I have long wanted to write a post about quicksand and clearly show in photographs and pictures what it is.

So, in the area underground, from a level of about 3-3.5 meters to a depth of 10 meters, there is water-saturated sand - quicksand.

We tried to make a well in the usual way - we made a collapsible drill from several sections and started drilling.

For convenience, we have installed a tripod.

Up to a depth of 3 meters everything went well. Then problems with quicksand began. How much we did not take out the sand, the depth of immersion of the drill practically did not change. This is a common occurrence on quicksand.

In the sand underground a cavity is formed voids with water. This cavity grows in width and practically does not deepen. So you can scoop out at least a few tons of sand until an underground cave is formed and the soil from above falls down. 🙂

Here's what the process looks like in a diagram.

Scheme of cavity formation during quicksand drilling

And here's what it looks like in reality. Spreading unique underground quicksand photo and the cavity formed as a result of drilling. We lowered the camera on a rope into the well.

The first photo is at a depth of about 3.5 meters in the transition layer between clay and sand. Those. where a normal well passes into a hollow cavity.

Transition between clay and quicksand

The next two photos are taken below - at a depth of about 4 meters.

At this level, a spherical cavity is visible, half filled with water. Because of such cavities, there are failures of the soil over quicksand.

Also visible are the roots of plants hanging in the void. It turned out that many herbs grow roots up to 4 meters! We didn't expect it, to be honest.

This is how the sand collapses in quicksand. Drilling in the usual way is useless. We will simply increase the underground cave. 🙂

Underground cavity in quicksand

Plant roots hang down into the cavity from quicksand

To solve this problem, you need to use a casing pipe. Which will not allow the sand to collapse, and the drill will go down slowly. There will be no cavity. The casing pipe must be periodically hammered deeper and deeper. In the picture, I painted the casing in red.

Drilling quicksand with casing

So we did. The casing was lowered into the well.

Then we began to drill inside the casing pipe and try to sink it deeper and deeper, periodically pumping out sand and water with a Vibrating Brook pump.

Vibration pump for pumping quicksand

We made three mistakes out of inexperience:

1. The casing pipe must be taken iron. We took a plastic one, which, when clogged, absorbs and does not go into the depths. In addition, the plastic pipe has thicker walls. This is also not good.
2. There must be no holes in the casing. Our pipe had a lot of drilled holes. Since they took what was at hand as a casing pipe.
3. Water cannot be pumped out of the well. This increases the external sand pressure on the casing and makes it difficult to drive deeper. You can even say more - it is better to pour water or mud into the casing pipe, thereby creating pressure inside the casing shaft and helping to move it lower and lower.

The foundation on the quicksand is obliged to provide, in rather difficult conditions, acceptable stability and design rigidity of the structure of the entire structure. After all, quicksand, in most cases, is considered as a piece of soil completely unsuitable for construction.

However, thanks to modern technology, the foundation can be built even in such, not the most acceptable, conditions. And in this article we will consider a typical quicksand foundation, offering our readers several options for the process of building a foundation in unstable ground conditions.

What is the danger of quicksand?

A typical quicksand is a very special type of soil, which is based on fine sand (dust) saturated with a large amount of water. Therefore, a quicksand under the foundation is just a nightmare for any developer: after all, such soil does not have sufficient rigidity and cannot withstand the weight of the building.

That is, a building erected on a quicksand will simply “pull” into the soil. Moreover, in the process of “immersion”, both the foundation and the walls of the building will simply burst under their own weight. However, such an effect can only be observed if the owner of the house ignores the danger of quicksand and does not take measures to level the insufficient stability of the soil.

As such countermeasures, either too deep foundations are usually used, penetrating through the quicksand in search of more stable soil, or too wide foundations, distributing the weight of the structure along maximum area which reduces ground pressure.

The technology of building foundations on quicksand

When deciding which foundation to build on a quicksand, it is necessary to take into account the depth of the unstable soil and the thickness of the sand layer itself.

The first parameter is defined as the distance from the zero level to the boundary of the quicksand. The second parameter is the depth of the quicksand itself - the distance from the beginning of the sand layer to a stable layer of soil.

Moreover, both the first and second parameters are determined using geological surveys carried out within the boundaries of the site. There is no other option to determine the depth of the quicksand and the distance from the zero level to stable ground.

As a result, if the depth of the quicksand does not exceed three meters, then in the process of constructing the foundation, the technology of shallow laying, strip foundation, should be used.

If the depth of the quicksand does not exceed one meter, and the depth of the stable soil is four to five meters, then during the construction process, a pile-type foundation with a monolithic grillage should be used.

With a significant depth of stable soil (more than six meters) and a shallow depth of quicksand (less than one meter), a monolithic slab is used as a foundation, poured over the zero level.

In areas where there is predominantly sandy soil, or there was once a river or lake, in the wetlands, the developer may expect an unpleasant surprise - the presence of quicksand in the thickness of the soil. Quicksand is called sand or sandy loam saturated with water. The problem is that it is fluid, it liquefies under load. What foundation to build on quicksand, what to look for in such a situation - we will talk about all this in this article.

Construction of the foundation of a house on a quicksand

Despite the fact that sand is often used as a cushion material (read about the sand cushion here), its presence in the ground can adversely affect the foundation. It all depends on the size of the grains of sand. As you know, sands by fraction are not only large and medium, but there are also small and dusty ones. The latter just pose a danger if they are present in the ground at the construction site. The fact is that when saturated with water, they acquire the property of fluidity, which negatively affects bearing capacity such soil. The situation is aggravated by impurities of clay, which are usually found in quicksand. Given the low resistance value of wet sandy-dusty soil (see the table below), it is unacceptable to place the base of the foundation on a quicksand.

How to find out that we are dealing with a quicksand

Geological research is indispensable. It is best to order engineering and geological surveys from a professional company before starting construction. But if you decide to make the foundation with your own hands, then you can save on such services:

• if your neighbors on the site have already built a house, it is likely that they have the necessary information on the ground. The easiest option is to ask them;
• independent study of the soil under the future development spot is reduced to digging a pit to a depth not lower than the GPG or drilling wells. The presence of a quicksand will be indicated by the sliding of the walls of the pit, filling the well with a pasty mixture of "liquid sand";
• if a quicksand is found during soil research, it is almost impossible to independently determine the thickness of a layer of fluid soil. Those. considering as the basis of the house a foundation on screw piles or a columnar base buried below a quicksand, you will have to fork out for professional services

Foundation options

In general, when it comes to building a house on a site with a quicksand, almost all types can be considered as its foundation - it all depends on the specific conditions:

• a pile foundation with a grillage is suitable in cases where the thickness of the quicksand is known and it is insignificant. Driven reinforced concrete piles or screw steel products can be used as supports. The idea is to place the bottom of the foundation below the quicksand. The binding of the supports is carried out with a reinforced concrete grillage;
• a tape shallow foundation can be used in two cases: the quicksand is at a significant depth (more than 3 m) or it is possible to install a drainage system for the foundation. The latter option is convenient on a site with a slope - by draining the quicksand, we simply level its negative properties;
• the foundation slab is most often used in cases where the load from the house is significant, and the quicksand is located close to the ground (1-2 m). In these situations, saving on the device of the above types of bases looks doubtful, therefore it is the slab that is poured

As an alternative, with a high GWL and a shallow occurrence of a quicksand, you can consider the option of building a bulk base. For these purposes, the required amount of material is brought to the site (as a rule, sand, gravel, etc. - non-porous soil) and then the foundation is erected on bulk soil.

Quicksand Precautions

Imagine a balloon filled with water and tied up. As soon as you pierce it, the water immediately rushes out. The situation is similar with quicksand: they behave more or less predictably while they are in the thickness of the soil and access to them is limited by the overlying layers. One has only to pierce the "shell", the flowing sand will break free. Therefore, when developing foundation pits (or deep trenches) for the foundation, in places where quicksand is possible, it is necessary to work with at least two people: one is engaged in excavation, the second controls the process.

Building a house on quicksand is a complex process. Quicksand is a combination of soil and water, localized at a certain depth. If it is necessary to build a foundation, a number of questions arise about how not to disturb this formation. Familiarize yourself with the options for the foundation on quicksand and the technology of their construction.

Do-it-yourself house on quicksand: features and types of quicksand

Thermal quicksand is a type of soil whose base contains fine-grained sand and a large amount of water. Since this mass is quite buoyant, it does not withstand a large load, and this negatively affects the construction process.

An improperly built house can simply be pulled underground, and with walls. Therefore, the construction of a building on quicksand should be taken with great responsibility.

In relation to the type of soil, several types of quicksand are distinguished, each of which has individual characteristics and features. Quicksand are:

• true origin - in the form of clayey sand, loam or sandy loam;
• false origin - in the form of gravel sand.

The first option is characterized by high hydrophobic characteristics. Such soil absorbs water well, has molecular interaction between particles. The floating state forms a special film with a minimum cleaning factor. The true composition is determined by external signs. The bottom of the well is filled with "cement milk", when taking the soil from the bottom of the quicksand, it instantly blurs. To determine quicksand on the site, the soil is taken to the laboratory.

If you dig a hole in the area, it will instantly fill with red water. After drying, a fairly dense mass is created. The floating layer makes it difficult to carry out installation work, the soil fills any recesses during construction. It's pretty hard to create a closed loop.

False quicksands are less dangerous, their composition does not have as strong molecular bonds. The water at the bottom of the quicksand is light, and easily evaporates from the soil. After drying, a mass with a slightly loose structure is formed. Before building a house on quicksand, determine the content of the soil and the type of floating earth in the laboratory.

Do-it-yourself foundation building on quicksand: how to deal with quicksand

Approach the fight against quicksand with special responsibility, start this process after determining the type of quicksand. There are three options for eliminating the negative consequences of quicksand:

• artificial drainage;
• creating a fence using sheet pile walls;
• fixation of quicksand on the soil.

The first option involves the open pumping of water from the quicksand. If it is necessary to drain the earth up to a depth of 600 cm, we recommend using wellpoints. With a greater depth of irrigation, specialists use special electro-drainage devices.

Sheet pile walls cut the quicksand layer. Thus, a certain pressure is created and the ability to withstand the load. A wooden grooved board is hammered to a depth of 10 m, and metal options are suitable for a depth of up to 35 meters. This method does not work in the presence of dense soils between quicksand.

Quicksand is fixed on the site in three ways:

• freezing;
• cementation;
• silicification.

The first option is rather unreliable. For its implementation, special freezing units are used, however, at a high temperature, the quicksand still thaws.

Silication is different high efficiency and involves pumping liquid glass into the soil. Suitable for false quicksand. Prevents ground movement and improves foundation strength.

At true quicksand Only the following methods are relevant:

• electrochemical;
• freezing;
• protective method.

When digging a pit or trench on a site, it is imperative to strengthen their walls.

In addition, in the process of combating quicksand, they equip a drainage system that is below the soil level. The quicksand contains small silt particles, connected with water, with the help of high-quality drainage, it is drained, the structure becomes strong and the soil can withstand the load. However, during the operation of the building, periodic revision of the drainage system is a mandatory process.

When the quicksand is located below the freezing of the soil, a variant of a shallow monolithic strip foundation is possible with the obligatory presence of gravel backfill.

If the depth of the quicksand is more than 50 cm, while the thickness is small, and there is solid soil under them, then we recommend stopping at the pile version of the foundation.

Quicksand foundation options: do-it-yourself shallow strip foundation

When laying a quicksand up to 150 cm on slightly heaving soil, we recommend stopping at a shallow strip foundation. If a basement is being built in the house, then the base rises above the soil, but in no case does it go deep into the earth.

Construction instructions shallow foundation:

1. Conduct a soil study to determine the type of quicksand on the site. Create drawings of the foundation, they indicate its size, thickness, pouring method.

2. Prepare the site for work. Remove vegetation and debris, level the surface, make a foundation pit, according to the size of the foundation.

3. Arrange horizontal drainage to prevent capillary rise of moisture from the lower layers of the soil. The depth of the foundation pit for the foundation should not exceed 70 cm. At the bottom of the pit, install a crushed stone pillow, then fill in the coarse-grained sand. Thoroughly tamp the base with a special tool, gradually moistening it.

4. At the height of the basement of the building, build the formwork. For its manufacture, use a laminated board, metal or plastic. We recommend to stay on the collapsible option. Check the evenness of the formwork installation with a level. Put a waterproofing film or roofing material inside the formwork - these materials provide additional waterproofing of the foundation on quicksand and prevent leakage of concrete milk during pouring.

5. Further, in relation to the previous calculations and drawings, reinforcement is performed. For this, special welded and anti-corrosion fittings are used. The number of elements is determined individually and depends on the overall size and weight of the house.

6. The next stage is the pouring of a shallow foundation. To work, you will need a high-quality concrete solution of at least Grade 300. To remove air bubbles from concrete and to improve its adhesion to the surface, special equipment is used in the form of a concrete vibrator.

7. Next, you need to level the surface with a regular board or special tools. The maturation time of the concrete composition is at least 26 days. During this time, the foundation is covered with a film to prevent precipitation from falling on its surface and protected from solar radiation.

8. After the concrete composition has dried, the process of waterproofing and insulation of the foundation follows. This is followed by backfilling the pit with sandy soil.

What foundation to make on a quicksand: the technology of erecting a slab foundation

A slab foundation is used if the quicksand lies deep on heaving and moist soil. The cost of building a slab foundation is several times higher than that of a strip foundation. However, this option is more durable and has good performance.

The slab foundation is also called floating, it can withstand large buildings, and when the soil is heaving or frost, it shifts directly with the whole house without damaging it.

Instructions for the construction of a slab foundation on a quicksand:

1. In relation to the type of soil, create foundation drawings on quicksand. They determine the size and thickness of the slab, its location, the method of pouring and other individual features of the structure.

2. Level the site, remove debris and vegetation. Fill it with rubble at least 50 cm, compact it tightly and fill it with water. Mark out the area using pegs and string.

3. Lay underground communications in the form of water supply and sewerage. Waterproofing and thermal insulation of the foundation are carried out before it is poured. To do this, a filling of insulation and polystyrene foam is laid on the surface, followed by a waterproofing layer in the form of roofing material or other rolled material.

4. For the manufacture of formwork for the slab foundation, use boards or a panel shield, about 50 cm high. Watch the strength of the formwork, as concrete is quite heavy in weight and exerts a large load on the base.

5. The prepared surface, without fail, is covered with plastic wrap, glue the joints between the materials using ordinary adhesive tape. The film will prevent the concrete solution from flowing out and make the slab movable when the soil is heaving.

6. To reinforce the slab foundation, a corrugated rod with a diameter of 1.2-1.6 cm is used. The material is laid in the form of a grid, with an interval of 15 cm. At the intersection of the rods, a wire is used for the bundle. Reinforcement is laid on top of plastic guides, the material must completely sink into the concrete solution.

7. Prepare the concrete solution. For these purposes, specialized special equipment or ready-made factory concrete is used. Since the scope of work is very extensive, a conventional concrete mixer will not work.

8. Pour the concrete mortar into the previously prepared formwork, level it and process it with a special vibrator. For smoothing, use the rule. The drying time of concrete is about 3-4 weeks in dry and warm weather and 5-6 weeks in cold weather. It is recommended to cover the foundation with plastic wrap to prevent it from getting wet.

Difficulties in building a foundation on quicksand: do-it-yourself pile foundation on quicksand

When the quicksand is close to the surface, we recommend stopping on a pile foundation. This option is relevant if there is powerful, stable soil under the quicksand.

This situation is typical on wet silty sandy loams, where it is not possible to drain the quicksand and the installation of piles remains the only option. Among the advantages of a metal pile foundation, we note:

• suitable for any type of soil;
• characterized by a minimum amount of earthwork;
• erected at any time of the year;
• the cost of construction is almost half that of a strip foundation;
• has a high bearing capacity.

Instructions for the construction of a pile foundation on quicksand with your own hands:

1. Clear the area from the top layer of soil by 10-12 cm. Mark up in relation to the previously drawn up drawings. The number of piles is determined individually depending on total weight building, its size and the type of quicksand located in the soil.

2. It is possible to use concrete or metal piles. We recommend choosing the second option. This method is less laborious, affordable and not inferior in efficiency to concrete piles. Not required for installation of steel piles special equipment, and the work is completed in 1-2 days.

3. Screw piles are ideal. These devices do not require pre-drilling. They are installed and screwed into the soil. Therefore, there is no risk of flooding the well and pumping out water.

4. Places for installation of piles are determined in the drawing, corner sections, intersections of walls, and also with an interval of 200 cm between walls of a bearing purpose are mandatory.

5. A minimum of two people are required to drive metal piles. The special design features a lever that must be turned when screwing. Be sure to check the evenness of the structure. It is not allowed to remove the pile from the soil and screw it in again in the same place.

6. For the installation of concrete piles, specialized equipment will be required. Wells are being built under them.

7. After reaching the solid ground, the pile is deepened into it by at least 100 cm. If necessary, the metal pile is built up. To remove excess foundation, use a grinder, and then equip the strapping with metal structures.

When performing any excavation work, safety precautions must be followed. If the integrity of the quicksand is damaged, the pit is flooded for several seconds. In addition, getting out of this mass is quite difficult. Therefore, when working, be sure to strengthen the walls of the pit with wooden boards, with a large depth of the pit, install a ladder to quickly climb to the top. Carry out all work with at least one, and preferably with two, three people.

Foundation on quicksand video:

Quicksand, as you know, is commonly called a water-saturated soil that can freely spread (float) in the thickness of the earth. In its composition, this formation resembles a thick mixture with a high degree of viscosity, consisting of groundwater, clay and sand. Preparing the foundation on a quicksand with your own hands will require the performer to have certain knowledge and skills in earthworks.

Before making a decision on the future foundation of the building, it is necessary to carefully examine the composition of the soil at the site of the proposed construction. To conduct such surveys, it is best to invite specialists, which will allow you to avoid errors in the calculations. In addition, you can get all the necessary information on the actual composition of the soil from your neighbors in the area (preferably from those who have recently completed building a house).

As for self-exploration of the site, you can explore the soil by drilling a well (using the available tools at your disposal) or after its deep manual opening. At the same time, the presence of a quicksand in the pit will be evidenced by the appearance of a liquid mixture of clay and sand in the mining, as well as a strong creep of its walls and subsidence of individual plots of land. In addition, during a comprehensive survey, you should obtain all the necessary data regarding such characteristics of the site being developed, such as:

• depth of freezing of water-saturated soil;
• groundwater occurrence data;
• the thickness of the quicksand itself (the depth of its location).

Based on this data, you can choose the type of foundation that would meet the basic design requirements. Of all the possible options for self-arranging the foundation on a floating ship, the following types of support structures seem to be realistically feasible:

• strip foundation foundations (with a quicksand depth of not more than 1.5 meters);
• supporting foundations based on reinforced concrete slabs;
• grillage pile foundations.

Using a strip foundation

With a quicksand thickness of less than 1.4 meters, you can use the option of preparing a shallow strip foundation. To implement this project, first of all, you should prepare a trench with a depth of about 0.6-0.7 meters, the bottom of which is covered with a layer of rubble and sand (i.e., a so-called pillow is being prepared). In addition, you will need to dig a drainage ditch located next to the foundation of the future building (at a depth just below the sole of the latter).

To do this, you will need to prepare another trench, laid parallel to the main one. The bottom of the drainage ditch is also covered with a cushion of gravel and sand, on which a layer of geotextile is then laid. Waste pipes are placed on top of the material, which have direct access to a special inspection well, which makes it possible to carry out preventive measures. At the end of the work, the trench with the drainage elements laid in it is covered with a layer of sand and gravel.

The arrangement of the foundation trench begins with the preparation of the internal formwork, for the manufacture of which ordinary boards or ready-made panels are used.

Note!
The open walls of the formwork must be laid with roofing material, which plays the role of waterproofing.

The preparation and pouring of concrete is carried out in accordance with generally accepted rules and regulations specified in the relevant documents.

Preparation of slab and grillage foundations

The advantages of a slab-type foundation include the following distinctive characteristics:

• ability to withstand increased loads;
• no deformations at significant temperature differences;
• possibility of application on wet soils with deep occurrence of quicksand.

It is recommended to use a monolithic slab in the construction of buildings of considerable volume, an example of which is a multi-storey brick house. At the same time, the dimensions and other technological parameters of the monolith should be selected taking into account the individual characteristics of the project being implemented.