Quicksand, as soil is commonly called water, flows freely in the thickness. In its own way, this is the formation of a thick mixture of a high degree consisting of water, clay, sand. Preparation on quicksand by hand will require the performer to have knowledge in carrying out the work.
When deciding on a future foundation, you need to carefully consider the composition of the soil in the area of the proposed site. To conduct research, it is better to invite specialists who will allow you to make mistakes. In addition, you will be able to obtain the necessary information about the actual composition from the neighbors of the site (preferably those who have recently completed houses).
Diagram of the device of a surface quicksand
concerns an independent area, you can explore it by drilling (using your available means) after opening it manually. This will be evidenced by quicksand in the development of a mixture of clay and sand, and strong sliding of walls and individual sections. In addition, during the complex process, you must provide all the necessary information regarding such a developed area,
If under a layer of soil
Based on this data, you can choose a foundation that meets the basic requirements. Of the possible options for arranging the foundation of the float, the following support structures are realistically presented:
What is the danger on quicksand?
quicksand thickness is 1.4 meters, use the shallow-depth belt option. To implement the project, you will first need to prepare a trench of about 0.6-0.7 at the bottom with a layer of crushed sand (i.e., the so-called In addition, you will need a drainage ditch next to the future building just below the bottom of the latter).
foundation
For this you need to prepare another trench laid by the main one. The bottom of the ditch is also covered with a cushion of sand, which is then covered with a layer of geotextile. material, pipes are placed that have access to the inspection well, making it possible to carry out activities. During the work, the trench is laid with a layer of sand and gravel laid in the drainage elements.
The construction of the foundation begins with internal formwork, the manufacture of which is made from ordinary boards and ready-made panels.
Attention! Open formworks require roofing felt to act as waterproofing.
Preparation for pouring concrete in accordance with generally accepted rules and regulations stipulated in the relevant documents.
Scheme on quicksand
The advantages of this type of foundation include the following characteristics:
Please note: It is necessary that the concrete base is continuous and rods with a diameter of mm are used for strengthening.
The foundation of a quicksand can also be made from so-called piles. The support category includes structures such as screw and reinforced concrete piles. what to pay attention to when arranging them is the correct choice of fixing the sole, which should be below the level of quicksand.
When laying a foundation on quicksand, stop on piles. For more information about this foundation method, see
stroim-gramotno.ru
Imagine: you start digging a hole for household needs, digging a well, or preparing the ground for a foundation. You are standing, although not on solid ground (the ground after all), but on a fairly solid surface... and suddenly you suddenly fall down. It was you who ran into quicksand.
Starting from a certain depth, quicksand can appear anywhere in your area. Until you start digging or do a geological examination, you will never know where it is. The quicksand has the ability to move. Having learned about the presence of quicksand in the ground, people are afraid to build capital. There are known cases when, due to quicksand when installing concrete rings for a well, multi-central structures suddenly shifted and buried the builders...
And sometimes, the owners don’t even realize that their entire land is covered in quicksand, they simply don’t encounter them. It depends on your luck.
Quicksand is a layer of soil saturated with water, measuring from 2 to 10 meters, which is capable of moving underground in a vertical direction. It can be found at a depth of a meter or less.
Quicksand is a sealed object (until you touch it). The smallest particles of soil from which it consists, due to their saturation with water, act as a lubricant along the edges of the quicksand, which is why it moves so easily underground.
To understand the phenomenon, we will give a very simplified comparison with quicksand. Imagine a ball (although in general quicksand is more like an amoeba), covered with a slippery layer on top and located in the thickness of the same, but not slippery balls or other material in which movement is possible. How will it move, what external action will influence it? The answers to these questions will give a rough idea of how quicksand may behave in the ground. And if our conditional quicksand ball is touched with something sharp, then the mass that breaks out of it, which was previously under pressure, will also turn out to be very slippery and will tend upward.
Quicksands are classified as:
The soils in which true quicksand are found are mainly clayey sands, sandy loams, and loams.
Until now, even scientists do not have a clear answer as to why quicksand is formed. It is logical that most of them are detected in places with water-saturated soils. The Moscow region is in a high risk zone in this regard. But even in the desert there are formations similar in action to quicksand. We're talking about scary quicksand.
However, our man basically begins to be interested in the “life” of quicksand exactly from the moment when he needs to go deeper into the ground.
The risk of encountering quicksand arises in cases when you need to:
Quicksand have always been, are and will always be in the soil, and at all times people have dug wells and holes and built strong houses.
Today the easiest way would be to entrust this matter to a team of specialists. Professionals will take on all the risks associated with quicksand, identify the presence of these dangerous objects, bypass them, and give expert advice: where on the site you can dig, to what depth, what buildings are generally permissible here, etc.
If you still decide to work on your own:
It is even more difficult to install a foundation in unstable soil with quicksand. At any moment the earth can move and the walls of the house can crack.
Possible solutions for building a foundation in the ground with quicksand:
There are ways to drain quicksand using professional equipment, but in private construction it is rarely used, because it is too expensive.
Of course, one can consider a site where quicksand are hidden somewhere in the depths as a disaster for the owners. But it is more constructive to realize that this is simply a feature of the soil that must be taken into account before carrying out all the necessary excavation work.
And one last thing. One way or another, having bypassed the quicksand, having adapted to its presence on the site, the owners sometimes completely forget about it. This is not entirely correct. You still need to remember about soil with quicksand.
If we are talking about a well, then during cleaning (and this will definitely be required over the years). There are known cases when a person went down to work at the bottom of a well, and there he began to be sucked in.
When using a house or a swimming pool, you need to be prepared for the fact that the foundation may still crack, and it is better to check it more often in order to correct the problem at an early stage.
taxi-pesok.ru
Often, on land with sandy soils that previously contained a wetland or river, future developers may be in for an unpleasant surprise in the form of quicksand. Usually this is sandy loam or sand, a layer of soil with various impurities and a high level of humidity. Such soils are characterized by fluidity and fragility, and can liquefy under various climatic changes or under significant loads. To build a foundation on quicksand with your own hands, you should take into account many different indicators and factors, conduct a thorough survey of the territory and select the most optimal foundation design.
Before building a foundation on a site, preparatory work should be carried out, the type of soil and the size of sand particles in it should be determined. By fraction, quicksand comes with large, medium and small particles. However, the most dangerous and unpredictable are dust particles, which, when saturated with moisture, become fluid, threatening buildings and structures with loss of load-bearing capacity and strength. The situation is aggravated by the presence of clay in the soil, which reduces the stability of the base of the building and the entire structure.
Before you begin to build a foundation on quicksand, it is necessary to conduct geological research and engineering surveys on your own or with the help of qualified specialists. Data on the actual condition of the soil and its composition can be taken from the nearest neighbors on the site, especially if they have recently built a house. You can independently examine the soil after drilling a well or excavating soil. If there is quicksand in a pit or well, there will be a liquid mixture of soil, clay and sand, sliding of the walls and subsidence of the earth.
If quicksand is discovered during site inspections or excavation work, it is almost impossible to independently determine its thickness and composition of the formation. It is advisable to contact a professional engineering company for more accurate calculations.
When planning to equip the foundation and having decided on the design of the foundation, first of all they dig a trench or foundation pit. After excavation, the groundwater content in the hole should be reduced using drainage systems, and in case of high water levels, pumps. After draining, in order to prevent the soil from getting wet and sliding, a base is quickly made in the form of lean concrete, which will help in the future to avoid problems with soil subsidence during the work. First, a drainage layer is laid from screenings or coarse crushed stone. Concrete mortar is poured on top of the crushed stone and allowed to set for 2-3 days in the warm season.
Before the construction of the foundation begins, it is necessary to lay a layer of waterproofing under the supporting structure with an overlap and its extension to the external walls. By the way, after carrying out the work, you should also carefully insulate the external elements of the base.
It is necessary to select the foundation design before starting work, taking into account the design loads of the entire building frame, floors and roof. In principle, according to experts, if the work is carried out correctly, any supporting elements can be erected.
If the quicksand is shallow in the area and at the same time the groundwater level is high, you can consider the possibility of preparing an embankment foundation. During foundation work and preparation for it, you should purchase only high-quality certified materials that will ensure the reliability and durability of the entire structure.
If you need to build a foundation on quicksand, but you cannot decide on the type of foundation, watch the video about the advantages of a pile foundation.
www.stroitelstvosovety.ru
Quicksand usually means a piece of soil that is absolutely unsuitable for building buildings. Therefore, the arrangement of a foundation on it requires compliance with a number of rules and conditions - in order to guarantee, even in difficult conditions, the necessary rigidity and acceptable stability of the structure of the entire building.
Before we begin to describe the features of the technology for constructing this type of foundation, I will explain that there are two parameters that determine the distance of the quicksand soil. The first is the distance from the quicksand boundary to the zero level, and the second is the distance from stable layers of soil to the beginning of the sand layer. Moreover, both of these parameters are determined during geological surveys that are carried out within the boundaries of the site.
So, if the quicksand lies at a depth not exceeding 3 meters, then when constructing the foundation of the structure, the technology of constructing a shallow strip foundation should be used. If - not exceeding 1 meter (stable soil is located at a depth of 4-5 meters), then - the technology of constructing a pile-type foundation using a monolithic grillage. In cases of significant occurrence of stable soil necessary for construction (more than 6 meters) and a shallow depth of quicksand (less than 1 meter), a monolithic slab is used as a foundation base, which is poured from above the zero level.
podmasterij.ru
The construction of a foundation on quicksand is a complex process, since here it is necessary to take into account the specifics of the deep occurrence of soil layers that are supersaturated with moisture. It is necessary to design construction work in such a way as not to disturb highly unstable formations.
This special type of soil is based on water and fine-grained sand; this buoyant mass (which explains the name) is not suitable for heavy loads. If the foundation is not designed correctly, the house can sag significantly. There are true and false quicksands.
This soil consists of loam, clayey sand, sandy loam, and exhibits high hydrophobic properties. The soil quickly and abundantly absorbs water; the particles are characterized by molecular interactions. Quicksand can be recognized by a specific film that has a minimum degree of purification. To determine the essence of the soil, you can use external signs: “cement laitance” appears at the bottom of the well; when a sample is removed from there, the latter instantly blurs. To accurately verify the presence of such soil on a site, the sample must be examined in the laboratory.
A hole dug in such an area will quickly fill with water, and the liquid will have a reddish tint. As it dries, it forms a dense, viscous mass. Such a floating layer can complicate installation work, since during the construction process soil can penetrate into any recesses. In such conditions it is more difficult to form a closed circuit.
The main component in this case is gravel sand. The formations are not as dangerous as in the previous case, since the composition does not contain strong molecular bonds. The liquid that appears at the bottom is usually light; it evaporates quickly, resulting in the formation of a loose mass.
In such difficult conditions, specialists design strip, slab and pile foundations. Each of the varieties is appropriate in specific situations, which will be discussed below.
If the quicksand is located no deeper than 1.5 m in soil of a slightly heaving type, the optimal solution would be a shallow strip foundation. In the case where the building design includes a full basement, the base is arranged in such a way that it rises above ground level (here additional structures cannot be immersed in the soil).
Such a base is advisable in a damp and heaving area, if the unstable layer is deep enough. The costs of materials and installation work in the case of a slab foundation will be significantly higher compared to a strip foundation. But such a solution is characterized by high stability and impressive operational capabilities.
The second name of the construction technique is floating foundation. During frosts and heaving of the soil, such a foundation can withstand serious loads, since it is able to shift along with the structure without causing damage to the latter.
If the quicksand is close to the surface, the only safe option is to install a pile foundation. This option will be appropriate only if there is a dense, stable layer under the water-saturated layer. The conditions correspond to wet silty sandy loams, which are extremely difficult to drain, so it is easier to install piles.
Advantages of the solution:
Compared to a strip foundation, the cost of a pile foundation is almost half as much.
The construction instructions depend entirely on the type of foundation chosen, so it is worth providing detailed guidance on each option.
After examining the site, drawings of the future structure are drawn up, which indicate the thickness, dimensions of the segments, and features of the fill. The area is cleared of debris and vegetation, leveled, and a pit is laid on it.
To prevent capillary rise of water from below, a horizontal drainage system is introduced. The maximum permissible pit depth is 70 cm, a crushed stone cushion is created at the bottom, and the top is covered with coarse sand, moistening and compacting it.
The height of the formwork must correspond to the future base; it is made of metal, laminated boards or plastic; it is most convenient to use collapsible variations. The cavity is filled with roofing felt or waterproofing film, and reinforcement is performed.
For pouring, high-quality concrete is required; when introducing it, vibrators are used to get rid of air bubbles. The surface is leveled and left to thicken for at least 26 days. The foundation must be covered with film to prevent the destructive effects of the sun and precipitation.
When the concrete has dried, you can begin waterproofing and insulation measures. Next, the pit is filled with sandy soil.
The design drawing is drawn up taking into account the specifics of the site. The thickness and size of the optimal slab, the method and location of its placement are calculated. The working area is cleared, leveled and covered with a 50-centimeter layer of crushed stone. The workpiece is thoroughly compacted and soaked in water. The area is marked using a cord and stakes.
Lay underground sections of sewer and water supply lines. Before pouring the base, all thermal insulation and waterproofing measures are carried out. A bedding consisting of polystyrene foam and insulation is placed on the workpiece, and it is covered with rolled waterproofing.
The formwork is formed from panel boards or boards with a height of at least 50 cm. The material must be durable and able to withstand heavy loads due to the weight of the concrete. The prepared surface is covered with polyethylene so that the joints can be fixed with tape. Thanks to the film, the concrete solution will remain inside the formwork and will not leak out. Such a slab will be movable in case of soil heaving.
Reinforcement is performed using corrugated rods, the diameter of which is in the range of 1.2-1.6 cm. The material is laid in the form of a mesh, and the joint areas are strengthened with wire. The reinforcement is placed on plastic guides and must be completely immersed in the solution.
The formwork is filled with concrete and, after leveling, a vibrator is applied to it. The rule will help straighten the surface. If the weather is dry and warm, the solution will dry within 3-4 weeks; in cold conditions it will take up to 6 weeks. To prevent getting wet, the foundation is covered with polyethylene.
The top layer of approximately 10 cm is removed from the area, markings are created on it in accordance with the previously drawn up drawing. Depending on the type of quicksand, the future weight and dimensions of the building, the optimal number of piles to be introduced is calculated.
Experts suggest using metal or concrete structures; the first option is most often used. Installation of metal piles is simpler, has a lower cost, and their efficiency and reliability are not inferior to concrete ones. Steel piles are installed without the use of special equipment; all manipulations can be completed in a couple of days.
Screw modifications do not require preliminary drilling; during the process of screwing them into the soil, there is no risk of flooding; there is no need to pump out water. All implementation points are indicated in the drawing, special attention is paid to corner areas, areas forming the intersection of walls, and load-bearing structures.
Screwing in steel variations can be done by 2 workers using a special rotary lever. During the process, the evenness of the insertion is constantly monitored. Concrete piles require the use of technology.
After the hard layer is reached, the pile is immersed another 1 meter. The structure can be expanded as needed. To remove excess you will need a grinder. At the final stage, a harness is installed for the introduced piles.
If a water-saturated formation is accidentally damaged, there is a high risk of its breakthrough, in which case flooding of the pit is likely. The essence of quicksand resembles a balloon filled with water - when sealed, the product is not dangerous, but during a rupture the flow cannot be controlled.
To minimize adverse effects, you must follow the recommendations of professionals:
To prevent problems from arising later, it is necessary to carefully examine the area being built. A professional study will help reveal the soil conditions; based on the information received, an economically feasible and safe construction algorithm is selected.
To build the foundation of a house on quicksand, you need to choose the best of three methods:
In the latter case, open pumping of water is organized. If the formation is located at a depth of no more than 600 cm, it is better to use wellpoints; if the level is lower, electric drainage devices will be needed.
Sheet piling walls are capable of blocking the layer of quicksand, they create pressure leading to load containment. The tongue-and-groove board is inserted into the soil up to 10 m; if metal products are used, it can be placed up to 35 m. This method cannot be used if there are dense layers of soil near the quicksand.
Quicksand can be fixed by three methods - freezing, silicatization or cementation. The most effective is silicatization - in this case, liquid glass is pumped into the soil, which helps to increase the strength of the base and eliminate soil mobility. Freezing is extremely unreliable; even after exposure to powerful refrigeration units, the quicksand will soon thaw.
An obligatory step is the creation of a complete drainage system lying below the problem level. Quicksand consists of small particles united by water, drainage helps dry this area, and the soil structure gains strength. During the operation of the building, it is important to periodically audit the system - this is a key safety measure.
If the quicksand is below the soil freezing level, it is permissible to install a strip monolithic base with a shallow backfill; here, a gravel backfill will be a mandatory element. If the quicksand is located below 50 cm from the surface and has insignificant thickness, a pile foundation can be installed (there must be solid soil under the aquifer).
stroypomochnik.ru
In construction practice, the concept of “quicksand” is encountered quite often. Especially when carrying out construction work in large cities. The nature of quicksand has not been fully studied; there are many hypotheses of their origin. There is also an assumption that the cause of the formation of quicksand is sewage leakage from sewer systems. But quicksand are also found in places where there are no traces of human activity.
Quicksand are some varieties of sandy loam and other fine-grained soils, liquefied by water, which under certain conditions become so mobile that they flow like liquid. I would like to note that quicksand and underground rivers are completely different things. If an underground river, as a rule, has a stable state, then the behavior of quicksand can only be predicted by conducting a sufficiently large volume of geological surveys. In its manifestation, quicksand is a volume sealed by nature itself, inside of which water-saturated fine sand is under pressure of several atmospheres. As shown by engineering geophysical studies performed using the method of spectral seismic profiling (SSP), quicksand in the ground are drawn as closed halos.
Don't touch it, otherwise...
Due to their mobility and low load-bearing capacity, quicksand are unsuitable for use as foundations. At the same time, a house can stand on quicksand and not experience any inconvenience, because quicksand can withstand very high pressure. But only under one condition - maintaining tightness. If opportunities arise for the quicksand to move (for example, a dug trench or pit), then the soil may simply “float away” from under the house. In this case, the foundation completely or partially loses its support, as a result of which those parts of the building that are located directly above the quicksand begin to sink into the ground. Then microdisturbance of the soil develops, and quicksand also begins to emerge through it.
The first manifestation of the beginning of the process is the flooding of basements. Sometimes it seems that the soil is rising there, but this is not so - in fact, the house is sinking. The rate of settlement depends on the work taking place in the neighborhood, on the condition of the soil, and on the degree of violation of hydrological conditions. The next stage is the development of cracks in the supporting structures of the house. So, as a result of the release of quicksand from under the southern section of house No. 8 on the street. Dvinskaya in St. Petersburg, this section lost support and fell off.
As a result of the collapse (in July 2002), 4 people died. In the process of carrying out work aimed at expanding the embankment of the Obvodny Canal in St. Petersburg, the contents of the quicksand lying there began to flow directly into the canal. House No. 48, located more than 50 m from the canal, immediately after the start of driving the sheet piling in its middle part, began to sharply sink into the ground and collapse. In a similar way, houses on Kashirskoe Highway in Moscow collapsed after they began to make a foundation pit for an underground garage at some distance from them. And as a result of the start of construction of a building in the park named after. Sakharov (St. Petersburg) was the slope of the dotted house located next to the construction site.
Another example is the Muruzi house on Liteiny Prospekt in St. Petersburg, where in 2006 there was a movement of soil under the foundation due to construction work on a neighboring site. The situation developed in exactly the same way during the construction of the Corinthia Nevsky Palace hotel (Nevsky, 57): after the neighboring buildings 55 and 59 burst at the seams, they had to be hastily resettled and demolished.
An insidious feature of quicksand is that during construction work and under the influence of an already functioning structure, its upper boundary rises, often coming very close to the surface. Thus, the slightest penetration into the ground, for example when repairing communications (which were still outside the quicksand when laid), can cause the most undesirable consequences.
We have built and will continue to build
Even in ancient times, builders encountered floating sands saturated with water. And when the need arose to erect stone buildings, they seriously thought about taming the quicksand. In St. Petersburg, which in the fullest sense of these words was built on a swamp, houses were installed on powerful wooden rafts, which served to evenly distribute the load. The tree did not rot due to lack of oxygen.
As time passed, construction projects became larger in scale, and methods of dealing with quicksand became more effective. Metro builders especially often had to use them in practice. When digging tunnels and mine workings, protective measures such as special shields, caissons and freezing were traditionally used.
The last method became the most popular, but it did not always justify itself. Confirmation of this is the erosion in the St. Petersburg metro between the Lesnaya and Ploshchad Muzhestva stations. The prerequisite for the accident was the accelerated construction of a deep stage for the 25th Party Congress, which was supposed to pass through aquiferous sands. To quickly pass through the quicksand, the technology of freezing the soil with expensive cryogenic equipment was used. In 1974, water rushed into the tunnel, which was still under construction. A hole 400 by 200 m and 3 m deep appeared on the surface. On Polytechnicheskaya Street. The asphalt heaved up, tram rails burst, several buildings tilted dangerously, cracks appeared, and the administrative building of the Red October plant was destroyed. Then the soil was frozen, but in 1995 traffic on the site had to be closed for 9 years - until new bypass tunnels were put into operation.
However, there were also successful examples of freezing quicksand. The experience of constructing a high-rise building of the Ministry of Railways on the Red Gate in Moscow can be considered truly unprecedented. When conducting soil reconnaissance, it turned out that part of the future pit is occupied by quicksand, and part by clay. Accordingly, the edge of the foundation of the high-rise part should have risen during the freezing process.
And the opposite edge will settle under the influence of the weight of steel and concrete structures. After carrying out control calculations, the designers decided to install the building with a deviation from the vertical so that after the ground thaws it will return to its normal position. At the same time, each tier had its own deviations from the vertical. As a result, after the foundation settled, the frame got rid of the initial tilt, receiving only a slight tilt in the opposite direction.
The Moscow State University building also stands on quicksand. During its construction, powerful freezing units located under the foundation kept the quicksand in a stable condition. In addition, the building was erected on a fundamentally new box-shaped foundation, which “adapts” to the behavior of the soil: it lowers or rises depending on where the quicksand break through. There are direct savings here: there is no need to fill a giant pit with concrete, as the Americans did when building their skyscrapers.
However, unfortunately, there are many examples of loss of control over quicksand. In St. Petersburg alone there are a dozen large scandalous objects. A pit near the Moskovsky railway station, on the site of which a shopping and entertainment complex is planned to be built by May 2010, the second stage of the Mariinsky Theater, houses on Nevsky Prospect, Kolokolnaya Street...
In general, according to experts, St. Petersburg needs a “Strengthening the Foundations” program, that is, weak soils, and one as large-scale as the façade restoration program.
Moscow floating
But it’s not only St. Petersburg that faces the problem of quicksand. Increasingly, alarming voices began to be heard in the press, fearing that the capital would soon begin to slowly go underground. Experts assess areas at the southern end of Gogolevsky Boulevard as ready to collapse into underground voids, call quicksand near New Arbat and Bolshaya Dmitrovka fraught with serious accidents, and point to the risk of horizontal ruptures in Filevsky Park, around which active development is taking place. The popular website Apartment.Ru provides the public with a list of potentially dangerous Moscow areas where it is undesirable to buy housing.
“Quicksand” is a well-known concept for Muscovites. Back in the 60s, craters and sinkholes began to appear on Khoroshevskoye Highway, which immediately fell into several new buildings. The voids under this area are a consequence of the constant draining of underground reservoirs. There is very interesting information that the total number of wells penetrating Moscow throughout the entire territory can reach 900 thousand. It should be borne in mind that the Moscow River, passing through the city, conducts at least a third of its waters underground. Naturally, they all accumulate in existing underground reservoirs, karst and artificial, ending up in Pleistocene sands. And this is a good condition for the formation of quicksand.
The emergency of 2001, when a house on Malaya Dmitrovka collapsed during the installation of a sewer, is fresh in the memory of Muscovites. On Aviatsionnaya Street (north-west of Moscow) on the banks of the Moscow River, construction of the Scarlet Sails residential complex, more than 190 m high, began back in the 90s. The powerful concrete foundation of the facility blocked the natural paths of groundwater that filled the Stroginskaya floodplain. It is unknown what the consequences of this construction will be.
Treatment or prevention?
Few residents of Ulyanovsky Prospekt in Krasnoyarsk know that their neighborhood is located on quicksand, which at one time (almost 20 years ago) raised serious concerns about the reliability of the buildings. Currently, the foundations of the houses are strengthened, and the quicksand does not pose any danger. The situation in Moscow Cheryomushki developed according to a similar scenario. Today, there are enough techniques that allow you to choose your own strategy for dealing with quicksand for each specific case. First of all, it is necessary to remember that quicksand can be both true and false (according to the classification of the Soviet scientist A.F. Lebedev). Thus, quicksand that has colloidal particles less than 0.001 mm in size, which essentially act as a lubricant, is called true, and quicksand, the properties of which appear only under significant hydrodynamic pressure of the water filtering through it, is called false. True quicksand undergoes severe heaving when freezing, weakly filters water, and when dried it becomes cohesive; microorganisms play a large role in its formation. Since true quicksands do not give up water well, when draining them, vacuuming and electric drainage are used; To drain false quicksand, wellpoints and tube wells are used.
To combat quicksand during the construction of large objects, the “wall in soil” method is popular today. It will be used in the construction of the second stage of the Mariinsky Theater in St. Petersburg. To successfully implement the long-term project, builders will have to drill 2,278 wells on the site and cement 2,190 of them. This will allow you to support both the pit itself and the buildings around the construction site.
The most important thing is not to forget that while in some places it is possible to build hundred-story buildings, in others even the construction of nine-story buildings is already becoming a dangerous undertaking. The success of any enterprise lies in its careful preparation. Therefore, before starting construction, it is necessary to conduct a competent geological survey of the site using the SSP method. Since quicksand are controlled by zones of tectonic disturbances, they should be mapped. The effectiveness of such a forecast of the impact of construction work on already built houses has been tested many times. So, if a zone of tectonic disturbances passes under the house, then you can be sure that construction work in the continuation of this zone will cause the release of quicksand.
fsr-stroy.ru
Every person, sooner or later, thinks about purchasing his own corner. First of all, when choosing, buyers, of course, look at their wallet. And only after that they are able to make a choice of what their corner will be.
The choice most often is between a house and an apartment; some have dreamed of their own home with a large garden or vegetable garden since childhood, and others will leave their preferences to an apartment in a high-rise building. In apartments everything is simple, you buy something ready-made and all you have to do is make repairs. When buying a house, there is a choice between: purchasing a ready-made house with renovations, where you can simply move in immediately after you have legally purchased it. But when it comes to buying land to build your home, you already have to do everything yourself, from an empty plot of land starting with the foundation, with your own strength and wallet. Of course, the construction of any house, no matter what it will be, even a high-rise building in which apartments are sold, begins with laying the foundation. This article will describe the foundation, but their variety is quite large. The modern world is developing, improving itself and, of course, everything that surrounds it, and the most important thing for a person is the place where he lives. And this is the main place in a person’s life, starting from the foundation.
This is exactly what this article will talk about, namely the foundation on quicksand.
To begin with, we should probably say briefly about what the foundation actually is. The foundation is a special type of structure; it is rather worth noting that it is load-bearing. This structure should be the strongest of all buildings, it is the one that can withstand all the loads built above, therefore it should be the most durable and it is on it that any construction company focuses the most attention. Yes, you can save money on wallpaper and furniture, but it is necessary that they stand and are glued not on ruins, but stand for a long time and serve “faithfully.” I think you have already understood that the foundation has been and will always be the most important part of any structure and absolutely any building. Since our article will be about a specific type of foundation, namely a foundation on quicksand, it’s worth saying a few words about it. This is the same ordinary foundation, but with its own peculiarity. Construction on the ground, but not everything is so simple, it has the property of fluidity. It is built on special plots of land that have a special shape, be it sand or loose earth in mountain roads. This type of foundation is most often used in recreation centers, in mountainous areas and, of course, in resort areas.
As with any other type of foundation, it also has its own characteristics and variety. And their variety depends solely on where exactly the construction will be done.
A shallow, strip foundation is the shortest type, designed for soil. It is located at the level of soil freezing.
Pile foundation - small layer thickness 0.5 - 1 meter. Passes through weak soil and installs on hard areas.
Slab foundation - if dense areas of soil are located at a depth of about a meter, and floating soil is about 1 -1.5 meters.
The choice of foundation depends only on your area and the depth of your floating foundation. And accordingly, how much your soil changes, how much it sinks and whether it has mobility.
To determine this, geological studies are being carried out. A small, wider hole is dug out, but at the same time as deep as your soil allows. And within a short time, changes are examined and changes in your soil are checked, if, of course, there are any.
After which you can already draw conclusions about what the depth is, and therefore what the view is. All studies are carried out within a month, and if the soil is not capable of large changes, then this can be determined in a matter of days and literally within a week it will be clear what you need.
You can also do this yourself, without calling any special services and without contacting any construction organizations. You just need to drill a well, and you will find out at what depth the quicksand is located and whether it exists at all. But in order to find out at what depth the dense soil is located, you will have to make a lot of effort. You need to find out the dense content, and for this you need to dig a hole through the floating layer, which is very difficult and after that, only you can take an ordinary stick or a long and thin material of something, on which a layer of dirt will be visible. And lower it down as deeply as possible until you feel that further immersion is impossible. This is how you can determine it yourself.
Of course, this is not a city on the water “Venice” and not a site of St. Petersburg” to build on completely liquid sites. In order to make your site durable and reliable, because no one wants their house or building to fall apart without lasting even a year, but to serve for a long time! That's why there are ways to combat the unwanted liquid flowing under your feet.
Methods for dealing with the layer:
The most important and fairly simple method is directly – the “artificial method of drying.” But this is far from the only way. To retain the floating mass, sheet pile walls are built, which prevent movement and do not disturb your site. A scientific way to fix the floating composition of the soil using additional physical properties.
The very first method is artificial, that is, the most ordinary pumping of water, so that the soil has a dense base, and it is favorable for further work and construction of buildings. A large pump is installed and, like an ordinary pump, it simply pumps out water from the ground.
The second method was described as: erecting walls to keep out the floating mass. These are small constructions of compaction walls to prevent water from getting into the soil on which the foundation will be built.
Also on this list was the scientific method. This is, using any means, to compact the layers of soil among themselves; the most common way of this method is the evaporation of liquids in the soil. From these liquid layers, special means cause the liquids to evaporate and, of course, the liquid layers disappear.
Of course, these methods can even be combined in one, that is, you can use all methods at once. On soil that is in a liquid state, walls are placed up to the dense base of the soil, after which we move on to the next method, all the moisture between these walls is destroyed using a pump. After which, special means are used that, with the help of their elements, evaporate all remaining moisture.
The main thing, of course, is the soil, and it is this that is divided into types. And this is exactly what you need to pay attention to. Swimming water is characterized by special species, namely:
The first, “true origin”, is hydrophobic in nature. Unfortunately, this soil absorbs water and any moisture that enters. Which causes great inconvenience.
And most often, such soil is sent to the laboratory in order to find out whether it is really possible to erect a structure or building on it and what is the maximum weight it can withstand.
Second, the so-called “false quicksand” are not as dangerous as “true” ones; their composition is much stronger than the first option, they are able to withstand heavier weight and not drown your building with walls. The water at the bottom of the quicksand is light and easily evaporates from the soil when it dries and forms a mass with a slightly loose structure.
In order to find out what kind of soil you have and what work needs to be done with it, the surest way is to take a piece of your soil to the laboratory.
In this case, the foundation is placed on small elevations, a high-quality drainage system is installed, most often built in a snake pattern, to hold large loads. The width of the tape is most often made with a margin, the load on the kidney increases, which means the structure will stand much longer and stronger.
This type of foundation stands on so-called “beams”, that is, on elevations. Moreover, these elevations should be supported not on floating trains, but on reinforced soils. To prevent the foundation from floating down, sooner or later it will still sink to a dense area. The material is most often screw piles or reinforced concrete.
If you have to build an object that is heavy in structure, then the best foundation is from a monolithic slab. Let's just say you want a strong house made of heavy brick, or there are plans to build or complete more serious structures. The use of thick, wide and durable slabs, the use of reinforcement, as a rule, a section of 12 mm in diameter is used.
It is worth saying that installing a monolithic slab involves digging a foundation pit, therefore this type is most often suitable for cases where quicksand lie to a considerable depth. A depth of less than one meter requires a number of additional measures to organize the drainage system.
To summarize, we can say that the whole choice lies solely on what your soil is like. To do this, you should submit it for examination to a laboratory, where they will find out the composition of your soil, whether it is “true” or “false.” As for choosing which type of foundation to install afloat, of course, for a more durable structure, it is worth making a foundation from a monolithic slab. It is the most durable and will last much longer, and taking into account experience, this particular design is able to withstand changes in the soil.
Also, you should not save on this, but it is better to come to specialists. After all, who else but they will be able to recognize all the difficulties and features of your soil, making it more durable, your structure will hold much stronger, and even if you need to demolish the walls, your foundation must remain so that you can continue to build something .
Quicksand, as is known, is the name given to soil saturated with water, capable of freely spreading (“swimming”) 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 a foundation on such soil will require the contractor to have certain knowledge and skills in carrying out excavation work.
Before making a decision on the future foundation of the structure, it is necessary to carefully examine the composition of the soil at the site of the proposed construction. To carry out such research, it is best to invite specialists, which will allow you to avoid errors in calculations. In addition, you can get all the necessary information on the actual composition of the soil from your neighbors on the site (preferably from those who have recently completed construction of a house).
As for independent exploration of the site, you can explore the soil by drilling a well (using the means at your disposal) or after manually opening it in depth. In this case, the presence of quicksand in the pit will be indicated by the appearance of a liquid mixture of clay and sand in the excavation, as well as a strong sliding of its walls and subsidence of individual sections of the earth. In addition, during a comprehensive survey you should obtain all the necessary data regarding such characteristics of the site being developed, such as:
Based on this data, you can choose the type of foundation that would meet the basic design requirements. Of all the possible options for independent arrangement, the following types of support structures seem realistically feasible:
If the thickness of the quicksand is less than 1.4 meters, you can use the option of preparing a shallow strip base. To implement this project, first of all, you should prepare a trench about 0.6-0.7 meters deep, the bottom of which is covered with a layer of crushed stone and sand (i.e., the so-called “cushion” is prepared). In addition, you will need to dig a drainage ditch located next to the future building (at a depth just below the base 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 bed of gravel and sand, on which a layer of geotextile is then laid. Sewage pipes are placed on top of the material, with 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 construction of a foundation trench begins with the preparation of internal formwork, for the manufacture of which ordinary boards or ready-made panels are used.
The open walls of the formwork must be lined with roofing felt, which plays the role of waterproofing.
Preparation and pouring of concrete is carried out in accordance with generally accepted rules and regulations stipulated in the relevant documents.
The advantages of slab-type foundations include the following distinctive characteristics:
It is recommended to use a monolithic slab in the construction of large buildings, an example of which is a multi-story brick house. In this case, the dimensions and other technological parameters of the monolith must be selected taking into account the individual characteristics of the project being implemented.
It is necessary that the concrete base is poured continuously, and reinforcing bars with a diameter of 13-15 mm are used to strengthen it.
The foundation can also be prepared using so-called grillage piles. This category of supporting products includes such well-known structures as modern screw and driven reinforced concrete piles. The main thing you need to pay attention to when arranging them is the correct choice of the location for fixing the base of the structure, which should be located below the level of the soil itself, saturated with water.
You can opt for screw piles. For more information about this device method, see below:
Many of our clients ask, what is quicksand? Some people think that they are being deceived and frightened by possible destruction, that the 8 cubic meters remaining in the well after cleaning. sand, nothing more than our incompletely fulfilled obligation. But let's figure it out.
Quicksand in the well- This water-saturated soil As a rule, these are sandy or sandy loam soils that can spread and liquefy.
Quicksands can be true or false.
True quicksand They consist of sandy loam and silty sand, saturated with water, and also contain clay and colloidal mixtures with a particle size of less than 0.001 mm.
They play the role of a lubricant between large soil particles, have hydrophilic properties and weakly release water. True quicksand is subject to severe heaving when frozen, and when dried it acquires coherence and plasticity; microorganisms play an important role in its formation. The nature of quicksand is currently unknown. Some scientists have suggested that the cause of the appearance of quicksand is sewage leakage from sewer systems. But such a statement is contradicted by the fact that quicksand are found in places where there are no traces of human activity.
False quicksand- This is finely porous sand saturated with water. Since the formation is located at depth, the water in the quicksand experiences pressure greater than atmospheric pressure. When the formation is opened, water under pressure enters the mine and carries sand with it. The pressure and power of the quicksand can be different, which greatly affects the performance of any work. With the technologies available today and the accumulated experience, it is possible to pass weakly powerful quicksand with one or two well rings.
More powerful quicksand pose a threat not only to wells, but also to workers. Metro builders periodically encounter such a serious enemy as quicksand. Even with advanced technologies, solid financial capabilities and enormous resources, it is not always possible to cope with the assigned tasks. The fight against this natural phenomenon has been going on for decades. The quicksand is filled with special drilling fluids, sometimes liquid nitrogen is used, but sooner or later the quicksand still reminds itself of itself.
In the Moscow region, most of the wells are located on quicksand, many of them are very successful, since the water flow in such layers is good, better than in clayey ones. It is quite possible to install an autonomous, home water supply with low consumption. The downside of a well on quicksand is that the bottom rises, it floats with sand, and there is a small debit. Such a well is more subject to seasonal fluctuations than a well located on clay. It has to be repaired and cleaned more often.
To the bottom It is recommended to lay a wooden board, and fill it with pebbles on top, thereby creating resistance to bottom movement. It is not uncommon that after digging, 3 rings of water are collected, and after a year there are 2.5 rings of sand and only 0.5 rings of water. The wood panel in this case performs a reinforcing function. It is also not recommended to pump out the water completely; it is necessary to leave at least 50 cm of water column in order to maintain dynamic balance in the system.
Returning to the beginning of the article, I would like to note that when located on quicksand, you should not require workers to remove sand in the amount that the owner requires for construction; there is an amount possible for removal.
If sand is removed excessively, the shaft ruptures, forming huge spaces between the rings, subsidence of the entire shaft is possible, as well as horizontal displacement of the rings, the formation of failures on the surface with a radius of up to 5-6 m from the well, in this case neighboring buildings may also suffer.
When working with quicksand, you must be extremely careful, observe all safety measures, fulfill all technological requirements in combination with the experience that only professionals have.
A fairly common case: a person contacts our company asking for help. The day before, to clean the well, he hired workers from neighboring countries, without specific skills. They carefully removed all the sand from the bottom, and the next day there was twice as much sand in the well. And no one knew what to do about it.
One can only envy the luck of these prospectors; not everyone is so lucky.
Prices Contacts The ability of sands in a water-saturated state to float, liquefy, suck in heavy objects, and spread has been known to builders since time immemorial. Quicksand can be rocks of various mechanical compositions, ranging from gravel and pebble sands to loams. Thus, the mechanical composition of the rock is not a decisive factor in the creation of its quicksand state. There is also no definite opinion regarding the characteristic mineralogical composition of quicksand. It is believed that they are characterized by an admixture of mica leaves and chlorite. However, mica sands are no more often quicksand than other types of sands.Different authors characterize quicksand differently. This is explained by the fact that rocks of different nature can be in a quicksand state, and therefore the manifestation of their quicksand properties will proceed differently. In the overwhelming majority of cases, quicksand properties manifest themselves in very fine sands, more or less silty and silty, and in general in non-cohesive rocks that do not have plasticity. In some cases, it is noted that quicksand sand, after drying, loses its quicksand properties. In other cases, dried quicksand, after its secondary saturation with water, becomes quicksand again.
Walls a pit dug in the quicksand soon after the passages begin to collapse. Blocks of sand fall out of them, which spreads along the bottom of the pit; the surface of the melted mass acquires a slope of up to 3-4°.
The movement of quicksand in the walls of pits, as well as in the base of hydraulic structures built on quicksand sand deposits at the bottom of a lake or sea, usually occurs suddenly. With such phenomena, huge masses of sand sometimes begin to move.
From the experience gained in relation to breakthroughs of quicksand into underground workings, swimming of pits, driving piles, liquefaction of sand underfoot in the face and other phenomena associated with quicksand, A. F. Lebedev gives a list of the following conclusions about the observations made on quicksand:
Thus, from what has been said it follows that the quicksand state is not a specific state, always characteristic of any type of rock, but appears or is created under certain hydrodynamic conditions. For some rocks, such conditions are difficult to create at large gradients, for others it is easier, and in “true quicksand” the movement occurs at negligible gradients.
In increasing the floating ability of sands the role of clay particles is that the latter become suspended more easily than others; due to this, the volumetric weight of the liquid phase increases, and with this the suspended water pressure increases, reducing internal friction between sand particles. Taking into account the influence of hydrodynamic pressure on the stability of loose rocks, we can derive the concept of a critical filtration gradient.
Based on descriptions of quicksand phenomena and experiments, the following provisions can be accepted:
The study of rock suffusion resources (mechanical and technical) can serve in some cases to identify the possibility of a rock acquiring quicksand ability due to the removal of small components. Since the ease of transition to the quicksand state is facilitated by the difficulty of water loss, the impurities that impart this property to the rock must be some kind of hydrophilic colloids adsorbed by the surface of the rock particles.
As an indication of the presence of resources in the sand that facilitate its transition to a quicksand state, it is desirable to have a simple determination of any physical property directly related to the hydrophilicity of the colloids in the rock, such as water content, the upper limit of plasticity and the amount of swelling.
Thus, to evaluate the ability of sand to transition to a quicksand state The following characteristics can be used: natural porosity, water saturation, granulometric composition. To identify the properties of true quicksand, we can recommend determining swelling and yield strength. Since colloids of true quicksands irreversibly collapse upon drying, all determinations should be carried out on samples that have retained natural moisture, and the characteristics should be reduced to the weight of the dry mass, taking into account natural moisture.
Signs indicating the tendency of the rock to pass into a quicksand state are: high porosity (43-45%) and the mechanical composition of the two dominant fractions in the rock, which differ sharply in particle diameter, this facilitates the possibility of suffusion with a low content of the finest of these fractions ( 2-4%) or with a higher content of fine fractions of other diameters, but with the hydrophilicity of their components.
The ability of many sands that have reached a quicksand state to regain strength after stopping movement is used by builders when driving piles. Driving is carried out with frequent blows of low force, the pile easily enters the sand. The sand around the pile does not swell, and sometimes, on the contrary, even sinks. A short time after driving, the pile acquires a very high load-bearing capacity. This phenomenon is explained by the ability of quicksand to form thixotropic structures. Impacts, shaking and vibration destroy the thixotropic structure and the sand “floats”. After some time, in a calm state, the structure is restored, and with it the strength of the sand, which it had in natural conditions.
It is known that thixotropy phenomena are characteristic of colloids. Therefore, the manifestation of thixotropy in quicksand should be attributed to the presence of hydrophilic colloids in them.
When drilling in aquiferous sands, especially with the use of a bailer, sand is often supplied from the bottom into the well. However, not always when a “plug” forms in a well drilled in sand, these sands should be considered quicksand. Under the influence of the difference in hydrostatic pressure created as a result of the work of the bailer in the well and outside it, filtration occurs through the sand at the bottom of the well with a significant gradient of pressure drop. This gradient may turn out to be greater than critical for a rock that is generally not inclined to easily transition to a quicksand state in the bottom and walls of a pit.
Thus, assessing the ability of sand to transform into a quicksand requires not only studying the composition and properties of sand in the laboratory, but also studying hydrogeological conditions and predicting their changes at different times during construction work.
The main techniques for overcoming the difficulties created by quicksand during construction are freezing, chemical fixation and drainage. All these methods were successfully used in the construction of high-rise buildings and the metro in Moscow.
Any rock can be frozen, and chemical fixation and drying is possible only if the rock yield is sufficient. Thus, silicatization is possible in sands with a filtration coefficient of 2 to 80 m/day, that is, in medium-grained, clean fine-grained and clayey sands.
Good results with drainage of quicksand allows the use of wellpoints, reducing the cost and speeding up the construction of a water reduction system with frequent placement of wells.
One of the difficult situations for constructing a building is the presence of quicksand in the soil - a mixture of soil particles and water. Quicksand, as a rule, is localized at a certain depth and, if not damaged, is quite stable. However, when trying to build a buried foundation, quicksand can cause a lot of trouble for builders.
How to build a foundation on quicksand? There are several methods, and their choice depends on the location and depth of the unstable soil layer. Therefore, before choosing any method, you must order a geological survey of the building site. During the study it is necessary to determine:
You can fight quicksand in only one case - if it is possible to arrange a drainage system below the level of its occurrence. Quicksand is a suspension of small dusty particles of sand with admixtures of clay in water and has a semi-liquid consistency with high viscosity. High-quality drainage with water removal can dry up quicksand and prevent its further occurrence. At the same time, during the operation of the building, it will be necessary to regularly inspect the drainage system.
The quicksand itself is not dangerous if its integrity is not damaged. Therefore, if it is not possible to drain the quicksand, it is necessary to choose a method of constructing the foundation that will avoid contact of the foundation with the quicksand, or will reduce this contact to a minimum.
If, as a result of geological studies of the soil, it was found that the quicksand is located at a significant depth, below the freezing depth of the soil, for a private house you can choose a monolithic shallow strip foundation with gravel backfill, or, if the size and weight of the buildings are significant, a slab foundation on gravel-sand preparation.
If the quicksand is located at a depth of no more than 0.5 meters and its thickness is insignificant, and there are hard and stable soils underneath it, then it is better to opt for a pile foundation with a concrete grillage or using screw piles. The piles are buried into hard layers of soil by at least 1 meter, and a thickening is made at the base to prevent the piles from being pushed out by frost heaving forces.
Such a foundation is made when quicksand lies at a depth of at least 1.5 meters on slightly heaving soils. If it is necessary to build a basement, it is equipped by raising the base above the ground, without deepening the underground part of the foundation.
Used in the case of deep-lying quicksand on heaving and wet soils. called floating - its design allows it to withstand a significant load of the building, and during frost heaving and soil movement, the foundation moves along with the entire building, without deformation.
Such a foundation is made if the quicksand is located at a close distance to the soil surface, but its depth is small, and below there are solid, stable layers of soil. This situation is typical for wet silty sandy loams, when groundwater is shallow. They feed the quicksand, and drainage turns out to be an insufficient measure to drain the soil. Therefore, the only way to create a stable and reliable foundation is to bury the piles to the depth of solid soil.
Metal piles are screwed into solid ground and continued to be buried at least a meter. If necessary, they are increased. Excess steel piles are cut off with a grinder, and strapping is attached on top: from metal structures - for welding, from wooden beams - using special heads.
During any excavation work in an area with quicksand, it is necessary to take measures against the breakthrough of quicksand. If its integrity is damaged, flooding of the pit can occur in a matter of seconds, and getting out of the viscous mass is very difficult.
Therefore, when working it is necessary:
