Civil Engineering Construction - Assignment Example

Activities involved in road works: Table of contents 1. Introduction 2. Activities involved in road works Groundwater control Slope stabilization using bolts, nails and anchor Retaining walls Foundations Trenching and deep excavation 3. Summary 4. References 1. Introduction: Construction of a road involves several activities particularly related to the ground. The work starts from determining the profile of a road. Once the profile has been determined, ground has to be customized to meet the desired levels as mentioned in the construction drawing. The ground needs to be cut and filled. This requires excavation, grading, filling, compaction and testing. In hilly areas, the region on the sides also needs to be restrained with the help of retaining walls or bracing so as to minimize the verisimilitude of land sliding. Sides of the road need to be provided with drains so that rain water may escape the road, and flow away through proper channel. Also, the road needs to be constructed with slopes so that the water would slide away towards the sides. In this paper, some of the activities that make part of the road construction process are discussed. 2. Activities involved in road works: 2.1 Groundwater control: Controlling the ground water level is the first and foremost requirement of slope stabilization. In sloppy areas, drainage design is of huge significance particularly because water coming from water reservoirs can enhance the pore water pressure and increase the level ground water. This adds to the pressure on sloppy areas and the land may slide. This is conventionally achieved through installing surface or subsurface devices within or near the unstable portions that would ensure the drainage of soil. There are several methods to control the ground water level. Some involve use of pumps to dewater the land. Others are based on such techniques that would reduce the likelihood of interference of water with the on-going construction without having to dewater the land. Typical groundwater control techniques are open sump pumping, pumping from wells or wellpoints, ground freezing and installing horizontal drains in the ground. Of these, first three pertain to the pumping and the last two enhance control over ground water without the use of pump. Different techniques are operated in various ways. For example, freezing is used to stabilize waterlogged areas. The technique involves insertion of freezing tubes in the soil. A freezing solution, commonly magnesium chloride is circulated through the tube at a temperature between -15 to -25 єC, that freezes the water around it. It converts such a soil into ice wall that is altogether impervious. “Frozen soil not only is an effective water barrier but also can serve as an excellent cofferdam” (UFC, 2004, p. 48).People can hence, work inside without the danger of collapse because of water pressure. Common equipment required for achieving control over ground water are pumps, drill machines, pipes, filters and metallic tubes. Method of controlling water is decided keeping in view the area to be drained, the finances available, length of operation, type of soil and effect of the ground water table on the conditions of near by residential areas. Ground water control increases the stability of slope, reduces the likelihood of erosion as well as siltation. However, it is important to consider the effects of interference with ground water level upon the quality of water on adjacent land. As a result of altering the ground water level, structures in the vicinity of the site may experience settlements and develop cracks. Also, lowering the ground water level raises the need to dig deeper for wells. This makes the people in locality incur undue expenses. In order to avoid such situations, techniques should be adopted to obviate the adverse effects of water without dewatering. This can be achieved by freezing the water as explained before. Ground water can also be controlled without dewatering by planting the land heavily. Trees in large numbers sufficiently consume underground water, add to the beauty of the area and add a lot to the environmental hygiene. Plantation not only consumes water, it is also a very cost effective way of controlling water. However, this technique can only be employed if the constructors have sufficient time to let the plants grow into trees. 2.2 Slope stabilization using bolts, nails and anchor: Bolts, nails and anchors are three kinds of ground inclusions. They are metal bars that are driven into the soil or rocks to hold them together and stabilize the slopes. They are taken as an alternative for piles in mountainous regions. Anchors are used in two ways; either actively that involves pre-stressed anchoring or passively that involves non-stressed anchoring. (California Coastal Commission, n.d.). Anchors are very reliable, cost effective and durable supports that can be employed in a vast majority of occasions where slopes are to be secured, stabilized or restrained. Rock bolt anchoring adequately combats external pressure, uplift, overturning and all kinds of seismic forces. Anchors are conventionally made in steel or high strength strands. Stranded tendons may be designed to resist very high loads. Bolts, nails and anchors are conventionally used in retaining walls, tunnels, bridges, mines, tower bases, dams and many other concrete structures. Anchors can be made both pre-stressed or non-stressed as required. There is no limit in terms of length of fabrication of anchors, some may be as long as hundreds of feet. They can resist very high loads very adequately. They help resist corrosion as they can be made with single or many layers of corrosion resistance. They are equally applicable in rocks, concrete and many soil types. Coiled or coupled tendons get installed with minimum inconvenience in areas where otherwise installation would be a hectic process. Selection of nails, anchors and bolts serves to decrease the overall retention system in size and thickness, yet the efficiency is maintained. Bolts, nails and anchor may be employed as a means of slope stabilization when immediate results are required. However, they are relatively costlier as compared to such other ways of stabilizing slopes as vegetation. When there are no time constraints, the best method is to grow more trees on slopes. Their roots serve as a reinforcing network for the soil and the slope gets stabilized. Use of bolts, nails and anchors obviates the need to construct deep foundations for retaining structures, thus a projects’ visual impacts are minimized. This makes the project environment friendly and the stakeholders (residents in the locality) feel good. 2.3 Retaining walls: Retaining walls have many types namely, gravity walls, sheet piling retaining walls, cantilever retaining walls, block retaining walls, cinder block retaining walls, concrete retaining walls, counterfort retaining walls and rock retaining walls. Likewise, there is a wide range of materials in which retaining walls are conventionally made that include but are not limited to masonry, concrete, stone, steel, brick and timber. Cost of construction is low for cheaper, locally and readily available materials like stones or bricks and higher for materials imported or fabricated like concrete. Different types of retaining walls have their own advantages and disadvantages as well as methods of construction. For example, thickness of cantilever walls is constant. They are tied with the footing, thus take the shape of an inverted T. They adequately support soil and restrain it from collapsing. Such types of retaining walls can particularly be seen in the basements of homes. Their construction is relatively easier as the section does not vary along the length. On the other hand, counterfort retaining walls are triangular in shape. They are also cantilever walls. The triangular walls that join the footer with the top of the face wall lend such retaining walls additional strength and support. Hence, they have added walls in comparison to simple cantilever walls. Fig: Retaining wall (ABC, 2010). Concrete plant is required to cast the retaining walls if they are to be made in concrete. Also, steel shuttering is commonly used for larger walls, though wooden shuttering may be employed for constructing smaller walls. In other cases, other materials like bricks and stones etc. have to be provided as needed. Before fixing the formwork and binding the steel, the ground is cut as per the drawings using excavator. It is temporarily restrained using anchors, struts and bolts so that the retaining walls may be cast without inconvenience of land sliding. Retaining walls fundamentally resist the lateral pressure of earth. Therefore, they are designed keeping lateral pressure of earth in view. Lateral earth pressure is found out after considering the unit soil weight, slope and the type of soil in terms of its plasticity, and other characteristics as well as level of ground water. Once constructed, the shutters are removed and the spaces are backfilled and compacted. Being an earth related operation, construction of retaining walls is also affected by the weather. Earth may readjust its profile because of the stresses induced in it as a result of cutting and excavation, giving rise to land sliding. It should hence, be ensured that the slopes are adequately restrained before casting retaining walls. Retaining walls may fail if not designed prudently. Retaining walls that can not resist the lateral earth pressure crack, bow or tilt up. In a vast majority of cases, retaining walls become cracked or moved because the soil underneath becomes eroded because of rain water flow. This can result into the failure of retaining wall. It is important to ensure proper drainage of water that may accumulate behind the retaining wall. This can be achieved by providing drainage pipes or weep holes behind the wall. A filter barrier must be provided in the drainage system so as to ensure that dirt does not clog the drain. Retaining wall, if properly constructed, adds to the safety of the buildings in the vicinity. The buildings in the surrounding are protected against land sliding. 2.4 Foundations: Foundations are fundamentally classified into four types, namely strip foundations, raft foundations, pad foundations and pile foundations. They have further types. Strip foundations have trench foundations, raft foundations have shallow rigid raft foundations. Similarly, there are many types of pad and pile foundations, each one having its own advantages and disadvantages. For example, strip foundations consume less money to be built as less ground has to be excavated and less concrete has to be poured while raft foundations are quicker to be built because all ground can be rapidly dug and concreted. Pad foundations are also economical as they save concrete, but they are also very time consuming as each pad has to be individually attended. Different types of pad, strip, raft or pile foundations may be chosen for the same circumstances and location based upon their suitability to the project owner in terms of time and economy. Also, among the different types of foundations, a particular type is chosen depending upon the ground conditions. In case of soils with very less bearing capacity, pile foundations are employed. They are extended deep into the Earth till they rest upon a hard strata. Ready mixed concrete is required to cast the pile foundations which necessitates the availability of a concrete plant and concrete pump in the vicinity of the site. Fig: Foundation information (San Antonio Remodelers, 2008). Foundation is designed depending upon the DL, WL and LL of the building and the estimated self weight of the foundation itself. Alongside, soil’s bearing capacity plays a fundamental role in determining the size of footing. Bearing capacity of soil is inversely proportional to the area of contact between footing and the soil. Once the foundation has been designed as per the loads and bearing capacity of soil in a particular location, ground is excavated manually or using an excavator. Manpower, excavator, saw are the required resources for excavation. It is important to decide the location of dumping excavated sand prior to conducting the operation. Excavation is particularly a very risky operation particularly if the ground is unstable. In hilly areas, laborers working underground are susceptible to be buried under soil as a result of land sliding. Therefore, measures need to be taken in order to ensure that the sides of excavation and higher areas are adequately restrained against collapse or land sliding. Also, as they go deep down into the Earth, workers feel suffocation. They may loose breath in extreme conditions, therefore have to be provided with O2 cylinders as a precautionary measure. Site for dumping excavated sand should be chosen after consideration of all environmental and ethical factors. Often, it so happens that the contractors deposit soil in or near to the residential areas. The sand gets blown away by wind and may pollute the residential environment. Also, excavation and foundation casting is a very noisy process. People living in the vicinity of the construction site may feel disturbed as a result of the continuous day and night operation. It remains the responsibility of the owner of project to ensure that acoustic barriers are provided on the site in case work has to be continued in the night. 2.5 Trenching and deep excavation Excavators, compactors, manpower and the particular soil of refill material are the materials and equipment required for trenching and deep excavations. Plant may be hired or bought if not conventionally available on site. Trenches are excavations whose depth exceeds the width. Once the site investigation reports have been prepared, the engineer identifies the volume of excavation, determines the work area, site for dumping the excavated soil, and the existing underground service pipe routes. Nature of excavation varies according to its purpose. Earth might have to be excavated for road works, making basements, and trenches etc. There are several ways to deal with the excavated material. It can be used in backfilling anywhere on the site as required or else deposited to other site where it may be required. Before the commencement of earthworks, all underground pipes, services and cables should be clearly demarcated. The formation level may have to be lowered or raised as per the demand of a particular site because of service pipes. The underground water level is lowered in order to make the ground more stable. Pumps are commonly employed to dewater the site. This may disturb the natural flow of water. As a result of this, earth walls on the side of excavation may burst because of excessive pore pressure. Such collapses are the biggest hazards commonly encountered in making trenches and excavation. Therefore, sheet piles are installed in order to cater for any risk of collapse. Foundations of structures in the locality need to be provided with supports. Installation of sheet piles also serves the purpose. Cut-off walls or shoring may also be employed for the same reason. Selection of the most appropriate option is governed by the strength of soil, type of soil, excavation depth, availability of finances and duration of operation. Once, the soil has been excavated, it is compacted in order to increase the bearing capacity of the loose mass. This is done by using compactors. Cutting and making embankments are fundamentally earth works. All kinds of operations pertaining to earth are heavily influenced by weather. It takes considerable time to cut the ground and it all may be ruined by a heavy rainfall. Therefore, all earth works should be planned keeping the weather forecasts into consideration. In deep excavations, workers should be provided with O2 cylinders in order to facilitate breathing. Two fundamental types of environment effects are seen in excavation. First is the superficial change that may occur because of rainfall. The other one is the change induced by seasonal conditions whose effects can be seen in the soil for long. Therefore, excavation activity should be properly planned. Sumps can be made to store rainwater that would otherwise fall into the excavation. 3. Summary: In this paper, five activities have been discussed namely, foundations, retaining walls, groundwater control, slope stabilization techniques and the excavation and trenching. These activities make an integral part of the road construction process. Construction of a road involves many works related to the ground other than making the road itself. Upgrading and construction of any road involves all such operations as making trenches, embankments with appropriate slopes, controlling ground water so as to ensure that the water will not destabilize the sloped embankments, making retaining walls and piling. It also needs to be ensured that the road constructed is provided with side drains in order to allow rain water to escape the road so that the road remains intact. Provision of health and safety equipment is necessary on the site not only to ensure safety of workers, but also to facilitate the work. It is equally important to make sure that the activities are environment friendly. It remains the ethical and legal responsibility of the constructors to protect the environment. 4. References: Advanced Builders & Contractors, (2010). Retaining walls. Retrieved from http://www.abcinca.com/retaining_walls.html. California Coastal Commission, (n.d.). Attachment 3: Overview of Engineering Techniques to Reduce Grading. Retrieved from http://www.coastal.ca.gov/landform/attach3.html. San Antonio Remodelers, (2008). San Antonio Foundations. Retrieved from http://www.sanantonioremodelersonline.com/maincategoryinfo.php?category=Foundations. United Facilities Criteria, (2004). Dewatering and groundwater control. Retrieved from http://www.wbdg.org/ccb/DOD/UFC/ufc_3_220_05.pdf. Read More