GB 50021-1994 Geotechnical Engineering Investigation Specification GB50021-94 GB50021-1994 Standard download decompression password: www.bzxz.net

1. Engineering inspection of foundation bearing capacity construction process (I) Inspection methods and standards for foundation construction process 1. "Geotechnical Engineering Investigation Code" (GB50021-94) Section 2 Load test
Article 9.2.1 Load test can be used to determine the bearing capacity and deformation characteristics of rock and soil. The flat plate load test is suitable for shallow foundations, and the spiral plate load test is suitable for deep foundations or soil layers below the groundwater level. Article 9.2.2 Load tests should be arranged at representative locations and foundation bottom elevations. Article 9.2.3 The technical requirements for load tests should comply with the following provisions: 1. Avoid disturbing the rock and soil when excavating the test surface, and lay a cushion layer of appropriate thickness under the pressure plate, and install the *test device as soon as possible.
2. Flat plate pressure plates should use circular pressure plates, and the area can be 0.25m2~0.5m2. In rock formations, the size of the pressure plate should be determined according to the density of joints and fissures. The area of ​​the spiral plate head can be 200cm2~500cm2, and a smaller head can be used for hard soil. Rigid pressure plates should be used for load tests in soil layers. 3. It is advisable to use heavy objects or hydraulic jacks to evenly load. The loading method can adopt the method of maintaining relative stability of load settlement by grades, the method of unstable settlement (fast method) and the method of equal settlement rate. The measurement accuracy should reach 1% of the maximum load. 4. The settlement of the pressure plate is measured using a dial indicator or an electric displacement meter. In addition to measuring the settlement of the pressure plate, the stratified settlement of soil layers at different depths under the pressure plate, the rise and fall of the soil surface around the pressure plate, and the lateral displacement of soil layers at different depths can be measured when necessary. 5. The test should be carried out to the destruction stage, and the test can be terminated when one of the following situations occurs: 1. The rock and soil around the pressure plate have obvious lateral extrusion, bulge or cracks. 2. The settlement develops approximately at a constant rate or accelerates over time within 24 hours. 3. The settlement exceeds 1/12 of the diameter or width of the pressure plate. 4. When the ultimate load is not reached, the maximum pressure shall reach 2.0 times the expected design pressure or exceed the first inflection point by at least three load levels. wwW.bzxz.Net
Article 9.2.4 The analysis of the load test results shall include the following: 1. Draw the pressure and settlement, and settlement and time curves. 2. Using the initial straight line segment of the pressure and settlement curve, calculate the deformation modulus according to the homogeneous isotropic semi-infinite elastic medium. 3. According to the characteristic points of the pressure and settlement, settlement and time curves or the deformation of the ground around the pressure plate, and the lateral displacement of the soil under the pressure plate, determine the temporary plastic load and ultimate load, and provide the foundation bearing capacity. 4. The spiral plate load test can also estimate the consolidation coefficient of the soil based on the settlement and time curve.
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