Category: Road Construction

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Earth Works Road Construction

Loader Operator Techniques used in Pit

In  any  pit-type  operation  the  loader  is  the  key  (major  role)  machine  in  determine  the  rate  of production.  To  ensure  that  this  machine  is  worked  continuously  and  efficiently  the  following points should be observed :

(1)     Although  most  loaders  are  extremely  manoeuvrable  and  can  load  under  awkward conditions,  the  best  production  is  obtained  if  the  angle  of  turn  and  walking  distance  is
kept to a minimum.

(2)     Ensure the loader operator keeps the floor of the excavation clean and level.

(3)     Provide  a  near  vertical  face  on  a  stockpile  to  assist  loading  efficiency.  If  possible  the operator should have his back to the wind.

(4)     Most loader-digging is done with the bucket flat or tilted to a slight downward angle. This position gives maximum penetration into banks and high spots, and cuts a smooth path for the loader’s tracks or wheels. The flat position is bets for pushing up a quantity of loose material, but the bucket should be turned down steeply for spreading and grading so that the material will flow freely from the bucket.

(5)    For normal soils, the method is to force the bucket into the toe of the bank and then lift. It is often desirable to crowd the filled bucket against the upper part of the bank to break up the material so that it will slide down to the where it can be picked up easily on the next pass.

Categories
Earth Works Road Construction

Earthworks – Loading and Hauling Material

Equipment Most Commonly Used

Where haul distances render dozer operation uneconomical, material is moved either by loading into trucks or by means of scrapers.

A  variety  of  trucks  is  available  for  hauling  loose  materials  on  earthworks  jobs  as  well  as  the conventional  highway truck, there are off-highway  vehicles which  have  fewer axles than their highway counterpart and whose axle loads exceed the regulation limits.

(a)  Highway Trucks  with  general  purpose  tipping  bodies  are  suitable  for  the  cartage  of materials  from  outside  sources  to the  site  of  work,  and  for  the  cartage  and  distribution  of material on the site.

They can operate at comparatively high speeds on the site but require a reasonably firm and smooth ground surface. As they bog easily they are unsuitable on soft sites.

Their  main  application  is  for  very  long  hauls  where  haul  roads  are  good  and  axle  load limitations apply (e.g. for hauling selected fill from a pit outside the limits of the works).

(b) Off-Highway Trucks  are suitable for hauls of up to 3 km at relatively high speed on good haul  roads  but  at reduced  speed  when  working  on  soft  ground. They  are  usually  the  most suitable equipment for hauling shot rock (unless the lead is very short in which case a dozer might be used).

Their axle loads are usually high and, unless they are equipped with abnormally large tyres they may bog on wet sites. Also, one large vehicle may do more damage to a haul road than several small ones.

Their  larger  body  offer  a  bigger  loading  target  for  the  loader  bucket  which  may  increase production of the loader. The high sided body of some of the larger wagons may however, be unsuitable  for  some  types  of  loaders.  (This  possibility  should  always  be  investigated  when matching loaders and trucks).

Owing  to  their  large  capacity  they  are  more  economical  than  smaller  machines  under conditions where they can develop their speed and where they are not delayed by restrictions at the loading and tipping points, but the breakdown of a large carrying unit causes a greater proportional loss of output than that of a smaller unit.

Categories
Road Construction Roadway Excavation

Earth Works – Drilling and Blasting

As the cost of drilling is a significant proportion of the total drilling and blasting operation   the  use  of  as  large  a  drill  hole  as  possible  will  result  in greater hole spacings and reduced footage. However, the choice of hole size and drilling pattern is  frequently  restricted  because  of  the  depth  of  face  possible  and  the  degree  of  fragmentation required.

Material should be produced in a manageable size without the need for additional treatment. In a cut to fill operation, the material size is restricted by the maximum thickness of rock fill that can be compacted by the rollers available. This then places a limit on the drill hole size and spacing. Alternatively,  it  may  be  more  economical  to  hire  larger  rollers  capable  of  compacting  deeper layers.

Deep faces (where possible) offer economy in the use of explosives but, for safety reasons, when using  front  end  loaders  for  loading  of  the  broken  rock,  a  maximum  face  of  10  meters  is recommended.

A  decision  to  drill  and  blast  need  not  slow  down  production.  The  blasting  operation  must  be matched to the capabilities of the earth moving fleet and the total operation should be planned so that intermittent unscheduled blasting does not interfere with the project’s continuity.

Productively  can  be  maintained  by  working  several  faces  and  arranging  blasting  to  be undertaken at times when there is the least likelihood of interruption to other operations.

A blast should be designed to be as large as possible within circumstantial restraints, to ensure that the overall percentage of “Low productivity” material is kept to a minimum and that a minimum of productive time is lost in preparing and moving equipment.

In addition to producing the  necessary quantities, the designed  blast  must achieve a degree of fragmentation which still not adversely effect the cost of handling during succeeding phases of earth moving.  A  well  designed  blast  should  allow  loading  to  be  undertaken  without  any  dozer stockpiling  being  required.  

When blasting adjacent to batters, holes should be more closely spaced and more lightly charged. Unless per-splitting is adopted, all batter holes should be shot on the last delay or shot separately after the main charge had been set off (perimeter blasting). Shooting should always be to a near vertical free face parallel to the holes; and the blast should be designed so that back break and damage to the sub graded and batters is minimized. To avoid such damage, “pin cushion” blasting (no free face) in conjunction with ripping should not be used

Categories
Road Construction Roadway Excavation

Earthmoving Operations-Ripping

The  rippability  of  any  rock  is  materially  affected  by  the  nature  and  composition  of  the  rock. Sedimentary rocks generally offer the best opportunity to rip, whilst metamorphic rocks present
the least opportunity. However decomposed and weathered igneous and metamorphic rocks can often be ripped economically.

Rock with frequent bedding planes and cracks can usually also be ripped economically whereas massive (thickly bedded) rock formations generally must be drilled and blasted.

Some physical characteristics which favor ripping are :-

•    Fractures, faults and planes of weakness of any kind.

•    Weathering resulting from temperature and moisture changes.

•    Brittleness and crystalline nature.

•    Frequent cracks and bedding planes.

•    Large grain size.

•    Moisture permeated clay, shale and rock formations.

•    Low compressive strength.

Ripping will be difficult if the rock formation is :-

•    Massive and homogenous (i.e. lacks bedding planes and cracks).

•    Non crystalline and therefore not brittle.

•    Without planes of weakness.

•    Fine-grained with a solid cementing agent.

•    Of clay origin where moisture may impede ripping because it makes the material plastic.

The following are some further practical matters to be considered when  ripping  –

(1)     When working a cutting always keep the outside deeper than the center. If the center is kept low, all plant tends to work away from the toe of the batter and it is expensive and difficult  to then  excavate the  toe.  In  hard  material,  perimeter  blasting  or  pre-splitting  of batters even when the rest of the cutting is not blasted helps to position the batter toe and tends to stabilize the batter face.

(2)     Rip in straight lines, never turn with the ripper buried as this can result in damage to the tyne tracks and frame.

(3)     Do not leave  blasting until all rippable  material  is removed unless there  is over 3  m of material  still  to  be  excavated.  Shallow  holes  require  an  excessive  footage  of  drilling compared to the volume loosened and as such are uneconomical.

(4)     To obtain penetration the tractor should not be jerked or tracks spun as this causes damage to the unit. Raising the tyne with the hydraulic cylinder will sometimes break out the rock.

(5)     When  working  on  side  drains and  in  the  vicinity  of  batter  toes  the  “radical  arc”  or “adjustable  parallelogram”  rippers  are  preferred  as  the  angle  of  penetration  is  variable, thus enabling material to be both ripped and lifted out.

Categories
Asphalt Paving Road Construction

Asphalt Paving Job Control

For  effective  control  of  asphalt  paving  works  a  comprehensive  understanding  is necessary of each of the following:-

(1)     Specification requirements,
(2)     Plant capabilities,
(3)     Construction processes,
(4)     Inspection requirements.

When faults occur, it is essential that they are quickly recognized, their cause determined and the necessary corrections made promptly.

 Planning of Supervision of Asphalt Paving

Supervision  commences  prior  to  the  start  of  the  asphalt paving,  when  the  engineer  and  project engineer with  contractor’s  manager, laboratory manager  and  supervisor  to  discuss  plans  and  arrangements  for  the carrying out of the works. Matters affecting the quality and timing of the works and the control of traffic that should be discussed, include:-

•    Rate of delivery of asphalt mix to the site,
•    Sequence of operations and safeguards to ensure continuity,
•    Number and types of rollers needed,
•    Matching of asphalt mix supply and paving speed,
•    The chain of command for giving and receiving instructions,
•    Reasons for rejecting the asphalt mix and/or suspending work,
•    Weather and temperature requirements,
•    Traffic control,
•    Lift thickness,
•    Spreading and rolling sequences,
•    Spreading and rolling temperatures,
•    Planning to minimize joints.

Before Paving Starts

Before  the  paving  operation  begins,  a  check  should  be  made  to  see  that  all  necessary inspections and preparations have been carried out. In particular check that:-

(a)     Base or roadway surface is properly prepared,
(b)     Traffic control arrangements are satisfactory,
(c)     Paving and compaction equipment is in good condition and adjustment,
(d)     Hand tools are available on the job,
(e)     Guidelines are in place,
(f)     Asphalt Paver screed is heated to operating temperature,
(g)     Inspectors and supervisors are familiar with the adjustments and settings of the type of
Asphalt Paver  being  used.

Categories
Road Construction Soil Tests

Soil tests to check strength of soil

Following test can be mostly used when we want to check the strength of soil in civil engineering. 

  • CBR 
  • Field Density 

California Bearing Ratio (CBR)

The CBR is a measure of the resistance of a sample of soil to penetration under controlled conditions of density and moisture content. It is defined as the percentage of load required to force a piston into the testing sample to the standard load required to produce the same effect on a standard material (crushed California limestone).

The soaked CBR test is a measure of the strength of soil of the paving material when saturated, which is the worst condition expected during the life of the  road . For a soaked CBR value, the compacted sample is soaked for four days before testing.

 

COMPACTION TESTS

 

The object in compacting a pavement is to improve its properties, in particular to increase its strength of soil and bearing capacity, reduce its compressibility and decrease its ability to absorb water. Compaction tests are carried out to determine whether the density of the pavement achieved during compaction complies with requirement of the specification.

Maximum Dry Density and Optimum Moisture Content

For any soil aggregate, or crushed rock there is a moisture content at which, for a given compactive effort, maximum dry density is achieved. This moisture content is referred to as the optimum moisture content.

To determine the degree of compaction of a paving material, a laboratory test is carried out to find the maximum density which can be achieved by compacting the material in a mold with a given number of blows of a standard hammer.

Samples of the test material are compacted at varying moisture contents and the dry density calculated. Results are graphed and the M.D.D. and O.M.C. determined.

 

Field Density

 

To test the compaction being achieved by the rollers, a field density test is carried out. One method of doing this consists of digging a hole, measuring its volume by filling it with sand of known density, weighing the material taken from the hole and finding its moisture content. The density measured in the field is then compared with that achieved in the laboratory after subtracting the weight of moisture in both materials.

A second method is to use a nuclear moisture density meter. Using this method the dry density of the material is calculated from the “count” read from the gauge of the meter which is calibrated for each material.

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ABC Laying Road Construction

Motor Grader Operation for Road Finish Level

There are a number of methods to control the final finish of a  road surface  by using motor grader. No matter which method issued the motor grader will set the Moldboard to the trimming tilt and at 45°. With this tilt the cutting edge is almost vertical to the road surface and only scrapes the surface. It is also advisable to use new cutting edges or reasonably flat surfaced edges. By lightly moving over the surface the material is trimmed from the high sections and deposited into the lower sections. The  motor grader  should start at one edge and move to the other side of the road using several passes. A roller should follow the motor grader to compact the surface and care should be taken not to let the surface become dry.

Methods of Control.

Straight edges.

If the final road surface level is not required to be accurate but the finish surface is to be smooth, as in maintenance work, then this straight edges method is suitable.A profile board can be constructed for this purpose. This board is constructed to have a 3 percent difference from one end to another and is generally about 2 meters in length. The board is used with a spirit level to find the cross fall and without a spirit level to see any variations in flatness along the length off the road. This board can be easily carried in a Site Engineer’s vehicle for spot-checking.

String Line.

This method is acceptable for most classes of roads and has the advantage of being very quick when working with the motor grader. It however requires a surveyor or technician to do the initial setting out. Once the setting out has been done it should not have to be done again other than to replace damaged pegs. Two wooden pegs of say 1 to 1.5 meters are securely placed outside the shoulder edge on both sides of the road. A nail is then driven into the side of each peg at reduced level that has been calculated to give a height 300mm above and parallel to the designed finish road surface. A string line is strung between the upper and lower nails, for straights and between the two nails for curves. The Site Engineer/Site Supervisor then reads a tape measure vertically down from the string line and informs the  motor grader operator  as to the depths of cut or fill required.

 

Box Pegs.

This is a very accurate method of control but is very time consuming. So it is not used extensively any more. After the material has been placed and compacted, the surveyor or technician hammers small wooden pegs into the surface at the correct reduced level. The  motor grader operator  then trims to the tops of the pegs. This method requires a laborer to clean the top of the peg after every pass of the motor grader in order that the operator can see the peg. Pegs can also be knocked out and have to be replaced. As the material is already compacted the pegs are very difficult to hammer in to place.

 

High Tech

This is only used in highly specialized areas such as Freeways leveling and not in general use. This method would include Laser leveling etc. The manufacturer’s methods would have to be followed and the Motor Grader fitted with the special controls.

Categories
ABC Laying Road Construction

Optimum water of Material by using motor grader

 In order manage optimum water of road pavement, we have to add some water or have to dry the material to achieve optimum water of material by using motor grader 

Adding Water.

The above method of moving a windrow from one side to another can be used to add water to a premixed or single type material. As each layer is exposed the water tanker will place water on
until the mixed material is to the required water content.

Dry over wet material.

If the material is worked in the layers from side to side the wind and the sun will dry the surface of the layer. Over one day quite an amount of water can be removed.

A simple test for optimum water content.

1. Take a handful of the mixed material and squeeze hard in the palm of the hand.
2. Using both hands gently break the roll of material in half.
3. If the material falls apart then it is too dry.
If it is muddy on the hands and sticky it is too wet.
If it breaks clean with no ‘crumbs’ then the material is close to optimum.

 

Spreading Materials and Shaping of Surface.

1. The surveyors should place the pavement edge pegs on both sides of the formation. The windrow to be spread should be placed just to the centre of the edge of pavement peg on one side.

2. The mouldboard is set to the approx height (thickness) of the layer required with the tilt being in the general position and angle of 45°. A sufficient cut is made into the windrow for the material to flow along the mouldboard and form the layer at the required depth.

3. Using this as a base more material is cut and moved across this surface to spill over the edge and extend the base. On wide  roads  this may take a few passes to get all the material to the far edge and spread.

4. After the far edge pegs have been reached the surface is lightly motor graded to the other side to bring the material to edge pegs.

Mouldboard and the wheels of the motor grader.

Only when the final shape of the finish surface has been approximated should a roller be used. Rolling should start from the outside and move towards the centre, and on curves should start at the inside and move to the outside of the curve.

If ‘Box’ type construction is not being used then the roller should leave the edge 150mm until the rest of the pavement has become firm enough to support the roller.

Categories
Motor Grader Road Construction

Techniques on Using a Motor Grader.

There can be variations on the exact techniques of motor grader that are described here, but generally similar type methods will be used with only operator preferences and site conditions changing.

Mixing Materials and Adding Water by using motor grader.

Some times two types of material may have to be blended in order to get the specified base or sub-base material. For example, Natural hillside gravel may have a high clay content, which can be reduced with the addition of sand.

A method of combining these two materials is as follows;

1. Stockpile the gravel material along the road at the correct rate. Use the motor grader to level out this material into a pad just wide enough to drive the tipping trucks on. The blade can be set at the general tilt and say 30° and the motor grader drives over the stockpiles flattening and shaping them. If a square blade is used then there is no control over the material flow and segregation of the material can occur.

2. Place sand on the previous layer using the same technique as above.

3. In order to give the motor Grader as much room to work, no pavement edge pegs are placed until the material has been completely mixed.

With the mouldboard being set at the mixing tilt and placed at approx 45° and raised on the side away from the windrow, a cut is taken from the side so that both layers are cut. The material as it
moves along the blade is rolled by the shape of the mouldboard and so mixed.

If water is to be added then it is placed on the new pad that has been formed using a Water Bowser with spraybar fitted. This is repeated on each layer.

This is repeated with new layer being placed on the top of the previous using the above method. When all the material has been moved they the motor grader will then form a new windrow on the other side of the roadway.

4. Using the above techniques of motor grader , the material is moved to the opposite side of the roadway. This is repeated, moving the material from side to side, for 4 to 6 times by which time the material should be thoroughly blended and the correct percentage of water has been added. The operator will then tell the surveyors to place edge pegs on one side of the road formation and place the windrow approx 100 to 200 mm from these pegs.

Categories
Motor Grader Road Construction

Maintenance of motor grader – 1

Servicing.

A Motor grader is a high performance machine and should be treated as such. The manufacturer’s guide to maintenance of motor grader should be followed using only the approved lubricants and service schedules. If incorrect or substandard servicing is done then the life of the machine will be shortened and the running costs increased.

Tyres.

The rubber tyres of a motor grader are expensive, so every care should be used to stop undue damage.

  •  Direction of rotation.

Care must be taken in fitting of tyres of motor grader to follow the manufacture’s instructions. If a drive tyre is not installed to the correct direction of rotation then the ‘lugs’ will quickly be damaged.

RULE: Looking down on the rear drive tyres the drive lugs will form a ‘V’ pointing to the front. The front wheels will form the ‘V’ facing the rear.

  •  Size of tyres.

As the driving tyres of motor grader are all rotating at exactly the same speed of rotation, if tyres of different diameters are used (Old with New) then the larger diameter tyres wear quickly to become the same size as the old tyres.

  •  Wheel slip.

Wheel slip of motor grader causes excessive wear and cutting. The motor grader operator with experience and training should know the correct amount of material to move.

Maintenace of motor grader’s cutting edge .

It is essential that the cutting edges be replaced or turned when they reach the limit of wear. This is about 2 cm from the mouldboard. A cutting edge of motor grader is double edged so when one edge wears out it can be turned to use the new edge. If this is not done then damage to the mouldboard could be such that a new backing surface has to be welded on to the mouldboard causing down time and losses.

There are may be additional maintenance of motor grader which can be arise when it is working during the night.