How do you determine the bearing capacity by using Deflectometer (LFWD)?

A Light Falling Weight Deflectometer (LFWD) is an instrument used to determine the bearing capacity of a pavement or road surface by measuring the deflection caused by a falling weight dropped onto the pavement.

Here's a general overview of the process:

Setup and Calibration:Set up the LFWD on a stable base near the area of interest. Calibrate the LFWD to ensure accurate measurements. Calibration typically involves dropping the weight onto a known reference surface to establish a baseline measurement.

Instrument Placement:Position the LFWD over the point on the pavement where you want to measure the bearing capacity.

Loading and Measurement:Raise the weight to a predetermined height above the pavement. Release the weight to allow it to fall freely onto the pavement surface. Sensors in the LFWD measure the deflection of the pavement caused by the impact of the falling weight. The deflection is usually measured in millimeters.

Data Collection:The LFWD records the time-history of deflection values as the pavement rebounds after the impact. Data is collected and processed to calculate various pavement parameters, including the deflection basin (the shape of the deflection curve), rebound velocity, and deflection at specific time intervals.

Analysis:The deflection data is typically analyzed using pavement design software or specific analysis algorithms. The analysis considers factors like pavement thickness, material properties, and the load-bearing capacity of the subgrade soil.

Bearing Capacity Estimation:The bearing capacity of the pavement is estimated based on the deflection data and the properties of the pavement layers and subgrade. The specific method for estimating bearing capacity can vary depending on the pavement design methodology and the standards or guidelines being followed. Common methods include layered elastic analysis, backcalculation, and empirical correlations.

Reporting:The results of the LFWD testing, including the estimated bearing capacity and any other relevant pavement parameters, are typically documented in a report.

It's important to note that the accuracy and reliability of LFWD measurements depend on several factors, including the quality of equipment calibration, the consistency of test procedures, and the proper interpretation of data. LFWD is a useful tool for assessing pavement condition and bearing capacity, but it is often used in conjunction with other pavement evaluation methods to obtain a comprehensive assessment of the pavement's performance. Additionally, local guidelines and standards may dictate specific procedures and criteria for LFWD testing in your region.

Bekir Salih Firincioglu

Thanks Gaurav H Tandon for your response.

"The specific method for estimating bearing capacity can vary depending on the pavement design methodology and the standards or guidelines being followed. Common methods include layered elastic analysis, backcalculation, and empirical correlations."

This is the section I need in detail.

Marcelo Llano

Hello,

LFWD provides an elastic response, and bearing capacity is a plasticity problem. Two types of response that is better not to combine because mechanically those carry different meanings.

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