Kpc Roads Manual_full Version

Mine Planning Department 1-1

1 INTRODUCTION

1.1 General Criteria Effecting Haul Roads

Surface mine haul roads are used for transporting products and equipment around a mine site, to the preparation plant, to dump areas, to and from stockpile areas, out of pits, etc. As such all of the aspects of highway engineering, including road grades, curve elevation, sight distance, stopping distance, adequate drainage, etc., must be followed to facilitate construction of safe and efficient haul roads for the transport of product and equipment to its destination.

The standards used for the design, construction and maintenance of mine haul roads directly impact on: Truck productivity Truck maintenance and operating costs Road safety

With correct management, the overall impact of the above three factors can be optimised in order to achieve the lowest overall total haulage cost for the mine. With too little spending, damage to trucks increases and production is lower. Excessive expenditure however on the other hand provides diminishing benefits and will result in an increase to the overall cost of hauling. The ideal is to find the optimum point where the overall total benefit is the greatest.

1.2 Main Influencing Factors

The challenge for the engineering design of a haul road is to optimise the road design to maximise productivity while living within the constraints of providing a safe work environment, an overall mine design, the existing mine topography, and the budget for haul road construction. Listed below are some of the main factors for consideration in the search to optimise the total overall cost of haulage. As trucks get bigger their productivity increases but the standard, size and quality

of the construction and maintenance of roads must also improve to cope with the increased loads.

Reducing the roughness of roads will in turn reduce the damage to trucks through fatigue, twisting and shock to the truck frame and main components.

Reducing the roughness of roads and improving the surface of the road can provide significant benefits in the life and therefore the cost of tyres.

Reducing the number of intersections and improving the design of intersections will provide significant benefits to not only truck maintenance but also to truck productivity through improved cycle times.

Improving the design of road pavements will provide reductions in the rolling resistance of the road which will lead to a reduction in fuel costs and truck maintenance, as well as an increase in truck speed and productivity.


Improving the surface material of a road pavement will also reduce the long term cost of watering and maintaining the road and will also produce a safer road with shorter truck cycle times.

Perfecting curve designs, optimising road grades and improving road alignments will lead to reduced truck maintenance and improved truck speed and productivity.

Improving road crossfalls and road drainage will lead to improved road pavements which will reduce truck and road maintenance costs and will lead to improved truck speed and productivity.

Optimising the average payload of trucks while at the same time minimising spillage.

Reducing the overloading of trucks and spillage will result in reduced road and truck maintenance and improved tyre life.

Improving the initial standard of road construction can result in a significant reduction in maintenance and maintenance costs. The life cycle cost of a road being significantly influenced by the life of the road.

Even though the effects of haul road quality on productivity and costs are well known in a general sense, there is presently very little that an engineer can do to put values on some of these design options. This is because there are too many variables in the cost equation and much of the information required is either not monitored or is hard to compile.

1.3 This Manual

The planning engineer, design engineer, construction engineer, operations or maintenance supervisors may utilize the contents section of this manual as a checklist to assure that all elements of have been considered in the planning, construction or maintenance of a haul road.

This manual endeavours to provide easily referenced design data, guidelines and maintenance criteria, to assist mine personnel involved in haul road construction and maintenance.

When considering the design or construction of a haul road though it is necessary to take into consideration all factors that relate to the total design of a specific road. To consider only a few aspects in isolation will not necessarily achieve the best overall result in terms of safety and productivity.


2. PLANNING OF A HAUL ROAD

2.1 The Aim

To provide safe, well engineered, high quality haul roads at the lowest overall total cost to satisfy the requirements of the long term mine plan.

2.2 Planning of Haul Roads

Good haul roads do not just happen they are planned.

There are several basic considerations in haul road planning. Most important, one must follow all safety procedures in both the design and construction of a new roadway. A maximum effort should be made to follow current mining plans when laying out and planning haulage roads. Aerial photographs and contour plans will be extremely useful in the planning and routing of roadways. Particular attention must always be made to the fact that current and accurate survey information is being used.

Grades, road widths, and curves must be maintained within the limits of present and/or planned haul truck specifications, since all these factors can limit speed, and hence production.

Grades in most mining operations are adverse (against the loaded haul), which increases haul cost per km. Operators must balance these increased costs against decreased distances effected by steeper grades, and the increased construction costs of flatter roads.

At KPC it is recommended that sustained grades should be kept as low as possible, and should rarely exceed 8%.

In those areas susceptible to slippery conditions due to weak pit material, in-pit water, rainfall and run off, grades should where ever practical be reduced further. For further information refer also section 3.5

2.3 Design Life

This manual has adopted a distinction between in-pit haul roads and main haul roads. As such two sets of standards will be recommended. In-pit haul roads are of a lower standard and are recognised as generally being rougher, less permanent, steeper, shorter and slower than main haul roads. Main haul roads on the other hand are of a higher standard and are more permanent, better quality and longer in length. The reason for this is that in-pit roads are generally more temporary in nature and will therefore not be in service long enough to provide the benefits resulting from the higher standard of construction appropriate for a main haul road.


The main impact associated with in-pit roads is on total truck cycle time and the fact that the rougher roads have a greater impact proportionally on truck and tyre damage and hence costs. For this reason the standard (construction and maintenance) of in-pit roads must not be allowed to slip too low and every effort should be made to make more use of main haul roads.

The impact of main haul roads is more to do with a greater volume of traffic traveling over the road for a longer life. For this reason a higher standard of road is appropriate and factors such as rolling resistance, grade, intersection design, speed, curve design, etc., become more critical.

The final design standard of a road or section of road will ultimately be determined by the estimated length of time that the road will be in use, and by what type and volume of traffic will travel on the road. In all aspects of the design, one should endeavor to allow for the possibility of future expansion and larger equipment.

At KPC it is recommended that an in-pit road shall be a high volume pit or dump road that will be required for up to six months; or a low volume in pit or dump road required for up to twelve months.

A main road shall be high volume pit, dump, or ex pit road that will remain in place for in excess of six months; or a low volume pit, dump or ex pit road that will remain in place for over twelve months.

2.4 Design Speed

Drivers in general travel a road at the speed at which they feel to be safe at the level of risk which they are prepared to accept. Drivers also tend to match their speed to the perceived radius of horizontal curves as determined by the apparent rate of movement of objects on or near the curve. Usually drivers maintain their speed over crests unaware of what may lie beyond their field of view and few anticipate hazards. Most must see a hazard to be aware of its presence.

Where a design speed is cited it means that a vehicle can travel at that speed without being exposed to hazards arising from curtailed sight distance, inappropriately superelevated curves, severe grades or pavements too narrow to accommodate the design traffic volume. The selection of the design speed for a haul road is significantly affected by the type of haul truck being used and anticipated to be used. For economic consideration the trucks should be able to travel at their maximum unloaded speed to reduce cycle times and thus increase productivity.

It is generally accepted and recommended that the 85 percentile speed be adopted as the design speed based on the unloaded top speed of the present and known future haul equipment.


It is recommended that at KPC the design speed for trucks for in-pit roads be 40 kph while the design speed for trucks on main roads be 60 kph. It should be noted that this is quite different to the KPC mine site speed limit for trucks or light vehicles.

2.5 Bend Radius & Superelevation

Like other vehicles, trucks must slow down to drive around curves, bends or corners. This generally requires deceleration and gearing down followed by acceleration and gearing up once the corner is passed. This adds to the wear and tear on a truck and perhaps more importantly reduces the cycle time for the haul, thereby lowering productivity.

The fastest speed at which a truck can navigate a corner with safety depends on many things, including the traction available from the road surface and the superelevation of the road. Generally drivers are also less comfortable with tight bends and high superelevation. There is also an increased likelihood of a driver losing control of a truck in wet conditions if the bend or superelevation is too tight.

The superelevation or banking of a road at a curve allows the use of higher speed. In theory a truck approaching a correctly designed superelevated curve at the correct design speed can maintain the same speed throughout the curve, with safety, even in poor traction conditions.

On ascending grades, and in slippery areas however superelevation will need to be reduced; otherwise slow moving vehicles may slide crossways down the superelevation. For this reason a superelevated curve needs to be designed to suit both the radius of the curve as well as the range of vehicle speeds using the curve. Refer to section 3.8 and Table 1.

Accordingly at KPC curves should be constructed to the maximum radius permissible under the conditions and at an appropriate superelevation. Refer to section 3.8 and Table 2

2.6 Cycle Time from Pit to Dump Station or Stockpile

In general terms all haul routes should be planned in order to minimise the truck haul road cycle time.

Generally this will be where the shortest possible distance between the pit and the dumping location, and return, can be used. This however is not always possible and may in some instances result in a slightly longer distance being traveled in order to avoid or minimise the impact of a particular incline.


2.7 Engineering Input

If in doubt about any aspect of haul road design or construction during and following the planning stage of the road, an engineers assistance should be sought to help in surveying, determining grades, constructing profiles, and solving drainage problems. When the final layout of the road is selected, soil samples may need to be obtained to determine road base conditions. Field work should also include investigation of existing availability of materials for sub-base and surface construction. Whenever possible, suitable local materials should be used.

2.8 Road Design Procedures

In summary the following steps are necessary in the design of a haul road:

1. Determine source and destination points of the haul road. 2. Determine most economical routes from topographical and other maps. 3. Field inspect these possible routes in order to select the most favourable. 4. Determine the life and standard of the road or sections of the roads in terms

of whether it is in-pit or main haul road. 5. Determine grades on this route and resultant speeds for loaded and

unloaded trucks and modify route if necessary. Some negotiation may be necessary to select the best compromise between haul truck performance and haul road construction cost.

6. Design horizontal and vertical curves for the proposed route and check for satisfactory sight and stopping distances.

7. Check drainage requirements. 8. If the haul road needs to cater for light vehicles or specialized vehicles such

as graders, explosive trucks, water trucks a check should be made of the road geometry with respect to applicable sight distances, stopping distances and vehicle performance characteristics.

9. Check haul truck and tyre performance on entire route and modify route if necessary, if modifications are necessary, return to step 5.

10. Conduct a detail survey along the proposed alignment contours of country along the route and peg centrelines, check contours with design grades, and drainage proposal.

11. Test soil properties along the route and design road construction accordingly.

12. Design curve superelevation and horizontal curve widening, with respective transition lengths.

13. Final cost estimates may now be made.


3. ROAD GEOMETRY

3.1 Introduction

Haul road geometry and layout depends largely on pit life, terrain, nature of resource, pit depth, the length of time the road will be used, and the economic limits of the haul road excavation. These factors most often determine the characteristics of mine haul roads. Haul roads should conform to good engineering practices within economic limitations and should have the following characteristics:

1. Ample passing width 2. Good sight distance for safety 3. Long radius superelevated curves 4. Lowest possible adverse grades with grades optimised to truck

capability. 5. Good surface 6. Adequate drainage 7. Regular maintenance 8. Be built on the basis of present haulage requirements with provision also

for future planned equipment requirements.

As far as is economically feasible, all geometric elements of haul roads should be designed to provide safe, efficient travel at normal operating speeds. The ability of the vehicle operator to see ahead a distance equal to or greater than the stopping distance required is the primary consideration. This section of the manual addresses the effect of speed, slope, and vehicle weight on stopping distance, as well as design criteria for vertical and horizontal alignment.

3.2 Stopping Distance, Grade and Brake Relationships

From a safety standpoint, haul road grades must be designed to accommodate the braking capabilities of the vehicles having the least braking potential which will most frequently traverse the haul route. In the majority of cases, rear dump trucks, by virtue of their function, size and weigh are the vehicles most likely to have the longest stopping distance requirements.

The Society of Automotive Engineers (SAE), recommended practice Jl66 has developed values for permissible service brake stopping distances. The following stopping distance curves Figures 1 to 4 depict stopping distances computed for various grades and speeds in each SAE test weight category.

Tests carried out by V.E. Dawson, indicate that to preclude fade, a 61 metres braking distance should be considered the maximum allowable.


Although some tested vehicles were able to exceed this limitation and still execute a safe, controlled stop, statistics indicate that a 61 metres restriction permits a reasonable margin of safety. Each stopping-distance graph illustrates this 61 metres maximum braking distance as a near vertical line increasing with velocity. Increases of distance for speed reflect distance consumed by driver perception and reaction time. Inclusion of this stopping-distance restriction completes the stopping-distance graphs.

Using these graphs the maximum operating speed and descent grade can be found for a known truck weight category by reading vertically along the maximum permissible stopping-distance limitation line. At grade curve intersections, read left to find velocity. An example is given on each of the Figures 1 to 4.

Figures 1 through 4 have been based primarily on mathematical derivations. They do not depict results of actual field tests, but are presented simply to offer an indication of the speed and grade limitations that must be considered in designing a haul road for a general truck size. Actual field-testing has proven that many haul trucks can and do exceed these theoretical capabilities. This empirical data, however, does not encompass a wide range of speed, weight and grade situations.

While haul truck manufacturers may equip their products with brake systems that meet or exceed these criteria, there is no indication of how brake performance may vary with changes in service, grade, road surface, or initial speed. However, the stopping-distance limitations set forth provide the basic data from which performance under different conditions may be deduced.

Before detail road layout begins, it is recommended that manufacturers of the trucks that will ultimately use the road should be contacted to verify the service brake performance capabilities of their products. In all cases, verification should reflect the capabilities of wheel brake components without the assistance of dynamic or hydraulic retardation. In the absence of such information Figures 1 to 4 need to be used.

It is recommended that at KPC, in the absence of other more specific braking information, stopping distance determinations for both in-pit and main haul roads will be based on Figures 1 to 4 of this manual.

Table 1 sets out details of the loaded and unloaded weights of the main trucks in the current KPC truck fleet. Generally for all considerations the loaded truck weight of the largest vehicle the CAT 789 should be used. In some cases though there may be a justification to adopt a lower standard for where smaller trucks only will use a road or where unloaded trucks only are expected to travel:


Figures 1& 2


Figure 3 Stopping Distance for Vehicles of 90,000 to 180,000kg GVW

Missing

Figure 4 Stopping Distance for Vehicles over 180,000kg GVW


Table 1 Weights of KPC Trucks

Truck Type

Loaded Weight kg

Unloaded Weight Kg

CAT 789 318,000 122,000 CAT 783 250,000 97,000 CAT 777 161,000 65,000

Volvo A35 ? ? Ginaf ? ?

3.3 Sight Distance

Sight distance is defined as "the extent of peripheral area visible to the vehicle operator". It is imperative that sight distance be sufficient to enable a vehicle travelling at a given speed to stop before reaching a hazard. The distance measured from the driver's eye to the hazard ahead must always be equal to or exceed the required vehicle stopping distance.

On vertical curve crests, the sight distance is limited by the road surface. Figure 5, Case A, illustrates an unsafe condition. The sight distance is restricted by the short vertical curve and the vehicle cannot be stopped in time to avoid the hazard. Case B shows a remedy to the dangerous condition. The vertical curve has been lengthened, thus creating a sight distance equal to the required stopping distance.

On horizontal curves, the sight distance is limited by adjacent batters, steep rock cuts, trees, structures, bunds, etc. Case C illustrates a horizontal curve with sight distance restricted by trees and steep side cut. Case D shows that by removing trees and laying back the slope (benching), the sight distance can be lengthened to equal the required stopping distance.

Note: Where horizontal and vertical curves occur together, it may not be economical to provide a horizontal sight distance in Case D by benching. An alternative solution to this case (and for sharp horizontal curves) would be to increase the radius of the curve.

3.4 Vertical Alignment

Vertical alignment is the establishment of grades and vertical curves that allow adequate stopping and sight distances on all segments of the haulage road. A safe haulage environment cannot be created if grades are designed without consideration for the braking limitations of equipment in use. The same is true for situations where hill crests in the road impede driver visibility to the point that vehicle-stopping distance exceeds the length of roadway visible ahead. Design practices relevant to the foregoing parameters are presented in the following subsection


Figure 5 Sight Distance Diagrams


3.5 Maximum and Sustained Grades

Theoretical maximum allowable grades for various truck weight ranges in terms of emergency stopping situations have been discussed under Section 3.2 and quantified by the stopping-distance curves given in Figures 1 to 4. Defining maximum permissible grades in terms of stopping capabilities alone, however, is somewhat misleading in that no consideration is given to production economics.

Figure 6 is a performance chart similar to those supplied by truck manufacturers. Although the graph reflects performance characteristics for a specific make and model of truck, it represents the impact of grade on performance. Two different symbols have been superimposed to show how the attainable speed is influenced by a vehicle operating on a 5% and 10% grade under both laden and unladen conditions.

It is apparent from the chart that a reduction in grade significantly increases a vehicle's attainable uphill speed. Thus, haul cycle times, fuel consumption, stress on mechanical components and maintenance costs, can be minimised to some extent by limiting the severity of grades.

By relating the 10% to 5% grade reductions to the stopping-distance charts in the previous section, it can be seen that safety and performance are complementary rather than opposing factors.

At KPC it is recommended that a maximum sustained road grade of be 8% be adopted

It should be noted that the 8% grade is a maximum and where ever possible significant operational savings may be possible if the grade is reduced. Figure 6 shows that is some situations a change in grade from 10% to 5% allows the approximate doubling of both the downhill and uphill speed of a truck in both the empty and fully loaded conditions.

3.6 Vertical Curves

Vertical curves are used to provide smooth transitions from one grade to another. Their lengths should be adequate to drive comfortably and provide ample sight distances at the design speed. Generally, vertical curve lengths greater than the minimum are desirable, and result in longer sight distance and hence improved safety. However, excessive lengths can result in long relatively flat sections, a feature that discourages good drainage and frequently leads to "soft spots" and potholes. The absolute minimum length of vertical curves should not be less than 30 meters.


Figure 6


As a simplification, the recommended vertical curve to be used at KPC should be based on: (i) Vertical curve length 150 m (ii) Vertical curve radius 1500 m

The following series of graphs Figures 7 to 14 show recommended minimum lengths of vertical curve versus stopping distances for various algebraic differences in grade. Each figure represents a different driver's eye height, ranging from 1.8 to 6.1 metres.

Example :

To illustrate the use of the vertical curve charts, first select the graph that indicates the lowest driver's eye height for vehicles in the haulage fleet. Then, from the stopping-distance charts Figures 1 to 4, find the required stopping distance for the appropriate operating speed, vehicle weight, and grade. Use the steeper of the two grades to take into consideration the most critical situation. Read right to intersect the appropriate algebraic difference and down to find the vertical curve length.

An example is given in Figure 7 for a stopping distance of 70 m and an algebraic change of grade (g1 - g2) of 10%, gives a required curve length (L) of 80 m. Having this information and applying it to the formula given in Figure 15, the final vertical curve design can be completed.

The recommended vertical curve design criteria for current KPC trucks

1. Object Height is 0.20 m 2. Drivers Eye Height for a) CAT 789 ??? m b) CAT 783 ??? m c) CAT 777 ??? m d) Volvo A35 ??? m e) Ginaf ??? m NB : For calculations of length of vertical curves and stopping site distance the least eye height should be used for major haul trucks. Therefore Figure ?? applies at KPC which is the closest available chart for a drives height of ??? m.


Figures 7& 8


Figures 9 & 10


Figure 11& 12


Figure 13 & 14


Figure 15


Figure 16


3.7 Horizontal Alignment

Horizontal alignment during haul road design and construction deals primarily with the elements necessary for safe vehicle operation around curves. Far too often curves are created without considering proper width, superelevation, turning radius, or sight distance. Correct horizontal alignment is essential to both safety and efficiency throughout a haulage cycle. Figure 16 helps to explain this relationship and shows how critical dimensions can be calculated.

It must be emphasized that any recommendations are based on providing maximum safety without taking construction economics into account. Due to the physical constraints particular to many mining areas, the resultant cost of construction may increase significantly. Safety, however, should allow no tradeoffs, and any alterations to design criteria should be accompanied by a compensatory reduction in operating speed. Using the site distance curves previously discussed and the following information the minimum horizontal curves may be derived.

3.8 Superelevation

Vehicles negotiating short-radius curves are forced radially outward by centrifugal force. Counteracting forces are the friction between the tyres and the road surface, and the vehicle weight component due to the superelevation. The basic formula is :

RVfe

125

2

=+

Where: e = superelevation rate, m per m f = side friction factor; v = vehicle speed, km per hour; And R = curve radius, m.

There are practical limits to the rate of superelevation; these being governed by weather conditions, the speed of slowly moving vehicles and the higher wheel loads carried by the inner wheels of the vehicle not travelling at the design speed.

Extensive testing has been conducted by several authorities in an attempt to quantify the friction factor that should be adopted. Generally this factor ranges from 0.1 to 0.32. Depending on the speed, the friction factor also increases as the speed decreases.


Table 2 Road Superelevation Rates

Superelevation Rates in Metres / Metre for given Vehicle Speed and Radius of Curve

Radius of Curve (m) Vehicle Speed (kph)

20 25 30 35 40 45 50 55

50m 0.06 0.10 -- -- -- -- -- --

75m 0.04 0.07 0.09 -- -- -- -- --

100m 0.03 0.05 0.07 0.10 -- -- -- --

200m** 0.02 0.03 0.04 0.05 0.06 0.08 0.10 --

300m 0.02 0.02 0.02 0.03 0.04 0.05 0.07 0.08

400m 0.02 0.02 0.02 0.03 0.03 0.04 0.05 0.06

This table serves two purposes. It indicates superelevation rates, and recommends proper curve and speed relationship. For example, a vehicle travelling at 35km per hour approaching a 100m curve superelevated at 0.03 should be advised to slow to 20km per hour.

** At KPC the recommended minimum bend for a main haul road is 200m.


Refer to Table 2 for recommended superelevation rates where the friction factor has been neglected to allow for the large variation in road surface conditions that are encountered on mine sites. This table serves two purposes. It not only indicates superelevation rates, but also recommends proper curve and speed relationships, highlighting the impact of road surface conditions. For example, a vehicle travelling at 35 km per hour approaching a 100 m curve superelevated at 0.03 should slow to 20 km per hour.

Superelevated curves needs to be designed to suit the radius of the curve and the range of vehicle speeds using the curve in both wet and dry weather

Accordingly at KPC curves should be constructed to the maximum radius possible under the conditions and at the matching superelevation giving by Table 2.

3.9 Development of Superelevation

The portion of a haul road used to transform a cross slope section into a superelevated section is considered the runout length. The generally slower speeds at mining sites make the positioning of the runout less critical. The prupose of the runout however remains the same in that it assists a driver in the manoeuvring of a vehicle through a curve. For design criteria for this shall be that one-third of the runout length shall be in the curve and two-thirds on the tangent.

Runout lengths vary with the design speed and the total cross slope change. Recommended rates of cross slope change are shown in Table 3.

Table 3 Variation in Superelevation on Run-Out Lengths

Speed of Truck V (kph)

Cross Slope Change

(m/m/10m length) 15 0.025 20 0.025 25 0.025 30 0.021 35 0.018 40 0.016 45 0.014 50 0.013 55 0.011


Example :

To illustrate the use of this table assume a vehicle is travelling at 30 km per hour with normal cross slope of 0.04 m/m to the left. It encounters a curve to the right necessitating a superelevation rate of 0.06 m/m to the right. The total cross-slope change for 30 km/hour is 0.021 m/m per 10 metres.

Thus total run out V(1) = (0.1 x 10) metres 0.021

V(1) = 47.6 metres (use 48 metres).

One third of this length should be placed in the curve and two thirds on the tangent. Refer Figure 17.

Accordingly it is recommended that at KPC superelevated curves be constructed with an appropriately designed transition into the curve.

3.10 Horizontal Curve Widening for Sharp Curves.

Widening of pavements on curves is used to maintain lateral clearance between vehicles equal to that provided on straight sections.

By applying the whole of a widening to the inside of the curve, the same effect is achieved as if a plan transition curve were applied. Plan transition may be applied by using normal road design principles but is not considered essential on low volume roads. Also ease of design and construction is facilitated by using the widening application as shown in Figure 18.

Switchbacks or other sharp curves must also be designed to take into consideration the minimum turning path capability of the vehicles being used. Figure 18 illustrates the additional road width needed by a turning truck.

3.11 Combination of Horizontal and Vertical Alignment

In the design of haul roads, it is important that horizontal and vertical alignment compliment each other. Poorly designed combinations can accentuate deficiencies and produce unexpected hazards.

Although the alternatives available to a haul road designer are limited, it would be prudent to consider the following potential problem conditions.

Avoid introducing sharp horizontal curvature at or near the crest of a hill. The driver has difficulty perceiving the curve, especially at night when

the lights of his vehicle shine ahead into space. If a curve is absolutely necessary, start it in advance of the vertical curve.


Avoid sharp horizontal curves near the bottom of hills or after a long sustained down grade. Trucks are normally at their highest speed at these locations.

Figure 17 Transition Curve Determination


Figure 18


If passing is expected, design sections of haulage road with long tangents and constant grades. This is especially important in two-lane operations.

Avoid intersections, near the crest of vertical curves and at sharp horizontal curvatures. Consider the sight distance in all four quadrants.

3.12 Haul Road Classifications - Classes

In order that specific haul road designs produced for varying haul conditions can be categorized, two (2) different classes have been nominated for KPC.

These are : -

Main - The permanent main haul roads linking pits and the ROM area. Also some of the longer term main pit ramps or dump roads. This will generally be the more permanent haul road network.

In-pit - The secondary or in-pit haul roads that are used either infrequently or over a shorter period of time. These roads tend to be more temporary and are then abandoned or dumped out. The life usage of such roads is less and does not warrant the extra cost or effort to build them to a higher standard.

Note:

1. These are only general classifications and before a particular class is nominated for a new haul road a simple cost benefit analysis should be applied to see which class provides the most suitable and cost effective solution.

2. Variations to the above classes are always possible dependent on the particular need.

At KPC it is recommended that an in-pit road shall be a high volume pit or dump road that will be required for up to six months; or a low volume in pit or dump road required for up to twelve months.

A main road shall be high volume pit, dump, or ex pit road that will remain in place for in excess of six months; or a low volume pit, dump or ex pit road that will remain in place for over twelve months.

3.13 Pavement Widths

The haul road designer must be very concerned about the road width. Sufficient room for maneuvering must be allowed at all times to promote safety and maintain continuity in the haulage cycle. Unlike passenger and commercial vehicles which have somewhat "standarized" dimensions, truck sizes vary considerably. Thus requirements have to be defined for particular


sizes rather than for general types. Complicating the problem is the need to specify additional widening for curves. Refer Section 3.10

Because of the large number of influencing variables, the following guidelines for determining width are separated into individual categories. Recommendations presented are values for the size of traveled lane to be provided and do not take into consideration the additional dimensions necessary for subbase outslopes, drainage facilities berms, etc. These items are discussed separately, and their dimensions must be added to those of the lane to determine the total roadway widths.

Width criteria for the traveled lane of a straight haul road segment should be based on the widest vehicle in use. Designing for anything less than this dimension will create a safety hazard due to lack of proper clearance. In addition narrow lanes often create an uncomfortable driving environment, resulting in slower traffic, and thereby impeding production.

Rules of thumb for determining haul road lane dimensions vary considerably from one reference source to another. Many of the guidelines specify a constant width to be added to the width of the haul vehicle. This method is sufficient for smaller vehicles, but it is not advisable for computing lane widths to accommodate larger trucks. To compensate for the increase in perception distance created by greater vehicle width, the space allocated for side clearance should vary with vehicle size.

A practical guideline for establishing the vehicle to lane width ratio is contained in the AASHO Manual for Rural Highway Design. The AASHO Manual recommends that each lane of travel should provide clearance, left and right of the widest vehicle in use, that is equivalent to one half the vehicle width. Adding credence to this recommendation is the fact that a number of large surface mines base their haul road widths on this criterion. By incorporating this guideline, both safety and efficiency will be enhanced.

Currently at KPC with the CAT 789 as the widest truck it is recommended that a minimum single lane width of 15.5m is adopted and a minimum double lane width of 27.0m is adopted.

Table 4 and Figure 19 illustrate the recommended minimum widths that should be provided for various lane configurations.


Figure 19 Minimum Haulroad Widths on Straight Sections


Table 4 Recommended Minimum Lane Widths

Truck Type

Truck Width W (m)

Recommended Single Lane

Width 2W (m)

Recommended Two Lane Width

3.5W (m) CAT789 7.7 15.4 27.0 CAT785 6.7 13.4 23.5 CAT777 5.1 10.2 17.9 Volvo

Ginaf

Note: Pavement widths must be increased on sharp curves, on embankments, in cuttings, and where other special consideration must be given to accommodate larger occasional vehicle, broken down vehicles and safety requirements.

3.14 Special Consideration for Additional Lane Widths

Special consideration must be given to road segments that may have to accommodate larger equipment such as shovels, drills, etc. A safety hazard will exist if the design road width is less than that necessary for the movement of such equipment. Prior to selecting a final design width, make the following assessments, and establish a dimension sufficient for all possible users :

1. Define the width of all equipment that may have to travel the haul road. 2. Solicit dimensional data for any anticipated new machines. 3. Determine the overall width of any equipment combinations including

light vehicles that may be involved in a passing situation. 4. Delineate the location of haul road segments requiring a greater than

normal width.

In cases where the passage of unusually wide machinery is occasional, there is no reason to establish additional lane widths equal to half that of the vehicle. Although in most instances Table 4 will serve as an excellent guide for the road designer, there are exceptions for single lane construction that must be acknowledged.

3.15 Cross Slope (Crossfall of the Pavement)

It should be noted that cross slope (crossfall) is described in the following ways :

1. As a percentage crossfall i.e. between 2% to 4% crossfall. 2. As a slope i.e. 1:50 to 1:25 3. As a rate of cross slope i.e. 20 mm to 40 mm drop for each metre of

width.


Cross slope - the difference in elevation between the crest and the road edge, must be given consideration during haul road design and construction. From the standpoint of reducing a driver's steering effort, a level surface would be most beneficial. Adequate drainage, however, requires that a cross slope be created. To accommodate both drainage and steerability, a balance must be established between a slope that will allow a effective removal of surface water without adversely affecting vehicle control.

Both the theoretical and practical aspects of initiating a constant drop across the breadth of roadways have been fully studied and documented. Although the majority of this work has been conducted in relation to urban and rural highway design, the criteria developed are equally applicable to surface mine haul roads. In nearly every published reference, the recommended rate of cross slope for surfaces normally constructed on mine haul road is 1% to 4%. (See Figure 20).

Mine operators should consider 1% to 4% as the limiting criteria for design. Special consideration must be given to determining when to use the maximum and minimum rates since the applicability of each depends on surface texture.

Cross slopes of 2% are applicable to relatively smooth road surfaces that can rapidly dissipate surface water. In most cases, minimum slope is best suited to surfaces such as asphaltic concrete. However, there are conditions which warrant the use of the 2% minimum criteria for surfaces of lesser quality. When mud is a constant problem, excessive cross sloping can cause vehicles to slide. This possibility is especially pronounced at slow operating speeds on grades of more that 5%. Therefore, where a mud problem cannot be feasibly eliminated, cross slopes should be limited to the minimum value. Road maintenance should insure that the road surface is kept smooth and drains properly.

In situations where the surface is relatively rough or where mud is not a problem, a 3 to 4% cross slope is advisable. The greater inclination permits more rapid drainage and reduces the occurrence of puddles and a saturated sub-base, which can weaken road stability. On well constructed gravel and crushed rock roads, the 2% criteria is preferable.

Of equal importance to degree of slope is the direction it should take in relation to various road configurations. Since the placement of high and low lane edges determine slope direction, it is necessary to define the circumstances under which the left edge should be higher that the right or vice versa. In the case of multiple lane construction, both sides of the final pavement may be equal, with a high point or "crown" at one of the intermediate lane edges.


Figure 20 Typical Haulroad Cross-Sections


The cross slope direction for single lane construction is governed by adjacent land features. In cases where the haul road is cut into existing ground, the high lane edge may be placed on either side. However, on fill sections, the highest lane edge should be nearest the most severe outslope.

For two, three and four lane surfaces, a crown is appropriate. On dual and four lane roads, the cross slope should be constructed to provide a continuous drop across two lanes in one direction and the same slope across the other in the opposite direction. The two lanes sloping toward the same edge of road should be lanes for vehicles traveling in the same directions.

The recommended cross slope for all KPC haul roads is 3% to 4%

For main haul roads the road surface should be a uniform and well compacted pavement surfacing of fine crushed graded red mudstone. As such a 3% to 4% crossfall will promote good drainage without compromising surface traction in the wet.

For in-pit haul roads the road surface will be of a lower standard and will therefore provide poorer traction and will resultantly be less uniform and less able to shed water. As such a 3% to 4% crossfall is felt the best balance between drainage and traction.

The recommended cross slope for pavement shoulders should be 4% to 6%.


4. HAUL ROAD CROSS SECTION

4.1 Subbase

A well drained stable road base is one of the most important fundamentals of road design. Placement of a road surface over any material that cannot adequately support the weight of traffic will severely hamper vehicle mobility and control. Moreover, lack of a sufficiently rigid bearing material beneath the road surface will result in excessive rutting, sinking, and overall deterioration of the road surface. Thus, a great deal of maintenance will be necessary in order to keep the road serviceable.

A pit may elect to forego the use of subbase materials and accept infringements on mobility in the interest of economics. In other words, it may be less expensive to allow some segments of the road to hamper, but do not prohibit, vehicle movement, rather than incur the cost of constructing a good road base. Although this may appear economical at the onset of road construction, the eventual results will nearly always be undesirable.

If the road surface is not constantly maintained, rutting will occur and create sections where vehicles must slow down to negotiate adverse conditions. Over a period of time this will represent a considerable time loss to the production cycle. More importantly, these adverse conditions pose a serious threat to vehicle control and will create an unsafe haul road. Therefore, it is important that stability of the haul road be guaranteed throughout its length.

In areas where the road surface is underlain by natural bedded stone formations, it is sufficient to place only the desired road surface material directly on the bedded stone. However, the bearing capacity of other subsurface materials, or areas of fill, must be defined to determine if they can adequately support the weight of vehicles intended to be used.

4.2 Bearing Capacity of In-Situ Materials

Defining the bearing capacity of soils is a detailed procedure that should be accomplished by a qualified soils engineer. Only in this manner can the capacity of a particular soil be determined. However, general information is available on the bearing capabilities of various soil groups.

The information in Table 5, when compared with vehicle tyre loads in kPa, identifies soil types that are inherently stable as road base and those that must be supplemented with additional material. The tyre loading for most haulage vehicles laden to design capacity, will not exceed 800 kPa. Although the tyre loading my be somewhat less, depending on the number of tyres, their size, ply rating, inflation pressure, and overall vehicle weight, this figure can be utilized when determining subbase requirements. Any subgrade that is less consolidated than soft rock will require additional material in order to establish a


stable base; therefore, the designer must determine the amount of additional material that should be placed over the subgrade to adequately support the road surface.

Table 5 Presumptive Bearing Capacity Of Soils (NB: Use with caution when specific test information is not available)

MATERIAL

Kpa

Hard, sound rock Medium hard rock Hard pan overlying rock Compact gravel and boulder-gravel formations; very compact sandy gravel Soft rock Loose gravel and sandy gravel; compact sand and gravelly sand; very compact sand- inorganic silt soils Hard dry consolidated clay Loose coarse to medium sand; medium compact fine sand Compact sand-clay soils Loose fine sand; medium sand; medium compact sand inorganic silt soils Firm or stiff clay Loose saturated sand clay soils, medium soft clay

5,700 3,800 1,150

960

765 575

480 380 290 190

140 95

Table 6 Soil Classifications Found at KPC and their Recommended CBR

Soil Type

CBR

Subgrade material Poorly drained (saturated) but well compacted siltstone and sandstone 7 Well drained, well compacted siltstone or silty sandstone fill 15 Well drained, well compacted sandstone fill 20 Surfacing material Hard burnt red mudstone with mainly gravel size fragments (2mm to 60mm) and between 10% & 30% of silt and clay (minus 75 micron)

15

Hard burnt red mudstone in a distribution from coble size to a matrix comprising sand and between 10% & 20% of minus 75 micron

30

Hard burnt red mudstone in a distribution from coble size to a matrix comprising sand and between 5% & 10% of minus 75 micron

60


Table 7 Interrelationship Of Soil Classification And Probable CBR (NB : Use with caution when tests are not available)

DESCRIPTION OF SUBGRADE PROBABLE CBR Extremely poor subgrade. Worst basaltic clay areas. Old water courses. Loose or saturated sands. Heavy clay with Plasticity Index 60 or over. Silt (unless very highly compacted.).

Heavy clay with Plasticity Index of 50.

Heavy clay with Plasticity Index of 40. Very poor subgrades. Disturbed Silurian clays. Disturbed Tertiary clays. Average to fair basaltic clays. Average to fair basaltic clay.

Poorly compacted soils (loam, sandy loam, light clay loam etc).

Undisturbed Tertiary clays.

Silty clay with Plasticity Index of 30. Soil capable of carrying construction traffic.

Sandy clay with Plasticity Index of 20. Undisturbed Silurian Clays.

Sandy clay with Plasticity Index of 10. Normal well compacted soil (loam, sandy clay, light clay loam well drained).

Well compacted deep well drained sand Silurian reef

2

2.5

3

4

4.5

5

6

7

12 15

4.3 CBR Curves

One of the most widely used methods of making this determination is through the use of curves commonly referred to as CBR (California Bearing Ratio) curves. This system, although developed in 1942, continues to be used by highway designers for evaluating subbase thickness requirements in relation to subgrade characteristics. To be completely accurate, it necessitates CBR tests to precisely determine the bearing capabilities of both subgrade and subbase materials. These tests can be conducted by a soil-testing laboratory at


relatively minimal cost simply by submitting samples of the subgrade and subbase materials.

4.4 Determination of Subbase Thicknesses

The curves on Figure 21 depict subbase thickness requirements for a wide range of CBR test values. To serve as a general indication of the subbase thicknesses required for various subgrade soil types, ranges of bearing ratios for typical soils and untreated materials are included at the bottom of the graph. It must be emphasized that these ranges are extremely vague. Actual test results may prove the bearing ratios for a specific soil group to be considerably better than the value depicted on the chart. Although it is not a recommended practice, the CBR ranges reflected by the graph may be utilized, in lieu of actual test results if only general information is desired. In this approach, the lowest possible CBR value presented for a given soil type should be used.

As shown by the curves, final subbase thicknesses are determined by vehicle wheel loads as well as soil type. Wheel loading for any haul truck can be readily computed from the manufacturers specifications. By dividing the loaded vehicle weight over each axle by the number of tyres on that axle, the maximum loading for any wheel of the vehicle can be established. In every case, the highest wheel loading should be used for the determinations. When a wheel is mounted on a tandem axle, the value should be increased by 20%.

To provide a readily available indication of the wheel-loading characteristics of currently manufactured vehicles, the chart on figure 21 is divided into three categories. Each category represents the range of wheel loadings, under fully loaded conditions, that may be anticipated for vehicles in a given weight class. Classifications do not represent the higher wheel loads that will be incurred by tandem axles in each weight range.

After wheel-loading and CBR values have been established, the chart may be employed to compute subbase requirements, as illustrated by the following example. It must be noted that the graphic plot for any wheel load never reaches zero. This open dimension is the depth allocated for the placement of final surface material. When the recommended thicknesses for various surfaces fail to consume the open dimension, the remaining space must always be filled with a subase having a CBR of 80 or greater. Crushed rock is preferred.

4.5 Example : Pavement Thickness Design

A haul road is to be constructed over a silty clay of medium plasticity with a CBR of 5. The maximum wheel load for any vehicle using the road is 18 200 kg. Fairly clean sand is available with a CBR of 15 to serve as a subbase material. The Road surface is to be constructed with a good gravel which has a CBR of 80.


Figure 21


Step A. The 18 200 kg wheel-load curve intersects the vertical line for a CBR of 5 at 700 mm. This means that the final road surface must be at least this distance above the subgrade.

Step B. A clean sand CBR of 15 intersects the 18 200 kg curve at 350 mm, indicating that the top of this material must be kept 350mm below road surface.

Step C. An intersection of the 80 CBR for gravel and the 18 200 kg wheel load occurs at 150 mm. Since this will constitute the final surface material, it should be placed for the remaining 150mm. Completed subbase construction for this example is detailed by Figure 22.

Following the determination of subbase depth requirements, proper placement procedures must be implemented. Regardless of material used, or depth, the subbase should be compacted in layers never exceeding 200 mm. To ensure stability of the final surface, subbase materials should exceed the final desired surface width by a minimum of 600 mm and must always be compacted whilst at its optimum moisture content (i.e. moist, never wet or dry). Proper compaction equipment usually consists of heavy impact rollers. Each layer must be subjected to repeated passes of the compacting equipment until it fails to compress under the weight of the vehicle.

4.6 Surface Materials

On many occasions, little consideration appears to be given to the construction of a good haul road surface. In fact, development of a haul road is frequently accomplished by simply clearing a path over existing terrain.

While this practice is undoubtedly the most economical means of road construction in terms of initial cost, the benefit is seldom long-lived. Failure to establish a good haul road surface will result in increased vehicle and road maintenance costs and will severely retard the ability of a vehicle to safely negotiate the route. These difficulties are usually greatest on earth and bedded rock surfaces. Greater vehicle maintenance is required on rock surfaces as a result of excessive tyre wear. It is virtually impossible to construct a bedded rock surface free of jagged edges. Thus, the tyres of trucks are continually cut by scuffing.

4.7 Earth Roads

Earth Roads, unless thoroughly compacted and stabilized, may cause both vehicle and road maintenance difficulties. Dust problems are frequent during dry season and, if not controlled, the dust can contaminate air filtration components, brakes, and other moving parts, making frequent replacement of these items necessary. Moreover, dust represents a major safety hazard to the vehicle operator in that it can become so dense that visibility is severely reduced. Eliminating the dust problem requires continual wetting of the surface, which represents yet another maintenance cost.


Figure 22


When subjected to heavy wetting, nonstabilized earthen roads become extremely slick and severely defaced by erosion. Thus, reduced vehicle controllability from a slippery surface creates a safety hazard, and maintenance must be increased to eliminate erosion gullies. Jagged rock and unconsolidated earth surfaces should always be avoided in a safe haul road design.

4.8 Selecting the Best Road Surface

Many of the available road-surfacing materials may be used to maximize safety and reduce road maintenance requirements. However, the field can be narrowed considerably by determining those which are most appropriate for use in haul road construction. This determination is based on the road adhesion and rolling resistance factors characteristic of different surface types; that is, the resistance factors acting between the road and tyre. Road adhesion coefficients play an important role in determining a vehicles potential to slide. Since the principal concern is haul road safety, primary emphasis should be placed on these characteristics. Table 8 shows coefficients or road adhesion, determined through years of research, for various surfaces. It must be noted that as the values decrease, the potential for a vehicle tyre to begin sliding increases.

A beneficial side effect of selecting a road surface that has a high coefficient of road adhesion for safety is that operational efficiency will increase as well. Rolling resistance has a direct effect on vehicle performance. It is commonly defined as the combination of forces a vehicle must overcome to move on a specified surface. This factor is usually expressed in kg of resistance per ton of gross vehicle weight caused by the bearing friction losses resulting from tyres sinking in loose material. For the majority of road surface materials, an increase in coefficient of road adhesion can be directly related to a reduction in rolling resistance.

Table 8 illustrates this point by presenting the rolling resistance values associated with several road surface materials and their road adhesion characteristics. The data indicates that a good road surface will, in many cases, decrease operational costs by reducing resistance to travel. Thus, safety and economics, again, work together.

Asphaltic concrete, crushed stone or gravel, and stabilized earth are the most practical construction materials for developing a haul road surface that will ensure maximum safety and operational efficiency. Because each of these materials has merits that are applicable to specific haul road situations, they are discussed separately in the following pages.


Table 8 Rolling Resistance for Various Surface Types

SURFACE TYPE

ROAD COEFFICIENT

(APPROX.)

ROLLING RESISTANCE

KG/TON GROSS VEHICLE

WEIGHT (APPROX)

Cement, asphalt, soil cement Hard-packed gravel, cinders, or crushed rock Moderately packed gravel, cinders, or crushed rock Unmaintained loose earth Loose gravel and muddy rutted material

0.8 0.7

0.6

0.5 0.4

15 to 20 30

45

80 100 to 160

NB : 10 kg/t rolling resistance equals 1% of equivalent road gradient

4.9 Asphaltic Concrete (Hot Mix Asphalt)

Because of the relatively high cost of asphaltic concrete surfaces, a pit must determine if the benefits of increased speed and reduced road maintenance will offset the investment. In most cases, the determining factors will be the length of haul and the required life of roadway. If the roadway life is relatively short, an asphaltic surface will be difficult to justify. If, on the other hand, the haul road is to be considerably long and in service for a number of years, the placement of asphaltic concrete may become feasible.

4.10 Compacted Gravel and Crushed-Stone/Fine Crushed Rock (F.C.R.)

The majority of mines presently utilize gravel and crushed rock surface haul roads. When constructed and maintained properly, both materials offer a stable roadway that resists deformation and provides a relatively high coefficient of road adhesion with low rolling resistance. The greatest advantage of gravel and crushed rock surfaces is that safe and efficient roadways can be constructed rapidly at a relatively low cost.

In some cases, the base and wearing surface may consist of the same type of materials. For example, a fine crushed rock wearing surface may often overlay a coarser crushed rock base. While base materials may consist of particles as great as 100 mm in size, the surface however must be much more refined.

The following specification in Table 9 present an example of a F.C.R. wearing surface that has proven suitable on mine haul roads. Any crushed rock or


gravel that meets or exceeds the specifications presented in the illustration will qualify as an adequate surface material.

Table 9 Typical Grading For A Fine Crushed Rock Surface Material

SCREEN SIZE (MM)

MATERIAL PASSING PERCENT

37.5 25 19 9.5 4.75 2.36 425 um 75 um

100 98 92 82 65 53 33 16

Liquid Limit Plasticity Limit Plasticity Index (Recommended) Optimum moisture content during placing

25.2 15.8 10.0

12.2%

The percentage of fines in the gravel will effect surface stability in very wet or hot, dry weather. Therefore, roads that are subject to very wet weather should not have more than 10% fines to prevent muddy, sloppy conditions. Those subject to hot, dry weather should not have less than 5% fines in order to prevent drying and loosening.

After a haul road is constructed using gravel or crushed rock materials of this type, frequent road maintenance is required. Most of this maintenance will consist of periodic grading to remove small ruts and potholes that will inevitably be created by passing traffic. The exact maintenance schedule required will depend greatly on traffic, and it must be developed to accommodate conditions at each individual location. In some cases, traffic may be heavy enough to realize benefits from a continuous maintenance schedule. Refer Section 8.

In most quarrying operations, it is recommended that both gravel and crushed rock are readily available from stockpiles of finished products. It is often difficult to derive an exact construction cost for haul road pavements. The expense of constructing a gravel or crushed rock roadway will always be considerably less than that of asphaltic concrete.


4.11 Compaction of Pavement Materials

As KPC have their own self propelled compactors and vibrating rollers, precise compaction of the various road pavement layers is possible. Although is not essential it is highly desirable that some form of compaction equipment be used, to ensure that high quality roads are constructed. At least 4 passes of a sheepsfoot roller is required on clayey materials found in the area. However the vibrating flat roller is more suitable for general earthworks and for locally imported crushed rock.

Four to six passes are usually sufficient to compact these materials if wetted to their optimum moisture content (OMC) or slightly wetter. If the material should move under the weight of the roller, allow the material to dry out by turning it over with a grader, and then apply the roller once again. If a proper subbase and base are established prior to placing top material, the depth of surface material need not exceed 150mm. To achieve a uniform layer, placement should be accomplished with a grader or an equivalent piece of equipment. Following placement, the material must be thoroughly compacted. It is recommended that either rubber-tyred or steel rollers be used for compaction. Heavy rubber-tyred vehicles can also be employed when rollers are not available. However, rubber-tyred vehicles must be run repetitively to cover the entire road width, and compaction will not be quite as good.

4.12 Stabilized Earth/Soil Subgrade

Stabilized earth is defined herein as any soil that, through special procedures or additives, has been transformed from a naturally unconsolidated state to a degree of stability that will accommodate the weight of haul trucks. Achieving this level of stabilization involves incorporating soil binders such as cement, asphalt, calcium chloride, lignosulfates, or hydrated lime.

Although these materials will not create an adequate haul road surface, they can significantly reduce the quantity of base material required. In fact, often the various soil binders can be mixed directly with subgrade soils to create a platform for the road surface, making the construction of a subbase unnecessary. At other times soil binders will reduce the amount of subbase or base material required. The potential of a specific binder to reduce or make unnecessary subbase or base material depends on the inherent strength of the material with which it is to be incorporated and the weight of vehicles that will use the haul road. Final determinations of feasibility must be made by a qualified soils engineer who has evaluated the effects a binder will have on the subgrade or base material at a particular haul road location. The application of various additives can be discussed in general terms, however.

Asphalt impregnation and soil cementing, by virtue of their somewhat higher costs, should be utilized primarily for permanent haul roads. On occasion, they may prove beneficial in areas where the subgrade is extremely weak and would require large quantities of off-site subbase for stabilization. In these instances,


the addition of asphalt and portland cement to small quantities of fill material can create a stable base.

Calcium chloride, lignosulfates, and hydrated lime are more economical than asphalt impregnation and soil cement, but are not nearly as effective. These substances are best employed to supplement crushed stone or gravel bases to increase their mechanical stability. Although the construction of any haul road will benefit from the use of these additives, they are most applicable for road segments that are subject to constant relocation.

4.13 Recommended pavement for KPC

Refer Figure 23


Figure 23

Mining Services Department 5-48

5. DRAINAGE

5.1 Catch Drain

Catch drains or cut-off drains are located at the top of cut slope behind the top of the batter. Their purpose is to intercept the flow of surface water and seepage water within the upper soil layer and to prevent scouring of the cut slope face. Figure 24 shows the required shape and position of catch drains with respect to the batter crest.

Care should be taken to ensure that provision of a catch drain in certain soil types does not initiate a scour problem.

The recommended treatment of catch drains is grassing for longitudinal drain slopes less than 10% and rock lining for longitudinal drain slope above 10%.

5.1.1. Catch Drain Type A is to be used whenever possible, particularly in erodable country. The flat and level bottom is adopted to keep flow velocities to a minimum. For longitudinal slopes less than 10% a flow depth of 200mm maximum is permitted and for slopes above 10%, a flow depth of 100mm maximum is permitted. The limiting depths of flow are required to keep the velocity to a non-scour value. The width of the drain is chosen to suit the natural side slope and the required drain capacity. When the drain reaches the design depth for its particular width, the flow must be diverted to a cross culvert or drainage channel.

5.1.2. Catch Drain Type B may be adopted where the flow is small, the longitudinal slope of the drain less than 10%, the area is constricted in width and the in-situ material is impermeable and not prone to scour.

5.1.3. Catch Drain Type C may be used in conditions similar to Type B. This is generally used on roads where heavy vegetation at the top of the batter necessitates minimum disturbances.

5.2 Drainage Provisions

Soil erosion by water is a common problem that can plague the operation of safe and workable haulage roads. Erosive action on haulage roads can cause ruts and washouts, and can saturate the soil, causing instability. The proper use of drainage facilities can alleviate this problem, resulting in safer, more efficient haulage roads.

5.3 Subsoil Drains

The function of subsoil drains is to drain the pavement or to lower the water table in the vicinity of the pavement. These drains are only used in special circumstances where ground water is a problem.


Figure 24


Careful consideration should be given to the location and construction of the outlet of subsoil drains to enable maintenance crews to periodically check and clear outlets. Marker posts should be provided to facilitate easy location by the maintenance crews.

5.4 Cross Shoulder Drains

Cross Shoulder drains (mitre or boxing drains) are designed to drain the pavement through the shoulder, usually via a coarse permeable filter media. Owing to the difficulty in maintaining a clear outlet to such drains, this may not always be a practical option.

5.5 Special Drains

Special drains may be required to handle individual problems such as diverting drainage from cross culverts under the formation clear of properties, to an acceptable discharge point. The shape, extent or type of lining in such drains should be discussed with a civil engineer.

5.6 Catch Banks

The provision of catch banks may be a suitable alternative to catch drains where intercepted flow is relatively small and the ground slope permits the type of treatment shown in Figure 25. The banks disperse the intercepted water in abroad, shallow stream to the surrounding surface and are usually protected and grassing.

The spacing of the banks varies according to site requirements and overland run-off, decreasing with steep side slopes. or large surface flows.

The length of the banks depends on the clearance to the fenced boundary and the spacing of the banks.

5.7 Table Drain Configuration and Location

Many factors influence final table drain configuration, including soil type, depth of road base, storm design frequency, local restrictions, percent of grade, and predicted runoff from contributing land areas.

However, general recommendations may be made to provide the operator with basic design concepts. Table drains are recommended for nearly all applications, owing to the relative ease of design, construction, and maintenance. (See figure 26)

1. The table drain cross slope adjacent to the haul road should be 4:1 or flatter except in extreme restrictive conditions. In no case should it exceed a 2:1 slope.


Figure 25


Figure 26


2. The outside table drain slope will vary with the material encountered. In rock it may approach a vertical slope; in less consolidated material, a 2:1 slope or flatter.

3. Where practical, the table drain should be located in undisturbed earth or rock; avoid placing ditches through fill areas.

4. In a cut-fill section, slope the haul road toward the high wall. Carry drainage in a single table drain.

5.8 Table Drain Capacity and Protection

Table drains must be designed to adequately handle expected runoff flows under various slope conditions. The primary consideration is amount of water that will be intercepted by the table drain during a rainstorm. Various methods to determine runoff flows are described in a separate document known as the KPC Rainfall and Runoff Manual.

After runoff flows are calculated, ditch design become a function of percent of grade, V-configuration (4:1, 2:1, etc.), and the depth of flow. In the V-table drain, as well as other configurations, depth of flow depends on percent of grade and the texture of material lining the table drain. Loose and porous linings and low percentage grades reduce flow rates and increase depth; smooth, impervious linings and steeper grades create the opposite effect. To alleviate excessive erosion that may result from high flow velocities, certain table drain lining materials must be incorporated as the grade increases, except when the table drain is in non erodable material. Some general rules to be followed for various grades in erodable soils are designed below. Please note that these are general rules and are by no means recommended to supersede the guidelines provided in the KPC Rainfall and Runoff Manual.

1. At up to 3% grade, the drain may be constructed without benefit of a liner except in extremely erodable material such as sand, or easily weathered shales and silts.

2. At a 3% to 5% grade, the drain should be seeded and protected with jute matting until a substantial grass lining can be established.

3. At grades over 5%, the lining should consist of dumped rock placed evenly on both sides to a height no less than 150mm above the computed maximum depth.

5.9 Estimation of Peak Flowrate

When utilizing the KPC Rainfall and Runoff Manual to develop peak flow rates, the 10-year, recurrence interval should generally be used. The rainfall intensity generated by a 10-year storm is recognized as the applicable standard for road drainage design. Moreover, the volumes of water associated with this type of storm are well in excess of normal runoff conditions and necessitate the design of drainage facilities capable of handling extreme, rather that mean, rainfalls.


The above return period may be varied to best suit economic considerations of each particular case. Quite often it can be more economical (with small catchment areas) to allow the haul road to be over topped for short periods rather than install large expensive culverts. The 10-year, recurrence interval storm could thus be too conservative and this could be reduced to the point where delays and damage due to over topping become economically unjustifiable because of lost production time and/or vehicle and road damage.

In the event that a table drain grade must be altered to accommodate changes in topography, the depth of the table drain must be changed accordingly. Whether an increase or decrease in grade occurs, new volumes should be computed based on the flow in the preceding table drain segment and the volume of water generated by the contributing area contiguous to the new grade.

By consulting table 10, the appropriate table drain depth needed to accommodate a specific volume of water may be derived. After determining the slope and finding the waterflow (in cubic metres per second), consult the corresponding table drain configuration table where the cubic metres per second is found. At the extreme left of this line will be the depth necessary to accommodate the flow for that table drain configuration.

In some cases, additional depth may be required. In all cases where a subbase must be placed, the depth of the flow must not exceed the lower level of the subbase material. In cases where a freeboard is required, the depth of any table drain shall exceed the centerline depth of flow by a minimum of 150mm. Where placement of a table drain lining material is recommended, it shall also be increased 150mm on each side.

Table 10 CAPACITY OF V-DRAINS (m3/sec) (For typical soils at KPC)

Slope (%) Geofabric Protection * Rock Protection ** Dept

h

(m) 0.5 1 2 3 4 5 6 7 8 9 10

0.3 0.18 0.20 0.28 0.35 0.40 0.45 0.49 0.53 0.35 0.37 0.40 0.4 0.39 0.43 0.62 0.76 0.87 0.61 0.66 0.72 0.77 0.81 0.86 0.5 0.72 0.79 1.12 1.38 0.99 1.10 1.21 1.31 1.40 1.48 0.6 1.17 1.29 1.83 1.39 1.61 1.80 1.97 2.13 0.7 1.76 1.95 2.76 2.10 2.43 2.72 0.8 1.97 2.79 2.45 3.00 3.47 0.9 2.70 3.82 3.36 4.12 4.75


Geofabric to be securely fastened to soil in accordance with manufacturers requirements. Geofabric to extend 150mm above nominal depth of both batter drain.

Rock protection shall consist of 0.3m dia. Rocks (40kg nom. Weight). Allowance should be made during drain excavation to ensure the required finished profile.

It is important to note that the table drain should be kept at all times of debris or any material that would alter design capacity.

5.10 Culverts

Culvert sections are the most efficient and effective means of conveying free-flowing drainage away from the haulage road, and must be incorporated to alleviate the potential of water overflows onto haul road segment. Any accumulation of water on the haul road can seriously impede vehicular control and promote road degradation.

To achieve the most efficient drainage scheme, the designer must consider culvert location, sizing, placement, and inlet/outlet controls. Numerous factors affect each of these design considerations. Therefore, each parameter is discussed as a separate category below.

5.11 Culvert Location

1. Culverts should be located at all road drainage low points unless natural water courses are present.

2. A culvert should be installed at all road intersections and prior to switchback curves on the upgrade beginning of curvature.

3. Whenever a haulage road segment requires a transition from a through-cut to a cut-fill, a culvert should be installed to intercept drainage prior to spilling over an outslope.

4. Culverts should be placed in natural watercourses intersected by haul road. 5. In cut-fill sections, culverts may be placed at various intervals along the

drain to intercept drainage and convey it to natural drains below the fill slope. This procedure can significantly reduce the size of drain required by breaking runoff areas into small segments.

The following culvert spacing is recommended:

1. Spacing should not exceed 300m on grade from zero to 3%. 2. Spacing should not exceed 240m on grade from 3% to 6%. 3. Spacing should not exceed 150m on grade from 6% to 9%. 4. Spacing should not exceed 100m on grade 10% or greater.


5.12 Type and Size of Culverts

For the majority of haulage-road culvert installations, corrugated iron pipe is most appropriate. Since this type of pipe is relatively light, high in strength, and ussually readily available, it can be easily adapted to a variety of situations. Although other materials can be utilized, corrugated iron is currently used extensively and has proven to be reasonably reliable if installed correctly.

Regardless of material, the culvert must be able to accept the maximum runoff flow from the drainage channel to be completely effective. Also, the pipe diameter must be large enough to accept maximum flow without creating a backup at its inlet.. Figure 27 may be utilized to determine pipe sizes for various flows. Flows in cubic metres per second on the left side may be read to their intersection with the diagonal graph line and then down to the corresponding minimum pipe diameter necessary to accept the flow. This minimum is indicative of a full flowing pipe without any water backup at the inlet. In some cases, however, it may be desirable to place a smaller, less expensive pipe and allow a small backup of water. The dashed lines on the chart are included to depict how much head will be created behind the pipe if its size is restrictive. To determine the amount of head created by a given pipe size and cubic metres per second, read from the cubic metres per second column until the dashed line is intersected, then down. For example, a flow of 0.30m3 per second intersects 0.6m of head at the 450mm pipe and will pond 150mm above the top of the pipe (1.e. 600 minus 450mm). However, it must be emphasized that the practice of creating an inlet head is discouraged. The most beneficial design requires that a pipe handle the entire volume without backup. If the example above for 0.30m3 per second were to be followed without creating a backup, the intersection of the diagonal will show that a pipe diameter of approximately 550mm is required.

Therefore once the culvert size has been calculated the next largest pipe size (in this case 600mm) should be selected or a multiple number of smaller diameter pipes with a total capacity in excess of the calculated discharge rate (eg. 2-450 diameter pipes with a combined capacity of 0.34m3/sec).

5.13 Recommendation of Culverts Size

It is recommended that KPC hold in store stock the following sizes: a. 600mm nestable Armco b. 1000mm nestable Armco c. 1200mm nestable Armco d. 1400mm nestable Armco

NB: Under certain circumstances the available cover from the top of the road to the culvert may prelude the use of corrugated iron or even concrete pipes. (see 5.10.5 Placement for Typical Cover Requirements). In these cases, a low profile box culvert may be suitable. If this type of problem is encountered a road engineer should be consulted.


Figure 27


5.14 Grading of Culverts

When designing culverts it is important to check the grade of the culverts to ensure that velocity in the pipe culvert falls within the general limits for siltation and scouring. These limits are generally considered to be 0.6 metres/second (minimum velocity) to prevent silting, and 3.7 metres/second (maximum velocity) to limit scouring.

The designer should refer to the pipe manufacturers design charts when carrying out these checks.

5.15 Placement

After the location and pipe size have been selected and the pipe is ready for placement, consideration must be given to depth of cover over the pipe in relation to the vehicles that will use the road. It is suggested that for support of vehicle weight under 45,000 kg, a minimum cover of 600mm over the pipe be used. For support of vehicle weights over 45,000kg, minimum cover should be 1 metre.

In all cases, the fill should be hand-tamped in 100mm layers from the bottom of trench to provide a stable, compacted base for the culvert.

5.16 Inlet-Outlet Controls

At all culvert inlets, a protective encasement or headwall consisting of a stable non erodable material should be provided.

1. Flow from drains or culverts shall never be discharged over a fill outslope. In fill situations, the discharges must be conveyed away by pipes, flumes or drains lined with non erodable material.

2. At any discharge point, where flow velocity exceeds the Soil Conservation Services recommended maximum for various soil types, erosion protection must be provided. Examples are shown in Figure 28.

TABLE 11 SLOPE PROTECTION AT CULVERT OUTLETS

Outer Velocity (m/sec)

Slope of Embankment (%)

Treatment Recomended

0. to 0.6 Under 10 Establish vegetation 0.6 to 1.5 Over 10 Riprap 1.5 to 4.5 All slopes Riprap Over 4.5 All slopes Energy dissipator


Figure 28


5.17 Incline and Ramp Drainage

Problems are often experienced with drainage water flowing from the main haul road table drains, down into pit areas. This creates siltation and an excessive pit water problem. To help to overcome this, two procedures should be adopted.

Firstly the haul road itself should dip prior to commencing the main decent into the pit. This will prevent the bulk of the water from running down the road into the excavation. Diversion drains should be installed to take all road drainage away from the ramp.

Secondly the table drains should be lined with a suitable non-erosive material and be constructed with energy dissipaters at suitable intervals to ensure that velocities are controlled. The water that does find its way into the excavation must be directed to the lowest point (this point will provide a lateral drainage sump) where a pit dewatering can be located.

Table 11 depicts the various treatments that may be anticipated for erosion control dependent on discharge velocity. Details are presented in Figure 29 for the riprap and energy dissipater treatment techniques as a guide for proper construction. The lengths of these devices will be entirely dependent on slope lengths and must be determined for each individual situation.


Figure 29


6 ADVISORY SIGNS

6.1 Introduction

Each haul road exhibits its own peculiarities and may require more or less signage. In any case, proper care must be taken to ensure that all signs installed are at a height and location that is within the eyesight of all drivers operating all vehicles likely to be traveling on a given road. Even vehicles with the most restricted visibility.

6.2 Speed Limit Signs

Speed limit signs should be posted on segments of the haul road alignment that require slower than normal rates of travel to safely negotiate a hazardous condition. Some of the more advantageous locations for posting speed limit reductions include road segments that precede: The commencement of a long descending haul road or pit ramp, Changes in descending haul road grades. Entrances to congested areas, such as pit, the ROM, maintenance areas,

overburden dumping points, vehicle crossings, fuel station, etc.; Unusual road alignments, such as severe vertical and horizontal curves,

narrow lanes, and areas of restricted sight distance; and Areas subject to material spills or other frequent obstructions.

6.3 Stop Signs

From a production viewpoint, it is best to avoid interruptions in the haulage cycle; however, this may not be compatible with road safety. Although vehicle stopping points along the haul road should be kept to a minimum, they must be considered necessary for safety in some cases. Areas where the placement of stop signs should definitely be considered are as follows: Any secondary access road at the point it intersects with the main haul road; Intersections where sight distance does not exceed vehicle stopping

distance for the recommended speed of travel; and Haul road intersections with public roads.

6.4 Curve and Interse

Documents

Kpc Roads Manual_full Version