soil nailing - design nail stabilisation

8/19/2019 Soil Nailing - Design Nail Stabilisation

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SOIL NAILING

:Software

SNAP-2 (Soil Nail Analysis Program)

https://www.fhwa.dot.gov/engineering/geotech/software/snap2/snap2.zip

Dr Hammida


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Soil nailing

بی یحث ل س و- ا رد جل ا ةب ر- ما سمل ا ب ةدن ا سل ا

یة ب ا رت ل ا تارد حن م ل ا بی ث يف ریما سمل ا ةی ن ق مدخت ست س الا نا ر د جل ا ةی دا ا ف ن ألا ولای عد حایسی سأ ت ل ا

لخص ت و .ةق ی معل ا ق ی رطلا زرغ يفا ب ضق ةل ی وط ةی ن دعماذطق م ل ا م ا م ا ر ی غ صل ا ثی ح ب ھم ی عد دا ر م ل ا ردحن م ل ا

ترق ھ خ ا ب ضق ل ا ف ا س م ىلإ ةب رت ل ا ةلت كا دعاب ن ود د حم ا ی ھن الا طور خم جرا خ ةق طن م يف ةت ب ث مثیحن م ؤ ی

قرار سطح ت سا ب رت ل ا م ةق ی ق ر ةی طغ ة ق ب طب ردحن م ل ا ھج نة اعلى و ا س رخل ا وا رجحل ا و ذ ق م ك ب ش ب ةحل س م ی مدعم

یة ن دعم ی ب ث ة حی ف صب فوذق م ل ا نوت ی ب ل ا ةق ب ط ىلع ھسف ن را م سم ل ا امیر ویثب سمل ا نیب ةب رت ل ا زجح اھت مھم ةی ئ ا شن إ

لشك ا ةع ب ر م


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been used instead of shotcrete. Bearing plates are then fixed to the heads of the soil

nails. The soil at the base of this first stage is then removed to a depth of about 3 to 6

feet. The installation process is repeated until the design wall depth is reached. The

finished soil nails produce a zone of reinforced ground.


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details of a soil nail wall:


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Soil nail provides a resisting force against slope failures.

- Its construction process is faster than other similar methods. The

construction procedure starts, drilling into the soil, where the nail, steel

bar, is going to be placed. After the drilling has been completed, exact

depth must be provided by the geotechnical engineer, the nail must be

inserted into the drilled hole. Then, it must be grouted into the soil to

create a structure similar to a gravity wall. After placing the nail, a shot-

Crete layer is usually placed as a facing material, to protect the exposed

nail, and then other architectural options are placed over the shot-Crete,

creating an aesthetic finish to the project .

- The grouted soil nail hole typically has a minimum diameter of 4

inches. Centralizers are placed around the soil nail to maintain an

even thickness of grout around the bar. For permanent

applications, nails may be epoxy-coated or provided with a

protective sheath for corrosion protection


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SOIL NAILING

Soil nail concept: Unlike the ground anchor that stresses to "seal" the

ground, soil nail is "passive", that is, it develops tension only as the grounddeforms laterally. Soil nails are normally used to stabilise natural or

excavation slopes.


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1) face failure seems to be a structural failure of the concrete facing, mostly

un-related to the soil nail or screw. If you are able to successfully install the

nail and facing, then face failure should not happen.

2) screws may have more uniform tension along nearly the entire length of

the rod, as the anchoring helix is generally on the end.

3) screws do not impart as much stress into the looser surface zones,instead they only anchor in the competent material where the helices are.


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Strand Anchor post Tension - شد ال


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Strand Anchor


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The difference is in soil nails vs. tieback anchors

Soil nails are usually shorter with much lower lower design loads than

tieback anchors. In length, soil nails usually are between 70% AND

100% x the wall height .

Grouted tieback anchors are usually longer than 30 feet with 40 to 60feet being more normal for most applications . Sometimes, tieback

anchors are much, much longer than 60 feet.

Soil nails are usually installed at closer spacings than tiebacks. Nails

may be installed at an area of approximately 25 SF per nail (5' x 5')

while tiebacks may be installed at an area of approximately 120 SF per

nail (sometimes more, sometimes less).

Tiebacks are active support members. They push on the retained soil

harder than the earth and surcharge pressures would push on the

wall. Soil nails are passive support members. They provide their

support as the soil mass begins to mobilize.

Both soil nails and tieback anchors might have similar corrosion

protection details. Every tieback anchor is usually proof or

performance tested.

Most soil nails are not tested. Usually a small percentage of the nails

are tested or non-production nails are tested.

Soil nail tendons are usually Grade 60 or 75 threadbar

tendons. Tieback tendons are usually either threadbar tendons (Grade

60 to Grade 160) or multi-strand tendons (Grade 270).

Soil nail walls are soldier beamless walls. Shotcrete and nails are thesupport. There may be a second or permanent facing of shotcrete or

even a precast facing attached to the nails.


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Tiedback walls often use soldier beams, lagging, and tiebacks with a

precast or cast in place concrete permanent facing when required.

Soil nail walls become economical when the retained soils have a little

cohesion and when it may be expensive to install soldier

beams. Uncontrolled ground water can be a big problem when

constructing either tiedback or soil nail walls.

Both tiedback and soil nail walls are meant to be constructed from the

top down, in a cut situation.

If your wall is a fill or embankment wall, anchored walls are usually not

the best wall type. Try an MSE wall or conventional concrete wall.

Tiebacks can be made in most types of soil except soft clays and silts,and in all types of rock. The capacity of the anchors in soil will varydepending upon grain size and installation method. The denser,granular soils will typically produce higher capacity tiebacks. We haveinstalled tiebacks with lengths in excess of 200 feet and testedcapacities of over 500 kip for landslide stabilization

Soil Nailing works – 1


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The excavations work has left a 4.5 meter high 60° battered banking to

the rear of the proposed dwellings. The banking is to be retained by

driving 5 meter long steel nails into the ground at 1 meter centres. ‘

Soil Nailing works – 1-1

Deep excavationEarth nailingEarth protectionEarth work

ExcavationShore protectionsoil nailingThe excavations work has left a 4.5 meter high 60° battered banking to the rear of

the proposed dwellings.The banking is to be retained by driving 5 meter long steel nails into the ground at 1 meter

centres.


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‘X’ marks the spot.


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once all the nails are in place they will be covered with a stone

wall.

Soil nailing – 2

The basic principle of soil nailing is to place rebar into the

natural soil in an effort to increase its tensile strength and shear

strength. Soil nailing is used when the natural soil has adequate

compressive


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Soil nailing – 2-1


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Soil nailing is used when the natural soil has adequate compressive

strength, but low levels of tensile and shear strength. In this condition,

soil nailing serves to improve the load-bearing behavior of the natural

soil.

The original subsoil is therefore turned into a composite body which, in

terms of load-bearing behavior, is similar to a gravity wall capable of

taking up external forces so that the soil is integrated into the structure as

a structural component.

Soil Nails – 3

Construction of a Soil Nail Wall Excavate soil Drill hole Install and grout nail Test selected nails Place reinforcement Place shotcrete

Finish shotcrete Install Did, than brand


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Soil nail wall construction sequence


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Wedge analysis – Nails Design The equilibrium of a simple triangular active failure wedge behind the excavation

face was examined to estimate the development of axial soil nail forces in response to

the deepening excavation (Figure 10).

This approach is commonly used for soil nail design, although the complexity of the

mechanisms varies (SAICE 1989). For the

problem modelled in the centrifuge, only three forces were considered: the self-weight

of the failure wedge = (W)

the resisting force mobilised on the failure plane (R) and the sum of the individual

soil nail forces (T).

For a fully mobilised failure mechanism the resisting force R would act at an angle φ

as shown in Figure 10, where φ is the soil friction angle. The soil nails were assumed

to carry only axial loads, disregarding any bending or shear stiffness they might

possess.

The failure wedge was assumed to mobilise at a slope angle β. This slope anglew asvaried to find the maximum axial soil nail force (T). For a horizontal soil surface and

smooth vertical retaining wall, the wedge analysis provides the same solution as the

active Rankine earth pressure case

The soil nail loads were calculated for various depths of excavation by simply

dividing the total calculated soil nail force (T) by the number of nails intersecting the

failure wedge. The calculated forces (based on horizontal soil nails) are plotted with

the observed loads. As no failure wedge intersects soil nails for excavation depths of

up to 30 mm (1.5 m at prototype scale), zero soil nail force was assumed up to thisdepth.


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ails Reinforcement Design

self-weight of the failure wedge = (W )


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nail force = (T )

active Rankine earth pressure =( R )


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SMSE wall for steep terrain.


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soil nailing - design nail stabilisation

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