Hydrodrill

Anchor Stays

A stay is a structural element working in traction to transmit forces to:
- ground or rocks;
- an anchor structure.

The functional elements of a stay of type a are:
- the headpiece made up by the locking device and the distribution plate connected to the support or the structure to be supported;
- the free part, intermediate, comprising the assembly of reinforcing elements in harmonic steel that connect and transmit the traction between the headpiece and the active part. The reinforcement can be in the form of rods, wires or stranded cable, protected by single or multiple sheaths in polyethylene or polypropylene;
- the active part (foundation) by means of an anchor through cementing a mixture for injection based on cement or resin.

With stays of  type b the active part is composed of an end distribution plate that acts on the back of the of the shore part.

Classification

Depending on the duration of the operation we distinguish between:
- temporary stays: meant to perform their function for a period of less than two years.
- permanent stays: meant to perform their function for a period equal to or longer than two years.

Depending on the initial tension we distinguish between:
- pre-stressed stays: stays which are subjected to a stretching force greater than their working force.
- partly stressed stays: stays which are subjected to a stretching force equal to or less than their working force.
- non pre-stressed stays: stays which are not subjected to any stretching.

Construction materials and elements 

a. metal reinforcement
The reinforcement can be made with: :
- multiple strand reinforcement type c.a.p. with a variable number of strands, usually from 2 to 12 strands, with the following characteristics:

Number of strands

Maximum tension (MT)

2

30

3

45

4

60

5

75

6

90

7

105

8

120

9

135

10

150

11

165

12

180


- steel rods type Dywidag: of variable diameter from 26.5 to 32 to 36 mm according to the variable tension from 15 to 45 metric tons.

b. injection mix
Whenever not specified otherwise by the project the characteristics and the composition of the cement mix are:

Product

Data

Cement type 325-425

Kg 100

Water

40 to 45 litres

Calcareous or silicic aggregate

Kg 0-30

Bentonite

Kg 0-4

Optional additives

Fluxing, antishrinkage material


Means of execution


- drilling: using a rotary percussion head or rotary head with diameters variable from 100 mm to 240 mm either dry, with water circulation, stabilizing mud or cement, with or without a temporary lining according to the stability of the bore hole walls. Tools used are continuous flight augers, jackhammers or cutters with triple blades, triple cones or with bits in widia. The bore hole is purged by using compressed air or the same drilling fluids or by a mechanical conveyor in the case of a continuous flight auger.
- positioning reinforcement: with the above characteristics.
- injection of stays through simple filling or repeated injection under pressure: in the case of poorly composed ground) using the above methods.
- tensioning and testing using hydraulic jacks and an hydraulic power unit suitably calibrated for the expected working loads. Dywidag rods are secured by a threaded nut and the associated counter-plate using a torque wrench or a special hydraulic system.

Back to top