First, the main reasons why the rammed expanding head ratio is insufficient or too large are:
A. the geological data is inconsistent with the drilling data;
B. Too much and too little compacted expansive material;
C. Ramming and expanding construction technology is not implemented according to the construction specifications, resulting in excessive uplift height H. ..
The main measures taken are as follows: First, try ramming and expanding. According to the rammed expansion, please design and confirm whether the rammed expansion head meets the design requirements. In the process of construction, the feeding height of rammed expansive materials shall be calculated according to the requirements of specifications, and strictly controlled during construction, and shall not be increased or decreased at will. Strictly control the lifting height h of external rammer pipe. The synchronous sinking of internal and external rammer pipes must reach the design height, which is generally controlled at 0.3m, so that the rammer head concrete can be compacted with the surrounding soil layer.
Second, the diameter of the pile cannot be guaranteed, and the main reasons for necking are:
A. In muddy soil, due to the vibration of the casing of this layer, the concrete can't be poured smoothly, and it is filled with muddy soil, which leads to the necking phenomenon of this layer.
B. When sinking the pipe in the saturated clay layer, pore water pressure is generated due to the forced disturbance and extrusion of the soil, and the pile pipe is pulled out and squeezed into the newly poured concrete, so that the local diameter of the pile body is reduced.
C the consistency of concrete is too large, and the workability is poor. When pulling out the pipe, the pipe wall produces friction on the concrete, resulting in necking.
D adjacent piles are too close, and when adjacent piles are constructed, the concrete is squeezed too much by the soil squeezing effect when it does not reach the initial setting state, resulting in necking. The main measures taken are as follows: First, control the slump of concrete at 8- 10 cm. Secondly, control the speed of tube drawing, and "slow drawing and close beating" during tube drawing. For the part where the designed pile spacing is less than 4d, the jumping construction method is adopted. Row pile foundation shall be constructed in staggered rows, and group pile foundation construction shall be reasonably arranged by jumping at intervals. The first batch of piles will be constructed for 7 days, and then the rest will be constructed. Although this method can ensure that the diameter will not shrink during construction, due to the extrusion and arching of pile soil after construction, it will produce great negative friction on the constructed pile, resulting in tensile stress during installation. If the strength of the pile is not enough, it will easily lead to pile breakage. In practical engineering, the measured ground elevation before and after construction is quite different, some of which are as high as 0.2m, and the settlement observation of pile top is raised after excavation. Therefore, when using this method, it is necessary to ensure that the design strength of the constructed pile reaches 60%. If overnight warehouse jumping construction is adopted, it will only increase the possibility of broken piles.
Third, the main reasons for broken piles:
A. The speed of pipe drawing is too fast, the concrete has not flowed out of the pile pipe, and the surrounding soil quickly retracts, resulting in broken piles.
B. The initial setting state has not been reached after the pile is formed, and shear force is generated to cut the pile due to the different wave velocities of the upper hard soil layer and the lower soft soil layer caused by vibration.
C. The particle size of concrete coarse aggregate is too large, and the phenomenon of "bridging" occurs in the pipe when pouring concrete, resulting in broken piles.
D concrete pouring is discontinuous and the intermittent time is too long. The concrete poured first has exceeded the initial setting, which leads to the phenomenon of concrete delamination one after another, or caused by mud injection during pouring.
Main control measures taken:
1, reasonably organize the construction to avoid the interruption of concrete pouring process. If the interruption time exceeds the initial setting time of concrete, concrete shall be poured again.
2. Reasonable arrangement of construction sequence. If the pile jumping method is adopted, it is necessary to ensure that the strength of the constructed pile reaches 60% before the construction of the adjacent pile.
3. Control the tube drawing speed, which is 0.5m/min in muddy soil.
4. Strictly control the particle size of coarse aggregate according to the specification requirements.
Four. It is difficult to control the elevation of reinforcing cage during the construction. The main reasons are:
A. the lowering elevation of reinforcing cage is inaccurate;
B. Due to the great change of geological conditions, the concrete settlement caused by pulling out the outer pipe at each pile position is different, which leads to the different elevation of the reinforcing cage before and after pulling out the outer pipe;
C the fresh concrete is in a flowing state, and the reinforcing cage sinks into the concrete due to the vibration of adjacent piles sinking into the pile pipe. Can effectively solve the problem of reinforcing cage.
Firstly, according to the design elevation, pile frame height and ground elevation, the length of steel wire rope for hoisting steel bar is calculated. Make a mark on the cigarette machine. Ensure that the reinforcing cage is controlled every time it is lowered. Excavate the pile position that has been constructed. Find out the height difference of the reinforcing cage, calculate the system error when the reinforcing cage is low, and improve the system error in advance when it is reduced. By adopting the above method, the elevation of the reinforcing cage is effectively controlled.
Five, pile pipe water or mud back cover is not firm. The main methods are: winding hemp rope or cardboard when sealing the bottom with precast concrete pile tip; Choose reasonable pile sinking technology to shorten pile sinking time.
Intransitive verbs strengthen quality control and on-site management. In addition to technical reasons, quality problems are more human factors and management problems.
The above is the introduction of the control measures of rammed expanded piles provided by Zhong Da Consulting Company for construction workers. For more knowledge of architectural terminology, please pay attention to the architectural knowledge column of Zhong Da Consulting.
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