Professor William Powrie and Dr Jeffrey Priest Work Area 1: Railway foundations / sub- base.

Professor William Powrie and Dr Jeffrey Priest

Work Area 1: Railway foundations /

sub-base

Current work• Influence of PSR on sub-base performance

– Testing using Hollow Cylinder Apparatus (HCA)– Work being undertaken by Anna Mamou

• Pore pressure response of embankments– Testing using advanced tri-axial tests– Work undertaken by Aingaa Sellaiya

• Influence of suction on soil stiffness– Testing using modified Resonant column– Work undertaken by Louise Otter

Adapted from Brown, S.F., “Soil Mechanics in Pavement Engineering”, Géotechnique 46, No. 3, 393.

Background: Rotation of principal stresses as train passes over

Influence of PSR on sub-base performance

Representative stress paths can be applied to soil specimens to determine the influence of PSR on material behaviour

BackgroundModelling of track behaviour has allowed us to quantify variation in direction of major principal stress at different depths below the centre line (Ko = 1.0).

Advanced cyclic testing on soil specimens using Hollow Cylinder Apparatus

HCA allows both axial and shear stress to be applied to specimen independently

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1170 1171 1172 1173 1174

Number of Cycles

Axia

l loa

d, k

N

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Torq

ue, N

m

Torque, NmLoad Cell, kN

Effect of PSR at different stress ratios

-0.1

0.4

0.9

1.4

1.9

0.01 0.1 1 10 100 1000 10000

Cycles/Time (minutes)

Axi

al S

trai

n ε%

Material A (7%, clay),e=0.24, PSR CyclicStress Ratio 4.28

Material A (7%, clay),e=0.236, PSR CyclicStress Ratio 4.28

Material D (11% clay), PSR Cyclic StressRatio 1.5

Research will investigate how material properties (Clay/Sand), magnitude of stress ratios, etc. influence the effect of PSR

Climate change impacts on embankment behaviour

• Many of the UK’s railway embankments were built >100 years ago from loosely compacted clay fill. The clay fill is highly heterogeneous and has high volume change potential.

• During dry summers, embankment shrinkage causes track deformation requiring train speed restrictions. During wet winters, embankment swelling and loss of shear strength can cause major slope failures and network disruption. This has been linked to weather influencing pore water pressures within the fill.

Finite element modelling using Vadose/w of a site at Charing, near Ashford showed saturated and unsaturated water flow in response to a climate boundary condition.

Changes in pore pressure lead to shrink/swell behaviour of embankment

Laboratory testing using advanced triaxial apparatus will be conducted to investigate changes in soil behaviour as a result of cycling pore pressure

Influence of suction on soil stiffness

• Near surface soils are likely to be unsaturated at some point during the year. In future climate scenarios, unsaturation is likely to be greater in degree and persist for longer periods

• When unsaturated, pore water within the soil will be in suction. What influence will this have on soil stiffness? What factors, such as soil density, soil fabric, etc, affect it?

Unsaturated Soil

[email protected]

Matric Suction

[email protected]

Degree of suction related to the water content in the soil. However, although suction increases its influence of soil behaviour will reduce

Resonant Column adapted to allow both internal air pressure and water pressure to be controlled. Resonant column allows non-destructive testing of soil specimens

Soli Stiffness (Gmax) Vs. Water Content

0

50

100

150

200

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300

350

0 2 4 6 8 10 12

Water Content (%)

Max

imu

m S

hea

r M

od

ulu

s (M

Pa)

clayey sand (11% clay) with WC=10%clayey sand (11% clay) with WC=4%clayey sand (11% clay) with WC=8%clayey sand (11% clay) with WC=2%Sand Mix (0% clay), wc =10%Sand Mix (0% clay), wc = 8%

Recent publications1. Quinn D, Hayward M, Baker CJ, Schmid F, Priest J. A., Powrie W., (2010). "A

full-scale experimental and modelling study of ballast flight under high speed trains." Proc. IMechE: Part F: J. Rail and Rapid Transport, 224:2, 61-74 DOI: 10.1243/09544097JRRT294

2. Priest J. A., Powrie W., Yang L. A., Grabe P.J., Clayton C. R. I., (2010). "Measurements of transient ground movements below a ballasted railway line." Geotechnique, 60(9), 667-677 DOI: 0.1680/geot.7.00172

3. Priest J. A., Powrie W., (2009). "Determination of dynamic track modulus from measurement of track velocity during train passage." J. Geotech. and Geoenvir. Engrg. Volume 135, Issue 11, pp. 1732-1740  DOI: 10.1061/(ASCE)GT.1943-5606.0000130

4. Yang L. A., Powrie W., Priest J. A., (2009). "Dynamic stress analysis of a ballasted railway track bed during train passage." J. Geotech. and Geoenvir. Engrg. Volume 135, Issue 5, 680-689  DOI: 10.1061/(ASCE)GT.1943-5606.0000032

5. Holscher P, Werweij A, Coelho B, Kremer A, Priest J. A., Powrie W., (2009). "Field test for reduction of maintenance of railway transition zones." 17th International Conference on Soil Mechanics & Geotechnical Engineering, Alexandria, Egypt 5-9 October 2009