Key points for construction of observation points at Yuncheng observation markers

Description :

　　There is a saying in China that in order to become rich, one must first build roads. Road traffic has a great impact on urban economic development. The transportation networks in cities with excellent economic development in Guangdong are relatively complete. In order to better drive development, there are many planned and under construction highways in Guangdong. Today, we will introduce a highway currently under construction in Guangdong.

　　This expressway is called Luoxin Expressway, which is a fast track between Luoding in Yunfu and Xinyi in Maoming. The entire expressway is built according to the standard of a two-way four lane highway, with a designed speed of 100 kilometers per hour. The construction of this expressway will further improve the expressway network in northwest Guangdong. Luoxin Expressway has been under construction since 2016, and it is expected that the Luoding section will be completed and opened to traffic by the end of 2020.

　　The construction of the Luoxin Expressway is relatively difficult, with workers clearing roads and building bridges by water. The starting point of this expressway is located in Weidi Town, Luoding City, Yunfu, and ends in Hehua Town, Gaozhou, Maoming. Along the way, it will connect with the Luoyang Expressway and also intersect with the Baomao Expressway. At the endpoint, this expressway will connect with the Pubei Beiliu (Qingwan) Highway under construction in Guangxi, with a total length of about 130 kilometers.

　　The Luoxin Expressway is equipped with 3 service areas, 2 parking areas, and 11 toll stations along the entire route, with a total of 12 interchanges and 4 connecting lines. In addition, the construction of this expressway requires the construction of many tunnels and bridge projects, which are difficult to construct overall and involve a large amount of work. The estimated total investment for the construction of this expressway is about 15.56 billion yuan. Currently, the progress of this expressway is relatively smooth.

　　The period of settlement observation should reflect the settlement deformation law of buildings. Settlement observation of buildings (structures) has strict time constraints, especially observation must be carried out on time, otherwise the original data of settlement observation cannot be obtained, resulting in incomplete observation results. The retesting of other stages must be carried out regularly according to the progress of the project, without missing or supplementing the measurement, only in this way can accurate settlement conditions or patterns be obtained. It is generally believed that buildings built on sandy soil layers have mostly completed their settlement during construction, while buildings built on clay soil layers have only a partial settlement during construction, and therefore, the settlement period is variable. 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. Accuracy requirement editing

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