ASSIGNMENT 1: CONSTRUCTION TECHNOLOGY 1. Differentiate between disturbed soil & undisturbed soil. Disturbed samples are generally obtained to determine the soil type, gradation, classification, consistency, density, presence of contaminants, stratification, etc. The methods for obtaining disturbed samples vary from hand excavating of materials with picks and shovels to using truck mounted augers and other rotary drilling techniques. These samples are considered disturbed since the sampling process modifies their natural structure. Undisturbed samples are used to determine the in place strength, compressibility (settlement), natural moisture content, unit weight, permeability, discontinuities, fractures and fissures of subsurface formations. Even though such samples are designated as undisturbed, in reality they are disturbed to varying degrees. The degree of disturbance depends on the type of subsurface materials, type and condition of the sampling equipment used, the skill of the drillers, and the storage and transportation methods used. 2. What is the difference between net ultimate bearing capacity, gross bearing capacity & allowable bearing capacity of the soil? Gross Bearing Capacity combines the total upward pressure of both applied load and selfweight + overburden soil pressure above the foundation. Ultimate Bearing Capacity The generally accepted method of bearing capacity analysis is to assume that the soil below the foundation along a critical plane of failure (slip path) is on the verge of failure and to calculate the bearing pressure applied by the foundation required to cause this failure condition. This is the ultimate bearing capacity. Net Ultimate Bearing Capacity By neglecting the overburden soil pressure above the foundation, we get Net Ultimate Bearing Capacity. Allowable Bearing Capacity The allowable bearing capacity is the ultimate bearing capacity divided by an appropriate factor of safety. 3. Differentiate between immediate elastic settlement and long term consolidation settlement in soil. Immediate settlements are estimated using equations from elasticity theory, while long-term settlements are calculated using the concepts of consolidation. Consolidation: a special case of compression in which the soil is saturated and fine-grained, and the changes in volume are time-dependent and occur when water is expelled from the voids Settlement: a decrease in elevation experienced on or within a soil as a result of compression 4. What is Atteberg's limit? The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil: its shrinkage limit, plastic limit, and liquid limit. Depending on its water content, a soil may appear in one of four states: solid, semi-solid, plastic and liquid. In each state, the consistency and behaviour of a soil is different and consequently so are its engineering properties. The Liquid Limit (LL) is the moisture content at which a fine-grained soil no longer flows like a liquid. The Plastic Limit (PL) is the moisture content at which a fine-grained soil can no longer be remoulded without cracking. The Shrinkage Limit (SL) is the moisture content at which a fine-grained soil no longer changes volume upon drying—any loss of moisture is compensated by the entry of air into the pores. Thus, the boundary between each state can be defined based on a change in the soil's behaviour. Thus, the boundary between each state can be defined based on a change in the soil's behaviour. 5. What is an open drive tube sampler? Undisturbed samples are may be obtained from boreholes by open drive samplers or piston samplers. Open drive samples consist of thin-walled tubes which are pushed or driven in to the soil at the bottom of the hole and then rotated to detach the lower end of the sample from the soil. Most soft or moderately stiff cohesive soil can be sampled without extensive disturbance in thin-walled seamless steel tubes having diameter not less 50 mm. the lower end of the tube is sharpened to from a cutting edge and the other end is machined for attachment to the drill rods. The entire tube is pushed or driven in to the soil at the bottom of the hole and is removed sample with inside. The two ends of the tube are then sealed and sample shifted to the laboratory. 6. What is Sp. Gr. Value? Specific gravity G is defined as the ratio of the weight of an equal volume of distilled water at 4 degree Celsius temperature and both weights taken in air. The knowledge of specific gravity is needed in calculation of soil properties like void ratio, degree of saturation etc.