Foundations provided for machines are called machine foundations.
These foundations have to be specially designed taking into account the impact and vibration characteristics of the load and the properties of soil under dynamic conditions. Thus the design of foundations of Turbines, Motors, Generators, Compressors, Forge hammer and other machines having a rythmic application of unbalanced forces require special knowledge of theory of harmonic vibrations.
All the above consideration are made in the design of machine foundations because inertial forces of rotating elements of machine contribute dynamic loads in addition to their static loads. Moreover, the machinery vibration influences adversely the foundation supporting soil by densifying it which may result differential settlement of the foundation.
Machine foundations must fulfil the following design requirements.
A machine foundation should be safe against shear failure.
It should not settle excessively under static loads.
There should be no resonance due to dynamic force i.e the natural frequency of the foundation soil system should not be coincide with the operating frequency of the machine.
The amplitude at operational frequency of the foundation system must be within telerable limits.
The vibrations of the foundation soil system must not annoying to the workers working in that area.
It should not create bad effect on the other precision machines and instruments.
Types of Machines Foundations
Machine foundations are broadly classified into the following three types, depending upon the type of machines for which they are provided:
Penetrometer is a fantastic little invention which geotechnical engineers and technologists find very handy. It is a small handheld gauge which contains a telescoping rod which can be pushed into the soil. The distance the rod goes into the soil corresponds to a compressive strength on the dial.
Measurement of Soil
The pocket penetrometer measures the compressive strength of the soil. Most penetrometers available today contain units of tons/ft2or kg/cm2, and the compressive strength is read directly from the gauge. Some common conversions are:
1 ton/ft2= 2000 psf = 13.9 psi
1 kg/cm2= 98.1 kPa
A pocket penetrometer is a primative instrument that is subject to many errors such as non-uniform soil. As a minimum, you should take a series of measurements in one area and average them. The penetrometer shouldnot replace laboratory testing or field analysis, or be used to produce foundation design data.
Geology is the science which is devoted to the study of earth. It deals with all the features of the earth’s surface and with the origin, composition, structure and inhabitants of the earth.
Branches of Geology
The subject of geology is very large and it is divided into several branches which are as follows:
Physical Geology: It is concerned with the work of natural processes which bring about changes upon the earth’s surface.
Mineralogy : It includes the study of minerals.
Structural Geology : It includes the study of stratified rocks in the earth’s crust.
Petrology: The discussion of different types of rocks is known as petrology.
Stratigraphy : It is concerned with the study of stratified rocks and their correlation .
Palaeontology : It deals with the study of fossils.
Historical Geology : The study of stratigraphy and palaeontology is included under historical geology. It gives us a picture of the land and seas, the climate, and the life of early times upon the earth.
Economic Geology : It deals with the study of minerals of economic importance.
Mining Geology : It is concerned with the study of application of geology to mining engineering.
Engineering Geology : It includes the study of application of geology to Civil Engineering.
Surveying is the art of making Such Measurements as Will determine the relative positions of points on the surface of the earth in order that the shape and extent of any portion of earth’s surface may be ascertained and delineated on a map or plan. It is essentially a process of determining positions of points in a horizontal plane.
Levelling is the art of determining and representing the relative heights or elevations of different points on the surface of the earth. It is the process of determining position of points in a vertical plane.
Surveying and Levelling are frequently considered as distinct operations. However, in its comprehensive sense, the term surveying includes levelling.
Purpose of Surveying
The primary purpose of survey is the preparation of a plan or map. The results of surveys when plotted and drawn on paper constitute a plan. A plan is therefore the representation of to some scale, of the ground and the objects upon it is projected on a horizontal plane. The representation is called Map if the scale is small while it is called Plan if the scale is large e.g a map of Pakistan and a plan of a Building.
Primary Division of Surveying
Surveying may be divided into two general classes:
1) Geodetic Surveying
In Geodetic surveying also called Trigonometrical Surveying, it is necessary to take into account the curvature of the earth. Since shape of the earth is spheroidal, the line connecting any two points on the surface of earth is curved or is an arc of a great circle.
2) Plane Surveying
In a plane surveying the curvature of the earth doesn’t take into account, as the surveys extend over small areas. The earth’s surface is considered as a plane, the line connecting any two points as a straight line and the angle of polygons as a plane angles. It is therefore involves knowledge of geometry and plane trigonometry. American surveyors put the limit at 250 km2 for treating the survey as plane.