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This post was last edited by “Hasty Passerby” on March 6, 2019, at 09:59. Guide to Construction Precautions During the Rainy Season. Since the start of construction, we’ve finally managed to overcome the “post-holiday syndrome” and gotten back on track. Now, we must face various challenges brought about by construction during the rainy season. It is reported that in the coming period, we will experience gentle spring rains, continuous rain during the Qingming Festival, unceasing plum rain, and fierce summer storms. Construction during the rainy season can not only affect the overall construction progress and quality, but also compromise construction safety. Therefore, it’s necessary to go through this construction protection guide. - Protection of construction sites during the rainy season – Drainage issues on the 1F floor. Before the rainy season arrives, it is necessary to carefully inspect the underground areas of the project that are most at risk. Ditches with dimensions of 300mm×500mm (b×h) should be installed along the ground surrounding the main structure. During rain, pumps should be used to drain water from these collection pits into the drainage ditches on the surface ； Inspect the drainage facilities both inside and outside the site to ensure they are in good condition, so that water can be drained quickly after heavy rain. Based on the actual conditions, the principle of using the sump wells at the construction site as the nearest locations is adopted as the centralized point for on-site drainage. There are also living areas and office areas, where it is necessary to check for any leaks, ensure that the drainage slopes are correct, and verify that the drainage channels are unobstructed. For the protection of construction materials on the 2nd floor, sufficient protective materials such as rubber hoses, waterproof materials, and tarpaulins should be prepared in advance. The construction materials stored at the site must be protected from water and moisture; all materials brought into the site need to have measures put in place to protect them from rain. All materials should be stored at a safe distance of at least 3 meters away from the slope of the foundation pit, to avoid storing materials that are prone to scattering nearby the slope. - Precautions for construction during the rainy season – Reasonable scheduling on the 1F: Prepare a construction plan in advance based on local weather forecasts, and arrange the construction activities accordingly. For certain sub-projects that are susceptible to rain, in order to ensure construction quality and safety, efforts are made to schedule their execution on sunny days. For example, in exterior wall waterproofing projects, construction in rainy or snowy weather makes it difficult to form the waterproof layer, and it increases the moisture content in the insulation and leveling layers, resulting in reduced adhesion between the flexible waterproof material and the substrate, or even bulging and damage to the waterproof layer. Protection measures for 2F sub-projects – Concrete work: It is necessary to keep an accurate track of weather forecasts, and concrete pouring should be avoided on rainy days. In case of heavy rain, the following measures should be taken: (1) When heavy rain occurs during concrete pouring, compact the already poured concrete thoroughly. Then, as required by the specifications, create construction joints in appropriate locations, stop pouring immediately, cover the area with plastic sheeting, and secure the sheeting to the rebar to prevent it from being blown away by the wind. During the pouring of the roof concrete, if light rain occurs, vibration, tamping, and covering should be carried out promptly to prevent the cement slurry from escaping. (2) After the rain, strengthen the treatment of temporary construction joints by removing any residual mortar or weak areas, and clean away any dirt or water accumulation in the beams, slabs, and walls; concrete pouring can proceed only after acceptance. (3) Ensure high quality of concrete. During construction in the rainy season, concrete mixers are required to adjust the amount of water used in concrete according to the actual moisture content of sand and gravel. Regular inspections should be carried out at the mixing plants to check the storage areas for sand and gravel as well as the cement warehouses, to assess the mud content in sand and gravel and to ensure that the cement is properly protected from rain. Reinforcement work (1) When carrying out reinforcement work in rainy weather, it is advisable to set up temporary protective shelters to prevent rainwater from falling on the hot welds. If the welding area is relatively humid, it must be wiped clean with a dry cloth and dried using an oxy-acetylene flame before welding, to ensure that the joint remains dry and free of any residual moisture. (2) During lifting, if there is water accumulated on the components, it must be removed before installation; however, the coating must not be damaged. When installing high-strength bolt joints, the friction surfaces of the components should be clean, free of water droplets, and must not be exposed to rain or in contact with dirt, oil, or other contaminants. (3) When storing rebar at the construction site, it should be placed in a location on higher ground that is protected from rainwater; simultaneously, the bottom of the rebar should be elevated by at least 200 mm using materials such as wooden planks. For processed rebar, it should be placed as much as possible in a rain-protected area within the rebar processing shed, to prevent it from being corroded and rusted by rain. Masonry work: The stability of masonry structures is greatly influenced by binders such as mortar and the moisture content of the materials used. These factors are significantly affected during construction in the rainy season. Therefore, the following points should be taken into consideration during masonry construction: (1) The project’s laboratory technician should regularly measure the moisture content of sand and stone, depending on the weather conditions. It is necessary to measure this moisture content before construction begins, adjust the mix proportions accordingly, and strictly control the consistency of the mortar. (2) Construction should not be carried out during heavy rain; when finishing bricklaying, place a layer of dry bricks on top of the bricks to prevent the mortar from being washed away by heavy rain. (3) Bricks must be piled up in clusters during the rainy season, and watering should be avoided. When building walls, it is necessary to use a proper combination of dry and wet bricks; bricks that are too moist should not be used in the wall construction. The building height should be ≤1 m. (4) During wall construction in the rainy season, mortar tends to flow. If this is not corrected, it not only affects the neatness of the wall surface but also leads to problems such as the wall tilting, uneven thickness of the mortar joints, and irregular horizontal joints. Earthwork and foundation work are greatly affected by the rainy season; therefore, the following points should be taken into consideration when carrying out such work during the rainy period: (1) When digging foundation trenches or ducts during the rainy season, attention must be paid to slope stability. If necessary, the slope gradient can be appropriately reduced or supports can be installed. During construction, stricter inspection of slopes and supports should be carried out ； For the already excavated foundation trenches or ducts, it is advisable to install supports; for those still under excavation, it is best to slow down the slope formation with supports, or to suspend work if time is not a constraint. (2) To prevent the slope from collapsing due to rainwater, wire mesh can be installed on the slope and covered with 50 mm thick fine aggregate concrete; alternatively, the slope can be covered with plastic sheeting. (3) During the rainy season, the construction area should not be too large; it should be completed in phases, section by section. After excavating the foundation pit to the specified elevation, conduct timely acceptance and quickly pour the concrete cushion. (4) To prevent the excavation pit from becoming waterlogged, drainage ditches and sump wells must be constructed within the pit during excavation, and necessary drainage measures must be arranged. (5) For underground pools and basements, measures to prevent floating after concrete pouring should be considered during construction. (6) When rainfall is heavy, earthwork construction should be halted, and excavation work on soft soil foundations (trenches) should be stopped during rainy days. The earthwork piled up at the construction site should be removed before the rainy season arrives. Once the foundation construction is complete, the backfilling work around the foundation pit should be carried out promptly. When stopping artificial precipitation (drainage), it is necessary to verify the anti-floating stability of the box foundation as well as the buoyant force exerted by groundwater on the foundation; the anti-floating stability coefficient should be ≥ 1.2. If the anti-floating stability coefficient does not meet the requirements, pumping should continue until the load imposed by the upper structure during construction allows the anti-floating stability coefficient to be satisfied. There are indeed many challenges associated with construction during the rainy season, so it’s very important to take preventive measures in advance. At the same time, as we continuously identify and solve problems, we can also learn more techniques and make faster progress.