Basic requirements for settlement observation of Shangluo observation mark

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　　Basic requirements for settlement observation of Shangluo observation mark

　　Based on work experience, during the construction phase, the frequency of observation should be higher. Generally, the observation period is determined by 3 days, 7 days, or 15 days, or by increasing the number of layers and loads. The specific observation period should depend on the foundation and loading during the construction process. When temporarily suspending work, observation should be conducted once during the suspension and once again during the resumption of work to check the changes in building settlement during the suspension period. This serves as a basis for determining whether the method and frequency of settlement observation should be adjusted after resuming work. After completion, the frequency of observation can be reduced, depending on the type of foundation soil and the magnitude of settlement rate. Generally, there are different periods such as one month, two months, three months, six months, and one year. Whether the settlement has entered a stable stage should be determined by the relationship curve between settlement amount and time. For key observation and scientific research projects, if the settlement in each of the three observation cycles does not exceed twice the measurement error, it can be considered as entering the stable stage. For settlement observation in general engineering, if the settlement rate is less than 0.01-0.04mm/d, it can be considered as entering the stable stage, and the specific value should be determined according to the compressibility of the foundation soil in each region. According to the prepared settlement measurement plan and the determined observation period, observation should be carried out in a timely manner after the observation point is stable. Generally, high-rise buildings have one or several underground structures, and observation should start from the foundation. Settlement observation points (temporary) should be buried at the designed positions on the longitudinal and transverse axes of the foundation (foundation edge). Observation can only be carried out after the temporary observation points are stable. The elevation values of the settlement observation points observed are the basis for comparison in future observations, and their accuracy requirements are very high. N2 level precision leveling instruments are generally used for measurement, and each observation point elevation should be observed twice during the same period. Comparing the observation results, if the height difference between the same observation points does not exceed ± 0.5mm, we can consider the observed data to be reliable. As the structure rises one level, temporary observation points are moved up one level and observed until+0.00, and then observation points are buried according to regulations (for ease of observation, observation points can be set at+500mm). Then, every layer of construction is retested until completion. When conducting settlement observations during the stages of pile driving, excavation of foundation pits, and continuous layering of the upper part after the completion of the foundation, it is necessary to record various factors that affect settlement changes and anomalies, such as the construction progress, increased load capacity, warehouse loading and unloading tonnage, building inclination cracks, etc., for each observation. After weekly observation, the observation data should be promptly organized to calculate the settlement amount, settlement difference, average settlement amount and settlement velocity of the observation point for the current period. If there is an abnormal change in the amount of change, the client should be immediately notified to provide a basis for taking preventive measures, and the number of observations should be appropriately increased. On the other hand, observations of different periods should follow the principle of "five determinations". The so-called "five determinations" refer to the benchmark points, base points, and settlement observation points on the observed object that are commonly used as the basis for settlement observation, and the points should be stable; The instruments and equipment used should be stable; Observers need to be stable; The environmental conditions during observation should be basically consistent; The observation route, mirror position, program, and method should be fixed. The above measures objectively ensure that the subjective uncertainty of observation errors is minimized as much as possible, so that the measured results have a unified tendency; Can ensure the comparability between each retest result and the observation result, making the observed settlement more accurate.

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