CIHT Midland Branch Paper Competition 2010/2011 Moorgate Track Slab Helena Turner Pavement Consultancy Helena Turner Slide 1

CONTENTS Brief Scope Background Site Investigations Calculations Results Conclusion Helena Turner Slide 2

BRIEF Helena Turner Slide 3 Redevelopment of St Pancras Hotel

BRIEF Increased train movements have raised ground- borne noise, at St Pancras on the Moorgate line New noise dampening rail fixings proposed Re-use existing slab, to minimise disruption Helena Turner Slide 4 What is the current condition of the concrete? What is the predicted remaining life, until onset of concrete failure?

SCOPE Helena Turner Slide 5

SCOPE Thameslink is used by an average of 9.3million passengers per year -Area of track between King’s Cross & Farringdon -Costly & disruptive to shut down tracks -Costly to refit railings -Curvature limits engineering solutions Some cracking is already present Other investigations for -Reinforcement -Drainage -Forces on rails Helena Turner Slide 6

BACKGROUND Helena Turner Slide 7

Not a standard railway track bed Similar to a rigid pavement construction BACKGROUND Helena Turner Slide 8 PQC Lean Concrete Brick

Non-Intrusive Visual Condition Survey Ground Penetrating Radar SITE INVESTIGATIONS Helena Turner Slide 9 Reinforcement 190mm PQC 400mm Lean Concrete

SITE INVESTIGATIONS Intrusive Coring Helena Turner Slide 10 xx xx

CALCULATIONS Helena Turner Slide 11

CALCULATIONS Methodology Calculate the annual loading Analysis to find maximum stress at base of PQC layer Use of Packard Fatigue line to find number of loads until failure Helena Turner Slide 12 No. loads until failure = annual loading Remaining life (years)

CALCULATIONS Design – Traffic Loading 4 axles per coach, 12 coaches per train, 362 trains per day = 6.34 million axles per year (2 axles per bogie)  future predicted traffic = 3.17 million bogies per year Helena Turner Slide 13

CALCULATIONS Design - Slab Thickness of slab based from cores and GPR results Assumed stiffness for modelling the structure as a multi-layer elastic system Helena Turner Slide mm PQC 400mm Lean Concrete 30,000 MPa PQC 5000 MPa Lean Concrete 100 MPa Brick

CALCULATIONS Design - Track Axle load = 10 tonne (98.1 kN) Fixing contact area = 0.03m 2 Load split: Helena Turner Slide mm 600mm 60%20%

RESULTS Helena Turner Slide 16

RESULTS Helena Turner Slide 17 Spacing between rails (gauge) = 1430mm Spacing between axles = 2000mm Input loads at 12 points to find maximum stress Point (due to symmetry) Maximum stress point = 1.46MPa Line of symmetry Stress point

RESULTS Design Tensile Splitting Strength = 3.76 MPa Stress = Tensile Strain 1.46 = million load repetitions = 3.17 million bogies per year 4 to 5* years until onset of concrete failure *Failure constrained by internal reinforcement, therefore must be used in conjunction with reinforcement condition data, which may extend effective slab life. Helena Turner Slide 18

CONCLUSION Helena Turner Slide 19

CONCLUSION Under current loading, the concrete should not fail for at least another 4 to 5 years Client to decide on the most cost effective noise solution to noise dampening based upon the expected remaining life of the existing slab NB. The slab is designed to withstand cracking, with reinforcement constraining concrete failures, reducing crack propagation and allowing continued use. An increased level of monitoring of the slab should commence from this point, with potential localised repairs required to extend the life of the structure. Helena Turner Slide 20

QUESTIONS Helena Turner Slide 21 Thank you for your time, any questions?