Mackintosh/JKR Probe Test This is a dynamic penetrometer test used to check the consistency of the subsoil. Mackintosh Probe which has 30° cone penetrometer while JKR Probe has 60° cone penetrometer. The cone is driven directly into the soil by dropping the 5-kg hammer through a free height of 280mm. The probe is unable to penetrate into medium strength soil and gravelly ground.
The correlation between the allowable pressure of the soil and the number of blows of the hammer for penetrating a depth of 300mm has been established by JKR in 1975 and is widely used in Malaysia for foundation design.
1 ton/sq ft = 10 tonnes per sq m
Test Procedure 1. Connect steel cone to the bottom of a steel rod. 2. Straighten the steel rod perpendicular to the ground surface on the point to be tested. 3. Measure every 0.3m length of the steel rod and mark it with a chalk. 4. Lift the hammer to the maximum position and then release. 5. Count the number of blows that causes the rod to penetrate 0.3m. 6. Record the data for the number of blows for every 0.3m penetration into the Mackintosh Probe test form. 7. Remove the hammer set, and connect a new steel rod on top of the original rod in the final 0.3m. 8. Mark again the rod for every 0.3m interval. Continue with the hammer blows and repeat the same work process. 9. The blows should be stopped when: a) Numbers of blows reach 400 times for a 0.3m penetration because the soil has high bearing capacity, or b) The depth of penetration reaches 15m. Detail site investigation is required by using boring test. 10. Clean the steel rod, steel cone and connector after they have been used. Apparatus a. 1.2m long steel rods b. Steel cone c. Connectors d. Hammer set e. Measuring tape f. Chalk g. Puller
PROPOSAL TO USE MACINTOSH/JKR PROBE FOR SAFE MOVEMENT OF MACHINERY AT THE SITE It is proposed to use the Mackintosh Probe to determine the bearing capacity of the soil before moving a heavy machinery from one place to another at the site. 1. The weight of a heavy machinery will be determined from the machine catalogue. 2. The number of 1.5m x 6m x 20mm thick steel plates which can be placed under the whole machine is determined. From this number and weight of the machine will be used to calculate the pressure on the ground. Say, for a normal piling machine with a 11tonnes hammer, 3 numbers of the steel plates can be placed under the whole machine and the pressure is 2.6 tonnes per m2. 3. From the correlation chart, the number of blows required to drive the probe to a depth of 300mm is 15. 4. Mackintosh probe test will be carried out at selected points along the path of the machine to a depth of about 5 m. 5. If the top 2m has the number of blows less than 15 per 300mm, movement of machine will not be allowed until the soil is further compacted and steel plate placed in advance. Extra Precautions while moving machinery close to public road 1. If a heavy machine has to work close to a public road, measurement will be taken to determine the limit the machine is allowed to move beyond without extra precautions. 2. Beyond this limit, steel plates will be moved by other machinery. The piling or similar machine will not be allowed to move the steel plate. 3. The steel plates will be properly placed along the path of the machine before the machine is allowed to move to the work location.
