli Taoyuan high-rise residential project is large and deep. We are optimistic about the development prospect of Xinjiang Zhonghe, and it is difficult to deal with it

due to the idea of quasi biological polyaminoic acid preparation before construction, reliable technical measures were taken during construction and successfully treated to ensure the smooth progress of these two pile foundation projects. After the construction of these two pile foundation projects, they are all class I and class II piles through the inspection of acoustic transmission method, dynamic vibration wave method and drilling core pulling method. Among them, class I piles account for 90% and the construction quality is excellent

3. Construction preparation measures

before construction, according to the engineering geological survey data, determine which piles have karst caves (if necessary, make a drilling hole at each pile position designed), the type, size and location of karst caves, and make preparations in advance

for the pile position where the drilling shows underground karst cave, the drilling hole can be pressure grouted before the hole is formed. If the drilling hole is easy to be filled, it indicates that the karst cave is small and not connected, and the pile can be directly flushed. If it is difficult to be filled after long-term pressure grouting, it indicates that the karst cave is large or connected. It can be filled with mortar, yellow mud, etc. and then the hole can be flushed

for the pile position with karst cave, the drilling rig should be padded with steel frame (e.g. made of channel steel or I-beam vertically and horizontally). In this way, in case of large collapse hole, the drilling rig can be supported on the ground by steel frame, which is safe and avoids loss

before punching, mud, yellow mud, rubble, long steel casing or precast reinforced concrete casing, gunny bag, quick setting cement, sand and gravel and other materials shall be prepared

when opening holes, low hammer and dense punching shall be carried out, and the wall shall be formed by repeated impact. During the hole forming process, the slurry supply must be ensured to keep the slurry surface in the hole stable

when the hole is formed in the clay layer, the stroke is 1 ~ 2m, add clean water or thin mud, and often remove the mud block on the hammer; When the hole is formed in the sand layer, the stroke is 1 ~ 2m, and the mud specific gravity is controlled at 1.3 ~ 1.5. Wash and dig the slag frequently, and throw yellow mud when necessary to improve the mud concentration; When the hole is formed in the bedrock, the stroke is 3 ~ 4m, the mud specific gravity is about 1.3, and the slag is frequently removed

Copyright © 2011 JIN SHI