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Fallingweight instrument application in highway engineering detection
Release time:2018-06-20
The falling weight deflectometer

In the evaluation of pavement design and bearing capacity, falling weight deflectometer (FWD) is the strength of the pavement is currently the most advanced one of the non-destructive testing equipment, the measurement result is more accurate, and a large amount of information. Compared with the traditional Backman beam deflection measurement, Is convenient, fast, safe, saving manpower, simulation of applying the dynamic load characteristics of the actual situation .
The federal highway administration through the analysis and comparison, verify that FWD is the ability of dynamic evaluation of equipment bearing good pavement, and selected FWD as an important equipment for evaluating pavement strength when applying SHRP. Shell oil company has been officially incorporated into the Shell FWD pavement design manual. The falling weight deflectometer plays an important role in the carrying capacity of pavement measuring instrument.
 
Working principle

FWD through the computer control system for the hydraulic system to start falling, a quality drop from a certain height free fall, the impact force on the bearing board and passed on to the pavement, thus exerting pulse load on the pavement, causing the road surface to produce instantaneous deformation, distribution from the measured deformation of different position sensor for the detection of surface layer structure the system will record, signal transmission to the computer, the determination of dynamic bending in dynamic load deflection and deflection basin. The test data can be used for backcalculation of pavement layer moduli, so as to scientifically evaluate the bearing capacity of pavement.
 
The practical application in engineering detection

The construction process control testing

A section of highway subgrade engineering construction ended and tested after completion to pavement subbase construction, at the end of the construction base, was analyzed by FWD deflection testing on the layer, found in section 400m base top surface deflection is large, through the acquisition of the deflection basin data of pavement structure layer modulus calculation the results show that subbase modulus is extremely uneven and the values of most than subgrade modulus value. According to the design of pavement structure layer modulus of top-down the law of diminishing the decision layer construction quality problems. The construction unit may, according to the results promptly ordered the construction unit rework, to eliminate the quality problems, to avoid the adverse social impact and greater economic losses.

In the application of rigid pavement void identification on

When mud, void under concrete slabs, the grouting or back cover is an effective method to repair, but it should be based on accurate evaluation of void condition based, otherwise it may cause decreased or even accelerate the destruction of pavement performance. Therefore, the cement concrete pavement, the position and severity evaluation method of reliable foundation plate cavity, to take timely and effective measures, to restore normal pavement performance, are generally faced with cement concrete pavement maintenance management problems.
By using the FWD test plate deflection angle, the load is set to 3, the deflection as the horizontal load as ordinate, corresponding to the 3 level of the load deflection value indicated on the plane; draw the linear fitting line, and the extension of a straight line with the axis intersection; if the board support is good that line will be extended through the origin of coordinates, or within the distance from the origin of 0.05mm, more than 0.05mm will be considered void, usually deviate from the origin, void of the situation is more serious, the theoretical basis of this method is: theoretical calculation and field test show that, before the note corer, 0 load plate regression curve projection angle the deflection should be 0, or close to 0. The advantage of this method is quick and simple, does not need the deep theoretical foundation, suitable for on-site assessment, good results were achieved in practical application at home and abroad, is a worthy approach.

Brand history

Ph is Nix - Carlbro - Grontmij - Sweco
1965, 1999, 2005, 2015

Sweco is the largest European architectural and engineering consulting firm. Grontmij A/S in 2015 to become a member of the Sweco group. Holland Grontmij grontmij company is a leading world of sustainable design, engineering and management consulting, planning and design, water, energy, transportation and monitoring areas active in sustainable development. Grontmij company merged was founded in 1987 in Denmark Carl Bro road consulting company. Carl Bro company in the pavement technology and test equipment production experience, the falling weight deflectometer has high reputation in the world, has been in the world more than 45 countries.
 
In 1965, the world's first manual falling weight deflectometer
In 1968, the world's first trailer FWD
In 1981, began to measure the deflection basin using multiple seismic geophone is the world's first
In 1984, the world's first vehicle mounted FWD
In 1997, the world's first light falling weight deflectometer
In 2005, the world super heavy falling weight deflectometer above the first 300kN deflectometer
Since 2007, PRIMAX series of falling weight deflectometer

purpose

To the completion of inspection, whether the standard bearing capacity evaluation
Stage of road maintenance, pavement prediction of residual service life, maintenance decision section
Evaluation of cement concrete pavement void and joint transfer of force
Access to airport road surface grade PCN value to evaluate the strength of airport pavement
The dynamic real-time calculation of the deformation modulus of pavement structure
Backcalculation modulus
 
technical specifications

Load characteristics 10kN (LWD)
7~150kN (FWD)
7~250kN (HWD)
7~350kN (SHWD)
Half sine pulse waveform
The pulse duration of 20-30ms, pulse rise time: 10-15ms
Load sensor The resolution of 0.1kN, the precision for the full range of 1% + 0.1kN
Bearing plate The 4 fraction bearing plate (with rubber cushion)
300mm and 450mm diameter optional
Deflection sensor Seismic velocity sensor
Number: 1~3 (LWD), 1~18 (FWD/HWD/SHWD)
Range: 1~2200 microns
Precision: better than the full range of 0.2% - 1 micron
The length of the sensor test beam: 3 meters
Temperature sensor Table, air, road pavement structure layer 3, optional infrared thermometer pavement
The accuracy of plus or minus 1 DEG C, resolution 0.1 C
Distance sensor 0.1% accuracy is better than the whole
Test speed 35 seconds per point, about 65 points per hour (related measurement distance)
Data acquisition system All channels (temperature, deflection, distance and load) are synchronous acquisition
Resolution: 16
Sampling rate: 4kHz/ channel, optional 10kHz/ channel
Size and weight 4300 x 1840 x 1520mm (trailer type, vehicle type depends on the size of the vehicle)
1180kg (excluding hammer)
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