development of design guidelines for flood ...

25th ARRB Conference – Shaping the future: Linking policy, research and outcomes, Perth, Australia 2012

DEVELOPMENT OF DESIGN GUIDELINES FOR FLOOD RECONSTRUCTION WORKS Dr Owen Arndt, Queensland Department of Transport & Main Roads, Australia Jothi Ramanujam, Queensland Department of Transport & Main Roads, Australia Siva Sivakumar, Queensland Department of Transport & Main Roads, Australia Ian Reeves, ARRB Group, Australia ABSTRACT From January 2010 to April 2011, Queensland experienced numerous disaster events in the form of tropical cyclones and major flooding. The magnitude of these events is unprecedented in Queensland’s recorded history with all of the state being declared a natural disaster zone. 8211km (25%) of the Queensland Department of Transport and Main Roads’ (TMR) road network was damaged: a damage bill of over $5 billion dollars. The Transport Network Reconstruction Program (TNRP) was initiated by TMR to manage the recovery and reconstruction of the transport network damaged by these disaster events. One aspect of the program was to develop a set of design guidelines for the reconstruction of the road network (the TNRP Design Guidelines). Whilst these Guidelines make reference to existing TMR and Austroads guides, manuals and codes as much as possible, there was a need to develop additional design criteria to cover issues such as the provision of more resilient treatments to address specific damage experienced, funding eligibility, achieving cost effective solutions and other issues. This paper discusses the development of specific design criteria in the TNRP Design Guidelines, especially in regard to the provision of infrastructure resilience.

INTRODUCTION The purpose of this paper is to discuss the development of design criteria by the Queensland Department of Transport and Main Roads (TMR) to order to aid its road reconstruction works as the result of prolonged high intensity rainfall and flooding events between January 2010 and April 2011. The paper identifies damage occurring to the network, the contributory causes and design solutions developed to help mitigate future damage. The paper also discusses other criteria such as the need for geometric road design involvement in these reconstruction projects.

Disaster Events and Resulting Damage After almost a decade of drought, Queensland experienced the following disaster events: • January to April 2010 - tropical cyclones Olga, Neville, Ului & Paul, causing major flooding • September 2010 - South-west Queensland flooding • October 2010 - South-east Queensland flooding • November 2010 to January 2011 – Queensland flooding & Tropical Cyclone Tasha which included major flooding in Toowoomba, Locker Valley, Ipswich & Brisbane, with considerable loss of life and damage • February 2011 – Category 5 tropical cyclone Yasi & Queensland monsoonal flooding.

© ARRB Group Ltd and Authors 2012

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• April 2011 – South-west Queensland flooding. The magnitude of these events was unprecedented in Queensland’s recorded history with all of the state being declared a disaster zone. It is estimated that the rainfall experienced ranged between Q100 and Q500 events. Of all public assets, the road network received the greatest damage. 8211km (25%) of TMR’s (state owned) road network was damaged, requiring more than $5 billion dollars to reconstruct. Road elements damaged, and approximate proportions of the total damage bill for each, are given below: • damage to pavements – 85% • damage due to slope instability – 10% • damage to bridges, culverts and floodways - 5%. More recently, South-west Queensland has experienced further damaging rain events during January to March 2012. As of April 2012, the effect of this damage was still being assessed.

Transport Network Reconstruction Program (TNRP) In order to manage the recovery and reconstruction of the transport network, TMR developed the Transport Network Reconstruction Program (TNRP). Some aspects of this program are given below: • Funding Sources. Most of the funding for TNRP comes via the Natural Disaster Relief and Recovery Arrangements (NDRRA), which is 75% funded by the Australian Government and 25% by the Queensland Government. A small amount of funding (titled Complementary Works, which is not eligible for NDRRA funding) is provided from TMR’s normal annual works program. • Work Types and Timelines. NDRRA criteria define Recovery Works as those immediate urgent repairs necessary to restore essential services and maintain public safety. Recovery Works must be completed within 60 days from declaration of an NDRRA event. Reconstruction Works are defined as permanent repairs designed and constructed to ‘current engineering standards’. Reconstruction Works are to be completed by June 2014. • Organisational Structure. A Statewide Project Office (SPO) has been set up in Brisbane to coordinate the program. Twelve Regional Project Offices (RPOs) have been established across Queensland to support TMR regional offices in the planning, design and delivery of works in their areas. • Delivery Methods. Because of the size of the program, approximately 60% of the work will be delivered by contractors, 30% internally by TMR and 10% by local councils.

NDRRA Funding Eligibility The NDRRA policy provides for the reconstruction of essential public assets to ‘pre-disaster standard / level of service, in accordance with current engineering standards/requirements and building codes / guidelines, while maintaining the same asset class and/or asset immunity level’. This means that NDRRA funding will generally not cover improvements to the road network such as increased levels of service, increased flood immunity (e.g. increasing the height of bridges), realignment of roads, provision of additional signage etc. Such works can only be funded under Complementary Works.

TNRP Design Guidelines The TNRP Design Guidelines (TMR, 2011a) were developed for the SPO to guide designers of TNRP reconstruction works. The intention of producing these guidelines was to: • reference all relevant TMR and Austroads design documents in a single location (but not to reproduce content of the existing documents)


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• clarify appropriate application of design criteria in the circumstances of TNRP • outline work types eligible for NDRRA funding, and those requiring Complementary works funding • include new and updated design criteria that had not yet been released into the various TMR design documents, including: – criteria to improve Resilience (the ability of the road network to absorb a disaster event and return to a state of acceptable operating conditions) – criteria to deliver more fit-for-purpose solutions, especially for ‘brownfield sites’ (to enable delivery of appropriate infrastructure within the available NDRRA budget). Development of the guidelines was considered important because of the large number of contractual staff working on the program who were not familiar with Queensland’s road network, materials and/or practices. These staff (who came from interstate, overseas and from other industries) were hired to help deliver the enormous program because TMR did not have adequate resources to deliver it alone. The TNRP Design Guidelines were authored by the Engineering and Technology Division of TMR. A review of the guidelines were undertaken by ARRB and subsequent comments included. It is intended that most of the new design criteria in the guidelines will be adopted into TMR’s normal design guides eg Road Planning and Design Manual (TMR, 2001), Pavement Design Manual (TMR, 2009) etc. This paper now discusses the learnings gained in authoring these guidelines, especially around the nature and extent of damage to the network. Also discussed is the associated design criteria developed to address these learnings, particularly criteria for increasing the resilience of the network.

PAVEMENTS Types of Damage Pavement damage resulted from either flooding of the pavement (where the roadway remains submerged for a period of time) and/or sustained heavy rainfall. In some cases, pavements were completely washed away. In other cases, pavements were weakened due to moisture infiltration and saturation. Re-opening of roads after floodwaters dissipated was a priority. As a consequence, pavement damage including rutting, cracking, potholes and flushing became widespread.

Figure 1: Examples of pavement damage as a result of the disaster events


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Assessment of Pavement Damage An assessment of whether or not a road section has been damaged by the disaster events would ideally include a visual assessment and a before and after assessment of deflections, rutting and roughness. Due to the limited time-frame for the TNRP program, the nature of distress and the multitude of damaged sections to be investigated, it was not always practical (nor necessary) to undertake all of these assessments. As a minimum, the TNRP Guidelines require a visual assessment to be undertaken by experienced practitioners. Where a visual assessment is inconclusive, and/or there is historical evidence of poor pavement performance, the Guidelines recommend that supplementary assessments be undertaken.

Pavement Characteristics in Queensland The following pavement types are common in Queensland: 1. High Intensity Low Intervention (HILI) pavements. These are generally thick pavements comprising bound layers beneath significant asphalt base and surfacing layers. They are normally located on higher order roads (e.g. arterial roads and motorways) in south-east Queensland and in some provincial cities along the Queensland Coast. 2. Granular pavements which meet TMR’s technical standard for unbound pavements (TMR, 2010), normally with a sealed surface. These are located extensively throughout Queensland wherever standard granular materials are available. 3. Thin, low-cost pavements comprising non-standard granular materials normally with a sealed surface. They are typically used on lower volume roads which are common and extensive in the more arid areas of western Queensland. Limited amounts of funding are normally available to build and maintain such roads. The thicknesses of existing pavements (particularly older ones) for the 2nd and 3rd pavement types above usually do not meet current design requirements. This is mainly the result of increased traffic loads and increased pavement design standards over time. Many of these pavements were constructed in the 1960’s for a 20 year design life, and have generally delivered excellent service until the recent flood events.

Pavement and Subgrade Learnings The following learnings on pavement and subgrade performance were gained during the recent disaster events: • HILI pavements (Type 1 above) delivered acceptable performance during the disaster events. • Granular pavements (Types 2 and 3 above) recorded significant damage as a result of the disaster events. • Previously rehabilitated pavements incorporating foam bitumen stabilised or insitu cement modified layers showed much greater resistance to water infiltration and damage under flooding and sustained heavy rainfall events. TMR (2000) had previously identified these performance advantages for foam bitumen stabilisation. • Expansive soil subgrades (which exist over about 30% of Queensland) show much greater resistance to water infiltration and damage when lime stabilised. • Performance of thin pavements comprising non-standard materials was variable. These materials are known to be vulnerable to moisture ingress and rely on regular resealing to prevent the infiltration of moisture through surface cracks and on shoulder maintenance to prevent ponding of water adjacent to the seal edge.


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Provision of Pavement Resilience When authoring the TNRP Guidelines, it quickly became apparent that NDRRA funding would be insufficient to reconstruct all pavements to withstand rainfall events such as those recorded during the disasters. For this reason, the traditional practice of basing the pavement solution on the lowest whole-of-life cost was adopted in the Guidelines. In some situations (eg on higher standard, higher traffic volume roadways), a more resilient pavement solution may be necessary. In other situations (eg lower traffic volume roadways), it may be more economic in a whole-of-life sense to simply repair the roadway after each rainfall/flood event. In any case, the Guidelines recommend identifying and addressing contributory causes where possible, even if this does not leave sufficient funds to fully reconstruct the pavement. For example, improving formation and pavement drainage and application of a new sealed surfacing may be a more cost effective solution (in a whole-of-life sense) than the provision of a completely new pavement for which contributory causes have neither been identified nor eliminated. Recommended methods of improving resilience in the Guidelines include: • reducing the moisture susceptibility of the pavement and subgrade eg by providing sealed shoulders, modifying/stabilising pavements and subgrades, overlay or substitution of existing pavement materials with new bound materials • improving pavement drainage e.g. reinstating or deepening of table drains, cleaning subsoil drains and culverts, repairing surface cracks, adding a geotextile seal, incorporating a drainage blanket at subgrade level • providing increased flood protection on the downstream side of floodways to resist shoulder and embankment batter erosion • increasing under-drainage capacity for waterways • providing concrete pavements on floodways and approaches to low-level bridges.

Pavement Work Types TNRP pavement work types were categorised as follows: • Pavement patching. The repair of isolated pavement failures, such as potholes, depressions and bumps, shoving of pavement and surfacings, and flushing of seals. • Part-width pavement rehabilitation. Pavement repairs to one or more segments of the road cross section e.g. rehabilitating one-lane of a two-lane carriageway, rehabilitating outer wheel paths and shoulders. Usually undertaken by boxing out the damaged area/s of pavement and replacing with new material or modifying/stabilising the existing damaged area/s of pavement in-situ. • Full-width pavement rehabilitation. Rehabilitation of the pavement over the entire cross section by overlaying the existing pavement, stabilising the existing pavement, and/or boxing-out and replacing existing pavement.

Part-Width Pavement Rehabilitation Significant lengths of the road network comprising granular pavements experienced excessive rutting in the outer wheel paths and/or shoulders with the centre of the roadway generally appearing intact. The challenge for designers was whether to rehabilitate the full width of the road (adopt full-width pavement rehabilitation) or just replace the damaged section/s (adopt part-width pavement rehabilitation). Considerations for part-width pavement rehabilitation included the suitability/longevity of the residual pavement, the limited time and cost available for testing and analysis of the residual pavement and the interface of the new and residual pavement. © ARRB Group Ltd and Authors 2012

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Eventually, the process in Figure 2 was adopted to ascertain an appropriate rehabilitation treatment where project timelines did not allow a full suite of tests to be undertaken. This process attempts to strike a balance between maximising the existing asset, minimising the amount of testing required and achieving acceptable performance from the final product. The additional tests indicated in Figure 2 include sampling from trenches or pits and laboratory testing. Visual inspection of residual pavement

Pass

Fail or uncertain Pass

Deflection test Fail or uncertain

Part-width pavement rehabilitation

Pass Additional tests Fail or uncertain

Full width pavement rehabilitation

Figure 2: Determination of the suitability of the residual pavement and subgrade under a part-width pavement rehabilitation treatment Note: Additional tests include laboratory testing of samples from trenches and pits and use of ground penetrating radar.

DRAINAGE STRUCTURES Types of Damage Inspections of drainage infrastructure have revealed the following damage: • Scour/failure of a shoulder/verge/batter slope at pipes and culverts, mainly the downstream batter, sometimes with loss of pipe/culvert units (as shown in Figure 3) as a result of: – erosion of the batter caused by overtopping – loss of precast endwalls – undermining and loss of aprons or wingwalls. • Scour/failure of a shoulder/verge/batter slope not at a cross drainage structure (mainly the downstream batter) due to overtopping as a result of: – stream/creek migration (as shown in Figure 4), including misalignment of rail drainage infrastructure with road drainage infrastructure – runoff from longitudinal drainage bypassing drainage structures (refer Section titled ‘Geotechnical’ for further information). • Scour around bridge abutments and piers (refer Section titled ‘Bridges’ for further information). • Depressions in the roadway and/or partial or whole embankment collapse as a result of scour from flow around the outside of a pipe/culvert (refer Section titled ‘Geotechnical’ for further information).


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Figure 3: Complete failure of supporting material around pipes

Figure 4: Stream migration at culverts The immunity level provided by existing drainage infrastructure on TMR’s network varies considerably. Some bridges may have greater than Q100 immunity, others may overtop much more regularly. In the same way, some pipes and culverts may have Q50 immunity whilst others may overtop every few years. Typically, the less important and lower traffic volume roadways provide much lower levels of immunity (for reasons of affordability) and are generally more prone to scour/failure from overtopping.

Need for Hydrologic/Hydraulic Assessment There are instances where damage to drainage infrastructure was made worse by the scouring of streams/creeks. This particularly occurred where streams/creeks downstream of cross drainage structures increased in waterway area, which lowered the tailwater level and increased velocities through the drainage structures. This resulted in increased scour at bridges and increased scour to downstream batters at pipes and culverts where overtopping occurred.


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To ensure satisfactory hydraulic performance of drainage infrastructure, the TNRP Guidelines recommend undertaking a hydrologic and/or hydraulic assessment when any of the following apply: • a change in the required road immunity • a noticeable change in the hydrologic characteristics of the structure’s catchment as a result of the flood event • a noticeable change in the hydraulic parameters with respect to cross section, gradient and roughness of the stream as a result of the flood event. Hydrologic/hydraulic assessments were not mandated for all drainage infrastructure damaged under TNRP because of the time, effort and cost that this would require.

Provision of Increased Embankment Resilience to Overtopping Erosion of a downstream shoulder/verge/batter due to overtopping was a common mode of failure. The TNRP Guidelines state that all road sections damaged due to overtopping (especially those with a history of overtopping damage) with immunity lower than 50 year ARI should be made more resilient. This can be achieved through the following strategies: • Improved pipe/culvert capacity: as more floodwater is channelled under the road, the risk of scour to embankments and pavements is reduced. • Reduced head: in order to minimise ‘damming’ effects (differences in upstream and downstream water levels), the risk of scour is reduced if the road surface is at the same level as the channel base. It may be possible to apply this design treatment on some floodways on lowly trafficked roads where a lower immunity can be accepted. However if there is high upstream velocity, there are still risks associated with uplift pressure on the pavement and possible scouring from pooling. • Increased scour protection: provide/improve downstream batter protection in accordance with the following: – Maximum slope of downstream batter 1V to 3H – All shoulders should be sealed – All downstream batter protection shall extend to at least the toe of the batter – All downstream embankment batters at culverts to be protected with grouted rock, reinforced concrete or wire mattress. – For culverts, with an embankment height less than 2 meters, vegetation of batters may be used if it remains lush and thick for the entire year – For culverts, batter protection on the downstream side of the road embankment shall extend along each carriageway past the culvert (in both directions) for a distance twice the height of the road embankment.

Improving the Stability of Pipe/Culvert Ends Prior to the disaster events, precast endwalls were not required to be anchored in any way to the pipe/culvert or to the steam/creek bed. The disaster events resulted in numerous precast endwalls washing away, particularly those on the downstream side, often leading to embankment failure. To improve the stability of precast endwalls, the TNRP Guidelines require installation of cut-off walls (mandatory on downstream side, optional on upstream side). The Guidelines also require that consideration be given to the provision of adequate anchoring (off back of wall into embankment). The TNRP Guidelines also set more general requirements for pipe/culvert ends, as follows:


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• All cross drainage systems (culverts and floodways) must have a cut-off wall on the downstream side of the structure to mitigate undercutting of aprons. If the upstream embankments are erodible then a cut-off wall should be included on the upstream side as well. Minimum depth of cut-off wall is 450mm. • All downstream headwalls are to be permanently attached to the culvert. • The headwall, apron and cut-off wall are to be integral.

GEOTECHNICAL Slope Failures Over 400 slope failures (cut, fill or natural slopes) were recorded under TNRP. While the repair cost is significant, these slopes represent only a small percentage of the total number of slopes on the TMR network. Many of the slope failures occurred on range sections in mountainous and hilly terrain. Some were on major highways but most were on minor roads with relatively low traffic volumes. Many of the minor roads had a history as logging or bullock tracks originally built for pastoral communities some 100 years or more ago and have since been upgraded. Roads in range sections often lacked design to any formal standard or were designed to outdated standards (with respect to both slope stability and drainage). Original construction techniques were also of lesser standard than now (eg little benching for embankment widening; over blasting of rock cut batters etc). And these roads were typically constructed using local materials eg from adjacent cut material with inadequate compaction. Early upgrades of these roads typically consisted of formation widening whilst maintaining similar horizontal and vertical alignments. The end result was narrow shoulders, steep cuts and steep embankments. Due to available funding, maintenance of these roads over time has been limited to minor repairs e.g. removal of cut batter slip debris, correction of depressions where embankment movements have occurred.

Figure 5: Examples of slope failures as a result of the disaster events

Slope Failure Mechanism Current TMR drainage design standards require minimum Q10 runoff flows (1 in 10 year Average Recurrence Intervals (ARI)) for longitudinal drainage, and Q50 / Q100 flows for cross drainage pipes/culverts. However, existing drainage infrastructure on range sections typically would provide a much lower ARI.


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Rainfall runoff during the recent disaster events often exceeded Q100 flows. Consequently, runoff entered slopes at unplanned locations in amounts that overwhelmed the dry in-situ strength of the soil/rock materials. Observations at failure sites in south east Queensland during and shortly after the 11 January 2011 event showed the following: • Cut slope failures as a result of: – overland sheet flow from natural slopes running over cut slopes causing the slopes to become saturated. – concentrated runoff at low points causing scour/soaking of cut slopes. • Fill slope failures as a result of: – runoff from the road surface on longitudinal gradients being unable to enter drainage structures (often set at right angles to the road alignment) finding low points at which to flow over the road. – runoff bypassing blocked table drains and pipes/culverts inlets finding low points to flow over the road. – runoff from property accesses graded down to major roads, bypassing blocked table drains and culvert inlets, finding low points to flow over the road. • Failures at pipes and culverts, as a result of: – scour from flow around the outside of the pipe/culvert resulting in a depression in the roadway to partial or whole embankment collapse. This is often the result of the pipe/culvert being blocked, broken/dislocated or being of much smaller size than that required to handle major events. – scour of the downstream fill slope from overtopping. – partial embankment collapse from water flowing into cracks in the road surface as a result of previous embankment movement or inappropriate construction methods adopted to widen existing embankments.

Geotechnical Design Standards The TNRP Design Guidelines set various criteria for reconstructing failed slopes, including the following: • Cut Slopes – maximum 2V to 1H batter slope for unreinforced cuts, maximum 10V to 1H batter slope for reinforced cuts – minimum 4m wide bench at the top of any 7m high single continuous cut batter – minimum factor of safety of 1.5 for soil like materials with representative ground water conditions. Pore water pressure (Ru) less than 0.15 shall not be used, even with appropriate drainage systems. • Fill Slopes – maximum 1V to 2H batter slope for earth fill, 1V to 1.5H better slope for rock fill – minimum 4m wide bench at the top of any 10m high single continuous earth-fill batter slope – minimum factor of safety of 1.3 during construction (short term conditions), 1.5 for long term conditions. The requirements above are in addition to the maximum slope criteria within TMR’s Road Planning and Design Manual (TMR, 2001). TMR (2001) criteria tend to be more conservative, but have a proviso that TMR’s geotechnical section be contacted if slopes steeper than the maximum are used.


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The TNRP Guidelines state that NDRRA funding will be used to reconstruct all slope failures to the above criteria, unless it is uneconomical / impractical to do so. Unfortunately, there are a significant number of failed slopes where the criteria could not be met, particularly on the lower order roads. In such cases, the TNRP Guidelines require all remedial works to be carried out to bring the assessed slope risk to level 4 (low risk) or better in accordance with TMR’s slope risk assessment methodology. This methodology is based on the NSW RTA Slope Risk Assessment methodology (RTA, 2011).

Drainage for Slope Stability Whilst the geotechnical design criteria above will provide improved slope resilience, high levels of resilience can only be obtained if drainage requirements are also considered. A proposed method of improving slope stability through improved drainage is to map drainage paths for major rainfall events. This includes determining drainage paths over cut and fill slopes, as well as along/through drainage structures. Cost effective measures of directing these flows to locations where they will do the least damage can then be identified. This could be achieved through preparation of an inventory of salient asset details, for example: • location and shape of the existing natural drainage paths • location and size of the existing catch banks/drains • size and condition of the existing road longitudinal and cross drainage • road geometric details eg crossfall, grades. Mapping of all drainage paths for major rainfall events is currently not required under the TNRP Guidelines. TMR is currently considering the practicality and affordability of requiring this practice as part of all road designs. Lower-cost measures to improve drainage to cater for a major event include: • Using catch banks, eco-socks and/or batter chutes to direct flows from the natural slope away from cut slopes. • Restoring/enlarging existing road longitudinal drainage. Where enlarged drains in cuts (new or existing) require the toe of cut slopes to be over-steepened, the drain and slope toe could be protected either with shotcrete or grouted riprap, or a boulder masonry wall or similar could be used. • Designing drains to appropriately accommodate flows where there is a change in direction e.g. skewing pipes, splaying inlets to batter chutes. It is common in Asia to superelevate drainage structures like table drains. This is easy to do with shotcrete, although operators would need training. • Using cold-mix bunds and suitable structures such as batter chutes to discharge flows to appropriate locations. • Using spigot and socket pipes at locations where there are likely to be ground movements eg in side-long ground in mountainous terrain (comprising a large cut on one side and a large fill on the other). • Providing wingwalls to all pipes/culverts. • Providing suitable protection to downstream fill slopes at low points and/or at pipes/culverts.

BRIDGES Damage to Bridges TMR bridge infrastructure generally performed well under the disaster events as compared to the road network. However, the following damage was recorded (Pritchard, 2011):


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• loss of two timber bridges • scour around piers and piles (including pier settlement) • scoured bridge abutments at numerous locations • washed out bridge approaches (as shown in Figure 6) at numerous locations In addition to the above, there was damage to bridge barriers in instances where flows overtop bridges.

Figure 6: Scoured road approach at bridge abutment

Contributing Factors The amount of damage at bridges tended to be higher where the following occurred: • soils were more erodible • water flow velocities were higher • bridge waterway area, as compared to the creek/stream/river waterway area, was smaller (this creates increased water flow velocities and headwater levels at bridges) Where scouring occurred around bridge piers, bridges with shallower foundations (especially older bridges) tended to record more damage. Rigid reinforced concrete and stone pitching abutment protection was found to break up due to high hydraulic uplift pressure, particularly when the stream velocity was greater than about 3 4m/s. Reinforced concrete and stone pitching erosion protection used on bridge approach embankments also broke up when the bridge was overtopped and the stream velocity exceeded about 3 – 4m/s. It was observed that breakup of erosion protection on bridge approach embankments generally started with erosion around the toe of the batter.

Improved Scour Protection at Bridge Abutments and Piers The TNRP Guidelines recommend that heavy-duty abutment protection, in the form of gabions and wire mattresses, be used where scouring has occurred at abutments and piers respectively. Gabions are containers or baskets made up of wire mesh and are filled with cobbles or coarse gravel. Figure 7 shows the use of gabions for spill through abutment protection. A thinner


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version of a gabion is known as a wire mattress. Whereas gabions typically take the shape of a brick, wire mattresses have a short vertical dimension and large lateral extension.

Figure 7: Heavy-duty gabion spill through abutment protection Gabions and wire mattresses have several advantages when compared with other means of abutment and pier protection, such as: • their loose and porous structure reduces their susceptibility to uplift forces • they can be stacked easily in stable configurations • the flexibility of the wire mesh allows gabions to mould themselves so as to restore their stability and provide adaptability to the site conditions • relatively small rock sizes can be used to provide similar protection effectiveness to that of much larger rock units. Design criteria for the provision of gabions and wire mattresses at abutments and piers are provided in the TNRP Guidelines. In locations of very high velocity flow, soil anchors may be necessary to stabilise the gabions and wire mattresses. The durability of the wire in gabions and wire mattresses is questionable in saltwater environments as the galvanised wire tends to deteriorate relatively quickly, which affects durability of the entire solution. Armouring the stream bed against scour is considered to be a means of last resort because of the potentially adverse impacts on boat traffic, recreational activities (i.e. jumping from bridges) and fauna movement along the riparian corridor.

Improved Scour Protection at Bridge Approaches The TNRP Guidelines recommend that where the height of the embankment is less than 500mm, slope protection at bridge approaches is not needed unless there is a history of scour. Where scour protection is applied, the Guidelines require it to be placed along each carriageway past the abutment (in both directions) for a distance three times the height of the road embankment, but not less than 10 metres.

Replacement of Damaged Bridge Barriers The TNRP Guidelines require the following action with regard to damaged bridge barriers: • The barrier should be replaced with a barrier conforming to Australian Standard 5100 ‘Bridge Design’ (AS 5100) if the existing deck has sufficient structural capacity to support the design load. © ARRB Group Ltd and Authors 2012

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• Where AS 5100 specifies a performance level higher than ‘Regular’, the deck must be modified to provide a higher level of protection. Exemption based on impractical or uneconomic criteria shall be via the normal design exception process. • Where a ‘Regular’ level barrier or less is required by AS 5100 and the deck cannot support the current barrier design loads, a risk analysis for an existing bridge shall be undertaken in accordance with Clause 10.5.1 of AS 5100.1. If the bridge conforms to these criteria, barrier of lesser performance level may be installed. The minimum strength for replacement rails is 50% ‘Low’ performance level.

GENERAL PROVISION OF RESILIENCE In order to make a road network more resilient to a future disaster events, the drainage flow paths must firstly be identified for such events (e.g. at least Q100 event or greater). The effect of these flows on pavements, drainage infrastructure and slope stability must then be considered, for example: • overtopping of longitudinal drains – affect on pavement performance • inundation of roadway for significant periods of time – affect on pavement performance • overland sheet flow and concentrated flow from natural slopes – affect on cut face stability • flow from overtopping of longitudinal drains unable to enter drainage structures crossing the road at low points – affect on fill batter stability • overtopping at pipes and culverts – affect on downstream batter slope, endwall and pipe/culvert unit stability • flow through and over bridges – affect on stream bed and abutment stability Mapping of all drainage flow paths is not currently a requirement of the TNRP Guidelines. After identifying the effect of these flows on roadway infrastructure, treatments such as those given below can be provided to improve the level of resilience: • stabilised pavements and subgrades • increased longitudinal and cross drainage capacity • improved scour protection to downstream batter slopes at pipes and culverts • increased anchoring of endwalls including mandatory provision of cut-off walls • improvement of catch banks/drains and batter chutes • greater use of spigot and socket pipes • improved scour protection to bridge abutments, piers and approaches • sufficient ongoing maintenance. Design criteria for several of these treatments are provided in the TNRP Guidelines. The TNRP Guidelines recognise that funding is likely to be insufficient to build a completely resilient network. In this context, the Guidelines state that designers must consider improving the resilience of their projects by: • identifying all infrastructure that has been damaged • unless unaffordable, designing infrastructure at all damaged sites with an improved tolerance to damage.


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ROAD GEOMETRY The damage caused by the disaster events did not have any immediate impacts on TMR’s road geometric design unit. However, because the road network was being reconstructed, issues around road geometry did arise. This section discusses some of those issues and how they were resolved.

Road Design Classes If a full and thorough geometric assessment of an existing road is undertaken as part of the delivery of a road project, it is likely that a number of design exceptions will be identified. Designers will often try to improve these geometric elements to a standard within the Normal Design Domain (range of design values within road design guidelines that have been traditionally used for new roads: refer Austroads (2006) for further information). An example of this is increasing the radius of an existing sharp horizontal curve. This can have a significant impact on project scope. Prior to the development of the TNRP Guidelines, TMR had limited criteria to define the extent of geometric road design involvement required for the range of road projects typically undertaken. This situation has caused much debate between project managers and road designers, particularly for road rehabilitation projects. On one side, there was a belief that because the road alignment should largely remain the same, there was no need for road designers to become involved, even when the road was being widened to cater for an overlay and/or wider carriageway. Road designers argued that because the geometry was being changed, it may well affect driver perception and choice of speed. In turn, this could affect safety, particularly where the road was being widened. Although additional guidance on this issue was being developed in TMR prior to TNRP, the large scale of work undertaken under TNRP gave greater urgency to its resolution. Also, the issues of constructability and primary intent of reinstating the pre-existing condition under TNRP needed further clarification. These issues highlighted the importance of defining appropriate criteria for the level of road design involvement for the various road projects. To define the level of geometric road design involvement, the TNRP Guidelines identify four road design classes (A to D), the types of projects in each class, the road design approach or steps required for each, and the geometric parameters requiring assessment. Table 1 provides a summary of some of the information provided. TNRP generally comprises Class B, C and D projects (predominantly C and D). Part-width and full-width pavement rehabilitation projects will fit into either of these categories depending on whether formation widening, overlays and/or increases in seal width are required. Pavement Patching is considered maintenance and does not fit under any of the road design classes.

Geometric Requirements when using Structural Overlays On rural roads, it is common practice for TMR to apply structural overlays to existing pavements to extend pavement life and cater for increasing vehicle loads. Structural overlays require the formation to be widened if the existing carriageway width and side slopes are to be retained. This is expensive because of the additional earthworks required and the need to lengthen pipes and culverts. Sometimes, services are also required to be relocated and resumptions are required. To meet budgetary requirements, past TMR practice has tended towards narrowing carriageway widths and/or steepening side slopes when applying structural overlays, in order to avoid formation widening. Carriageway widths have now become so narrow in places, and sides slopes so steep, that engineers are increasingly hesitant to continue this practice any further. In addition, guiding principles from legal proceedings indicate that road projects should not make the road less safe (Cox and Arndt, 2008). Clearly, decreasing carriageway widths and/or increasing side slopes is likely to make the road less safe, even if by only a marginal degree for each overlay applied.


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Table 1: Road design classes Road Design Class

Applicable Project Types

A

• New roads • Complex, high risk and/or relatively expensive projects involving modification to existing roads e.g. o Duplication of existing roads o >500m realignment of existing road o New climbing / overtaking lanes

All

B

• Sealing of an unsealed road • Restoration projects (roads and/or intersections) involving increases to the earthworks footprint for most of the project length e.g. o Shoulder widening o Overlay and widening

All

C

• Restoration projects (roads and/or intersections) where the earthworks footprint does not change or there is localised marginal change to the footprint. This includes projects with: o Significant increases in seal width o Structural overlays o Surface shape correction o Full shoulder seal projects (if the change in seal width is likely to significantly increase driver speed, use Class B)

As a minimum:

D

• Maintenance type projects that do not involve structural overlays, formation widening or significant increases in seal width, but where some heavy / specialised plant is required, as given by the examples in the dot points below. Where the pavement is not being rehabilitated/ reconstructed, the roadway must have retained its shape with respect to crossfall and grade to classify as Class D. o Pavement rehabilitation o Minor overlays (small height increase) o Resheet of unsealed road o Reseal o Part shoulder seal

Geometric Parameters Assessed

• Crossfalls • Superelevation • Flow path depths at curve transitions • Geometric elements that have a significant crash history in spite of appropriate mitigating treatments already in place None

Minimum Design Criteria for Assessed Parameters* • EDD (where an EDD exists), if a brownfield site • Design exception, if an exceptional circumstance • NDD for all other instances • EDD (where an EDD exists), otherwise NDD • Design exception where prohibitively expensive to justify • EDD (where an EDD exists), otherwise NDD (apply mitigating devices to sites with crash histories relating to geometry identified in road safety audit/s)

• None (apply mitigating devices to sites with crash histories relating to geometry identified in road safety audit/s)

* Acronyms used in this column: NDD - Normal Design Domain, EDD - Extended Design Domain, refer Austroads (2006) for further information.


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To address this issue, the TNRP Guidelines defined criteria for applying structural overlays to two-lane, two-way rural roads. These criteria include carriageway width, based on criteria from the TMR State-Controlled Priority Road Network Investment Guidelines (TMR, 2011b): • Vision Seal Width – the desired long term carriageway width interpreted from TMR’s Road Planning and Design Manual (TMR, 2001). • Interim Seal Width - the carriageway width for a particular road link acceptable within a twenty-year term, based on affordability and making maximum use of the existing asset. These values are usually less than the Vision Seal Widths (often by a value of 1m). In Queensland, it is common practice to pave and seal the entire carriageway width (traffic lanes and shoulders) to reduce maintenance requirements. The vision and seal criteria above adopt this practice. The amount of rainfall experienced during the recent disaster events reinforces the need for this practice to continue, and the TNRP Guidelines reinforce this requirement.

Need for Formation Widening The TNRP Guidelines state that formation widening is necessary when overlaying where the new pavement is unable to be placed on the existing formation. The new pavement is deemed to be able to be placed on the existing formation if all of the following criteria are met: • The new carriageway width is at least equal to the greater of: – the Interim Seal Width, plus any curve widening and verge requirements – the existing carriageway width, where it is greater than the interim width and where a majority of the road link is constructed to this existing width – the width required for cycling requirements – 9m, if on embankment and the batter slopes are steeper than 1 on 4 • On low embankments up to 1m high (desirably 2m) and in cuttings, the maximum edge slope of the pavement layers is the steeper of: – 1 on 4 – the existing batter slope • On higher embankments, the maximum side slope of the pavement layers is 1 on 2. An example illustrating the above is shown in Figure 8. These criteria mean that TMR will allow the narrowing of carriageways when applying structural overlays, but only to a minimum of the Interim Seal Width. If a carriageway width equal or greater than the Interim Seal Width cannot be achieved, the formation must be widened. In addition, these criteria ensure that batters are only steepened to the maximum values in the Road Planning and Design Manual.

Interim seal width Surface of overlay * Surface of sub-grade

* Surface of existing formation

Figure 8: Example indicating where the absolute minimum carriageway width criteria has been met * Maximum side slope of pavement layers: On low embankments and in cuttings – steeper of 1 on 4 and existing batter slope On higher embankments – 1 on 2


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Design Criteria when Widening of the Formation is Required Where formation widening is required, the TNRP Guidelines promote the adoption of a Vision Seal Width where the cost is less than, equal to, or marginally greater than, that required to construct an Interim Seal Width. This situation can commonly occur on embankments because widening to Interim Seal Widths usually involves ‘sliver’ widening, in which a wider formation has to be constructed first because of the standard size of plant used. It is then cut-back in order to ‘rigidly’ conform to the required formation width. Widening to cater for a carriageway width equal to the Vision Seal Width has the following major advantages: • It is likely that the formation will not need widening again in the foreseeable future (unless there is a major increase in traffic volume). This results in a low whole-of-life cost solution. • It will cater for a nominal future overlay constructed to an Interim Seal Width (if and when required). Generally, formation widening on embankment and in cuttings can be undertaken by either steeping batters (if appropriate) or by widening the earthworks footprint. Criteria for each of these are given in the TNRP Guidelines. An example of formation widening on embankment by widening the earthworks footprint is given in Figure 9.

New formation to cater for vision seal width1 Interim seal width Surface of overlay #

*

* Surface of sub-grade

*

#

Surface of existing formation

*

Figure 9: Example of formation widening on embankment by widening the earthworks footprint (widening both sides shown) * Maximum fill slopes: On low embankments – maximum of 1 on 4 (desirable 1 on 6) On higher embankments – maximum as per geotechnical requirements (refer Section titled ‘Geotechnical’) # Alternative (preferred) treatment 1. Use interim seal width if vision seal width is more expensive to construct and complementary works funding is not available to cover the difference.

Verge Requirements TMR, 2001 sets a minimum verge width of 0.5m (1.0m desirable) on embankments when roadside barriers are not required. This value is measured from the shoulder edge to the hinge point (dimension ‘L’ shown in Figure 10). It is based on the interstate practice (outside of Queensland) of allowing for rounding of the verge either side of the hinge point. It is normal practice for these states not to fully seal their shoulders. There has been a long term debate within TMR as to the need for verges in this situation. Support for the provision of verges is often based around the following arguments: • Verge rounding will occur naturally, whether or not it is specifically allowed for. And therefore, a width for verge widening should be provided, otherwise the rounding of the outside of the shoulder will occur.


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• Verge rounding provides a more forgiving surface for out-of-control drivers travelling from the carriageway onto the batter. Counter arguments include: • Provided sealing is extended to the hinge point and batters are quickly grassed / vegetated to protect against erosion, verges do not round to any significant degree. • Whether or not verge rounding occurs, it is the width between hinge points that is important. Adding an extra width for the verge is, in effect, providing a wider road. This generally results in a safer road, but one that is more expensive. Strategic investment programs generally dictate what widths are affordable (refer Vision and Interim Seal Widths in the previous section).

Figure 10: Verge width ‘L’ and verge rounding At an internal meeting, TMR construction and maintenance engineers gave strong support for the argument in the second last dot point i.e. that verges do not round to any significant degree provided the considerations listed are applied. Based on this outcome, the TNRP Guidelines removed the requirement for verges in this situation only if: • sealing is extended to the hinge point to protect against natural rounding, and • batters can be quickly grassed / vegetated to protect against erosion.

Design Documentation Given the magnitude, urgency and nature of the TNRP works, a key requirement was to minimise the amount of documentation but still be able to: • unambiguously define the works intended by TNRP • produce a “workable” record of the road afterwards, bearing in mind that TMR did not currently have suitable plans for all of the affected roads. The Guidelines allow documentation of TNRP project work for Road Design Class D (and sometimes for Class C) in the form of ‘type cross section and strip diagrams’. Importantly, the Guidelines covered how the documentation would complement existing working plans and the need for the new documentation to reference the relevant extents on the existing plans. This was necessary because many existing plans were in imperial units and/or had a different chainage datum to current practice. Likewise, the Guidelines covered the documentation requirements for Road Design Class B and C works based on Mobile Laser Scanning (MLS) surveys. While new working plans would be produced in these cases, in most cases the new plans would have to be complemented by the existing working plans for many relevant features that were not picked up by the MLS survey.


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CONCLUSIONS The disaster events of January 2010 to April 2011 have dramatically illustrated the vulnerability of Queensland’s state road network to prolonged high intensity rainfall and flooding. Slope failures and damage to pipes, culverts, bridges and pavements have been recorded. One quarter of the road network was damaged in some way. In authoring the TNRP Design Guidelines, one of the most important considerations was in regard to the provision of resilience. In particular: • what was required to make TMR’s network resilient to future disaster events • what level of resilience was affordable. To deliver cost effective reconstruction solutions (in a whole-of-life sense), the Guidelines emphasise the importance of addressing the contributory causes of damage in design. These generally relate to inadequate formation and pavement drainage, overtopping and scour of embankment batters, moisture sensitive pavement materials, high velocity scour in drainage channels and streams, moisture entry into and weakening of cut and embankment batters and erosion of the toe of embankment batters. The Guidelines recognise the trade-offs that are necessary when ‘disaster-proofing’ each damaged road segment. Some treatments are either impractical or collectively prohibitively expensive. Nevertheless, application of the Guidelines will result in improved resilience of many of the damaged road segments against future flooding and rainfall events. For other road segments, mostly the lower trafficked roads, vulnerability will be reduced to some degree but not greatly. TMR will continue to consider the affordability and practicality of providing a resilient network, including the requirement for all drainage paths to be mapped for major rainfall events.


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REFERENCES AS 5100, Australian Standard 5100 Bridge Design, Standards Australia, Sydney, Australia. Austroads 2006, Guide to Road Design, Part 2 ‘Design Considerations’, Pub. No. AGRD02/06, Austroads, Sydney, Australia. Cox, R.L. and Arndt, O.K. 2008, The Geometric Design of Restoration Projects and Low Volume Roads – Axiom or Oxymoron?, 23rd ARRB Conference, Adelaide, 2008. Pritchard, R. 2011, 2010/11 Queensland Floods and Cyclone Events: Learnings for Structures, Proc. 2011 8th Bridge Conference, Sustainable Bridges: the Thread of Society, Austroads, Sydney, Australia, October-November 2011. RTA 2011, RTA Guide to Slope Risk Analysis, Version 4, TP-GDL-(TBA), Roads and Traffic Authority, New South Wales, March 2011. TMR 2000, Characteristics of Foam Bitumen Stabilisation, Engineering and Technology Forum, Queensland Department of Transport and Main Roads, August 2000. TMR 2001, Road Planning and Design Manual, Queensland Department of Transport and Main Roads, Brisbane, Australia. TMR 2006, Drafting and Design Presentation Standards Manual, Queensland Department of Transport and Main Roads, Brisbane, Australia. TMR 2009, Pavement Design Manual, Queensland Department of Transport and Main Roads, Brisbane, Australia. TMR 2010, Main Roads Technical Standard MRTS05: Unbound Pavements, Queensland Department of Transport and Main Roads, Brisbane, Australia. TMR 2011a, Design Guidelines – Transport Network Reconstruction Program, Queensland Department of Transport and Main Roads, TNRP-SPO-DG-PM-0020, Brisbane, Australia. TMR 2011b, State-Controlled Priority Road Network Investment Guidelines, Queensland Department of Transport and Main Roads, Brisbane, Australia.

ACKNOWLEDGEMENTS The authors would like to acknowledge the efforts of the following individuals from the Queensland Department of Main Roads in the preparation of this paper: David Griffin, Funding Liaison Manager, TNRP Mike Jovanovic, Director (Bridge Design) Dr William Weeks, Director (Hydraulics) Juan Delgado, Principal Engineer (Design & Processes) (resigned) John Woodsford, Contractor (Geotechnical) Dr Emeka Ezeajugh, Senior Geotechnical Engineer Peter Evans, Deputy Chief Engineer (Pavements, Materials & Geotechnical) Dr Ross Pritchard, Deputy Chief Engineer (Structures) Ricky Cox, Director (Special Projects – Road Planning & Design)


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Mike Whitehead, Principal Engineer (Road Design Standards) David Wilson, Contractor, TNRP James Ward, TNRP Technical Coordinator


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AUTHOR BIOGRAPHIES Dr Owen Arndt Owen Arndt holds the position of Director (Road Planning and Design) within the Queensland Department of Transport and Main Roads (TMR), where he manages a specialist road design team of approximately 30 people. Owen has extensive experience in the planning and design of urban and rural roadways, motorways, intersections and interchanges. His experience also covers the management of road and noise barrier construction projects. Owen has developed and updated numerous road design standards for TMR and Austroads, undertook major research projects, developed and delivered road design training courses and provided specialist advice and reports on road design standards and projects. In 2011, Owen coordinated the development of the Transport Network Reconstruction Program Design Guidelines for the reconstruction of TMR’s network damaged by the recent disaster events. Jothi Ramanujam Rama has 38 years of experience in road construction and design projects in a number of countries including Sri-Lanka, Nigeria, United Arab Emirates, Brunei and Australia. He currently holds the position of Principal Engineer (Pavement Rehabilitation) in the Department of Transport and Main Roads. In his 23 years with the Department, he has been involved in major pavement investigation works, pavement performance studies, R&D works on insitu stabilization including pioneering work on foam bitumen stabilisation and hot in-place asphalt recycling. Rama has written a number of reports and technical papers for both local and international conferences such as Transport Research Board Conference in Washington, USA. Rama compiled and published the Queensland Transport Pavement Rehabilitation Manual in 1992 and won a Merit Award for this work under the Departments Excellence Award Scheme. Siva Simakumar Siva Sivakumar is the Principal Geotechnical Engineer with the Queensland Department of Transport and Main Roads. He joined the Department in 1998. Since his graduation in 1983, Siva has worked predominantly in the geotechnical engineering field. He has been involved in major projects in Australia, Malaysia, Thailand and Sri Lanka. Experience that Siva has gained during his career includes planning, design and construction supervision of major and minor roads and bridges; site investigation works for buildings, bridges, roads, tunnels and slopes; stability and settlement analyses of embankments on soft ground; design of shallow and pile foundations, retaining structures including tunnel walls, cut and fill slopes including remedial works; construction supervision of earth and concrete works; monitoring and interpretation of geotechnical instrumentation. He has given technical input in Geotechnical Engineering to the numerous large projects that the Department has embarked upon in recent years. He also played a lead role in the development and maintenance of the Department’s geotechnical standards. Ian Reeves Ian Reeves has over 40 years road engineering experience gained from a long career with the Queensland Government prior to joining the ARRB Group in August 2010. Building on his grounding in both operational and specialist (geomechanics and pavements) roles, Ian progressed through a variety of technical and executive leadership roles and has held representative positions on the US Strategic Highway Research Program, various Austroads committees and the World Roads Association (PIARC). Ian’s most recent role with the Queensland Department of Transport and Main Roads (TMR) was as General Manager Engineering and Technology (Chief Engineer) – a position held for four years. This role ensured that TMR had the technical systems and specialist engineering capability to meet the current and future demands and risks associated with the management of some $54 billion of road infrastructure and an annual $3+ billion works program across Queensland. Ian assisted TMR with the review of the TNRP Design Guidelines and a number of the TNRP reconstruction projects in regard to alignment with the design guideline requirements.


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Copyright Licence Agreement The Author allows ARRB Group Ltd to publish the work/s submitted for the 25th ARRB Conference, granting ARRB the non-exclusive right to: • publish the work in printed format • publish the work in electronic format • publish the work online. The Author retains the right to use their work, illustrations (line art, photographs, figures, plates) and research data in their own future works The Author warrants that they are entitled to deal with the Intellectual Property Rights in the works submitted, including clearing all third party intellectual property rights and obtaining formal permission from their respective institutions or employers before submission, where necessary.


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