FWD and LWD Test Results Comparison and Numerical Simulation by FEM Based ABAQUS Software

Using Non-Destructive (tests) in pavement response analysis is increasing in the world due to its high speed field testing, measuring equipment accuracy, without any destructive effect on pavement surface. On the other hand road construction procedure must be able to meet the best layer quality and economic feasibility. Now quality control of constructed layer is being done by compaction percentage using sand cone traditional method. In recent years LWD application as a non-destructive and portable device is increasing. This device is capable to evaluate layers structural condition with high accuracy in a short time. LWD performance is the same as FWD and sometimes called PFWD. A circular frequency load applies in 25 milliseconds at different stress levels and the deflection will be measured by several transverse or longitudinal geophones. Finally the elastic modulus of pavement layers will be determined by back-calculation procedure by means of Boussinesq’s equation in a homogeneous, isotropic, linear elastic semi-infinite space. The following equation below represented for surface elastic modulus.In this research FWD and LWD test have been proposed to be done on pavement subgrade soil on same locations and stress levels, then correlation of both tests results determined. Also compaction test conducted at 5 point due to evaluate LWD efficiency in layer compaction quality. Results show good agreement between LWD and FWD modulus and the average modulus has maximum correlation factor. The equation represented below shows the relation between compaction percent and average modulus of LWD. The high determination factor equal to 0.923 shows the data points fit well. Compaction (%) = 0.347ELWD + 6.215 3 FWD and LWD Test Result Comparison … / Brazvan et al., In addition the field tests are simulated using finite element based ABAQUS software. The soil element modeled as AXISYMMETRIC due to load condition and soil material is defined by linear elastic and linear elastic perfect plastic Drucker-Prager extended model. A frequency semi-sine load is applied to meet the real state test condition. The CAX4 axisymmetric 4 node bilinear elements have been used to model discretization. Deflections resulted from elastoplastic 3D FEM and LWD have higher determination factor which is shown at figures below. Also the time history of field tests and FEM models compared and the time history of plastic model and LWD results are in good agreement which can be seen at following figure. Numerical model shows that plastic strains will be eliminated at final loading cycles and the strains will be reversible. This concept is similar to LWD field test procedure. The FEM model proved that in small limit of vertical stress, the soil behavior can be considered as linear elastic.