Cable anchoring and grouting techniques

1. CABLE ANCHORING
AND GROUTING

2. CABLES
• A cable is A flexible structural component that offers no
resistance when compressed or bent in a curved shape.
Technically we can say cable has zero bending rigidity.
• It can only support tensile loading.
• Cables are often used in engineering structures for support and to
transmit load from one point to another when used to support
suspension roofs, bridges and trolley wheels, cables form the main
load carrying element in the structure.

3. Continued
 Being inextensible the cable has constant length before and after the load is
applied. as a result once the load is applied the geometry of cable remains
fixed.
The easiest structure type to think is a tension structure to resist only tensile
force and of these, the simplest are those which sustain only unidirectional
tension as represented by a cable or thin rod.
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4. MATERIALS
Steel, nylon ropes or plasticated cables may be used for
different structures
• Steel Cables : The high tensile strength of steel
combined with the efficiency of simple tension, makes
a steel cable the ideal structural element to span large
distances.
• Nylon and plastics are suitable only for temporary
structures, spanning small distances.
other structural members like masts, compression rings,
arches or beams and compression struts may be of concrete
or steel preferably. Struts may also be of timber.
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Types

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Multi-wire tendon (Clifford, 1974)
Birdcaged multiwire Tendon (Jirovec,
1978)
High capacity shear dowel (Mathews
et al,1986)
Birdcaged strand (Hutchins et al,
1990)
Bulbed strand (Garford, 1990)
Ferruled strand (Windsor, 1990)
Coated single strand (Hunt & Askew,
1977)
Single strand (Hunt & Askew, 1977)

7. APPLICATION
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1. Suspended type cable
2. Stayed type cable

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• A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is
hung below suspension cables on vertical suspenders.
• This type of bridge has cables suspended between towers, plus vertical suspender cables
that carry the weight of the deck below, upon which traffic crosses. This arrangement
allows the deck to be level or to are upward for additional clearance.
• The main type of force in a suspension bridge are tension in cables and compression in the
pillars.
SUSPENDED TYPE CABLE

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• The suspension cables must be anchored at each end of the bridge, since any load
applied to the bridge is transformed into a tension in these main cables.
• The main cables continue beyond the pillars to deck-level supports, and further continue
to connections with anchors in the ground.
• The roadway is supported by vertical suspender cables or rods, called hangers,
• The bridge will usually have two smaller spans, running between either pair of pillars
and the highway, which may be supported by suspender cables or may use a truss bridge
to make this connection. In the latter case there will be very little are in the outboard
main cables.

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SUSPENSION TYPE CABLES

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STAYED TYPE CABLE SUSPENSION TYPE CABLE

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• Suspension bridges have a high strength to weight ratio. They are flexible (can also be
disadvantage) and can span long distances with no piers therefore good on very high places,
across water etc. and they require little access from below aiding construction.
• They can be very thin and therefore less visible.
• They have an elegant look. The area spanned by a suspension bridge is very long in proportion
to the amount of materials required to construct bridges.
ADVANTAGES

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• Flexibility Disadvantages
Suspension bridges are flexible, which is an advantage until conditions became severe. Instability in
extremely turbulent conditions or during strong earthquakes may require temporary closure. In 1940,
high winds caused the Tacoma Narrows bridge, near Seattle. Washington, to collapse.
• Foundation Disadvantages
When built in soft ground, suspension bridges require extensive and expensive foundation work to
combat the effects of the heavy load on foundation towers.
• Heavy Loads
Flexibility also becomes a disadvantage when heavy, concentrated loads are involved. Suspension
bridges are not generally used for regional rail crossings that carry maximum weight loads, which adds
dangerous stress to the structure.
DISADVANTAGES

15. Assumption
 Cables are pure tension members.
 Used as:
1. Supports to suspension roofs.
2. Suspension bridge
3. Trolley bridge
 Self weight of cable is neglected in analysis
of structure.
 When used as cables for antennas or
transmission lines, weight is considered.
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• A cable-stayed bridge has one or more towers (or pylons), from which cables support the bridge
deck diagonally
• There are two major classes of cable-stayed bridges: harp and fan. In the harp or parallel
design, the cables are nearly parallel so that the height of their attachment to the tower is
proportional to the distance from the tower to their mounting on the deck.
• In the fan design, the cables all connect to or pass over the top of the towers. The fan design is
structurally superior with minimum moment applied to the towers but for practical reasons the
modified fan is preferred especially where many cables are necessary. In the modified fan
arrangement the cables terminate near to the top of the tower but are spaced from each other
sufficient to allow better termination, improved environment protection, and good access to
individual cables for maintenance.
STAYED TYPE CABLE

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STAYED TYPE CABLES

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COMPONENTS OF STAYED-TYPE CABLE

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• In the cable-stayed bridge, the towers are the primary loud-bearing structures which transmit the
bridge loads to the ground.
• A cantilever approach is often used to support the bridge deck near the towers, but lengths further
from them are supported by cables running directly to the towers. This has the disadvantage,
compared to the suspension bridge, that the cables pull to the sides as opposed to directly up,
requiring the bridge deck to be stronger to resist the resulting horizontal compression loads; but has
the advantage of not requiring firm anchorages to resist the horizontal pull of the main cables of the
suspension bridge.
• By design all static horizontal forces of the cable-stayed bridge are balanced so that the supporting
towers do not tend to tilt or slide, needing only to resist horizontal forces from the live loads.
LOAD BEARING MECHANISM OF CABLE-STAYED
BRIDGES

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DECK
CABLES
PYLONS
PILE CAP
PILES
SOIL

21. ANCHORING
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• The cable-stayed deck is in compression, pulled towards the towers, and has to be stiff at all
stages of construction and use.
• A great advantage of the cable-stayed bridge is that it is essentially made of cantilevers, and
can be constructed by building out from the towers.
• cable-stayed bridges possess higher stiffness and display smaller deflections when compared
with suspension bridges
• Construction time is less for cable stayed bridges. Cable Stayed Bridges require less cables
ADVANTAGES OF CABLE-STAYED BRIDGE

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• Base or substrate should have sufficient strength to take loads
• Anchoring can be done in hard concrete, loose concrete, stone masonry and brick masonry
• Anchors are available heaving high and low strength as per requirements
• Anchoring may require base plates, adhesives as per site requirements • now, many companies
provide anchors and
ANCHORING

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ANCHORING IN STAYED-
TYPE CABLE
ANCHORING IN
SUSPENSION-TYPE CABLE

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• Anchoring is required to join a component or member tο existing member. Normally, it is
done by breaking the substrate or existing surface, put some concrete and steel member
• In case, such arrangement has been forgotten, it is broken and redone
• In such case, anchoring technique can be used, and anchors fixed
CONSTRUCTION OF ANCHORING

26. Excavations and other engineering constructions in the ground are central to many civil and mining
projects.
Ground reinforcement includes among other methods, the techniques of ground anchoring, cable
bolting and rock bolting. Ground anchors tend to be longer with higher capacity, and are usually
associated with civil infrastructure projects.
Rock bolts tend to be shortest with lowest capacities .
Cable bolts are used in stability problems that lie between the two, and are commonly used in
mining engineering.
CABLE ANCHORING

27. • In the majority of moderately weak to strong rocks , rotary or rotary percussive open hole
drilling with air flush , followed by normal tremie grouting techniques , will achieve the required
grout/rock bond capacity.
• Where fissures or voids are detected by loss of flush, by water ingress, by water testing, or
inability to maintain a head of grout within the bore, then pre-grouting operations or alternatively
pressure grouting operations may be required.
• Normally cement grouts are injected but if fissures are known to be wide, sanded mixes may be
used.
• In coarse grained weak rocks similar techniques or alternatively rotary water flush drilling can
be used and in most conditions a reasonable anchorage capacity can be obtained.
ANCHORS IN ROCKS

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29. • In order to enhance the capacity of the anchorage within the normal range of fixed lengths,
either under reaming or soil fracturing systems have been employed
• More recently, the single bore multiple anchor system has been allowed efficient use of non-
enhanced bore holes and attained loads of 3500kn.
• The fracturing of soil prior to tendon installation, generally involves a larger diameter steel
manchette, which after treatment remains in-situ.
• Treatment may be carried out over a 2 or 3 day period prior to tendon installation, by repeatedly
injecting grout through manchette valves at 1/2 m centers in the fixed length.
• The anchor tendon is then, after pre grouting treatment, installed and grouted within the large
tube.
• The tube must efficiently transfer the entire load from anchor tendon and internal grout to the
external grout and then into the ground.
• It must not exhibit creep losses and it must not in anyway degrade (by corrosion) in any way
such that there is a reduction in bond capacity or performance within the grout body which may
reduce the capacity of the anchor within its intended lifetime
ANCHORS IN CLAY

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31. ANCHORS IN GRANULAR MATERIALS:
• Anchors are in the majority of instances
installed in granular deposits by drive drilling
with a knock-off bit or by use of duplex
drilling techniques.
• Drive drilling involves the percussion driving
of a strong casing with a conical lead bit
resulting lateral soil replacement and no flush
recovery. The lead bit is knocked off the casing
allowing tendon installation and pressure
grouting during withdrawal. There are
limitations in the depth penetrable.

32. GROUTING
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