South African Pavement Design Method (SAPDM) Revision. RPF Feedback 7 th May Louw Kannemeyer

Transcription

1 South African Pavement Design Method (SAPDM) Revision RPF Feedback 7 th May 2008 Louw Kannemeyer

2 Historical Overview SAMDM The SAMDM used since 1980s in various forms Any method is better than no method National DoT insisted that consultants design using SAMDM Attempt to introduce more Science and reduce Art ELSYM 5 SAMDM used for developing design catalogues in 1984 and 1995 TRH 4 Wide-scale design software implementation since 1995 MEPADS, Rubicon, Cerano Further development of engineering models slowed down because of a lack of funding since early 1990s Slide 2

3 Typical SA Pavement and SAMDM SA Pavement Structure 35mm Wearing course 150 mm Crushed stone base 150 mm Cemented subbase 150 mm Granular upper selected subgrade 150 mm Granular lower selected subgrade In situ subgrade Current ME Damage Model Asphalt Fatigue Freeme 1970s Permanent Deformation FOS Maree 1970s to 1980s Effective Fatigue and Crushing Failure De Beer 1980s Vertical Strain Criteria Dorman and Metcalf 1965 Vertical Strain Criteria Dorman and Metcalf 1965 Vertical Strain Criteria Dorman and Metcalf 1965 Slide 3 Current SAMDM has number of limitations, i.e. no damage models for plastic deformation in Asphalt layers, number of models outdated, etc, etc

4 SAMDM - Current status Slide 4 Summary Classical ME design method - single estimate of bearing capacity Critical layer approach distress mechanisms disconnected Separated resilient response and damage models Material resilient response Recommended M r and Poisson s Ratio values Conflict between slow and dynamic test results Users are disillusioned with the method Counter-intuitive and inadmissible results Extreme sensitivity of the method to input data Inconsistent input Resilient response (FWD, MDD, Laboratory) Strength parameters Statements made that ME-design is not possible due to: Too many unexplained effects (chaos) Getting the right answers for the wrong reasons (i.e. SAMDM correctly predicted expected life, but predicted failure layer as being subgrade, yet it actually is base!) SAMDM require extensive revision!!!

5 Slide 5 SAPDM Revision Theory Overall objective To develop a design method that is: Accurate (theory must agree with reality) Impartial in terms of pavement type selection Unbound (Crushed stone, natural gravel) Stabilised (Cement, Foamed-bitumen, Emulsified-bitumen) HMA Concrete (not included in flexible pavement design R&D process) Pavement Design Task Group Submitted R&D framework in November 2005 Characteristics of new pavement design method R&D topics Demand analysis (Traffic and environment) Material resilient response models Pavement resilient response models Damage models Probabilistic and recursive schemes Each R&D topic have a number of identified R&D needs Each R&D need translated into one or more detailed project briefs to address the need November 2006 = Reality

6 Slide 6 New South African Pavement Design Method (SAPDM) Pavement Performance Information System (LTPP) Material Classification Concept Pavement Number Concept Validate and Calibrate ME Analysis System Mechanistic-Empirical Analysis System Two components Engineering models Simulation schemes Based on separated response analysis Resilient response and damage models Static resilient pavement response analysis Damage modelling Pavement system as a whole contribute to permanent deformation Stiffness reduction for bound layers Reflective cracking excluded Material resilient response and damage model calibration Imposed stress/strain Field variables Temp, MC, Dens, etc.

7 SAPDM Revision Current Status South African Pavement Design Method Process Pavement Performance Information System (LTPP) 50 Projects Completed February 2008 Mechanistic-Empirical Analysis System (MEAS) Phase 1 Develop Detailed Project Briefs November 2006 Phase 2 - Inception Phase (22 Projects) July 2007 Investigate available solutions Finalize project methodology Finalize cost and resource allocation Inception Report Peer Review November 2007 Phase 3 Project Delivery Immediate Deliverables (12 to 18 months); Short Term Deliverables (18 months to 3 years); Medium Term Deliverables (3 to 5 years), and Long Term Deliverables > 5 years. Slide 7

8 SAPDM Revision PPIS PPIS developed as Internet website Slide 8

9 SAPDM Revision PPIS Table View Slide 9

10 SAPDM Revision PPIS Graphical View Slide 10

11 SAPDM Revision PPIS Representation of 50 Captured Sections Slide 11

12 SAPDM Revision PPIS Typical Performance Trends Granular Base / Cemented Subbase Slide 12

13 SAPDM Revision PPIS Typical Performance Trends Asphalt Base Slide 13

14 SAPDM Revision PPIS What Next? Launch PPIS website and obtain feedback from the industry; Perform ongoing improvement of the concept of web-based access to pavement performance information; Review Bitumen Stabilised Material Project Sections and include 15 sections into PPIS; Incorporate the Data Collection Framework into the SANRAL Manual M1; Standardize submittal of all design data with the Project Design Documentation based on the proforma electronic PPIS Database File. Development of a First Level Performance Based Design Method. Slide 14

15 SAPDM Revision MEAS Phase 2 Outcomes P r i m a r y P a v e m e n t R e s p o n s e M o d e l Geometry Thi ckness, da C Thickness, ds Thickness, du HMA Stabilised Unbound granular Material resilient response models Primary pavement response model Load-pulse duration Stress feedback Yield strength Loading: Magnitude Contact stress Location Vehicle speed Damage models Plastic strain Fatigue Plastic strain Effective fatigue Structural layers Subgrade Crushing failure Slide 15

16 SAPDM Revision MEAS Phase 2 Outcomes The Costs? Phase Start date End Date Estimated Cost Cumulative Cost Immediate (18 months) Apr 2008 Dec 2009 R R Short-term (3 years) Apr 2008 Mar 2011 R R Medium-term (5 years) Apr 2008 Mar 2012 R R Long-term (10 years) Apr 2008 Mar 2017 R R Slide 16

17 SAPDM Revision MEAS Peer Review Phase 2 outputs from the individual projects was synthesised into a single summary report. All Reports subject to peer review: Prof Andre Molenaar (Netherlands); Prof Fred Hugo (Stellenbosch), Dr Pieter Strauss Dr Pieter Poolman, University of Oregon USA Dr Andre Smit, National Center for Asphalt Technology (NCAT), Auburn, USA Dr Imad L. Al-Qadi, Center for Transportation, University of Illinois, USA Dr Don Christensen PE, Advanced Asphalt Technologies, USA Dr Ramon Bonaquist PE, Advanced Asphalt Technologies, USA. Slide 17

18 SAPDM Revision MEAS Peer Review having an extremely advanced pavement design engine implemented in an inadequate planning process will not address South Africa s needs Must take full cognisance of the in-service operating conditions of the pavement and the impact thereof on the design inputs Functional performance simulation must be an integral part of the pavement design process A comprehensive cost-benefit analysis procedure assessing different lifecycle strategies and including cost and benefits for road users as well as road authorities must form part of the final deliverable For the successful implementation and utilisation: Be easy to use on a day to day basis by pavement engineers Keep input data to essential minimum that is readily available to the user Relay on results of test equipment generally available in practice Not require knowledge that goes beyond what can reasonably be expected of an educated pavement engineer in practice Slide 18

19 Initial condition SAPDM Revision MEAS??? R o u t in e m a t e r ia l t e s t d a t a M a t e r i a l c l a s i f i c a t i o n s y s t e m N o n - s t a n d a r d t e s t r e s u l t s a n d M E - d e s ig n i n p u t - Pumpi ng Disint egrat ion P ot holes P umping Subgrade undulati on Shoulder E dge break/erosion V egetation Blocked drain Riding quali ty Skid resist ance Design investigation Operating conditions Climatic region Construction qualit y Maintenance frequency Drai nage conditions History Geometry Legislation Vehicle operations Materials ( initial) Centre-line survey (new) As-built (rehab design) Routine test result s Test-pit and cores Quarry and borrow-pit Materials ( detail) Mix-design (new and rehab) Non-standard t esting (new and rehab) Traffic survey None - Strat ificat ion Classified count (rehab) WIM survey (rehab) Mechanical survey Rut (rehab) Riding quality (rehab) Deflect ion (rehab) DCP (rehab) Visual condition survey Surface distress Ravelling B leeding/f lushi ng S urface t exture S urface f ail ure Information systems E nvironmental and spatial variation information system Materials design input information system Contact stress information system Traffic volume and axle load information system Deflection and DCP data B inder conditi on Structural distress Deformation - Rut - Shear Cracks - Crocodile - Longitudinal - Block - Transverse Legend: Mechanistic-empirical models Information systems S t r u c t u r a l R e f l e c t i o n T h e r m a l Rutting models Roughness models Ravelling models Pothole models Edge-break models Texture depth and skid resistance models R u t d e p t h R u t v a r ia t i o n Pre/post -processing Analysis processes Life-cycle strategy Monte-Carlo input Recursive time-step Distress feedback Economic assessment ME input P avement Number Deflection analysis module Deterioration modelling Cracking models Slide 19

20 SAPDM Revision MEAS What Next? Finalise the end product framework and inter dependencies; Adjustments to the current project plan based on: Inclusion of functional performance simulation (roughness, texture, friction ) Close gap between PMS and Design; Inclusion economic analysis of design alternatives and maintenance strategies; Consideration of the project funding available. Project teams to re-evaluate project deliverables and how it will fit in to final product as first task during phase 3 Get common understanding of envisaged end product. Revised Phase 3 to start June Slide 20