A project is located in the west of Zhejiang, frame shear structure, 22-storey five-star hotel and has 61,000 square meters. There are two basements in this hotel, its design uses bored pile and the pile diameter ranging from 0.7 to 1.5 meters as well as depth ranging from 7 to 56 meters. The soil texture is pebble, mixed soil and limestone. According to the geological exploration reports that use limestone as its bearing layer, the underground geological conditions are typical karst landscape. According to the geotechnical conditions of the site and the nature of the proposed building, the project is designed with 573 pile foundations. It meets a series of problems like oblique rock, karst cave. Struck hammer or lost hammer and floating reinforcement cage in the process of pile.
If happen oblique rock or boulder, we can see from a digging part of region that its underground geological condition is very complicated and the limestone surface is fluctuated, therefore, it will meet oblique rock or boulder in the piling process.
When deals with karst cava, it usually develops in the limestone area, its pile is above the larger cave, so large area collapse and large deep leakage will happened in this construction, moreover, some piles collapsed at the last moment of pouring concrete, which not only wasted the pouring concrete, but also needed to drill pile once again.
If struck hammer, lost hammer or buried hammer is happened, the construction also happened struck hammer or lost hammer, but the most serious consequence is buried hammer.Reinforcement cage floating, this problem mainly happened in some shorter pile, because it is very short, and its resistance to mud is relatively small, so this phenomenon would happen in pouring concrete.
Pile foundation sinking, after the pile is completed, we found that some of the piles fell below the normal elevation after the excavation, this happens when all quality control indicators are qualified during construction. So the only reason is that pile foundation sinking after pouring concrete completion.
There are a series of problems in construction, such as shield-tube sinking, judgment of final hole, determination of bottom pile residue, control of pouring concrete, pile deviation, plus residue, etc.In view of the importance of pile foundation construction, the company convened a meeting in the initial stage of construction to clarify the duties of the pile foundation construction team, general contractor, supervisor and other parties, and held a special meeting on the problems to research and deal with problems, thus achieving good result.
When met oblique rock or boulder, it will easily make pile foundation to deviate in the pushing process.
First: use high
strength big stone or steel that backfill in the hole, and change to use large
punching to break oblique rock or boulder. If rectify once not in the place,
then do it several time until it corrects.
Second: The concrete portion of the pile hole is directly poured out by the concrete, and then re-punched.Third: Use enlarge pile diameter requires that the large and small holes should be tangent, and the large holes should be deflected in oblique rock. When the inclined rock is corrected, the designed drilling hammer required in the original pile position to impact the required depth.The karst cave should be treated differently, research exploration report should be carefully research before punching, and know about karst cave in which height, all of them should be prepared before entering it.
Although difficult construction of pile foundation has objective reason like complicated geological condition, objective organization is a key to guarantee successful pile. Good organizational management is reflected in the standard construction process and acceptance procedures, and strict safety and quality control. For example, in response to the construction conditions at the site, we have held targeted coordination meetings from time to time to negotiate the treatment of inclined rock, karst caves and piles that are difficult to form in the construction and other series of problems, and finally promote successful pile.