5.4 Equipment for foundation and pile driving
Pile driving equipment comprise of the following:
1.Driving rig
2.Guiding leaders
3.Pile hammer with accessories
4.Additional aids for pre boring and jetting
5.Boiler for steam raising or air compressor
1.Driving Rigs
Driving rig provides basic operations of lifting the pile, holding the pile in position, hammering it into the ground or of pulling it out of the ground and guiding the pile in the desired direction of movement. The rig supports the boom and winch mechanism, driving hammer, the guiding leaders and a platform for mounting of auxiliary equipment such as a jet pump, drilling auger, steam boiler or air compressor.
2.Guiding Leaders
The leaders guide the pile and the hammer during an operation which extends to the entire height of the rig. In case of piles to be driven below, the level of the rig into excavations, trenches or water telescopic or extensible leaders can be used. The leader should enable the hammer to deliver blows axially to the pile.
During the process of driving, the driving rig should be strong and stable. In case a boom is used, adequate space should be available between the pile top and the point of the hammer to work. There are two types of rigs, viz., skid–mounted and crane-mounted.
The skid–mounted rigs are provided with rail wheels or with long steel rollers for movement.
The crane mounted rigs are mounted with a crawler or a truck chassis with a swinging deck. In the case of floating pile driving, both the rigs can be mounted on a barge.
3.Driving Hammers
Pile driving hammers impart energy required to drive the pile into the soil. The routinely used pile hammers work by hitting the pile on its head.
The vibratory and sonic type are two new types of hammers.
Hammers are classified as:
(i)Drop hammers
(ii)Single-acting hammers
(iii)Double-acting hammers
(iv)Differential-acting hammers
(v)Diesel hammers
(vi)Hydraulic hammers
(vii)Vibratory hammers and
(viii)Sonic hammers
(i)Drop Hammers
This is the simplest form of hammer which does not use any external source of power. The only mechanism needed is to lift the hammer through a cable. Although the process is slower, it is more efficient as it uses only the gravity.
The drop hammer is basically a block of suitably shaped cast-iron with its center of gravity centered near the base in order to facilitate smoothness of fall.
(ii)Single-acting Hammer
The functioning of single acting hammer differs from drop hammer only in the manner of lifting of the ram after each blow. A conventional single-acting hammer employs a piston connected to a ram at its bottom end and moving inside a cylinder. The hammer may be of an open type or closed type.
Stream power or compressed air is used in the single-acting hammer without any adjustment or alterations and the pressure remains unchanged. This pressure ranges from 5.6 to 10.5 kg/sq.cm and used depending on the size of the hammer and its weight. The operation of the single-acting hammer costs less compared to a double-acting hammer but its speed is slower.
(iii)Double-acting Hammer
In this type of hammer, the motive fluid acts on both sides of the piston. This assists the force of gravity in striking the blow by raising the ram to the top of the driving stroke and then driving it down in its down stroke.
An equivalent energy of the single acting hammer can be developed by dropping the ram through a shorter distance and thereby reduces the energy loss. Stream or compressed air is used as the motive fluid.
Depending on the hammer weight and the weight of the ram, these hammers are available in light, medium and heavy duty models.
Two types of hammers are available, viz., open end and close end. The close-end model is used for under-water driving with-out followers. This hammer is capable of fast driving in light or medium heavy piles in moderately hard soils.
Its advantage is the speed and the disadvantage is that it should be supplied with a stream or air at the specified pressure. It is specially suitable to drive steel piles.
(iv)Differential-acting Hammer
Advantages of single-acting and double-acting hammers are combined with differential-acting hammer. But, it suffers with their disadvantages. That is, it uses a heavy ram weight, as followed in single-acting hammer and a high speed of operation, as followed in double-acting hammer. Thus, it derives the advantage of use under a wide range of pile driving conditions.
It uses 25 to 30 % of less steam compared to a single-acting hammer. This hammer is available in open and closed models and could be used, using either steam or compressed air. Lubrication system is similar to that used in single-acting hammer. The principle advantage of the differential-acting hammer over the double acting hammer is its larger ram weight. Due to the wide range of ram weight and operating speed, it suits any type of pile and field conditions.
(v)Diesel Hammer
The working of this hammer is different from other types. It does not depend on the motive fluid, but has a self contained power source. This is more efficient as the hammer is designed to deliver driving energy to the pile in three forms. This is not efficient in hard driving or in extremely cold weather.
(vi)Hydraulic Hammer
In this type of hammers, the differential principle of hydraulic fluid is utilized in place of steam or compressed air. It uses a high pressure, which comprises of oil pump, piston, cylinder, fluid lines and fittings, etc. This arrangement reduces the volumetric requirements of the unit and results in a compact hammer.
Because of the use of hydraulic pressure, more driving force and ram speed are available with high economics is achieved. It has the advantages of lower set up and moving costs, saving in time due to absence of steam boiler or air compressor, lower fuel costs, increased speed and easier handling due to the compactness of size. Further, the hammer performance is unaffected by the reactions of the pile being driven.
(vii)Vibrating Hammer
With the use of conventional driving hammers blows are struck on the pile head with certain frequency and due to this the pile moves down. Friction develops on the surface of the pile before the next blow. This could be overcome if the pile is driven continuously.
The vibratory hammer takes care of this and allows the pile to move continuously, thereby eliminating surface frictional resistance. In this process, the pile sinks fast into the soil due to its own weight and the weight of the driver assembly.
The hammer comprises of a vibratory unit which produces vibrations to oscillate the pile along its vertical axis and a clamping device which transmits these vibrations to the pile. The driving power for the vibrators are given by internal combustion engines or with electric motors. Vibrations are generated by movement of counter rotating shafts to which eccentric weights are fixed.
(viii)Sonic Hammer
It works on the principle of vibration with some modification. In this, the frequency of vibration used in driving a pile is its resonant frequency. When a device is powered by sonic waves it expands and contracts in proportion to the frequency of vibration.
Thus, when the pile is energised to its resonant frequency, it alternatively expands and contracts a small amount depending on the speed of the sound in the material of which the pile is made.
Expansion of pile at the tip displaces the adjacent soil. Further, the contraction of the pile reduces the friction and because of this pile sinks automatically. Thus, the sonic effect is double fold and because of this the pile is inserted at a fast rate.
Frictional resistance is developed at the soil – pile interface. Frictional resistance can be improved by:
i)Increasing the density of the soil which is more possible in granular soil.
ii)Increasing the roughness of the pile surface.
iii)Cast – in situ piles in all type of soils.
iv)Driven piles in granular soils.
v)Increasing the surface area of the pile.
5.5 Equipment for compaction, batching and mixing and concreting
Types of Rollers and Compactors
Compaction equipment mainly consists of static rollers and other vibratory compactors. These rollers and compactors may be grouped into the following major classes:
1.Static Smooth Wheeled Rollers
These rollers are used with or without ballast and may be provided with three wheels or two wheels of equal width called tandom type. These rollers are generally used for most of the work. But, these rollers are not effective on uniformly graded sand, gravel or silt and on cohesive soil with high moisture content due to poor traction.
These static rollers, also called as dead weight rollers, are diesel powered. These rollers rely on the weight only to compact the materials by passing over them. Units of 8 to 10 tonnes can impact a pressure of 20 to 40 kg per linear cm are generally in use. Rollers with weight up to 1 ton are used for light work.
1.Sheeps foot or Pad–foot Rollers
These rollers are suitable for cohesive soils. These may be self-driven or tractor driven and especially useful when the water content is on the higher side. The mass of the drum can be varied by adding ballast. For effective rolling, the lift thickness should be small and the contact pressure under the projection are very high. These rollers are specially recommended for water-retaining earth works.
2.Pneumatic-tyred Rollers
In pneumatic-tyred rollers, wheels are placed close together on two axles and placed such that the rear set of wheels overlap the lines of the front set to ensure complete coverage of the soil surface. In order to avoid the lateral displacement of soil, wide tyres with flat treads are provided. The compaction produced by these type is better than that of the smooth wheel rollers.
Static Compaction Equipment
These rollers can be used on any type of compaction, in general. Light weight rollers of 3 tons for foot path construction whereas for road construction heavy rollers are used. Static rollers with weight of 8 to 10 tons are used for works ranging from earth work and sub-bases to bituminous road surfacing materials. Tandom roller is preferred as a finishing roller on wearing course.
Static compaction rollers and compactors may be classified in to the following groups :
1.Towed static smooth compactors
2.Static sheepsfoot or pad foot compactors
3.Static three wheel self-propelled compactors
4.Static tandom compactors
1.Towed Static Smooth Compactors
These are the old type of compactors. These are the first type of rolling compaction equipments used. These were pulled by men or horses. During the rein of Romans, these were used to smoothen roads and paths.
2.Static Sheepsfoot or Pad–foot Compactors
On the surface of the roller projection resembling that of sheep's foot, i.e., club-shaped and tapered are provided. These feet are also called as lugs which are of different shapes. When earth fills are compacted, the feet penetrate deep into the loose material during the first pass and compact the soil from the bottom up. Sheepsfoot rollers provide a kneading effect and break the earth lumps and thereby reduce air voids in a cohesive and in other fine grained soils.
3.Static Three-wheel Self-propelled Compactors
The compactors have three rolls, a small split steering roll in the front and two large drive rolls mounted on rear axles at both the ends. These rollers weigh 8 to 10 tons. This is the most used type applications for a variety of works, viz., earth work compaction, sub – base or base course rolling and for bituminuous road rolling.
4.Static Tandom Compactors
Tandom compactors have two equal sized rollers and one centered in line- tandom. As these rollers have a smooth surface, they are suitable for compacting bituminous layers. Improvements have been made on these type of compactors as tandom vibratory compactors. Large size tandom vibratory compactors are generally preferred now-a-days as they can be used either as static compactor or as a vibratory compactor as per the requirement.
Vibratory Compaction Equipment
Vibratory compactors can be categorized into the following groups:
1.Tandom vibratory compactors
2.Towed vibratory compactors
3.Towed sheepsfoot and tamping–foot vibratory compactors
4.Self–propelled vibratory compactors
5.Hand-guided vibratory compactors
1.Tandom Vibratory Compactors
Two types are available, viz., single–drum vibrating or double-drum vibrating. In the compactors with double-drum vibrating system, two tandom wheels are provided with separate controlled vibrators in the front and rear rolls. Comparing single and double drum vibratory compactors, the output of double drum vibratory compactor is to be 80% more than the single–drum vibratory compactor. The double-drum vibratory type has an option to operate the single drum or the double-drum.
2.Towed Vibratory Compactors
This type of compactor is especially used for compacting cohesive soils, fine and coarse grained mixed soil and rock materials. The heavy type towed vibratory compactor is used in earth dam and embankment constructions. Because of the large amplitude, it shows more impact motion and therefore preferred for compacting cohesive soils, fine grained soils and mixed fine or coarse grained soils.
3.Towed Sheepsfoot or Tamping–foot Vibratory Compactors
This type of compactor is useful in highly cohesive soils and soft rocks. The kneading and crushing effect of the feet improves the compaction performance. The compactors are provided with sheepsfoot or tamping–foot vibratory equipment. Tamping-foot are larger than the sheepsfoot and hence has a more contact area.
4.Self–propelled Vibratory Compactors
These compactors are available with a weight of 8 to 10 tons dead weight. In one type, large vibratory steel roll in the front and two rubber tyres at the rear. The rubber tyres may be smooth or with treads. The smooth one can be used for bituminous work. In the other type vibratory steel roll is in the front and two static steel rolls at the rear of the multi purpose work.
5.Hand-guided Vibratory Compactors
Compactors of this type have duplex or double vibratory compactors with dual roll vibration and dual roll drive. These vibrators are small in size and thereby enable cross country mobility and excellent gradeability. They have a provision for dual roll drive. These are especially used for compacting trenches, slopes, parking lots, small repair jobs and sports grounds, etc.
Rubber-tyred Compaction Equipment
Pneumatic-tyred rollers are provided with the tyre-configuration of odd numbers, viz., five, seven, nine, etc. with a certain degree of overlap. Even number of tyres are provided on the rear axle and odd number on the front axle. Rubber-tyred or Pneumatic-tyred compactors have been used for earth, a works for cohesive and non-cohesive soils. These are generally self-propelled and are built over a wide range of weights.
These type of compactors are very efficient and produce more uniform compacted surface than steel rollers. These are used for stabilised soils in airfield, embankment and load construction applications. These type of rollers have the following advantages compared to steel rollers.
1.Surface of the layer is not bridged, but uniform.
2.Bituminous layers, compacted by rubber-tyre rollers show better sealed to keep dirt and moisture.
3.Post-compaction by traffic is negligible when compacted by rubber-tyred rollers.
Deep Compaction Techniques
Rollers and compactors are useful for compacting materials on the surface. But field conditions may demand compacting at a deeper depths. Some of the vibration methods are Vibro-compaction, Vibro-displacement compaction. Another method which of recent origin is called heavy damping which is discussed below.
The most basic and simplest way of compacting loose soil is by repeated dropping of a weight on the ground. The method is also known as deep dynamic compaction or deep dynamic consolidation. This method consists of allowing a very heavy weight (up to 400 kN) to fall freely on the ground surface from a height of 15 to 40 m. This leaves an impression on the ground.
The tamping is then repeated either at the same location or over other parts of the area to be stabilized. In the case of non-cohesive soils, the impact energy causes liquefaction, followed by settlement as water drain. Fissures formed around the impact points, sometimes facilitate drainage in some soils. This method has been successfully used to treat various types of soils and fill deposits up to 20 m thick. This method can be used on densifying soils both above and below the water table.
CONCRETING EQUIPMENT
Concreting generally involves: batching and mixing, handling and transportation, placing, finishing and curing.
A concrete plant is provided with arrangements for :
1.Receiving all ingredients for making concrete, viz., aggregates, sand and cement and water.
2.Weighing each ingredient of concrete for each batch of the mix.
3.Mixing these ingredients thoroughly to form a concrete of required consistency.
Concrete Batching and Mixing Plant
Batching comprises of proportioning of ingredients of concrete, viz., aggregate, sand, cement and water, separately for each batch. In the construction field, batching and mixing plants consists of the following:
1.Aggregate Feeders
Aggregate feed bins are made available for each size of aggregate and sand and mix based on volume. In important jobs, weighing system is adopted.
Aggregate feed bins are loaded by the following methods:
1.By shovels directly into the bins.
2.By lorries tipping directly into the bins.
3.By means of boomscrapers from the aggregates stored in bulk heads on the ground.
2.Cement Silos
Cement is stored in silos. Cement is filled to the silos by the cement carrier by pumping. For each batch mix, required cement is got after proper weighing. This weighed cement is carried to the mixing unit through the enclosed conveyor belts.
3.Water
Water is an important ingredient which decides the quality of concrete. A proper quantity of water based on the water cement ratio has to be added. Because of this the water is to be measured correctly.
The measured water from the measuring tank is delivered to the mixer when already aggregate, sand and cement are charged into the drum of the mixer. Thus, after each charge the measuring water tank is filled up from the water tank to the required quantity.
The water from the measuring tank is supplied to the mixer through the adjustable spray bar so as to attain homogeneous mix within a shortest time.
4.Mixing Unit
Mixing unit consists of two steel parallel shafts provided with adjustable paddle mounted on external supports provided with bearings.
The mix from the mixer discharges into a hopper for delivering into the concrete dumpers directly or into the bin where the mix is stored temporarily.
The mix is then taken to the construction site. The quality of concrete produced following the above procedure is very high quality.