How to survey a site yourself

Recommendation points

• Geodesy objectives
• Equipment
• Stages of engineering geodesy
• Where to begin
• Drawing up a center line
• Layout work

Even large construction companies sometimes neglect geodetic surveys for individual housing construction, while private developers consider this activity unnecessary. Our site will tell you when and why geodesy is needed, what is included in the survey program and how to carry it out without involving contractors.

Geodesy objectives

In general, geodesy is the science of measuring the earth’s surface, dividing it into sections and making maps. The outlines of continents, countries and individual regions known to date are entirely the merit of this scientific discipline. In construction, it is customary to operate with the concept of engineering geodesy, which makes it possible to compare the dimensions and shape of the object being built with the territory, taking into account the features of the relief, the location of nearby buildings, communications, boundaries of sites and stationary objects.

The reasons why private builders refuse to carry out surveying are simple: being full-fledged owners of their own land, people believe that they can build as they want. This is facilitated by the ability to perform a topographic reference of the object to obtain a technical passport for housing after the fact.

Timely conducting of geodetic surveys allows not only avoiding conflicts with the state cadastre. No matter how thoroughly the construction project was developed, its support requires careful control over the shape and size of the building being erected, which is very difficult to do without a specific frame of reference associated with the surrounding area.

Due to the neglect of geodetic studies before and during construction, the shape of the building can be significantly distorted, which leads to difficulties in comparing individual parts of the building structure, complications in the implementation of mechanical connections and connections, the formation of significant eccentricity of loads.

The lack of geodetic control over the building after construction makes it impossible to assess the correctness of calculations based on the hydrogeological situation and to establish in time the abnormal behavior of the building structure due to fluctuations in the lithosphere or soil shrinkage. Most of the destruction of private houses in the first years of operation could be predicted by timely geodetic measurements. Collapse could often be avoided by taking appropriate foundation strengthening or soil drainage measures.

Equipment

Engineering geodesy is a very precise science. The boundary deviations of geodetic measurements for construction purposes are no more than 10 mm, in other targeted surveys the tolerances are even smaller. Such high accuracy cannot be achieved without special equipment designed for leveling, linear and trigonometric measurements..

Surveying instruments cost hundreds of dollars, but they don’t have to be purchased. In almost any large city in Russia, you can rent such equipment and complete all the work in a day or two, while spending a minimum of funds. Here’s what you need to measure:

1. Linear quantities can be measured geodesic tape. It differs from conventional construction with a long, light and stiff measuring web, which can be stretched without sagging and elongation under load. Some tape measures have a built-in dynamometer, according to which the desired degree of tension is selected in accordance with the length. At distances over 30 meters, the tape measure is ineffective, it is better to use a laser rangefinder.

2. Trigonometric measurements are designed to accurately determine the angles between straight lines. Such a need inevitably arises when marking the lines of demarcation of areas, determining the axes and boundaries of buildings. You can use mathematical relations, but if you can get it into use laser protractor– work will go much faster.

3. Deviations from the horizontal plane can only be set using optical or laser rotary level. This is the most expensive piece of equipment and, moreover, quite specific to use, but this is the only way to correctly conduct a topographic survey..

Stages of engineering geodesy

In general, geodetic survey is reduced to compiling a set of points on the ground, for each of which coordinates and a deviation in height are determined. Coordinates are determined using the Cartesian system formed by geodetic points, heights – by points called benchmarks.

Geodetic survey methods are quite the same type, but there are several stages of research:

1. In the course of engineering and geodetic surveys, a drawing of a layout base is drawn up – a grid with a fixed step is applied to the terrain plan, which is usually 2-3 times less than the smallest size of the object under construction. The axes of the generated grid are parallel to the main axes of the building. On the drawing, elevation differences, cardinal points, binding to state and local geodetic points are noted. In kind, a set of reference points is formed, allowing you to measure at each key point of the drawing from at least two positions.
2. During stakeout work, the boundaries and axes of the structure are determined. After the high-rise and plan location of buildings is fixed in the construction project:
   • using the geo-survey method, the dimensions of foundation pits are determined;
   • set out the boundary lines of the base and the zero point;
   • determine the location of auxiliary buildings on the site;
   • install landmarks necessary for positioning landscape design objects.
3. Executive filming is being carried out during the construction of the building box. After shrinkage of the foundation, or the installation of interfloor ceilings, a second survey is carried out at the initial key points. This way you can determine whether the nature corresponds to the design forms, sizes and position..
4. Control measurements are carried out in the same manner as executive surveys, but after 2–5 years after the house was put into operation. Their goal is to confirm that the original position of the building and the shape of the adjacent relief have been preserved within the permissible deviations..

Where to begin

Geodesy of a site begins with the removal of its boundaries in nature. This task is usually performed by specialists from the state land cadastre. Using the closest trigger points and benchmarks of the planned geonet, the surveyor will determine the location of the boundary corner points where the stakes will be driven in, as well as the average elevation of the level surface.

After completion of the removal, the developer is free to carry out further geodesy independently. Initially, it is recommended to determine the distance of the points from each other using a filament rangefinder built into the optical level. After that, the corners of the plot are checked using the Egyptian triangle:

1. On a long thread, 12 equal segments are marked with knots.
2. The thread is pulled on the hairpins to form a triangle, the sides of which are 3, 4 and 5 segments.
3. The triangle is oriented by the angle between the sides with 3 and 4 line segments to the corner of the plot so that one of the sides is aligned with the border.
4. The deviation of the apex of the triangle from the marking line is measured along the perpendicular to the border of the plot.
5. The deviation is divided by the distance from the corner peg, according to the table of tangents, the angle that needs to be subtracted / added to 90 ° is determined.

Such a control check is the only way to make sure that the boundaries, and therefore the area of ​​the land plot, are determined correctly. Otherwise, stakeout should be done again.

Drawing up a center line

The procedure for conducting engineering geodesy is determined by the severity of the relief and the area of ​​the investigated area. In small areas (up to 10-12 are) with a visually flat surface, it is sufficient to measure the elevation along the boundaries and determine the general slope. If a large area is being investigated through which a beam or slope passes, the surface should be divided into squares with a side from 10 to 50 m.The steeper the relief formations, the smaller the mesh should be in this area.

To draw up a geodetic drawing, a plan is used, on which a plot of a certain shape is displayed, the coordinates of the boundary corner points and the distance between them, as well as the angles between the boundary lines are indicated. If necessary, the plan is covered with a square grid, intersections of lines are indicated according to the checkerboard scheme. Latin letters with a digital index, denoting each intersection, are taken out in a separate journal, where coordinates and elevation marks are subsequently put down. If the dimensions of the site are greater than the range of the level, several locations of the station are marked in advance on the plan, between which there is at least one common transfer point. Also, a conditional benchmark is marked on the plan, as a rule, at the point of the greatest elevation.

The points are taken out to nature according to the landmarks installed on the boundaries of the site with intervals corresponding to the grid step. An outside observer visually compares the location of the point with the two extreme landmarks in the forward and transverse directions. Small stakes or hairpins are installed in the locations of the points, any interference in the form of bumps or pits must be planned in advance.

After installing the level at the station and leveling the level, a sequential survey of each point is performed with the determination of the elevation. When surveying each point, the same massive shoe or thrust bearing is installed under the staff. Elevation data is recorded in the log, after which the station moves to one of the points with a distance of 3-4 grid steps and a survey is carried out from a different angle.

The results of 2-3 surveys from different points are compared with each other in order to determine the so-called discrepancy – a discrepancy between the readings. If the discrepancy exceeds 5 mm / 100 m, the survey is carried out again, with an allowable error, it is used to find the average values. The final elevation figures are recorded in the log, on the plan the arrows indicate the direction of the slopes. The results allow the designer to choose the optimal level of the ground level and foundation, as well as to accurately estimate the amount of earthwork.

Layout work

For stake out work, the grid is applied to the site plan at a frequency appropriate to the size of the building. The coordinate system axes should be parallel to the main building axes. The corners of the building, the mating points of the foundation parts and pile driving are selected as key points..

Layout work can be divided into marking and leveling. During the marking, the red lines of buildings and their boundary points are set out in nature. The simplest way to determine the position of neighbors is a direct linear intersection, in which the required distances from two stationary points are plotted, the position of which is known from the alignment basis. As a guide, you can use the corner boundary points of the site, pillars, wells, wells, etc. You can also determine the position of the point by setting the perpendicular aside from the baseline, for which you will need to stretch the Egyptian triangle, or use the methods of angular serifs using a laser goniometer.

Leveling accompanies the entire construction process from the underground part of the building to the roof. If the construction team does not have a surveyor, during the alignment work on the site, 2-3 permanent milestones are installed – poles hammered in such a way that they are not affected by seasonal ground fluctuations and weather factors. The zero point, determined by the project, is marked on the milestones during the initial leveling, then the hydrostatic level is controlled. Periodically, the marks on the posts need to be checked against each other..

Geodetic tracking is used in many construction operations:

• To level the bottom of trenches and ditches, stakes are driven in, on which the required level of backfilling or soil removal is marked.
• The installation of the formwork in a common horizontal plane is carried out along the upper edge, on which a leveling rail or target of a laser axis builder is installed.
• When installing reinforcement using geodetic methods, the thickness of the upper protective layer is determined.
• By leveling it is easy to assess the horizontalness of the masonry.
• When constructing frame structures, support rods help to maintain geometry with high accuracy.
• The presence of marking and leveling poles allows you to build glazing in a single horizontal level and along the front.
• Shooting with a level helps to coaxially position the elements of the rafter system and the frame of the curtain facade.

Geodesy methods are very diverse. It will be very useful for a developer who is seriously thinking about conducting geodetic research on his own, it will be very useful to study the Textbook of E. Klyushin for Universities “Engineering Geodesy”, where the basic methodology is set out in an accessible form, recommendations are given on keeping a journal and drawing up drawings.