It is suitable for the construction of plain fill, miscellaneous fill, sandy soil, silt, cohesive soil, collapsible loess, muddy soil, ancient wells, ancient tombs, mined-out areas, flood control, water shortage and other suspicious foundations.
(2) After foundation treatment, the bearing capacity is high, the group stiffness is general, and the settlement deformation is small;
According to the theoretical experience and experimental data of this technology for many years, the characteristic value of bearing capacity of composite foundation is limited to 600kPa. However, the numerical values obtained in engineering practice are still large, such as: the characteristic value of bearing capacity of lime-soil pile is 3000kPa(s=2.57mm), and that of composite foundation is1500 kPa (s = 8.57 mm); The characteristic value of bearing capacity of plain soil piles is 750 kPa(s=6.27mm).
(3) According to different soil conditions, the pile body can be made into beaded, expanded and tray-shaped;
The diameter of rammed expanded pile is not only related to the assumed kinetic energy, but also related to the mechanical properties of foundation soil. When the kinetic energy is the same as the filler, its diameter changes with the soft-hard transformation of natural foundation soil. The lower the strength of natural foundation, the larger the pile diameter, which makes the piles form beaded shapes with different diameters, and makes the soil between piles bite like dog teeth, which increases the friction between piles, thus achieving the goal of average stiffness of foundation treatment. The compaction energy of filler and soil layer layout are also interrelated. According to the engineering requirements, the tamping energy is controlled and adjusted to achieve the purpose of beading, expanding head and pallet. The maximum pile diameter after tamping can be 2.5 ~ 4.0 times of the hole diameter.
(4) The disposal depth is "deep":
At present, the treatment depth of DDC pile has reached 30m, and that of SDDC pile has reached 50m.
(5) The compaction scale and pile diameter are large:
The compaction scale of a single pile can reach 600 ~ 2000 mm, and the pile diameter can reach 600 ~ 3000 mm depending on the equipment used.
(6) High kinetic energy, overpressure and strong compaction mechanism;
The characteristic of dynamic compaction construction technology in hole is that it has a strong compaction effect on the surrounding soil during construction. The compaction scale is generally 2 ~ 2.5 times of the pile diameter. At present, the weight of the rod hammer for equipment construction is 2 ~ 4 tons, the weight of the olive hammer for full-active remote control and active decoupling is 8 ~ 15 tons, and the lifting height from the air can reach 15m or more.
(7) It has the mechanism of dynamic coagulation and chemical coagulation:
Under the action of high kinetic energy and overpressure rammer, the material particles filled in the hole suddenly stop splitting, compacting, secondary arrangement, combination and coagulation; Active cementitious materials stop chemical curing during the release of tamping energy, and with the passage of time, the higher the strength.
(8) Common materials can reduce the project cost:
It is very common that materials used for DDC foundation treatment can be obtained on site. According to the requirements of engineering type, garden premise, surrounding conditions and upper layout on foundation treatment depth, bearing capacity and settlement deformation, pile materials can be taken from the site and confirmed by comparison. Materials such as plain soil, sandy soil, gravel, cement soil, building solid dregs, industrial waste, lime soil, concrete and other materials that have no corrosive inclusions and do not purify groundwater can be used as pile fillers. According to the types of pile fillers, it can be divided into: plain soil pile, lime soil pile, cement soil pile, gravel mixed soil pile, concrete pile, ballast soil pile, quicklime pile, fly ash pile, concrete pile and so on.
Because of the high tamping energy of this method, any material that can be filled into the hole can achieve the envisaged goal under the action of high kinetic energy and overpressure rammer. The limit of its particle size is determined according to the kinetic energy pressure of ordinary equipment. Under special conditions, as long as the required particle size can be put into the hole, the overpressure kinetic energy hammer can destroy it in the hole, hit the bottom of the hole and squeeze it into the pile. According to the technological characteristics of process equipment and piling, this ratio is limited. For active materials, the capacity of the loader bucket is used to stop mixing. As long as the loader rolls and stirs several times and the pressure of the special-shaped rammer expands with high kinetic energy according to its proportion, the material can be destroyed and stirred evenly. Therefore, there is no strict requirement on the particle size and mixing method of the filler, and it is generally put into the hole and stirred by the loader.
(9) High construction efficiency:
At present, the level of construction mechanization and initiative is high, and the construction speed is extremely fast.
Due to the rapid growth of supporting projects in China, and the serious shortage of site funds in recent years, there are many engineering environments for backfilling and reclamation at the seaside, hillsides and valleys. In order not to waste, save or enrich site funds and space funds, most supporting and envisioning units use foundation treatment to manipulate the vacancy of earthwork backfilling, and dynamic compaction is widely used in multi-storey and low-rise buildings, oil tanks, equipment and dock gardens. Dynamic compaction is more economical than other deep foundation treatment and other foundation treatment methods. Generally, the bearing capacity of the foundation after foundation treatment is required to be between 180kpa~200kpa. Combined with the field theory, the matters needing attention or control in dynamic compaction engineering are briefly discussed.