CN1869341A - Method for raising testing precision of H-FWD using acceleration transducer - Google Patents

Abstract

The invention relates to a method to improve H-FWD testing accuracy by adopting acceleration sensor to test groundsill, paving quality and rigidity. It could rapidly and accurately test the deformation behavior of groundsill material and paving. The invention improves the testing accuracy by adjusting the sole plate inertial force.

Description

Adopt acceleration transducer to improve the method for portable benkelman beams deflectometer (H-FWD) measuring accuracy

In repaiied the shop of construction of banketing and road, its rigidity (deformation characteristic) was important mensuration project.Traditional planar loading experiment, methods such as CBR test not only need counter-force equipment, and length consuming time, the expense height.In recent years, be the dynamic loading method of representative receive much concern (shown in Figure 2 is the notion of portable H-FWD) with portable benkelman beams deflectometer (H-FWD).H-FWD transports by manpower or carrier, lifts weight by manpower or easy device, produces impact weight.By measuring impact load and the just following amount of bow (settling amount) of the point of load that takes place, can infer the rigidity that repair ground and shop.

The present invention is a kind of method that adopts acceleration transducer to improve the H-FWD measuring accuracy (the portable benkelman beams deflectometer of modified form is called for short EH-FWD), is used to test ground, quality of mating formation and rigidity.It has structurally done bigger improvement to existing portable H-FWD, can improve measuring accuracy greatly.

The process of the test of existing portable H-FWD

(1) removes the loose material of foundation surface, make its surface level and smooth as much as possible.

(2) portable H-FWD is set on the test position of ground.

(3) ball freely falls from the height of setting, and at this moment writes down maximum loading P _iMaximum settlement amount δ with load central authorities _i

(4) each measuring point is provided with height of drop more than 3 or 3.

(5) order is from low to high tested.

(6) in identical height free-falling more than 5 times or 5 times.

Said process can obtain under the sustained height, and the average of peak load and settling amount is tried to achieve coefficient of subgrade reaction K by load pressure P and settling amount δ _FWD

[formula 1] $K_{\mathrm{FWD}}=\frac{P}{\mathrm{\δ}}$

The problem that invention solves

In the test process of existing portable benkelman beams deflectometer, exist bigger defective.Following analysis shows, with the impact force P of the ring test of measuring one's own ability and impact force P to ground reality _SBetween, exist certain error, and measuring accuracy is produced bigger influence.

1. the relation of power is seen Fig. 3 (compare with impact force, deadweight is left in the basket) between weight, backing plate and the ground.Is F by backing plate to the impact force of ground _PS, can get:

[formula 2] F _PS(t)=F _HP(t)-M ₂a ₂(t)

[formula 3] F _HP(t): the impact force between ball and the backing plate.

[formula 4] M ₂a ₂(t): the inertia force of backing plate.M ₂And a ₂(t) be the quality and the acceleration of backing plate respectively

2. in static load test, the acceleration a of backing plate ₂(t) value goes to zero, so M ₂a ₂(t) inertia force of backing plate can be ignored, and promptly has:

[formula 5] F _PS(t)=F _HP(t): the power of the ring test of promptly measuring one's own ability and equal to the compressive force of ground.

And in the dynamic loading test, the acceleration a of backing plate ₂(t) value does not go to zero, M ₂a ₂(t) inertia force of backing plate be can not ignore, in this case:

[formula 6] F _PS(t) ≠ F _HP(t): we can say have the error of can not ignore to produce between the impact force of the ring test of measuring one's own ability and the actual impact force that passes on the ground.

3. therefore to accurately test the deformation characteristic of ground, must revise the inertia force of backing plate.But, in existing H-FWD, do not test the acceleration a of backing plate owing to adopt settlement gauge to test the settling amount of backing plate ₂(t), so can't revise the inertia force of backing plate.

The method that problem solves

In order to solve the above problems, the invention provides the modification method of the inertia force of backing plate.Its principle is to replace the settlement gauge in the existing measuring technology and the ring of measuring one's own ability with acceleration transducer.

1. the correction of backing plate inertia force:

(1) tests the acceleration a of backing plate by being arranged on acceleration transducer on the backing plate ₂(t) (see figure 1).

(2) with the acceleration a that tests ₂(t) multiply by the mass M of backing plate ₂, can draw the inertia force M of backing plate simply ₂a ₂(t) also revised.

2. the calculating of the impact force between ball and the backing plate

(1) tests the acceleration a of spheroid by the acceleration transducer in interior plant spheroid ₁(t) (2) are according to newton's the 3rd law, F _HP(t) the suffered impact force of (impact force of ball and backing plate) and ball is big

Little equating,, direction (symbol) is opposite, promptly

[formula 7] F _HP(t)=-M ₁a ₁(t)

M ₁, a ₁(t) be the quality and the acceleration of spheroid (built-in acceleration transducer) respectively.

3. the calculating of backing plate settling amount δ

At this, by acceleration a to test ₂(t) carry out the settling amount δ that numerical integral method is calculated backing plate

(1) with t acceleration a constantly ₂(t) and t+ Δ t acceleration a constantly ₂(t+ Δ t) tries to achieve the t+ Δ t settling amount δ of backing plate constantly _{P, t+ Δ t}

[formula 8] ${\mathrm{\δ}}_{p,t+\mathrm{\Δt}}={\mathrm{\δ}}_{p,t}+v_t\mathrm{\Δt}+[\frac{a_2\left(t\right)}{3}+\frac{a_2(t+\mathrm{\Δt})}{6}]\mathrm{\Δ}{t}^2$

Wherein, v _tBe the t speed of backing plate constantly.And can obtain:

[formula 9] $v_{t+\mathrm{\Δt}}=v_t+\frac{\mathrm{\Δt}}{2}[a_2\left(t\right)+a_2(t+\mathrm{\Δt})]$

(2) initial time (t=0), the settling amount of backing plate and speed are zero, and through type 8 and formula 9 can be calculated each settling amount of backing plate constantly.Certainly when the backing plate rigidity is far longer than the rigidity of ground, the settling amount δ of backing plate _PEquate substantially with the settling amount δ of ground.

(3) it should be noted that when the Integral Processing of reality,, depart from because small shaking can take place the unstability (difference of particularly compressing and stretching) of acceleration transducer and charge amplifier.Therefore, when the acceleration signal Integral Transformation of testing was become rate signal, its baseline can drift about in time and produce error.When consequently vibrations had stopped actually, the speed that calculates was but still continuing, so need revise them.

4. address this problem and to be revised the acceleration of measuring.

(1) make displacement, speed and acceleration correction value are  _t, it is defined as follows:

[formula 10]  _t=a _t-(β ₀+ β ₁T)

[formula 11] ${\hat{v}}_t=v_t-({\mathrm{\β}}_{0}t+\frac{1}{2}{\mathrm{\β}}_1{t}^2)$

[formula 12] ${\widehat{\mathrm{\δ}}}_t={\mathrm{\δ}}_t-(\frac{1}{2}{\mathrm{\β}}_0{t}^2+\frac{1}{6}{\mathrm{\β}}_1{t}^3)$

(2) herein, introduce two conditions:

1. the value of speed when finishing is zero behind the integrated acceleration of having proofreaied and correct.

The infall process of the integrated acceleration of 2. having revised, the most similar to the infall process before revising (least square and be minimum).

(3) by calculating, can obtain correction factor β ₁And β ₀

[formula 13] ${\mathrm{\β}}_1=\frac{28}{13}\·\frac{1}{T^2}[2v_T-\frac{15}{T^5}{\∫}_0^T{\mathrm{\δ}}_t(3T{t}^2-2t^3)\mathrm{dt}]$

[formula 14] ${\mathrm{\β}}_0\frac{v_T-{\mathrm{\β}}_1{T}^2/2}{T}$

(4) with this correction factor β ₁And β ₀Can the corrected Calculation acceleration and integration after settling amount.

So far, ask for required every index (settling amount δ, the impact force F of distortion index of ground _PS(t)=F _HP(t)-M ₂a ₂(t)) all can try to achieve.

5. simultaneously, owing to omitted the ring of measuring one's own ability, the structure of backing plate is also simplified greatly.

6. in sum, the present invention compares with traditional method following characteristics:

(1) inertia force of correction backing plate: the inertia force that produces when backing plate is subjected to impact force is revised, and improves the measuring accuracy of portable FWD.

(2) simplified structure: the present invention respectively installs acceleration transducer at ball and backing plate and replaces the ring of measuring one's own ability.

The form that invention is implemented

The present invention is the test ground, the method for the rigidity of mating formation, and test sequence is as follows:

(1) removes the loose material of foundation surface, make its surface level and smooth as much as possible.

(2) test position of this equipment (EH-FWD) to ground is set.

(3) ball freely falls from set height, and at this moment each acceleration constantly of ball and backing plate is measured.

(4) acceleration of Ce Lianging is proofreaied and correct by formula 10～14.

(5) with the acceleration of having proofreaied and correct, but through type 7～9 is tried to achieve each loading P (t) and settling amount δ (t) constantly.

(6) change the height of drop (differing heights more than 3 or 3 is set) of ball, and the sustained height ball falls 5 times or more than.

Though utilize the loading P (t) of each time test and settling amount δ (t) can directly obtain coefficient of subgrade reaction K _FWD, but in order to reduce the constant error of test, preferably try to achieve coefficient of subgrade reaction (with reference to Fig. 4) with the maximum loading and the recurrence of maximum settlement amount of each time test.

In order to gather the various information of impact process, we have developed signal and have taked treatment system.System has the processing function that reduces noise.Test, the flow chart of resolving, as shown in Figure 6.

The example of test

Verify system of the present invention by field trial: adjust height of drop, the record impact process.Shown in Figure 5 is the example of test waveform.Among the figure, Ch0 is the signal that is embedded in the sensor test acceleration in the ball, and Ch1 is the signal that is fixed on backing plate upper sensor testing acceleration.

1. maximum loading and the maximum settlement amount with each time test returns coefficient of subgrade reaction.As shown in Figure 4.

2. according to the result of these demonstration tests and analysis afterwards, as can be known:

(1) Kai Fa test macro is feasible in practice.

(2) Ce Shi coefficient of subgrade reaction also is rational.

The effect of invention

Elaborate explanation by above, when the deformation characteristic (rigidity) that detects foundation material and mat formation, the present invention can test fast and accurately, and for the defective that has dynamic loading equipment now, by correction, improved its measuring accuracy to backing plate inertia force.

Brief description of drawings:

Fig. 1: adopt acceleration transducer to improve the small-sized FWD structural outline (EH-FWD structure chart) of the method design of portable benkelman beams deflectometer (H-FWD) measuring accuracy by the present invention

Fig. 2: former H-FWD structural outline

Fig. 3: backing plate stressing conditions

Fig. 4: the example of resolving figure output

Fig. 5: the example of testing acceleration signal

Fig. 6: test, the flow chart of resolving

Claims (1)

1. The present invention is the method that a kind of employing acceleration transducer improves H-FWD (portable benkelman beams deflectometer) measuring accuracy.It is characterized in that: on the backing plate of H-FWD, acceleration transducer is installed is replaced existing sensors and measure one's own ability ring.By resolving the settling amount of impact force and backing plate, revise the inertia force that the previous method lower bolster produces, thereby improved the measuring accuracy of H-FWD.

Images