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Construction in rainy season

Sichuan Province is located in the subtropical humid climate zone, with an average annual rainfall of 1000mm. In particular, the rainfall from June to October each year accounts for more than 60% of the whole year. For construction projects in this period, rain proof construction is particularly important

I. characteristics, requirements and preparations of construction in rainy season

construction in rainy season is different from concrete construction in winter. It is mainly based on the notice of rain, typhoon and flood prevention issued by the local meteorological department; Or depending on the impact of rainfall on individual buildings

1. Characteristics of construction in rainy season:

(1) uncertainty. Due to the limitations of science and technology, the meteorological department can not provide timely and accurate prediction services between various control modes; Severe weather such as rainstorm and mountain torrent often comes unexpectedly, which requires early preparation and preventive measures for construction in rainy season

(2) sudden attack. The rain has serious damage to the scouring or soaking of the building structure and foundation. It must be protected quickly and timely to avoid causing losses to the project

(3) the rainy season has a great impact on outdoor construction (such as earthworks, roof works, etc.). In order to ensure the smooth progress of the project, a full estimate should be made in advance and reasonable construction arrangements should be made

2. Requirements for construction in rainy season:

(1) when preparing the construction organization plan, the subdivisional works that are not suitable for construction in rainy season shall be arranged in advance or delayed according to the characteristics of construction in rainy season. Effective measures shall be formulated for projects that must be constructed in rainy season to carry out surprise construction

(2) reasonable construction arrangement. Outdoor work shall be paid close attention to in sunny days, indoor work shall be arranged in rainy days, and outdoor operation time and working face shall be minimized in rainy days

(3) pay close attention to the weather forecast, make preparations for flood control, and reinforce the projects under construction if necessary

(4) do a good job in preventing rain and moisture of building materials

3. Preparation for construction in rainy season

(1) site drainage. The roads and facilities on the construction site must have smooth drainage, and try to stop the rain and dry the water. Prevent surface water from draining into the basement, foundation and trench. Dangerous rocks shall be treated well to prevent landslides and landslides

(2) rainproof of raw materials, finished products and semi-finished products. The cement shall be received first and sent later, so as to avoid long-term moisture affecting the activity of the cement. Semi finished products such as wooden doors and windows that are susceptible to moisture and deformation shall be stacked indoors. Other materials shall also be protected from rain and drained around the materials

(3) drainage and rainproof measures for on-site houses and equipment shall be taken before the rainy season

(4) prepare sufficient water pumps and related equipment for drainage, and prepare an appropriate amount of plastic cloth and asphalt felt rainproof materials

II. Construction measures in rainy season

construction in rainy season mainly solves the drainage of rainwater. For the construction site of large and medium-sized projects, it is necessary to make an overall plan for the temporary drainage system, including two parts: preventing the off-site water from flowing into the site and draining the off-site water. The principle is upstream water interception and downstream apron; Pit bottom pumping and ground drainage. During the planning and design, it shall be considered comprehensively according to the maximum rainfall and rainfall period over the years and in combination with the terrain and construction requirements of various regions

temporary drainage ditches and intercepting ditches are generally set around buildings to prevent off-site water from flowing into the site. The design shall comply with the following provisions:

(1) the longitudinal slope gradient shall be determined according to the terrain, which shall generally be less than 3% of the new satellite functions of LEGO factories around the world, less than 2% in flat areas and 1% in swampy areas; The general requirement is that the accumulated water on the site can be drained in time without excessive workload of the drainage ditch. The author's region generally adopts 2%

(2) the slope gradient of the ditch shall be determined according to the soil quality and the depth of the ditch. The cohesive soil slope is generally 1:0.7~1:1.5

(3) the size of the cross section shall be determined according to the maximum flow that may be encountered during the construction period. The maximum flow shall be calculated according to the catchment area after finding out the maximum rainfall over the years during this period according to the local meteorological data

design and calculation of drainage ditch: ①

flow: q=v · w

where: q-flow (m3/s)

v-flow rate (m/s)

w-flow sectional area (M2)

flow rate: ②

where: C-flow rate coefficient (l/s)

r-hydraulic radius (m)

i-longitudinal slope of ditch bottom (%)

flow rate coefficient: c=ry/n ③

where n-roughness coefficient is between 0.025 and 0.035 for soil ditches, The stone ditch is between 0.040~0.055

y- when 0.1

when 1

hydraulic radius: r=w/x ④

in the formula, x-wet perimeter (m) is shown in Figure 1:

flow sectional area is calculated as follows:

Figure 1 flow sectional area calculation diagram

w=bh+mn2 ⑤

wet perimeter is calculated as follows:

m in the above two formulas is the slope coefficient

according to formula ① ~ ⑥ above, the shape and size of the temporary drainage ditch can be determined to meet the requirements of preventing off-site water from flowing into the construction site. The drainage at the construction site is relatively simple: for the foundation pit drainage below the ground, as long as the corresponding flow is determined, the matching water pump can be selected or the artificial drainage can be organized, and others will spend thousands of yuan more; The construction site above the ground can only be provided with corresponding drainage channels to prevent ponding on the site

in addition, the impact of rainwater on the divisional works of buildings is multifaceted. Corresponding measures shall also be taken for some outdoor divisional works greatly affected by rainwater so as to ensure the smooth progress of the project

1. Earthwork and foundation works:

earthwork and foundation works are greatly affected by rainwater. If relevant preventive measures are not taken, it may have a serious impact on construction safety and

building quality. Therefore, pay attention to the following points during construction in rainy season:

(1) when excavating foundation trench (PIT) or pipe trench in rainy season, pay attention to slope stability. If necessary, the slope gradient can be properly reduced or the support can be set. Strengthen the inspection of slope and support during construction; For the excavated foundation trench (PIT) or pipe trench, it is better to set support; For those under excavation, slow down the slope with support or stop construction when the construction period is not tight

(2) in order to prevent the slope from being washed down by rain, steel wire sheets can be nailed on the slope and 50mm fine aggregate concrete can be plastered; Plastic cloth can also be used to cover the slope

(3) the working face of construction in rainy season should not be too large, and should be completed by stages section by section and piece by piece. After the foundation is excavated to the elevation, it shall be accepted in time and the concrete cushion shall be poured; If the foundation is soaked by rain, necessary excavation and backfilling shall be done to restore the bearing capacity of the foundation

(4) in order to prevent the foundation pit from soaking, drainage ditches and water collecting wells shall be built in the pit during excavation, and necessary drainage forces shall be organized

(5) the construction of underground pool and basement shall be considered carefully. If the advance is not well considered, in case of heavy rain after pouring and tamping, the basement and pool will often float up

(6) the earthwork backfilled before the rain shall be rolled in time to form a certain slope on its surface, so that the rain water can be discharged dynamically from the internal motor and electrical accessories

(7) in case of heavy rainfall, large-area earthwork construction shall be stopped

(8) for the earthwork accumulated at the construction site, measures shall be taken around to prevent rainwater scouring. For example, place stones around to prevent the earthwork from being washed into the excavated foundation trench (PIT) or pipe trench by rainwater, or bury some completed foundation structures

after the foundation construction is completed, the backfilling around the foundation pit shall be paid close attention to. When artificial precipitation (drainage) is stopped, the anti floating stability of box foundation and the buoyancy of groundwater to the foundation shall be checked and calculated. The anti floating stability coefficient shall not be less than 1.2 to prevent major accidents of foundation floating or tilting. If the anti floating stability coefficient cannot meet the requirements, continue pumping until the construction superstructure load can meet the anti floating stability coefficient requirements. In case of heavy rain and the water pump can not reduce the ponding height in time and effectively, the ponding shall be quickly poured into the box foundation to increase the anti floating capacity of the foundation

2. Masonry engineering:

the overall stability of masonry mostly depends on the water content of adhesives such as mortar and masonry materials, both of which will be greatly affected during construction in rainy season. Therefore, the following key points should be mastered during construction in this period:

(1) bricks must be stacked in a centralized manner in rainy season and should not be watered. The dry and wet bricks shall be properly matched when building the wall. Bricks shall not be put on the wall when the humidity is high. The masonry height should not exceed 1m

(2) stop work in case of heavy rain during rainy season. At the end of bricklaying, a layer of dry bricks shall be placed on the top cover of the brick wall to avoid heavy rain washing the mortar. After the heavy rain, the newly built wall washed by the rain should be turned over to the top two bricks:

(3) the window wall and independent brick column with poor stability should be added with temporary support or cast ring beam in time to increase the stability of the wall

(4) during masonry construction, internal and external walls shall be built at the same time as possible, and attention shall be paid to the connection between corners and T-shaped walls at the same time. In case of typhoon, temporary support shall be added in the direction opposite to the wind direction to protect the stability of the wall

(5) the mixing amount of masonry mortar should not be too much, and it should meet the masonry needs. The mixed mortar shall be prevented from being washed by rainwater

(6) if the construction continues after the rain, the verticality and elevation of the completed masonry must be rechecked; And check the mortar joints of the masonry. Necessary remedial measures must be taken for the places seriously scoured by rainwater

3. Concrete works:

(1) before painting the formwork isolation layer, the weather forecast shall be mastered in time to prevent the isolation layer from being washed away by rain:

(2) in case of heavy rain, concrete pouring shall be stopped and the poured parts shall be covered. For cast-in-place concrete, the reserved positions of several construction joints shall be considered according to the structural conditions and possibilities

(3) during construction in rainy season, the determination of water content of coarse and fine aggregates of concrete shall be strengthened and the water consumption shall be adjusted in time

(4) before large-area concrete pouring, it is necessary to understand the weather forecast for 2-3 days and try to avoid heavy rain. A large amount of rain proof materials shall be prepared at the concrete pouring site in case of sudden rain during pouring

(5) the backfilling under the formwork support shall be compacted, and the base plate shall be added, and the settlement shall be checked in time after the rain

(6) steel bar welding, butt joint and other work shall not be carried out in case of rain. In case of urgent need, rain proof work shall be done or the construction site shall be moved indoors; The newly welded rebar joint shall be protected from rain to prevent the joint from being suddenly cooled and brittle, which will affect the quality of the building

4. Hoisting works:

(1) the stacking place of components shall be flat and solid, and the surrounding areas shall be well drained. Ponding and soaking in the component stacking area are strictly prohibited to prevent the soil from sticking to the embedded parts

(2) the subgrade of tower crane must be 15cm higher than the natural ground, and it is strictly prohibited to soak the subgrade in rain

(3) when hoisting after rain, the stability of the tower crane shall be checked first, and the trial hoisting shall be carried out after confirming that the safety of the tower crane is not damaged by rain. The components shall be hoisted to about 1m, and the hoisting shall be carried out after several times of stabilization

(4) rainy days may affect the sight of the crane driver. If the driver has no experience in hoisting in rainy days, it is best to stop hoisting; Or ask an experienced driver to do it

(5) when the construction is stopped, the hook of the tower crane shall be retracted and close to the tower body, and it is not allowed to

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