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Comparison of RAPTOR measurements with falling weight deflectometer deflections using backcalculation
Published in Inge Hoff, Helge Mork, Rabbira Garba Saba, Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields, Volume 3, 2022
Structural capacity of pavements is usually evaluated by deflection measurements performed by a Falling Weight Deflectometer (FWD), which applies a stationary impulse load on the pavement. In recent years, there has been an increasing interest in applying high speed continuous deflection measurements for network level applications. Examples of continuous deflection devices are the Traffic Speed Deflectometer (TSD) and the Rapid Pavement Tester (RAPTOR), which continuously measure the pavement response due to a constant loading from the wheel moving on the pavement. These devices overcome the limitation of an FWD since they operate at traffic speed and require no traffic disruptions. However, the response of the pavement due to the continuously moving load is different than the pavement response to an FWD impulse load. Due to the viscoelastic nature of asphalt concrete the pavement response under a moving load is delayed in time resulting in an asymmetric deflection basin around the loading wheel. The dynamic FWD impulse load generates a wave transmitted through the pavement structure, and thus inertia becomes significant (see e.g. Maina et al. (1996) and Cao et al. (2019b)). Deflections obtained from a continuous deflection device can therefore not be expected to be the same as deflections measured by an FWD.
Nondestructive Tests
Published in Rajib B. Mallick, Tahar El-Korchi, Pavement Engineering, 2017
Rajib B. Mallick, Tahar El-Korchi
A falling weight deflectometer (FWD) is extensively used for estimation of pavement layer moduli and for determination of the structural condition of pavements. The information obtained from FWD testing can be used in structural analysis to determine capacity, estimate expected performance life, and design a rehabilitation plan for pavements. Deflections prior to and after pavement rehabilitations are done to evaluate the effectiveness of specific rehabilitation methods. An FWD can also be used to test load transfer efficiency (LTE) of joints within concrete pavements. American Society for Testing and Materials standards are available for the use of an FWD for pavement deflection-based testing (see ASTM 4694, 4695–96). Standard calibration procedures for load cells and deflection sensors are also available.
Application of falling weight deflectometer for the estimation of in-situ shear strength parameters of subgrade layer
Published in Andreas Loizos, Imad L. Al-Qadi, A. (Tom) Scarpas, Bearing Capacity of Roads, Railways and Airfields, 2017
H. Nabizadeh, E.Y. Hajj, R.V. Siddharthan, S. Elfass, M. Nimeri
Falling Weight Deflectometer (FWD) as a nondestructive device has been routinely used in the pavement industry for the purpose of in-situ evaluation of structural capacity of in-service pavements. The FWD simulates pavement responses under a moving truck wheel though it applies a stationary impact load to the pavement surface. The measured applied load in conjunction with the vertical surface displacements at different radial distances from the load application (called deflection basin) used as the input for backcalculation algorithms to estimate the in-situ resilient stiffness of the various pavement layers. The backcalculated layer stiffnesses have been used as an indicator of the pavement structure’s adequacy subjected to the standard traffic loading.
Influence of seasonal and diurnal FWD measurements on deflection-based parameters for rigid pavements
Published in International Journal of Pavement Engineering, 2022
Hamad Bin Muslim, Syed Waqar Haider, Karim Chatti
Evaluating a pavement's structural capacity involves measuring and analyzing deflections measured with a Falling Weight Deflectometer (FWD) to estimate the layer moduli values. These measurements are essential in assessing pavement structural performance at the network and project levels. However, temporal variations (i.e. seasonal temperature and moisture and diurnal temperature changes) influence these measurements. The temperature differential between the top and bottom of the Portland Cement Concrete (PCC) slab results in curling, affecting the measured deflections using FWD. Thus, when a mid-slab deflection basin is obtained with curled down slab (the slab surface is warmer than the bottom) or corner deflections are obtained when the slab is curled up (the slab surface is cooler than the bottom), the slab may be unsupported resulting in considerable deflections. Such temperature dependant response of the PCC slab affects the critical deflection-based parameters, i.e. the elastic modulus of a slab (Epcc), modulus of subgrade reaction (k), and the Load Transfer Efficiency (LTE). These parameters are essential to evaluate the rigid pavement structural and joint condition, respectively. Also, elevated temperatures cause the concrete slabs to expand. Such expansion of the PCC slab, coupled with slab curling, results in locked joints. As a result, deflection testing conducted at joints when locked results in lower deflections and higher load transfer efficiencies, which is misleading for the overall load transfer capabilities of the joint.
Resilient modulus estimation using in-situ modulus detector: performance and factors
Published in International Journal of Pavement Engineering, 2022
Sang Yeob Kim, Dong-Ju Kim, Jong-Sub Lee, Thomas H.-K. Kang, Yong-Hoon Byun
Several field testing methods are used to evaluate the resilient modulus of subgrade. Non-destructive testing methods have been widely used in the field to evaluate the modulus of subgrade due to their fast and repeatable procedures. One of the most widely used testing methods for measuring pavement surface deflections is the falling-weight deflectometer (FWD). Back-calculation programmes can be used to determine the moduli of multiple layers in pavements after measuring a deflection basin (Li et al. 2018). However, such back-calculation programmes may not provide a unique set of elastic moduli for multi-layered pavements (AASHTO 2008). A lightweight deflectometer (LWD), which is a portable version of the FWD, can be used to control the subgrade compaction quality (Xu and Chang 2013, Schwartz et al. 2017, Duddu and Chennarapu 2022). Recently, Jibon and Mishra (2021) used LWD inside a Proctor mould to estimate the resilient modulus for different soil types and water contents. However, FWD and LWD can only be applied to ground surface, and their influence depth is limited to one to two times the diameter of the plate (Nazzal et al. 2004).
A probabilistic approach to detect structural problems in flexible pavement sections at network level assessment
Published in International Journal of Pavement Engineering, 2022
Luis Fuentes, Katherine Taborda, Xiaodi Hu, Emile Horak, Tao Bai, Lubinda F. Walubita
Road agencies ordinarily evaluate the performance of their road network, both for functional and structural condition on a routine basis (Rabbi and Mishra 2019). Functional condition refers to the characteristics generally associated with roughness and surface texture (including friction) – which are usually evaluated through parameters such as the International Roughness Index (IRI) (Abudinen et al. 2017, Fuentes et al. 2019), Mean Profile Depth (MPD) (Fuentes et al. 2012, Fuentes and Gunaratne 2010) or Mean Texture Depth (MTD) (Adams and Kim 2014), skid resistance typically expressed as Skid Number (SN) (Fuentes et al. 2010, Fuentes and Gunaratne 2011), etc. On the other hand, road agencies encourage the use of non-destructive testing (NDT) to assess the structural condition of pavement structures to avoid intrusive/destructive testing that could cause additional damage to the pavement. The most commonly used NDT equipment for pavement structural evaluation is the falling weight deflectometer (FWD) that has the potential to quantify the pavement structural strength through back-calculation analysis of the individual layer elastic modulus (Ei) (Walubita et al. 2012, Solanki et al. 2014).