ADVERTISEMENTS:
The following article will guide you about how to design and construct landscape.
Landscape Design:
ADVERTISEMENTS:
The most efficient, functional and aesthetically pleasing landscape should be developed to satisfy the needs of the people who will use and maintain it. The planting design should be compatible with the existing environmental conditions. The design should enhance the quality of life for the users.
Good landscape design and the arrangement and placement of plants are all based on certain plant characteristics and time-tested design principles. The visual characteristics of plant size, form, texture, and colour contribute to the functional and aesthetic qualities of a planting design.
Plant size should be the primary consideration. Large plants, such as shade trees, should be located first; the smaller trees, shrubs, and finally the ground covers should be arranged to provide a sense of support or framework to the overall design. Shade and evergreen trees, such as maples or spruce, are the most dominant plants in the landscape design.
They provide background, visual weight and structural framework. Ornamental trees, such as flowering crabapples and birches, are used as focal points or dominant elements because of their seasonal and picturesque branching characteristics.
ADVERTISEMENTS:
Tall shrubs help establish vertical edges to an outdoor space, create screens, enhance privacy, or provide a neutral background. Small shrubs are also used to define edges and spaces without blocking views; they can connect and link unrelated or separate plants, and define areas and space on the ground.
The features of a landscape can be physically described by the visual qualities or the elements of design. The principles are the fundamental concepts of composition to organize the features to create a beautiful landscape.
Elements of Design:
a. Form:
It is an important consideration in a planting composition. The most common plant shapes are the spreading and rounded forms. These two basic plant forms have the most application in planting design; they create neutral patterns in contrast with more unusual forms of plants.
ADVERTISEMENTS:
Columnar and pyramidal-shaped plants have visual characteristics that suggest vertical edges in an outdoor space. They create a major contrast with the more common rounded or spreading plants. The picturesque and drooping forms of plants are useful as accents or focal points in the planting design when used sparingly. Common plant forms are well established.
Form is the steady characteristic of plants. Form can also be created through the massing of plants. The overall mass creates a different form than an individual plant. A contrast form within the composition will have greater emphasis. Natural plant forms should create the size of the composition. The significance of overall form depends on the viewing place. Vertical forms add height, horizontal forms add width.
Form is also the main determining factor of a formal or informal garden. Geometric forms with straight edges are typical of formal gardens. They are based on an established style. An informal garden has more naturalistic, organic forms. They are normally found in gardens imitating nature. Form compatibility is also a major component of unity in design. One or two striking forms are good for contrast and emphasis, but generally all other forms should have some similarities for a unified look.
b. Texture:
ADVERTISEMENTS:
It refers to the visual roughness or smoothness of a plant. The texture of the foliage, twigs and branches is coarse, medium or fine. Texture effects are most visible at close range and in smaller landscape plantings. Coarse-textured plants tend to be dominant and attract attention.
They usually have dense foliage or broad leaves. Fine-textured plants appear delicate and tend to recede from view. They usually have fine foliage or needle leaves. In planting composition, medium-textured plants should dominate and contrast with either the coarse or fine textures.
A plant can generally have a coarse, medium or fine texture. Plant characteristics that create coarse texture are leaves with very irregular edges, varied colors and thick branches. Most plants are medium texture because they cannot be described as having either coarse or fine texture.
They are characterized by medium-sized leaves with simple shapes and smooth edges. The average- sized branches are not densely spaced nor widely spaced. Characteristics that create fine texture are small foliage, thin leaves, thin stems, tiny twigs, long stems and delicate flowers.
Texture affects the view of distance and scale. To make a space appear larger, locate plants of fine textures along the outer perimeter, the medium textures in the middle and the coarse textures near the viewer. To make a space appear smaller, place the coarse textures along the outer perimeter and the fine textures near the viewer. Bold colors increase the contrast and the texture appears coarser, while soft colors flatten texture.
c. Color:
It is one of the most visual plant characteristics. It includes the Color of leaves, flowers, fruit, branches, and bark. Green is the predominant plant color, but has seasonal variations. With evergreens, the same color is present year round. The color of the summer foliage has the longest seasonal effect and the most importance in design composition.
A variety of greens have more visual appeal when displayed against a uniform neutral green background. A common mistake is to use too many different colors. Plant color can be used as an attractor, to call attention to some area in the landscape. Dark-coloured plants contrasted with light- coloured plants create focal points in a planting composition.
Nature is in colour. Light is source of all colors. We react emotionally to different colors in different ways. Color has the power to influence and brings out the feelings. For example, bright colors create a sense of joy and happiness. Dark and gloomy colors create a sense of sadness and fear.
Plants should be arranged for summer foliage effects first, and then color characteristics of flowers, fall foliage, fruit, or branching. Foliage color varies with texture. Fine-textured leaves are more reflective and tend to be weaker in overall visual effect. Plant colors can also be used to suggest certain emotional or psychological feelings. Dark greens give a somber, gloomy feeling. Lighter greens suggest gaiety and cheerfulness.
There are 3 dominant groups of colours in the colour wheel:
The Primary Colors are the main colors. They are always seen as the strongest and powerful colors and these are used in logos and posters to make energy and strong statements. The primary colors are Red, Blue and Yellow. These three are the core colors which cannot be generated by mixing other colors together to produce it. No combination of colors can create any of the core colors and thus they are known as the primary colors simply because they are the original colors.
2. Secondary Colors:
Secondary Colors are the combination of the primary colors to produce another color. There are 3 secondary colors: orange, purple and green. Orange is the product of mixing yellow + red, Purple/ indigo is the mix of blue + red, and green is the product of blue + yellow. The mixture ratios for the colors are equal.
3. Intermediate or Tertiary Colours:
Intermediate Colours are made from combining the secondary and the primer colors together and usually with the color next to one another. There are 6 Intermediate colours, light green: green + yellow, Light orange: Orange + Yellow, orange red: red + orange, violet- purple + Red, indigo: blue + purple, dark Green: blue + green. The Intermediate colors create a sense of softness and have the ability to lower the intensity of the primer and secondary colors if they are used together in a good composition.
Contrast Color Schemes:
There are 6 groups of contrast color schemes:
1. Monochromatic:
Monochromatic colors are made out of one color but in different tones ranging from the softest to the darkest tone. The more white is used to lower the tone value, and to increase the value black is used. This color composition creates a harmonious and comfortable feeling.
2. Complementary:
Complementary colors are directly opposite to each other on the color wheel.
3. Double Complementary:
Double complementary color consists of a pair of complementary colors on the color wheel.
4. Split Complementary:
Split complementary colors consist of two colors that join its complements on the color wheel.
5. Triad:
Triad color scheme combines three colors obtained by placing an equilateral triangle on the color wheel. By rotating the triangle on the color wheel different combinations can be obtained.
6. Tetrad:
Tetrad colour scheme is obtained by any four colours on the colour wheel, which are adjacent to one another.
Color has three dimensions:
1. The hue, means color such as red, green, blue
2. The tone or intensity, means the brightness or dullness
3. The value, means lightness or darkness
Color Value:
The values associated with color are independent of materials and forms. A different meaningful device is provided by the great range of light reflection in the color scale. Colors, which reflect light brilliantly, appear to advance toward the viewer, and those that absorb light appear to recede.
For example yellow and red are called bright and pleasant, black and deep blue colors are called dark and gloomy. The degree of projection and depression of architectural forms can be altered, highlighted or subdued by the colors of their surfaces.
The value of colors is divided into 3 groups:
i. Color tones,
ii. Chromo colors, and
iii. Neutral colors
i. Color Tones:
Color tones are the effects of the light beams from the brightest to the darkest. It’s the same with tonal colors, where white and black are used to create different color values. The lightest value contains more white and the darkest contains the most black. Color tones are very important and useful in producing three- dimensional spaces.
ii. Chromo Colors:
Chromo colors are the creation from mixing two contrast colors in certain ratios, which creates a tonal value flowing from the two colors. Chromo colors create a dull color from the original colors, which are used to show dark and gloomy side of life.
iii. Neutral Colors:
Neutral colors are black and white. They are neutral because they have no strength and power, but yet they can increase or decrease the value of colors. These two colors have value when mixed together and the tone value change from white to black.
White turns into grey and finally into black. Neutral colors also mean chromo colors because the creation from both mixtures produces colors which have lost the originality of its core colors. Neutral colors can create a comfortable and less stressing environment.
4. Line:
Line in the landscape is created by the edge between two materials of a long linear feature. Lines can be used to create many varieties of shapes and forms. They control movement of the eye and the body. Landscape designers use lines to create patterns, spaces, forms and an organized theme in a landscape.
Three primary line types create form in the landscape: bed lines, hardscape and plants. Bed lines are created where the edge of the plant bed meets another surface material, such as turf, groundcover, gravel, or patio pavers. Hardscape lines are created by the edge of the hardscape. Plants are used to create different shapes of lines. Line can also be created by long and narrow materials like a fence or wall.
Lines should be dramatic, done with a sense of flamboyancy and be very expressive in their shape in curvilinear design. Curvilinear lines that have weak edges will not be visually interesting or pleasing to the eye. Curvilinear, meandering lines suggest a naturalistic look that invites the user to casually stroll through and experience the landscape.
On the other hand, linear lines such as those found in a straight hedge or the edges of paving materials suggest quick, direct movement. Angled lines can create opportunities for creating the “bones or the framework of the landscape”. Lines that interconnect at right angles create an opportunity for reflection, stopping or sitting. Through skillful use of lines in the landscape, the designer is able to direct the attention of the viewer to a focal point.
5. Scale & Proportion:
Good proportion and scale have no hard and fast rules. Scale can be understood most simply as relative size. Scale usually bears reference to the size of a thing or object that appears to have a pleasing relationship to other things or to the design as a whole. It essentially relates to some finite measure of universal application or a standard of known dimension.
Proportion is the relationship of the width to the length of an area or the relationship to parts of an organization. Relative proportion is the size of an object in relation to other objects. Absolute proportion is the scale or size of an object. An important absolute scale in design is the human scale (size of the human body) because the size of other objects is considered relative to humans.
Plant material, garden structures and ornaments should be considered relative to human scale. Human scale, on the other hand, refers to the relationship between the size of composition and the observer. Other important relative proportion is the area to be planted. The fixed parameters of the garden decide to some extent how spaces and patterns can be used.
A long, thin garden needs to be handled in a different way than a rectangular, square or triangular garden. A long and narrow garden can improve by breaking its length into separate spaces. A garden may appear longer by establishing a long axis.
Principles of Design:
1. Unity:
Unity is achieved by linking elements and features to create a consistent character in the composition. Scattered groupings of plants and unrelated garden ornaments are the opposite of unity. Hardscapes and plants can be unified by blending similar characteristics, but some variety is also important to create interest. The simplest way to create unity is through the use of a design theme or a design style. Unity may also be obtained by restricting a garden to a certain class of plants—perennials, roses, or annuals.
Unity in design can be achieved by reducing the number of different elements such as plant species, sizes, forms, colors or textures. A basic principle in planting design is to group plants together in groups of three, five or seven rather than scattering them. Young plants may first appear as small individuals, but as they grow and mature they should be viewed as a group unless they are designed as individual specimens.
Scattered plants or groups of plants can be connected with beds of ground covers or low shrubs. A simple experiment will indicate whether the design has unity. Cover up certain elements in the design; a bed or border or a group of plants. See whether the design suffers because of the exclusion. If not, the part covered is unnecessary.
2. Balance:
Balance is the concept of equal visual attraction and weight on central axis. Balance is either formal (symmetrical) or informal (asymmetrical) in nature. Formal balance is achieved when the same objects are placed on either side of an imaginary axis. Many historic gardens are organized using this concept. In formal balance, the mass or weight or numbers of objects on either side of a central axis should be exactly the same.
Plants are frequently clipped, lines tend to be straight and edges are clearly defined. Informal balance is achieved by equal visual weight of different forms, color or texture on either side of an axis. The mass can be achieved by combinations of plants, structures and garden ornaments.
Plants should be irregularly placed on either side of an imaginary axis so that the mass or weight on either side of the axis appears to be balanced. Curved lines, obscure and merging edges and natural contours identify asymmetry in the garden.
3. Focal Point:
Dominant features that capture attention are called focal points. Focal points are used to draw attention to a particular location. They are the features or objects in a garden that draw the eye and lead the visitor towards them. They play a pivotal role both in movement round the garden and in the composition as a whole.
It suggests that one element in the composition has authority over other subordinate parts. Dominance may be created by size like a shade tree or by form, texture, color or location of the elements within a design. The dominant element becomes the focal point.
Major contrast is a similar design principle where one element is so different that other parts of the composition are subordinated to that element, such as a bed of red salvia flowers against a background of green yews. Garden ornaments also attract attention because they are often different from plant material.
Form and color are usually contrasting the most with plants. Sculptures, planters and furniture have forms which are easily different from plants.
A focal point can be carried out in a number of ways, such as:
A dramatic fountain at the end of an avenue.
The perfect positioning of a simple garden pot at the end of a wall.
i. A pot or obelisk in a formal setting.
ii. A bench under a rose-covered trellis.
iii. A mound swinging under an apple tree.
iv. A piece of sculpture half hidden in a border.
v. A gate leading out of the garden to the landscape beyond.
vi. A pool set to catch a reflection.
A garden can only support a certain number of focal points. A small garden should have only one. A large garden can have a few more, if they are sited in different areas. A single object in well positioned place is always more effective. The important factor is that the focal point should attract for some purpose. It can be to divert from the area passing through, to lead on to some other view or some other part of the garden.
1. Repetition and Rhythm:
Repetition is created by the repeated use of elements or features to create patterns or a sequence in the landscape. Repeating line, form, color and texture creates rhythm in the landscape. Simple repetition is the use of the same object in a line or geometric form like a square in an organized pattern.
They are planting design principles achieved when similar plant characteristics are introduced and repeated to help create the feeling of recall or unity in the composition. Interconnection is a principle similar to repetition whereby different plants are linked together by overlapping or touching similar plants. Fences, walls or beds of ground cover are frequently used to link elements together in the landscape.
2. Transition:
The effective use of sequence is often employed to create visual movement in the landscape. It is an important consideration to take into account in the development of the overall planting pattern. For example, sequence could be an orderly natural combination of plant material. In this case, low objects would appear in the foreground, intermediate objects in the middle ground and tall objects in the background.
The theme of a planting composition may be informal, curved or natural. The style may give a formal, linear or symmetrical theme. By following a definite order or style, the design does not have a fragmented or uncoordinated appearance. The most visually pleasing designs are not created by chance, but follow a specific order, theme or style which carries throughout the landscape.
Plant Selection:
1. Mature Size and Proper Spacing:
Many plants are available in different varieties. These varieties often vary in mature size, flower color and leaf appearance.
2. Long or Short Life:
Plants vary in their life span. People who love to work in the garden and enjoy change will prefer short-lived plants like perennials. Those who want a landscape that gets installed and then needs minimal care need to consider this when choosing their plants.
3. Evergreen and Deciduous:
Most people want plants that don’t lose their leaves (evergreens). However, there are certain advantages to deciduous trees. For example, maybe it’s best that patio trees provide shade in the summer and allow the sun to heat things up in the winter. However care should be taken because some trees lose their leaves in the spring, not the winter (jacaranda and tipu tree for example).
4. Potential Root Damage:
Do not plant large trees too close to a sidewalk, driveway or the house. Plants vary in their potential to cause root damage.
5. Pests and Diseases:
It’s not a good idea to plant something that has constant pest problems. This is something that changes frequently as foreign insect and disease invasions occur.
6. Weather Conditions:
Climate zones can be restrictive and they change noticeably from one place to the next. It is necessary to consider prevailing weather conditions of the site before selecting plants for planting.
7. Soil Conditions:
Some places have poor soil. Some plants don’t care and others do. The one common soil deficiency that can be detrimental to plants is deep drainage. In order to check soil’s drainage, dig a hole 18 inches deep and fill it with water. If water is still there 4 hours later there’s a problem. In this case it’s best to not choose plants that require good drainage because many plants need it. Another option is to build raised planter beds. This will accommodate smaller plants only.
Design Guidelines:
The basics of quality landscape design apply to all projects.
The following are a few of the guidelines to be employed:
1. Preserve and enhance existing natural landforms and vegetation and use regionally native plant materials as far as possible.
2. Adopt design solutions that minimize adverse impacts on the natural habitat.
3. Prevent pollution by reducing fertilizer and pesticide requirements: use integrated pest management techniques, recycle green waste and minimize runoff throughout the design process.
4. Plan low maintenance landscapes responding to energy conservation and prefer the use of water-efficient plant material.
5. Install standardized, water-efficient irrigation systems to minimize opportunities for vandalism to key components such as controllers and backflow preventers.
6. Screen incompatible elements such as chain-link fenced service, storage, utility, loading, delivery, mechanical areas and heavy traffic from view with architectural walls or dense evergreens. Use mass plantings, berms and architecturally compatible fencing as screens and buffers.
7. Combine massing of trees and shrubs with fencing and signage to create attractive and interesting entries.
8. Use thornless and non-toxic plant material near children play areas.
9. Use site amenities which are durable, well-constructed and vandal-resistant.
Design Process:
A landscape design process includes scrupulous analysis and design of the site, plant selection and development of design details.
1. Site Analysis:
A complete site survey and analysis of existing conditions should be undertaken including an inventory of both natural and built features.
Site factors of fundamental concern relative to both the retention of existing, as well as the installation of new, plant materials include:
1. Visual factors.
2. Climatic data.
3. Existing vegetation.
4. Soil.
5. Hydrology.
6. Topography/slope analysis.
7. Spatial analysis.
8. Program analysis.
9. Circulation patterns.
10. Noise factors.
11. Security requirements.
12. Maintenance requirements.
2. Programming:
Before a landscape design is begun, development of a program is necessary. The program consists of a description of user requirements and environmental design objectives. User needs, environmental problems and maintenance capabilities should be carefully and thoroughly studied. The extent of the planting will vary with each class and category of facility. The function and prominence of the facility should be the guiding factor in determining the scope of design.
3. Conceptual Design:
After site analysis and program data, work on a conceptual design should begin. This involves arranging of plant material masses to satisfy the needs and requirements established by the site analysis and program. Plant masses should be arranged in terms of intended use and size rather than according to species or variety.
The primary concern of the conceptual design phase is to provide solutions to the functional requirements of the site so that preliminary cost and phasing plans can be developed. The hardscape items like pavement, seating, steps and walls should be included.
4. Specification of Plant Materials:
After a satisfactory conceptual design is developed and adequate funding is assured, a final plan should be prepared. This involves interpreting the desired forms and sizes of plant masses into specific plant selections. A thorough knowledge of available plant materials and their characteristics is required.
5. Final Landscape Plan:
The final landscape plan consists of a series of working drawings and a set of specifications. These documents are used by the landscape contractor for bidding and constructing the project. Working drawings, with the exception of construction details, are based on a scale drawing of the site.
The type and number of drawings required for a particular project may vary, but usually include the plans described below:
i. Planting Plan:
The planting plan shows the location and names of all plant materials.
The following information about each plant species should be included on or with the plan:
a. Common and botanical names.
b. Size.
c. Type of root preparation (i.e., container-grown, balled and bare-rooted).
The required quantity of each plant should be indicated in the plant list.
ii. Staking and Layout Plan:
The locations of trees, shrubs, plant beds, hedges and other elements which pertain to planting are illustrated on the staking and layout plan. The exact location of each element is determined by measuring distances from established baselines. In the case of very large sites, from coordinates of a grid system developed for the site.
iii. Landscape Grading Plan:
The landscape-grading plan includes information for finish grading of lawns, henna and shrub beds. This plan should be coordinated with other grading and drainage plans for the project.
iv. Irrigation Plan:
An irrigation plan should include the location, size and type of sprinkler heads, drip emitters, pipelines, manual or automatic valves and the water source and meter. Symbols for the various components of the system should be included. Detail drawings which illustrate back-flow prevention devices, system construction and assembly requirements or installation of various components of the system may be added to the plan.
v. Construction Details:
Detail drawings are used to clarify the construction requirements of various components of a landscape project such as paved landscape areas, retaining walls, footbridges, benches and fences. Detail drawings should include sizes and dimensions of materials to be used and construction techniques. Cross sections and elevations may be used to convey this information.
vi. Specifications and Cost Estimation:
Specifications for the project include technical data to support information contained in the working drawings. Cost estimates may be used for establishing a budget and a phasing schedule for construction of the project.
Landscape Construction:
Planting a lawn, filling flower beds and designing walkways comprise only half the landscape design work. Today’s landscape designer should also take into consideration issues like sustainability, drainage, shape, pests and diseases harmful to trees, shrubs and flowers.
Landscape construction roots can be traced to the early public parks in Europe and Great Britain. Parks were popular places for carriage rides, leisurely strolls and courtship rituals. They need to be induced with a sense of culture and civilization maintaining the unspoiled beauty of nature.
It involved defining broad paths for horses and pedestrians, constructing bridges over streams, clearing unsightly rocks and dead trees and providing benches and shelters for people. Wealthy people had servants to tend to their private gardens. In rural areas people planted only vegetation which could be harvested and sold. The advent of residential suburbs made homeowners have front and backyards for landscaping.
There are broadly three types of landscape construction:
1. Residential properties meant to be lived in by individuals and families. They may be bungalows, huge mansions or housing complexes.
2. Commercial facilities such as office buildings, restaurants, shopping malls, amusement parks, golf courses and stores.
3. Environmental design projects like a botanical garden.
Landscape designers need to be sensitive regarding the use of plants for low maintenance and low water, irrigation designed for maximum efficiency and minimal waste, materials from recycled, renewable or sustainable resources, and projects approached in an environmentally conscientious manner to create beautiful landscape.
Site clearing is the first step in preparing the site for new construction. It covers vegetation removal and structural demolition. All organic matter must be cleared from the construction so that sub-grades may be properly prepared. Topsoil is typically stripped to a depth of 10-15 cm (4″-6″) and stocked for later use for plants and embankment stabilizing grasses.
A. Earthwork:
After a site has been cleared and stripped of its organic soil, it is prepared for general excavation. Typically, top and bottom of slope grade stakes are set to indicate to operators where embankment cuts and fills begin and end. Remove intended trees and other types of vegetation from an area to be graded.
In some cases, all existing plant material should be chopped and mixed with topsoil. This technique often proves to be an excellent way to restore a similar type of vegetative cover. Sod should be removed or broken up to prevent lumping during reuse. Earthwork operations are divided into cut, fill, trenching and bulk excavation.
Earth is moved to create platforms for new construction of all roads, buildings, parking and lawns. Sub-grades are generally set before trench or bulk basement excavation. Work is scheduled to avoid long delays or multiple handling.
Cut operations lower the sub-grade. It may be prepared to receive topsoil for planted areas. Scrapers may be used to shape embankments for large areas and bulldozers for deep cuts. Cut slopes may rest at 1:2 in most soils, but a 1:3 or 1:4 slopes is more stable and needs less maintenance cost.
Long slopes may need bench terracing for stability. The area surrounding the proposed building site is graded to rough sub-grade before footing excavation to minimise the cost of excessive trenching or bulk excavation. Well points or curtain drains may be needed to lower the water table during construction. Test pits and borings during early exploration indicate the presence of ground water.
A backhoe is normally used for trenching of utilities. It has a normal reach of 180 cm (6 ft). Extensive or heavy duty trenching may employ a larger power hoe of 240-300 cm (8-10 ft) reach, or a wheel or chain trencher. Chain trenchers have an excavation capacity of 38- 380 ml (50-500 cubic yards) per hour; depending on model type. Large trenches require slip-form bracing to prevent trench wall collapse. They are backfilled immediately after each pipe segment is laid. Basin structure pits are usually dug during this operation.
B. Fill Operations:
Cutting and filling can be conducted simultaneously. The fill portion must be compacted to predetermined construction standards. Fill for planted areas should be compacted to retain 30 percent minimum porosity. Fill material must be put down in 150-200 mm (6-8 in) layers. Compact and test each layer to conform to specified densities.
Topsoil is added at the end to bring the grades to the levels and slopes shown on the grading plans. All surface areas intended to fill are normally roughened to create a mechanical bond between the sub- grade and the new fill. Fill is systematically placed in specified layers or lifts (15-30 cm or 6-12 in.) and compacted by proper machinery.
Scrapers may place the soil in accurate lifts by setting discharge rate and bin blade height. They are the most economical method for executing large area fills. Trucks deposit piles which need spreading by bulldozer to the specified lift depth. This method is typical for light to medium construction.
Each lift must be compacted to achieve the specified density of 95%. This will match rate of infiltration and bearing capacity of undisturbed earth. This operation is also called “controlled fill placement” and is repeated until the new sub-grade elevation is achieved. Soil types determine the method used for compaction.
General fill is usually subsoil taken from on-site cut and should be structurally suited to avoid differential settlement or excessive swelling. Good site design balances cut and fill and avoids sites with unsuitable construction soils.
2. Trench and Foundation Backfill:
Backfilling of pipe and foundation trenches requires controlled lifts and careful compaction to avoid differential settlement and trench wall slump. Sands for pipe and aggregates for perforated drain are used as bedding. Backfill material should contain graduated particle sizes, but should not contain large stones, which may create air pockets.
Structural fill is placed under building floor slabs. It needs very strict placement and compaction. It consists of graded aggregate base material placed In 15 cm (6 in) lifts, and vibrated and rolled to achieve 95% density. Such structural fills should not exceed 90 cm (3 ft) in normal circumstances for cost and stability.
C. Drainage and Utilities:
Placement of sanitary and storm sewer basins and pipes begin after cut and fill operations are completed. Thus it helps to connect outfalls to subsequent building drains, site curtain drains, and other temporary dewatering and construction runoff filtering systems. Newly buried pipes should have sufficient soil cover in areas subject to heavy vehicular traffic.
Most thin wall (steel and polymer) pipes require 75 cm (30 in) of soil cover to prevent crushing. At this stage of construction, sub-grades may be 30-45 cm (12-18 in) below finish grades. All drain basins require controlled backfills to prevent lateral shifting in vehicular pavements. Most basin pits are dug with a power hoe.
D. Grading:
Grading operations prepare the site to receive pavements, plantings and all other, site improvements. The site is surveyed to set finish layout and grading stakes. Stakes are offset from road centerlines and pavement edges to avoid interference with subsequent construction operations. Grade stakes are normally offset 30-60 cm (2-3 ft) from proposed pavement edges. There are many types of equipment that can be used to do grading.
In case of grading rocks, the initial site design and the ultimate grading plan should be prepared based upon the knowledge of the composition and other characteristics of the soil and rock to be moved. Rock is generally considered to be any material which requires blasting before it can be dug or moved by machines. The cost of blasting and moving rock is 7 to 10 times higher than moving cohesive soil.
The most useful data in preparing a grading plan of rock is:
I. The depth of soil cover to rock,
II. Amount of easily breakable top layer of rock,
III. Amount of rock to be blasted,
IV. Type of rock.
Rock is typically classified into three major groups:
1. Igneous:
Igneous rock is solidified from a molten state, either at or beneath the surface of the earth. It is crystalline. Typically it does not exhibit a grain. It breaks irregularly depending on its composition.
2. Sedimentary:
Sedimentary rock is made from the sedimentation of soil, plant and animal remains. Rock hardened as a result of pressure, time and the deposition of natural cements at ocean depths. It will fracture along the planes of sedimentation
3. Metamorphic:
Metamorphic rock consists of previously igneous or sedimentary rock. Rock was altered by extreme heat and pressure at great depths or along tectonic fault lines. It often exhibits some staining or foliation. Rock may fracture naturally or during blasting and excavation.
When soil or rock is dug or blasted out of its original position, it breaks into particles or chunks. This creates more space and adds to its mass. This increase in volume is called swell. When soil is placed in a new location with nominal compaction, these voids are filled and some shrinkage occurs. Compaction will not compress rock excavation to its original volume because rock swells. Grading involves two phases: rough grading and finish grading.
Rough grading is necessary after all cut and fill operations have established approximate elevations for proposed sub-grades. Bulldozers, road graders and hand labor are needed to precisely set edges and create uniform slopes. Grading under slabs and pavement structures requires precision within 1.5 cm (1/2 in).
Finish grading is the final placement of topsoil between pavements and structure. Soil depths may vary by planting type. This is completed after major planting of trees and all other activities.
E. Grading Criteria:
Grading becomes an integral part of the design process on par with the location of buildings, circulation planning and use of all landscape qualities. In many cases the grading scheme is a primary determinant in the total design. Grading may be done for a number of functional and aesthetic reasons.
F. Methods of Expressing Slope:
Slope is expressed in terms of a percentage, proportion or degree.
1. As Percentage:
Percentage of slope is expressed in the number of meters rise in 100 m. of horizontal distance. It is referred as rise/run. For example, if the slope rises 2 m. in 100 m, it is considered a 2 percent slope. The percentage of slope can be calculated by the following formula-
G = D/L x 100
G = gradient in percentage
D = vertical rise
L = horizontal distance
2. As Proportion:
Slope can also be expressed as a ratio of the horizontal distance to the vertical rise like two to one (2:1). The ratio method is normally used for steeper slopes like 4:1 (25%).
3. As Degree:
Slope is expressed in degrees only on large scale earth moving projects like strip-mining and other extractive operations.
4. Spot Elevations:
Spot elevations are used to establish limits of slope, to locale contour lines and to provide detail for establishing control points, which cannot be obtained by contour lines. The elevation of any point on an accurately drawn contour plan may be determined by interpolation.
G. Making a Contour Map:
Contour lines show the height above sea level (in meters). Most maps have contour lines every 10 m. Contour lines evenly spaced and wide apart indicate a uniform and gentle slope. Contour lines evenly spaced and close together indicate a uniform and steep slope. The closer the contour lines are to each other, the steeper the slope.
Terms normally used in a contour map are given below:
i. Hill Top:
This is a point or small area of high ground. Here the ground slopes down in all directions.
ii. Valley:
Contours indicating a valley are U-shaped and tend to parallel a major stream before crossing it. The more gradual the fall of a stream, the farther each contour parallels it. The curve of the contour crossing always points upstream.
iii. Ridge:
A ridge is a line of high ground with minor variations along its crest. All points of the ridge crest are higher than the ground on both sides of the ridge.
iv. Spur:
A spur is a short, continuously sloping line of higher ground normally jutting out from the side of a ridge.
v. Saddle:
A saddle is a dip or low point along the crest of a ridge.
1. Field Survey:
All intersection points of a grid are marked on the ground with temporary stakes, the elevation of each intersection point are taken with a transit or level and the elevation data is plotted on a gridded plan of the site. Normally, 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 100 cm, 50 cm. or 25 cm (5 ft. 2 ft, or 1 ft) can be located and plotted on a map. Often this can be done by eye, since few contour maps require great precision.
3. Preparing a Site Grading Plan:
Grading of a site should be thought of as a systematic process that begins with the analysis and understanding of the existing site and ends with an overall detailed grading plan.
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 the natural drainage systems and direction of flow, which exists on the site.
Determine how existing landform would affect proposed use areas, such building locations, roads, parking areas, walkways, plazas and lawn areas.
Define general use areas, set building floor areas by spot elevations, and draw 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 containers.
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.
7. 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, walkways and swales. Establish critical spot elevations.
2. Set the building grade circuit i.e., floor elevation, stops, walls, terraces etc.
3. Draw in preliminary contours at 1.5 m or 3 m (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.
4. Complete all contour alterations within the property line or project limits.
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 on the proposed grading plan, and, adjust the amount of one or both to make them balance.
Grading of outdoor areas is aimed at controlling surface storm water runoff while providing safe and efficient pedestrian and vehicular movement. Essentially all surfaces should have some slope or pitch for proper drainage.
10. Earth Fill against Buildings:
Earth fill against buildings may be desirable for insulation or aesthetic reasons. It is important to note that soil and related moisture may cause decay and promote the growth of insects damaging or destroying some of the materials used in the construction of the building. The exterior surfacing and structural system of a building determine the height to which fill may be brought up against a structure.
H. Roadways
The principles and criteria for the design of major urban and rural highways are determined by the concerned authorities. The standards for streets and local access roads in residential, institutional, commercial and industrial areas are determined by local standards. Roadway design consists of two major phases.
1. Alignment of the road-giving it horizontal and vertical direction.
2. Grading the adjacent landscape to the road edge.
The designer of a roadway should go beyond merely satisfying the engineering requirements and see the user as an active player in the landscape.
The following criteria should be considered during the grading phase of the roadway:
1. Remove extra soil to expose potential vistas.
2. Use roadside mounds to screen undesirable views.
3. Improve the soil adjacent to a road to enhance the growth of plants.
4. Blend the new slopes with the existing terrain.
Typically, swales are shallow, have a parabolic cross section, and are very wide, while ditches are deeper and have a narrower geometric configuration.
Storm water management swales are commonly used in grading to move water gently from one part of the site to another. Their function is to collect and divert the flow of surface runoff away from critical parts of a site. At their terminus, swales must either spread the channelized water into sheet drainage or empty the water into a ditch, stream or underground drainage system.
The slope of the channel determines the velocity of flow and consequently the erosive potential. Since the side slopes of the swale do not affect this rate of flow, they may be much steeper and respond to other design criteria.
Grading around existing trees should be managed with great care, using one or more of the following techniques:
1. Avoid grading, cutting or filling above the root zone of a tree. For most species it means staying outside the drip line of the tree. The weight of the grading equipment driven over the root zone will tear foot hairs and compact the soil, thereby restricting vital water and air from flowing to and being assimilated by the roots.
2. If filling around an existing tree cannot be avoided, then the tree must be protected. This technique permits adequate flow of air and water to the roots of the tree.
3. In another way a deck is constructed, with footings which do not disturb the root system around tree. The deck’s layout can be adjusted to the specific site conditions. When buildings or other such structures are involved, it is better to use lightweight footings with crawl spaces rather than on-grade slabs with compacted sub-grades.
I. Erosion Control by Grading:
Most erosion is caused by flowing water. The size and shape of a watershed, the porosity of its soils, and the length and gradient of its slopes and channels are key determinants. They control the volume and velocity of runoff and the risk of erosion. Several site grading techniques can be employed to limit the size, shape, length and gradient of these slopes.
Gradients can be reduced by extending the length of a slope. This uses more land but reduces the amount of erosion and slumping of hillsides. Diversion swales, ditches and dikes can intercept and divert runoff from the face of a slope.
J. Parking Areas:
In grading of parking areas, the minimum and maximum gradients required for vehicular access and parking areas are often the major determinants for the grading plan of a site. The recommended maximum cross slope for a parking area is 10 percent.
The steeper transitional area between bays can be taken up by a planting bay and a ramp. In extreme circumstances single-loaded parking bays may be used to fit steep slopes. Similarly, a combination of ramps and segmented parking bays may be used to achieve a grading solution on a slope with existing vegetation.
K. Estimating Earthwork:
Techniques for estimating earthwork quantities are only approximate. Three methods are normally used to prepare estimates of the quantities of grading needed. They are Grid or Borrow Pit Method, Average End-Area Method and Contour Method. Contour Method is commonly used by landscape architects because it is very accurate for making final grading adjustments and for preparing cost estimates.