Shear Strength Tests - Lab Report Example

Shear Strength Tests Introduction The primary aim of shear box test is to find the consolidated drained shear strength of a soil sample such as sand soil. Shear strength is the primary property of the soil since the structure is normally dependent upon the soils shearing resistance. The shear box test entails diverse component for determining diverse kind of soil and rock. The test procedure is employed to firm the cohesive soil to soft the vane and to determine the angle of shear resistance of cohesion less soil, the small shear box processes is normally employed and the drained peak and residual shear strength parameters of the cohesive soils. The large shear box procedures are normally utilized in the determination of same properties of the gravely soils. For the drained residual shear strength parameters of remolded clays, the small ring shear procedure is utilized. Test procedures 1.1 Sample Volume, Weight, Density, Porosity Top and bottom was joined using shear screws half of the shear box and solid 3mm plate was placed at the bottom of the shear box then the height d1 from the top of the plate to the bottom shear box was measured. A container containing sand weighing 0.1g was poured evenly into the Shear box from 5cm height 10mm from the top. The scraper was used to level the sand, and the weight of the sand sample within the shear box was measured. The thickness of the second plate 3mm plate, tp, and its weight was measured and recorded. Vernier ruler was used to measuring the distance from the top of the plate to top of the box at all 4 corners to 0.1mm then the average was recorded as d2. Sample volume, weight, density, and porosity was calculated. The computation of the porosity was based on sands grains possessing relative density Gs of 2.65. 1.2 Loading the Sample Vertically The Piston was weighed and gently placed on the top plate, and the vertical loading hanger was aligned onto the piston. The Vertical spindle was gently threaded until in contact with the piston. The locking nut was adjusted to keep the spindle in place and the load was placed on the lower hanger through turning handle. The lower hanger lever gave a 10 times multiplication of the load at the loading point, and the weight were recorded. 1.3. Readying Sample for Shearing The screws were joining the top and the bottom half of the box was removed, and all the dials were set to zero to ensure they fully engage and the coefficients value for each division was recorded. The horizontal and corresponding vertical gauges had coefficients of 0.01 mm/division. 1.3 Shearing the Sample The Shear Rig was switched to ensure the travel rate is set to 0.5mm/minute and set to run and the timer was started. All the dial gauge readings were recorded at the start time and the intervals of 1 minute. The readings were taken until Proving Ring readings pass their underlying peak. Apparatus The main apparatus used in the experiment include I. Shear Box Rig, including 3mm plates, piston, dial gauges and 2kN Proving Ring. II. Hanger weights 1kg, 2kg, and 5kg III. Loose sand IV. Glass Pouring Jar V. Scales accurate to 0.1g VI. Timer accurate to 1 second VII. Vernier Ruler accurate to 0.1mm Results Sand Take Gs=2.65 Ram Set at 0.5mm/minute, Hanger Multiplier is 10 Proving Ring 1.87N/division (Ring 1155-16-11927C2Kn) Peak shear=329.12N over 60mm by 60mm area= 84.93N Peak shear stress T-maximum=84.93/1000*1/(0.06*2)=23.6kN/m2 For Norma load stress= 10.648KN/m2 Parameter Value Mass Sand Sand and Jar Initially (g) 336.5 Sand and Jar after Pouring (g) 203.1 Mass Sand Ms (g) 134.6 Volume Sand Shear Box Plan Area AS (mm2) 3600 Top Bottom-Plate to Top Box d1 (mm) 33.72 Top Plate Thickness tP (mm) 3 Depth Top Plate to Top Box d2 (mm) 6.6 (All 4 corners) 7.4 6.5 6.5 d2 Average (mm) 6.8 Depth Sand dS = d1 – tP – d2Average (mm) 23.8 Volume Sand VS = ASdS x10-3 (cm3) 83.88 Dry Density γS = MS/VS (g/cm3) 1.6 Porosity n = (GS- γS)/GS 2.05 Mass Top Plate - MPlate (kg) 0.0685 Mass Piston - MPiston (kg) 0.5427 M1 = MPlate + MPiston (kg) 0.6112 Hanger Load (kg) 5 Hanger Load x Lever (10) = M2 (kg) 50 Total Load (M1+M2) (kg) 50.6112 Total Load (M1+M2) x(9.81/1000) (kN) 0.5 Normal Stress σn = Total Load/(0.062) (kN/m2) 219.4 Vertical Gauge Coefficient 0.01mm/division Proving Ring Coefficient 0.002mm/division Proving Ring Gauge Coefficient 1.87N/division Horizontal Gauge Coefficient 0.01mm/division Time (mins) Horizontal Gauge Reading Movement of Box mb (mm) Proving Ring Reading Movement of Ring mr (mm) Soil Displacement mb – mr(mm) Shearing Resistance τ (N) Vertical Gauge Reading Vertical Movement (mm) 0 0 0 0 0 0 0 500 5 1 14 0.14 90 0.18 -0.04 -0.021 498 4.98 2 39 0.39 155 0.31 0.08 0.043 498 4.98 3 72 0.72 295 0.59 0.13 0.070 500 5.00 4 110 1.10 325 0.65 0.45 0.241 502 5.02 5 150 1.50 339 0.678 0.822 0.440 506 5.06 6 192 1.92 345 0.69 1.23 0.658 509 5.09 7 238 2.38 349 0.698 1.682 0.899 512 5.12 8 286 2.86 346 0.692 2.168 1.159 515 5.15 9 269 2.69 285 0.57 2.12 1.134 506 5.06 Soil Displacement Mb-Mr(mm) Shearing Resistance T(N) 0 0 -0.076 108.46 -102.71 192.61 -0.07 233.75 0.284 40.898 -295.84 297.33 -312.26 314.16 -312.11 323.51 2.498 329.12 -3.012 329.12 Movement of box Mb(mm) Vertical Movement(mm) 0 5 0.14 4.98 0.39 4.98 0.72 5.00 1.10 5.02 1.50 5.06 1.92 5.09 2.38 5.12 2.86 5.15 2.69 5.06 . Discussion The internal angle of the friction attained from the direct shear box was relatively lower that the one attained from the ring shear test. The direct shear box possesses the box of its sides equally stressed making it register lower bound values. The perforated grind plate employed to hold the sample tight during the testing within the direct shear test caused unexpected stress concentration around them. Moreover, the stresses mobilized at the predetermined shear plane are lower by a small fraction leading to the development of the lower bound values of the strength parameters attained. The structures appearing within the direct shear box sample before and after failure depict that the central portion of the underlying portion of the specimen. Assessment failure mechanism within the direct shear box depicts that kinking was the dominant mode of deformation, which is different from the underlying measurement. As the displacement escalated, the strains multiplied within a discrete arrangement and at the diminishing positive angles to the corresponding horizontal. A continuous zone segregating the top from the underlying bottom of the box marks the terminal of shearing as failure is reached. The loading sides of the box result in stress concentrations coupled with the local straining is intense, unlike the ring where the stress concentration is solely on the exterior edges. The peak angles of friction in computed in the result affirm the findings. There is a broad inconsistency within the results from the prevailing conventional test, but the relatively close arrangement for the underlying symmetrical test. Moreover, the direct shear data miscalculate the peak plane strain and the direct shear angles of friction Conclusion Discrepancy amidst the conventional direct shear test and the corresponding simple shear test is relatively bigger and escalates with the degree of dilation within the soil. The extra error is probably to stem from the underlying boundary measurements underestimating the real rate of dilation within the soil on the central plane. References BS 1377-1 1990 Soils for Civil Engineering Purposes Part 1: General Requirements and Sample Preparation BS 1377-7 1990 Soils for Civil Engineering Purposes Part 7: Shear Strength Tests (Total Stress) Smith’s Element of soil mechanics 8th Edition by Ian Smith http://www.uic.edu/classes/cemm/cemmlab/Experiment%2012-Direct%20Shear-pdf Read More