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The following corrections are to be made for measurements taken with a tape because tape can never be practically used under specified standard conditions. The chain survey is the simplest method of surveying. 1. Ideal Conditions 1) A tape accurate to 0.00305m or 0.01 ft should be used. Refraction correction a) completely eliminates curvature correction b) partially eliminates curvature correction c) adds to the curvature correction d) has no effect on curvature correction Ans: b. Tape Corrections: Precise measurements of distance is made by means of a steel tape 30 m or 50 m in length.Before use it is desirable to ascertain its actual length (absolute length) by comparing it with the standard of known length, which can be done for a small fee by the Survey and Standards department. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S>> Surveying and leveling by R. Subramanian, Oxford university press, New Delhi. Surveying is an art of determining the relative positions of various points on, above or below the surface of the earth by means of direct or indirect measurement of distance, direction and elevation. If there are n equal spans per tape length, the sag corrections per tape length is given, by, Cs = nl1(mgl1)2 / 24P2 = l(mgl1)2 / 24P2 = l(mgl)2 / 24n2P2 ………….(4a). are done in the office. Here in we have gathered some pdf lectures on surveying. A rod is 1/4 of a chain or 16.5 feet. stream W = the weight of the length of tape between supports in newtons (N). effects which act in a predictable manner and therefore can be corrected by mathematical methods. This results in an increase in the tape length, making the measured length shorter. It’s us required only when the tape is suspended during measurement. The coefficient of expansion for steel varies from 10.6 x 10-6 to 12.2 x 10-6 per degree centigrade and that for invar from 5.4 x 10-7 to 7.2 x 10-7. In this method the lengths of lines marked on the field are measured, while the details are measured by offsets and ties from these lines. 58. MODULE-I-B. The correction for temperature Ct is given by the formula: Tm is the mean temperature in the field during measurement; To is the temperature during the standardization of the tape; L = Measured length; There are two cases possible: 1. Temperature correction per tape length = Ct, Hence the length of the tape at 32oC = 30 + Ct. Now true length of a line = L’ / L x its measured length. = the differences in height between the extremities of each of these. If the slopes are given in terms of vertical angles (plus or minus angles), the following formula may be used: The correction for the slope = l – l cos 0 = 2l sin2 0 / 2, = l versin 0 (-ve) --------------------------(7). = h2 / 2l ------------------------(6), hence, Cs = (h12 / 2l1 + h22 / 2l2 + ….. + hn2 / 2ln) -------------------------------(6a), When the slopes are of uniform length l we have, Cs = l / 2l (h12 + h22 + ……… + hn2) = ∑h2 / 2l -------------------------(6b). It is required only when the tape is suspended during measurement. Acre = 10 square chains 10 chains = 660' 66' 660' x 66' = 43,560 sqft (acre) Figure 2: Surveyor’s Chain Other multiples of the chain are still in use today. Let l1 l2, etc. Po= the pull under which the tape is standardized in newtons (N). Define Surveying. Apr 07, 2018. For very precise work, the coefficient of expansion for the tape in question must be carefully determined. Hence the correction i… In surveying, tape correction(s) refer(s) to correcting measurements for the effect of slope angle, expansion or contraction due to temperature, and the tape's sag, which varies with the applied tension. The measurement of this linear horizontal distance between two points on the earth surface is known as linear measurement. It is required only when the tape is suspended during measurement. SURVEYING – I UNIT I INDRODUCTION AND CHAIN SURVEYING 1. Since the tape is not used in the field under standard conditions it is necessary to apply the following corrections to the measured length of a line in order to obtain its true length: Correction for absolute length, (ii) Correction for temperature, (iii) Correction for tension or pull, (iv) Correction for sag, and (v) Correction for slope or vertical alignment. Where Cp = the correction for pull in metres. Since the accuracy of the whole survey work depends upon the accuracy of the base line, it should be laid off on the ground level as much as possible. Example 12.3: A survey was conducted with a 20 m chain and plan of the field was drawn to a scale of 1 cm = 5 m. The area of the plan was found to be 62.8 cm2. 2. (iv) In the method of stepping while measuring sloping ground, plumbing may be crude. Correction for Absolute Length: - It is the usual practice to express the absolute length of a tape as … L = 30 m: L’ = 30.004914 m; measured length = 452.343 m. ~ True length = 30.004914 / 30 x 452.343 = 452.417 m. Example 2: - A line was measured with a steel rape which was exactly 30 m at 18oC and a pull of 50 N and the measured length was 459.242 m. Temperature during measurement was 28oC and the pull applied was 100 N. The tape was uniformly supported during the measurement. 2) Locating various objects by chain & cross staff surveying. If the chain that is employed for measuring length is not equal to the true length, then the length measured won’t be correct. What is the horizontal length? The tape may be standardized when supported horizontally throughout its full length or in catenary. 12/17/2017 SURVEYING and LEVELLING 3 OBJECTIVES Explain the methods of measurement of distance Describe the construction of standard chain and tape Explain the method of … When a field measurement is taken, the acceptable error may be more or less than what the chain was designed for. Introduction to chain surveying and their components, types of chains, errors in chain surveying, corrections for chain surveying, principles and procedures. in which Ct = the correction for temperature, in m. a = the coefficient of thermal expansion. Correction for Slope or Vertical Alignment: - (Fig 2) This correction is required when the points of support are not exactly at the same level. For every precise work its value must be ascertained. ~ Combined correction = 0.00351 + 0.00357 m. True length of tape = 30.00708 m, True length of the line = 30.00708 / 30 x 459.242. Corrections. 5) Locating given building by chain and compass traversing, (One full size drawing sheet) If l is the length of any one slope, and h the difference in height between the ends of the slope, = l – l (1 – h2 / 2l2 – h4 / 3l4 – etc..), =(h2 / 2l + h4 / 3l3 + etc.) A = the cross-sectional area of the tape, in sq.cm. Thus we have, (Pn-Po)l1 / AE = l1(mgl1)2 / 24Pn2 or (Pn-Po) Pn2 = W2AE / 24, ~ Pn = 0.204 W √AE / √(Pn-Po) …………………………………………..(5). Tm = the mean temperature during measurement. [���RA��{]���^�Q6d�z`~#A R�7W���tb�o����{�����m�WZ�Qx��h�Z��R�JGA��*�%E�`bq��,����i}�W?��6������~�oq�7W���\'�$��u�q%�_}���u��O~#�4l9�ZG�,�6�����:��+�$P�H�������� rM�p(i��^;%�����z��?�����y���r���k��N|����s�p��3����D�2"�@�����x������:^ė �d�?G�}�g���@����j�/7���:�>���� w&PtG� ����~-�5=;m��H�����=+�ZTk`&u&j���i7��?���3���c�CAnj='oa 4. in which Pn = the normal tension in newtons (N). REFERENCES – Surveying Notes Pdf 1. It is the exercise of physically measuring horizontal distances. Correction for incorrect alignment = d2 / 2l ( - ve), Lesson 6. Corrections In Chain Surveying, Last modified: Friday, 6 December 2013, 5:26 AM, The sign of the correction is plus or minus according as T, The value of E for steel may be taken as 19.3 to 20.7 x 10, The correction for sag (or sag correction) is the difference in length between the arc and the subtending chord (i.e., the difference between the horizontal distance between supports and the length measured along the curve). Surveying instruments- temporary and permanent adjustment concept, principle of reversal. endobj Example 4: - The downhill end of the 30 m tape is held 80 cm too low. Where Ca = the correction for absolute length. It is given by the formula. = the lengths of successive uniform slopes. A correction is said to be plus or positive when the uncorrected length is to be increased, and minus or negative when it is to be decreased in order to obtain true length. By V Ranjith Kumar Asst Professor 12/17/2017 SURVEYING AND LEVELLING 1 12/17/2017 SURVEYING and LEVELLING 2 CHAPTER 2 MEASUREMENT OF DISTANCES-CHAIN SURVEYING. %PDF-1.5 ... Chain Survey Steps - Method for Performing Chain Surveying. Wha t are the fundamental principles of surveying? Tape Correction, Sag Correction, Pull Correction and Temperature Correction. 1. 1 0 obj no angular measurements are made. lt1, lt2 etc. LAB #3: SURVEY OF AN AREA BY CHAIN SURVEY (CLOSED TRAVERSE) Objective: To survey an open field by chain survey in order to calculate the area of the open field. m = the mass of the tape, in kilograms per metre. 3. l1 = the distance between supports in metres. The combined correction can be application two ways: (i) By decreasing each staff reading by the amount 0.0673 D 2 and then finding, the reduced levels and (ii) By first finding the reduced levels of the points in the usual way and then increasing them by the amount 0.0673 D 2. Correction for Absolute Length: - It is the usual practice to express the absolute length of a tape as its nominal or designated length plus or minus a correction. Linear measurement can be achieved by various instruments. It is well to note here the distinction between the nominal or designated length and absolute length of a tape. The correction for the measured length is given by the formula. Introduction to tape surveying and their components, types of tapes, errors in tape Introduction to principle of surveying 2. in which l = the length of the tape = nl1, and l1= l/n. This is most suitable adapted to small plane areas with very few details. It is the exercise of physically measuring horizontal distances. Chain surveying is the branch of surveying in which only linear measurements are made in the field. After participating in this fieldwork students will become more comfortable with handling chain and ranging rods. Rods are commonly used in early highway right-of way descriptions. For surveying, we need to have some prerequisite conditions. This is most suitably adapted to small plane areas with very few details. 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Correction and temperature correction be a parabola apply corrections to get the true result document is highly rated by Engineering! Document is highly rated correction in chain surveying pdf Agricultural Engineering students and has been viewed times... M or 50 m in length, making the measured length too great this correction plus., is 10 chains, or 660 feet height between the nominal or designated length and length.

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