PROPOSED METHODOLOGY FOR CONDUCTING PULL OUT TESTS ON 40mm DIA DYWIDAG BAR ANCHORS

Procedure or steps to perform test:

1.         It is proposed to use 40mm dia Dywidag Bar Anchors below foundation level of S-40, in 3 rows. Hence it is suggested to conduct minimum 3 pull out tests (desirable 5) in the area of application of these Dywidag Bar Anchors.

2.         Prepare a 7-8m wide x 20m long x 3m high working bench for the test area. Select locations for drilling of anchors at a rough distance of 4-5m between adjacent anchors.

3.         At each test locations prepare the hill slope surface by removal of lose boulders prepare a level surface area of 2.6m x 2.6m on the hill slope for casting of 2.0m x 2.0m size reaction pad at each test locations.

4.         Set up the drilling rig at desired anchor location. Erect the rig in such a manner, so that drill hole can be drilled more or less perpendicular to the hill slope.

5.         Drill a 125mm dia or 150mm dia x 9.0m deep borehole adopting rotary cum percussion drilling technique in a dry manner i.e. just using compressed air. While drilling the hole, air-flushing of the hole will be done from time to time, to remove the drill cuttings from the hole, to keep the hole clean and free.   After completion of drilling up to desired depth, flush the hole for about 5 minutes to remove all the drill cuttings from drill hole. Remove the drill string from the borehole.

6.         Lower the assembled 40mm dia x 8.5m fixed length bar anchor into the drilled hole, leave a 300mm gap between the bottom of the drilled hole and the bottom of the anchor to act as over drilling portion.

7.         Lower the 20mm / 25mm dia grout pipe up to the bottom of the drilled hole in order to carry out grouting of the hole in ascending manner.

8.         Prepare neat cement grout using 53 grade OPC and neat water adopting a water cement ratio of around 0.40 in a double drum mixer. Allow a mixing time of 2-3 minutes as a minimum. Transfer the grout from Double Drum Mixer to a Colloidal stirrer and keep the grout in an agitated manner till the grouting of the hole is completed. Use anti-shrinkage compound like CEBEX-100 for flaw-ability of the grout.

9.         Complete all the pipe line connections from stirrer to grout pump to water swivel head to grout pipe assembly lowered in the drill hole. Ensure that the grout line is free by passage of compressed air. In case, it is found choked or blocked due to any obstructions get it cleared before commencement of grouting.

10.     Grout the annular portion between the 40mm dia bar anchor and 125mm dia / 150mm dia drill hole, completely using neat cement grout. Grouting should be done till good quality grout starts overflowing from the top of the drill hole. Collect minimum 6 Nos. of samples of grout in 75mm x 75mm x 75mm size moulds for carrying out laboratory tests on grout cubes to check crushing strength of grout.

11.     As the grout starts overflowing from top of the hole, start lifting of grout pipe in a gradual manner while continuing the grouting.

12.     Observe the depth of top of grout for about 30 minutes. If there is loss of grout from the sides of the drill hole, compensate for this loss of grout by injecting additional grout in the drill hole.

13.     After Completion of the grouting of the hole the grouted anchor should not be disturbed for minimum 3 days.

14.     Subsequently provide a 100mm thick PCC layer below the RCC test pad of 2.5m x 2.5m size.

15.     Arrange appropriate shuttering on sides of test pad. Provide steel reinforcement as per design in the pad. Arrange suitable Trumpet Pipe Assembly symmetrically around the grouted Dywidag Bar anchor. Complete the casting of 2.0m x 2.0m x 0.8m size reaction pad around the test anchor. Collect 6 cube samples of concrete for further testing.

16.     After casting of reaction pad cover it with wet lesion cloth and every day sprinkle sufficient water on it for 10-15 days to allow complete curing the reaction pad.

17.     Conduct 7 days, 14 days, 28 days crushing strengths on cube moulds of concrete used in the reaction pad.

18.     By carrying out laboratory tests on cubes of grout as well as concrete that both grout and concrete have achieved desired strength of 30Nmm² or 300 Kg/mm².

19.     Before starting the arrangements for conducting pull out test on test anchor, clean the threads of projecting portion of test anchor and lightly lubricate it with oil.

20.     Place 200mm x 200mm x 45mm thick solid steel plate on the anchor pad.

21.     Place 200 Tonne capacity central hole hydraulic jack around the test anchor on the 200mm x 200mm x 45mm solid steel plate.

22.     Place 145mm (H) x 70mm (Dia) domed spherical nut on the top of hydraulic jack. Manually screw on the domed nut to the extent possible.

23.     Erect 2 vertical Datum Bars in front of the test anchor. Arrange 2 dial gauges of 50mm range x 0.01mm (least count) with the help of datum bars to measure elongation of Dywidag Bar.

24.     Connect the hydraulic jack to pump or power pack with appropriate hose pipes. Make all the arrangements ready for conducting the pull out test. Pull out test will be conducted in a cyclic manner. The maximum load to be applied in each cycle are summarized below. Each of this load will be maintained for minimum 15 minutes.

Cycle No.

Maximum Load for the Cycle

Maximum Load in kN

1st Cycle

0.2 x ¦pu

264 kN

2nd Cycle

0.3 x ¦pu

396 kN

3rd Cycle

0.4 x ¦pu

528 kN

4th Cycle

0.5 x ¦pu

660 kN

5th Cycle

0.6 x ¦pu

792 kN

6th Cycle

0.7 x ¦pu

924 kN

7th Cycle

0.8 x ¦pu

1056 kN

8th Cycle

0.8 x ¦pu

1056 kN

¦pu= Minimum Guaranteed Ultimate Strength

25.     The details of loading/unloading to be followed in each cycle are presented in Table-1. Approximately one pull out test will be completed in approximately 4-5 hours.

26.     Elongation/Contraction of anchor will be recorded with help of 2 dial gauges.

27.     From the readings of the load and corresponding elongation a graph of load v/s elongation will be prepared for the complete test.