Source: Nantong second construction group and Luban union of construction engineering
.
With the popularization and application of “skip BIN method” construction technology, this kind of construction technology with multiple advantages is gradually replacing the traditional construction technology of retained post cast strip
.
Nantong No.2 Construction Group Suzhou renhengcang Street project in complex conditions of large-scale deep foundation pit engineering, using “jump warehouse method” to replace the “post pouring belt” construction, solved the safety and quality problems left by the traditional post pouring belt, “jump warehouse method” construction in the successful implementation of the project, also provides a reference for the practice of learning
.
The project covers an area of 38546 m2, with a total construction area of 135785.22 m2, 105880.34 M2 underground and 29904.88 M2 above ground
.
There are three underground floors and two above ground floors
.
The foundation is piled raft foundation, the main structure is frame structure, and the roof is sloping roof
.
The perimeter of the foundation pit is 988m, and the excavation depth is 18.45 ~ 21m
.
1
.
Due to the special geographical location of the project, the retaining structure and pit division design is close to the moat in the East, zhangjiaxiang River in the north, and Metro Line 1
.
The project adopts pit division construction, which is divided into four blocks: ① and ④ the retaining structure of blocks mainly adopts the support form of bored pile + CSM waterproof curtain + diaphragm wall; ② and ③ the thickness of 1000mm is adopted within the 50m protection range of blocks adjacent to Metro The underground continuous wall adopts I-shaped steel joint; the groove section of the underground continuous wall is reinforced by triaxial mixing pile, and the skirt of triaxial cement soil mixing pile is set in the pit
.
Effect drawing of foundation pit support: Excavation in area 1 of large pit shall be carried out first until the bottom plate of the first underground layer is formed in area 1, excavation in areas 2 and 4, construction of underground main structure in areas 2 and 4, excavation of earthwork in area 3 and construction of main structure in area 3 after the bottom plate of the first underground layer is formed in areas 2 and 4
.
2 support system design support system: ① block foundation pit adopts three concrete supports, in which the first support is also used as excavation and material stacking platform; ② and ③ block adopts one concrete support + three steel supports, and the steel support adopts prestressed servo system; ④ block adopts two concrete supports; the support system adopts diagonal brace and side truss The steel column with bored pile is used as the vertical support structure system of horizontal support system
.
Foundation pit supporting profile supporting model drawing due to the large construction area of foundation pit, in view of the problem of how to prevent through cracks and control structural surface cracks after the construction of concrete structure, the project department has carried out comparative analysis on the construction scheme
.
Combined with the successful experience of many projects in recent years, the “skip BIN method” has been used instead of the post pouring belt, which has been studied by the group company and the project department After research and demonstration, the paper puts forward optimization suggestions, and decides to retain two post pouring belts, cancel other temperature post pouring belts, replace the original design post pouring belt and expansion strengthening belt construction method, and adopt “skip BIN method” construction
.
What is “skip BIN method” construction? The construction principle of “skip BIN method”: divide the super long concrete block into several small blocks with the uncracked calculation length as the bin size
.
After short-term stress release, connect several small blocks as a whole, and rely on the concrete tensile strength to resist the temperature shrinkage stress in the lower section
.
The maximum size of the single side of the hopping block should not be greater than 40m × 40m, the pouring interval of the adjacent concrete blocks should not be less than 7d, and the hopping joint should meet the requirements of the construction joint
.
The construction technology advantages of skip BIN method (1) by skip BIN method, the post pouring belt is changed into construction joint, the construction technology is simple and the construction period is shortened
.
(2) It avoids the long construction period of the post cast strip and the long-term retention of the bottom support bent, provides the construction space for the next process, and saves the cost at the same time
.
(3) The pouring time of the sub warehouse block is about 7 days, the stress release time of the first pouring area is sufficient, and the concrete on both sides is more closely combined, which is conducive to the construction and improves the construction efficiency
.
(4) By optimizing the concrete mix proportion, controlling the quality of raw materials and the temperature and slump of concrete, strengthening the second vibration and second plastering in the process of concrete pouring, the shrinkage cracks of concrete are reduced, the compactness and tensile strength of concrete are improved, and the hidden danger of leakage is reduced
.
(5) The construction of skip BIN method makes the structure integrity formed in advance, which is conducive to the early intervention of basement transportation machinery, convenient material turnover and transportation, and improves the construction efficiency
.
The project belongs to super long concrete structure, with three underground floors and a construction area of 40000 m2
.
There are enough construction flow sections to organize the construction of “jumping warehouse method”
.
(2) The temperature and humidity of underground engineering in construction change greatly, but after the underground backfill, the temperature and humidity change little in the normal use stage
.
In such a construction environment, the temperature stress in the construction stage is far greater than the tensile capacity of concrete materials, and it is difficult to resist completely by the method of resistance
.
Therefore, we should adopt the method of “both resistance and release”, “release first and then resist”, and finally “resistance first”
.
This shows that the environmental conditions of underground engineering are most suitable for the construction of “skip BIN method”
.
(3) The skip BIN method is adopted for construction, that is, the whole structure is divided into sections according to the construction joints, poured one section after another (skip one section for pouring one section), and then filled and poured into a whole after not less than 7 days
.
With this scheme, the temperature difference and shrinkage at the initial stage of construction can be avoided, the temperature expansion stress during construction can be greatly reduced, the cracks can be effectively controlled, and the construction progress can be accelerated
.
3
.
The construction scheme of “skip BIN method” is implemented
.
The skip bin construction scope of the project is above the negative three roof
.
The (E-D and T-U) axis post cast strip is reserved for the block division of the project to solve the shrinkage deformation of reinforced concrete and reduce the temperature stress
.
Location Division: the plane size of the basement structure is 140m × 309m
.
The first and second floors of the basement are planned to be divided into a / B / C3 areas
.
A is divided into 11 blocks, B is divided into 10 blocks, C is divided into 6 blocks
.
Temporary construction joints are set between blocks
.
The location of the temporary construction joints is mainly based on the combination of the bearing platform location, the area of single pouring concrete floor, the progress of earthwork excavation, the support section removal and other factors The section division of the second floor is shown in the following figure: the partition diagram of the second and third floor hopping
.
Due to the negative and positive Zero construction of the basement, the temporary storage yard problems such as concrete pouring, reinforcement, woodworking shed, etc
.
are considered
.
It is planned to complete the non stack bridge slab area first, and remove the non support beam area first
.
After the top slab of the basement in the non support area is poured, the material storage yard will be gradually transferred
.
Considering the problem of concrete pouring in the front slab area of the station, the middle part should be removed first
.
After the concrete pouring in this part is completed, it should be removed from the middle to both sides, and one area should be removed after pouring
.
Considering that some parts can not be poured with the sky pump, it is proposed to use the ground pump
.
Construction sequence diagram of positive and negative zero structure non stack bridge slab area construction sequence diagram of positive and negative zero structure non stack bridge slab area construction technology measures 1
.
Raw material control: C35 grade commercial concrete is used for beam and slab of the project, with concrete 60d strength as index, and slump controlled at 150 ± 30mm
.
Concrete gravel grading: 5-40mm continuous grading; mud content less than 0.5%; concrete sand: 2.8-3.0 medium sand; mud content less than 1.5%
.
The principle of concrete material control and mix proportion design is to improve the tensile strength as much as possible under the condition that the compressive strength meets the requirements, and reduce the temperature shrinkage and drying shrinkage of concrete from two aspects of reducing the amount of cement and water consumption.
.