Multi strand anchors

Multi strand anchors are used in construction for over 50 years.

Tensioning minimizes or eliminates anticipated deformations of the system and deformations at the civil engineering measure. This applies both to temporary structures and permanent tie backs. As long as the grout used for anchoring is load-bearing, the anchor force is unlimited because the number of strands that can be combined in the anchorage is variable at will.

Bonded length: The anchor is fixed in the borehole using grout (cement mortar) and can transfer the forces to the loadbearing soil via bond and skin friction

Unbonded length: Each strand is uncoupled from the borehole using individual ducts so that it can freely extend in the unbonded length. This way, tension can be applied to the anchor system

Anchor head: The anchor head transfers the anchor force to the substructure and thus to the structure that needs to be anchored

Once the grout has sufficiently hardened, the load bearing capacity of each anchor is tested during an approval test.

Multi strand anchors consist of next main elements:   1 – structural elements; 2 – individual insulating sheath; 3 – sealing rings; 4 – seporators; 5 – corrugated sheathing for permanent anchors corrosion protection; 6 – grout tube; 7, 11 – corrosion protection compound; 8 – bearing plate; 9 – wedge pate; 10 – wedges.

Standart

Breaking point, MPa

Strand diam, mm

Cross-sectional area, mm2

Ultimate load, kN

GOST R 53772-2010

1770

12,4

93

165

1670

15,2

139

232

1770

15,7

150

266

EN 10138-98

1860

12,5

93

173

1860

15,0

140

260

1860

15,7

150

279

Installation technology

The designed depth drilled wells. In unstable soils are sand, gravel, etc. for well drilling using special drilling tools with casing. Lowered into the borehole padevy the anchor. Through injectione tube filles cement mortar cavity inside a corrugated pipe anchor and well space. After 40-60 minutes perform secondary injection of cement at the  anchor root. Grout pressure 2-4 MPa.

After curing of the cement stone anchor after 28 days is needed to carry the tensioto prevent movement of a primary held design. The tension produced by a special hydraulic hollow jacks to the load exceeding the 1.5 times to check the safety factor. After the load is reduced to design and install the attachment anchor. The clamping shut with a special protective cap and fill with cement mortar or other means to provide corrosion protection.

Multi strand anchors

Equipment, required for installation of AtlantJet anchor piles include a drill rig, grout pump, mixing plant and casing.

FIGARO drill rigs

Compact drill rigs sgaro are designed with separate hydraulic unit and developed for soil anchors and piles installation.

Rotary heads with high torque ensure high productivity of the rigs. Rigs Figaro Maschine can be mount on crawlers. Hydraulic stations depending on operating conditions are supplied with diesel, electric or pneumatic drive.

The 3-wheeled drill rig Figaro Pauk was designed for use on steep slopes and embankments. This allows drilling to be carried out with low machine weights and in difficult and dangerous on-site conditions.

Drill Figaro Lafette FL400

Drill Lafette is used for underground construction works:

  • Installation of augercast piles;
  • Reinforcement of buildings foundations;
  • Jet-grouting;
  • Installation of anchors.

Figaro Lafette FL400 is intended to work with hydraulic excavator of over 18-t weight.

MINI mixing/injection unit

MINI unit is designed for cement grout preparation and injection.

MINI unit consists of Mixing plant MINI and grout pump GP-40.

Hydraulic scheme of the pump allows to control grout flow rate and grout pressure. Low pressure mode allows achieve max. flow rate of 40 l/min at pressure of 4 MPa.The unit can be equipped with weighting terminal which allows automatic load of components according to set weight ratio.

Tension

The installed tension anchors is performed with the hydraulic jack.

Anchoring Sysytem

Generalized Kranz's force equilibrium method for stability analysis of an anchored wall

The polygon of forces acting on the soil wedge at limit equilibrium involves the active earth pressure of the retained soil Pa, the shearing resistance of the soil (i.e., Sс and , and the wall reaction Pa. The polygon of forces acting on the structural wall element involves the soil pressure PA. The resisting prestress anchor load required to maintain equilibrium, the passive resistance of the foundation soil Pp, and the basal soil reaction Fb. The decision power of the polygon allows you to define the horizontal projection Pa bearing capacity of the anchor, which leads hatched the prism in a state of marginal stability.

Kranz equation is used to define the factor of safety

FS = RL/Rm  with  RL =Fand Rm = T.

Bearing capacity calculation

Anchors and piles bearing capacity according DIN 1054-2005:

Fd = π D lqsk  with  D = dw kd

dw – well diameter,

kd – anchor diameter enhancement factor,

lk – anchor root length,

qsk – anchor skin friction.

Recommended values of anchor diameter enhancement factor shown in Table:

Soil type

Enhancement factor kd

Gravel

2,0

Sand

1,5

Sandy clay, clay loam

1,4

Clay

1,3

Rock

1,0

In the Table below you can see calculated skin friction values

Soil type

Skin friction, qsk, kPa

Medium and coarse gravel

200

Sand, semigravel

150

Sandy clay, clay loam, clay

100