The application prospect of pumped suction reverse circulation drilling in Guangdong civil engineering and building construction in the Shenxun area is described by Chen Yongbao Training Yizhou Architects, No. 518028, and the application prospect of the pile type in Shenzhen area is analyzed.
K key-fixed pumping reverse circulation drilling enlarged base pile expansion head 1 commonly used pile types and limitations in deep training areas 1.1 manual digging peri-expanded pile This is the most widely used pile type in high-rise buildings in the deep training area in recent years Many years of practical experience in the application of this technology has been very mature, technical advantages are also quite obvious, but there are still limitations in application, including the following: (1) trial training building foundation design guidelines "in the provisions of the length of the l ~15m Time Path In order to meet the needs of the construction market, many developers tend to develop small high-rise residential buildings with 12 to 18 floors. Most of their column bottom axial forces are between 4000 and 8000 kN. Manual digging piles will lead to excess capacity due to bearing capacity. Without economy, immersed pipe piles need to increase the area and number of piles due to the lack of bearing capacity of single piles, and sometimes it is easy to cause serious squeezing effect. In addition, the internal force of the bottom of the high-rise building's high-rise building's podium and the pylon building is very far away, and the current design is often the use of manual digging piles, which will cause the piling pile foundation bearing capacity surplus is too large, and therefore not economic.
It can be seen that there is a discontinuity in bearing capacity between manual digging piles and cast-in-place bored piles. It is necessary to introduce new pile types.
(2) Precipitation is a major problem in construction. If it is not handled properly, it will affect the progress of construction, and it will cause land subsidence and affect the safety of surrounding buildings. The adoption of measures such as recharging will in turn increase the cost of the project, and will also cause some difficulties in construction due to the large rainfall in the coastal housing season.
(3) When encountering solitary rock or excavation of moderately weathered rock formations, blasting construction is required, the examination and approval procedures are cumbersome, the construction cost is high and the danger is large; the passing sands and soft soils are more difficult and more dangerous. The construction conditions were poor and the casualty rate was high. 1.2 Prestressed pipe piles With the continuous improvement of technology and price reduction, the application of prestressed pipe piles is increasing year by year. The advantage is that it can fill the bearing capacity between manual digging piles and immersed pipe piles. The sites with deeper buried rocks have certain technical advantages, but they also have certain limitations in application. Bao Jian a) The construction noise and ground vibration are large, the construction machinery is cumbersome, and the construction in urban areas will be greatly restricted. Weeping) Most of the weathered rocks in this area are shallow and shallow. It is more economical and reasonable to use large-diameter rock-socketed piles. i3) Granite residual soil, which is widespread in South China, is structurally strong, and its intensity decreases suddenly in the event of a disturbance. Piles, sometimes pile length has reached the design length, but the penetration is still very large, because they did not dare to collect the hammer in time and cause waste.
1.3 The immersed cast-in-place piles and rammed piles have low bearing capacity and the construction quality is not easy to guarantee. Therefore, there are fewer and fewer applications in high-rise buildings. In addition, they are like conventional punched or drilled piles or large diameters. Hammering cast-in-place piles and other types of piles are also used in some deep training courses, but they are not used much due to high cost or noise.
Chen Yong's application of pumping reverse circulation drilling to expand the bottom in Shenzhen area 2 pumping reverse circulation drilling to expand the bottom pouring pile This is a new type of pile introduced into the deep training area in the late 1990s, in fact, all types of similar Drilling and enlarging piles and piles and various positive and negative circulation piles have been used for a long time in many areas in and abroad. It is actually an improvement and improvement of general bored piles. The profile is shown as the construction process. It is very close to the general bored pile, but there is only one more hole expansion procedure.
2.1 The key issues in the application Because Shenzheng City has not yet fully implemented the technical code for construction of pile foundations (CGJ94-94), the survey report only gives the standard value of pile end bearing capacity for manual excavated piles and bored piles. The standard value of the limit side resistance of the pile is given.
In fact, under the conditions of construction quality assurance and geological conditions, the thickness of the sediment in drilled and expanded piles is far better than expected; in addition to the shallow buried foundation rock in deep training areas, the ratio of length to diameter of large diameter piles is often small, even if JGJ94-94 specification calculation is also based on end bearing. However, an enlarged head with a long pile with a long aspect ratio of >30, which can give full play to the body's lateral resistance, may not fully function. It is worth noting that in any case, the bearing capacity of drilled and expanded piles is often controlled by the concrete strength of the piles, and the strength of the piles should be checked.
The quality of the clearance hole is the key to the construction of drilling and expanding piles. If the sediment is too thick, the force of drilling and expanding piles will be dominated by lateral resistance, and the advantage of expanding the head will not be realized. However, from the perspective of drilled and expanded pile construction in the area, the results of core-pulling tests in many projects show that the thickness of the sediment is very small or almost zero. The author believes that the reasons are as follows: a. Drilled and expanded piles are made of granite weathered layer as the pile end bearing layer, covering the soil layer is also dominated by residual granite soil, high strength, hole wall stability is also good, rarely collapse hole Reasonable enlargement of the head shape is the key to clearing the hole. When the bottom is extended, the bottom of the hole will form a certain angle of inclination G/h/D. Because the bottom of the hole is a solid, weathered rock, as long as the bottom angle is properly adjusted, the sediment will follow The bottom of the inclined hole slides into the suction hole and is sucked out. There may be sediment in the suction hole. However, there are few sediments on the bottom of the hole. As long as enough pumps are provided to suck the reverse circulation mud, it is a positive cycle. More than 40 times, the cleaning effect is good; d. The concrete has been cleaned more than 3 times before the bottom of the concrete, the residual sediment at the bottom of the hole is not much, and most of them are pieces of strong weathered rocks, (6) is a piece of material Planting pods are also one of the reasons for less sediment.
In the process of popularization and application of drilled and expanded piles, the biggest problem is that people generally have doubts about the stability of the borehole wall. However, the author believes that the following points can be avoided by paying attention to the following points: namely, a. In strong weathered hard rock, the proper head pressure and mud concentration are selected; after the test at the bottom of expansion, the steel cage, downcomer, and the third clearing hole are placed immediately, and the concrete is poured immediately after the cleaning is completed. Otherwise, the reinforcement cage should be lifted. The above steps.
The prevailing strong weathered granites in this area are most suitable for the pile foundation bearing layer.
2.3 Technical Advantages (1) The coverage of the bearing capacity is wider than that of the application.
For the first level, up to 2500mm, the largest diameter of the enlarged head up to 4000mm bearing capacity 1000 ~ 5xl04kN, suitable for low-middle high-rise building staff activity.
(2) Project cost is low and economy is good.
Compared with manual digging piles, drilled and expanded piles can greatly reduce the amount of concrete because they do not need to be poured. When the design value of bearing capacity is deep in the deep-seated areas where the weathering is intense, it is most suitable for the bearing layer of the pile type, and the clay soil layer is mainly used to facilitate the use of the original soil for slurry production. Although the rainy season is long and the rainfall is high, the groundwater level is not good for the digging pile construction, but it has no effect on the drilled and expanded piles.
t on the sub-disc, such as 1m of Guangdong civil engineering and construction (4) no precipitation, low vibration, low sound exposure, construction can be concentrated in construction areas, and can be carried out throughout the day, so the construction speed.
2.4 Technical limitations (1) Construction site conditions subject to restrictions: The particle size is larger than the diameter of the drill suction hole kl5n ship pebble layer, there is a thicker thick conglomerate sand layer and other strong permeable layer, there is confined water in the soil layer, No groundwater or groundwater level is low; (2) muddy at the construction site, waste mud disposal is more troublesome; (3) discerning strong weathering and residual soil from the discharged residue requires some experience is not as intuitive as the digging pile; (4) when the pile diameter is large It is not necessarily more economical than digging piles, and comparisons of detailed plans are required; (5) Complex processes, various types of equipment, and large technical content require the establishment and improvement of site management, construction organization design, construction inspection methods, quality assurance systems, etc. The requirements of the team and the supervision company are also high; (6) The local application time is still short and the experience is not enough. The relevant personnel still lack sufficient confidence in their application.
3 Projects A1 and A2 Building of New Baokang Commercial Center are 17-storey residential buildings of the same design, all with the same height of 45m. They adopt a short-limb shear wall structure and each building area is about 8000m2. The design has no podium and basement wall. The burial depth of the direct landing is 3.5m. The axial force of the bottom wall is 2800~6500kN. The soil layers from top to bottom are artificial fill, gravel sand, gravel cohesive soil, fully weathered granite and strong weathered granite, and strong weathered rock. Depth of 18~25m, the standard value of the dirty end bearing capacity is 2500kPa. The driven piles may seriously affect the bearing capacity of the pile due to the displacement of the soil on the slope of the foundation pit, or even cause the displacement or fracture of the pile, while the large diameter end bearing Pile is the best choice.
If manual digging piles are used, the pile diameter must be greater than 15m, then the required pile diameter must be 1.4m, plus the retaining wall about 1.7m, and most of the column bottom axial force is only about 3000kN. Such a large pile diameter is too wasteful.
In view of the actual situation of the project, we decided to boldly use the recently introduced drill-expanded pile, and carried out the economic comparison between the pile type and manual digging piles. Table 1) shows that drilling and expanding piles can save about 30.8% of the funds. 1 Economical Comparison of Two Pile Types Pile Average Pile Size ç ¼ Dosage unilateral cost total length Jn æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²… æ²…) 1.1 The filling factor.
Due to the lack of experience, the diameter of the enlarged head is only designed to be 1.5 diameters. Its side wall inclination is only 18°. In such a cautious situation, many people including the entrapment supervision engineer still have the quality of clear bottom and the stability of the wall of the head hole. Say doubts, but the final core-pulling results and main structure settlement observation results are very satisfactory. The sediment thickness of most core samples is close to zero, and only the maximum settlement of the main body is only lmm. As long as the geological conditions can be fully grasped, the construction is strictly controlled. Quality, reasonable design and construction, drilling and expanding piles to achieve all-around, "fast, good, and provincial results."
4 Summary 4.1 Pumping Reverse Circulation Drilling The introduction of peri-bulging piles has changed the monotonicity of the pile type in the Shenxun area, and it is a necessary supplement for manual digging piles. It has broad application prospects and may even replace artificial digging in the future. Hole piles become the main pile type in South China.
4.2 Drilling and Expanding Piles are particularly suitable for the following cases 3(1) Small high-rise buildings and high-rise building podium foundations i2) High-rise buildings that do not use digging piles due to excessive groundwater volume or precipitation will damage the surrounding buildings i3) Noise and vibration Reason fF turn to page 17) Guangdong, civil engineering and construction should be selected to dry high places, and should set up a cement storage warehouse, pay attention to do a good job of drainage around it to prevent the cement damp aggregates; (2) the cement must carefully sieved before joining Ash tanks, so as not to block the pipe caused by broken pile i3) Before each drill pipe sinking, the drill pipe verticality shall be checked and adjusted to > 1.5% to open the drill; (4) High pressure air pipe joints should be connected firmly, often Check the duct's level of strength and fatness because it breaks out and injure the person or the cement powder is sprayed into the eyes.) When the pipe plugging or mechanical failure occurs in the pile forming process, the drill pipe should be pulled out immediately to prevent the drill from being buried. , And try to clear the pipeline; (6) Each pile must be continuously constructed after drilling, and it is strictly forbidden to drill without ash spraying. (7) To prevent powder breakage, the ash tank can be used on the basis of the amount of cement used for each pile. Increased 50~lkg margin, after pile Charles cement margin, the amount of cement to ensure that not less than a predetermined value; ⑶ strict application of the transfer system, a group of problems encountered during construction or related instruction must daphne sharp, clear, and timely treatment to the next one.
7 Application prospects of powder jet piles 7.1 Advantages of powder jet piles A large number of engineering practices show that the squirt jet piles have the following advantages compared with other soft ground treatment methods: (1) Powder jet piles use powders as reinforcement materials and do not need to be injected into the foundations. Additional water, it can fully absorb the groundwater, after the reinforcement of the foundation pile bearing capacity is higher than the similar grouting piles, solid Ch then page 11) should not adopt the multi-layer construction of the pile.
4.3 When designing large-diameter piles, designers should first make manual and digging piles to make technical and economic comparisons between digging piles and drilled and expanded piles.
The knot effect is also better.
(2) The soil-cement pile reinforced with this method forms a composite foundation with the surrounding soil layer without the need of pre-compression to obtain a higher composite foundation bearing capacity and composite deformation modulus, and the compression volume of the reinforced soil pile body is only 0.6. About %, the settlement of the lower layer can also reduce the total settlement of the foundation.
(3) Low-pressure operation is used during construction, which is safe, reliable, non-polluting, vibration-free, low-noise, and has no adverse impact on the surrounding environment and buildings.
(4) According to different soil conditions and design requirements, the types of reinforcement materials such as cement, lime powder, slag powder, etc., and their reasonable mix ratios can be selected respectively.
7.2 Application Prospect Analysis Powder jet pile as a new method to deal with soft soil foundation, has achieved good results in the application of highway soft foundation treatment. Several soft ground road sections treated with powder jet piles in this project, settlement observation results It shows that the design has achieved the desired effect. The soft foundation treated by this method has good integrity and water stability. The composite foundation has the advantages of strong bearing capacity and reliable quality. It will be widely used in the construction field.
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