Landscape : Grading

Grading

C O N TE N TS

1. GRADING BASICS 2. IMPORTANCE OF GRADING 3. PRINCIPLES OF GRADING TECHNIQUE 4. GRADING PLANS 5. GRADIENT 6. SPOT ELEVATION 7. INTERPOLATION 8. FIELD SURVEY AND PLOTTING CONTOURS 9. GRADING OF DEFINED AREA 10. GRADING OF OPEN AREAS 11. IMPLEMENTATION AND CONSTRUCTION 12. FINAL GRADING PLAN 13. CUT ANF FILL 14. RECOMMENDED GRADINGS 

EARTHWORK COMPUTATIONS – Average Depth Method – Average End area Method – The Contour Method 16. REMOVAL OF WATER FROM SITE 17. GRADING AND DRAINAGE 18. SUBSURFACE SYSTEMS AND STRUCTURES 19. SURFACE SYSTEMS AND STRUCTURES 20. GUIDELINES FOR GRADING PLANS 21. GRADING FOR STREETS AND ROADS 22. PAVEMENTS AND PAVINGS 23. FREQUENTLY ASKED QUESTIONS 

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G R A DI N G B A SI C S

 Grading is the process of modification of existing landform to accommodate new structures, parking and circulation and to ensure positive drainage.  Consideration must be given to utilities such as: water, gas, power, communication services, and sewerage for disposal of wastewater, and storm water.  Grading process requires a careful change of contours so that they support the integration of building with the site.

P O R T A N C E O F G R A DI N

 The land nay be graded or adjusted to suit the architectural or engineering requirements, or the architecture may be adopted to meet variations in the ground level so that the original surface is disturbed the least.  Extensive alterations in the landform may lead to unstable conditions resulting in erosion, landslides, floods, and a complete destruction of ecosystem.  Knowledge of grading technology is useful in site planning process. It is needed to make detailed leveling between building and the landscape on any site.  Site planning grading takes care of the adjustment necessary between fixed levels, structures, and use areas within the boundaries of a site.  In many cases the grading scheme is a primary determinant in the total design. • •

E S O F G R A DI N G TE C H N

1. The ground surface must be suitable for the intended purpose or use. 2. The visual result should be pleasing. 3. The result of any grading must have positive drainage. 4. The grading plans should attempt to keep new levels as close as possible to the original state of the land. 5. When ground is reshaped it should be done positively and at the scale of the machinery. 6. Top soil must be conserved wherever possible. 7. The quantity of cut should be approximately equal to the quantity of the fill. •

 Three principal goals in development of a grading plan are : – Keep unwanted water from entering a building. – Keep surface run off from creating damage to property or people during periods of heavy rainfall and subsequent runoff. – To accommodate the structure on site with disturbing the site to minimum.

G R A DI N G PL A N S

 These are the technical documents and instruments by which we show and calculate changes to the 3d surface of the land. These are a result of the grading process.  Contour lines are used to indicate the extent of that change.  Existing contours are shown in dashed line and the new form is shown by solid lines drawn where this varies from the existing form.  The process of developing grading plans involves manipulation of three factors:

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– Gradient. (G) – Horizontal distance. (H) – Difference in elevation between two points. (D) G = D/H

 The quantities of Cut and Fill are calculated from these drawings.  The drawings must be accurate to deliver exact cost estimates.  Landscape architects, engineers, and architects who do grading plans, as well as the contractor who does the actual grading, should understand a common terminology. • • •

G R A DI E N T

 Gradient refers to the changing elevation along the Earth's surface or the rate of the slope.  It is expressed in % or ratio or degrees. – 1% slope = 100:1 – 10% slope = 10:1 = 6o

 Percentage of slope is expressed as the number of meters (feet) rise in 100 m (100 ft) of horizontal distance, typically referred to as rise/run.  If the slope rises2 m (2 ft) in 100 m (100 ft), it is considered a 2 percent slope. The percentage of slope can be calculated by the following formula:  Where  D=vertical rise, mm (ft)  L=horizontal distance, mm (ft)  G = gradient, %

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Elevation of point B=48 347 mm Elevation of point A =47 463 mm Vertical difference D=884 mm Horizontal difference L= 35 357 mm There fore:

 Proportion of Slope can also be expressed as a ratio of the horizontal distance to the vertical rise , such as three to one (3:1). The ratio method is used typically for slopes 4:1 (25%) or steeper.  Degree of Slope is expressed in degrees only on larges scale earth-moving projects such as strip mining and other extractive operations. •

SP O T EL E V A TI O N S

 Spot elevations provide additional information beyond that given by the contour lines. They indicate Micro grading.  Spot elevations are used to establish limits of slope, to locate contour lines, and to provide detail for establishing control points that cannot be obtained via contour lines.  Typical locations for taking spot elevations are:       

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Top and bottom of steps. Tops of retaining wall. Outside entrances to buildings. Inside floor levels of buildings. Corners of all structures. Beak points. Centers of all swales.

IN TE R P O LA TI O N

 The elevation of any point on an accurately drawn contour plan may be determined by interpolation.  In the figure, point A lies about 7/10 the distance from contour 53 to contour 54; thus, A has an approximate elevation of 53.7. • •

U R V EY & PL O TT IN G C O N T

 All intersection points of a grid are marked on the ground with temporary stakes.  The elevations of each intersection point are taken with a transit or level and the elevation data is plotted on a gridded plan of the site.  The elevations of critical high or low points that fall between the intersections are also located on the plan.  Once all spot elevations have been determined, contours at regular intervals [typically 1 000 mm, 500 mm, or 250 mm (5 ft, 2 ft, or 1 ft)] can be located and plotted on a map, as shown in Figure ahead.  Often this can be done by eye, since few contour maps require great precision. • • •

TRANSIT SURVEY GRID

CONTOURS INTERPOLATED FROM GRID

A DI N G F O R D EF IN E D A R

 Slopes of less than about 2 percent in the open landscape appear flat to the human eye. However, in areas adjacent to built structures, even the slightest slope becomes noticeable because of the relationship of the grade to mortar joints, roof lines and other level architectural features.

Perimeter Edge Level: Figures schematically illustrate alternative methods for manipulating a surface for drainage while allowing at least one peripheral edge to remain level.

Two Perimeter Edges Level: Figures schematically illustrate drainage schemes applicable when two perimeter edges need to be level.

 Entire Area Level:  Some circumstances, such as rooftop landscapes or enclosed courtyards, require that the entire surface of the enclosed area be level.  Figure ahead illustrates two ways that an area can remain level and still drain properly by the use of porous surface material, such as sand/gravel the use of individually elevated Each case requires an adequate system beneath the pavers to carry required rainfall effectively.

These alternatives are applicable to relatively flat surfaces as tennis courts and other types of courts.

A TI C G R A DI N G F O R O PE N

 Preparing site grading plan – Grading of a site should be thoughtful systematic process that begins with an analysis and understanding of the site and ends with an overall detailed Grading plan. – Site Analysis:  Study the general lay of the land by using topographic maps and site visits.  1. Determine high points, low points, ridges, and valleys.  2. Note natural drainage systems and directions of flow that exist on the site. – Site use concept:  Determine how existing landforms would affect proposed use areas, such as building locations, roads, parking areas, walkways, plazas, and lawn areas. –

SITE ANALYSIS (EXAMPLE)

SITE USE CONCEPT (EXAMPLE)

 Schematic grading plans:  Define general use areas, set building floor a areas by spot elevations, and diagram drainage flow using slope arrows pointing along the direction of flow. This will help in the following procedures:  1. Developing a general landform concept.  2. Locating swales and surface water flow.  3. Locating drainage receptacles.  4. Calculating water runoff for various areas.  5, Defining an area that could be altered (raised or lowered) with limited impact on drainage or existing trees. This area could be used to help balance any surplus cut or fill. –

BASIC AREA GRADING

 Grading by spot elevations  Grade by spot elevations and form preliminary contouring, using the following steps in the order shown (always strive to keep disturbed areas as small as possible): 1. Set tentative gradients and spot grades on roads, walks, and swales. Establish critical spot elevations. 2. Set the building grade circuit, i.e., floor elevation, steps, walls, terraces, etc. 3.Draw in preliminary contours at 1 500 mm or 30 000 mm (5- or 10-ft) intervals, depending upon the scale of the project and topographic change. Make certain that all gradients and slopes are within the maximum/minimum criteria for a particular use, i.e., lawn, roadway, terrace, and cut slope or embankment. 4. Complete all contour alterations within the property line or project limits. •

GRADE BY SPOT ELEVATIONS (EXAMPLE)

 Preliminary Cut-and-Fill Calculations:  Do preliminary calculations (if needed) to determine whether there is a balance between the amount of earth to be cut out and the amount of earth needed for fill.  Final Grading Plan: 1. Prepare final road profiles. 2. Indicate changes in direction or rate of slopes. 3. Show spot elevations for all critical points, including manholes, inverts, drainage structures, tops and bottoms of all walls, steps, and curbs at intersections and/or other critical points. 4. Draw proposed contours and complete The final grading plan 5. Complete an estimate of the amount of cut and fill based upon the proposed Grading plan, and, if needed, adjust the Amount of one or both to make them Balance.

E N T A TI O N & C O N ST R U

The following steps should be highlighted in the specifications regarding the construction process: 1. Collect and submit soil samples for all areas to be disturbed. 2. Erect tree protection fencing to encompass all feeder roots within the drip zone of existing trees designated to remain. 3. Protect all existing pavements and site structures designated to remain. 4. Strip existing sod to a 2-1/2- to 4-inch depth and either compost or stockpile for future use. 5. Strip and stockpile topsoil separately. 6. Erect temporary erosion control structures to halt the flow of sediments off the property or onto existing paved surfaces and structures. 

7. Install gravel aprons at all egress points off the property to lessen the tracking of soil and debris onto roadways. 8. Remove any unsuitable soils and debris from the site. 9. Prior to filling, scarify subgrade to a depth of 6 inches; and moisture-condition to obtain the desired compaction. 10.When filling, place soil in 8-inch lifts. Moisture-condition each layer of soil, and compact before additional fill is placed. 11.Allow for settlement and shrinkage of soil when determining final grade. 12.After final sub-grade elevations have been established. •

 Following conditions must be avoided or re - evaluated : – Grading that results in radical loss of vegetation and/or topsoil. – Grading that interrupts in natural drainage. – Grading that results in aesthetic degradation. – Grading on difficult slopes(excess of 25%) in floodplains, estuaries, or bogs, or in other environmentally unique conditions. – Grading in areas susceptible to natural disasters, such as mud slides or along earth quake fault lines.

T H E FI N AL G R A DI N G PL A N

 The essential information that a grading plan includes:

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1. Existing and proposed contours. 2. Spot elevations at the corners of all structures such as buildings, walks, walls, parking lots, and streets. the corners are referred as reference points, and the slopes are uniform between unless noted otherwise. 3. Spot elevations at all high points and low points. 4. Contours that cross pavements are uniform mechanical lines while contours on the surface of ground are drawn freehand. 5. Spot elevations at top and bottom of steps and ramps. 6. The elevation of ground before the entrance. 7. Spot elevations at drainage inlets marked as “rim” elevations and the “invert” elevations

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C U T A N D FI LL

 The process of removal of earth from one part of site to achieve required grading and the place and using the dug up earth to achieve required grading by filling it at another place on the same sit.  The amount of material from cuts roughly matches the amount of fill needed to make nearby embankments, so minimizing the amount of construction labor. •

 When soil is dug or blasted it looses the original position and adds to the bulk result in increase of volume, this is termed as a swell.  When the soil placed in new location with nominal compaction, the voids present there are filled and this is called as shrinkage.

Standards for grading around a typical building.

Surface drainage can be achieved by pitching surfaces to natural drainage feature and systems. 

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Grading to create berms. Berms can be created for noise and wind barriers or for additional soil depth above unfavorable sub-grade conditions, such as a high groundwater table. 

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Grading to create level areas . Relatively flat gradients are needed for sports fields, outdoor terraces, and sometimes for areas near buildings. 

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Grading to modify existing landforms . Deep gullies, narrow ridges, or steep slopes can be modified to create more useful and attractive landforms. 

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Grading for increased site interest . Grading can help emphasize a site's topography or add interest to an otherwise flat site. 

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Grading related to good views. 

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Grading to expose vistas 

Grading related to bad views. 

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Grading to fit structures to sites. 

Grading to facilitate better plant growth 

Grading to emphasize or control circulation. 

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RE CO MM EN ED GR AD IE NT S

RE CO MM EN ED GR AD IE NT S

Schematic grading for outdoor basketball court

Schematic grading for outdoor tennis court

Schematic Grading of football/Soccer/hockey field

T H W O R K C O M P U T A TI

 Earth work computations require measuring irregularly shaped areas on plans and sections. The quickest way to do this manually is to use an instrument called compensating polar Planimeter.  There are three methods used to estimate earthwork volumes: 1. The average depth method, 2. Average end area method and, 3. The contour method. 

V E R A G E D EP T H M ET H O

 It is most often employed to estimate excavation quantities. 1. A grid is placed over area that is to have the earth work quantities estimated. 2. The existing elections are estimated from the topographic plan, or the original survey grid may be used if available. 3. The new elevation are recorded for each point. 4. The difference in the elevations are found for each point in the grid. 5. The differences in elevation are then averaged for each corner of the grid square to find n average depth for that grid. 6. This is repeated for each grid.  Very accurate. Suitable for small areas. –

E R A G E E N D A R E A M ET H

 It utilizes sections cut through the site at regular intervals.  The end area of cross section, is averaged with the adjacent section and then multiplied by the distance between the sections to obtain the volume.  Cut and Fill: – The new profiles after the cut or fill are placed over existing ones and the are to be cut and filled in the section are calculated and the multiplied separately with distance between two contours to get the volumes.

T H E C O N T O U R M ET H O D

 It uses existing and proposed contour pairs to estimated volume.  This method is not as accurate as the others.  Does not require use of grid or preparation of section .  The area between existing contour and the proposed contour is calculated.  This area is multiplied by the value of contour interval to obtain volume.

M O V AL O F W A TE R F R O M

One of the principle objective of grading plan is to collect transfer, and dispose of surface water. There are various methods of removal of water from a site . They are as follows: 1 . Surface runoff – It is the first and most visible method of removing water from a site. – The precipitation that is not absorbed into the soil accumulates across the site the site and is collected in swales or into subsurface storm sewer systems. – Ultimately all of the runoff in a watershed is combined into freshwater tributaries which find their way into the sea. 

M O V AL O F W A TE R F R O M

1 . Subsurface runoff – It is the second method of removing water from a site. – In this method the water is allowed to percolate through the soil and become a part of ground water supply or an aquifer. 2 . Evaporation – Includes evaporation of water from water bodies, plants and other sources of surface water. 3 . Transpiration – The fourth method is absorption of water by plants for photosynthesis.

 The drainage process begins with three primary considerations: – Determine where the water is coming from – Where it needs to go – How it traverses the site

 An analysis of the site its context relative to the development of a grading plan should document, as minimum : 1. The topographical characteristics of the site. 2. Any unusual type soil type. 3. Fixed elevations or points. 4. Areas to be kept dry and their corresponding elevations. 5. Location and extent of existing sewer system.

R A DI N G A N D D R AI N A G

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 To avoid problems associated with drainage the designer must not leave anything to chance. Though each site is different, following the criteria mentioned below, some of drainage problems may be solved. – Ensure that the water flows downhill, and perpendicular to the contours. – Combination of natural methods of removal of water from site must be identified and combined with the artificial ones. 

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E ST IM A TI N G R U N O FF

 The most common techniques for estimating runoff are : – Soil conservation method – Runoff curve number method – Rational method – The small storm hydrology WQV method.  The SCS Runoff method is more sophisticated model useful for larger watersheds and larger design storms.  The rational method is more commonly used for small watersheds.  Modified rational method: – This

method for calculating runoff rate assumes1. Rainfall intensity is uniform throughout the duration of the storm. 2. Precipitation falls on the entire drainage area for duration of the storm 3. Peak discharge of the rainfall is equal to at the time of concentration. 4. Time of concentration is atleast six minutes.

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R A TI O N AL M ET H O D

 STEP1: choose an appropriate design storm, delineate the watershed, identify outlet and calculate watershed area (A) in hectares.  STEP 2: determine app. Runoff coefficient (C) based on land cover characteristics and hydrologic soil group. In landscapes with several soil types, composite value of C is used. If the design storm return period is greater tan 10 years, multiply runoff coefficient (cf).  STEP 3: calculate the time of concentration for the watershed (Tc) in minutes, using Kirpich formula.  STEP 4: Calculate rainfall intensity using Steel formula  STEP 5: calculate the peak discharge (Q) using the formula: – Q=KCIA  

F A C E SY ST E M S A N D ST R U

 Subsurface runoff is collected in area drains, catch basins, and trench drains.  The are drain should be located at the lowest point in a drainage area. It is conceptually like a big shower drain through which all of the water falling in a specified area passes. • Trench drain is term that has been given to any linear drain, this structure is often used at bottom of the slope where water needs to be collected to protect an adjacent area.

 The catch basin is also a drain but it is designed to catch debris in its base below the pipe that transfers the water to a point of disposal. When the lid of the catch basin is lifted, the debris and sediment would otherwise have clogged the drainage system can be removed.  Subsurface collection is often accomplished with perforated pipe set in ditches filled with gravel 

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Dry wells provide an underground disposal system for surface runoff: but their effectiveness is in direct proportion to the porosity of surrounding soils, and they are efficient only for draining small areas. High rainfall runoff rates cannot be absorbed at the rather low percolation rates of most soils, so the difference is stored temporarily in a dry well. Efficiency is reduced during extended periods of wet weather when receiving soils are saturated and the well is refilled before it drains completely.

R F A C E D R AI N A G E SY ST E

 Surface drainage systems intercept and collect storm water runoff and convey it away from a building and site with the use of large inlets and storm drains.  Surface and Subsurface systems typically require discharge either through a pumping station or by gravity drainage to an adequate outfall.  Surface drainage systems are designed to collect and dispose of rainfall runoff to prevent the flow of water from damaging building structures (through foundation leakage), site structures, and the surface grade (through erosion). • •

 The two basic types of surface drainage are: – The open system and – The closed system.

 The open system, which utilizes a ditch/swale and culvert, is used in less densely populated, more open areas where the flow of water above grade can be accommodated fairly easily.  The closed system, which utilizes pipes, an inlet/catch basin, and manholes, is used in more urban, populated areas, where land must be used efficiently and water brought below the surface quickly to avoid interference with human activity. The two systems are commonly combined where terrain, human density, and land uses dictate. 

 Swales are shallow channels with parabolic cross section. They may be very wide at times. They are used to divert water around a building. They are not used where wind flow is more than 1.2 m/s.  Ditches are also channels with a deeper section. They are used wind velocities are higher. 

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 A pervious or porous paving system is often used for parking and other hard site surfaces. This drainage system allows water to percolate through the paved surface into the soil, similar to the way the land would naturally absorb water. •

Porous Type Paving

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D EL IN E F O R G R A DI N G PL A

1. New runoff must never be purposefully diverted from its natural course on one property so as to become a nuisance to other property. 2. Always consider some method to retard the velocity of the water so that it might be absorbed into the soil. 3. Design the grading and drainage plan as to respect, reinforce and duplicate the existing natural systems. 4. While on occasions there are few alternative, a drainage plan with more than one outlet course is considered good planning. 5.

5. Avoid draining large paved area across pedestrian paths. Catch basins and trench drains can be used to collect the substantial quantities of runoff created by parking lots. Or pedestrian plazas. 6. Identify any areas that appear to be appropriate for drainage structures. Sinks, depressions, or long channels are always primary candidates for a catch basin or drains. 7. In the design, subsurface systems begin at higher elevation of the site and work their way towards the lower elevations. Surface drainage systems are generally preferred to underground systems for two reasons: – Cost – Ecology

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 Avoid the following while providing drainage to site: – System that necessitates the location of drainage line that ruptures a foundation or passes under a slab. – Avoid cutting a hole in a ground beam for a pipe. 

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N G F O R ST R E ET S A N D R

 The road has a constant slope and thus presents more problem.  The function of the road is to serve as an path for vehicles and as an adjunct to the drainage system.  A road must be designed: – in conformance to strict design standards, maintaining appropriate grades, curvatures and sight distances. – To minimize fluctuations across variable terrain. – To have a constant slope or gradient. – To provide shortest route possible. – To minimize cut and fill. – As far as possible parallel to the contour lines. –

P A V E M E N TS

 Pavement:  Pavements are classified as being either flexible or rigid and as either monolithic or unit. Additionally, they are porous or non-porous.   

 The pavement material receives traffic wear and transfers loads to the base and sub grade.  They may be classified in three ways: – Material  Soft cover  Hard cover – Construction  Flexible pavement  Rigid pavement – Porosity  Porous  Non porous – Structure  Unit  monolithic • 

 Flexible Pavements: – Flexible monolithic pavements consist of aggregates. shredded rubber, or polymers which are mixed with an asphalt or proprietary binder and placed on a prepared base to create a seamless monolithic surface. – These pavements may be porous or non. porous, and firm or resilient, depending on aggregate and binder composition. – Asphalt and resilient athletic surfacing are common examples and are typically 40100 mm (1 1/2- 4 In) thick, – Flexible unit pavements typically consist of dry-laid, sand swept, butt jointed concrete. brick, stone. or synthetic paving units placed on a sand setting bed and d prepared aggregate base. – These pavement by virtue of their butt joint construction are porous to semiporous.

 Rigid Pavements: – Rigid pavements (i.e. reinforced cone are structurally different than flexible pavements, Pavement loads are distributed internally within the Rigid pavement and transferred to the subgrade over a broad area, in a manner similar to that found in a concrete spread footing. – Rigid monolithic pavements are typically constructed as cast-in-place reinforced concrete slabs. Rigid unit pavements require paver to be mortared or glued to a reinforced concrete base.   

TYPES OF PAVINGS

Q U E N TL Y A S K E D Q U E ST

1. 2. 3. 4. 5. 6. 7. 8. 9. 

LAWS OF CONTOUR METHOD OF CALCULATING CUT AND FILL VOLUMES CONSIDERATIONS OF WORKING ON A SLOPING SITE SLOPES FOR OUTDOOR FUNCTIONAL ACTIVITIES IMPORTANCE OF GRADING STEPS OF GRADING KINDS OF PAVINGS CONSTRUCTION DETAILS OF PAVINGS INTERPOLATION

BI BL IO G R A P H Y

1. Time saver standards : landscape architecture 2. Landscape architecture graphic standards 3. Landscape architecture construction :  Harlowe C. Landphair 4. Landscape architecture : Michael Laurie