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Showing posts from April, 2020

Contouring

A contour or a contour line may be defined as a line joining the points having the same  elevation above the datum surface. The process of tracing contour lines on the surface of the earth is called contouring and the maps upon which these lines are drawn are called contour maps. The constant vertical distance between any two consecutive contours is called the contour interval. The horizontal distance between any two adjacent contours is termed as the horizontal equivalent and depends upon the slope of the ground. The contour interval depends upon the nature of the ground, scale of the map, purpose and extent of the survey. The contour interval of any survey is inversely proportional to the scale of the map and it should be constant throughout the survey. The following are important characteristics of contours: All points in a contour line have the same elevation. When the contour lines are uniform spaced, it indicates a uniform slope and when they are straight, parallel

Earth pressure theory

A structure used for maintaining the ground surfaces at different elevations on either side of it, is called a retaining wall. The material retained or supported by the structure is called backfill which may have its top surface horizontal or inclined. If the position of the backfill lies above the horizontal plane at the elevation of the top structure, it is called the surcharge and inclination of the surcharge to the horizontal is called surcharge angle The ratio of horizontal stress to vertical stress is called the coefficient of earth pressure (K) Earth pressure at rest The lateral pressure exerted by the soil when the retaining wall has no movement relative to the backfill, is called earth pressure at rest Coefficient of earth pressure at rest When the soil is at elastic equilibrium (i.e. at rest), then the coefficient of earth pressure at rest (K 0 ) is given by The value of  K 0 for loose sand is 0.4, for hard clay 0.5, for soft clay and dense sand it is 0.6.

Lacey silt theory of canals

According to Lacey, a channel is said to be in regime state in the following three conditions: The channel flows in unlimited incoherent "alluvium of the same character as that transported material. The silt grade and the silt charge are constant The canal discharge is constant  In actual practice, these conditions are seldom met with. Thus, Lacey gave the idea of initial and final regime for the channels. The channel is said to be in initial regime when it only attains final section but does not secure its longitudinal slope. The channel is said to be in final regime when it attains its section as well as longitudinal slope. According to Lacey, There is only one section and only one longitudinal slope at which the channel will carry a particular discharge with a particular silt grade. He found that in final regime, the channel cross-section becomes semi-elliptical. The eddies are generated from the bed and also from its sides, both normal to the surface of the gene

Chain surveying

Chain surveying is system of surveying in which the sides of the various triangles are measured directly in the field and no angular measurements are taken. The simplest kind of surveying is the chain surveying and is most suitable when the  ground is fairly level and open with simple detail, plans are required on a large scale and  area to be surveyed is small The principle of surveying is triangulation. It consists of the arrangement of framework of triangles because a triangle is the only simple plane figure, which can be plotted from the lengths of its sides measured in the field. Since an equilateral triangle can be more accurately plotted than an obtuse angled triangle, therefore, the triangles formed in a chain survey should be nearly equilateral as possible. Such triangles are known as well conditioned triangle or well shaped triangles. In a well conditioned triangle, no angle should be less than 30° and greater than 120° The terms commonly used in chain surv

Working stress method and limit state method of design

In this article, we are going to know about the assumptions & limitations of working stress method of design and  Limit state method of design and Comparison between working stress method and limit state method Working stress method Working stress method is used for the reinforced concrete design where concrete is assumed as elastic, steel and concrete act together elastically where the relationship between loads and stresses is linear. Permissible (allowable) stress = ultimate or yield stress / factor of safety. Thus, in working state method working stress ≤ permissible stress The factor of safety for bending compressive strength in concrete is taken as 3 The factor of safety for yield strength in steel is taken as 1.78 Assumptions of working stress method Plane section before bending will remain plane after bending Bond between steel and concrete is perfect within elastic limit of steel The steel and concrete behaves as linear elastic material All tensi

Compaction

Compaction is the process in which soil particles are artificially re-arranged and packed together in closer state of contact by mechanical means in order to reduce the void ratio, permeability, compressibility and increase the degree of denseness, stability, bearing capacity and shear strength of the soil. (In order to modify the engineering properties of soil). Compaction is different from consolidation in regard that in compaction decrease in volume of soil takes place due to reduction of air voids which is carried out by mechanical means instantly whereas consolidation is a gradual natural process in which reduction in volume of soil takes place due to expulsion of pore water. In consolidation, soil mass is always saturated whereas in compaction it is saturated. Compaction can be brought about by the use of rollers, vibrators or rammers. The compaction of the soil is represented in terms of its dry unit weight. Compaction characteristic of the soil are first analyzed in the la