north bexhill access road - ground engineering

North Bexhill Access Road:Use of Ground Improvement by CMCs to Support a Reinforced EarthEmbankment

Frederic Bedoin – VM Chief Engineer

Josh Chastney – CR Geotechnical Engineer

9-Oct-18 Ground Engineering - Transport Geotechnics - 03/10/18 1

North Bexhill Access Road Project Introduction

Project Overview and constraints

Ground Conditions / Geotechnical Hazards

Initial Proposals

Alternative VE Solution

CMC Rigid Inclusion

Design Principles

Methodology

FE models

Conclusions

Agenda

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North East Bexhill

Gateway Road (2015)

HASTINGS

BEXHILL

Bexhill to Hastings

Link Road (2015)

Queensway Gateway

Road (2016-2018)

H

E

E

H

North Bexhill Access

Road (2016-2018)

North Bexhill Access Road,

East SussexPart of Bexhill to Hastings strategic network

E

Project Overview

9-Oct-18 Ground Engineering - Transport Geotechnics - 03/10/18

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North Bexhill Access Road Alignment

Sidley (A269)

Project Specifications

£15.0m scheme.

Lead Designer: CampbellReith

2.4km single carriageway road linkingSidley in the west and the Bexhill andHastings to the east.

Constraints Crossing the Combe Haven Valley

Within a Flood Plain

Presence of an ecological corridor

Road level required at 6m above thewatercourse.

Deep Alluvium

Original Proposal –Piled Bridge


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20m clear span bridge with piledabutments.

1 in 3 unreinforced embankmentslopes.

Driven piles + LTP below approachembankments.

Flood plain maintained underlyingbridge and with floodcompensations ponds

Ecological corridor maintainedunderlying bridge

Ground Conditions


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Majority of alignment directly underlain bysilts and clays of the Tunbridge WellsSand and the Wadhurst Clay.

Ground Investigation within the vicinity ofthe Combe Haven revealed a buriedvalley infilled with alluvium up to 8m bglcontaining fibrous peat layers up to 1m inthickness.

Strong limestone encountered withinbedrock strata at depth.

Shallow groundwater and within an areasusceptible to flooding.

Weathered

Bedrock

Flood Plain

Ground Conditions


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Weathered

BedrockPeaty Alluvium

Geological Cross Section


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Combe Haven Watercourse

Original Ground Profile

Superficial Alluvium Infilling

Buried Valley

Finished Road Level

CPT Log


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Soil Conditions

Soft alluvium with bands of peat: upto 6.5m thick, qc=0.5MPa

Weathered Mudstone: 2m thick,qc=1MPa

Mudstone beyond: qc>4MPa

Value Engineered Solution (70 degree reinforced slopeand CMCs) 10

Embankment with 70⁰Reinforced Earth slope.

Precast culvert instead ofbridge.

Ground Improvement : CMCs

Load Distribution Mat of600mm

Increased area of floodcompensation ponds

Inclusion of numerousmammal and amphibiantunnels.

Design Life: 120 Years.

CMC Rigid Inclusions


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Design Principles

Group of concrete or mortar unreinforced* columns installed with a displacement* tool down to a more

competent layer

Increase the stiffness of the soil mass to globally reduce both total and differential settlements by

sharing the load of the structure between the soils and the CMC

To be associated with a distribution mat under uniformly distributed loads (slabs, embankments)

Worldwide recognized technique

0

500

1000

1500

2000

2500

3000

0

50

100

150

200

250

300

350

400

450

Cum

ula

ted

Yearly



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Design Principles

Piles CMC

100% of the load

in the piles

No load in the soil

Share of the load

between the CMC

and the soil

EmbankmentEmbankment

WP/LDM (granular layer)LTP (geogrid)

WPBasal reinforcement

(not systematic)



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Design Principles

Load Sharing System

Load Distribution via a Load Distribution Mat (not a LTP as per BS8006 definition)

Load-bearing layer

QP(0) + FN = Qmax = FP + QP(L)

Dense soil

Soft

soil

Distribution

mat

Rigid

inclusions

q0 QP(0) QP(0)

qS qS

QP(z)

z z

FP

FN

N N

hc

QP(L) QP(L)



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Methodology

CMCs embedded 0.5 to 1m within stiffer material (weathered Mudstone)

Use of a Soil Displacement Auger (Minimum spoils)

Grouting whilst extraction of the tool under low pressure

1 - Drilling down to the stiff layer:- horizontal soil displacement

- no surface spoils

2 - Grouting up to the surface:- computer control Improved soil/column friction ratio

No surface spoils

Soil displacement



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Finite Elements Calculations

Long Section for settlements:

Total < 75mm,

Differential < 1/250

Verification of the interface with existing

embankments

Verification of the stress in the CMCs

(no need for reinforcement)

Global Stability check (c/phi reduction

analysis)


Ground Engineering - Transport Geotechnics - 03/10/18

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9-Oct-18

Controls/Monitoring

Calibration

Drilling/Concreting logs

Static Load Tests

Settlements Monitoring

ConclusionGeotechnical Valued Engineering Solution:

Significant saving on material using a 70° slope RE embankment

Replacement of the bridge by a precast culvert

Ground improvement by Controlled Modulus Columns

Use of a CMC rigid inclusion solution:

Under Reinforced Earth Embankment up to 6m high

Lighter basal reinforcement (geotextile) and no need for reinforcement in the CMCs

Reduction of the settlements

Increase of the soil bearing capacity

Increase of the global stability

Execution and controls of the CMCs:

789 rigid inclusions of 7.5m average installed in 3 weeks

1 rig with soil displacement auger

Monitoring of the settlement during the embankment construction


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Conclusion


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Conclusion


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Conclusion


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Conclusion

9-Oct-18Ground Engineering - Transport

Geotechnics - 03/10/18

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Conclusion

9-Oct-18Ground Engineering - Transport

Geotechnics - 03/10/18

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Thank You

www.menard-group.com

[email protected]

north bexhill access road - ground engineering

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