CSP technique (Cased Secant Piles). This technique is applied in soil with feeble bearing capacity and requires the use of the drilling rigs equipped with a double rotary head (Double Rotary) with a power at least 250 kN/m

Чертеж последовательности устройства и армирования секущихся буронабивных свай.

The Double Rotary technique (double rotary head) represents a combination of two methods of bored piles construction– use of the continuous flight auger (CFA technology) with use of casing that allows to construct the bases without bentonite solution in any soil conditions, including feeble and flooded ones. The technology allows to install separate bored piles and diaphragm walls from secant piles with the guaranteed vertical deviation less than 1,0-1,5 mm diameters of 660 mm, 820 mm, 1020 mm and up to 23,5 m in depth.

The technology is absolutely safe for construction of bored piles near the existing buildings.

Рисунок 1. Установка SR-65 в работе

The increased bearing capacity of the bases of such piles in case of a driving of feeble soil is reached due to application of an casing (protects soil round the borehole from decompaction and excess carrying out of more feeble soil on a surface the auger) and submission of a concrete compound under excessive pressure.

Technological Sequence of Operations

Pile is formed in the following way (figure 2):

Рисунок 2. Технологическая последовательность формирования сваи
Рисунок 2. Технологическая последовательность формирования сваи

1. Drilling begins with insertion of casing to a small depth, then in case of rotation of the continuous auger and an casing in different directions reached the given depth. Thus the advancing of an casing that doesn’t allow ground waters to penetrate in a casing cavity with a razuprochneniye at the expense of this environmental soil remains;
2. After the given depth is reached through hollow part of the auger begin submission of concrete with simultaneous rise of the auger and casing. Filling an casing the soil loosened by the auger quits along auger blades up and is removed by means of a cleaner;
3. After filling of the casing with concrete it is extracted;
4. The reinforcing frame falls to a body of the received pile by means of a vibratory driver. This technology allows reducing considerably time and financial expenditure on a construction of bored piles. With this technology using Soilmec rigs it is possible to construct bored piles with a diameter up to 1000 mm and up to 23,5 m in depth (under protection of an casing).

This technique is commonly used for:

– rows of the secant piles;
– piles drilled by the auger in unstable and water-saturated soil;
– piles or boreholes with very small tolerance specified for plumbness.


Design feature of the equipment is installation of the continuous hollow auger in casing (a figure 1).
The special drilling rigs equipped with two rotary heads are developed for the Double Rotary technology: the upper rotator sets the continuous hollow screw in motion, and lower – turns an upsetting pipe in an opposite direction.
For execution of piles on this technology of JSC Delta Drilling Company uses SR-65 boring machines of Soilmec firm.


1. Can be applied in all types of dispersible soil (incoherent dense soil, silts, solid clays).
2. Absence of noise and significant vibrational influences allows suit piles near the existing buildings.
3. High performance – till 20-24 piles up to 23,5 m in depth in change.
4. High quality of filling of a slit with concrete due to submission of concrete under pressure.
5. Parameters of drilling are controlled by the high-precision onboard computer.
6. Option of constructing diaphragm walls from secant bored piles.