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Soil-Cement Piles (DSM Technique)

Technique of deep soil mixing (Deep Soil Mixing - DSM), is offered for the first time in Japan in the early fifties of the 20th century, and in the USSR in the early sixties, and is becoming more and more common. The method of the wet mixing of soil (wet mixing methods - WMS) is most widely applied as the most universal and suitable for all types of soil . 

ABI 14-17 drilling rig

Method

  • The technology of deep soil mixing consists in manufacture the soil-concrete of columns by means of the special boring an mixing tool consisting of the hollow rod and a special working unit. In the course of drilling a small and agitation of soil to water cement mortar or other chemical reagents (lime, ashes, slag, bentonite, etc.) occurs.. 
  • A main objective of process of mixing is uniform dispersion of binding elements in soil for the purpose of fast and productive receiving chemical response of hydration.  
  • The method of wet soil mixing allows to set on a place bored piles (soil-concrete columns) with a diameter from 400 mm to 1200 mm (is defined by diameter of the tool) and with a maximum length of 26 m. This method is alternative option jet grouting. 
  • Distinguish methods of soil-cement pile construction: on the first filling of cement suspension is carried out in the course of dipping of the tool to a project mark (forward stroke) or in the course of extraction of the tool (return motion), and on the second – as in case of direct, and return motion of the tool. The diagram of the device, composition and quantity of the given compound is selected depending on the required parameters of a tsementogrunt, providing thus necessary strengthening characteristics. The quantity of the begun to rock cement compound is assigned at the rate on one running meter of a column. Strengthening characteristics are defined by the volume of the given suspension, soil conditions and a consistence of the received compound. For achievement of the best results of multiplexing soil-concrete columns, process of agitation repeats several times. Uncreased density of a soil-concrete it is reached by adding in a compound of a betonit. 
  • Parameters of DSM technology are controlled throught the entire period of manufacture, and also after its execution. In case of works fix the column trunk length, speed of rotation of the adder, speed of dipping of the adder and quantity of the begun to rock cement compound. Durability of soil -soncreteis subject to normal tests on standard cubes.

Drilling tool, 800mm diameter.

 

Technological Sequence of Operations

As per figure the main operations are:

1. Layout of the mixing tool over a drilling place. 
2. Dipping of the mixing tool in soil with rotating speed of the auger 20-80 RPM. Drilling happens without percussions to simultaneous submission of a cement compound from the so-called monitor which is on the end of the tube. 
3. In process of dipping of the mixing tool on the required depth making small and agitation of soil with given under pressure of 2-10 atm is carried out. n with In/C from 0,5 to 1,2. After achievement of a project mark of the lower end, there comes the phase of formation of columns of DSM.
4. In the course of extraction of the tool from a slit the received compound of soil and suspension mixes up repeatedly and is condensed. 
5. The ready pile received by method of wet mixing of soil it is necessary to wait time for its hardening now

При необходимости для армирования грунтоцементных колонн используют двутавровые профиля, стальными трубы или отдельные арматурные стержни.

 

 Completed pile after excavation

Equipment

The mixing tool is mounted on the high speed boring drive of the MDBA series of the ABI 14-17 drilling rig with the suspended suspension submission device. In boring drives of the MDBA series the tooth gearing that allows to avoid such negative the moment as noise, the increased wear, constant need for maintenance and monitoring isn't used. Connection of the tool with the boring drive of the MDBA series is executed using sliding rods. The injecting pump realizes submission of suspension through a swivel joint of the boring drive directly in a hollow tip of a mixing head.

The tool representing the mixing head consisting of a boring pipe, cross beams and a tip of the spiral drill diameter of the tool makes 800 mm and is constructed according to a geological structure of soil. 

Soil types

Application of technology of the wet mixing is most effective and expedient in sandy and sandy soil. Availability of ground waters isn't contraindication to application of a method. In the downlink soil the dry method using lime and cement is more effective.

Application of the DSM technology

- construction of bored piles;
- fixing (stabilizing) soil of buildings and constructions foundations ;
- construction of shoring (alternative to the classical diaphragm wall method also secant bored piles);
- installation of antifiltrational veils;
- gain (solidifying) of slopes, road embankments;
- planimetric gain of foundations;
- lowerings of rig vibrations with dyna mic influences.

Advantages

- Absence of vibrations — can be applied in places with high concentration of constructions and in residential areas.
- Low noise — thanks to special construction of the boring drive without use of the mechanism of tooth gearing noise level is minimized.
- Productivity — high frequency of rotation of the auger increases the daily productivity of a drilling equipment.
- Profitability — lowering of expenses at the expense of the small expenditure of cement, use of a local filler, absence of need for dredging, is more economic than jet cementation of soil (jet grouting).
- Environmental friendliness — absence of need for transportation of a filler and export of soil from a place of operations, and also in utilization and processing of the polluted soil.

Яндекс.Метрика