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Excavating and Earth-Placing Machinery

Excavating and earth-placing machinery

Bulldozers (‘dozers’) are used for cutting and grading work, for pushing scrapers to assist in their loading, stripping borrowpits, and for spreading and compacting fill. The larger sizes are powerful but are costly to run and maintain, so it is not economic for the contractor to keep one on site for the occasional job. Its principal full-time use is for cutting, or for spreading fill for earthworks in the specified layer thickness and compacting and bonding it to the previously compacted layer. It is the weight and vibration of the dozer that achieves compaction, so that a Caterpillar ‘D8’ 115 h.p. weighing about 15 t, or its equivalent, is the machine required; not a ‘D6’ weighing 7.5 t which is not half as effective in compaction. The dozer cannot shift material very far, it can only spread it locally.

A dozer with gripped tracks can climb a 1 in 2 slope, and may also climb a slope as steep as 1 in 1.5 provided the material of the slope gives adequate grip and is not composed of loose rounded cobbles. On such slopes of 1 in 1.5 or 1 in 2 the dozer must not turn, but must go straight up or down the slope, turning on flatter ground at the top and bottom. It is dangerous to work a dozer (and any kind of tractor) on sidelong ground, particularly if the ground is soft. Dozers cannot traverse metalled roads because of the damage this would cause, and they should not be permitted on finished formation surfaces. Sometimes a flat tracked dozer (i.e. with no grips to the tracks) can be used on a formation if the ground is suitable.

Motorized scrapers are the principal bulk excavation and earth-placing machines, used extensively on road construction or earth dam construction. Their movement needs to be planned so that they pick up material on a downgrade, their weight assisting in loading; if this cannot be managed or the ground is tough, they may need a dozer acting as a pusher when loading. This not only avoids the need for a more expensive higher powered scraper, but reduces the wear on its large balloon tyres which are expensive. The motorized scrape gives the lowest cost of excavation per cubic metre of any machine, but it need a wide area to excavate or fill and only gentle gradients on its haul road. It cannot excavate hard bands or rock, or cut near-vertical sided excavations.

The face shovel, or ‘digger’ can give high outputs in most types of materials, including broken rock. It comes in all sizes from small to ‘giant’; but for typical major excavation jobs (such as quarrying for fill) it would have a relatively large bucket of 2–5m3 capacity. The size adopted depends on what rate of excavation must be achieved, the capacity of dump trucks it feeds to cart away material, and the haul distance to tip or earthworks to be constructed. The face shovel would normally be sized to fill a dump truck in only a few cycles. The machine can only excavate material down to its standing level, and work a limited height of excavation face. Hence, if a deep excavation is required, the face shovel must ‘bench in’ and must leave an access slope for getting out when it has finished excavating. It must stand on firm level ground when working, and is not very mobile. It works in one location for as long as required, moving its position only as excavation proceeds. Its major advantage is its high output and ability to excavate in most materials.

The hydraulic excavator used as a hoe or backacter, cuts towards the machine. It is highly versatile. The larger sizes can cut to a depth of 6 or 7 m and excavate a face of the same height, slewing to load to trucks alongside. It can be used for lifting pipes into trenches, and ‘bumping down’ loose material in the base of a trench with the underside of its bucket. It can usually excavate trenches in all materials except rock; but sometimes has trouble in getting out hard bands of material that are horizontally bedded or which dip away from the machine.

It can have a toothed bucket capable of breaking up a stony formation, or be fitted with a ripper tooth for soft rock or a hydraulic breaker for hard materials, or have a smooth edged bucket for trimming the base of a trench. A wide range of such machines are available, the smallest size often being used on small building sites; the larger sizes being used for large trench excavation and general excavation

of all kinds.

The dragline’s principal use is on river dredging work from the bankside, and for other below water excavation. Although the machine is slow in operation and has a smaller rate of output than an equivalent hydraulic backhoe, it can have a long reach when equipped with a long jib and can excavate below its standing level. With a 15-m jib, it can throw its bucket 20–25 m out from the machine; hence its use for river bed excavation and bankside trimming. The dragline can also be operated to cut and grade an embankment slope below its standing level, or for dumping soil or rock on such a slope. A trained operator can be skilled at placing the bucket accurately to a desired position. The dragline offloads its material to dump trucks, but this tends to be a messy operation because the swing of the bucket on its suspension cable tends to scatter material.

The wheeled loader is widely used for face excavation in soft material, but its predominant use is for shifting heaps of loose spoil and loading them to lorries. It may have a bucket size of up to 5m3; it is very mobile and, being soft tyred, can traverse public roads.

The grab has a low output rate, but is used when sinking shafts in soft material, especially when sinking caissons kentledge fashion. It is also used occasionally for the job of keeping aggregate hoppers filled with concrete aggregates from stocks dumped by delivery lorries at ground level.

The clamshell bucket has a pincer movement, hydraulically operated, and is principally used for the construction of diaphragm walls. The bucket is fixed to a long rod which is lowered and raised down a frame held vertically (or at an angle) so that it can cut trenches up to 30 m deep in soft material, usually up to 0.6 m wide. The machine rotates so the clamshell can be emptied to a waiting dump truck.

Trencher in action

Trenching machines can be used either for excavation of pipe trenches or construction of shallow diaphragm walls. They have a bucket chain cutter delivering material to the side of the trench or by additional conveyor belt can deliver to dump trucks. For hard ground the machine has special cutters cutting a groove at either side of the trench, with a third bucket cutter chain to remove the dumpling of material between.

Lattice Boom Crawler Cranes

4:39 PM Civil Engineering , Machinery

Lattice boom crawler cranes are very common on most types of construction projects. They are versatile in that many attachments to perform many different types of work such as draglines and clamshells for excavation, pile drivers, dynamic compactors, ‘‘wrecking’’ balls for demolition, augers for drilling holes, and magnets for moving metal objects can be easily attached and used. There are several boom configurations that can be used.

Figure 1 Parts of a lattice boom crane.

A guy derrick crane uses a back boom as a derrick that can be anchored temporarily to other structures to counterweight the load as it is lifted and placed. The lifting cable comes from the back of the cab of the crane, over the derrick boom and then through the lifting boom to the load, thus transferring the compressive force of the load to the derrick. This crane can boost capacity 800% over a basic crawler crane.

A crawler tower crane is less costly than a true tower crane. The main boom is vertical with a luffing boom attachment. The compressive load is transferred to the crane cab and counterweights down this vertical boom. Maximum boom and jib combination are approximately 4800.

The sky horse configuration is similar to the guy derrick, except the back boom is shorter than the lifting boom. It is not temporarily secured during the lift. This crane can approximately triple the capacity of a standard crane.

A ringer lift attachment at the base of a crawler crane is used for heavy lifting. The ring helps to stabilize the crane to the lifting surface. The crane can have a sky horse boom configuration with a luffing jib attachment. Typically a great amount of counterweight is attached for balance. The counterweight is supported on the structural ring. Ringer lift cranes can lift and swing mega-heavy loads.

Figure 1 is adapted from an illustration in the Mobile Crane Manual published by the Construction Safety Association of Ontario and shows the basic parts of a lattice boom crane. Because of the crawler tracks and the instability caused by the moment created at the end of the boom by the load, these cranes move slowly and must travel on a level stable surface. If necessary, the crane can build its own road as it moves forward. This portable surface must be level and stable enough to support the crane’s weight and also the weight of its load. When planning a lift, how and where the crane travels to its lifting position with its load must be planned. Provision for avoiding obstacles and having a stable travel surface must be made.

Consideration of Tracked or Tired Machinery in Excavating and Earthmoving

3:31 PM Civil Engineering , Construction Management , Machinery

Whether the working equipment moves on tracks or tires has a major influence on productivity (how much dirt can be moved or excavated in a certain amount of time or how fast material can be transported). Both types of movements offer advantages and disadvantages based on working and surface conditions.

Usable force available to perform work depends on the coefficient of traction of the work surface and the weight (lbs) carried by the running gear or wheels. The amount of tractive force necessary to push or pull a load is important for sizing the right machine. Manufacturers provide rimpull or drawbar pull tables for most of their equipment models showing tractive power that can be delivered at specified operating speeds. This information can be used to verify a machine’s ability or capacity to work in specified job conditions (primarily rolling or surface resistance and grade resistance) and achieve the desired production.

Coefficients of traction vary based upon the travel surface. They measure the degree of traction between the wheel or track and travel surface. Slick surfaces have lower coefficients of traction than rougher surfaces (assuming both surfaces are relatively level and flat). Coefficients of traction for rubber-tired vehicles range from 0.90 for a concrete surface, 0.20 for dry sand to 0.12 for ice. Typically, coefficients of traction tables are available in equipment performance handbooks. The better the traction generated by the piece of equipment on the travel surface, the shorter the travel time and less wear and tear on the piece of equipment. Simply stated, maximum tractive effort (drawbar or rimpull in pounds) equals the equipment weight multiplied by the coefficient of traction of the travel or work surface.

This formula calculates the maximum amount of force that can be generated for a load on a surface. Excess tractive effort generated by the equipment will cause the tires or tracks to spin. Overloading will cause this result. The machine’s engine provides the power to overcome the resistances and move the machine. The engine must be sized or matched to meet the tractive effort required to the capabilities of the machine. The model selected would be appropriate if it can generate enough tractive effort to perform the specific task without overburdening the machine.

Tracked equipment is designed for work activities requiring high tractive effort (drawbar) or the ability to move and remain stable on uneven or unstable surfaces. Tasks such as pushing over trees, removing tree stumps, or removing broken concrete flatwork require a very high pushing force. The tracked bulldozer is ideal for this type of work. Tractive effort results from the track cleats or grousers gripping the ground to create force necessary to push or pull dirt, material, or any other piece of equipment. Tracked equipment is most efficient when used for short travel distances less than 500 ft. Figure 1 shows a typical piece of heavy construction equipment running on tracks. Most loaders on construction sites run on tires.

Figure 1 Tracked loader at work

Tracks can be metal or rubber. Metal tracks are more durable and can withstand much greater abuse than rubber tracks. Heavy-duty dirt moving equipment will almost always run on metal tracks. Rubber tracks are lighter and best for smaller equipment working in organic matter and surfaces requiring minimal disturbance. Tracks come in varying widths and thicknesses. The width of the track shoe determines the ground pressure. The wider the track the more surface area covered and the wider the load distribution. Wider track shoes have greater flotation on the work surface. The heavier the track, the more power required to make it move. Narrow track shoes are better for harsh irregular hard work surfaces. Shoes are typically designed with single or double grousers. Single grouser shoes are better for developing traction and double grouser shoes typically are less damaging to travel or work surfaces.

It should be noted that tracked equipment typically marks or gouges the surface on which it is operating. Skid-steer types of equipment (bulldozers and loaders) will gouge the surface with the track cleats when they turn. To avoid ‘‘customizing’’ a parking lot surface, plywood can be laid, on which the tracked equipment can maneuver, and rubber or padded tracks or use a tired piece of equipment could be used. A hot asphalt surface typically will mark or rip with tires or tracks unless the surface is protected.

Tired equipment is more mobile and maneuverable than tracked equipment. Machines can achieve greater speed and therefore are better for hauling. However, pulling ability is reduced to reach a higher speed. Tired equipment is more efficient than tracked equipment when the distance is greater than 500 ft. The tire diameter and width, tread design, and inflation pressure influence the ability to roll. The larger the tire, the more power required to make it roll. Tread and track design influence the ability to grip the travel surface. A more pronounced deeper tread grips better. The inflation pressure also influences how much resistance the tire has on the travel surface. The less the inflation pressure, the greater the surface area covered by the tire, the harder it is to roll and more buoyant the equipment.

Rolling resistance is the resistance of a level surface to a uniform velocity motion across it. It is the force required to shear through or over a surface and is also termed wheel resistance (e.g., a truck tire developing friction on the road surface as it turns). Rolling resistance has two components: surface resistance and penetration resistance.

Surface resistance results from the equipment trying to rollover the travel surface material. Penetration resistance results from the equipment tires sinking into the surface. Obviously, this resistance will vary greatly with the type and condition of the surface over which the equipment is moving. Simply put, soft surfaces have higher resistance than hard surfaces.

On a hard surface, a highly inflated tire has less rolling resistance than a less inflated tire, primarily because of less tire surface area coming in contact with the road surface. A highly inflated tire has greater rolling resistance in sand than a less inflated tire because it will sink deeper into the rolling surface. The rolling resistances shown in Table 1 are adapted from John Schaufelberger’s book, Construction Equipment Management. The table shows several surfaces and their rolling resistances. Rolling resistance is expressed in pounds of resistance per ton of vehicle or equipment weight. The rolling resistance is greater for a loaded piece of equipment than when it is unloaded. Use the loaded weight of the equipment (equipment including fuel and lubricants plus load) in tons when calculating resistance.

When there is no real penetration into the travel or operating surface, the rolling resistance is about 40 lbs/ton. The weight of the equipment should include the load. When a tire sinks in the mud until it is stable, the rolling resistance as it tries to climb out of the rut increases about 30 lbs/ton (2000 lbs) for each inch of penetration.

Example

92,000 lbs/2000 lbs/ton = 46 tons.

Rolling resistance = 46 tons (50 lbs/ton) = 2300 lbs.

Penetration resistance = 200(46 tons) (30 lbs/ton/inch) = 2760 lbs.

Total tractive effort = 2300 lbs + 2760 lbs = 5060 lbs.

With this number, the equipment manager can refer to the manufacturer’s performance specs to select a piece of equipment that can generate enough power (in this case rimpull) to overcome this resistance.

Grade resistance is the force-opposing movement of a vehicle up a frictionless slope (does not include rolling resistance). The effort required to move a vehicle up a sloping surface increases approximately in proportion to the slope of the surface. The effort required to move a vehicle down a sloping surface decreases approximately in proportion to the slope of the surface. For slopes less than 10%, the effect of grade increases for a plus slope and decreases for a minus slope. The required tractive effort increases or decreases 20 lbs per gross ton of weight for each 1% of grade.

Renting Versus Purchasing Construction Equipment

9:34 PM Civil Engineering , Construction Management , Machinery , Mechanical Engineering , Quantity Survey

For the contractor who is new in the construction business, the decision whether to rent or purchase equipment is usually quite easy to make because, lacking surplus cash and without a well-established credit rating, the only viable alternative is renting.

For the older, more mature construction business, the decision may be a great deal more difficult. This contractor, who is more likely to be in a position in which funds and credit sources are available for equipment investments, has to determine if such investments are justified. Buying construction equipment is justified only where the investment promises net benefits in comparison with the alternative of renting equipment and investing the cash elsewhere.

A contractor does not necessarily have to own any construction equipment in order to carry on business. In most parts of the country there are many companies in the construction equipment rental business offering competitive rental rates on a large selection of equipment. There can be distinct advantages to renting equipment, including:

1. The contractor does not have to maintain a large inventory of specialized plant and equipment where individual items are used infrequently.
2. The contractor has continuous access to the newest and most efficient items of equipment available.
3. There is little or no need for equipment warehouse and storage facilities.
4. There is a reduced need for the contractor to employ maintenance staff and operate facilities for their use.
5. Accounting for equipment costs can be simpler when equipment is rented.
6. There may be significant savings on company insurance premiums when a contractor is not maintaining a inventory of plant and equipment.

However, when the construction operations of a contractor generate a steady demand for the use of certain items of equipment or plant, there can be distinct financial benefits gained by owning equipment. There can also be a marketing advantage to the contractors who own their own equipment due to the perception that these contractors are more financially stable and committed than others who own no equipment. In fact, some owners require contractors who bid on their projects to list on the bid the company-owned equipment they propose to use in the work. This information is utilized in the owner’s assessment of the bidder.

Where a comparison of equipment ownership with the rental alternative strictly on the basis of cost is needed, the full cost per unit of time of owning an item of equipment has to be determined. To estimate the full ownership cost, the following aspects of equipment ownership have to be considered:

1. Depreciation expense
2. Maintenance and repair costs
3. Financing expenses
4. Taxes
5. Insurance costs
6. Storage costs
7. Fuel and lubrication costs

Depreciation

In everyday usage the term “depreciation” refers to the decline in market value of an asset. To accountants the term has a more narrow meaning having to do with allocating the acquisition cost of an item of plant over the useful life of that asset. The way this allocation of cost is calculated may or may not reflect the loss of market value; more often than not it does not. Also, the allocation of depreciation costs considered here is not related in any way to tax considerations. For tax purposes a completely different depreciation schedule may be adopted.

The process of allocating the cost of the item over its useful life is known as “amortization,” and there are several depreciation methods available to calculate amortization of an asset. Here we will consider three methods:
1. The straight-line method
2. The declining-balance method
3. The production or use method

Maintenance and Repair Costs

The costs of maintenance and repairs of plant and equipment comprise a factor that cannot be ignored when considering ownership costs. Equipment owners will agree that good maintenance, including periodic wear measurement, timely attention to recommended service, and daily cleaning when conditions warrant it, can extend the life of equipment and actually reduce the operating costs by minimizing the effects of adverse conditions. All items of plant and equipment used by a construction contractor will require maintenance and probably also some repairs during the course of their useful life. The contractor who owns equipment usually sets up facilities with workers qualified to perform the necessary maintenance operations on equipment. It is the cost of operating this setup that we have to consider and include in the total ownership charges applied to items of plant and equipment.

Construction operations can subject equipment to considerable wear and tear, but the amount of wear varies enormously between different items of equipment used and between different job conditions. The rates used in the following examples are based on the average costs of maintenance and repair, but since these costs can vary so much, the contractor formulating equipment operating prices should adjust the rates for maintenance and repairs according to the conditions the equipment is to work under. Again, as in many places in estimating, good records of previous costs in this area will much improve the quality of the estimator’s assessment of probable maintenance costs.

Maintenance and repair costs are calculated as a percentage of the annual depreciation costs for each item of equipment. When depreciation is calculated using the straight-line method, as in the examples 6 and 7 that follow, the result is a constant amount being charged yearly for depreciation and then a second constant amount is allowed for maintenance and repairs. Realistically, depreciation will be high in the early years of ownership, while actual maintenance and repair costs in these years should be low. The relative values of yearly depreciation and maintenance costs will gradually reverse until, in the later years, low depreciation will be accompanied by high maintenance and repair bills. Using a constant amount yearly for these two expenses, therefore, would seem reasonable as the variance of one factor is offset by the countervariance of the other factor.

Financing Expenses

Whether the owner of construction equipment purchases the equipment using cash or whether the purchase is financed by a loan from a lending institution, there is going to be an interest expense involved. The interest expense is the cost of using capital; where cash is used, it is the amount that would have been earned had the money been invested elsewhere, that is, the forgone interest revenue. Where the purchase is financed by a loan, the interest expense is the interest charged on the loan. In both cases the interest expense can be calculated by applying an interest rate to the owner’s average annual investment in the unit. The average annual investment is approximately midway between the total initial cost of the unit and its salvage value.
Thus:
average annual Investment = (Total Initial Cost + Salvage Value)/2

The interest rate used to calculate the financing expense will vary from time to time, from place to place and also from one company to another depending mostly on its credit rating and how good a deal it can get from the lending institution. In the examples that follow, we will use a rate of 6%.

Taxes, Insurance, and Storage Costs

Just as with investment expenses, significant variations can be expected in the cost of the annual taxes, insurance premiums, and storage costs together with fees for licenses required and other fees expended on an item of equipment. Where these expenses are known, they should be added into the calculation of the annual ownership costs of the equipment. In the case where information on these costs is not available, they may be calculated as a percentage of the average annual investment cost of the piece of equipment. The interest expense rate and the rate for taxes, insurance, and storage costs are often combined to give a total equipment overhead rate. Below we will use an equipment overhead rate of 11%, which comprises 6% for the investment rate and 5% to cover taxes, insurance, and storage costs.

Fuel and Lubrication Costs

Fuel consumption and the consumption of lubrication oil can be closely monitored in the field. Data from these field observations will enable the estimator to quite accurately predict future rates of consumption under similar working conditions. However, if there is no access to this information, consumption can be predicted where the size and type of engine are known and the likely engine operating factor is estimated. This operating factor is an assessment of the load under which the engine is operating. An engine continually producing full-rated horsepower is operating at a factor of 100%. Construction equipment never operates at this level for extended periods, so the operating factor used in calculating overall fuel consumption is always a value less than 100%. The operating factor is yet another variable with a wide range of possible values responding to the many different conditions that might be encountered when the equipment under consideration is used. In the examples that follow, the specific operating factors used can be no more than averages reflecting normal work conditions. Again, there is no good substitute for hard data carefully obtained in the observation of actual operations in progress.

When operating under normal conditions, namely, at a barometric pressure of 29.9 in. of mercury and at a temperature of 60ºF, a gasoline engine will consume approximately 0.06 gallons of fuel for each horsepower-hour developed. A diesel engine is slightly more efficient at 0.04 gal. of fuel for each horsepower-hour developed.

Equipment Operator Costs

Whether a contractor decides to rent or own the equipment used on its projects, the cost of operating the equipment has to be considered. In some situations rentals may be available that include an operating engineer as part of the rental agreement. This variety of rental agreement is sometimes available for excavation equipment, and it can be a preferred alternative when the rental company offers a high-caliber equipment operator who is familiar with the particular excavation unit and is capable of high productivity.

More often than not, however, equipment is rented without an operator. So, just as in the case in which the contractor is using company-owned equipment, the labor costs for operating the equipment have to be calculated and added to the estimate. The usual way to price these costs is to apply an operating engineer’s hourly wage alongside the equipment hourly rate and then use the expected productivity of the equipment to determine a price per measured unit for labor and a price per measured unit for equipment. Example 5 illustrates this method of pricing equipment and operator’s costs. Note that the unit prices for labor and for equipment should always be considered separately as the labor prices have to be included in the total labor content of the estimate so that “add-ons” can be applied to this amount at the close of the bid.

Example:

Where the hourly cost of an excavator is $172.00, the wage of an operator for this equipment is $40.00 per hour, and the expected productivity of the excavator is 50 cu. yd. per hour, the unit prices for labor and equipment would be calculated thus:
Labor
$40.00/50 cu. yd.
= $ 0.80 per cu. yd.

Equipment

$172.00/50 cu. yd.

= $ 3.44 per cu. yd.
These unit prices can now be applied to the total quantity of excavation that this equipment is expected to perform in accordance with the takeoff.

Company Overhead Costs

Where the equipment ownership costs calculated in accordance with this chapter are to be used as a basis of rental rates charged by the contractor to others for the use of the contractor’s equipment, the full rental rates should include an amount for company overhead costs and amount for profit. Company overhead costs are basically the fixed costs associated with running a business. They may include the cost of maintaining a furnished office, office equipment, and personnel together with all the other costs of business operation. Since the rental rate quoted by a contractor to another party for the use of the contractor’s equipment is, in a sense, a kind of bid, the same considerations should be applied to the markup on the rental rate as are applied to markup on any of a contractor’s bids.

Analysis of Top Equipment Related to Civil Engineering, Concrete, Heavy Construction, Lifting and Access for Year 2013

12:21 PM Civil Engineering , Machinery , Mechanical Engineering

The slowdown in China, difficulties in the mining industry and the depreciation of the Yen led to a reshuffle in the global construction equipment industry last year.

Revenues for the world’s 50 largest construction equipment manufacturers fell -10% last year to US$ 163 billion, as a variety of factors impacted on this cyclical industry.

Analysis of Top Equipment Related to Civil Engineering, Concrete, Heavy Construction, Lifting and Access

The most profound came from a downturn in the global mining industry, which pulled revenues down for equipment manufacturers around the world. Although the Yellow Table attempts to measure revenues from construction equipment sales and excludes companies that serve only the mining industry, it is inevitable that a downturn in mining will impact on many of the companies in the league table. This is due to the blurred margins between the two industries and the wide variety or different equipment used for mining in different parts or the world.

For example it was the downturn in mining that was the main driver for the near US$ 10 billion decline in first-placed manufacturer Caterpillar's equipment revenues in 2013, compared to 2112. Indeed, this was a factor for all of the lone-line manufacturers in the top 10, all of which saw their revenues decline in Dollar terms last year.

However, the greatest impact from the downturn in mining last year was felt by drilling equipment specialist Boart Longyear which fell eight places from its position in 2012 to no. 49 in this year’s ranking.

Revenue share by country and by region among global equipment manufacturers

But aside from this decline for a heavily mining dependent manufacturer, the downturn seems to have hit companies in the broad earth moving equipment industry harder than manufacturers in niche areas. As well as seeing a fall in revenues in 2013 - the year that rankings in this year’s Yellow Table are based on - half of the companies in the top 10 have seen their share of total revenues decline since last year's study. For example, Caterpillar’s share is down to 19.0%, compared to 21.8% in last year’s Yellow Table, Komatsu has fallen to 10.8% from 11.3%. Hitachi, Zoomlion and Sany also saw their shares fall.

Despite some small gains for the other five companies in the top 10, the net result was that these large companies accounted for 62.8% of the top 50’s revenues in this year's study. This was the lowest the proportion has been since 2010, when a surge for several mid-sized Chinese manufacturers squeezed the market shares of the larger players. The Chinese market also had a part to play in this year’s edition of the Yellow Table, with the country's continued slowdown in construction and the high population of young machines available from the 2009/10 stimulus boom depressing revenues for domestic manufacturers.

This saw the likes of Zoomlion and Sany lose places within the top 10, and Lonking, XGMA and Chenggong also fall further down the table. However, XCMG, Liugong and Sunward held their ground, while Shantui moved up two places.

But the net result was that the share of the top 50’s revenues claimed by Chinese manufacturers fell to 14.4% in this year’s Yellow Table. In absolute terms, the Chinese manufacturers in the Yellow Table had total revenues of US$ 23.5 billion last year, compared to US$ 30.6 billion at the peak - about a -23% decline in the space of two years.

Currency Effects

For the Yellow Table, a rate of US$ 1 = JPY 97.63 was used, which puts the Yen some -22% weaker than the rate of US$ 1 = JPY 79.85 that prevailed just a year ago. The weaker Yen has been a boon to Japanese manufacturers’ exports over the lasr year. Revenues in Yen terms rose for many as a result in 2013. Komatsu’s revenues from construction equipment sales in the 2013 calendar year were JPY 1,723 billion, compared to JPY 1.678 billion the previous year - a +2.3% increase.

Top 10 company shares

Similar effects came into play for other Japanese manufacturers in the Yellow Table, and contributed to slides down the rankings for Hitachi, Kobelco, Tadano and Furukawa. Although other Japanese manufacturers held their ground, or even gained a few places in Kubota’s case, the net result was that their share of total revenues fell from 23.1% in 2012 to 22.4% this year.

The decline in share and absolute revenues among Chinese and Japanese manufacturers last year, combined with Caterpillar’s big drop in sales had a posiTive impact for the European companies in the Yellow Table. They saw their share of the top 50's revenues rise from 26.0% this year from 21.1% last year. However, this was as more to do with technical points about how the Yellow Table is compiled than a sudden surge in revenues.

Equipment Industry Cycles

The first point is thar CNH has been reclassified as an Italian company in this year's Yellow Table, following its incorporarion with Fiar Industrial into a new Italian entity, CNH Industrial. Other changes in favour of the European share are the addition of Sennebogen and Hiab to the ranking this year, two companies for which data has newly become available. They add a further 1.0% of the top 50 revenues to the European total.

But the revenue increase was still useful in terms of European companies' placinps. Both Volvo and Liebherr moved up within the top 10, and JCB also did well to gain two places at no. 12. Further down the table, other European gainers included Wacker Neuson, Fayar and Haulote. What's more, there were no disastrous declines - no European company fell more than two places in this year's Yellow Table.

Positions in the Yellow Table are based on sales in the 2013 calendar year in US Dollars. Currencies have been converted to Dollars based on the average exchange rate over the course of 2013. Data was gathered from a variety of sources including audited accounts, company statements and reputable third-party sources. In Japan, India and certain other countries, the use of the fiscal year (ending March 31 ) has made it impossible to establish calendar year information. In these cases, fiscal year results were used. In some cases Engineersdaily has made an estimate of revenues based on historical data and industry trends. while every effort has been taken to ensure information in this report is accurate, Engineersdaily does not accept any liability for errors or omissions.

Types of Mechanical Dredgers

9:20 PM Civil Engineering , Docks and Harbours , Machinery , Mechanical Engineering

Dredgers may be broadly classified into these main groups or types depending upon the method used to transport loosened material from the sea-bed to the water surface. These are:

1. Mechanical dredgers;

2. Hydraulic dredgers.

3. other types

1. Mechanical Dredger

Mechanical dredgers use grab or bucket to loosen the in-situ material and raise and transport it to the surface.

Bucket Dredger

A stationary dredger, fixed on anchors and moved while dredging along semi-arcs by winches. The bucket dredger is one of the oldest types of dredging equipment. It has an endless chain of buckets, that fill while scraping over the bottom. The buckets are turned upside down and empty moving over the tumbler at the top. The dredged material is loaded in barges.

Bucket Dredger

The dredging action starts when a bucket reaches the bottom of the ladder, where it loosens and scoops up a quantity of material. This material is carried in the bucket to the top of the ladder where, at the highest point of the chain, the bucket overturns and the contents are discharged. The material falls into drop chutes and into a barge moored alongside the dredger. Each bucket then returns empty on the underside of the chain to the bottom of the ladder where the cycle begins again. The size of a bucket dredger is usually described by the capacity of the buckets, which is in the range 100-900 litres.

Bucket ladder dredgers are able to dredge almost any material up to the point where blasting is required, and if fitted with ripper teeth may even be directly able to dredge weak rock. A minimal amount of water is added to the dredged material during careful use of the buckets. This is advantageous to production and costs, especially when dredging in silt and mud.

In operation, a bucket ladder dredger is held accurately in position by up to six moorings or anchors and the bucket ladder moved from side to side to excavate material.

Grab Dregder

A stationary dredger, moored on anchors or on spudpoles. The dredging tool is a grab normally consisting of two halfshells operated by wires or (electro)-hydraulically. The grab can be mounted on a dragline or on a hydraulic excavator of the backhoe type.

Grab Dredger

Grab dredgers, sometimes called clamshells, can exist in pontoon and self-propelled forms, the latter usually including a hopper within the vessel. The pontoon type grab dredger again comprises a rectangular pontoon on which is mounted a revolving crane equipped with a grab. The dredging operation consists of lowering the grab to the bottom, closing the grab, raising the filled grab to the surface and discharging the contents into a barge or, if appropriate, onto the adjoining bank. The size of this type is determined by the capacity of the grab bucket, which can vary between 1.0 and 20 m3 , depending upon the crane power.

The self-propelled grab hopper dredger is basically a ship which has one or more dredging cranes mounted around a receiving hopper. It is easily moved from site to site under its own power and also transports the dredged material to the disposal area. The size of this type of dredger is expressed in terms of the hopper capacity and can range from 100 to about 2.500 m3. The smaller vessels have a single crane, but some of the larger craft have up to four. Production depends upon crane and grab size, water depth and, in the case of the self-propelled variety, on the distance to the material disposal site.

Grab dredgers are usually held in position while working by anchors and moorings but a few are fitted with a spud, or pile, which can be dropped onto the bottom while the dredger is operating.

Backhoe Dredger

A stationary dredger, moved on anchors or on spudpoles. A spud is a large pole that can anchor a ship while allowing a rotating movement around the point of anchorage. Small backhoe dredgers can be track mounted and work from the banks of ditches. A backhoe dredger is a hydraulic excavator equipped with a half open shell. This shell is filled moving towards the machine. Usually the dredged material is loaded in barges. This machine is mainly used in harbours and other shallow waters.

BackHoe Dredger

About the Author

Arslan Zulfiqar He is a student of B.Sc in Transportation Engineering at "University of Engineering and Technology, Lahore, Pakistan"

Types of Hydraulic Dredgers

12:12 PM Civil Engineering , Docks and Harbours , Machinery , Mechanical Engineering

Hydraulic Dredger

The principal feature of all dredgers in this category is that the loosened material is raised from its in-situ state in suspension through a pipe system connected to a centrifugal pump. Various means can be employed to achieve the initial loosening of the material. If it is naturally very loose, suction alone may be sufficient, but firmer material may require mechanical loosening or the use of water jets. Hydraulic dredging is most efficient when working with fine materials, because they can easily be held in suspension. Coarser materials – and even gravel – can be worked but with a for greater
demand on pump power and with greater wear on pumps and pipes.

Suction Dredger

A stationary dredger used to mine for sand. The suction pipe is pushed vertically into a sand deposited. If necessary water jets help to bring the sand up. It is loaded into barges or pumped via pipeline directly to the reclamation area.

Profile or Plain Suction Dredger

Plain Suction Dredger

In its most simple form this type consists of a pontoon able to support a pump and suction pipe and to make the connection to the discharge pipe. More sophisticated vessels have separate suction and delivery pumps, water jets at the suction inlet and articulated suction pipes. While working, a dredger may be held in position by one or more spuds or, in deeper water, by a complex system of moorings. Plain suction dredgers are mainly used to win fill material for reclamation, with the material being placed ashore through a floating pipeline. Very long distances can be pumped by the addition of booster pumps in the line. Material may alternatively be loaded directly into barges moored alongside. The normal measures of size are the diameter of the discharge pipe, which can vary between 100 and 1000 mm, or the installed horsepower.

Modern suction dredgers can recover material from great depths and can also extract sand from below a clay overburden. Known as a deep suction dredger, this type offers the potential to recover fill material from depths up to 100 m. Production is very dependent upon the permeability of the material dredged and is best in clean sands.

Cutter Suction Dredger

A stationary dredger which makes use of a cutter head to loosen the material to be dredged. It pumps the dredged material via a pipeline ashore or into barges. While dredging the cutter head describes arcs and is swung around the spudpole powered by winches. The cutter head can be replaced by several kinds of suction heads for special purposes, such as environmental dredging.

Cutter Suction Dredger

When the in-situ material is too compact to be removed by suction action alone, some form of mechanical loosening must be incorporated near the suction mouth. The most common method is a rotating cutter; the main feature of the cutter suction dredger. This is mounted at the lower end of the ladder used to support the cutter drive and the suction pipe. The loosened material then enters the suction mouth, passes through the suction pipe and pump (or pumps) and into the delivery line.

Cutter suction dredgers operate by swinging about a central working spud using moorings leading from the lower end of the ladder to anchors. By pulling on alternate sides the dredger clears an arc of cut, and then moves forward by pushing against the working spud using a spud carriage. A generally smooth bottom can be achieved, and modern instrumentation allows profiles and side slopes to be dredged accurately. Some of the larger cutter suction dredgers are self-propelled to allow easy movement from site to site.

Cutter suction dredgers are mainly used for capital dredging, especially when reclamation is associated with the dredging. Smaller vessels can be dismantled into sections and moved by road or rail for work in inland waterways, sludge lagoons, reservoirs and similar isolated areas. Large heavy-duty cutter dredgers are capable of dredging some types of rock which have not been pre-treated.

An alternative form of loosening is the use of a rotating bucket wheel at the suction mouth. Bucket wheel dredgers are most commonly used in mineral dredging operations and to date have not found general favour among the major international dredging contractors.

Trailing Suction Hopper Dredger

A self propelled ship which fills its hold or hopper during dredging, while following a pre-set track. The hopper can be emptied by o bottom doors or valves (dumping) or by pumping its load ashore. This kind of dredger is mainly used in open water: rivers, canals, estuaries and the open sea.

Trailing suction hopper dredgers, commonly known simply as ‘hoppers’ or ‘trailers’, have a hull in the shape of a conventional ship, and are both highly seaworthy and able to operate without any form of mooring or spud. They are equipped with either single or twin (one on each side) trailing suction pipes. Material is lifted through the trailing pipes by one or more pumps and discharged into a hopper contained within the hull of the dredger. The measure of size of a hopper or trailer dredger is the hopper capacity. This may range from a few hundred cubic metres to over 20000 m’ – increasingly larger vessels have been constructed in recent years to allow economic transport of the dredged material, especially for reclamation projects.

Reclamation Dredger

A stationary dredger used to empty hopper barges. A suction pipe is lowered into the barge. Extra water can be added by water by water jets to facilitate the suction process. The dredged material is pumped by pipeline ashore, to a reclamation area, or to a storage depot.

Barge Unloading Dredger

Barge unloading dredgers are used to transfer material from hopper barges to shore, usually for reclamation. A barge unloader is basically a pontoon supporting a suction pump for the discharge, and a high pressure water pump used to fluidize the barge contents by jetting. The mixture is then pumped through a pipeline to the point of reclamation or disposal.

Other Types of Dredgers

Specialized types of dredger are usually of small size and output. They include simple jet-lift and air-lift, auger suction, pneumatic and amphibious dredgers.

Jet-lift dredgers use the Venturi effect of a concentrated high-speed stream of water to draw the adjacent water, together with bed material, into a delivery pipe. The jet head has no moving parts so blockage by wires and other dock debris is minimized. These dredgers are relatively small units and some can be manoeuvred on spuds alone.

Air-lift dredgers are very similar to the jet-lift dredgers but the medium for inducing water and material flow is high pressure air injected at the month of the suction pipe. As with jet-lift dredgers there are no moving parts in the flow system. Hard or other difficult to loosen materials cannot be dredged.

Amphibious dredgers have the unusual feature of being able to work afloat or elevated clear of the water surface on legs. They can be equipped with grabs, buckets or a shovel installation.

All the above specialist types of dredger (and others) have been developed for specific situations and generally for small scale work such as narrow canals, industrial lagoons and reservoirs. Some types have been developed to handle contaminated sediments with minimum disturbance. They are not normally employed for large scale maintenance or capital dredging work.

A further type of dredger is the plough or bed leveller. This consists of a blade or bar which is pulled behind a suitable tug or work-boat. The method can be used for direct dredging over short distances and for levelling off the bed to the desired depth when a trailer or grab dredger is operating. It may also be used to pull material from close to quay walls and other places where a trailer cannot reach into a more accessible area. Sometimes the trailer itself operates the level1er if no tug or work-boat is available.

Water Injection Dredger

A self propelled dredger which brings the sediment to be excavated into suspension with waterjets. This suspension is denser than water. It will be carried away by gravity and currents. Water injection dredging is mainly used for maintenance in harbours.

A relatively recent development in dredging equipment is the water injection dredger. This can be very effective in some material in order to fluidize it and create a turbidity current of higher density than the surrounding water. The bed material then moves in its own current. The system works best in mud and fine sand beds and has been used successfully in a number of port areas. Careful assessment must be made of the likely destination of the turbid water.

About the Author

Arslan Zulfiqar He is a student of B.Sc in Transportation Engineering at "University of Engineering and Technology, Lahore, Pakistan"

Best Practices Regarding 'Micro Hydro' Programmes

5:00 PM Civil Engineering , Hydraulics , Hydro Power , Machinery , Mechanical Engineering

Micro hydro can be best benefited from by following the best practices extracted from the lessons learned.

The Critical Factors

Micro hydro programmes and projects need clear objectives. Is the project or programme:

o An investment in social infrastructure (that will be considered in the same way as a training scheme, a safe water supply, school, a health programme?);
o A programme to sell as many micro hydro schemes as possible (regardless on the users' needs); and
o To create small profit making enterprises that are financially self-sustaining.

Financially self-sustaining projects have cash generating (usually day time) end-uses to produce cash flow and increase the use of the plant (load factor). Lighting-only systems will have the greatest difficulty in achieving financial sustainability.

Subsidies are likely to be necessary if micro hydro schemes are to substantially improve the access of poor people to electricity.

The cost of micro hydro plants is dependent on location and standards although effective management can contain this.

The form of ownership of micro hydro plant is probably less important to success than creating an effective business-like style of management.

Selecting and acquiring micro hydro technology that is appropriate to the location and task remains a necessary condition for success (wrongly sized plant and inappropriate standards remain a constant threat).

Best Practice and Profitable End-uses

It is easier to make a profitable micro hydro plant socially beneficial than to make a socially beneficial plant profitable

Profitable end-uses are difficult to develop because of the limited size of the local market and the general difficulty of small and micro enterprise development in remote locations.

Financial institutions willing to finance micro hydro should consider funding associated end-use investments in order to build profitable load.

It may well be that micro hydro should be promoted for its role in securing livelihoods, or developing small enterprises, rather than as an ‘energy programme’.

The choice of end-use can affect those who benefit from micro hydro and will therefore effect the poverty and gender impacts, even if not all the community has direct access to the energy.

Best practice and Tariff Setting

The financial performance of all micro hydro plant could be improved if the average tariff was kept in line with local inflation.

Life line tariffs under which the richer consumers cross subsidise households that cannot pay will spread the poverty reducing benefits of micro hydro - as long as the total revenue is adequate.

While there is clear evidence that demand is sensitive to the tariff charged (many potential users would be excluded by full cost covering tariffs in many locations), there is also evidence that the ability of some people to pay is higher than originally thought.

Best Practice for Governments

Governments need to assign clear responsibilities for micro hydro development and the development of the necessary ‘enabling environment’. Best Practice suggests that this would ideally be part of assigning more general responsibilities for the provision of decentralised energy services to rural (or marginalized).

Governments need to treat all energy supply options equally (‘offer the full menu of options’) and to favour what best meets the needs of the consumer in different locations.

Governments need to ensure fair competition between competing supply options and provide equal access to aid and other concessional funds, subsidies, tax breaks and support.

Plans for the expansion of the electricity grid should be rule based, and in the public domain to reduce the uncertainty about when the grid will reach a particular location. Clear rules should be published regarding the actions the grid supplier must make to compensate micro hydro owners when the grid arrives (either to buy out the plant at written down costs or to buy the hydro electricity produced).

While government finance tends to favour large scale energy investments (in say power or fossil fuels), micro hydro has the opportunity of utilising local capital (even the creation of capital through direct labour to build civil works) and it is part of the new trend towards ‘distributed’ power with much reduced costs of transmission.

Best Practice for Regulation

Regulation should aim to produce a structure of incentives that result in the needs of consumers being met most cost-effectively. It should be technologically neutral, and at costs that are in keeping with the scale of the investment and the ability of the various parties to pay.

Regulation should be transparent, stable and free from arbitrary political interference so as to foster competition between suppliers of technology, services and finance.

Regulation should set standards that are appropriate to the project cost and the ability of the various actors to pay.

Quality and safety standards should be enforced to prevent the users being exploited by shoddy equipment and installations.

Regulations should be designed so that they do not merely increase the opportunities for “rent seeking behaviour" of officials.

Regulations should be set so that: independent power producers can supply power to the grid at ‘realistic’ prices; and connection standards are appropriate for the power to be sold. Rules should be transparent and stable.

Best Practice in Financing

Best practice suggests that the expansion of micro hydro will continue to need both ‘soft funds’ and funds at commercial rates, particularly if micro hydro is to meet the needs of people with low money incomes.

Funding will be needed to cover capital costs, technical assistance and social/organisational ‘intermediation’.

Micro hydro development will need to leverage funds from many sources including those for small enterprise development, livelihood development, technical assistance social infrastructure, as well as the more usual energy and environment sources.

Micro hydro will need to widen the menu of financing options for acquiring both debt and equity, including leasing, novel forms of debt guarantee, and novel forms of collateral (e.g. in Peru the hypothecation of the cash flow from energy end-use, and municipal loans guaranteed by ‘intercept’ on revenues from Central government).

Loan conditions should be simplified, and collateral conditions modified to suit local conditions for asset (land, equipment) ownership.

Some financial institutions are likely to require training to understand the special needs and risks of micro hydro, or to build on analogous experience in other forms of rural investment.

Best Practice for Smarter Subsidies

Subsidies should be designed to achieve clearly stated objectives and should develop rather than destroy markets.

A particular problem with current subsidies provided by bilateral donors is that they have a tendency to ‘pollute the well’ – that is, they use their subsidies to spoil the market for others.

Smart subsidies should:

o follow pre-established rules that are clear, and transparent to all parties;
o focus on increasing access by lowering the initial costs (technical advice, capital investment) rather than lowering the operating costs;
o Provide strong cost minimisation incentives such as retaining the commercial orientation to reduce costs;
o remain technologically neutral;
o cover all aspects of the project including end-use investments, particularly to encourage pro-poor end-uses; and
o use ‘cross subsidies’ within the project to pay for life line tariffs and other ‘propoor’ recurrent cost subsidies (e.g. enable transfer from richer sections of the community, and commercial users to marginal connections).

Best Practice for Donors

Build programmes on a thorough understanding of what has already been tried before in the country and elsewhere.

Adopt funding strategies that enhance (rather than duplicate or destroy) local capabilities including organisations, regulatory frameworks, and technical capacities.

Maintain the ‘full menu’ of options, so as to give micro hydro the same chances for funding as other decentralised energy supply options.

Ensure funds build markets rather than destroy them - apply the principles of ‘smarter subsidies’.

Ensure funds are available for both micro hydro and associated end-uses. Give particular attention to the encouragement of pro-poor end-uses (and the views of women as major players in traditional energy systems).

Ensure funds are available for all aspects of project development.

Use soft funds to leverage access to large flows of more conventional loan and equity finance.

Be transparent to make others aware of what you are doing and try to harmonise activities with other donors, partners, equipment suppliers, contractors, and government programmes.

Best Practice for Project Developers

Project developers who have the skill and tenacity to put all the elements of a micro hydro plant together are crucial to the success of programmes, and are likely to be the main constraint to programme expansion, particularly if their costs cannot be covered by grants

Successful micro hydro programmes will need to be sufficiently large to produce sufficient work for the project developers and to achieve economies of scale in the supply of such services - such as where there are a number of plant in the same area allowing for costs of site visits to be shared by a number of installations.

Financial institutions and regulatory agencies need to strike a balance between their need for project developers they regard as credible (speaking English with formal qualifications in engineering and accountancy) and their cost. Best practice probably requires lower cost project developers with specific practical experience with micro hydro and the communities that use them.

The costs of ‘intermediation’ in project development should be recorded, and attempts made to cover them directly with grant funding.

Efforts should be made to estimate the realistic size of the market for micro hydro, taking into account, costs, alternatives, and the likely availability of finance, so as to determine whether the process of project development can be put on a more sustainable financial basis (including grants). Additionally the scale of project development capabilities should be increased sufficiently so as to reduce unit costs by capturing the economies of scale.

Technical assistance services should be separated from credit functions to ensure that sound judgements are made about the financial viability of each project (with or without subsidies) and credit worthiness of project owners.

Consideration should be given to productive end-uses from the outset, and treat micro hydro investment as a small enterprise (regardless of actual ownership structure).

Endeavour to create a business like management structure, even if co-operative or other forms of joint ownership are used.

Attempt to institute rules for tariff setting and for inflation adjustments that are technical and routine rather than arbitrary and politicised (e.g. link the price of electricity to some other freely traded commodity - such as a staple crop, kerosene, or candles).

Successful programmes include activities that stimulate demand for hydro and the financial and other support activities that are available.

Successful programmes include activities that lobby for changes in the ‘enabling environment’ created by government, financial institutions and donors. These are probably most effective when operating as an ‘Energy Forum’ combining the interests of all people interested in rural, ‘alternative’, or decentralised energy options.
Project development would benefit from technical catalysts who can work in close proximity to villagers at relatively low cost.

Best Practice for Capacity Building

There would appear to be no short cuts in developing local capacities. The process takes a long time and is costly, but without such capacities micro hydro programmes cannot succeed.

Local capacities to build micro hydro plants locally appear to substantially reduce costs

Local capacities to manage, operate and maintain micro hydro plants are a necessary condition for success and resources will need to be devoted to building this capacity.

Best Practice for Management of Micro Hydro Plant

Regardless of ownership structure, it would appear that the successful management of micro hydro plants requires a ‘corporate structure’ that minimises political interference (e.g. from municipal authorities or powerful community members) by providing clear delegated authority to a management to achieve clearly stated objectives related to profitability, coverage, and the quality of the service to be provided.

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