Ten common problems in civil engineering construction and their solutions

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Ten common problems in civil engineering construction and their solutions 1. Settlement of backfill soil: http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/6afacc22bc19abda47feb0e818ef091e.jpg If the settlement is uniform, there is generally no problem; however, if the settlement is uneven, it can have an impact on the building once it reaches a certain level. Cracks appearing in the floor due to settlement indicate that the situation is quite serious. Common causes: 1. Excess moisture content in the backfill soil ； 2. The layers were not compacted as required. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/faff70984ada5feeee4cd14bffaa4d7a.jpg Measures to be taken: 1. Before construction, appropriate dewatering measures should be implemented based on the local groundwater level (such as wellpoint dewatering, curtain systems for water suppression and sand control, or dewatering within the excavation site); in addition, water barriers should be installed around the foundation trench. 2. Control the moisture content (by sun-drying or applying lime); the inspection method at the construction site is to tightly squeeze the lime-soil into a ball with the hand, and it should crumble easily when gently pinched between two fingers. (Rolling out, drying, replacement of soil) 3. Compact in layers; the thickness of each layer should not exceed 300 mm, and the number of ramming strokes should be >3 ； 4. The subbase of the road surface must be fully covered with stones. II. The construction at the top of the pile does not meet the standards. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/006979b71f0a5cd9049226ab3a057ed1.jpg Common causes: 1. Displacement or bulging at the top of the pile, or fracture in the pile body ； 2. Pile driving fails to meet the design requirements. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/a4014ca12852d255a1f82dd140815d75.png Measures to take: 1. Ensure accurate positioning; if it is detected that the pile is not vertical during the driving process, it should be corrected promptly so that the upper and lower sections of the pile remain on the same axis. 2. If the elevation of the pile top is lower than the designed elevation, first level and roughen the pile top, then join the pile with plain concrete of one strength grade higher than that of the CFG pile’s core concrete to reach the designed pile top elevation. III. Water leakage in the basement: http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/9213e1fcd2e2fe82cf29aa02118b218a.jpg 1. Damage to the waterproofing layer during installation (external protection with internal application method) ； Protection layer: 15 mm thick, protected with 1:3 cement mortar) ； 2. Inadequate concrete vibration (P8 commercial concrete, waterproofing agent) ； 3. Construction joints were not treated in accordance with the specifications (a common issue). http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/ec375e2c3c4231d5b1dffdcf4c13daa6.png Pre-control: water-stop steel plates, water-stop strips ； Before the second pouring, the surface is chiseled, the construction joints are washed with pressurized water, and plain cement slurry is applied…… Post-construction control: At the leakage points, a \"V\"-shaped groove with a depth of not less than 50 mm is created; after washing, the area is treated with a leak-sealing agent and JS waterproof coating, and then protected with 1:2 cement mortar. Measures for sealing the openings reserved for pipes in floor slabs: 1. The openings should be sealed only after the pipes passing through the floor slabs have been properly installed. 2. Before setting up the bottom formwork, remove any debris and loose concrete from the opening in advance, and moisten the walls of the opening and the pipe walls with clean water. The formwork should be in close contact with the bottom of the floor slab. 3. Before pouring the concrete, apply a 15-mm-thick layer of cement mortar on the tunnel walls and pipe walls; then, pour C20 fine aggregate concrete mixed with an expanding agent in two stages. Pour the concrete to half of the slab thickness for the first time, and then carry out the second pouring once the concrete has begun to set. 4. During the pouring of concrete, use rebar rods to vibrate the concrete thoroughly in order to prevent honeycombing or pitting on its surface, which could create channels for leakage. 5. The surface of the poured concrete should be recessed 10 mm below the floor level; it should be smoothed with waterproof mortar twice. The areas around pipes and corners should be made into small rounded corners or beveled edges. At the openings, the rounded corners should extend 30–50 mm beyond the edges of those openings. Finally, round the corners and polish them. 6. The formwork at the bottom can be removed only after the concrete has reached its strength. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/22416382624a5f56f46968a9109419b7.jpg IV. Poor appearance quality of concrete
http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/9e98da8f2f9614688b2695d17aa40ed4.jpg 1. Apply release agent
http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/426cc7b663a22a327992987a0a428808.jpg 2. Use sealing strips to join the formworks; moisten them with water, and remove wood chips and impurities ； 3. Vibrate thoroughly (insert quickly and pull slowly); maintain a distance of 2 meters from the feeding port, and feed material in layers ； 4. Finish the raw slurry surface; pay attention to maintenance (film) ； http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/963f0dc2a77a27f6f81741a1bc416b56.jpg 5. Protect the finished products! 6. During winter construction, it is necessary to ensure that the temperature of the material before it is placed in the formwork is above 5 degrees. 5. The fillness of the mortar joints is not satisfactory. Common causes: 1. The workability of the masonry mortar is poor, which directly affects the density and fillness of the mortar joints in the masonry. 2. The methods for placing dry bricks on the wall and for bricklaying are incorrect; the \"three-one\" bricklaying technique is not followed. 3. The horizontal joint contraction is too large. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/47d6615a0149b0f1fd0a179e8f266d38.jpg Improvement measures: 1. Improve the workability of mortar. The consistency of the mortar should be adjusted in a timely manner. Before masonry work, the bricks must be watered and moistened 1–2 days in advance; the moisture content should be maintained at 10%–15%. Care must be taken to prevent the use of dry bricks in construction. 2. When laying bricks, the “3-1” brick-laying method (i.e., one brick, one shovel of mortar, and one squeeze) or the “2-3-8-1” brick-laying method should be used. 3. It is strictly prohibited to lay long rows of mortar, which can cause voids in the base mortar as well as irregular brick laying, resulting in insufficient filling of the mortar. (Horizontal joint width: 8–12 mm) 4. During the masonry process, it is required to fill all gaps with mortar before scraping the joints. VI. Cracking and delamination in the plastering of exterior walls http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/ef4ecd9096ba9fe3da95cca12bdda8fd.jpg 1. Reinforcing bars are not installed at the junctions between partition walls or filler walls and concrete, as required by the drawings and specifications, resulting in cracks along those junctions. 2. Improper base treatment or failure to clean it thoroughly, insufficient watering, and dehydration of the plaster mortar all affect adhesion. 3. Plastering was not carried out in the proper layers as per the operating procedures; the mortar was not prepared properly and was used incorrectly. 4. Division strips should be installed when applying plaster over large areas. 5. Within 200 mm on either side of masonry door and window openings, 300 mm for masonry; at corners, 450 mm for masonry and 600 mm for other areas. No scaffolding holes shall be left within this range. 6. Structural columns. 1) Use double-sided tape to seal gaps and prevent grout leakage ； 2) Starting from 5 leather-tag bricks, move backward first and then forward. Reinforcement of 2A6 shall be installed at intervals of 500, with a spacing of not less than 1000 mm. VII. Formwork sub-projects: 1. When the beam height is >550 mm, tie rods must be installed at intervals of 500 mm ； 2. The gaps in the wall column formwork can be sealed using mortar and tape respectively to prevent grout leakage ； http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/ce20ab0d5b1a1f1a536556f8f3e4781e.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/b73a65c3b3d389ca582b2c681b4555db.jpg 3. The longitudinal and transverse spacing between beam-supported vertical pipes should be ≤1.2m. The spacing between the wooden beams at the bottom of the beam structure should be ≤300 mm. 4. The formwork for wall columns is made of standard wooden beams of 50 ×100 dimensions, or channel steel or square steel, with a spacing of ≤400. Wall columns with an excessively large ceiling height must be equipped with screws, with a spacing of ≤ 500 between them; the first row of screws should be less than 200 mm above the ground, while the top row of screws should be less than 300 mm above the ground. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/252ae46b22b83f948c697fcc6347c90d.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/597bad3f51129007e66f233b55aa0060.jpg VIII. Scaffolding sub-projects 1. The scaffolding must be erected on a hardened surface (it must not be suspended in the air); it is strictly prohibited to build it on soft substrates. 2. Do not forget to install the ground bar (at a height of 25 from the ground) as well as the beam reinforcement bars (welded together with flash welding, diameter Ф14～25mm) ； Threaded connection >= 25) ； Note: Welding has been largely phased out, as it increases the brittleness of the rebar, potentially leading to brittle fracture at the joints. X. Misalignment of embedded parts: 1. The column center line is fixed with small nails to facilitate the use of tension cables ； 2. Measure the elevation before installing the bolts to control the height. 3. Bolt installation is complete; the technician verifies the dimensions on-site, 39. http://img.civilcn.com/d/file/zhishi/gcgl/2020-01-13/99e2b44e3346876df901525afe313d6e.png