As a new type of building structure, prefabricated buildings have the characteristics of light weight and convenient installation, and are widely used in various industries. Like all types of buildings, a solid foundation is required to withstand the impact of high winds on the building structure and ensure the safety and service life of the building.
of course. Our steel structure foundation design has some special designs to enhance the stability of the entire building structure. Let’s take a look at the specific construction process together!
（1）. The site is leveled
Site leveling is to transform the natural ground within the scope of the building into the plane required by the design through manual or mechanical digging, filling and leveling to facilitate site layout and civilized construction. The three links and one leveling work is usually carried out by the construction unit, so site leveling has also become an important content before the start of the project.
The leveling of the site should consider meeting the requirements of the overall planning, production and construction technology, transportation and site drainage, and try to balance the excavation and filling of the earth, reducing the amount of soil transportation and repeated excavation and transportation.
The general construction process arrangement for site leveling is: site survey→remove ground obstacles→calibrate leveling scope→set leveling base point→set square grid, measure elevation→calculate earthwork excavation and fill volume→level earthwork→site rolling→acceptance
After determining the leveling project, the construction personnel should first go to the site to conduct surveys to understand the topography, topography and surrounding environment of the site.
Understand and determine the approximate scope of the site leveling site according to the general building plan and planning. Before leveling, the obstacles such as trees, wires, poles, pipes, houses, tombs, etc. must be cleaned up within the leveling area of the site. Then, according to the elevation required by the general plan, the reference elevation is introduced from the leveling base point as the base point for determining the earthwork calculation.
The general requirements for leveling the site are as follows:
1. The leveling site should be well grounded for drainage. The surface slope of the leveled site should meet the design requirements. If there is no requirement in the design, the slope should generally be not less than 0.2% toward the drainage ditch.
2. The leveling of the site should be regularly measured and checked whether its plane position, horizontal elevation and slope gradient meet the design requirements. Plane control piles and leveling control points should be protected by reliable measures and retest and inspect regularly.
（2）. Positioning and laying out and earthwork excavation
1 . Positioning & paying off
1.1 According to the given permanent control coordinate and leveling point, leading test to the site as per the requirement of the building overall plane. Set measure control net in the project construction range,including controled basic line, axes and leveling basic point; Do the work of measure and check of axes control. Controled net must be far away from the building,structure building,earthwork mechanical operation and transport line,as well as be of protection mark.
1.2 Axis orientation of the building should be done to control measurement and verification;earthwork measurements for positioning & paying off, set the gantry board, release the pit(tank) excavation gray line,the upper edge and bottom edge as well as standard logo.Gantry board pile should generally be left pit edge about 1.5-2.0m,in order to facilitate preservation. Elevation,the axis should be reviewed and make sure to be correct before the site preparation and foundation pit excavation.
2.1 Before the excavation, make sure the plan of the foundation pit excavation and the ground water control according to the project structure form,depth of the foundation pit, geological conditions,surrounding environment, construction method,construction period and ground load etc.
2.2 The earthwork and the construction materials stacked on the edge of the foundation pit,or the mobile carriers and excavation machines along the edge, should generally be away from the top edge of the pit not less 2m, and the stacking height should not exceed 1.5m. In the vertical edge of the pit,this safe distance should be appropriately increased. Spoil should not be stacked on the edge of the pit in the soft soil area.
2.3 The ground around the foundation pit should be treated with waterproof & drainage.Prevent rainwater and other surface ground water to immerge into the earth around the foundation pit. When the foundation pit has been excavated, clear up the bottom and check the slot timely. Reduce exposure time,prevent the insolation and rain to destroy the original structure of the foundation soil.
3 . Control of the positioning &paying off
Content of the control is checking the positioning pole,axis,position and the geometry size.
According to the layout red line or the building square grid, check the positioning pole of the building as per the overall design plan.Theodolite and standard steel rule could be used for checking.Check the axis and geometry size of the foundation pit and the slot gray line as per the design basic plan, and also whether the direction is consistent with the plan.The project axis control pole should be set far away from the building more than twice of the excavation depth.Leveling point elevation may be cited to the building(structures) which has been stably built.Or set the leveling point at a little far away from the building and properly protect it.Timely check and verify the position of the control pole and level elevation during the excavation.
4 . Control of the earthworkexcavation
Content of the control is checking excavating elevation,section size,slope and drainage.
General earthwork excavation section shall be from the top layer to the bottom in turn,making certain slope at any moment.If in the use of mechanical excavators,a shallow pit with the depth within 5m could be excavated in one time.Soil of 200~300mm thickness should be reserved when closing to designed bottom elevation or slope edge, manually excavate and repair, digging side in the meantime slope repairing to ensure that no disturbance of the soil and elevation design meeting the requirement.Even if the elevation is much deep,no backfill with loose soil,sand, grave or low strength grade concrete could be used to fill with pressure to the design elevation.When there is soft soil in the part of the foundation,which could not meet the design requirement, should discuss with reconnaissance,design and the construct department to solve.
（3）.Rebar,framework and concrete project
1.1 When the cushion irrigation is completed and concret reach to 1.2MPa, bind the rebar with surface elastic line, no leakage buckle is allowed. Hook part of the column reinforcing must be bound with bottom bar in the angle of 45°,with point of connection totally bundle up.
1.2 The first stirrup is bound at 5cm from the bottom,the last is bound at 5cm from the base top.As the elevation control reinforcing and positioning reinforcing, once more positioning reinforcing need be bound at the top of the column reinforcing.After the upper and bottom stirrup as well as positioning reinforcing has been bound,adjust the column reinforcing to the point with the well character wood frame for temporarily fixing.Then bind other stirrups to ensure the column reinforcing to keep the shape. Two layers of the positioning reinforcing must be changed after the basic concrete irrigated.Bottom and the side of the reinforcing bar should be set padding block for protecting,with the thickness of design and distance of the padding black must be not more than 100mm(depending on the designed diameter of reinforcing bar) to prevent the common quality defects of reinforcing bar exposure.Pay attention to the protection of the finished steel,no collision,resulting of reinforcing bar shift.
2. Framework project
2.1 Framework will be immediately installed after the reinforcing bound and relevant professional construction completed. Small steel framework or wood mould is adopted, fixed by shelf pipe or lumber. When the prick basic slope is less than 30°,inclined mould will be adopted for supporting,in the use of bolt straining with bottom reinforcing to prevent floating.
2.2 Air permeable and vibrator hole is set on the upper of the mould.When the slope is not more than 30°,steel wire mesh will be used to prevent the drop of the concrete,with well character wood set on the upper to control the position of the reinforcing bar.No impact on the mould with heavy object.No build falsework on the hanging mould.Ensure the mould firm and tight.Clear up the saw dust,dirt and other sundries before the concrete irrigation.Wood mould should be watered with irrigating.Slab joint and hole must be blocked up.
3. Concrete project
3.1 Concrete irrigation should be processed step by step,with intermission time being not more than initial set time,which usually is not more than 2 hours.Firstly,5~10cm thickness concrete could be irrigated to make the reinforcing fixed,in order to ensure the reinforcing bar to be right position.Sidestep type base should be wholely irrigated by each step height.When one step has been irrigated, pause about 0.5 hour waiting for going down,and then irrigate the upper step.Blanking for each step,thickness of each step is the effective vibration length of the vibration bar.Prevent the beehive,pitting surface or hole because of the deeply blanking,unreal vibration or leakness,sand flooding from the foot of the hanging.
3.2 Plug vibrator is adopted in the concrete vibration,with distance of the plug being not more than 1.25 times of the effective length of the vibrator.Upper step vibrating bar will plug into lower step about 3~5cm.Try to prevent to impact the embedded part and embedded bolts to avoid embedded parts shift.
3.3 Concrete leveling:If the surface of the concrete is comparatively large,vibrate one time by the board vibrator after the concrete irrigation,then scape smoothly using the scrape pole,and then twisted by wooden float.Check the surface elevation of the concrete before surface finishing, immediately correct if any false.
3.4 Concrete irrigation: While the irrigation,observe regularly whether the mould,kickstand, reinforcing bar,bolts and the reserved holes and pipes being any shift.If there is any transform,shift or displace, stop irrigating right now,repair in time and make the mould fixed, and then continue irrigating.
3.5 Concrete maintenance: The irrigated concrete should be covered and watered after about 12 hours.Common temperature maintenance must be not less than 7 days,special concrete maintenance must be not less than 14 days.Expert for checking and confirming to prevent the concrete surface crack because of the maintenance being not in time.
3.6 Mould removed:Mould of side could be removed when the concrete strength reach to ensure it will not be destroyed in the removing.Expert should check the concrete strength before the mould removed.
4 . Earthwork backfill
The same kind of soil should be used in the backfill and control the moisture content of the soil within the best range.When the different sorts of soil is used in the backfill,should regularly separated lay.Soil layer with high water permeability should be set under the soil layer with low water permeability,without mixed.Side slope couldn’t be closed by the soil with low permeability,in order to make moisture remove and keep basic soil stable,as well as prevent water sac and shift.
Backfill should start from the lowest layer,fill and press from below to up layer in the whole length.
In the undulating terrain of the place,rub should be prepared.Build the ladder shape slope of 1:2, every step with height of 50cm and width of 100cm.While subsection construction, the slope of the joint for every layer should be made more than 1:1.5,grinding track overlapping 0.5~1.0m, distance of staggered joint for the lower and upper layer should be not less than 1m. Joint should be at important parts such as base,wall corner and column,ect.
Stated falling height should be prepared when the backfill,preparing the earth falling gradually in the effect of driving,stacking,alternation of wet and dry,and oher Natural factors.The falling height should be confirmed according to the construction character,backfill height,backfill sorts,press coefficient and the groundwork,ect.When the earth is mechanically pressed by layers,the falling height(percent of the backfill height):for sand is 1.5%;for powder clay is 3%~3.5%.