Special Foundation Works Curs-transfer Ro-21mar-4b1ccc

7/30/2019 Special Foundation Works Curs-transfer Ro-21mar-4b1ccc

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SPECIAL FOUNDATION WORKS

Support material


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Contents:

1. Diaphragm walls2. Sheet piles walls3. Ground anchors4. Reinforced fills5. Soil nailing6. Bored piles7. Displacement piles8. Micropiling9. Deep mixing10.Deep vibration11.Deep drainage12.Grouting13.Jet grouting


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1. DIAPHRAGM WALLS

Glossary

Clamshell (or grab): Excavation tool with two jaws to remove soil, rock or debris from an

excavation by an intermittent operation. Jaws are attached to a steel frame. There are two maintypes of clamshells.

mechanical grabs using steel cables to open/close the jaws; hydraulic grabs using hydraulic circuits to open/close the jaws.

Hydrofraise (or cutter or mill): Excavation tool with rotating wheels fitted with steel picks to

remove soil, rock or debris from an excavation by a continuous operation.

Chisel: Heavy steel tool used to break up obstructions, boulders and hard strata encountered in the

excavation or for socketing into hard soil or rock. There are particular types of chisels used to

rectify an excavation trajectory, to extract stop ends, etc.

Kelly (bar): Shaft, often telescopic, connected between the power drive and the digging tool which

allows deep excavation.

Cable(s): Steel cable(s) suspending the digging tool which allows deep excavation.

Excavation crane: Crane used to handle the excavation tool (clamshell or hydrofraise).

Handling crane: Crane used to handle the reinforcement cages and other equipment.

Water stop: Special flexible element attached longitudinally to a stop end in such a way that halfof the water stop is embedded in concrete in a panel after the concreting and stop end extracting

operations. When constructing the adjacent panel, the other half of the water stop is released and

also becomes embedded in concrete. As a result, the water stop surrounded in concrete at the

contact zone between two panels helps to limit water leakage through this critical surface. Two

water stops can be installed at a same joint if required.

Overlap: The distance of a panel excavation into the material of an adjacent panel to ensure

diaphragm wall continuity when no stop ends are used. The overlapping technique (no stop ends) is

always used for hardening slurry walls, often used for plastic concrete walls and sometimes used

for cast-in situ concrete walls where a hydrofraise (mill) can be employed to breakdown hard

concrete at joints.

Filter cake: Thin pastelike deposit formed by bentonite particles aggregating as water drains from

the suspension to the ground through the edge walls of the excavation during its progress. This

filter cake allows the bentonite suspension pressure to be maintained above the ground water

pressure such that the excavation edge walls remain stable.

Cutting back: Removal of surplus concrete (protrusions, etc) and bentonite cake when exposing

the diaphragm wall panels.

Trimming: Removal of surplus concrete above the cut-off level

Capping beam: Reinforced concrete beam built above the cut-off level to connect the cast-in situ

diaphragm wall panels together and/or to connect to overlying structural elements.


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Air lift: Pumping technique in which air is pumped into the base of a suction pipe to cause reduced

density of material in the pipe and induce upward flow to evacuate solids and fluids (flushing). The

air lift technique may be used to clean/replace the bentonite suspension before concreting.

Pre-blasting: Preliminary operation consisting in drilling holes along the alignment of a diaphragm

wall to place explosives in very hard material and blast it before commencing the diaphragm wall

excavation.

Lean concrete: Very low strength, low fines concrete poured in a panel excavation to stop

bentonite loss, to fill voids or to fill panel excavation deviation. The characteristics of the lean

concrete should allow its re-excavation with normal tools.

Concreting curve: Diagram representing the volume of poured concrete versus depth.

Excavation curve: Diagram representing the excavation depth versus time.

Desanding unit: Plant to remove sand and silt in order to clean the support fluid during excavation

and before concreting.

Specific materials and products used for the execution of diaphragm walls

Bentonite

Bentonite is a clay containing mainly the mineral montmorillonite.

Bentonite is used in support fluids, either as a bentonite suspension or as an addition to polymers. It

is also used as a constituent part of hardening slurries and of plastic concrete.

Bentonite can contain additives (i.e. polymers) in aqueous suspension.

Bentonite used in bentonite suspensions shall not contain harmful constituents in such quantities as

can be detrimental to reinforcement or concrete.

Polymers

Polymers can be used as rheological additive to bentonite suspensions with a content of 0,1 1,5

mass % in relation to bentonite dry weight or as sole constituent.

Polymers are materials formed of molecules from chained monomeric units.

There are different types of polymers ranging from natural gums to specially tailored blends of

synthetic products.

Support fluids

Bentonite suspensions

A bentonite suspension shall be prepared with either natural or activated sodium bentonite.

In certain cases, e.g. when the density of the suspension has to be increased, suitable inert materials

may be added.


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Others than in exceptional circumstances, the fresh bentonite suspension shall meet the conditions

shown in Table 1 and the "re-use" or "before-concreting" bentonite suspension shall meet the

conditions shown in Table 2.

At the stage "before concreting", an upper limit value between 4 % and 6 % for sand content may

be used in special cases (e.g.: non load bearing walls, unreinforced walls).

The values in Tables 1 and 2 may be modified in special circumstances, for example in the case of:

soils or rock with high permeability or cavities where loss of bentonite can occur;

high piezometric ground water levels (confined or artesian conditions);

very soft soils;

salt water conditions.

A bentonite suspension with sufficient flow limit can be required by the design, e.g in order to

reduce penetration into the ground.

Table 1 Characteristics for fresh bentonite suspensions

(1) see Table 2 , notes 1 to 3 for the test procedures

Table 2 Characteristics for bentonite suspensions

Notes(1) The Marsh value, the fluid loss, the sand content and the filter cake can be measured, for

example, using the tests described in the American Petroleum Institute document "Recommended

Practice Standard Procedure for Field Testing Water-Based Drilling Fluids" (reference: AmericanPetroleum Institute Recommended Practice 13B-1, June 1, 1990).


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(2) The Marsh value is the time required for a volume of 946 ml to flow through the orifice of the

cone. A volume of 1 000 ml may be used, but in this case, the Marsh values given in tables 1 and 2

should be adjusted.

(3) The duration of the fluid loss test may be reduced to 7,5 min. for routine control tests. However,

in this case, the values for fluid loss and filter cake shall be adjusted. The fluid loss for the 7,5 min.

test will be approximately half of the value obtained in the 30 min test.

(4) Indicative values

Polymer solutions

Polymers may be designed to work in conjunction with bentonite or to be used as stand alone

support fluid.

Its use shall be based on full-scale trial trenches on the site or on the basis of comparable

experience in similar geotechnical conditions.

NOTE: EN 1997-1 defines comparable experience as an experience which relates to similar works

in similar conditions and is well documented or otherwise clearly established.

Fresh hardening slurries

The characteristics of the slurry shall be suitable to ensure satisfactory performance during

execution.

A hardening slurry may be prepared with calcium bentonite or activated sodium bentonite.

NOTE 1 Hardening slurries are generally used in the precast concrete diaphragm wall technique

and for slurry walls.

NOTE 2 Hardening slurries serve as support fluid during excavation, and, together with the finesfrom the natural ground, form the final, hardened material.

Admixtures may be used to adjust setting time of the slury and its consistency during excavation

and during any subsequent insertion of elements.

Concrete

Unless otherwise stated, the concrete used in cast in situ concrete diaphragm walls or in precast

concrete diaphragm walls shall comply with SR EN 206.

For correct execution, the cast in situ concrete shall be designed to avoid segregation during

placing, to flow easily around the reinforcement, and when set, to provide a dense and low

permeability material.

The specified properties of the hardened cast in situ concrete, related to strength and durability,

shall be compatible with the consistency requirements.

In the case of a maximum aggregate particle size of 32 mm, the concrete mix shall have the

following characteristics:

sand content (d 4 mm) greater than 40 % by weight of the total aggregate ;

fine particles (d 80 m) in the concrete mix (including cement and other fine

materials) between 400 kg/m3 and 550 kg/m3.


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The minimum cement content shall be related to the maximum aggregate size in accordance with

Table 3.

Table 3 Minimum cement content for concrete

The water/cement ratio shall not exceed 0,6.

The admixtures allowed for concreting using tremie pipe(s) may be:

water reducing/plasticizing;

high range water reducing/super-plasticizing; and

set retarding.

Admixtures may be used:

to give a mix of high plasticity;

to avoid bleeding, honeycombing or segregation that might otherwise result from a high

water content ;

to prolong the consistency as required for the duration of the placement ; to cater for any interruptions in the placement process.

Fresh concrete

Concrete used for diaphragm walls shall:

have a high resistance against segregation ;

be of high plasticity and good cohesiveness ;

have good flow ability ;

have the ability to self-compact ; and

be sufficiently workable for the duration of the placement procedure.

The slump test or the flow table test may be used to evaluate the consistence of the fresh concrete.

The consistence ranges of the fresh concrete in different conditions of use shall comply with Table

4.


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Table 4 Consistency ranges for fresh concrete in different conditions

Consistency of the concrete should be monitored with time. A minimum slump of 100 mm after

four hours is recommended.

Plastic concrete

Plastic concrete shall be designed in order to obtain the required deformability and permeability,together with adequate workability and strength.

Plastic concrete is used for cut-off walls when, in addition to low permeability, high deformability

is required.

Their constituent parts are:

fine grain material (e.g. silt, clay or bentonite);

cement or another binder;

well-graded aggregates;

water;

and possibly additions and admixtures.

For plastic concrete limiting w/c ratio does not apply.

Considerations related to design of diaphragm wall made of panels

The panel dimensions should take into account the dimensions of available excavating equipment,

the method and sequence of excavation, panel stability during excavation and concrete supply.

The terminology used to define the dimensions and details of panels is shown on Figures 1 and 2.


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Key:

1 Wall thickness 7 Guide-wall2 Horizontal length of reinforcement cage 8 Cut off level3 Cage width 9 Vertical length of reinforcement cage

4 Length of panel 10 Reinforcement cage5 Platform level 11 Depth of excavation

6 Casting level 12 Concave portion of curved joints

Figure 1 Geometry of a panel


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Key:P PrimaryS Secondary

1 Starter

2 Intermediate3 Closure

Figure 2 Schematic examples of different types of panels and joints (plan view)

The width of the excavating tool shall be at least equal to the design wall thickness.

The design of the wall shall take into account the discontinuity of the reinforcement at the joints

between the panels and between adjacent cages in the same panel.

Space shall be allowed between reinforcement cages of adjacent panels to accommodate the type of

joints to be made and to take account of the construction tolerances.

Space shall be allowed in the reinforcement cage for the installation of the tremie pipe.

A reinforced concrete capping beam should be constructed along the top of reinforced concrete

diaphragm walls, where it is necessary to distribute loads or minimize differential displacements.

In exceptional cases where it is necessary to provide structural continuity across the joints, special

techniques are available.

Design shall consider that diaphragm walls cannot be expected to be completely watertight, since

leakage can occur at joints, at recesses or through the wall material. Damp patches and droplets of

water on the surface of the wall cannot be avoided under normal circumstances.

Design should not normally consider continuity of reinforcement between the cages and across the

joints but it may be constructed in exceptional circumstances.

Panel stability during excavation

The length of the panels and the level of the support fluid shall ensure the stability of the trenchduring excavation.


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The excavation tools or procedures, especially where chiselling or blasting are used, can have an

influence on the trench stability.

Special precautions in chiselling and blasting have to be taken e.g in loose soil overlying a hard

rock.

To ensure trench stability the level of the support fluid shall be adjusted with respect to the highestpiezometric ground water level anticipated during excavation, and the support fluid level shall

always remain at least 1 m above the highest piezometric level.

In the case of loose sand or soils with cu < 15 kPa, it can be necessary to stabilise the soil by

increasing its strength or by raising the level of the support fluid and/or to increase its density

during excavation, and to minimize the time during which the trench is left open.

In case where a loss of support fluid can occur (e.g highly permeable, coarse soils or where there

are voids in the ground), special measures may be adopted, for example :

increasing the flow limit of the fluid by increasing the bentonite content in the

suspension; adding a filler material to the bentonite suspension, either at the mixing plant or directly

in the trench;

in the case of voids, filling the trench to an appropriate depth with lean mix concrete orother suitable material, and reexcavating;

grouting the layers concerned before excavating the trench.

The ground water level can change in relation with execution (e.g case of closing a box). Risk on

trench stability in relation with change in water level due to construction should be considered.

Also possible mitigation measures (e.g. dewatering as a way to reduce pore pressure) should be

considered.

The stability considerations shall take account of the following factors:

stabilizing forces due to the support fluid ; groundwater pressures ; earth pressures, including the three-dimensional geometry of the problem ; shear strength parameters of the soils ; effects of adjacent loads ; constructions details of adjacent structures.

The trench stability during excavation includes two aspects:

the local stability of the soil at the walls of the trench; the overall stability of the excavation.

The trench remains stable as a result of the stabilizing forces of the support fluid acting against the

walls of the trench:

in case of bentonite suspensions, the support effect in fine-grained soils is due to theformation of a filter cake. In coarser soils, this effect is due to a limited penetration into

the pores of the soil;

in the case of polymer solutions, the support effect is caused by the seepage pressure ofthe liquid flowing into the soil.

The penetration depth, which increases with time, is significant in the case of silty or sandy soils,but remains small in the case of clayey soils.


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Reinforcement cages

The reinforcement within a panel may comprise one or more cages within the panel length.

Multiple cages and joints

The minimum clear distance between two cages in the same panel shall be at least 200 mm.

The maximum clear distance between two cages in the same panel should be 400 mm

The minimum clear distance between the ends of the cages and the joints formwork including

water-stop if any, shall be 100 mm and shall take into account the verticality tolerances, the shape

of the joints and the possible use of water stops.

A clear distance of 200 mm is recommended between the ends of the cages and the joints formwork

including water-stop if any.

In the case of the concave portion of curved joints, except special cases, the cage should not enterinto the concave portion of the joint.

This does not apply to the case of diaphragm walls with continuous horizontal reinforcement across

the joints.

Execution of diaphragm walls

Construction sequence

The phases of execution differ with the type of wall and support fluid used.

In the general case a support fluid is used.

The basic sequences for cast in situ concrete diaphragm walls are:

excavation, generally with a bentonite suspension or other support fluid; cleaning the excavation including recirculation of bentonite; placing the reinforcement; concreting; trimming.

The basic sequences for precast concrete diaphragm walls are:

excavation, generally with a hardening slurry, sometimes with a bentonite suspension ; cleaning the excavation. When a bentonite suspension is used, it is replaced by a

hardening slurry. If required by the design, a stronger material such as mortar or

concrete may be placed at the bottom of the excavation, to support the precast panel and

applied loads ;

placing the precast element.

The basic sequences for cut-off slurry walls are :

excavation with a hardening slurry. In some cases (e.g. excavations of long duration), a

different support fluid may be used, which has then to be replaced by the hardeningslurry;

when required, placing elements such as membranes, reinforcement or sheet piles; trimming and protective capping.


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The basic sequences for plastic concrete walls are:

excavation, generally with a bentonite suspension; cleaning the excavation; concreting; trimming.

Preliminary works

Working platform

The working platform shall be stable, above the water table, horizontal and be suitable for traffic of

heavy equipment and lorries.

The area along the line of the wall shall be clear of underground obstructions.

Special care is to be taken for excavating and backfilling trenches in case of removal of disturbedsoil or underground obstructions.

Excavation and backfilling are to be done symmetrically along the axis of the wall, to a depth

corresponding at least to the level of undisturbed soil, with sufficient width and depth with regard

to the guide-walls.

The top of the working platform should be at least 1,5 m above the highest water-table anticipated

during excavation, taking into account possible fluctuations.

Guide-walls

Guide-walls shall be designed and constructed:

to ensure alignment of the diaphragm wall, to serve as a guide for the excavating tools, to secure the sides of the trench against collapse in the vicinity of the fluctuating level of

the support fluid,

to serve as a support for the reinforcement cages or prefabricated panels or otherelements inserted in the excavation until the concrete or hardening slurry has hardened,

to support the reaction forces of stop end extractors when necessary.

Guide-walls are usually made of reinforced concrete with a depth normally between 0,7 m and 1,5

m depending on ground conditions.

In the case of cut-off walls excavated continuously, if ground conditions should permit, guide-walls

may not be necessary.

Guide-walls should be propped apart until the excavation of the panel takes place.

The distance between the guide-walls should normally be 20 mm to 50 mm greater than the width

of the excavating tool.

The top of the guide-walls should normally be horizontal and have the same elevation on both sidesof the trench.


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Excavation

Supporting the walls of the excavation

Except special ground and site conditions, a support fluid shall be used during excavation.

In some cases, it can be possible to excavate using water as a support fluid.

In certain soils with cohesive properties or in rock, dry excavation may be used, provided the

ground strength is sufficient to ensure stability of the sides of the trench.

In soils where no comparable experience is available, a trial excavation should be made.

During excavation, the level of the support fluid will fluctuate, but it shall not be allowed to

drawdown below the level required for excavation stability.

The level of the support fluid shall remain above the base of the guide-walls, unless there is no risk

of caving of the soil below the guide-walls.

Excavation sequence

The excavation may be carried out continuously or in panels.

The sequence of excavation, panel lengths and distances between panels being excavated, depend

on the ground conditions, the type of wall, and the type of excavating tools.

The excavation of a panel shall not be started before the concrete, the plastic concrete or the

hardening slurry in the adjacent panel or panels has gained sufficient strength.

The use of chisels, other tools, or blasting, which affect the nearby panels already filled with

concrete or hardening slurry shall not be made before the material in these panels has sufficient

strength to resist the stresses developed during these operations.

Loss of support fluid

When a sudden and significant loss of the support fluid occurs during excavation, the excavation

shall be refilled immediately with an additional volume of support fluid, possibly containing

sealing materials.

If this procedure is insufficient, the excavation shall be backfilled as quickly as possible with lean

concrete or other material which can be readily re-excavated.

In situations where significant loss of support fluid can occur (e.g. highly permeable soils, cavities),

an additional volume of support fluid, and possibly sealing materials or suitable fill, shall be stored

in a readily accessible area.

Forming the joints

Stop ends shall be of adequate strength and properly aligned throughout their length.

The joints are normally formed either by using steel or concrete stop ends or by cutting into the

concrete or hardened material of the previously cast adjacent panel. In some cases, waterstops can

be incorporated into the joints.


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In the case of stop ends which are extracted laterally, the extraction shall be made upon completion

of the excavation of the adjacent panel.

In the case of stop ends which are extracted vertically, the extraction shall be made gradually

during the setting of the concrete.

Placing the reinforcement or other elements

Reinforcement cages, precast concrete panels or other elements (such as sheet piles, membranes)

shall not rest on the bottom of the excavation, but shall be suspended from the guide-walls.

Concreting and trimming

Concreting in dry conditions

Particular care shall be observed when concreting in dry conditions, to avoid segregation.

Direct pumping may be used in dry excavations.

Vibration of the concrete shall not be used.

Specific slump values are required for dry conditions.

Concreting under support fluid

The time elapsing between the start of excavation and commencement of concreting shall be kept

as short as possible.

The tremie pipe shall be clean and watertight. Its inner diameter shall be at least 0,15 m and 6 times

the maximum aggregate size. Its outer diameter shall be such that it passes freely through the

reinforcement cage.

The number of tremie pipes in a panel shall be adjusted to limit the horizontal distance the concrete

has to travel.

In normal circumstances, the horizontal distance the concrete has to travel should be less than 3,0

m.

Where there is more than one cage per panel, at least the same number of tremie pipes should be

used.

When several tremie pipes are used, they shall be arranged and supplied with concrete in such a

way that a reasonably uniform upward flow of the concrete is assured.

When starting concreting, the support fluid and the concrete in the charged tremie pipe shall be

kept separate by a plug of material or by other suitable means.

To start concreting, the tremie pipe shall be lowered to the bottom of the trench and then raisedapproximately 0,1 m.

After concreting has started, the tremie pipe shall always remain immersed in the fresh concrete.


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The tremie pipe shall remain immersed into the fresh concrete for at least 6 m at the beginning of

concreting and before the first section of the pipe is drawn. Immediately after extracting the first

section, the immersion depth shall not fall below 3 m.

The immersion depth may have to be reduced when the concrete approaches ground level to

facilitate concrete flow.

An adequate supply of concrete shall be available throughout the whole placement process to

enable a controlled smooth operation.

In order to ensure concrete integrity, the rate of concrete rising over the full height of the panel

should not be less than 3 m/h.

Since the top of the cast concrete may not be of the required quality, sufficient concrete shall be

placed in the panel to ensure that the concrete below the cut-off level has the specified properties.

The required quality of the concrete at the cut-off level is achieved by providing a height ofconcrete above the cut-off level.

The height of concrete above the cut-off level depends on the cut-off level, the wall dimensions and

the number of tremie pipes.

Trimming

Trimming of the concrete to cut-off level shall be carried out using equipment and methods which

will not damage the concrete, reinforcement or any instrumentation installed in the panels.

Where possible, some trimming above cut-off level may be carried out before the concrete has set.


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2. SHEET-PILE WALLS

Legenda tubes + sheet piles

b U box piles + U sheet pilesc Z box piles + Z sheet pilesd H beams + Z sheet piles

Fig. 1 Examples of combined walls

Legenda sheet piles e tie rod

b strut f anchor plate or screenc waling g variable angled rock dowel h ground anchor or tension pile

Fig. 2 Example of a sheet pile wall structures


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Legenda hammer

b driving cap

c sheet piled leadere pile guide

Fig. 3 Examples of a sheet pile driving rig with fixed leader


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Legenda hammer

b cushionc leaderd sliding guidee driving cap

f leader slide

Fig. 4 Example of a driving cap

Legenda claw b tongue c driving direction

Fig. 5 Driving direction for Z-sheet piles with tongue and claw interlocks


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Legenda sheet pile b waling c strut d support bracket e bag filled with concrete

Fig. 6 Bags filled with concrete or cement mortar in order to obtain a good connection

between waling and sheet piles

Driving of sheet p i les

Sheet piles are installed in the ground by one or a combination of the following methods:

impact ; vibration ; pressing.

Vibrating is in many circumstances the most efficient method. In combination with leader guiding

it is also a very accurate method of driving sheet piles to the required depth. However, if very

dense sands and gravel above groundwater level or stiff clay layers have to be driven through,

vibrating may be ineffective. In these cases either driving assistance or impact driving may be

required. When obstacles are present and cannot be removed, either predrilling or careful impact

driving are the best methods to be used.

Generally driving with a vibrator causes a higher level of vibration in the surrounding ground than

impact driving. High frequency vibrators, where the eccentricity of the rotating mass can be varied

during the start up and stop phases of the driving process, can considerably reduce the adverse

vibrations of the process on the surrounding ground.

Vibrations from impact hammers and vibratory drivers are normally considerable and can travel

over relatively long distances. Foundations which are subjected to vibration will pick up part of

these vibrations and transfer them to the various elements of the supported structure. As a result

damage can be caused to sensitive buildings near to the source of the vibrations. Special care is

necessary if such structures are founded on loose sand, especially if it is saturated, because it is

subject to sudden settlement resulting from vibrations in the ground.

Where vibration or noise is considered a problem, pressing the sheet piles into the ground may

be a solution. Normally pressing is effective in cohesive soils. In difficult soil conditions pre-

boring and sometimes water jetting can be effective in assisting the sheet pile to reach therequired depth.


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Different types of pile driving equipment suitable for the installation of the sheet piles are

available. The most common types are:

free falling hammers ; diesel hammers ; hydro hammers ; air hammers ;

high and low frequency vibrators ; high frequency vibrators with a variable eccentricity of rotating mass; high frequency vibrator with continuously variable excentricity and resonance free start and

stop phases ; pressing systems.

Installation and driving assistance

Driving method

In the 'pitch and drive' method a single or double sheet pile, is driven to full depth before pitching the

next one. This simple procedure has the advantage that the top of the sheet pile has only to be lifted adistance equal to the length of the pile above the ground surface. Moreover it easily can be guided

manually into the interlock of the sheet pile which has already been driven.

In the case of dense sands, stiff cohesive soils and in soils containing obstructions, the 'pitch and

drive'method can lead to de-clutching problems in the free leading interlock and occasionally to rather

large deviations from the required position.

"Panel driving"and "staggered panel driving", enables better control of the position of the sheet piles

along the wall length. At the same time the danger of declutching is minimised.

As a whole panel is pitched it is not necessary to drive all the sheet piles to full depth in order to

maintain sheetpiling operations. If obstructions are encountered, individual sheet piles can be left

high without disruption to the installation process.

"Staggered driving" is a particular form of "panel driving" which may be applied when difficult soil

conditions are encountered. The sheet piles in the panel are driven in a sequence indicated in figure

7.

The disadvantage of the "panel driving" method is that interlocking the sheet piles requires

individual piles to be lifted to twice their length.


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Legenda direction of sheet pile installationb d riving d irect ion (1 3 5)c driving direction (4, 2)d upper guide

e lowerguide

Fig. 7 - Example of staggered driving of sheet piles D.2

Driving assistance

It is often necessary to loosen very dense sand layers.

Normally applied methods are

a) low pressure jetting with low water volumes

pressure : 1,5 Mpa to 2,0 MPa ;

discharge : 2 I/s to 4 1/s per tube ; diameter of pipes : approx. 25 mm ; number of pipes : 1 to 2 per sheet pile.

The pipes are welded to the sheet piles and left in situ.

b) high pressure jetting

pressure : 25 Mpa to 50 MPa (at pump outlet) discharge : 1 1/s to 2 1/s ;pipe diameter : 20 mm to 30 mm ; nozzle diameter : 1,5 mm to 3,0 mm.

c) predrilling, with or without cement bentonite.

d) blasting in special cases.


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Low pressure jetting is mainly used in dense non-cohesive soils.

Low pressure jetting with low water volumes, in combination with a vibrator, enables sheet piles

to penetrate very dense soils. In general the soil characteristics are only slightly modified and there

is practically no settlement, although special care has to be taken when the sheet piles have to

carry vertical loads.

In addition, low pressure jetting is sometimes used for pre-treatment of the soil prior to piledriving.

High pressure jetting or fluidisation can be very effective in very dense soil layers.

Limited amounts of jetting fluid, water or sometimes cement-bentonite, are introduced into the

ground through nozzles fixed to the sheet pile at a short distance above its tip. As a result of the

limited water consumption this method permits effective control of the pile. The soil properties

are only adversely effected in a limited area around the sheet piles. The overall performance will

not be significantly influenced.

Pre-drilling is sometimes carried out prior to the sheet pile driving. The soil is locally loosened bythis process. Normally flight auger drills are used.

Facturing by blasting is normally carried out if the sheet piles have to pass hard obstructions in the

soil or if they must penetrate bedrock.

Timber sheet piles and walings

Timber for sheet piles and walings in permanent sheet pile wall structures is normally of high

durability.

Tropical hardwood normally meets this requirement without any preservation. However

coniferous species when used in waterfront structures, need to be impregnated by a preservation

fluid pressed into the wood under vacuum conditions.

Cutting, boring and similar operations should preferably be carried out in the factory before the

timber is impregnated. When impregnated timber is subsequently cut, bored or similarly re-

shaped, it is necessary to treat the affected area with special protecting liquid.

Joints

Normally timber sheet piles are jointed by tongue and groove type interlocks of a trapezoidalshape. However a rectangular shape is also used.

The dimensions of the tongue determine the size of the groove as shown in figure 8.


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LegendA Tongue and groove with trapezoidal shape B Tongue and groove with rectangular shape

Fig. 8 Shape and dimensions of tongue and groove interlocks of timber sheet piles

Corner sheet piles

Corner sheet piles generally have a square crosss section with grooves to conne the

adjacent sheet piles (see figure 9.)

Fig. 9 Example of a timber corner pile with grooves

Execution

Normally timber sheet piles are only used in retaining structures with a limited retained height.

Typical uses are:

vertical or nearly vertical embankments along canals and ditches; small quays in yachting harbours and similar.

Driving is usually carried out with light driving equipment. If a free falling mass is used the

height of the drop should not exceed 2,5 m.

When a vibrator is used, panels of several piles are driven as units.

In order to keep the sheet piling in the correct position, a guide frame is used. Low pressure water


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jetting is often used to assist driving work in sand layers.

In order to ascertain a proper tongue and groove connection, the sheet piles are often bevelled at

the "free" side of the toe as shown in figure 10.

Legenda driving directionb bevel width

c ground pressure

Fig. 10 Bevelling at the toe and driving direction


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3. GROUND ANCHORS

Ground anchors are covered by EN 1537.

Scope

to support a retaining structure; to provide the stability of slopes, cuts or tunnels; to resist uplift forces on structures,by transmitting a tensile force to a load bearing formation of soil or rock.

Two types of ground anchors:

pre-stressed anchorages consisting of an anchor head, a tendon free length and a tendon bondlength bonded to the ground by grout (figure 1);

non pre-stressed anchorages consisting of an anchor head, a tendon free length and a restraintsuch as a fixed anchor length bonded to the ground by grout, a deadman anchorage, a screw

anchor or a rock bolt.

Key1 Anchorage point at jack during stressing 6 SoiI Urock

2 Anchorage point at anchor head in service 7 Borehole

3 Bearing plate 8 Debonding sleeve

4 Lold transfer black 9 Tendon

5 Structural element 10 Grout body

Figure 1 - Sketch of a ground anchor

Drilling methods

The drilling method shall be chosen with due regard to the ground conditions so as to

cause either minimum ground modification or the modification most beneficial to the

anchor capacity and to allow the design anchor

resistance (Rd) to be mobilised.

Reasons forminimum ground modification are:

- to prevent collapse of the borehole wall during drilling and tendon installation (where

necessary a casing should be utilised) ;- to minimise loosening of the surrounding ground in cohesionless soils ;- to minimise change of ground water levels ;- to minimise softening of the surface of the borehole wall in cohesive soils and degradable


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rocks.

Techniques to counteract the water pressure and to prevent any blow-out, hole collapse and

erosion during drilling, installation and grouting operations shall be identified in advance and

implemented as and when required. In high water table situations it may be appropriate to use

heavy drilling fluids.

Possible preventative measures include

- the use of special auxiliary drilling equipment such as seals or packers;- the lowering of the water table, after the risks of general settlement of the ground have been

assessed;

- pre-grouting of the ground.

Grouting

Grouting meets one or more of the following functions:

a. to form the fixed anchor length in order that the applied load may be transferredfrom the tendon to the surrounding ground ;

b. to protect the tendon against corrosion ;c. to strengthen the ground immediately adjacent to the fixed anchor in order to

enhance ground anchor capacity ;

d. to seal the ground immediately adjacent to the fixed anchor length in order to limitthe loss of grout.

If a grout volume injected is in excess of three times the borehole volume at pressures not exceedingtotal overburden pressure, then general void filling is indicated which is beyond routine anchor

construction. In such cases general void filling may be necessary before grouting the anchor. For

functions c) and d) above only nominal grout consumptions should be expected.

Anchor grouting

Placement of grout should be carried out as soon as possible after completion of drilling.

When grouting by the tremie method, the end of the tremie pipe shall remain submerged in

grout within the fixed anchor length and grouting shall continue until the consistency of the

grout emerging is the same as that of the injected grout.

The grouting process should always start at the lower end of the section to be grouted. For

horizontal and upward inclined holes, a seal or packer is required to prevent loss of grout from

either the fixed anchor length or the entire hole.

Stressing

Stressing is required to fulfil the following two functions

- to ascertain and record the load carrying behaviour of the anchor ;- to tension the tendon and to anchor it at its lock-off load.

Stressing and recording shall be carried out by experienced personnel under the control of a

suitably qualified supervisor, provided preferably by a specialist anchor contractor or stressingequipment supplier.


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Investigation test

Investigation tests may be required to establish for the designer, in advance of the installation

of the working ground anchors, the ultimate load resistance in relation to the ground conditions

and materials used, to prove the competence of the contractor and/or to prove a new type of

ground anchor by inducing a failure at the grout/ground interface.

Acceptance test

Each working anchor shall be subjected to an acceptance test.

The objectives of the acceptance test are as follows:

a) to demonstrate that a proof load, which will depend on the test method, can be sustained bythe anchor ;

b) to determine the apparent tendon free length ;c) to ensure that the lock-off load is at the designed load level, excluding friction ;d) the creep or load loss characteristics at the serviceability limit state, when necessary.

Definitions

permanent anchorageanchorage with a design life of more than two years

temporary anchorageanchorage with a design life of less than two years

acceptance testload test on site to confirm that each anchorage meets the design requirements

suitability testload test on site to confirm that a particular anchor design will be adequate in particular ground

conditions

investigation testload test to establish the ultimate resistance of an anchor at the grout/ground interface and to

determine the characteristics of the anchorage in the working load range


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4. REINFORCED FILLS

Reinforced fill, covered by EN 14475, is an engineered fill reinforced by the inclusion of horizontal

or subhorizontal reinforcement placed between layers of fill during construction.

The scope of reinforced fill applications includes (Figure1):- earth retaining structures, (vertical, battered or inclined walls, bridge abutments, bulk

storage facilities), with a facing to retain fill placed between the reinforcing layers;

- reinforced steep slopes with a facing, either built-in or added or wrap-around, reinforcedshallow slopes without a facing, but covered by some form of erosion protection without a

facing, reinstatement of failed slopes;

- embankments with basal reinforcement and embankments with reinforcement againstfrost heave in the upper part.


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Definitions

fillnatural or man made material formed of solid particles, including certain rocks, used to construct

engineered fi ll

engineered fillfill which is placed and compacted under controlled conditions

reinforced fillengineered fill incorporating discrete layers of soil reinforcement, generally placed

horizontally, which are arranged between successive layers of fill during construction

reinforcementgeneric term for reinforcing inclusions placed within fill

fill reinforcementreinforcement which enhances stability of the reinforced fill mass by mobilising the axial tensile

strength of the fill reinforcement by soil interaction over its total length


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geosyntheticsfor the purpose of this European standard "geosynthetics" stands for "geotextiles and geotextile

related products"

foundation

foundation of a reinforced fill structure is the total area of the surface upon which the lowest layerof reinforcement is installed

facingcovering to the exposed face of a reinforced fill structure which retains the fill between layers of

reinforcement and protects the fill against erosion

full height facing unitfacing unit equal to the height of the face of the structure

discrete facing unit

partial height facing unit used to construct incrementally a reinforced fill structure

hard facing unitpanel or block usually of precast concrete with intrinsically low vertical compressibility and high

bending stiffness.

deformable facing unitpreformed steel grid section, a preformed solid steel section or a rock filled gabion with

intrinsically vertical compressibility and low bending stiffness.

soft facing unitsoil fill encapsulated in a geogrid or a geotextile facing with no bending stiffness.

facing systemassemblage of facing units used to produce a finished reir forced fill structure

rigid facing systemfacing system with no capacity to accommodate vertical differential settlement between fill and

facing.

semi-flexible facing systemfacing system with some capacity to accommodate differential settlement between fill and facing

flexible facing systempliant, articulated, facing system with capacity to accommodate differential settlement between fill

and facing

green facingvegetative cover or infill used without facing units or as an adjunct to reinforced fill structures

constructed using facing units

claddingfalse facing added in front of the facing to improve the aesthetics of a finished reinforced fill

structure


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design lifeservice life, in years, required by the design

temporary structuresstructures with a design life of 1 - 5 years (Class 1)

permanent structuresstructures with a design life of more than 5 years (Class 2 - 5)

Materials and products

Construction of reinforced fill involves the use of the following major components:

- fill material;- fill reinforcement, and if required;- facing system.

Fill materials

The fill used within the reinforced zone shall be selected to meet the properties required by the

design and the project specification.

The suitability of a reinforced fill material is dependent on a number of factors that shall be

considered when selecting the material:

- fill workability;- function and environment of the structure and long term behaviour;- fill layer thickness and maximum particle size;- facing technology;- vegetation;- drainage properties;- aggressivity of the fill;- fill - reinforcement interaction;- fill - internal friction and cohesion;- frost susceptibility.

Fill workability

The fill workability shall be such that it can be placed and compacted to produce the properties

required by the design.

Function and environment of the structure and long term behaviour

Some types of structure have a critical function where post construction settlement is very

important. e.g. bridge abutments, walls supporting railway tracks and buildings, or high earth

retaining structures etc. In these cases fill material which is easy to compact and which will have

subsequent low compressibility shall be selected.

Where a structure is exposed to flooding and subsequent rapid drawdown the drainage properties

of the fill shall be checked for compatibility with the design assumptions.


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Reinforcement products

Fill reinforcements can be made from metals, generally steel, or polymeric materials.

Facings

Facings can be produced in a variety of materials and configurations with a variety of facing-reinforcement connections and a variety of joint fillers and bearing devices.

Facing units and systems

Reinforced fill is constructed using successive layers of compacted, selected fill incorporating

intervening layers of horizontal or sub-horizontal fill reinforcement placed at spacing required by

the design.

Reinforced fill earth retaining structures, with a vertical, battered or inclined face (see Figure 2),

require a facing to retain the fill between the reinforcing layers. Depending on the particular

system, certain layers of fill reinforcements may however not be connected to the facing.

On shallow reinforced slopes, facing is generally not necessary. Such slopes are usually protected

by vegetation with / without erosion control materials.

The facing can be constituted of either hard units (typically made of concrete), or deformable units

(typically made from metal, steel grid or mesh, or gabion baskets), or soft units (typically made

from geosynthetic sheets or grids, or woven wire mesh).

Where hard or deformable facing units are used, these serve as a formwork against which the

selected fill is placed and compacted. Where soft facing units are used, it is generally necessary to

employ temporary formwork to maintain the face alignment during the construction of walls orsteep slopes.

Key:1 Earth retaining structures

2 Reinforced slopes3 Vertical

4 Vertical wall5 Battered wall

6 Inclined wall Steep slope7 Shallow slope

8 Some specific types of facings : panels, blocks, V2 elliptical

steel units, gabions9 Specific types of sloping panel, eg for bulk storage

10 Some common types of facings: planter units, wire mesh,wrapped around

11 No facing, erosion protection may be required12 Line of 4:1 face slope angle13 Line of 1:1 face slope angle

Figure 2 - Reinforced fill earth with a vertical, battered or inclined face


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Facing units

Hard facing units: Hard facing units are usually produced in precast concrete, either un-

reinforced or reinforced.

Concrete facing units may be full height panels, partial height panels, sloping panels, planter units, or

segmental blocks. Many types of concrete facing units are proprietary and form part of proprietary

systems.

The reinforcements are connected to the units either by means of devices embedded or

inserted into the concrete units, or they are simply clamped between the units.

Full height panels: As the name suggests, full height panels (see Figure 3) are precast to the

required full height of the specific reinforced fill wall to be constructed. The breadth of full

height panels is typically in the range 1 to 3 m and the thickness in the range 100 to 200 mm.

Figure 3 - Full height panels

Partial height panels: Partial height panels (See Figure 4) are the most common and typically

have heights in the range 1 to 2 m and thickness in the range 100 to 200 mm. Distinctive shapes

correspond to specific ways of fitting panels together, and to particular construction

procedures. Simple rectangular shapes are also available. The panels are fitted with connecting

devices embedded into the back face. The edges are usually provided with nibs and recesses, or

tongues and grooves.

Figure 4 - Partial height panels


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Segmental blocks: Facing units in the form of precast or dry cast un-reinforced concrete blocks

(see Figure 5) are usually referred to as modular blocks or segmental blocks. Units may be

manufactured solid, or with cores. The mass of these units commonly ranges from 20 and 50 kilos.

Unit heights typically range from 150 mm to 250 mm, exposed face length usually varies from

200 mm to 500 mm. Depending on the type of reinforcement, blocks may be provided with

connecting accessories (pins, rake). Otherwise the reinforcement is clamped between successive

courses of blocks.

Figure 5 - Segmental blocks

Figure 6 - King post and concrete planking

Deformable facing units

Semi elliptical steel units: facing elements of steel sheet (see Figure 7) formed into elliptical or

U-shaped half cylinders. Such units, placed horizontally, are typically 2 to 4 mm thick, 250 mm to

400 mm high and a few metres long. They are fitted with holes along the horizontal edges for

connection to the reinforcements.

Figure 7 - Semi elliptical steel units

Steel welded wire mesh: Facing units may be formed of open-backed welded wire mesh sections

(see Figure 8), either flat or pre-bent to the required slope angle. These units serve as a formwork

during construction. When used for inclined faces, such units may be vegetated to prevent long


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term erosion of the face. When used for vertical or battered faces, such units may have an inner

layer of stone or crushed rock, or be backed with a geosynthetic liner, especially for temporary

applications.

Figure 8 - Steel welded wire mesh

Gabion baskets: Facing units may also be formed using polymeric geogrid or woven steel wire,

galvanized or plastic coated, or galvanized welded wire mesh gabion baskets (See Figure 9) which

are filled with stone or crushed rock. The size of such gabion baskets is usually in the range of

0,5 m to 1,0 m in height, 2 m to 3 m in length and 0,5 m to 1,0 m in depth. The gabion baskets may

be supplied with an extended tail that forms a frictional connection to the main reinforcement

Figure 9 - Gabion baskets

Tyres: Facing units may also be formed with tyres. These tyres are of similar size and are generally

stacked in a staggered arrangement to form the facing.

Soft facings units

The most widely used soft facing unit is the so called wrapped facing (See Figure 10) in which

full width reinforcement, such as polymeric grid or geotextile, or woven wire mesh, is extended

forward from the reinforced fill to wrap around the face of each intervening layer of fill. Where

polymeric grids or woven wire meshes are used these may be faced, or backed, with a suitable

geotextile to guard against erosion of the face.

To construct such slopes to an acceptable alignment it is common practice to use temporary

formwork.


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Key1 Bags

Figure 10 - Soft facing units

Some typical reinforcement forms


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Figure 11 Steel reinforcement

Figure 12 Polymeric reinforcements


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5. SOIL NAILING

The objective of soil nailing is to improve the stability of the soil in cases where the stability

conditions are adverse. The stability is achieved by inserting soil nails, consisting of reinforcing

bars, into the soil. Soil nailing is generally applied in connection with excavations, slopes and

occasionally tunneling and for improvement of soil stability. The soil nails mobilise frictionalforces along their entire length, which contributes to increasing the stability condition. The amount

of nails and the length of installation of the nails have to be adjusted in relation to the stability

conditions, encountered during the ongoing activities. Protection against corrosion in case of long-

term stability problems is required in aggressive soil conditions.

A soil nail construction can involve the following material components for:

a) soil nail system;

b) facing system;

c) drainage system.

Terms and definitions

bearing plateplate connected to the head of the soil nail to transfer a component of load from the facing or

directly from the ground surface to the soil nail

drainage systemseries of drains, drainage layers or other means to control surface and ground water

facingcovering to the exposed face of the reinforced ground that may provide a stabilising function to

retain the ground between soil nails, provide erosion protection and have an aesthetic function

facing drainagesystem of drains used to control water behind the facing

facing systemassemblage of facing units used to produce a finished facing of reinforced ground

facing unit

discrete element used to construct the facing

flexible facingflexible covering which assists in containing soil between the nails

hard facingstiff covering, for example sprayed concrete, precast concrete section or cast in-situ concrete

production nailsoil nail which forms part of the completed soil nail structure

reinforcing elementgeneric term for reinforcing inclusions inserted into ground


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reinforced groundground that is reinforced by the insertion of reinforcing elements

sacrificial nailsoil nail installed in the same way as the production nails, solely to establish the pullout capacity

but not forming part of the soil nail structure

soft facingsoft facing has only a short-term function to provide topsoil stability while vegetation becomes

established

soil nailreinforcing element installed into the ground, usually at a sub-horizontal angle, that mobilises

resistance with the soil along its entire length

soil nail constructionany works that incorporates soil nails, and can have a facing and/or a drainage system

soil nail systemconsists of a reinforcing element and may include joints and couplings, centralisers, spacers, grouts

and corrosion protection

test nailnail installed by the same method as the production nails for the purpose of verifying the pullout

capacity and durability, and could be forming a part of the structure

proof loadload applied in the testing

Examples of uses of soil nailing

Soil nail systems are produced using a wide range of materials and configurations.

Vertical walls Slopes

Figure 1 - Safeguarding stability of excavations by the use of soil nailing


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Tunnel excavationKey1 ground surface

2 soil nails

3 tunnel advances

Figure 2 Safeguarding tunnelling operations by the use of soil nailing

In the case of excavations, the sequence of excavation and soil nailing has to be adjusted in order

not to comprise the stability conditions of the site. Typical methods of excavation in combination

with soil nailing operations are illustrated in Figures 3 and 4.

Key1 excavation

2 installing the nails

3 reinforced shotcrete (or prefabricated facing panels)

4 next excavation

Figure 3 Typical sequences of excavation and installation

Key1 bulk excavation to proposed formation

2 berm

3 installed nails

4 existing ground

5 local trimming of face required to achieve agreed tolerances prior to nail installation of nail row "N"

N Nth row

Figure 4 Bulk excavation to form benches and face for row "N" of soil nails


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Reinforcing element

The reinforcing element of the nail is usually produced from metals (typically steel) and to a lesser

extent from other materials, such as fibre reinforced plastics, geo-synthetics or carbon fibre.

NOTE: The reinforcing element may be a solid bar, a hollow bar, an angle bar or some other form

of cross-section.

When nails are to be grouted, they may be ribbed or profiled to improve the effective bond with the

grout.

Examples of soil nail systems

The soil nail systems include reinforcement bars, usually steel bars, inserted into and bonded with

the ground to the depth required with regard to safety conditions, and often provided with a head

plate and a facing system to ensure stability between the nails and also to avoid erosion problems.

There is a number of different soil nailing systems. Typical examples are given in Figure 5.

a) Pre-bored and grouted b) Self-boring

Key1 facing 6 coupler

2 head plate 7 inner spacer3 locking nut 8 grout annulus

4 outer spacer 9 reinforcing element

5 duct 10 drill bit

Figure 5 Typical components of soil nail system, pre-bored & grouted shown

with hard/flexible facing

FACING SYSTEMS

Facing systems are constructed using a variety of materials, configurations and connections to the

reinforcement. Facings exposed to frost should be protected by frost insulation and extra drainage.

The facing system shall be able to sustain differential settlements required by the design without

structural damage to the facing.

The suitability of the facing system shall be proven by comparable experience or by tests, proving

the serviceability of the system and the durability of the materials used for the design life of the soil

nail construction.


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Examples of facing systems used in a soil nail structure

Hard facing

The combination of soil nails and facing has to fulfill the function of stabilising the slope between

the nails, and shall therefore be dimensioned to sustain the expected maximum destabilising forces.

Figure 6 Constructed hard facing with concrete (either sprayed or placed or precast)

(should be improved)

Figure 7 Strengthening of existing retaining structures (should be improved)

Flexible facing

Flexible facings are designed to provide the necessary restraint to the areas of slope face between

the bearing plates, as well as erosion control. The selection of type of flexible facing is dependent

upon slope angle, soil friction angle value, slope height and predicted loading. The common

flexible facings include geogrids steel fabrics and geosynthetic.

Figure 8 Wire mesh


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Soft facing

The primary function of soft facing is erosion control and protection against surface ravelling. In

many cases, the soft facing has to reinforce the vegetation layer, either in the temporary or the

permanent situation. In some instances, nails serve only to retain the facing and not to stabilise the

slope.

Without facings

Nailing in case of critically inclined sliding surfaces (e.g. rock strata with reduced shear resistance),

however with a stable surface.

DRAINAGE SYSTEMS

Water is detrimental to slope stability and has to be drained away from the surface as much as

possible. In this way, general or local erosion etc. and critical water pressures behind facings may

be minimised (specially important in case of a full cover or with a vegetation layer.

Three essential measures have to be distinguished:

a) prevention of surface runoff water;

b) surface drainage;

c) subsurface drainage.

Interception of surface water run off

Figures 9 and 10 show examples of drainage above the soil nailing structure.

Figure 9 Trenched drains above the soil nail structure guided to the sides of the slope

Key1 e.g. Y-drains

Figure 10 Surface drainage above the soil nail structure

(e.g. in case of stratum water)


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Surface drainage

Systems for flexible and soft facings with vegetation layers but also possible behind hard facings

(sprayed concrete).

Key1 foot drainage

Figure 11 Seepage

Drainage systems for hard and impermeable facings

In case of concrete walls, prefabricated or cast in place, spread filters made of drainage material

and collector drains can be applied.

In any case, with impermeable facings, sufficient leakage holes have to be placed.

Key1 drainage material

2 collector drain3 weep-hole drain

Figure 12 Hard and impermeable facings

Subsurface drainage

Subsurface drainage will be required if water-bearing strata are predicted or encountered.

Subsurface drainage may be required if the groundwater table has to be lowered. Drainage

boreholes normally contain slotted or perforated pipes. They are normally wrapped with a

geotextile filter to prevent the ingress of fines. The characteristic opening size of the geotextileshould be chosen to minimise clogging while permitting water into the pipe.


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The number, length and pattern of the drainage pipes depend on the expected amount and regime of

water. The inclination of the boreholes is typically 5 %.

Figure 13 Subsurface drainage


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6. BORED PILES

The construction of bored piles is covered by EN 1536.

Definitions

The term pile is used for circular section structure and the term barrette for other shapes. Both are

bored piles.

bored pilepile or barrette formed with or without a pile casing by excavating or boring a hole in the ground

and filling with plain or reinforced concrete (Fig. 1) Designation for bored pile are given fig.8

barrettediscrete length of diaphragm wall, usually short, or a number of interconnecting lengths cast

simultaneously (e.g. L-, T- or cruciform shapes), used to support vertical and/or lateral loads. (fig.2)

end bearing pilebored pile transmitting actions to the ground mainly by compression on its base.

friction pilebored pile transmitting actions to the ground mainly by friction and adhesion between the lateral

surface of the pile and the adjacent ground.

skin frictionfrictional and/or adhesive resistance on the bored pile surface

negative skin frictionfrictional and/or adhesive action by which surrounding soil or fill transfers downward load to a

bored pile when the soil or fill settles relative to the bored pile shaft

continuous flight auger pile (CFA-pile)pile formed by means of a hollow stemmed continuous flight auger through the stem of which

concrete or grout is pumped as the auger is extracted (see figure 11, figure 12)

prepacked pilepile where the completed excavation is filled with coarse aggregate which is subsequently injected

with cement mortar from the bottom up.

pile base groutingpressure injection of grout below the base of an installed bored pile base in order to enhance

performance

under load

pile shaft groutinginjection of grout carried out after bored pile concrete has set for the enhancement of skin friction

by the use of grouting pipes which are installed down the shaft, normally placed with the bored pilereinforcement


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enlarged basebase of a bored pile formed to have an area greater than that of its shaft. For bored piles, normally

constructed by the use of special underreaming or belling-out tools (see figure 3).

integrity testtest carried out on an installed bored pile for the verification of soundness of materials and of the

pile geometry.

sonic testintegrity test where a series of sonic waves is passed between a transmitter and a receiver through

the concrete of a bored pile and where the characteristics of the received waves are measured and

used to infer the state of continuity and section variations of the bored pile shaft.

sonic coringsonic integrity test carried out from core drillings in a bored pile shaft or from a pre-placed tube

system

test pilebored pile to which loads are applied to determine the resistance deformation characteristics of the

pile and the surrounding ground

trial pilebored pile installed to assess the practicability and suitability of the construction method for a

particular application.

static pile testloading test where a bored pile is subjected to chosen static axial and/or lateral actions at the bored

pile head for the analysis of its capacity.

maintained load teststatic loading test in which a test pile has loads applied in incremental stages, each of which is held

constant

for a certain period or until pile motion has virtually ceased or has reached a prescribed limit (ML -

test).

constant rate of penetration teststatic loading test in which a test bored pile is forced into the ground at a constant rate and the force

is measured (CRP-test).

dynamic pile testloading test where a dynamic force is applied at the pile or the barrette head for assessment of pile

capacity.

socketbottom part of a bored pile in hard ground (usually rock)

groutfluid mixture of a binding and/or setting agent (usually cement), fine aggregate and water that

generally hardens after being placed in position.


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Shapes

Bored piles can be of two kind of shapes: with circular shape (see figure 1) and barrettes (see figure 2), provided the section is concreted in a single operation.

Bored piles can have:

uniform cross-section (straight shaft); telescopically changing shaft dimensions; excavated base enlargements; or excavated shaft enlargements

Te European Standard EN 1536 applies to bored piles with the following dimensions:

depth to width ratio larger or equal to 5 ; shaft diameter : 0,3 D 3,0 m (see figure 1, figure 3); dimension for barrettes :

Wi 0,4 m (see figure 2);

ratio between the dimensions :Li / Wi 6

where:

Li is the largest dimension of the barrette and

Wi is the least dimension of the barrette;

cross-sectional area of barrettes : A 10 m ;


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The European Standard EN 1536 also apply to piles with the following rake (see figure 4):

n 4 ( 76) ; n 3 ( 72) for permanently cased piles.

Shaft or base enlargements covered by the European Standard EN 1536 are:

base enlargements in non-cohesive ground :

DB/D 2 and

in cohesive ground :DB/D 3;

shaft enlargements in any ground : DE / D 2; slope of the enlargement in non-cohesive ground :

m 3 and

in cohesive ground : m 1,5

(see figure 3).

The provisions of the European Standard EN 1536 apply to:

single bored piles; bored pile groups (see figure 5); walls formed by piles (see figure 6).


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The bored piles which are the subject of the European Standard EN 1536 can be excavated by

continuous or discontinuous methods using support methods for stabilizing the excavation walls

where required.

Bored piles can be constructed:

of unreinforced (plain) concrete, of reinforced concrete, of concrete reinforced by means of special reinforcement such as steel tubes, steel sections

or steel fibres,

of precast concrete (including prestressed concrete) elements or steel tubes where theannular gap between the element or tube and the ground is filled by concrete, cement or

cement-bentonite grout.

(see figure 7).


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Excavation

When constructing bored piles measures shall be taken to prevent uncontrolled inflow of water

and/or soil into the bore.

An inflow of water and/or soil could cause for instance :

a disturbance to or instability of the bearing stratum or the surrounding ground; loss of support by the removal of soil from beneath adjacent foundations; unstable cavities outside the bored pile; damage to the unset concrete in the bored pile or bored piles recently installed nearby; voids in the shaft during concreting; washing out of cement.

There are increased risks in : loose granular ground; soft cohesive ground; or ground which is variable.


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In soils liable to flow into the bore or where there is a risk of collapse, means of support shall be

used to maintain stability and thereby prevent the uncontrolled entry of soil and water.

Common means of support of bore walls are :

casings;

support fluid; soil-filled auger flights.

Bored pile bores shall be excavated until they reach :

the specified bearing stratum, or the anticipated founding level,

and shall be socketed into the founding material where and as required by the design.

In cases of

unfavourable stratification of the bearing layers, founding on bedrock, or

sloping surface of the bearing layersthe excavation shall be carried down to provide full face contact.

Bored piles can be excavated in an intermittent or continuous process :

tools for intermittent excavation are for example: grabs, shells, augers, boring buckets and

chisels ;

tools for continuous excavation are for example: augers, drilling or percussion tools for

excavation combined with

augering or flushing methods for soil removal.

The employment of

temporary or permanent casings support fluids, or soil-filled flights of a continuous flight auger

can be necessary to support the excavation walls.

The type of boring tool shall

be appropriate to the given soil, rock, groundwater or other environmental conditions, be selected with a view to preventing loosening of material outside the bored pile and below

its base, and

allow the bores to be excavated quickly.

It can be necessary to change the method or tool employed to meet the requirements.

Special tools and/or techniques other than those used for excavation may be used for the cleaning

of bases.

In situations where water or support fluid is present inside the bore, the choice and operation of

tools shall not impair bore walls stability.

A piston effect with negative influence on the stability of the bored pile walls can occur and the

operating speed of the tool should be adapted accordingly.

Excavations supported by casings

Raking piles shall be cased over their entire length if their inclination is: n 15 (86) unless it can

be shown that uncased bores will be stable (see figure 4).


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Casings may be installed during the excavation process using :

oscillating or rotating equipment

or they may be driven prior to the excavation using :

piling hammers or

vibrators or other.

Where a bored pile is excavated

below the groundwater table in permeable ground, or in artesian conditions

an internal excess pressure shall be provided within the casing by a head of water or other suitable

fluid of not less than 1,0 m which shall be maintained until the bored pile has been concreted.

In unstable bores the casing shall be maintained in advance of boring.

The advancement in relation to the excavation shall be adjusted to suit the ground and groundwater

conditions.

The insertion of the casings ahead of boring is necessary to prevent an inflow of soil and

disturbance below the bored pile base which can affect the bored pile performance ("caving in",

"bottom heave"). The creation of a cavity outside the casing can endanger the integrity of a

concreted bored pile if and when the casing is withdrawn ("necking").

Zones of loosening can also move upwards to the surface and can there cause subsidence.

Excavations supported by fluids

The properties of a support fluid shall be in accordance with previously given conditions.

There are two types of excavations supported by fluids: direct circulation boring system (fig. 9) reverse circulation boring system (fig. 10)

The upper part of an excavation shall be protected by a lead-in tube or guide wall

to guide the boring tools; to protect the bore walls against collapse of upper loose soils; and for the safety of site personnel.

At all times during boring and concrete placement the level of support fluid shall be maintained :

within the lead-in tube or the guide wall, and at least 1,5 m above the external ground-water level.

Boring with continuous flight augers

Piles may be formed without other means of support of the bore, by using a continuous flight auger

in such a way that the stability of the bore is preserved by the material on the flights (fig.11, fig.12).

Continuous flight auger piles shall not be constructed with inclinations of n 10 (84), unless

measures are taken to control the direction of the excavation and the installation of the

reinforcement.

Boring with continuous flight augers shall be carried out as fast as possible and with the least

practical number of auger rotations in order to minimize the effects on the surrounding ground.


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Where layers of unstable soil are encountered with a thickness of more than the pile diameter, the

feasibility of the construction shall be demonstrated by means of trial piles or local experience

before the commencement of the works.

Unstable soils are considered to be :

uniform non-cohesive soils (d60/d10 < 1,5) below the groundwater table; loose non-cohesive soils with relative densityDr< 0,3; clays with high sensitivity; cohesive soils with undrained shear strength cu < 15 kPa.

Uniform non-cohesive soils with 1,5 < d60/d10 < 3,0 below the groundwater table can be sensitive.

During excavation the advance and speed of rotation of the auger shall be adjusted in accordance

with the soil conditions so that soil removal is limited to such an extent that :

the lateral stability of the bore wall will be preserved, and over-excavation will be minmized.

For this the boring tool shall be provided with sufficient torque and traction power.

The pitch of the flights shall be constant over the whole length of the auger.

A system of closure shall be provided in the hollow auger stem to prevent the entry of soil and

inflow of water during drilling.

When the required depth has been reached, the auger shall be lifted from the bore only if

the surrounding ground is stabilized by the rising concrete, or the surrounding ground remains stable.

If a pile can not be completed and the auger has to be removed, the auger shall be withdrawn byback-screwing and the bore hole shall be back-filled with soil or support fluid.

Unsupported excavation

Excavation without the provision of support to bore walls is permissible in ground conditions

which remain stable during excavation and where a collapse of ground material into the bore is not

likely.

The stability of the unsupported excavation shall be demonstrated by means of trial bored piles or

comparable experience before the commencement of the works.

The upper part of the excavation shall be protected by a lead-in tube unless

the excavation is carried out in firm soil, and the diameterD is smaller than 0,6 m.

Concreting and trimming

The interval between completion of excavation and commencement of concrete placement is

required to be kept as short as possible.

Prior to concrete placement the cleanliness of the bore shall be checked.

The bored pile trimming operation:

shall be carried out only when the concrete has obtained sufficient strength,


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shall remove all concrete which is contaminated or of lower quality than required from thetop of the bored pile, and

shall continue until sound concrete over the whole cross section is revealed.

Concreting in dry conditions

The procedure for placing concrete in dry conditions shall not be followed if there is standing waterat the base of the bore.

A check shall be carried out immediately before the placement.

If water is recognized concrete should be placed as for submerged conditions.

Concreting shall be carried out in such way as to avoid segregation. The concrete shall be directed

vertically into the centre of the bore by means of a funnel and an attached length of pipe so that the

concrete does not hit

the reinforcement, or

the walls of the bore.

The internal diameter of the concreting pipe shall not be less than 8 times the maximum size of the

aggregate.

Concreting in submerged conditions

In order to avoid mixing between concrete and bentonite, the instantaneous velocity of concrete

rising should not be less than 3 m/h.

The main purpose of the tremie pipe is the prevention of segregation of the concrete during

placement or its contamination by the fluid inside the bore.

Submerged concrete shall not be compacted by internal vibration.

Compaction is dependent on the flow characteristics of the concrete in relation to its self weight

and the surcharge of the fluid above the concrete column.

The tremie pipe, including all its joints, shall be water tight.

It shall be equipped at its upper end with a hopper to receive the fresh concrete and prevent spillage

of concrete which otherwise could fall freely into the bore, segregate or become contaminated.

The tremie pipe shall be smooth to allow free flow of concrete and have a uniform internal

diameter of at least

6 times the maximum size of the aggregate, or 150 mm

whichever is the greater.

The external shape and dimension of the tremie pipe, including its joints, shall allow its free

movement inside the reinforcement cage.

The maximum outside diameter of the tremie pipe including its joints should be not more than: 0,35 times the pile diameter D or the inner diameter of a casing ; 0,6 times the inner width of the reinforcement cage for piles; and 0,8 times the inner width of the reinforcement cage for barrettes.


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The immersion of the tremie pipe into the concrete should be not less than 1,5 m, particularly when

disconnecting sections of the pipe and when recovering and disconnecting sections of temporary

casing.

For piles with a diameterD 1,2 m the immersion should be at least 2,5 m and for barrettes at least

3,0 m, particularly when two or more tremie pipes are used.

When concrete is placed under support fluid:

a sample of the fluid shall be taken from the base of the bore, and any major filtercake or debris shall be removed from the bottom of the bore

immediately before the start of the placement.

Extraction of casings

The extraction of temporary casings shall not begin until the concrete column has reached a

sufficient height inside the casing to generate an adequate excess pressure.

to protect against inflow of water or soil at the tip of the casing; and to prevent the reinforcement cage from being lifted.

The extraction shall be carried out while concrete is still of the required consistency.

During the continued extraction a sufficient quantity and head of concrete shall be maintained

inside the casing to balance the external pressure so that the annular space vacated by the removal

of the casing is filled with concrete.

The supply of concrete, and the speed of extraction of the casing shall be such that no inflow of soil

or water occurs into the freshly placed concrete, even if a sudden drop of concrete level should

occur when a cavity outside t

Documents

Special Foundation Works Curs-transfer Ro-21mar-4b1ccc