Unit 12 Construction Surveying Part ⅠIllustrated Words and Concepts Figure 12-1 Elevations Determined by Transit and Leveling Rod Figure 12-2 A Plot Plan of Elevations and Location of a House Part Ⅱ Passages Passage A Construction Surveying Passage B The Survey of a Plot Plan
Unit 12 Construction Surveying Part Ⅰ Illustrated Words and Concepts Figure 12-1 Elevations Determined by Transit and Leveling Rod
Unit 12 Construction Surveying Part Ⅰ Illustrated Words and Concepts Figure 12-2 A Plot Plan of Elevations and Location of a House
Unit 12 Construction Surveying Part Ⅱ Passages Passage A Construction Surveying The construction industry is the largest in the United States and surveying is an essential part of that industry. A boundary survey and the preparation of the necessary topographic maps is the first step in the construction process. From these maps the positions of the structures are established and when the final plans for the project are available,
Unit 12 Construction Surveying Part Ⅱ Passages Passage A it is the duty of the surveyor to set the required horizontal and vertical positions for the structures. In other words, construction surveying involves the transfer of the dimensions on the drawing to the ground so that the work is done in its correct position. This type of surveying is sometimes called “setting lines and grades”. The work of the surveyor for construction projects is often referred to as layout work and the term “layout engineer” may be used in place of the term “surveyor”.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A Of necessity, construction surveying begins before actual construction and continues until the project is completed. Surveying is an essential part of the construction process and must be carried out in coordination with other operations in order to have an economical job and to prevent serious mistakes.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A The reader can readily understand the expense and inconvenience caused if one reinforced concrete footing for a building is placed in the wrong position. As another example, just imagine the problems involved if a few thousand feet of a sewer line are set on the wrong grade.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A Construction drawings show the sizes and positions of structures that are to be erected, such as buildings, bridges, roads, parking lots, storage tanks, pipelines, and so on. The job of the construction surveyor is to locate these planned features in their desired positions on the ground.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A He does this by placing reference marks ( such as construction stakes) sufficiently close to the planned work so as to permit the masons, carpenters, and other tradesmen to properly position the work with their own equipment (folding rules, mason’s levels, string lines, and so on).
Unit 12 Construction Surveying Part Ⅱ Passages Passage A he construction surveyor will find that his work is quite varied. One day he may be doing topographic work for a proposed building, while on another he may be setting stakes for pipeline excavation. It is often necessary for him to make measurements before and after some types of work, e. g., computing quantities of earthwork moved by a contractor. At other times, he will set stakes to guide the construction of foundations; he may be aligning the columns of a steel frame building, or checking a completed structure to see that it is correctly positioned, and so on.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A A construction project requires four kinds of surveys for its completion: (1) A property or boundary survey by a registered land surveyor to establish the location and dimensions of the property.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A (2) A survey to determine the existing conditions such as contours, man-made and natural features, streams, sewers, power lines, roads, nearby structures, and so on. This work may also be done by the land surveyor along with the boundary survey. (3) The construction surveys which determine the position and elevation of the features of the construction work. These surveys include the placing of grade stakes, alignment stakes and other layout control points.
Unit 12 Construction Surveying Part Ⅱ Passages Passage A (4) Finally there are the surveys which determine the positions of the finished structures．These are the “as-built” surveys and they are used to check the contractor’s work and show locations of structures and their components (water lines, sewers, etc.) which will be needed for future maintenance, changes, and new construction．
Unit 12 Construction Surveying Part Ⅱ Passages Passage B The Survey of a Plot Plan The Survey Plat The basic information for the plot plan is found on a survey plat which is drawn by licensed surveyors. They obtain the legal descriptions of the piece of ground from the deed to the property which they receive from the owner.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B Using surveying instruments and a tape or chain they locate a corner of the property in reference to a local datum which has been established by the town, city or village. This is usually a marker made of concrete and embedded in the ground, or it may be any other point which is designated by ordinance to serve the purpose.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B In a city, the marker may be placed on a street or a walk. It could even be a notch on the corner of a building. A surveyor’s plat is usually required by banks and other lending institutions before mortgages for building can be arranged.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B When a new subdivision is opened the surveyor may have to establish accurate direction lines, measure precise distances, and work out differences in elevation (level) from a datum point which is far away. After the surveyor locates a corner of the property or some central point, a stake is driven firmly in place or a concrete benchmark is set. This in turn becomes the point of reference for the location of streets and lots in the new community.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B When surveyors make a survey of a lot, the first thing they do is to establish a point of beginning which may be a mark on a walk or a corner stake. This point serves to help them locate the other corners of the piece of ground and also to relate elevations (levels) to the city requirements for that particular lot.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B Surveyors show much other information on their plat besides the location of the lot corners. They also indicate the location of utilities, and water and sewer mains. Unless the lot is almost flat they show the contour of the lot by using a series of contour lines taken at a uniform interval of levels or grades. They show trees, walks, drive ways, and streets on their drawings. See the Unit Cover Figure.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B Scales Used by the Surveyor Surveyors use a tape (graduated in metres and centimetres) or a chain (graduated in metres and decimetres) when making measurements. They make their drawings using a scale of 1200 or 1500 for plot plans (also referred to as site plans) and 11000 or 12000 for block plans or subdivisions.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B Elevations The height of any point on the lot is called its elevation and is measured above or below some point of reference. (The use of the word elevation in this sense must not be confused with the elevation of a house which is a view of the outside of the structure.) In the Unit Cover Figure the elevation of the point of beginning is 8.900m.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B This means that the elevation of this corner of the lot is 1.100m below the benchmark (top of fire hydrant，in this case) which has an elevation of 10.000 m. Elevations are usually given in metres. The elevations of all other points on the lot are determined by using a transit and a levelling rod in reference to the benchmark. See Figure 12-1.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B Contour Lines Contour lines are drawn on a surveyor’s plat or on an architect’s plot plan to show the slope of the ground. A contour line may be explained by thinking of the lowest contour line as the shore of a lake. If the water were to rise 0.5 m the shore line (contour line) would take on a new shape as the water covered more of the earth.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B Contour intervals are usually based on multiples of 100 mm (0.1 m), with small lots normally contoured in 500 mm (0.5 m) intervals. If the tracts are large or very hilly, contour lines may be at 1 m intervals. If the tracts are relatively level, intervals may be given at 300 mm (0.3 m) or less.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B The Plot Plan Architects use the information supplied by the surveyor’s plat in drawing the plot (site) plan. They draw the lot, accurately, using millimetres or metres. They indicate the north point, the lot and block number and the benchmark taken from a local city datum point. They also locate utilities, sewers, streets and public walks.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B They then locate the house, making sure that they have observed all of the area restrictions, front and side limitations, etc., established by local ordinances. They draw the contour lines showing the natural grade elevations. They then draw a second set of contour lines to show how the lot is to be sloped after the project is completed. These lines will determine the finished grade.
Unit 12 Construction Surveying Part Ⅱ Passages Passage B The finished grade elevations are shown in the small rectangles in Figure 122.The level of the benchmark given by the surveyor is designated, and the first floor is indicated so the excavator may know how deep to dig the hole for the foundation. In the plot plan, Figure 122, the architect established the first floor at 9.500 m in direct relation to the benchmark.