veloso presentation

7/29/2019 Veloso Presentation

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How to Enhance Ground Anchors Capacity in Soft Soils

POST GROUTED TECHNIQUES, A SOLUTION FOR ANCHORS

Veloso, Goncalo A. Geotechnical Engineer

Introduction

S.B.M.A. Technology

Post grouting Techniques and Design

Investigation Tests Results

Applications


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When permanent anchorages are required on a retaining structure, the firstconcerns for the geotechnical engineer are the ground conditions and the

anchor achievable capacity


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We design our anchors based on the existing ground properties, not thestrand capacity

S.B.M.A. Single Bore Multiple Anchor system

Can provide double the capacity of conventional anchors


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POST GROUTING TECHNIQUES AND DESIGN

As an alternative to conventional grouting techniques, anchors can be designedusing post grouting techniques, enabling the enhancement of the properties of

the soils and therefore increasing the capacity of the anchorages system

Grout up BoreholeGrout up BoreholeInsert anchor strands togetherInsert anchor strands together

with a post grouting pipe withwith a post grouting pipe with

manchetesmanchetes (TAM)(TAM)

4 8 HoursLater

Drill BoreholeDrill Borehole

Post GroutingPost Grouting

11stst StageStagePost GroutingPost Grouting

22ndnd StageStage

4 8 HoursLaterRepeat if

required

7 days after

PrePre--stressstress

ConclusionConclusion


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The design of a ground anchor in cohesive soils is done using the followingequation (Littlejohn, 1970) :

CuLDTf xxxx =

lengthfixedoverstrengthshearundrainedAverage-

factorAdhesion-

lengthanchorFixed-

DiameterBorehole-

LoadWorking-

Cu

L

D

Tf

0.45=This means that with conventional grouting techniques in cohesive soils,less than half the clays undrained shear strength is mobilized in tension.


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The design of a ground anchor in cohesive soils is done using the followingequation (Littlejohn, 1970) :

CuLDTf xxxx =

341 to.=

This means that with post grouting techniques in cohesive soils, we canenhance the working capacity of anchors up to 3 times or more aconventionally grouted anchor.

After post groutingAfter post grouting


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Post Grouting effect:


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Enlarged fixed length diameter by post grouting


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Post Grouted fissures in stiff Clay


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Section of exhumed post grouted anchor


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Section of exhumed post grouted anchor

BoreholeBorehole DiamDiam = 150mm= 150mm

Max.Max. DiamDiam. After post. After post

grouting = 210mmgrouting = 210mm


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INVESTIGATION TESTS RESULTS

Earlier this year were carried out investigation tests, to determine the

behaviour of post grouted S.B.M.A. anchors compared to conventionallygrouted S.B.M.A.s and determine the enhancement achieved by the use ofthese techniques.


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INVESTIGATION TESTS RESULTS

The results exceeded our expectations and the following results were

obtained:

For conventionally grouted S.B.M.A anchors

Average bond stress mobilized:

Up to 150 kN/m2

For Post grouted S.B.M.A. anchors

Average bond stress mobilized:

up to 450 kN/m2


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APPLICATIONS

-Installation of anchors in poor ground conditions

-Reduce the number of anchors on a project by proposing to the clienthigher loads and larger spacing between anchors

-Reduce the overall length of the anchor when space restrictions exist


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THANK YOU FOR YOUR TIME

WWW.KELLER-GE.CO.UK

WWW.SBMASYSTEMS.COM

WWW.THEANCHORMAN.COM
http://www.keller-ge.co.uk/http://www.sbmasystems.com/http://www.theanchorman.com/http://www.theanchorman.com/http://www.sbmasystems.com/http://www.keller-ge.co.uk/

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