Anchors, Dewatering, Protection Monitoring

Lecture #11 Anchors, Dewatering,

Protection of adjacvent buildings, Monitoring

Talajhorgonyzs (Meszlnyi Zs.) 2

Ground anchors - terms

Ground anchor : A structural element which transfers forces from the supported structure to tghe ground

_____________________________________ Anchor head : transferring load to the

structure (fixing, pre-stressing)) Free section : Connection between

fixed section and anchor head Fixed section : load transfer to soil (behind slip surface, overall

stability!) _____________________________________ HIGH RISK STRUCTURAL ELEMENT

!!!! Can cause progressive failure


Typical applications

Support of retaining structures Tunnel lining


Typical applications - EXAMPLE



Bridge abutment taking the horizontal forces Protection against uplift


Typical applications - EXAMPLE

Sheet piling temporary working platform anchoring concreting (under water level) pre-stressing



Ensuring the stability of high structures Protection against forces caused by flowing water



slope protection (e.g. rock slopes) Harbor


Ground anchor classification

based on life span: - temporary , T 2 years (e.g. deep excav.) - permanent (e.g. bridge abutment) corrosion! (soil conditions + life span) Type of fixed section: - grouted (load transfer by shear stress) - mechanuical (e.g. umbrella) - expanded body Cast: - precast - cast in place (temporary only !)


Grouted anchors Fixed section is the

grouted part (prestressing)

load transfer by shear stresses

Advantegous in dense (e 0,6) granular materialand stiff calys (Ic > 1,0)

Most typical in Hungary


Mechanical anchors Fixed section provided by a mechanical structure installation by driving pulling out causes the opening of the wings Resisance is caused by the passive resistance of the soil Larger movements at prestressing (special machine) temporary, small forces


Expanded anchors

An expanded body is driven in the soil

Inflating the body Resisance is caused

by the passive resistance of the soil

Advantageous in soft soils


Expanded anchor


Expanded anchor

Fixed section different stages


Grouted anchor

grouting tubes outside Anchor head


Grouted anchors Elements:

steel bar, threaded

Head : plate + screw nut

Conical tip

Ribbed PVC tube (fixed)

Smooth PVC tube (free)

Inner and oter grouting tubes

Spacer


Geometry

Anchor head above groundwater level (if possible)

Inclination between 15-30

Fixed section in good bearing capacity soil behind active slip surface

Internal stability (stability of the soil wedge)

Length of fixed section (experience), generally 6,o-8,o m

SOIL EXPLORATION


Construction


Horgony frsa friszappal (talajvz felett)


Talajvz alatti horgony pakker , vzelzrs


Horgony ellenrz fesztse


Elkszlt fesztett blokkolt horgony

Dewatering > Goals of dewatering

1. To keep the excavation

bottom dry

2. To prevent leakage of

groundwater or soils

3. To avoid sand boiling

4. To avoid upheaval failure

5. to keep the basement floor

from floating

http://www.dewateringconsultants.com/

Dewatering > Goals of dewatering > keeping the excavation bottom dry

Required depth of water table (below excavation bottom)

0.5 m if no heavy machines are present

1.0 m if heavy machines are working at the bottom of the

excavations

Dewatering > Goals of dewatering > preventing leakage

When using not perfectly water tight

structure (e.g. bored piles, sheet piles)

in sandy-gravelly soils with high

groundwater level, the defection of the

retaining wall may result in leaking of

water and/or soil to the excavation

Dewatering > Goals of dewatering > to avoide sand boiling

As the water level is lowered at the excavation bottom, a permanent potential

difference is caused and a permanent seepage is generated.

At the bottom the flow

direction is vertical (upward).

If the critical hydraulic gradient

is reached quick condition or

sand boiling occurs

(the seepage force equals

the weight of the soil).

Protection:

- increasing the flow path,

- decreasing the pressure difference

Dewatering > Goals of dewatering > to avoide upheaval failure

If the excavation is performed in low permeability (e.g. clay) layer underlain by a

large permeability (e.g. sand or gravel) layer, the excavation bottom can be

subjected to a significant water pressure.

If the water pressure is larger than the weight of the soil, upheaval failure occurs.

Dewatering > Goals of dewatering > to avoide basement floating

Dewatering > Methods > Open sump method

Dewatering > Methods > Open sump method

- Commonly used

- Very economical

- In high permeability soils large influence zone significant amount of water

- In low permeability soils local effect closer ditch spacing

Dewatering > Methods > Deep wells

Dewatering > Methods > Deep wells

- Tyical diameter: 120-200 mm

- Wells are to be located in the vicinity of the excavation

- In high to moderate permeability soils large influence zone significant amount of water

- In low permeability soils local effect closer ditch spacing (often well point is more economical)

Dewatering > Methods > (Vacuum) Well point

Dewatering > Methods > Well point

Dewatering > Methods > Well points

- Forced draining

- Wells are to be located in the vicinity of the excavation

- Can be used effectively in the case of low permeability soils

Dewatering > Methods > Well point

2008 PJ

Impervious layer

q

r1 r2

r

dh

dr

h2 h1 h

[ ]hr2

=

1

2

1

2

h

h

r

r

dhhq

k2r

dr

( )22212

1

hhrrln

qk

=

vAq =

drdhk=q

Field determination of k Pumping test test

2008 PJ

ASSUMPTIONS:

The groundwater is infinite in horizontal direction

The soil layer is homogeneous horizontal, has a constant thickness

The groundwater supply is ensured

The well is deepened to and impervios layer

The coeeficient of permeability is the same in each direction .


2008 PJ

t

y L

2r

ty

yr

Ly2

rL20

40k

+

=

q

y


Dewatering > Appropiate dewatering method

Dewatering > Influence range

Protection of adjacent buildings

Monitoring

Allowable settlements > Deformation types

Allowable settlements > Limiting values of deformation

Deep excavation Theory and practice

Allowable settlements > Limiting values of deformation

Deep excavation Theory and practice (Yen and Chang, 1991)

Allowable settlements > Decreasing movements

Soil improvement

chemical grouting, jet grouting

deep mixing

micropiles

Taking into account the characteristics of excavation induced defromation

reducing the unsupported length

decreasing the influence of creeping (reducing construction time)

corner effect

Increasing the stiffnes of strut-retaining structure system

increasing strut stiffness

increasing wall stiffness

cross or counterfort walls

Allowable settlements > Movements caused by construction defects

Leakage Dewatering

Removal of

sheet piles

Monitoring

Monitoring > Strain gauges > basic principle

Monitoring > Measurement of movements > retaining wall deformation (inclinometer)

Monitoring > Measurement of movements > Building settlement

Monitoring > Measurement of stresses > Earth pressure

Monitoring > Measurement of stresses > Water pressure

Underground structures, Deep Foundation Ground anchors - termsTypical applicationsTypical applications - EXAMPLETypical applicationsTypical applications - EXAMPLETypical applicationsTypical applicationsGround anchor classification Grouted anchorsMechanical anchorsExpanded anchorsExpanded anchorExpanded anchorSlide Number 15Grouted anchorGrouted anchorsSlide Number 18GeometryConstructionHorgony frsa friszappal (talajvz felett)Horgony frsa friszappal (talajvz felett)Talajvz alatti horgony pakker , vzelzrsSlide Number 24Horgony ellenrz fesztseSlide Number 26Horgony ellenrz fesztseElkszlt fesztett blokkolt horgonyDewatering > Goals of dewateringDewatering > Goals of dewatering > keeping the excavation bottom dryDewatering > Goals of dewatering > preventing leakageDewatering > Goals of dewatering > to avoide sand boilingDewatering > Goals of dewatering > to avoide upheaval failureDewatering > Goals of dewatering > to avoide basement floatingDewatering > Methods > Open sump methodDewatering > Methods > Open sump methodDewatering > Methods > Deep wellsDewatering > Methods > Deep wellsDewatering > Methods > Deep wellsDewatering > Methods > (Vacuum) Well pointDewatering > Methods > Well pointDewatering > Methods > Well pointDewatering > Methods > Well pointsDewatering > Methods > Well pointSlide Number 45Slide Number 46Slide Number 47Dewatering > Appropiate dewatering methodDewatering > Influence rangeDewatering > Influence rangeDewatering > Influence rangeProtection of adjacent buildingsMonitoringAllowable settlements > Deformation typesAllowable settlements > Limiting values of deformationAllowable settlements > Limiting values of deformationAllowable settlements > Decreasing movementsAllowable settlements > Movements caused by construction defectsMonitoringMonitoring> Strain gauges > basic principleMonitoring > Measurement of movements> retaining wall deformation (inclinometer)Monitoring > Measurement of movements> retaining wall deformation (inclinometer)Monitoring > Measurement of movements> retaining wall deformation (inclinometer)Monitoring > Measurement of movements> retaining wall deformation (inclinometer)Monitoring > Measurement of movements> Building settlementMonitoring > Measurement of stresses> Earth pressureMonitoring > Measurement of stresses> Water pressure

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Anchors, Dewatering, Protection Monitoring