Due to the development of society, the great improvement of material civilization, and the maturity and perfection of architectural design and construction technology, at the same time, the contradiction between the decreasing land resources and population growth is becoming increasingly prominent, and there are more and more high-rise and super-high-rise buildings. The importance of settlement observation is increasingly obvious. According to the current national standards, the foundation of high-rise buildings, towering structures, important ancient buildings and continuous production facilities, power equipment foundation, landslide monitoring, etc. Settlement should be observed. Especially in the process of high-rise building construction, settlement observation is applied to strengthen the whole process monitoring, guide the reasonable construction process, prevent uneven settlement in the construction process, and provide detailed first-hand information for survey, design and construction departments in time to avoid damaging the main structure of the building or producing cracks that affect the use function of the structure due to settlement, resulting in huge economic losses.
This paper discusses the application of settlement observation in the construction of high-rise buildings.
First, the basic requirements of settlement observation
1, equipment and personnel quality requirements
According to the characteristics of high settlement observation accuracy, in order to accurately reflect the settlement of buildings and structures under constant load, it is generally stipulated that the measurement error should be less than110-1/20 of the deformation value. Therefore, it is required to use precision level (S 1 or S05 level) for settlement observation, and the level ruler is also affected by environment and temperature difference. In the absence of indium alloy level ruler, try to use the first section ruler when using general tower ruler.
In order to meet the requirements of personnel quality, we must accept professional study and skill training, be familiar with instrument operation procedures and measurement theory, adopt different observation methods and procedures according to different engineering characteristics and specific conditions, analyze the causes of problems in the implementation process, and correctly use error theory for adjustment calculation, so as to complete various observation tasks on time, quickly and accurately.
2. Requirements for observation time
The settlement observation of buildings and structures has strict time limit, especially the first observation must be carried out on time, otherwise the original data will not be obtained, but the whole observation is incomplete. Re-survey in other stages must be carried out regularly according to the progress of the project, and no missing or supplementary survey is allowed. Only in this way can we get an accurate settlement situation or law. Two adjacent time intervals are called an observation period. Generally, the settlement observation of high-rise buildings is based on the observation period of a certain period of time (such as 30 days) or the observation period according to the load of buildings. No matter what method is adopted, it must be carried out on time according to the observation period specified in the measurement plan.
3. Requirements for observation points
In order to accurately reflect the settlement of buildings and structures, settlement observation points should be buried in the position that can best reflect the settlement characteristics and is convenient for observation. Generally speaking, the settlement observation points set on buildings should be vertically and horizontally symmetrical, and the spacing between adjacent points is15-30m, which are evenly distributed around buildings. Usually there are special settlement observation points on architectural design drawings. Then, the buried settlement observation points should meet the observation requirements of each construction stage, especially considering that the observation points are destroyed or covered by wall or cylinder construction in the decoration stage, and the observation significance cannot be lost because of continuous observation.
4. Settlement observation should always follow the principle of "five determinations".
The so-called "five determinations", that is, the datum points, working datum points and settlement observation points on the observed object, are usually said to be stable; The instruments and equipment used shall be stable; Observers should be stable; The environmental conditions during observation are basically the same; The observation route, mirror position, procedures and methods should be fixed. The above measures objectively minimize the uncertainty of observation error, make the measured results have a unified trend, ensure that the results of each retest are more consistent with the results of the first observation, and make the observed settlement more realistic.
5, measurement requirements
The operation methods and observation procedures of instruments and equipment should be familiar with and correct. Before the first observation, the indicators of the instruments used should be tested and corrected, and the measurement unit should identify them if necessary. After continuous use for 3-6 months, recalibrate the instruments and equipment used. In the process of observation, operators should cooperate with each other, coordinate their work, be cautious and check layer by layer.
6, settlement observation accuracy requirements
According to the characteristics of the building and the requirements of the construction and design units, the settlement observation accuracy grade is selected. In the absence of special requirements, the second-class observation method can meet the requirements of settlement observation in the construction of general high-rise buildings and structures. In the construction of Hebei Transportation Training Center, we adopted the observation method of second-class leveling.
The requirements of various observation indicators are as follows:
(1) Round trip difference, echo difference or loop closure difference: △ h = ∑ a-∑ b ≤ l √ n-, indicating the number of stations. (or △ h = ∑ a-∑ b ≤ 1.0 √ L-, where l represents the distance of the observation route);
(2) Front and rear sight distance: ≤ 30m;
(3) Sight distance difference before and after: ≤1.0m;
(4) The cumulative difference of sight distance before and after is ≤ 3.0m; (5) The height difference tolerance of the settlement observation point relative to the back viewpoint: ≤1.0 mm;
(6) The accuracy of the level is not lower than N2 level.
7, settlement observation results and calculation requirements
The original data should be true and reliable, and the records and calculations should meet the requirements of construction survey specifications. The results should be sorted out and calculated according to the principles of correctness, preciseness, order, step-by-step inspection and effective results.
Second, the specific test procedures and steps
1, establish a leveling control network.
According to the characteristics of engineering plane layout and site environmental conditions, the survey scheme is formulated, and the leveling control points (or urban precision traverse points) provided by the construction unit establish the leveling control network according to the requirements of engineering survey scheme and the principle of network layout.
Requirements:
(1) Generally, more than three leveling points should be arranged around high-rise buildings, and the spacing between leveling points should not be greater than 100m.
(2) At least two leveling points can be seen from the back of the instrument erected anywhere in the field, and each leveling point in the field forms a closed figure for closed calibration.
(3) Benchmarks should be located outside the scope of building excavation, ground subsidence and vibration zone, and the buried depth of bench marks should meet the requirements of second-class level (greater than 1.5m). According to the engineering characteristics, a reasonable leveling control network is established, and the elevation of each leveling point is measured together with the reference point, and the adjustment calculation is carried out.
2. Establish a fixed observation route.
The location of the settlement observation point shall be determined by the leveling control network at the site according to the embedding requirements of the settlement observation point or the layout of the settlement observation point designed in the drawing. A fixed observation route shall be established between the control point and the settlement observation point, and marker posts shall be made at the instrument erection site and turning point to ensure that all observations follow a unified route.
3. Settlement observation
According to the engineering survey plan and the determined observation period, the first observation should be carried out in time after the observation point is firmly established. Generally, high-rise buildings have one or several underground structures. The first observation should start from the foundation, the settlement observation point (temporary) should be buried in the design position on the vertical and horizontal axis (foundation edge) of the foundation, and the first observation should be carried out after the temporary observation point is stable.
The elevation value of the settlement observation point observed for the first time is the basis for comparison in subsequent observation, and its accuracy is very high. Generally, N2 or N3 precision level is used for measurement. It is also required that the first elevation of each observation point should be determined after two observations in the same period.
With the increase of each floor of the structure, the temporary observation point will be moved to the next floor, and the observation will reach 10.00, and then the permanent observation point will be buried according to the regulations (for the convenience of observation, the permanent observation point can be located at 500mm). Then every layer of construction should be retested until it is completed.
4. After sorting and checking the observation records, carry out adjustment calculation to find out the elevation value of each observation point. So as to determine the settlement.
Settlement per period of an observation point: △ c = hh, I-HN, I- 1.
N represents the observation point, and I represents the number of observation periods (I = 1, 2, 3 ...) and H 1=H0 = H0.
Cumulative settlement: △ c = ∑△ c (n), where n represents the number of observation points.
5. Statistical summary
(1), according to the settlement calculated by adjustment in each observation period, make statistics and summary.
(2), draw the settlement curve of each observation point. Firstly, the coordinates of the settlement curve are established, the abscissa is the time coordinate, the upper part of the ordinate is the load value, and the lower part is the settlement of each settlement observation period. Draw the measured settlement in the observation period corresponding to each observation point in the statistical table in the coordinates, draw the corresponding load value in the coordinates, and connect the lines to get the settlement curve corresponding to the load value.
(3) According to the settlement statistics and settlement curve, the settlement trend of the building can be predicted, and the settlement of the building will be fed back to the relevant departments in time to guide the construction correctly. Especially on the foundation with large settlement, it is more important to observe the uneven settlement of important buildings. The settlement curve can also be used to calculate the inclination of buildings caused by uneven settlement of foundation. Q=│△Cm-△Cn│/Lmn, △Cm and △Cn are the total settlement of point M and point N respectively, and Lmn is the distance between point M and point N. By analyzing the settlement observation results, we can also find out the main factors affecting the settlement of similar buildings in the same area, which is of great benefit to guiding the construction unit to compile the construction organization design and correctly guide the construction, and also provides valuable first-hand information for the survey and design unit to design more perfect construction drawings.
6. Observe the precautions:
(1) shall be measured in strict accordance with the requirements of the measurement specification.
(2) It is best to use the same level for forward and backward observation.
(3) Every observation must be carried out according to a fixed observation route.
(4) Avoid direct sunlight during observation, and the observation environment is basically the same.
(5) Read again after the imaging is clear and stable.
(6) Observe at any time, check at any time, and observe with a routine.
(7) Before and after the rainy season, joint measurement should be carried out to check whether the elevation of leveling points has changed.
(8) Feedback the settlement observation results to relevant departments in time. When the continuous settlement of the building exceeds 65438±0mm every day (24h), the construction shall be stopped and emergency measures shall be taken jointly with relevant departments.
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