Dongguan Taiwanese Club Building is planned to be located in the south of Dongguan, with convenient transportation, near the intersection of Dongguan Avenue and Hongfu Road in the south and Dongguan Avenue in the north. The main building has a frame-tube structure with 68 floors above ground, and the podium has a frame structure with 6- 10 floors above ground. There are three underground floors with a depth of about 15m, which will become a landmark building in Dongguan. The site is near the Huang Qishan fault.
2. Layout of investigation points and selection of investigation methods
According to the characteristics of this project as a super high-rise building and foundation pit level, after accepting the task, we have a detailed understanding of the design intention. Manual digging piles are planned for the main building, and prestressed pipe piles are planned for the podium. At the same time, we have collected geological data of nearby sites. According to the field survey and the survey data of the adjacent Guangying Mansion, there is a fault zone in the site, which runs northeast, basically consistent with the length direction of the site, passing through the main building area, and at the same time there is a sand layer with strong water permeability locally. According to the architectural features, design intent and preliminary geological data, it is determined that the exploration points are arranged with the main building as the center, the hole spacing is 7- 14m, and they are arranged along the axis, and the drilling spacing between the podium and the basement is 20-24m. Emphasis should be placed on the strike, distribution, scale and stability of the site fault zone, the choice of foundation bearing layer, the influence of groundwater on foundation pit excavation and manual digging pile construction, and the countermeasures to solve the problems. In view of the above survey points, in addition to routine drilling and coring, standard penetration and sampling for indoor routine tests, radon survey is used to evaluate the activity of fault zone, the comprehensive methods of sampling indoor test and in-situ test are used to evaluate the strength of fault zone, and indoor test and field pumping are used to evaluate groundwater.
3. Data processing and comprehensive research.
3. 1 About the fault zone in the site
In order to understand the distribution and activity of the fault zone in this site, the electrostatic A-card radon measurement method was used, and 4 survey lines were arranged, with a total of 68 measuring points. Through mathematical statistics analysis, it is concluded that the background value of the site is 17Bq/l, the lower limit of radon anomaly is 5 1Bq/l, and the average value of F 1 radon anomaly is only 8 1bq. The highest anomaly value is 1 12Bq/l, and the ratio with the lower anomaly limit is only 1.6 times. The average anomaly value of F2 radon is 66Bq/l, the highest anomaly value is 92Bq/l, and the ratio with the lower anomaly limit is 1.3 times. According to the following evaluation principles: anomalies with high abnormal values greater than 8 times the lower limit of anomalies. If the average value of high anomaly is in the range of 5~8 times of the lower limit value of anomaly, it can be considered that the fault has been strongly active since the recent geological age, but there are still strong active faults; If the average value of high anomaly is in the range of 3~5 times of the lower limit value of anomaly, it can be considered that the fault has been active since the recent geological age, but the activity is weak or not obvious now; Faults with high anomaly average value within the range of 1~3 times the lower limit of anomaly can be considered as faults that have basically stopped active at present. The result of this radon survey is that the ratio of the highest anomaly value of F 1 and F2 to the lower anomaly value is only 1.6 and 1.3 times. Therefore, it can be considered that the two faults in this site are all Holocene inactive faults and will not pose a threat to the safety of buildings. Through thermoluminescence dating of structural rocks and overlying materials of F 1 and F2, it can also be concluded that F 1 and F2 belong to non-Holocene active faults.
3.2 About the underground aquifer
In order to know the water content of rock and soil layers in the site, the permeability coefficient of soft water-bearing soil layer is determined by indoor test, and the permeability coefficient of main aquifer is obtained by combining indoor test and field pumping test. The results are shown in the following table.
Table of permeability coefficient of main aquifers Unit: m/d
LayerNo。 Name of geotechnical laboratory test results Recommended values of pumping test results report
2-4 medium (fine) sand 0.462 1.8 1.8
5-2 strongly weathered rock zone 0.096 2.0 2.0
F 1 structural breccia _ 0. 196* 0.05
Note "*" is the result of mixed pumping of strongly weathered rock zone and structural breccia.
For medium (fine) sand layer, considering that indoor samples are only taken locally, the field pumping test is more representative as a medium (fine) sand aquifer, so the recommended value is the pumping test value. Because the upper part of the strongly weathered rock belt is generally soil-like, and the lower part is gravel-like, only soil samples can be collected indoors, and the test results are few, while the pumping test results represent the whole strongly weathered rock belt, so the recommended value is the pumping test value. It is difficult to sample structural breccia, and it is also difficult to separate it from strongly weathered rocks by pumping in the field. Therefore, the pumping test results represent the comprehensive results of strongly weathered rocks and structural breccia. The permeability coefficient of F 1 calculated by weighted average method is 0.05m/d, which is consistent with the lithologic observation of structural breccia close to strongly weathered soil. The lithology of F2 is mylonite breccia, and its permeability is weaker than F 1. The indoor test result of strongly weathered rock sample with similar soil is 0.096m/d, which is not much different from the calculation result of 0.05 m/d for structural rock.
According to the permeability coefficient of each rock and soil layer, the total water inflow of foundation pit is 1200m3/d, and the water inflow of single well of manual digging pile (Ф 2000) is 400 m3/d when the foundation pit is not constructed, and it will drop to 42m3/d after the foundation pit is constructed (the groundwater has dropped below the foundation pit bottom).
4. Conclusion
4. 1 There are two fault zones, F 1 and F2, which are non-Holocene active faults and will not pose a threat to the safety of the Taiwan Business Hall building.
4.2 The two main aquifers in this site are medium (fine) sand and strongly weathered rock zone respectively, and their permeability grades are both permeability. The fault zone has weak water permeability and can be regarded as a non-water conducting structure.
5. Some understanding
5. 1 It is necessary and effective to carry out geotechnical engineering investigation by various means, especially for complex sites and important buildings.
5.2 The processing of survey data should be based on mathematical statistics, and more practical geotechnical engineering parameters can be obtained through comprehensive evaluation.
5.3 In the process of geotechnical engineering investigation, the selection of bearing stratum and the determination of its strength parameters are also important reflections of the investigation results, which are not described in this paper due to space limitations.
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