Development of a trench with a clamshell installation
The Slurry Wall method is a special technology for constructing a foundation and a fence before digging a pit; it consists in erecting vertical walls underground structures in trenches-slots before the start of rock mining inside the structure. It is used in the construction of urban underground structures (transport tunnels and metro stations, parking lots and garages, multi-tiered underground complexes, etc.), foundations of houses and bridges, retaining walls, anti-seepage curtains. The method is applicable to almost any type of soil. Restriction: flowing and quicksand, dispersed bulk, soils with large voids.
Application area of \u200b\u200bthe "wall in the ground" technology
As with any project, careful planning is the key to success. The beginner, however, must choose more carefully. Planning starts with evaluating the site. A large, flat, open site is ideal, but not generic. Therefore, evaluate the site regarding the layout of the slab and the movement of materials and equipment around the slab.
Once planning is complete, construction can begin on the floor and supports. Locations, heights and dimensions must be checked and verified for correctness. Crane time is costly if modifications must be made when the panel is suspended over the wrong nameplate or support.
The cost
The company "BEST-STROY" LLC works according to the method "Wall in the ground", the cost - from 22,000 rubles per cubic meter. m.
Installation of a wall in the ground
Basic technological operations of the wall device
Trench-slots are developed dry in the case of clayey soils with a low flow rate, to a shallow depth - up to 7 m. In other cases, when driving, they are filled with thixotropic suspensions, which keep the cut walls from collapse. After that, thixotropic 
suspensions are replaced with special materials: concrete, various mixtures, prefabricated elements that form bearing and non-bearing structures in the soil.
There are several ways to form individual panels, each with its own advantages. Typically, these strips are attached to the base plate after the side molds have been inserted, but before the reinforcement is placed. Using plastic supporting chairs instead of steel chairs is recommended to avoid rusting. Next comes the installation of attachments and inserts. Inserts are pre-fabricated ribbed steel sheets that are inserted into the panel to attach it to the base, other panels or roof system, or to attach building accessories after the shell is completed.
The device "wall in the ground" is advisable to use in difficult hydrogeological conditions, with a shallow bed of the water-resistant horizon (there is no need for dewatering, freezing, etc.), in the cramped conditions of existing buildings, during the reconstruction of existing enterprises. In the conditions of large cities, such as Moscow, when the density of buildings is very high, it becomes difficult to fence off the construction pit. The BEST-STROY company satisfies the demand for a technology in which, firstly, the subsidence of the foundation of nearby buildings is prevented, secondly, it becomes possible to locate in close proximity to the existing underground networks, and thirdly, the configuration of the pit can be quite complex - linear or broken outline.
Direct placement of chutes is the most economical method, but pumps and bucket also work. The sequence for lifting the panel should be determined in advance, but it is recommended to consider it immediately before installing the panel. The finish of the panel is limited only by the creativity of the architect and the ability of the contractor. Ordinary sandblasting or open aggregate coatings can be applied immediately after panel installation.
Several proprietary systems allow contractors to insulate panels during construction or post-construction. Starting your home with a slab based foundation instead of a traditional foundation foundation can significantly reduce your environmental impact during construction and can also provide significant financial savings.
The buried wall is effective in the construction of foundations in built-up areas, small underground structures at a considerable depth (usually about 20 m). Technological advantages make it possible to combine the production of basement and basement elements, including multi-storey underground structures.
Foundation Slurry wall
The Slurry Wall technology is available in two versions: bore-cutting and trenching. According to the first, the drill piles are made at a distance less than their diameter, and thus they engage, "cut" each other, eventually forming a solid fence of sufficient strength. The bored pile method provides an opportunity to fencing a construction site, a retaining wall, dewatering or an anti-seepage curtain, but it is not designed for arranging the foundation of a house. But the technology "trench development" is calculated! It provides technological advantages in the construction of multi-storey buildings, the design of which provides for a multi-tiered buried part, underground parking, garage, storage facilities, basement. Foundation The wall in the ground simultaneously serves as the walls of the basement of the building, simplifies construction, eliminates the need to dig a foundation pit, saves time, and reduces costs. Reinforced concrete anti-seepage curtain reliably protects the underground part of the building from groundwater, allows you to reduce the cost of drainage and pumping water from the foundation during the construction process.
By replacing concrete with better, more efficient building materials, you can eliminate many tons of greenhouse gas emissions from your building materials, as well as during further operation at home. Slab-based construction is a somewhat unusual home construction method that replaces the conventional foundation wall and basement with a concrete slab that rests directly on the class. This technique lends itself to most types of terrain, with the exception of highly sloping terrain.
Why build a slab on a level instead of a basement?
To save money and carbon emissions, and have a healthier, more durable home. Typically, the construction of a single family home in Canada begins with a poured concrete support followed by an 8 "thick foundation wall, typically 8 to 10 feet high.
The wall in the ground serves as a fence for the pit and part of the foundation around the perimeter
The bearing capacity of the base of the house must correspond to the weight of the structure being erected plus the weight of the base structure itself. The design takes into account soil conditions, the level of occurrence of the aquifer and bearing layers, the proximity and pressure transmitted by nearby buildings, the presence of communications in the ground under the territory of the construction site. When designing a foundation with a location below 3 meters, the freezing depth indicator is not taken into account. Calculation in progress bearing capacity, calculation of soil pressure, heat engineering calculation.
The basement foundation is designed to be buried four to five feet deep to protect the basement and basement floor from freezing temperatures. Since this creates additional space underground, it is a natural desire to claim that space, and therefore the born is a basement room.
Whether you start with a slab or foundation, if there is no bedding, both will lean on the dirt. Thus, one is not more “stable” than the other, or more susceptible to frost than the other, if properly insulated around the perimeter.
"Wall in the ground": technology
The method is based on the foundation technology based on the development of the trench. Narrow (0.6-1.2 m) and deep (up to 20 m and more) recesses are developed under the protection of a clay solution, which, due to a sufficiently high density, protects the cut from collapse inward.
In the case of a mobile basement, you effectively use a slab, only with a very expensive and poorly insulated wall. Imagine a slab level as a four-sided basement with much cheaper and more efficient walls. Skirt insulation is a very simple and cost effective solution that can be applied to foundations as well, as it will help reduce heat loss by keeping the basement walls at a much higher temperature.
Cost - environmental and financial
In addition to significant savings in construction costs, slab-based will reduce the risk of moisture and water ingress problems, a typical challenge faced by basements. Concrete is very expensive to buy and extremely energy intensive during production. The basement construction process requires 3 costly concrete truck crew visits; pour the leg once, pour the walls again, and pour the basement a third time. For every ton of concrete produced, one ton of greenhouse gases is emitted into the atmosphere.
The technological map of works is developed taking into account the results of engineering and geological surveys. Limitations for the application of the technology are associated with the presence of certain soil conditions: groups of building soils above a third, stained and sandy rocks with the inclusion of boulders over 300 mm in diameter; karsts, coarse soils with voids, quicksand soils, mobile silts, ground aquifers with excessive filtration exceeding the hydrostatic pressure of the protective clay solution.
Health, durability and comfort
After the basement foundation is completed, the decal should be built on top. This is another cost that will be incurred to create the surface on which the living space is built, compared to a slab that is ready to build. Despite how common common basements are, there is a general lack of understanding of the additional challenges associated with building underground. This may mean that in many cases the correct building methods are not followed in accordance with the principles of building science.
Schematically, the technology consists of a sequence of stages:
- arrangement of the foreshaft;
- trench development;
- lowering the reinforcing cages;
- pouring with concrete.
Preparatory stage: removal of all surface and underground communications outside the development area; the site was planned and arranged with reinforced concrete slabs; the territory is fenced; the preparation and cleaning equipment for clay solution was installed and prepared for operation.
Existing example: walls must be able to dry in at least one direction. In cold climates, walls above ground should be designed to dry primarily from the outside. But, since the soil for all purposes and tasks is "water", the walls of the basement must dry inside.
The cost of works when constructing a "wall in the ground" with a clamshell drilling rig like CasagrandeВ125 KRC
This happens for a number of reasons, the first of which is that we are finishing basements too early. Concrete is mostly water, and on the outside of the soil it takes at least 2 years to dry out completely inside. Second, since the National Building Code requires basements to be insulated and new home buyers tend to want a space finished, the cheapest way for developers to do this is to treat them like overhead walls. Thus, basements are usually insulated on the inside, long before unwanted moisture remains, and in the same way that we build above ground, where walls can dry out.
Preliminary stage: surface excavation and foreshaft - hard reinforced concrete structure, limiting the clearance of the working zone and corresponding in width to the dimensions of the future wall. The foreshaft protects against destruction and subsidence of the upper layers of the soil under its own weight and under the weight of grab equipment. The trench is being broken down into grabs.
Why we like slab construction
By sealing moisture-sensitive materials between a damp concrete wall and a polyethylene vapor barrier, we invite mold. Compared to a basement, a building above the ground has the advantage of providing more natural light. It also helps maintain clean cabin air quality as it reduces the chance of mold.
What's more, the slab-based structure can make your living space more comfortable. Thermal mass in an air-conditioned living space has the ability to absorb and store heat, which greatly helps to regulate internal temperatures. Homes with significant thermal mass inside the building envelope are also easier to keep cool in summer.
The rock is excavated under the protection of the mud with a grab or hydraulic cutter. The soil is removed to the surface, removed from the production area, and moved outside the construction site.
Development and concreting of a wall in the ground using technology and equipment from Bauer
Bringing a building project to the point where it is ready to frame the main floor can be done much cheaper with a slab on a level than a basement. With a slab, the same milestone is achieved without having to build an 8-foot concrete wall, and you don't have to build a wooden sub-floor on top.
This insulation can be paid for in the thousands of dollars that would have gone into purchasing concrete for the foundation wall. The floor slabs also easily combine underfloor heating, which offers a very balanced and comfortable environment, converting the concrete mass into one large radiator.
Protection of the mine with a thixotropic hydraulic solution allows excluding the use of pile or sheet piling, for the organization of artificial dewatering. Volumes are decreasing earthworks, and hence labor intensity. Construction time is reduced.
For development, specialized drilling equipment is used, in hard soils - hydraulic cutters, and in soft soils - grabs (two-jaw narrow wide-grip, fixed on a rigid rod), integrated in mass-produced installations as the main or suspended equipment or installed on crawler excavators.
One of the greatest benefits of radiant floor heat is that the farther you get from something that emits heat, the colder it gets. Thus, the heat is concentrated at ground level, where we rather gather in the highest points or houses where we are not. This contributes to an overall cooler temperature without sacrificing comfort.
Reducing environmental impact
Having created a slab house at home, you decided to replace the foundation walls with aboveground walls. In other words, you replace concrete walls a much more affordable and energy efficient wall.
Victims, problems and solutions
To be able to make an informed decision about this type of foundation, there are several precautions and problems that need to be addressed.Trenches are torn off in stages through one by separate sections - grabs, across the grapple width. And they serve bentonite solution in them. In accordance with the technology, that part of the solution that has mixed with the soil due to constant circulation enters the sludge separator, is cleaned of the rock and goes back to the sinkhole.
Then the open area is protected along the edges by removable or retained restraints (in the form of iron beams, piles or pipes) along the entire height. A pre-made reinforcing cage is lowered into it.
Your municipality may need plans that have been approved by an engineer, and some may not be familiar with stove-top houses. Be sure to check with your municipality before starting construction and even before going too far into your building plans.
While we are firmly committed to the slab-based design concept, we recommend that you carefully study your options before moving on with any plans. There are many legal grounds for starting construction with a foundation foundation.
Before concreting, the face is cleaned of sediment, soil particles, sludge mixed with a protective suspension. To do this, it is all removed and a new, cleaned one is uploaded. Concreting by the method of a vertically moving pipe. Vibrating units and hopper buckets or concrete pumps with a concrete paver equipped with a sleeve on a telescopic boom are used. A concrete pipe with a receiving funnel is placed in a trench, 0.3 m before reaching the bottom. The protective solution displaced during the concreting process is pumped out into a storage tank.
The slab in the classroom will require more overhead space, so in order to have the same size of the house, you will need to either line up or up. You may run into height restrictions when you decide to build, which means you might have to build rather than up. This is not always possible, of course, if your site is a city bay, leaving you with two options: a small house or a basement. Despite their disadvantages, basements are often very practical as they provide a significant amount of storage space. Without a basement, everything that was there must go into the rest of the house or the barn. Basements are usually used for mechanical rooms. Keep this in mind during the design phase if you choose a slab, as the mechanical systems must now be placed on the main floor. And don't be stingy with this space - think about everything you might need there: oven, boiler, water heater, air exchanger, water softener, septic pump, sulfur reservoir, central vacuum, etc. Given that you are doing a specific area of \u200b\u200bthe main floor for mechanical systems, it is as good as any to plan some storage and maximize the efficiency of that room.
After the concrete has gained strength, earthwork begins inside the perimeter. The excavation is being developed in layers. If necessary, according to the calculations of the horizontal load on the fence, the walls are strengthened with soil anchors. The design feature of which allows you to leave free space for the excavation for construction work.
Our technique
We use the following installations with an overhead grab bucket:
- BAUER GB-34 hydraulic grab: trench depth up to 60 m, width 0.3-1.2 m (built-in inclinometer, bucket set, hose and centrifugal pump, mixer, silo, slurry meter, concrete pipes)
- MAIT HR130
We use bore-injection ground anchors instead of installing a spacer system, which significantly expands the capabilities of the method.
Order a calculation of the cost of the Wall in the ground
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The method "wall in the ground", or "trench wall" (a special way of performing construction work), is one of the most important achievements of foundation engineering in the 20th century. Nowadays, with the help of this technology, complex construction problems are solved during the construction of underground structures, retaining walls, anti-seepage curtains, deep foundations, etc.
The main link of this progressive technology is the development of deep trenches without fixing the walls under a clay solution.The drilling of such trenches is possible in various and unfavorable engineering-geological and hydrogeological conditions: for example, in the presence of weak clay soils, quicksands, with a high level of groundwater without dewatering, etc. P.
A clay solution is a diluted suspension of bentonite clay, into which some additives are introduced (crushed minerals - barite, hematite, magnesite, etc.). This suspension has high stability and thixotropic properties, i.e. particles of the clay mineral montmorillonite, which is the main component of bentonite clay, do not precipitate, but remain in suspension for an indefinitely long time. The viscosity of the suspension decreases as a result of shaking. The suspension, depending on the concentration of clay and additives (weighting agents), has a relatively high density (1.1-1.3 g / cm3), therefore it exerts significant pressure on the trench walls, which is not perceived by the pore water of the surrounding soil. This pressure perceives the active lateral pressure of the soil, which ensures the stability of the walls of the slot (trench). A similar effect persists in soils with a high filtration capacity, since the pores of such soils are quickly silted up with clay of the solution (clogging phenomenon), the leakage of the solution from the trench stops and the suspension perceives the soil ripping.
A trench in the ground, filled with bentonite suspension, is an impervious curtain (it drastically reduces the inflow of water into construction pits) or a separating structure (the latter plays the same role as a separating sheet pile). However, much more often a trench filled with suspension is only the initial stage of work. It is used to erect a reinforced concrete structure in it (in the future, it will work first as a foundation pit, and then as a foundation structure), performed in a prefabricated or monolithic version.
The technological scheme of the wall installation in the ground (in one of the possible options) is shown in Fig. 9.9. The cut in the ground is made by a grab excavator with a flat bucket, which is suspended from a rigid rod. The width of the slot, depending on the size of the bucket, is set to 0.5-1.5 m; the depth of the wall - up to 100 m. The wall is given any shape in the plan: rectangular, round, in the form of a cross, "chamomile", etc., which is convenient if it is necessary to transfer large concentrated forces to the base.
Figure: 9.9. Stages of work by the "wall in the ground" method
a - excavation of soil from trenches under clay mortar; b - filling trenches with grouting solution; c - installation of panels; 1 - prefabricated panel; 2 - grab; 3 - grouting solution; 4 - clay solution
A free-standing wall when excavated on one side can only have a limited height. Therefore, in necessary cases, two types of fasteners are used: spacer and anchor (ground anchor). The latter type of fastening is of the greatest interest as a very progressive and efficient design. The ground anchor is arranged as follows (Figure 9.10). A horizontal or inclined well is drilled through the reinforced concrete of the trench wall (with or without fastening), a special device is introduced (hammered) into the well - an anchor sealing. A cable or rod is fixed in the seal. A distribution plate is installed on the trench wall, through which the anchor is pulled with a force that ensures the stability of the wall during excavation so that its displacement does not exceed a predetermined value. The length of the anchors is set so that the anchor (the active part of the device) is located outside the collapse prism, and the resistance of the anchor reaches the required value. Typically, the length of the anchor is 6-20 m (the active part is 1-6 m), the diameter of the active part is 0.2-0.4 m, the voltage (controlled by dynamometers or by the amount of cable or rod elongation under tension) - depending on the type of soil 150-200 kN. Ground anchors are placed in rows, in several tiers, which ensures the stability and immobility of walls of any height.
Figure: 9.10. Fastening the wall in the ground with injection-type ground anchors;
1 - collapse prism; 2 - wall in the ground (reinforced concrete); 3 - anchor strand (cable); 4 - rubber packer (seal); 5 - ruff (active part of the anchor); I - termination (active part); II - passive part; III - tension (stopper) device (dotted lines - the depth of soil development in the pit before installing the next anchor)
The “wall in the ground” method is most acceptable when erecting foundations near existing buildings, since it eliminates dynamic impacts on the soil (as when driving piles), provides minimal water inflows into the pit (therefore, it is not required to perform deep water lowering, which is dangerous for the buildings surrounding the pit ) and the stability of the soils of the foundations of the existing foundations is guaranteed, since the wall has sufficient rigidity and strength.
In world and domestic practice, there are numerous examples of the successful application of this method in the construction of massive buildings and underground structures in the immediate vicinity of existing buildings, the operation of which was not interrupted during construction work. Experience has shown that a trench filled with clay mortar remains stable even when it is being developed near the foundations of buildings (in areas near buildings, a wall in the ground is made with grabs 3-5 m long, which guarantees the safety of work). In such conditions, the approximation of new construction to existing buildings is limited only by the size of the equipment used, i.e. a few tens of centimeters.
"Walls in the ground" are classified:
By appointment - load-bearing, enclosing and anti-filtration;
By material - reinforced concrete, concrete, soil-cement, clay, combined;
By the manufacturing method - monolithic, prefabricated, prefabricated-monolithic.
Benefits
The slurry wall method has several advantages over other construction methods:
The possibility of constructing deep pits in the immediate vicinity of existing buildings and structures, which is especially important during construction in cramped conditions, as well as during reconstruction of structures;
Sharply decreases, and in some cases there is no need for a dewatering or drainage device; the volume of earthworks is decreasing;
There is no need for backfilling and, therefore, uneven subsidence of floors and blind areas during their operation are excluded;
It becomes possible to simultaneously carry out work on the construction of aboveground and underground parts buildings, which dramatically reduces the time of their construction;
The noiseless construction method. Measurements show that the noise level of a buried wall is lower than normal traffic noise.
The lowering of the groundwater level is excluded, since the concrete "wall in the ground" protects the structure from water penetration.
