The application of falling weight deflectometer

Since the evaluation indicators and standards specified in the current specification are based on the beckman beam test, the data measured by the falling weight deflectometer must be converted into beckman beam data through comparison test before strength evaluation can be carried out. However, the transformation relationship obtained by this simple regression analysis lost a lot of information of the measured data (especially dynamic information), and did not give play to the advantage of the measured sinker data form to evaluate the bearing capacity of the pavement structure.

This article is about three parts about the application of falling weight deflectometer:

1. Response (strain) or modulus of pavement structure inversion

2. Test and evaluate the comprehensive bearing capacity

3. Provide a basis for structural back analysis

1. Response (strain) or modulus of pavement structure inversion

Response (strain) or modulus of pavement structure inversion is falling weight deflectometer an important direction of the application, on the one hand, making use of the inversion software evaluation and service life of pavement strength forecast is falling weight deflectometer’s indirect application. On the other hand, on the geometry characteristic of the falling weight deflectometer, trying to use the geometry of the falling weight deflectometer itself to evaluate road strength, which is a direct application of the falling weight deflectometer.

2. Test and evaluate the comprehensive bearing capacity

The falling weight deflectometer can be used to test and evaluate the comprehensive bearing capacity of the subgrade and pavement of new and rebuilt highways. The falling weight deflectometer measurement speed is fast (about 408 per measurement point), has high precision (with a resolution of 1 DSM), good repeatability, small systematic error (≤2%), and better simulates the dynamic action of traffic load. The advancement and reliability of its technical indexes represent the development level of international road deflection detection technology, which is considered as ideal nondestructive testing equipment for pavement. 

3. Provide a basis for structural back analysis

In particular, the falling weight deflectometer provides an accurate measurement of multi-point deflection, which provides a basis for structural back analysis.

(1) pre-construction design stage

In the design stage before construction, the dynamic elasticity of subgrade and pavement materials can be measured by the falling weight deflectometer, which can be used as the design parameter. In particular, the falling weight deflectometer can provide basic data for project design.

(2) construction stage

During the construction stage, the falling weight deflectometer is inspected layer by layer, which facilitates relevant departments to timely find engineering quality problems and take prompt measures to ensure engineering quality and reduce economic losses.

After 1km of lime stable bottom base construction of a certain section of highway, the supervision department used falling weight deflectometer to carry out spot inspection of bending and sinking. It is found that the bending and sinking value of bottom base and top surface of about 500m was relatively large. After checking, it is found that the subgrade of this project has passed the test, and then the modulus of pavement structure layer is calculated by the inverse calculation of the unqualified section bending and sinking data. The results show that the modulus of base is very uneven, and the modulus of base is smaller than that of soil. According to the rule of decreasing design modulus of pavement structure layer from top to bottom, the construction quality of this layer is judged to have problems. According to the test results, the supervision department shall timely order the construction unit to rework. The elimination of quality hidden trouble ensures the quality of the project and avoids greater economic losses at the same time.

(3) submit (complete) the work acceptance test

In the acceptance stage of delivery (completion), the completed pavement shall be inspected by the falling weight deflectometer according to the quality inspection and evaluation standard of highway engineering. The comprehensive bearing capacity and construction quality of the pavement shall be evaluated according to the sub-bidding section of the whole line of information. This provides data for the acceptance of the project and the basis for evaluating the quality grade.