The main purpose of construction survey is to mark the position, shape, size and elevation of the building on the design drawings and documents with sufficient accuracy on site; Used to guide the construction and check the finished shape of the building; Both the calibration of building position and the detection of completed shape are based on the construction control network. Therefore, before the construction lofting, it is necessary to establish the construction control network with the corresponding elevation of the main building of the project.
1. Control network layout
Firstly, according to the information provided, the topographic map of the hydropower engineering survey area (scale: 1/2000) is obtained. Through the field survey of the original triangle points, traverse points and leveling points, the natural geographical conditions, traffic and people's feelings of the dam area are understood, and then the technical design of the first-level plane control network is carried out. Select the triangle points with relatively well-preserved and stable buried stones, and calculate the geodetic coordinates (and construction coordinates) of the control points from the azimuth angle; Layout of primary plane control network points. The control network scheme is determined. The net pier adopts the common steel standard of 1.2 meters high, and the foundation is dug into the bedrock. A steel plate with a central hole diameter of 16mm is installed at the top as an instrument platform for forced centering. After all the burying work is completed, field observation will be carried out after a period of time.
2. Control network measurement
Due to the high mountains and dense forests and poor visibility conditions in the survey area of general water conservancy projects, it is impossible to form attached or closed figures by conventional methods (triangulation or traverse network). Therefore, GPS is used to deploy and survey the network through satellite positioning. According to the surveying and mapping area and geographical conditions of the survey area, the point-connected primary network is arranged according to the requirements of secondary accuracy (equivalent to 8-second traverse), and GPS observation is carried out by static relative positioning method. The obtained measurement results all meet the requirements of global positioning system (GPS) measurement specification. When choosing a starting point, you should not choose a control edge that is too short. Controlling the long side with the short side will affect the accuracy of GPS fixation. In addition, if the number of known points is too small, it will affect the transformation accuracy in coordinate system transformation, and there is also a lack of inspection conditions between known points. Scientific network layout method should be divided into two levels. Firstly, three points are selected at the edge of the survey area, and a synchronization ring is measured by three GPS receivers (the synchronization ring can be observed statically for 2 hours to improve the calculation accuracy of its baseline vector), and this synchronization is regarded as an E-level network (or a first-level network), and then three points in the synchronization ring are regarded as the survey area.
When the known points are laid on the secondary network, not only the accuracy of the known points is high and uniform, but also the accuracy of the secondary network is greatly improved, which not only improves the coordinate system conversion accuracy, but also increases the necessary checking times between the known points.
Second, the construction lofting
In order to ensure the accuracy of lofting data, concrete construction lofting adopts the method of separating indoor and outdoor work and combining template lofting with template acceptance. People in the industry should draw sample plots according to design drawings, which should be carefully checked, and drawings and sample plots that have not been checked and approved shall not be set out. Site lofting adopts total station coordinate lofting or polar coordinate lofting. In the process of template lofting, strict quality control is carried out for the whole process, including that the observers, lofting personnel, demanders and inspectors are clear about their respective responsibilities, and all lofting processes have verification systems. During the inspection of the acceptance stage of the formwork, the formwork worker must check and accept the position of the formwork according to the lofting point before pouring concrete, and adjust the ones that do not meet the allowable error requirements of the formwork to meet the requirements of technical specifications.
Due to the progress of measurement technology, the digitalization of instruments and equipment; In the whole project construction, the layout of the building plane position is mainly carried out by polar coordinate method with high precision, and the stable total station is used for construction lofting. The precision index of the instrument is ranging: 2mm+2ppm, and measuring angle is 2? ; The instrument is sent to the relevant technical appraisal unit for calibration once a year.
Is it guaranteed to check the angle difference? 5? About, let the maximum value be m? =? 10? ; Instrument alignment error m =? 1mm； The calibration error of lofting point leads to M mark =? 5 mm. The setting-out requires high accuracy and simple operation, which reduces the labor intensity of workers and the occurrence of gross errors, can meet the needs of faster construction progress, and ensures the accuracy and speed of setting-out.
When setting out, the corner line of the building adopts the setting-out control point line of 0.5m outside the sideline and the setting-out control point line of plates, beams, columns and small walls according to the actual situation. At the same time, after calibrating the sample points, measure the actual sideline pile number after the last concrete pouring, and make the setting-out and detection records as the control basis for the next construction and the original data of the completed shape measurement data.
In the process of lofting, sometimes some pier samples are lofting by the rear intersection method, which is strictly in accordance with the requirements of the specification to ensure the accuracy required by the specification.
Three. Acceptance measurement
1. Acceptance measurement of quantities
The original topographic line of the construction area is one of the baselines for calculating the excavation amount, and shall be based on the original topographic map provided by the owner or the actually measured topographic map approved by the survey supervisor. Before the project starts, check the original topographic map provided by the owner, measure several sections or scattered points on the spot, and compare the indoor exhibition points on the map. The disputed part shall be reported to the owner or survey supervision engineer in writing in time, and the supplementary survey scheme shall be solved through consultation, and the topographic map of the measured part shall be submitted to the survey supervision engineer for approval. If the owner does not provide the original topographic map, the original topographic map must be surveyed before the project starts and submitted to the survey supervision engineer for signature and approval. The acceptance measurement of engineering quantity is generally carried out once a month. In case of independent dangerous rock blasting, deep hole cleaning and backfilling, the engineering quantity shall be measured and calculated in time and reported to the supervisor for signature. The quantities of earthwork excavation and backfilling shall be released separately during acceptance and measurement. The quantity of earthwork excavation should be divided into two layers: soil and stone, and the quantity of stones with different lithology. Earthwork backfill should distinguish the volume of various backfill materials. Generally, topographic map method or section method is used for engineering quantity acceptance measurement. The actual topographic map of the acceptance site should be surveyed by total station or ground photography, and the scale of topographic map should generally be within the range of1:200 ~1:1000, and the surveying and mapping range is 3m ~ 10m outside the engineering site boundary. When measuring the cross section with theodolite or total station, the sideline should also be 3m ~ 10m, and the cross section spacing should be within 5m ~ 20m according to the situation. Generally, the density of measuring points is less than 3cm on the map, and the measuring points are encrypted at the terrain changes to correctly reflect the terrain shape. When calculating the engineering quantity, the position and spacing of section lines on topographic map should be agreed with the survey supervision engineer, and the unified original topographic map and design section lines should be used.
2. Concrete pouring formwork inspection and acceptance measurement
In general, surveyors only participate in the acceptance survey of curves, surfaces and variable slopes. Generally, axis points and sideline points of survey lofting are used for inspection. Check whether the distance from the template surface to the axis or edge is consistent with the theoretical value (or the value indicated in the measurement submission). The inspection method can be steel ruler or total station, and the maximum deviation of measurement is allowed. 5 mm. Check the verticality of the formwork with total station or hanging vertical line. 3m high template at least check the upper, middle and lower three points. Is the deviation of steel rule allowed? 5 mm. Draw the inspection acceptance sheet and indicate the acceptance value. After signing the acceptance form, submit it to the quality inspector or the builder.
3. Building shape completion acceptance measurement
Generally speaking, it is necessary to measure the human body in the flow area. It mainly includes: spillway, overflow surface of discharge dam section, water inlet of unit, spiral cone tube, apron, lock wall, lock chamber bottom plate, etc. The profile method can be used to measure the shape, and a profiler or a prism-free total station can be installed on the profile to measure the three-dimensional coordinates of the profile points. Cross-sectional points on the horizontal plane can also be measured with a level, and the distance between points can be measured with a steel ruler. The density of measuring points is determined according to the physical characteristics of the building: the horizontal section or vertical section can be sparse,1m ~ 5m; Curves and slopes should be dense, 0.5m ~1m. The design line should be drawn on the completed body contour, and the measured points and their deviation values should be marked. The design values, measured values and deviation values of measuring points can also be listed in chart form. The final acceptance measurement of the hole shape can be summarized into a chart according to the measured values from the lofting point to the building sideline when lofting layer by layer. The survey data of physical completion acceptance shall be filed and saved, and submitted to the survey supervision engineer and the completion acceptance management department.
4. Metal structure and mechanical and electrical equipment installation acceptance measurement
The installation acceptance measurement of metal structures and electromechanical equipment mainly refers to the main rail, counter rail and side rail of arc doors, miter doors and plane doors, the lining of hydro-generator seat rings, pressure pipes, doors, tower cranes and bridge cranes. After installation and positioning, surveyors need to use the corresponding measuring instruments that meet the accuracy requirements and carry out acceptance measurement on the installation reference point. Gantry crane, tower crane and bridge crane (crown block) mainly check and accept the levelness, parallelism and spacing between two tracks. The main rail and auxiliary rail of radial gate, miter gate and plane gate mainly check and accept the levelness of sill, verticality of gate rail and deviation from installation axis. Hydro-generator seat ring and lining mainly check the acceptance levelness and the deviation from the center line of the unit, which requires high relative levelness accuracy, but generally? 0.2mm, so the steel ruler used should be inspected, with ball heads at the bottom and blisters at the top. Check and accept the deviation of each interface center of pressure pipeline relative to the installation axis and elevation base point. What is the measurement deviation? 10mm. Arrange the measurement data of completion acceptance and draw necessary charts. Submitted to the survey supervision engineer and the completion acceptance management department.