1 analysis of common problems in foundation engineering construction
1. 1 foundation moisture-proof failure
Imperfect moistureproof layer or plastering treatment of foundation engineering reduces the effectiveness of preventing groundwater from infiltrating upward along the foundation. After the external wall of engineering structure is damp, the surface of brick wall will fall off layer by layer after freezing and thawing and salinization, which will affect the structural strength and beautiful environment. The main reason for this phenomenon is poor management of mortar in foundation construction, and mortar is used as moisture-proof mortar. During moisture-proof treatment, the engineering base surface is not cleaned, watered or watered insufficiently, which reduces the adhesion between moisture-proof mortar and base surface. Or the compaction degree is not enough when plastering, and the maintenance measures do not dig mountains, which leads to premature dehydration of the moistureproof layer, and the strength and density can not meet the requirements and cracks appear.
1.2 foundation elevation deviation
When the foundation project is constructed to the indoor ground elevation, there are often problems of different elevations. If the foundation elevation deviation is large, it will directly affect the control of the elevation of the upper wall of the project. The main reason for this kind of problem is that the height difference of the foundation is relatively large, which greatly affects the control of the foundation elevation. In the process of construction, the foundation structure is wide, the bark poles of the foundation can't get close to each other, and the height difference between the foundation structure and the bark poles can't be effectively controlled. When large-scale brick foundation is built by plastering, due to the influence of plastering thickness uniformity and construction surface length, the laying speed often cannot keep up, the middle construction time is long, the mortar is not easy to be extruded, and the mortar joint is not easy to be thinned, resulting in empty drum phenomenon.
2. Quality control measures of foundation engineering on the construction site
2. 1 axis offset treatment measures
When positioning the defense line, the gantry plate should be set at the outer corner, and corresponding protective measures should be taken to avoid the displacement caused by soil accumulation at the edge of the groove or other operations. A permanent center peach should be set under the door dragon board, which should be driven into the ground to keep flush and its periphery should be sealed with concrete. When the gantry plate pulls the line, it should be checked with the middle pile first [2]. Generally, it is not recommended to control the axis of the transverse wall by laying feet in the foundation groove, and you can choose to set middle piles. The pile in the transverse wall is required to be flush with the ground. In order to facilitate the processing of arranging ruler and pulling the center line, no soil or materials can be piled between the center piles. When digging durian, you should choose to cover it with bricks to facilitate soil removal. When pulling the center line of trench wall foundation, we need to re-check the distance between adjacent axes to ensure that the center pile has not been displaced. In addition, in order to prevent the axis displacement caused by uneven foundation laying, after the foundation separation part is completed, the pull-through line needs to be rechecked, and the newly determined axis shall prevail, so as to finally complete the construction of the foundation straight wall part.
2.2 Foundation moisture-proof treatment measures
During engineering construction, the moistureproof treatment should be carried out after the foundation engineering construction is completed, and the butyl brick under the moistureproof layer of the 24cm wall should choose the full-butyl masonry method. During site construction, the foundation moistureproof construction should be arranged after the foundation room is backfilled, so as to avoid damaging the moistureproof layer during the filling construction. In general, the construction should be carried out in strict accordance with the design requirements of the drawings. In the case of no specific requirements in the design, an appropriate amount of waterproofing agent can be added to the cement mortar with a thickness of 2cm+0: 2.5 for construction [3]. In addition, the mortar and concrete in the moistureproof layer are carefully mixed with salt. In order to avoid the adverse effects of low temperature on the project, try not to construct at low temperature without heat preservation.
2.3 Treatment measures for foundation elevation deviation
Before foundation construction, the elevation of the grass-roots level should be comprehensively checked, and the local depressions should be leveled with fine stone concrete. The foundation skin pole can be made of small cross-section 2×2cm as shown in the method or steel bar. In concrete construction, the number of leather poles can be directly stuck in the center of the foundation structure. If you choose the outside of the foundation, you should check the elevation with a spirit level and proofread it with a spirit level. In addition, in view of the construction of foundation amplification foot, double-sided hanging line treatment is selected as far as possible to keep the level. During the construction of filled brick, small-area plastering method should be selected, and the top surface should be controlled to be higher than the height of the outer heel brick.
3 case analysis of quality control of foundation engineering in site construction
3. 1 project overview
Taking a project as an example, the foundation engineering includes a local basement and a single pile cap, in which the elevation of the basement floor is -6.3m, the elevation of the single pile cap foundation is-1.5m, and the average thickness of the cushion is 1 10 mm, which is quite different, so synchronous construction cannot be selected. Therefore, in the quality control of foundation engineering construction site, the key is to determine a reasonable construction sequence and do a good job in the construction lap joint between basement and single pile cap.
3.2 Construction scheme
Combined with the characteristics of this project, the basement construction mainly includes the basement top plate, bottom plate and shear wall side wall. The whole process involves many processes and contents. In order to ensure the construction quality of foundation engineering, the basement construction should be completed first, so as to avoid affecting the subsequent process of the project. Combined with the basement shear wall and the connected foundation, there are construction joints at the height of -0.4m, the basement shear wall part is constructed first, and the foundation beam with construction joints is poured together with a separate pile cap.
3.3 Engineering Construction Quality Management
3.3. 1 Foundation pile caps and beam construction foundation pile caps are made of M 10 cement mortar powder with a thickness of 230 M7.5 bricks, and the steel bars are mainly processed into semi-finished products by selecting qualified materials at the construction site [4]. Because the foundation beam is relatively clean, and the weight of the required steel bars is relatively large, on this basis, in order to ensure that the steel bars can be placed accurately, it is necessary to set up scaffolding as the maximum steel bar support before the steel bar binding, and then dismantle the scaffolding after the steel bar binding treatment is completed. 3.3.2 Floor construction After the completion of the floor concrete cushion construction, it is necessary to bind steel bars, especially in the process of binding, to strengthen the accuracy and firmness of the positioning of column and wall steel dowel. In this regard, we can choose to play ink lines on the cushion to control the spacing of floor reinforcement. For the binding treatment of the upper and lower reinforcement of the basement floor, the lacing shall be set in strict accordance with the construction drawing, and the basement doorway shall be reserved. Stair steel dowel embedding, can choose to use 3mm thick steel plate waterproof, construction joint height control in 300 mm, when pouring concrete floor, should choose the method of parallel propulsion, to ensure the continuity of construction, do not need to reserve construction joints. In particular, it is necessary to strengthen the concrete pouring management at the water stop to ensure its compactness and avoid leakage.
4 conclusion
Foundation engineering is an important part of building engineering, and its construction quality greatly affects the stability and strength of engineering structure. In order to improve the quality control of on-site construction foundation engineering, it is necessary to actively study the existing problems.
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