One of the difficult situations for building a building is the presence in the ground of a quicksand - a mixture of soil particles with water. Quicksand, as a rule, is localized at a certain depth and, if not damaged, is fairly stable. However, when trying to build a buried foundation, the quicksand can give the builders a lot of trouble.
Foundation on quicksand
How to build a foundation on quicksand? There are several ways, and their choice depends on the location and depth of placement of the unstable layer of soil. Therefore, before you decide on any method, you must necessarily order a geological study of the site for building. In the study it is necessary to determine:
- Depth of soil freezing( HPG);
- Groundwater table( GWS);
- Depth of occurrence of quicksand and thickness of its layer.
Methods to combat quicksand and choose the type of foundation
You can only fight with quicksand in one case - if there is a possibility of equipping the drainage system below its level. Quicksilver is a slurry of fine dusty sand particles with clay impurities in water and has a semi-fluid consistency with high viscosity. Qualitative drainage with drainage of water can drain quicksand and prevent its further appearance. In this case, during the operation of the building will have to regularly audit the drainage system.
Methods for combating quicksand
Quicksand itself is not dangerous if it does not damage its integrity. Therefore, if it is not possible to drain quicksand, it is necessary to choose a method of erecting a foundation that will avoid contact of the base with quicksand, or reduce this contact to a minimum.
If, as a result of geological studies of the soil, it has been found out that the quicksand is at a considerable depth, below the freezing depth of the ground, for a private house it is possible to choose a monolithic ribbon foundation of shallow foundations with gravel bedding, or if the dimensions and weight of the buildings are considerable, the slab foundation on the gravel-sand preparation.
If the quicksand is located at a depth of no more than 0.5 meters and its thickness is insignificant, and below it there are solid and stable soils, it is better to choose a pile foundation with a grill made of concrete or using screw piles. Piles are buried in solid layers of soil not less than 1 meter thick, thickening at the base prevents the ejection of piles by frost heaving forces.
Fine-grained band foundation on quicksand
Such a foundation is performed when the quicksand is laid at a depth of not less than 1.5 meters on weakly patchy soils. If it is necessary to build a basement, it is equiped by raising the basement above the ground, without burrowing the underground part of the basement.
- Preparation of the site is reduced to clearing the site, its leveling, digging a shallow pit and the arrangement of horizontal drainage. In the event that the groundwater level rises, drainage will prevent capillary rise of moisture. The depth of excavation is from 0.5 to 0.7 meters. The bottom of the pit is covered with rubble, on top of the rubble - coarse-grained sand. Thoroughly pound the padding, spilling it with water.
- Do formwork from boards or boards to the height of the basement of the basement. Lay the polyethylene film or other waterproofing material in the formwork to avoid leakage of concrete milk when pouring concrete, after which the reinforcement of the foundation is performed in accordance with the calculation.
- Fill formwork with M200 or higher concrete, remove air bubbles from concrete with a vibrator and level its surface. Maturation of concrete last at least 28 days, at this time the foundation must be protected from atmospheric precipitation and direct sunlight.
- After the concrete has dried, it is necessary to perform waterproofing of the foundation, and if necessary, its insulation, then backfill the excavation with sand.
Sample of foundation construction
Plate foundation on quicksand
Applied in the case of deep-lying quicksand in the abrasive and moist soils. Plate foundation is called floating - its design allows to withstand a significant load of the building, and with frost puffing and soil movements, the foundation is displaced along with the entire building, without deformations.
- Level the pad and perform padding with crushed stone and sand to a height of up to 0.5 meters. Tightly rammed it, spilling water. Produce a markup. They lay underground communications.
- Produce a horizontal hydro- and thermal insulation of the basement of the slab foundation: put a layer of insulation of expanded polystyrene on the prepared padding, and roll it with waterproofing.
- The formwork of the slab foundation is made of boards or plywood panels, the formwork height is about half a meter. The prepared surface is covered with a polyethylene film, gluing strip joints with adhesive tape. The film prevents the flow of concrete and concrete milk from the formwork, in addition, it will provide mobility of the slab in case of soil movements.
- The reinforcement is carried out by means of a corrugated rod with a diameter of 12-16 mm, laying it in a grid with a pitch of 15-20 cm. At the intersections, the bar is knitted with wire. To make the armature completely recessed in the concrete, the rods must be laid on the plastic guides.
- The concrete is poured into the prepared formwork, it is leveled and compacted with a deep vibrator and screed, smoothed with a rule. The concrete dries 4 weeks, at this time it must be protected from rain.
foundation foundation sample Pile foundation on quicksand
Such a foundation is carried out if the quicksand is located at a close distance to the soil surface, but its depth is low, and below it there are solid stable layers of soil. This situation is typical for wet silty sandy loam, when the groundwater is not deep. They feed the quicksand, and the drainage device is not sufficient to drain the soil. Therefore, the only way to create a stable and reliable foundation is the penetration of piles into the depth of hard soils.
- Site preparation is reduced to its cleaning from vegetation, debris and marking.
- Piles can be used as concrete or screw steel. The second option is preferable because of the price, in addition, screw piles can easily be installed without the use of special equipment. The advantage of screw piles is also the fact that their installation takes place simultaneously with drilling, so it will not be necessary to take measures against flooding the well and pump out water in case of damage to the quicksand.
- Piles are installed in the corners of the building, at the intersection of walls, and also every two meters under the bearing walls. Screw the metal piles together, using a lever inserted into special ears, checking their verticality level. Concrete piles are slaughtered with the help of special equipment.
Metal piles are screwed to a hard ground and continue to be buried at least a meter. If necessary, they increase. Surplus steel piles are cut off by a bulgarian, and the strapping is made from above: from metal structures - to welding, from a wooden beam - with the help of special headers.
Pile foundation on quicksand
Safety precautions
For any excavation work on a section with quicksand, measures must be taken against the breakthrough of quicksand. In case of damage to its integrity, the excavation of the excavation can occur in a matter of seconds, and it is very difficult to get out of the viscous mass.
Therefore, when working, it is necessary:
- Boiler walls reinforced with boards;
- In a pit with a depth of more than a meter, install a ladder providing a rapid ascent to the top;
- All work must be carried out by a team of two or more people.
