Shear box Lab Report Example | Topics and Well Written Essays - 1500 words

Shear box - Lab Report Example Introduction In soil mechanics, the term shear strength describes the magnitude of a shear stress that the soil can sustain (Roscoe 34). On the other hand, shear resistance of a soil occurs as a result of interlocking of particles and particle friction and possibly the bonding or cementation at particle contacts (Roscoe 45). Particle interlocking may cause a material to contact or expand in volume because of being subjected to shear strain (Poulos 560). As soil expands in volume, the density of its particles decreases causing its strength to decrease. This way, the peak strength is followed by the reduction in shear stress. It is always important to understand different values of Shear Strength of a soil sample (Schofield 20). This is because materials differ in their characteristics and tend respond differently when subjected to similar or different load conditions. This means that for one to design a project, he/she must understand the type of soil considering their variations in S hear Strength.In soil mechanics, Shear Strength is given by the formula ?f = c + ?n tan?----------------------------------------------------------------------------(1) c stands for cohesion, ? as an effective normal stress, ? as the angle of friction, ?f as the shear strength, and the shear box test, is defined by BS 1337: This experiment deals with shear resistance of a soil sample. ... The shearing resistance offered by the soil as one portion was made to slide on the other and measured at regular intervals of displacement. It was noted that failure occurred whenever the shearing resistance reached the maximum value that the soil could sustain. After obtaining the Shear strength it was plotted against horizontal displacement and on a separate graph, it was plotted against normal effective stress. The vertical displacement was also plotted against the horizontal displacement. Relevant calculation and interpretation were made and compared for purposes of making inference. Procedure In this experimental set up the first step entailed assembling the empty shear box without an upper and loading platens. In doing this, the two halves had to be screwed together. Screws marked â€Å"L† were in position as this was done. While ensuring that the apparatus move freely on the runners of the shear box, the box was filled with sand, which was then leveled off approximatel y 1 mm below the top of this box. The top platen was then placed on the sand. The platen was loaded on the top platen. The ball bearing was put in place. The hanger was then placed on the ball bearing and the weight was added on this hanger. The apparatus were adjusted to take up slack followed by reducing the proving ring dial gauge to zero. The two screws that held the lower and upper halves of the bow together were removed and screwed in those screws, which were marked â€Å"L†. After resistance was felt, each was adjusted further in ensuring the two halves get slightly separated. The motor was switched on and the maximum reading recorded on a proving ring dial gauge. The hallmark of the experiment when the circuit was switched off followed by slackening off the apparatus.