Question 2: The pre-drilling of pile foundation is mentioned in the construction contract. What is pre-drilling of pile foundation? Pre-drilling is construction survey. When the foundation pile is dug into the bearing stratum, check whether there are weak interlayer, cavity and other adverse geological effects in the range of not less than 5 meters below the bearing stratum of BenQ pile. Mainly for the foundation piles in karst areas, the bedrock at the bottom of the pile is inspected by drilling method before the pile is completed, which is basically one hole for one pile and porous for large piles. Generally speaking, after the pile design drawing comes out, the pile is dug in place, and before pouring concrete, you can select a point to survey the general stratum. In karst areas, it is best to investigate every pile. Related questions: 1. There are several possibilities for who will pay for the pre-drilling. (1) paid by the construction unit. Because there is a quotation in the bill of quantities, the construction unit will make a quotation regardless of whether there is this item or omission in the list. If there is this item, there is no dispute. If there is no such item, the expenses shall be included in other comprehensive unit prices. (2) At the owner's expense, we can entrust the test unit to carry out over-drilling through bidding or directly, and of course we can also entrust it to the survey and design unit of this project. (3) It shall be paid by the survey unit and included in the original survey and design tender offer. The survey unit shall consider this risk in the survey and design tender offer and shall not pay it as a new project. Due to the unpredictability of pre-drilling, whether it can be carried out can only be determined after the survey report comes out, so the cost should be paid separately by the owner and not included in the quotation of the original survey and design unit. If the original reconnaissance unit undertakes this task, the total cost of the reconnaissance unit is the original bid price plus the commission fee for this pre-drilling operation. 2. How deep should the super-front drill be drilled? Limestone has high strength, and it will be drilled to the bottom of the pile for 3 days (and >; 5m), the requirements of railway and highway extra-large bridges are higher, generally 8- 10m below the pile bottom.
Edit the example of complex karst foundation treatment in this section.
1 project overview
A 24-story trade building is planned to be built in the square in the city center. The engineering geological conditions and hydrogeological conditions of building foundation are complex, and karst and soil caves are developed. The foundation pit is 5m away from the seven-story library and the four-story cinema in the north and 4m away from the urban main road in the south. The construction of foundation treatment is difficult, and some new construction measures have been adopted in the construction, which has achieved good results. The building is a basement, and the excavation depth of the foundation pit is 4 ~ 4.4m It adopts the form of independent foundation with one column and one pile, and the maximum vertical load of a single pile is 2 1000kN. The original design is to excavate the foundation pit first, with rubble retaining wall around it and manual digging piles in the pit. Due to the large amount of groundwater extracted during the construction of manual digging piles, many places such as cinemas and libraries cracked and the foundation of buildings slipped. At the same time, the digging pile can't pass through the multi-layer karst cave, so the construction is difficult, which leads to the shutdown. In this case, the engineering foundation design was modified, the combination of punching and digging piles was adopted, and a set of scientific, reasonable and feasible construction procedures were formulated, which ensured the safety of adjacent buildings and the smooth construction.
2 Engineering geological and hydrogeological conditions
According to the survey report and the data of pre-drilled pile holes, the artificial fill layer and silt layer have been excavated in the foundation pit excavation, and there is a 6 ~ 9m thick covering layer under the foundation pit, and limestone under it. This area belongs to karst development area, with very complicated geological conditions, and soil caves and karst caves are developed, especially the karst caves in the main building are the most developed, with the deepest karst caves up to 32m and various directions. Caves vary in size, the largest distance from the roof to the ground is 2 1m, and the smallest is only a dozen centimeters. Some caves are completely or partially filled, while others are empty, forming sand hidden underground. The soil hole is shallow and often develops to the ground. Multi-layer karst caves are distributed on different planes, the rock surface is uneven, the height difference is large, and a large number of karst grooves are developed. The upper part of most bedrock is a massive weathered accumulation layer filled with black silt, which is thick. The groundwater in this site belongs to phreatic water and karst fissure water, and the groundwater system is connected with Yichang River not far away. The groundwater level in this site is high, often higher than the bottom of the foundation pit, and the flow is large, which is in a turbulent state. In some areas, groundwater from drilling holes or pile holes surged up, some caves were rammed through, and several pumps could not fill them up. Grouting water entered the underground river and flowed into Yichang River.
3 karst foundation treatment scheme
Due to the complex foundation, soil caves and karst caves are common, so the building adopts the form of one column and one pile, and the pile ends are required to be placed on stable and complete weathered bedrock. A. Drill 1 ~ 3 advanced boreholes for each pile hole, with the drilling depth not less than 5m, and enter the stable bearing stratum. Main purposes: to find out the stratum structure and distribution characteristics of each pile hole; Find out the distribution, size, scale, connectivity and filling of soil caves and caves; Find out the thickness of strongly weathered layer and the thickness of karst cave roof; ......& gt& gt
Question 3: How much do you need to do for manual digging pile super-drilling? Do you have any specifications? A few years ago, the country has cancelled the use of manual digging piles, which is very dangerous. If manual digging is cancelled, the corresponding regulations will be cancelled. At present, manual excavation is mostly used in places where geological or mechanical conditions do not permit. I remember that the bored pile was 10cm at that time, and it was checked with the corresponding arc model on the drawing. It is recommended to check other specifications of bored piles.
Question 4: What is advanced drilling technology? Advanced grouting, right? According to the geological radar forecast, when the surrounding rock in front is not well focused, use an air gun or a down-the-hole drill to drill holes, and then use an advanced small pipe to grout, and then excavate after solidification.
Question 5: The introduction of pre-drilling is mainly aimed at foundation piles in karst areas. Before the pile is completed, the bedrock at the bottom of the pile is inspected by drilling, which is basically a large pile with one hole and one pile. Generally, after the pile design drawings come out, the pile is dug in place and before pouring concrete. General strata can be surveyed at selected points, and it is best to survey each pile once in karst areas. Related questions: 1. Who will pay for pre-drilling? There are several possibilities. (1) paid by the construction unit. Because there is a quotation in the bill of quantities, the construction unit will make a quotation regardless of whether there is this item or omission in the list. If there is this item, there is no dispute. If there is no such item, the expenses shall be included in other comprehensive unit prices. (2) At the owner's expense, we can entrust the test unit to carry out over-drilling through bidding or directly, and of course we can also entrust it to the survey and design unit of this project. (3) It shall be paid by the survey unit and included in the original survey and design tender offer. The survey unit shall consider this risk in the survey and design tender offer and shall not pay it as a new project. Due to the unpredictability of pre-drilling, whether it can be carried out can only be determined after the survey report comes out, so the cost should be paid separately by the owner and not included in the quotation of the original survey and design unit. If the original reconnaissance unit undertakes this task, the total cost of the reconnaissance unit is the original bid price plus the commission fee for this pre-drilling operation. 2. How deep should the super-front drill be drilled? The strength of limestone is relatively high, the pile length is below 3-5d, not less than 3m, and the large-diameter pile is not less than 5m. It is drilled to the pile bottom for 3d (and >: 5m), and the requirements for railway and highway extra-large bridges are relatively high, generally 8- 10m below the pile bottom.
Question 6: What is a pre-drill? This is a pneumatic drill.
Question 7: Under what circumstances should advance drilling be carried out? When it is estimated that there may be karst caves, and when there are large stones on the rock surface during investigation-prevent the pile bottom from falling on the stones. wait for
Question 8: What does casing wall protection mean before drilling? Do you drill holes with pipes?
Question 9: What is a static drilling root pile? Definition of how to construct static bored pile;
Static drilling grounding pile foundation technology is a new patented construction technology, which is called static drilling grounding pretensioned prestressed concrete bamboo pile (hereinafter referred to as static drilling grounding bamboo pile). Compared with the traditional construction method, its novelty lies in the construction method of burying precast pile in the pile hole by using the self-weight of the pile body after drilling, which has the advantages of both the embedded construction method and the factory production of precast pile, adopts the method of grouting at the pile end and around the pile, and carries out the bottom expansion treatment on the pile end, and has the advantages of mixing pile and bottom expansion pile. It is a new technology which combines the advantages of various construction methods.
For reference (Zhejiang Standard Atlas 20 12 Zhejiang G37).
Advantages of static bored pile:
When this type of pile is adopted, due to the pile sinking technology of pre-drilling and pile bottom grouting, its construction method has good adaptability to geotechnical layer, little influence on soil squeezing effect, less mud discharge, less noise and less overall influence on environmental pollution.
Construction process of static bored pile;
The specific process of static drilling and grounding pile construction is as follows:
(1) drill positioning, drill hole.
(2) Drill a hole with a drill bit, trim the hole body, and after the retaining wall (3) is drilled to the bearing stratum, open the expanding wing to enlarge the hole.
⑤ Inject solidified cement slurry into the pile end and stir.
⑥ Fold the enlarged flange, lift the drill pipe, and inject solidified cement slurry into the pile body at the same time.
⑦ Pile sinking to the design elevation.
Question 10: What are the requirements for the over-drilling depth of the hand-dug belled pile? three