Unconfined compression test

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Unconfined compression test

Transcript of Unconfined compression test


2. CONTENT notitlepage1objective32theory43Equipmnet54procedure65Data and analysis7-166discussion177conclution188reference19 3. OBJECTIVEStudent should be able to : Measure the shearing resistance and shear force parameter ( c& ) of cohesive soils which may be undistributed or remolded specimens. 4. THEORY The unconfined compressive strength ( ) is the load per unit area at which the cylindrical specimen of a cohesive soil falls in compression.Where P= axial load at failure, A= corrected area = , where is the initial area of the specimen, = axial strain = change in length/original length. The untrained shear strength (s) of the soil is equal to the one half of the unconfined compressive strength,Unconfined Compression Testing Machine (Spring Type)Unconfined Compression Testing Machine (Proving Ring Type) 5. EQUIPMENT 1.Compression device2.Load and deformation dial gauge3.Sample trimming equipment4.Balance5.Moisture can 6. PROCEDURE 1. Excavate a hole in 1 meter depth to get 3 sample of cohesive soil at suitable site location. 2. Make sure that the samples are in undistributed conditions. Bring the samples to the laboratory for the further test. 3. Extrude the soil sample from tube sampler. Cut a soil specimen so that ratio ( L/d ) is approximately between 2 and 2.5. 4. Measure the exact diameter ( d ) ang ( L ) of the specimen. Record to date sheet. 5. Weigh the sample and record the mass on data sheet. 6. Calculate the deformation ( L ) corresponding to 15% strain ( ) . Strain ( ) = L / Lo Where Lo = Original spacimen length ( as measured in step 4 ) 7. Carefully place the specimen in the compression device and center it on the bottom plate. Adjust the device so that the upper plat attached with the specimen and set the load and deformation dials to zero. 8. Apply the load so that the device produces an axial strain at a rate of 1.0mm per minute, and record the load and deformation dial readings on the data sheet at starting from 10, 25, 50, 75, 100 devisions on the deformation dial. 9. Keep applying the load until ( 1 ) the load ( load dial ) decreases on the specimen significantly, ( 2 ) the load holds constant for at least four deformation dial readings, or ( 3 ) the deformation is segnificantly past 15% strain that was determined in step 6. 10.Draw a sketch to depict the simple failure. 11.Remove the sample from compression device and obtain a sample for water content determination. Determine the water content. 7. DATA AND ANALYSIS 1. Convert the dial readings to the appropiate load and length units, and enter these values on the data sheet in the deformation and total load columns. 2. Compute the sample cross-sectional area, Ao = / 4 x (d)2 3. Compute the strain , = L/Lo 4. Compute the corrected area, A= Ao /1- 5. Using A , compute the specimen stress , sc = = P/A 6. Compute the water content , w% 7. Plot the stress versus strain on graph paper. Show qu as the peak stress ( or at 15% strain ) of the test. 8. Draw Mohrs circle qu step 7 and show the undrained shear strength, su = c ( or cohesion ) = qu / 2 8. CONCLUSION Clearly more work is needed to quantify the reductionof unconfined compressive strength in saturatedrocks. From the data collected for this paper atentative rule of thumb could be proposed for thepreliminary estimations needed when working withgeomechanics classifications: well indurated strong rocks: UCSsat/UCSdry = 0,80-0,90 cemented medium strength rocks: UCSsat/UCSdry = 060-0,70 soft argillaceous rocks: UCSsat/UCSdry = 0,30 The perimeter purpose of this test is to determine the unconfined compressive strength which is then used to calculate the unconsolidated untrained shear strength of the soil under unconfined conditions. According to the ASTM standard, the unconfined compressive test strength ( qu) is defined as the compressive stress at which an unconfined cylindrical specimen of soil will fail in a sample compression test. The unconfined compressive strength is taken as the maximum load attained per unit area, or the load per unit area at 15% axial strain, whichever occurs first during the performance of a test. To determine the unconfined compressive strength which is then used to calculate the unconsolidated untrained shear strength of the soil under unconfined conditions. 9. REFERENCE 1. Donald Mcglinchey, Characterisation of bulk solids, 2005, CRC Press DT Afrika. 2. Mazlan Mohammad Abdul Hamid, Standard aggregate sieve analysis TEST, ASTM International - Standards Worldwide, (July 2008) ASTM C136-06, retrived from http://www.astm.org/ 3. Norliza Muhammad, concrete laboratory,(2006). Gradation Test. (2007), Norliza Muhammad, FajarBakti.Sdn.Bhd