09/11/2023
STANDARD PE*******ON TEST (SPT) (ការខួងដីធ្វើពិសោធន៏ SPT សម្រាប់សិក្សាគណនាគ្រឹះរបស់សំណង់តូចធំគ្រប់ប្រភេទ)
The standard pe*******on test is an in-situ test that is coming under the category of penetrometer tests. The standard pe*******on tests are carried out in borehole. The test will measure the resistance of the soil strata to the pe*******on undergone. A pe*******on emphirical correlation is derived between the soil properties and the pe*******on resistance. The test is extremely useful for determining the relative density and the angle of shearing resistance of cohesionless soils. It can also be used to determine the unconfined compressive strength of cohesive soils.
+ TOOLS FOR STANDARD PE*******ON TEST
The requirements to conduct SPT are:
1. Standard Split Spoon Sampler
2. Drop Hammer weighing 63.5kg
3. Guiding rod
4. Drilling Rig.
5. Driving head (anvil).
+ PROCEDURE FOR STANDARD PE*******ON TEST
The test is conducted in a bore hole by means of a standard split spoon sampler. Once the drilling is done to the desired depth, the drilling tool is removed and the sampler is placed inside the bore hole. By means of a drop hammer of 63.5kg mass falling through a height of 0.76m at the rate of 30 blows per minute, the sampler is driven into the soil. The number of blows of hammer required to drive a depth of 15cm is counted. Further it is driven by 15cm and the blows are counted. Similarly, the sampler is once again further driven by 15cm and the number of blows recorded. The number of blows recorded for the first 15cm not taken into consideration. The number of blows recorded for last two 15cm intervals are added to give the standard pe*******on number N value. If the number of blows for 15cm drive exceeds 50, it is taken as refusal and the test is discontinued.
+PRECAUTIONS TAKE FOR STANDARD PE*******ON TEST
1. Split spoon sampler must be in good condition.
2. The cutting shoe must be free from wear and tear
3. The height of fall must be 0.76m. Any change from this will affect the ‘N’ value.
4. The drill rods used must be in standard condition. Bent drill rods are not used.
5. Before conducting the test, the bottom of the borehole must be cleaned.
+ADVANTAGES OF STANDARD PE*******ON TEST
The advantages of standard pe*******on test are:
1. The test is simple and economical
2. The test provides representative samples for visual inspection, classification tests and for moisture content.
3. Actual soil behaviour is obtained through SPT values
4. The method helps to pe*****te dense layers and fills
5. Test can be applied for variety of soil conditions
+ DISADVANTAGE OF STANDARD PE*******ON TEST
The limitations of standard pe*******on tests are:
1. The results will vary due to any mechanical or operator variability or drilling disturbances.
2. Test is costly and time consuming.
3. The samples retrieved for testing is disturbed.
4. The test results from SPT cannot be reproduced
5. The application of SPT in gravels, cobbles and cohesive soils are limited.
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