Deflectograph Surveys
Lincs Laboratory provides a comprehensive carriageway assessment service utilising its own Deflectograph, coring equipment and materials testing facilities.
Our Deflectograph is a ‘Pavement Deflection Data Logging Machine’ designed and manufactured in 1985 and updated with the latest Series 4000 Recorder/Data Processing Unit in 2003. It is approved by the Department of Transport for all survey categories listed in their Departmental Standard by attendance at the Transport Research Laboratory annual correlation trials. Static daily calibrations are done on the beam movements and regular checks are made on our dynamic calibration site throughout the test season.
The Deflectograph is a fully self-contained lorry mounted automated measuring system. Peak deflection measurements and elapsed distance are recorded every three to four metres while the machine is in motion. These are stored on the on board computers hard drive and transferred to the office network via USB memory stick for processing at the end of each day. The machine is fitted with a ‘frame lock’ mechanism which allows the operator to take deflection measurements at pre-determined points on the carriageway. The survey speed is approximately 2.5km/h and survey rates can range between 13km to 20km per day depending on traffic conditions and working hours restrictions.
A Microsoft Windows based PANDEF compatible software package is used by the assessment team for analysis of the deflection data. All Deflectograph surveys and subsequent analysis of results are carried out in accordance with the Department of Transport Departmental Standard and Advice Notes. Deflections are temperature corrected to 20 degrees centigrade and are used, along with construction and traffic flow information to predict future life of the road and any overlay requirements. Output is customisable to a format which suits the need of the customer. HMDIF files can be produced for loading data into a UKPMS Pavement Management System.
When should deflectograph surveys be carried out?
Surveys must be carried out under prescribed conditions defined by survey category. The survey categories are defined in the current Department for Transport design manual, a summary table is shown below:
| Months of the Year (X in area refers) | Range of | Survey | |||||||||||||
| J | F | M | A | M | J | J | A | S | O | N | D | Pavement Temperature | Category | ||
| x | x | x | x | x | x | x | Band 1 | 1A | |||||||
| x | x | x | x | x | x | x | Band 2 | 1B | |||||||
| x | x | x | x | x | Band 1 & 2 | 2 | |||||||||
| x | x | Band 1 & 2 | 3 | ||||||||||||
Category 1A defines the preferred conditions for Deflectograph surveys. The highest confidence may be placed on the results in this category. The identification of long-life pavements should ideally be based on a Category 1A survey.
Category 1B extends the upper and lower limits of the temperature range allowed by including Band 2. The category is intended to allow for the situation that may arise when a survey planned for Category 1A does not comply with the specification because of unexpected changes in temperature taking place during the course of the survey.
Category 2 The wider temperature range obtained by adding Band 1 to Band 2 also applies to this category. The first part of September is included in Category 2 because after a hot dry summer, drying out of the subgrade may lead to measured deflections which do not truly reflect the conditions of the pavement.
Category 3 Surveys should not normally be carried out during the summer months specified for this category because of the difficulty in obtaining reliable, reproducible results.
Recent deflectograph contracts
Annually, our Deflectograph surveys the strategic road network of approximately 560km in Lincolnshire. Recent external surveys have included motorways and trunk roads in several Highways Agency areas, DPFO schemes and county road network surveys for Local Authorities and Metropolitan Boroughs throughout the UK.
