Construction Equipment and Miscellaneous Study Notes

INTRODUCTION

Earthmoving is the process of moving soil or rock from one location to another and processing it so that it meets construction requirements of location, elevation, density, moisture content, and so on. Activities involved in this process include excavating, loading, hauling, placing (dumping and spreading), compacting, grading, and finishing.

EXCAVATION EQUIPMENT

An excavator is defined as a power-driven digging machine. The various excavation equipment used in building projects are tractor, bull dozers, scraper, power showel, Dragline, Clam shells, hoes, dredgers etc.

(i) Scraper: It is a self-sufficient machine which can dig, haul and discharge the material in uniformly thick layers. It is generally drawn by a tractor. It consists of a cutting edge which is lowered capable of into the ground to make the cut. Scrapers are usually mounted on two or four pneumatic tyred wheels. An apron is provided in front of the container which opens and closes in order to regulate the flow of earth.

(ii) Power Shovel: It is used to excavate earth of all classes except rock and load it into wagons. They are mounted on crawless tracks. It consists of a mounting, cab, boom, dipper stick, dipper and hoist line.

Output of Power shovel: It is the quantity of excavated material in unit period of time and is expressed as cubic meter per hour

Where,

Tc = Time taken in one cycle of excavation

N = no of cycle in one hour

(iii) Draglines: They are used to excavate soft earth below the ground and to deposit or to load into wagons. The basic parts of a dragline include the mounting, cab, boom, hoist, cable, drag, chain and bucket.

(iv) Clamshell: It is used to excavate soft to medium materials and loose materials at or below existing ground surface. It consists of a bucket of two halves, which are hinged together at top. The bucket is allowed to reach on the top of loose material to be dug.

(v) Hoe: It is used to excavate below the natural surface to keep precise control of depth of excavation at close range work. It can exert high pressure so can excavate stiff material which can not be excavated by dragline.

(vi) Dredgers: These equipments are used for excavation of bed of the river, lake or sea for the purpose of deepening.

(vii) Trenches or Ditchers: These machines can excavate trenches of constant width with accuracy and speed. They utilize conveyor principle having a series of small cutting buckets attached to two endless chains supported by a boom that is lowered into the ground to the required depth.

COMPACTION EQUIPMENT

Compaction is a process of increasing density of the earth by removing the air voids. It takes place by four operations:

(i) Rolling: In this process heavy weights in the of the form of rollers are used to press the soil particles together. Smooth wheeled rollers are typical examples of compaction equipment which operate on at this principle.

(ii) Kneading: In this process kneading of soil while at the same time applying pressure is allowed. Sheep foot rollers are typical examples of compaction equipment which operate on this principle.

(iii) Vibrations: In this process the soil particles are shaken together in a compact mass. Vibrating rollers are typical examples of compaction equipment which operate on this principle.

(iv) Ramming: In this process the soil particles are forced to move closer together by pounding action Hand-temping and mechanical tempers are typical example which operates on this technique.

Different type of Compaction equipment are as follows:

(a) Smooth Wheeled Roller: Three wheeled or macadam roller and tandem rollers are the typical examples of smooth wheeled rollers. These rollers have either two or three rolls in line behind each other. The rolls are actually hollow steel drums which can be filled with water or damp sand to obtain the desired pressure. These rollers are most suitable for compacting gravels, sands and such materials where a crushing action is needed.

(b) Sheep's Foot Roller: This type of roller consists of a cylindrical steel drum with steel projection extending in a radial direction outward from the surface of the cylinder. They may be self-propelled but more common only they are towed by a tractor. Compaction obtained by the feet penetrating and applying a high vertical pressure while at the same time providing lateral pressure. This type of roller is more suitable for silt and clayey sand, clayey silt and medium to heavy clays.

(c) Pneumatic Tyred Roller: This type of roller consists of a box mounted on two axles. The front axle has one wheel less than the rear axle. The roller gives kneading action as well as compression to the soil underneath. These rollers are suitable for moderately cohesive silty soils, clayey, gravelly and clean sands of close gradation.

(d) Vibratory Compactors: They consist of a vibrating unit of either the out-of-balance weight type or a pulsating hydraulic type mounted on a screed, plate or roller in such a way that the net effect is an up and down vibratory movement of the compactor. These compactors are most effective for coarse-grained soils.

(e) Rammers: This type of compacting equipment consists of a relatively small area and is useful for compaction of trenches, foundation and slopes.

HOISTING EQUIPMENT

They are used for transporting materials or passengers vertically by means of a moving level platform. These equipments are used for lifting the loads, holding them in suspension during transfer from one place to the other and placing them at designated location. The various hoisting equipment generally used are pulleys, chain hoist, winches, and cranes.

(i) Pulleys and Sheaves: They are used for lifting rough surfaced and heavy objects. Alloy chains and wide ropes are used for this purpose.

(ii) Chain Hoist: They consist of two sets of chains namely the hand chain and the load chain. They can lift loads up to 50 tonnes.

(iii) Hoist Winch: This is a combination of gears, clutches and brakes. Diesel engine or electric motor is used as prime mover in case of power operated winches. The operation is controlled through a series of levers.

(iv) Crane: A crane is a device or machine for lifting loads by means of a rope. The use of cranes is mainly due to the need to raise the large and heavy prefabricated components often used in modern structures. The crane consists of a single grooved wheel, over which the rope is passed, suspended from a beam and is called a gin wheel. The gin wheel is manually operated and always requires more effort and hence suitable for light loads.

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