Design of a flexible pavement is influenced by the quantity and composition of the expected traffic, the subgrade strength properties, paving material properties, and the environment in which the pavement is to perform.
Despite the meticulous design calculations involved and improvements made to construction specifications, equipment, and construction processes over the years, premature failures and chronic pavement distresses continue to occur. Pavement deteriorates to a point where it is no longer satisfies the criteria under which it is designed, whether in terms of structural capacity, pavement roughness, riding quality or surface friction. The early decrease in the serviceability of pavement can be caused by a number of complex and sometimes competing variables such as:
- poor quality inspection and staffing
- fluctuations in levels of experience inspectors and project managers
- incompatibilities between new admixtures and construction materials
- implementation of new technologies and construction methods
- environmental constraints and recycled materials
- other issues unforeseen during design and construction phases.
The general failure areas in a typical flexible pavement include tensile stress failure of semirigid pavement layers, shear failures of surface and base courses, and compressive failures of the subgrade. Flexible pavements fail in two basic modes:
distortion (rutting, shoving, depression, raveling and corrugations), and
cracking (alligator, longitudinal, transverse, and block cracking).
To prevent, and to reduce the probability of premature pavement failures and poor long term pavement performance, the root causes of these problems have to be identified. It is a challenging task to determine the causes of pavement failures. Forensic investigations of pavement failures are critical, as the information gained can be used to improve our understanding of pavement construction, develop an optimal rehabilitation strategy, and to resolve construction disputes. Cawangan Kejuruteraan Jalan & Geoteknik (CKJG) now has a pavement forensic unit to conduct investigations on pavement failures. This new team is in the process of formalising the procedures and techniques for the forensic investigations.
In conducting forensic studies, the pavement forensic unit shall undertake the following general steps:
thorough review and analysis of existing quality construction records and tests,
non-destructive testing like Ground Penetrating Radar (GPR) and the Falling Weight Deflectometers (portable FWD),
field testing such as Dynamic Cone Penetration (DCP), coring, trenching, and
laboratory testing are also conducted to validate/confirm the initial hypothesis.
The root causes of the pavement failures often can be identified through these tools, in conjunction with thorough review of construction records and rehabilitation history. Application of non-destructive testing such as the Ground Penetrating Radar (GPR) and Falling Weight Deflectometer (FWD) are essential to identify problematic areas and probable causes. Field testing such as Dynamic Cone Penetration (DCP), coring, and laboratory testing have been found critical to these forensic investigations on flexible pavements. Laboratory tests are often required to complete the investigation especially if the repair strategy calls for in place recycling of the existing structure.
The outcomes from forensic studies can also be used to validate/change/modify the existing design plan, improve future design and to resolve the disputes involving construction claims. Rehabilitation strategy also requires knowledge of what is the main cause of the problem.
Some Common Terms:
Base course (Pavements); Compressive strength; Cone penetrometers; Falling weight deflectometers; Flexible pavements; Ground penetrating radar; Pavement design; Pavement distress; Pavement maintenance; Pavement performance; Pavements; Rehabilitation (Maintenance); Structural engineering; Triaxial shear tests; Texas; Forensic engineering; Load carrying