The Construction Methodology Of Lying A Sewerage Construction Essay

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Pipelines on land the pipes are first laid out, an operation called 'stringing' along the route. The pipes should handled with slings of canvas or other non-abrasive material to prevent damage to the pipes, which should not be dropped, dragged or rolled. Pipes requiring welding or other forms of jointing before being lifted into the trench are placed on timber skids. Long pipes should be cleaned out prior to alignment and jointing.

Trenching is carried out by special trenching machines or hydraulic backacters. Depending on the length and location, the joints in the pipeline may be completed before lifting into the trench, takes place using side-boom tractors or similar plant (Figure 1). Alternatively, the pipe may be lowered into position first and then jointed (Figure 2 ) . All pipelines should be sealed with night caps and the end of a day's work to prevent ingress of small animals and other objects.

The preparation of the trench for pipes will depend on the type of material used for the pipeline and will range from a bed of granular material to carefully shaped sand beds ( Figure 3 ). On no account should hard packing materials used to lift or pack up the pipes be left in position. Heavy pipes may be lifted by pneumatic elevators to remove the initial packing before being dead on sand bags or granular material.

The trench should be 300 mm wider then outside diameter of the pipe, additional room being necessary at each joint to provide sufficient room for joints to be made and inspected. In hard or rocky ground the trench should be taken deeper than the required depth and brought to levels or gradient with granular material. Backfilling should be completed as soon as the section of pipe has been tested, this will prevent the pipes floating in case of a storm. Testing should be preceded by cleaning, this is achieved by means of a 'foam-pig' ( a cylinder of material, such as expanded polystyrene, driven through the pipe). Pipelines crossing roads, railway lines or rivers should be sleeved, the sleeved being placed by the open trench method, power driven auger or thrust-boring. The diameter of the sleeve should be a minimum of 100 mm greater than the outer diameter of the pipeline.

Figure 1

Hoisting and laying 900 mm welded steel gas line

Figure 2- Hoisting and laying a 600 mm Figure 3- Preparing the sand base for a

Ductile iron water pipe 1.83 m dia steel pipeline

The reasons of different bedding type for vitrified clay (rigid) pipes and ABS (flexible) pipes are:

1.Trench width- one of the first things to consider is the trench width.

Vitrified clay pipes- this "rigid" material does not depend on sidefill stiffness, so the trench can be as narrow as the installer needs to make joint connections.

ABS pipes- as a "flexible" material it is dependent on side fill stiffness to limit deflections. Width of the trench should be increased because to allow compaction equipment to operate in the spaces between the trench walls and the pipe. The additional compaction is required to enhance the flexible materials sidewall stiffness.

2.Trench bottom- the bottom of excavated trench must be firm, even, and stable

Vitrified clay pipes- the trench bottom must be flat with hub or coupling holes provided so that the pipe is uniformly supported. No special bedding is necessary, unless the pipe is installed in rock. (In rock excavations, a six inc bed of sand or selected backfill is suggested to protect the pipe from sharp projections).

ABS pipes- the trench bottom must be provided with a minimum of 4 inches of bedding unless otherwise specified. The bedding materials varies by soil type. In rock excavations, a minimum cushion of six inches is required below the bottom of the pipe.

3.Compaction of backfill- the pipe once installed and inspected must be backfilled.

Vitrified clay pipes- special compaction of the backfill is not necessary except for meeting the requirements of normal compaction of the excavated area. Since cast iron is "rigid" , it does not depend on sidefill support.

ABS pipes- the "flexible" pipe design is dependent on sidefill support to gain "stiffness" to control deflections within acceptable limits. Compaction in six inch maximum layers is required to the springline of the pipe. Compaction around the pipe must be by hand.

4.Deflection- deflection in all piping materials must be controlled in order to prevent obstruction to flow and assure that the joints remain secure.

Vitrified clay pipes- because it is rigid, deflection of the pipe wall is almost non-existent.

ABS pipes- a flexible pipe is dependent on sidefill support to gain "stiffness" and some deflection of the pipe wall is both normal and expected. This deflection must be controlled within pre-determined limit to assure clearance for inspection, cleaning, meeting flow requirements and integrity of joint seals. The amount of allowed deflection must be determined before installation with a maximum of 5% deflection.

List down with explanation the contractor task in landscaping contract

A good contractor is the best option for maintaining community landscapes, and a services contract ensures that proper and timely care is given to all plants, including turf and woody ornamental such as shrubs, trees and palms. A realistic budget and specially-trained professionals are crucial elements of landscape protection. A contractor maintains landscape for plant health and longevity. Other than that, the contractor have expertise in horticulture, including evaluation and treatment of plant problems ( insect, disease, weeds, nutritionally ), proper chemical usage, mowing, pruning and edging methods, and other detailed requirements. A contractor with specially-trained staff, such as a certified arborist or pest control operator, is even more effective but may be more expensive at first. However, the additional cost in contracted maintenance fees is small price to pay compared to the cost of replacing turf and landscape plants damaged by disease and insects. Mowers, edging equipment, spreaders, sprayers, and specialized hand tools are needed to properly maintain planted beds and turf areas. A contractor also needs to understand the capabilities of the equipment to ensure optimum performance.

The specification should outline the services the contractor will perform, while the maintenance schedules should include a time frame for the various performance requirements contained in the specification. It should include at least, mowing and edging, pruning shrubs, palms, and trees, fertilization of lawn and landscape beds, insect and disease control, weed control and maintenance of the irrigation system. The maintenance schedule covers the entire contract period, stating in detail when the contractor is expected to perform the various tasks. The schedule can be used as management tool to monitor the contractor's performance. Contractors are usually expected to perform specific tasks, under normal climate conditions within a two to three week period. Therefore, the time frame stated in the maintenance schedule should be in monthly increments. This time period provide flexibility for the contractor.

The performance criteria should outline the contractor's specific activities in the areas of turf management, shrub, tree, palm, and bed maintenance, litter removal, and cleanup. The performance criteria should reference all materials and products to be used and provided by the contractor. Details regarding types of fertilizer, pesticides (insecticides, fungicides, herbicides ), and mulch should be included here with some provisions for equivalent alternatives.

Insurance requirement must be clearly defined in the contract, including performance evaluation, legal structure and language. It is important that the contractor's and the association's insurance on their own General Liability policy. Although the limits will be upon to the board of directors, the policy at the very least should be on a "comprehensive" form and an "occurrence" basis. The policy should include premises and product/completed operations coverage.

Second, the contractor policy should include the same form, basis, and coverage as the association. In addition, the policy as well as certificates provided should include the following coverage or endorsement, aggregate applies per project, XCU (explosion, collapse, and underground hazards) exclusion deleted, the association, its members, guests, and agents named as additional insured, contractual liability, and a hold harmless agreement in favour of the association for bodily injury, personal injury and property damage. Limits should be adequate for the extent of the services provided. The insured subcontractor selected by the contractor must be licensed to do business in the association's jurisdiction. The association should require the contractor to carry Workers Compensation insurance with employers liability and a waiver of subrogation for the work or job performed. Certificates should be sent to the association's insurance agent for review. The contractor's insurance requirements can be placed in the legal body, in the specifications under the heading of general requirements, or in an insurance section.

The contractor's key employee should be an ornamental horticulturist, whose knowledge and training is vital to landscape problem-solving. The horticulturist specializes in flowers, shrubs, palms and trees. The agronomist specializes in soil and turf management and may be beneficial for an association with large areas of turf. The size of the firm has little to do with the competency or capability to perform, and it is best not to place too much emphasis on size. Contractors should provide references, preferably from associations of similar size and landscape.

According to general standards, contractor shall show knowledge of location (specific site conditions), point out pre-existing conditions and plan for corrective actions, have a certificate of insurance with required coverage (including Worker's Compensation), provide written reports (monthly, due date, content, service tickets), provide all materials, tools, equipment, and labor, perform at highest standards, have a Green Industries Best Management Practises (BMPs) certificate of completion offered by University of Florida IFAS Extension Service, perform according to country, state and federal regulations (including any related to fertilizers and pesticides). The contractor shall finish all labor, supervision, equipment and materials as necessary to provide complete maintenance and irrigation of all shrubs, trees, palms, ground covers, annual and perennial plants and lawns, and shall provide such other work as may be required by these specifications to maintain the landscape in an attractive condition throughout the year.

Turf care, mowing and edging, all grass must be maintained at the recommented height, using mulching, rotary type, mowers. Mowing must be directed away from water bodies and impervious surfaces. Turfgrass clippings are a source of slow release nitrogen. Leaving the clippings, rather than removing and bagging them, reduces both fertilisation needs and the amount of plant material that must be disposed. For fertilization, do not fertilize when heavy rain is expected. Leave a ring of responsibility around or along water bodies. The use of deflector shields on fertiliser spreaders is recommended around or along water bodies and impervious surfaces such as sidewalks and roadways.

c) Briefly explain three (3) influencing factors for road design

First of the influencing factor of road design is type of subgrade. For estimation of the design moisture content under impermeable asphalt surfacing are classified into three categories.

In category one the water table is sufficiently close to the ground surface to control the subgrade moisture content. The type of subgrade soil governs the depth below the road surface at which a water table has a dominant influence. For non-plastic soils, sandy clays and heavy clays the water table will dominate the subgrade moisture content when the distance from the road surface is less than 1 m, 3 m , and 7 m respectively. The best and easiest method of evaluating the design moisture content is to take measurement below similar, existing pavements during the wet season. If there is no existing road in the vicinity, the design moisture content can be estimated from measurements of the depth of the water table and determination of the relation between suction and moisture for the subgrade soil.

In category 2, the water table is deep but the rainfall is sufficient to produce significant seasonal changes in the moisture conditions under the road. This situation occurs when rainfall exceeds evapotranspiration for at least two months of the year. The rainfall in such areas is usually greater than 250 mm per year and is often seasonal. In this case the subgrade moisture condition will depend on the balance between the water entering the subgrade through the shoulders and the moisture leaving the ground by evapotranspiration when the weather is dry. The design moisture content should be taken as the optimium moisture content.

In category 3, the permanent water table is deep, and the climate is arid throughout the year. Such areas have an annual rainfall of less than 250 mm. The moisture content of the subgrade is unlikely to exceed the optimium moisture content given by the standard compaction test and the moisture content should be used for design purposes.

Second factor that influence road design is skidding resistance. The skidding resistance of a road is a measure of the friction generated between the road surface and a tyre in wet condition. In any particular location, the friction depends on properties of both the road and the tyre, with climate factors also having an influence. The key property of the road surface in generating skidding resistance is the microtexture of the material in the surfacing which is in contact with vehicle tyres. In asphalt and exposed-aggregate concrete surfacing, the microtexture is determined by the fine structure of the surface of the aggregate particles. When a road is trafficked, its skidding resistance is reduced as a result of the polishing action of tyres on the microtexture. Accelerated polishing machine to assess the properties of different aggregate was designed. In this test, samples of aggregate are set in resin to form specimens which are mounted on the circumference of a wheel. This is then roated for a period of time while a rubber tyre is loaded onto the aggregate surface and a polishing medium trickled into the interface. At the end of the polishing process, the skidding resistance of the specimens is measured and compared with the results from specimens made with a control stone. Some aggregates perform better than expected whilst others appear to polish more and therefore give lower skidding. In order to give a satisfactory performance in terms of skidding resistance standards, the material should be provide particularly, it was necessary to review the requirements in the light of experience.

Third factor is initial cost. The cost of acquiring new right of way is a significant factor in the planning of any interchange. The cost of upon land for an interchange can vary from as a little as per square foot to as much as per square foot in a highly travelled and populated urban area. If buildings or other properties are in the potential right-of-way area, the cost per square foot may be much higher than per square foot and can exceed per square foot in special cases where major building are taken. Clearly, cost of right of way can be the controlling factor in the general economic feasibility of the proposed project. The larger the separation the more right-of-way area required and , hence, a possible increase in cost for acquiring the land. Pavement costs for the major road, and the entrance and exit ramps represent a second significant cost component. At the conceptual estimate level, pavement cost includes the preparation of subbase, the paving material itself, i.e., asphalt or concrete, and medians.

Pavement costs are estimated as a function of the total square feet of road surface area and the unit cost per square foot of surface area. The square foot of pavement area is determined by the width of the road, less curbs, and the length. The unit cost would cover subbase and all paving construction. Unit cost are likely to vary depending on the thickness of the pavement, the type of paving ,i.e. , jointed concrete paving, availability of materials and volume of current construction. Two primary cost components are earthwork and retaining structures associated with the major road. These two components can comprises between 10 and 20 percent of the total cost of construction. Earthfill is used to prepare the incline ramp for the major roadway from where the major road deviates from existing grade to the beginning of the bridge structure on either side of the bridge. If the major road passes under the cross road, earthwork consist of excavation existing soil and removing it from the site. Variations in cost also are due to the type and availability of materials, soil characteristics, haul distance, location of fill and volume of soil required. The major road is often bordered by a concrete retaining structure unless sufficient right-of-way is available to use sloped.

d) Briefly explain four (4) requirements of joints for cladding system.

The requirements of joints for cladding system are exclude wind, rain and snow, allow for structural,thermal and moisture movement, good durability, and easily maintained and maintain the thermal and sound insulation properties of the surrounding cladding. These requirements can briefly explain under two headings of suitable joints.

Filled joints are generally satisfactory if the cladding module is small since if incorporated in large module panels filled joints can crack and allow water to penetrate. This failure is due either to the filling materials being incapable of accommodating movement or a breakdown of adhesion between the filling material and the panel. Filled joints are not easy to construct and rely mainly upon mortars, sealants, mastics or preformed gaskets to provide the barrier against the infiltration of wind and rain. They are limited in their performance by the amount that the sealing materials can accommodate movement and certain extent their weathering properties such as resistance to ultra-violet rays.

Drained joints have been designed and developed to overcome the disadvantages of the filled joint by designing the joint to have a drainage zone and providing and air-tight seal at the rear of the joint. Drained joints have two components which must be considered, namely the vertical joint and the horizontal joint.

Vertical joints consist basically of a deep narrow gap between adjacent panels where the rear of the joint is adequately sealed to prevent the passage of air and moisture. The width of the joint does not significantly affect the amount of water reaching the rear seal since most of the water entering the joint (approximately 80 %) will do so by following over the face of the panel, the reminder ( approximately 20 %) will enter the joint directly and most of this water entering the joint will drain down within the first 50 mm of the joint depth. Usually the deciding factor for determining the joint width is the type of mastic or sealant being used and its ability to accommodate movement. Checks on the amount of water entering the drainage zone such as ribs to joint edges, exposed aggregate external surfaces and the use of baffles.

Baffles are loose strips of material such as neoprene, butyl rubber or plasticised PVC which are unaffected by direct sunlight and act as first line of defence to water penetration. The baffles are inserted, after the panels have been positioned and fixed, either by pulling them through prepared grooves or by direct insertion into the locating grooves from the face or back of panel according to the joint design. Care must be taken when inserting baffles by the pulling method since they invariably stretch during insertion and they must allow to return to their original length before trimming off the surplus to ensure adequate cover at the intersection of the vertical and the horizontal joint.

The adequate sealing at the back of the joints is of utmost importance since some water will usually penetrate past the open drainage zone or the baffle, and any air movement through the joint seal will also assist the passage of water or moisture. Drained joints which have only a back of seal or a baffle and seal can have a cold bridge effect on the internal face giving rise to local condensation, therefore consideration must be given to maintaining the continuity of the thermal insulation value of the cladding.

Horizontal joints are usually in the form of e rebated lap joint, the upper panel being lapped over the top edge of the lower panel. As with the vertical joints, the provision of an adequate back seal to prevent air movement through the joints is of paramount importance. The seal must also perform the function of a compression joint, therefore the sealing strip is of a compressible material such as bituminised foamed polyurethane or a performed cellular rubber strip.

The profile of the joint is such that any water entering the gap by flowing from the panel face or by being blown in by the wind is encouraged to drain back on to the face of the lower panel. The depth of joint overlap is usually determined by the degree of exposure ranges from 50 mm for normal exposure to 100 mm for severe exposure. It must be noted that the effective overlap of a horizontal joint is measured from the bottom edge of the baffle in the vertical joint to the seal and not from the rebated edge of the lower panel.

Intersection of joints is an important feature of drained joint design and detail since it is necessary to shed any water draining down the vertical and horizontal joints intersect because the joints are designed to cater only for the entry of water from any one panel connection at a time. The usual method is to use a flashing starting at the back of the panel, dressed over and stuck to the upper edge of the lower panel. The choice of material for the flashing must be carefully considered since it must accept the load of the upper panel and any movements made whilst the panel is positioned and secured. Also it should be a material which is durable but will not give rise to staining of the panel surface. Experience has shown that suitable materials are bitumen coated woven glasscloth and synthetic rubber sheet.

Typical filled and drain joints - - Typical horizontal joints -


Construction Technology, second edition by R Chudley.

Advanced Construction Technology, fourth edition by Roy Chudley and Roger Greeno.