English version TCVN 8867 2011

TCVN 8867: 2011 is converted from 22 TCN 251 98 as regulated in Section 1, Article 69, Law on Technical Standards and Regulations and point a, clause 1, Article 7, Decree No. 1272007NĐCP dated 182008 by the Government detailing implementation of some articles under Law on Technical Standards and Regulations. TCVN 8867: 2011 is composed by Institute of Transport Science and Technology, proposed by Ministry of Transport, verified by Directorate for Standards, Metrology and Quality, and announced by Ministry of Science and Technology.

VIETNAM STANDARDS

TCVN 8867 : 2011 First Edition

FLEXIBLE PAVEMENT – STANDARD TEST METHOD FOR DETERMINATION OF ELASTIC MODULUS OF PAVEMENT STRUCTURE USING BENKELMAN BEAM

HANOI - 2011

Table of Contents

1 Scope of application 4

2 References 4

3 Terminology and Definition 4

4 Equipment and Tools 4

5 Conduction 5

6 Processing deflection measurement results 7

Appendix A 9

Appendix B 11

Appendix C 13

Appendix D 14

Appendix E 18

Appendix F 22

TCVN 8867: 2011 is converted from 22 TCN 251 - 98 as regulated in Section 1, Article 69, Law onTechnical Standards and Regulations and point a, clause 1, Article 7, Decree No 127/2007/NĐ-CPdated 1/8/2008 by the Government detailing implementation of some articles under Law on TechnicalStandards and Regulations

TCVN 8867: 2011 is composed by Institute of Transport Science and Technology, proposed byMinistry of Transport, verified by Directorate for Standards, Metrology and Quality, and announced byMinistry of Science and Technology

FLEXIBLE PAVEMENT - STANDARD TEST METHOD FOR DETERMINATION OF ELASTIC MODULUS OF PAVEMENT STRUCTURE USING BENKELMAN BEAM

1 Scope of application

This standard provides regulations on test method for determining elastic modulus of flexiblepavement structure for highway, using Benkelman beam, for the purpose of evaluating load bearingcapacity of the new pavement or quality of the pavement in service

The following references are necessary for applying these standards For those with year of issuance,apply the versions stated expressly For references without year of issuance, apply the latest versionincluding amendment thereof (if any)

TCVN 4054:2005, Highway – Design Requirements;

TCVN 5729:1997, Expressway – Design Requirements;

TCXDVN 104:2007*), Urban Road - Design Requirements;

22 TCN 211-06*), Flexible Pavement – Design Requirements and Guidelines

For the purpose of this standard, the following terms are used:

3.1 Elastic modulus of pavement structure

Elastic modulus of pavement structure refers to a property of resistance to deformation of theembankment - pavement structure including the pavement and the working area of the embankmentunder the effect of standard wheel load

3.2 Rebound deflection

Rebound deflection pertains to recoverable deflection after the load is removed (when the standardwheel displaces from the measurement location)

4.1 Benkelman beam must have length from the front support beam to the beam tip of at least 2.0mand ratio of the beam lever shall not be less than 2:1 (Refer to Appendix B)

4.2 Prior to each working shift, it is necessary to verify the beam accuracy by comparing results ofvertical displacement measurement at the beam tip with the counterpart at the end of the end of thelever, at the rear of the beam, taking into account the ratio of levers of the beam If deviation is over5%, check linking at joints, hinges, pivots and the smoothness and sensitivity of the beam (Refer toAppendix B)

4.3 A test truck/trailer is a vehicle of which the rear axle is single one, dual (tyred) wheels and the gapbetween two dual wheels is at least 5cm, the test tyre of the rear axle must be new Parameters of thetruck’s rear axle are only in tolerances of 5% as compared to Table 1

Table 1 – Parameters of the standard truck’s rear axle

2 Wheel pressure on the pavement, p, MPa 0,6

3 Equivalent diameter of the dual wheel track, D, cm 33

*) Standards TCN and TCXDVN will be converted into TCVN

4.4 The load on vehicles must be symmetric, balanced, with no change of position and rear axle loadshall not alter during the pavement deflection measurement In the course of measurement, the truckmust be shielded to prevent rain penetration and material drops

4.5 To determine the axle load, we must conduct weighing the rear axle with vehicle weighing system

or using hydraulic jack with pressure gauge which is calibrated and the pressure scale not more than0.02MPa

4.6 To measure for examining pneumatic pressure inside the wheels to keep it unchanged duringpavement deflection measurement (See Appendix B)

5.1 Preparation

5.1.1 Prior to measurement, check the dual wheels track area Sb by jacking the rear axle up, cleaningand applying grease on the tyres, turning the greased tyres downward, then lowering the jack to tracethe wheels track on the cross-section papers The dual wheels track area Sb is defined as the area ofgrease trace on the cross-section papers Equivalent diameter of the truck’s dual wheels track is Db

and the wheels pressure on the pavement, pb are calculated with the following formula:

5.1.2.1 Sections are deemed as being homogeneous when holding identical factors like: Type ofembankment and pavement on moisturizing conditions, state of drainage, status of pavement surface,structure of pavement, type of the top soil, traffic volume and so on These figures will be obtained inreference to the road documents at road management agencies and data collected by siteinvestigation carried out by experienced expert teams (refer to Appendix A);

5.1.2.2 To choose representative sub-sections on each homogeneous section: The representativesub-section shall range from 500m to 1000m length On each representative sub-section, select 20test spots/lane For homogeneous sections which are particularly short but quite different from thesurrounding sections (those with complicated geological and hydrological conditions or soft ground),even less than 100m, still we have to measure for at least 20 test spots/lane

5.1.3 If the road to be evaluated fail to have basic data to apply the division of road into homogeneoussections as described in section 5.1.2, we measure as below:

5.1.3.1 For the stage of Detailed Design or Shop Drawings, conduct measurement on the wholealignment with density at least 20 test spots/1 lane/1km;

5.1.3.2 For the stage of investment project preparation, management of highway operation or otherworks comply with the Client’s requirements, conduct measurement with intensity of at least 5 to 10points/lane/1km

5.1.4 Choosing location of test spots (measurement points/test location)

5.1.4.1 Test spots of deflection measurement are preferably arranged in the outer wheel track (to be0.6m ÷ 1.2m from the road edges), which commonly has higher deflection than the inner one In case

it is visually observed pavement status in the inner wheel track and the outer one are damaged

uniformly, it is advisable to utilize two beams at the same time on both wheel tracks to take the largervalue as typical deflection value for the cross section of the measured lane.

5.1.4.2 For multi-lane driveway, checking visually shows that pavement status varies for lanes,measure the deflection for the weakest lane Measurement value at each position of lane will betypical for deflection at the road cross section (Refer to Appendix C)

5.1.4.3 To mark paint on test spots The first test spot and the 20th test spot should be coincide withthe cross section at station of Kilometer posts or piles with one hundred meters unit (H pile)

5.2 Deflection measurement along the pavement

5.2.1 Procedure of pavement (surface) deflection measurement

5.2.1.1 To get the truck advanced to the deflection measurement location, then to place themeasurement probe of Benkelman beam resting on the pavement in the middle of the gap of dualwheels couple after the truck To have the beam plunger vibrated slightly, then monitoring the pointer

of a dial indicator until the deflection is found stable (in 10s, pointer does not shift over 0.01mm),record the starting reading on the dial indicator (as I0)

5.2.1.2 The truck shall be moved forward with creep speed of about 5km/h until the rear axle of thewheels to be at least 5m far from the test spot, then knocking gently on the plunger to check thesensitivity of dial indicator To oversee the dial indicator until deflection becomes stable, then recordingthe final reading (referred to as I5) The difference of two readings on the dial indicator multiplied bythe beam’s lever ratio is the value of the pavement rebound deflection on the test spot (symbolized as

5.2.2 Measurement of pavement temperature: So as to adjust results of deflection measurement forcalculated temperatures later, it is a must to measure the ambient air temperature and pavementtemperature for once in 1 hour during deflection measurement along the pavement Measurement ofthe pavement temperature is only required for pavement structure with the asphalt top layer thickness

is 5cm or more This is how to measure the pavement temperature:

–A hole should be made with hammer and mandrel to a depth of 45mm on the pavement near thedeflection test point;

–Then the hole should be filled with water or glycerol to the half depth thereof, waiting for a fewminutes;

–Then insert a thermometer to measure temperature of the fluid in the hole until the temperature isunchanged, record measured temperature values (T0C)

NOTE 2:

- To prevent against solar radiation to Benkelman beam and the measurement probe and the plungerfrom settling down to the asphalt pavement in high temperature, with prejudice to the accuracy of themeasurement results, do not measure defection when the pavement temperature is over 40oC

- To prevent the measurement results being affected by the truck shadow or any object

5.2.3 To organize traffic safety during measurement process All members working for measurementsincluding drivers must be trained in measurement profession

NOTE 3: Traffic safety organization may be arranged by using barrier, traffic signs in combination withperson holding traffic control flag

6 Processing deflection measurement results

6.1 Processing deflection measurement results

6.1.1 Rebound deflection calculated at the test spot (i) representing the pavement cross section (Litt)

pb, Db , p and D are determined as in section 5.1.1 and 4.3

Km is the deflection adjustment factor to the most unfavorable season in a year;

Kt is the deflection adjustment factor at the measured temperature to that of the calculatedtemperature (TttoC)

6.1.2 When it becomes impracticable to monitor rules of deflection changes by season and bytemperature, it is allowed to use Km and Kt from observation performed in the locality for routes withsimilar conditions (See Appendix D)

6.1.3 After having determined calculated deflection of measurement location (Litt), it is necessary toeliminate crude errors from the set of collected values on each section by standards for elimination ofextreme observations in the theory of statistics and probability (Refer to Appendix E)

6.2 To determine typical deflection and typical modulus of elasticity for each test section

6.2.1 Value of typical rebound deflection on homogeneous section is calculated as average deflection

of the representative sub-section on such homogenous section

6.2.2 Depending on requirement and scope of the project, typical rebound deflection for each testsection is calculated for both directions for each direction or each lane of the test road section

6.2.3 Unless basic data is available for dividing the road into homogeneous sections as stated insection 5.1.2, value of typical rebound deflection for each test section is calculated by the followingformulae:

In which:

Ldt is typical rebound deflection for each test section;

Ltb pertains to average deflection of the test section, in mm Value Ltb is calculated by below formulae:

n is number of measurement;

δ is the mean square deviation of the test section, in mm Value δ is calculated by below formulae:

K is the probability factor taken upon grade and class of road, to be determined as below:

– Expressway and road grade l (classified by TCVN 5729:2007 và TCVN 4054:2005), urbanexpressway (classified by TCXDVN 104:2007), K = 2.0;

– Road grade ll (classified by TCVN 4054:2005), urban major roads (classified by TCXDVN104:2007), K = 1.64;

– Road grade lll (classified by TCVN 4054:2005), K = 1.3;

– Road grade lV to VI (classified by TCVN 4054:2005), frontage roads, inner city roads (classified byTCVN 4054:2005), K = 1.04

6.2.4 Value of typical modulus of elasticity for each test section (Edh) is determined with formulae:

Including:

0.71 is a constant of deflection measurement;

p indicates standard wheel pressure on the pavement, p = 0.6 MPa;

D refers to equivalent diameter of the standard wheel tracks area, D = 33 cm;

µ is Poisson’s ratio, µ= 0,3;

Ldt is typical rebound deflection determined in section 6.2.1

-………, day … month … year ……

SECTION DIVISION FOR EVALUATION OF FLEXIBLE PAVEMENT STRUCTURE STRENGTH

Poor drainage Poor drainage

++ ++ ++

(Signed and sealed)

Lab Line Agency

(Signed and sealed)

The Engineer

-………, day … month … year ……

CHECK SHEET OF REBOUND DEFLECTION DEVICES WITH BENKELMEN

Beam 1 – For left wheel

Beam 2 – For right wheel

Ratio of beam levers:

B

A

Kc =

Check deviation of beam satisfying requirements

Check the load on test truck axle load

Load :

Load satisfies requirements

Load is symmetric and balanced

- Measure axle load at the vehicle weighing system:

Load of test wheel rear axle, Q =

Name of weighing system:

- Measure axle load with hydraulic jack:

Reading on meter of jack p = MPa ; L = cm ; a = cm

Pressure of calibrated jack f = Mpa with load q = kN

Measure area of wheel track Sb

Calculate equivalent diameter of wheel tracks of the truck, in cm: Db= 1.13 Sb

Wheel pressure on the pavement (P ), MPa :

b b

S

Q P

Q is axle road of the test truck, kg;

p refers to reading on the meter of jack, MPa ;

L is the width of truck axle, is the spacing between two centers of the wheel track, in cm;

a refers to the distance from the jack position to the center of wheel track to be lifted by jacking, in cm

f refers to calibrated jack pressure, MPa;

q means the load corresponding to calibrated jack pressure, kN

(VILAS)

(Signed and sealed)

Lab Line Agency

(Signed and sealed)

The Engineer

-………, day … month … year ……

DATA SHEET OF REBOUND DEFLECTION MEASUREMENT USING BENKELMAN

Project: Sheet No : Number of sheets :

Region (Province):

Implementing agency:

Measured by: Time of measurement :

Measure with station direction increasing/decreasing:

Load conversion factor of truck axle Kq =

Ratio of beam lever 1, left wheel K1C =

Ratio of beam lever 2, right wheel K2C =

Km + Distance from truck center to

pavement center: Measurement hour : Pavement temperature:

io i5 littt i0 i5 littp

NOTE C.1:

io, i5 are readings on the dial indicator when the truck displaces from the test spot of 0m and more than5m;

Km is the deflection adjustment factor to the most unfavorable season;

Kt is the deflection adjustment factor at the measured temperature to that of the calculatedtemperature;

littt or littp refers to the rebound deflection at the left wheel or right wheel calculated by formulae:

littt or littp = KC x Kq x Km x Kt x (io- i5 )

lmax is the maximum value of littt and littp

(VILAS)

(Signed and sealed)

Lab Line Agency

(Signed and sealed)

The Engineer