43 loading procedure there are two methods for

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: in 4.3.1 and 4.3.2. of 4.3.1 Method Z - The loading system and bearing plate should be seated by applying a load of 3.1 kN ( 310 kgf) ( 0.007 MPa for a standard 75 cm diameter plate ), when the design thickness of pavement is less than 40 cm which is normally used for lightly loaded pavements. For heavy duty pavements a seating loading of 6.2 kN ( 620 kgf) should be used. The seating load will be allowed to remain until practically complete deformation has taken place, at this time a reading should be taken on the dial gauges and adjusted to ‘zero ’ reading. Cyclic loading under may be 3.1 kN (310 kgf) or 6.2 kN ( 620 kgf) seating load, as required, 8 IS I 9214 - 1979 Then without releasing used to assure good seating of the bearing plate. the seating load an additional 31 kN ( 3 100 kgf) [that is, a total 34.1 kN ( 3 410 kgf.) or 37.2 kN (3 720 kgf) load depending on the type of the pavement J should be applied to the plates and held until practically complete settlement has taken place. For recording observations, proforma given at Appendix A should be used. Prior to releasing the 31 kN ( 3 100 kgf) load, a value of KU will be computed for the average deflection at the plate rim by the formula: MPa/cm, KU=7 0.70 or kgf /ems/cm where d = deflection in cm. One of the procedures given in and should be then followed depending upon the type of subgrade and the value of uncorrected modulus of subgrade KU. For cohesive subgrades with KU equal to 0.555 MPa/cm ( 5.55 kgf /cm*/cm ) or less, the load will be released. For some clayey soils it may be necessary to plot a time-settlement curve to aid determiIn general, the load will be nation of practically complete settlement. held until the rate of deflection of the bearing plate is less than O*OOO cm/min ( that is, O-005 cm in 10 minutes ). This rate of settlement 5 indicates that the major portion of the settlement has occurred. ,For granular subgrades, or cohesive subgrade with KU equal to 0.555 lMPa/cm ( 5.55 kgf /ems/cm ) or more a load-deflection curve should be obtained by measuring the successive deformations caused by increasing the load in increments of 15.5 kN ( 1 550 kgf) to a maximum of 93 kN ( 9 300 kgf). The load should not be released between the increments of loading. Each increment of load shall be held for at least 15 minutes. The final load of 93 kN ( 9 300 kgf) shall be held until practically complete settlement is reached, but in not less than 15 minutes. In general the 0,21 MPa ( 2.1 kgf /ems ) load should be held until the rate of settlement of the plate is less than O*OOO cm/min ( that is, 0.002 cm in 2 10 minutes ). This rate indicates that the major portion of the settlement has taken place. 4.3.2 Method II -The plate shall first be seated by applying a load equivalent to a pressure. of 0.007 MPa ( 0.07 kgf /cm% ) and releasing it after a few seconds. A load sufficient to cause approximately a 0*85-mm 9 ISr9214- 1979 settlement should be applied and when there is no perceptible increase in settlement or in the case of clayey soils, when the rate of increase in settlement is less than 0.025 mm/min the average of the readings of the deflec,tion dial gauges should be noted. The load as measured by the pressure gauge attached to the jack or by the proving ring should be noted, both immediately before and after the deflection readings. The load should be increased until there is an additional settlement of approximately 0.25 mm and the load and d...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online