(3) Using dry one-way measurement, Ruo Qianwen to discuss Zhao Jixian, East China Institute of Geology, Jiangxi. Pro 344000 This article discusses several substantive questions about the application of satellite positioning technology in engineering surveys, and proposes practical measures and methods for reference.
2 Reference point Q 08 The control network has a very high relative positioning accuracy. The results belong to the Jia 84 global agreement geocentric coordinate system and the engineering control network belongs to a country or local concentric coordinate system for the conversion of positioning results. Usually when designing a network point, it should coincide with a certain number of original ground control points. The coincidence point is the reference point for the adjustment adjustment of the dead net.
Then, according to the scale and direction of the point under this coordinate, the positive 8 is converted into a national or local coordinate system through adjustment. Both theory and practice are proven. The accuracy of the reference point directly affects the accuracy of the 5-net. Therefore, it is necessary to discuss the accuracy and density of the reference point.
At present, China has built 15 two-level extension control points with high accuracy and strong reliability. But the point density is small. Can't actually use it yet. Most of the existing control points in China were observed in various periods before the 1980s. Due to the influence of the technical conditions and concepts of the instruments and equipment at that time, some control points had low accuracy and could not meet the accuracy requirements of the reference point.
At the same time, the control network has been tested for a long time. Due to the influence of natural and human factors, a considerable part of the points have changed. It is often difficult to judge whether the points have changed by feeling. Therefore, before the formal constraint adjustment. Must choose the degree. There are usually the following two methods for inspection and screening. Then use different reference points to carry out accuracy indexes such as mid-bit error and relative weakest edge relative error of various schemes. The necessary inspection and screening of the reference point can select the most ideal reference point 22 and the closed coordinate of the route, and select a number of 08 baseline vectors connected between the two reference points. Calculate the coordinate closure difference of this attached route. If the difference exceeds the limit value 44 calculated according to the accuracy of the observing accuracy and the reference point coordinates, it can be considered that the reference point is poor or the point is widely sold into the corresponding level. The specified accuracy, input = ±, + 5irr`D, the distance between the two reference points of L; m the denominator of the relative accuracy of the two reference points. 0 The accuracy of the dead net is related to the accuracy of the reference point. At the same time, the density of the reference point is also an important factor, and the density of the reference point is related to the teaching work.
Practice seven 1 call. ; 1 Find a system call; the punctual distance should be controlled, 6 is appropriate from 1 or so, in difficult areas or special shape control network, such as highway workers do not have a band; 1 call. Call 1; 1; the distance of the point can be controlled within 1 catch 1. Practice has proved that the observation accuracy of the Zheng 3 network is generally higher than that of the reference point. In order to reduce the influence of the scale, a position reference can be used to expand the engineering control network. Position reference.
The choice of 318 network points; the control network has the characteristics of high accuracy and the flexibility of the distance between the flexible points is not constrained. Have a better surrounding environment. To prevent or reduce multipath errors, the selection of dots does not require too much visibility from point to point. But the outlets must be in sight with the satellites in the sky. Generally requires a broad view. Obstacles with a height of more than 10 degrees. Simultaneously. The point selection should also take into account the surrounding environment and observation conditions, avoid or stay away from high-power radio transmission sources and high-voltage transmission lines, etc., to avoid the interference of the weekly magnetic field on the information of 8 satellites. The multipath error is one of the main errors of the 18 measurement, which is similar to the ground reflection error of the microwave rangefinder. It is affected by the secondary reflection signal. This kind of error is called! Attachment 1. It is difficult to make corrections too easily. It is necessary to avoid large areas of water, large metal objects and various reflective objects when selecting samples at the outlets.
To reduce the impact of multipath errors.
Program control network points often have many special requirements according to the needs of the project. For example, the primary network of Qinshan Nuclear Power Station. It is required that the nuclear island in the main plant area is not less than one control point. There are no less than two points on both sides of the through tunnel, and each point can meet at least two points. The selection of E-site control network points should fully consider the needs of the project, but do not emphasize the length of the side. Angle size and shape strength. It is convenient to construct and safe. stable. Convenient for long-term storage and use.
The phase center error and centering error of 418 antenna, the satellite signal received by the antenna is the result of the overall effect of the antenna. It is difficult to accurately determine which point on the antenna corresponds to the obtained observation, and it can only correspond to a point equivalently. Usually called the phase center. Experimental proof. The phase center varies with the direction of the receiving satellite. During operation, only one center can be aligned with the measurement mark. This center is usually called the geometric center of the antenna. The geometric center is determined by the manufacturer after a variety of tests on the antenna. The error of the positioning center has a greater impact on the precise positioning, especially the relative positioning of short distances. The measurement of the baseline edge of 1 or shorter is the main source of error. Engineering measurement, especially precision engineering measurement, has a short distance between points. The influence of the phase center error of the antenna 8 is more prominent, and it is also the main obstacle to improve the precision positioning. In order to weaken the influence of the phase center error, the operation method of the exchange antenna is generally used, and the specific method is to measure at the same time interval of two days. And swap the antenna and receiver. Due to the distribution of satellites and their operation in orbit, two adjacent days are at the same time. Accurately, it is 4 minutes ahead of the first day. In such a time period. The antenna phase center drift is the same and gives the direction sign. Orient the receiver antenna during operation. This can also reduce the influence of the phase center error. After the phase center is determined, it must be projected onto the ground point marker. That is centered. The centering error is controlled within ± 1.
56. Selection of the adjustment scheme of Qiaowang In order to make the results after adjustment have a better loss than the original old network, the original old network control points should be analyzed and demonstrated. If the original control 1 network has high accuracy, it can be used more. Old point. If the accuracy is not high, first perform pure 8 network adjustment according to the ground position reference and orientation. That is, unconstrained flat shame and then take the point where the coordinate difference of the coincidence point is relatively small to perform the Helmert transformation at first. In this way, the conversion parameters obtained by dimension-constrained adjustment are reliable.
6 Conclusion 13 The network has a high relative accuracy, but the result is the Jia 384 coordinate system, which must be converted to the national or local coordinate system before it can be used in engineering surveys. Therefore, in order to ensure that the datum point of the 8 network is sufficient Precision. At the same time, the reference point of the net should maintain a constant density or necessary conversion conditions.
Ignore. The selection of clever dots should not only consider a good satellite window to meet the needs of observation, but also have a better surrounding environment to prevent or reduce the impact of multipath errors. At the same time, it is necessary to meet the needs of the project and the ease of use of the field.
The phase center error of the 338 antenna is positive. 8 Under engineering surveys, turn to page 59. The distance m m leak survey cross-hole imaging borehole. (3) The imaging section is about 5 miles away from the baseline of the dam. Drill a hole for myou 3 with a nearly vertical gauge baseline and image the profile. From the wave velocity image, it is considered that the wave velocity value is greater than 23 and the dense contour area is a relatively complete bedrock area, the lower part of 1.3; the local low velocity 1.5 228 contour is closed, which is a small cave or karst development area, and the longitudinal wave in wave velocity image 2 The relatively low velocity value is between 1.23.88, which is consistent with the limestone revealed by the borehole geological data. Dolomite marble and other soluble rock distribution area.
A low-velocity closed area at the elevation of 27.361 1523 near You 1 hole in wave velocity image 1 was inferred as a karst cave. The upper part is 37.36 with an elevation of 2 holes, and 30 with an elevation of 1 to 4 holes is a ditch. Dissolved tank or broken zone affected area. Wave velocity image 3 has a large-scale karst cave development between the elevation of 3034 and 71 in the middle, and a karst trench in the shallow part of the middle. The dissolving tank communicates with the deep living hole in layers. This area is a multi-layer cave area for grouting holes. Located near the North-North East fault zone. Affected by the broken zone. Soluble rocks are extremely developed in this zone, which is the main cause of reservoir leakage. thus. The caves exposed around You 1 hole and the caves in the middle of You 6 and You 3 are the main leakage channels. The direction of its distribution should be perpendicular to the profile, that is, the direction near the vertical base line. Although there are local small caves in the deep part, they are not connected.
In addition, the elevation of wave velocity image 1 is 37.3, and the elevation of 2 is 35. The elevation of 3 is added to the upper part because there is no shortage of 7 in the well and the receiving detector cannot be coupled. As a result, there is no received data in this area, which is not explained in the non-imaging area.
4 conclusions can currently be applied to engineering geological survey, the technology mainly includes seismic electromagnetic waves. Resistivity imaging. But they are still in the stage of research and exploration. Cross-well seismic wave imaging is a new type of geophysical exploration technology. Applied to the leakage survey of Luowutian Reservoir in Shenzhen. The location of the main leakage channel and leakage point was determined. Very good results have been achieved.
The results of the survey can provide a scientific basis for future leakage control and reservoir expansion. But no geophysical method can be omnipotent. We believe that the success of this work and the ground electricity method and geology that we invested in earlier. The comprehensive application of drilling data is inseparable. This article highlights seismic waves and imaging technology from only one side. It is a role for the future of engineering geophysical prospecting new technologies and methods for water conservancy projects and engineering surveys. , Get the guidance and help of Zhao Shuyin, chief engineer of Shenzhen Geological Bureau and Ren Shukao, chief engineer of Beijing Hydropower Geophysical Prospecting Institute 1 and Dr. Pei Zhenglin, and we thank you!
1 Yang Wencai. Geophysical inversion and seismic tomography. Beijing Geological Publishing House. 1 Na 2 Yang Wencai and so on. New algorithm of tomography and its application in engineering inspection.
3 Cao Junxing, etc. Estimation of tomographic resolution when seismic waves travel across holes.
4 Zhao Yonggui and so on. Earthquake 71 and its geological interpretation. Geological Science! 1997.3215 Pei Zhenglin et al. Application study on seismic traveltime tomography between karst collapse wells.
Hefei Anhui Science and Technology Press. Make the mistake of applying 99 on page 56; Is 1 to weaken the effect of this error.
In addition to the directional placement of the antenna each time it is operated, the antenna-switching method is also used, Yuan Gang. Selection of datum points for 16 control network planes in urban areas of Ganzhou City.
Yucheng and so on. 8 Application in the construction of pumped storage power stations. Surveying and Mapping Pan Baoyu. Discussion on the accuracy and configuration of benchmark points of high-grade highway network.
Surveying and Mapping, foot 18 Xia Linyuan. 15 is used for engineering deformation monitoring if thousands of questions analysis. Surveying and Mapping Fu Wenxiang et al. Discussion on the Influence of Different Encryption Methods of the Network on Point Precision. Surveying and Mapping Bulletin. 1999.3 Jiangxi Surveying and Mapping, 1998, 3
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