Application of microwave oven drying method in geotechnical test
For a long time, "alcohol burning" or "electric oven baking" have been used as soil drying methods in testing soil moisture content in geotechnical tests, which is also the traditional method in the code. However, with the rapid development of microwave drying machinery and equipment technology, the old experimental methods can not meet the rapid construction requirements. From 1996 to 1999, our unit was in the process of constructing the construction of the Fei Lai gorge water control project.
When we test the moisture content of filling soil in geotechnical test, we adopt microwave oven drying method, which has been questioned many times by Party A. However, compared with the traditional method, it is proved that the oven drying method of microwave oven is feasible. And the experimental process is simple, fast and accurate, so the microwave oven drying method is advocated to be popularized in geotechnical experiments.
Shortcomings of electric oven drying method: too long time, 68 hours less, 8-10 hours more, and affected by uneven soil type, the drying effect is inconsistent, especially when the heat of this method is transferred from the surface of soil to the interior, and when encountering soil containing a small amount of organic matter, the baking temperature must be less than 70 C, resulting in the package. Part of the moisture contained in small pellets can not be completely volatilized, which seriously affects the accuracy of the experimental data.
1. Microwave oven baking time is determined by comparing methods. At the same time, microwave oven and oven are used to bake. The moisture content of the oven is measured according to the standard operation, and the test results of the oven are recorded and calculated. The time of microwave oven drying is determined by using a shorter time (e.g. 812 minutes). When each drying time is finished, the weight of the microwave oven is weighed by an electronic scale, and the microwave oven is re-baked. This step is repeated. The baking time of each repeated time is adjusted to 3 minutes, and the weight changes before and after the weighing are changed twice.
Application of microwave oven drying method microwave oven drying method is extremely high accuracy. Because of the high frequency microwave radiation in the oven chamber, high temperature is generated inside the soil particles, heat is transferred from the inside to the outside, and water evaporation effect is excellent. In large-scale and large-area earthwork filling construction, it is necessary to divide into several technological processes according to the construction rules, and do a lot of geotechnical tests (including relative compactness of filling, parameters of soil mechanical properties, etc.) in the whole process, so as to provide the basis for quality inspection and evaluation and the start of the next working procedure.
If the traditional test method is adopted, the construction progress may be affected by the lag of the test work because of the long test time. In the relative compactness test of embankment (dam) filling, microwave oven baking time is very short, and the time is usually less than 30 minutes, which can solve the time problem in this test. The application of this test method can promote the continuous construction of each working procedure and speed up the construction progress. Therefore, it is necessary to popularize the application of microwave oven baking method in the construction of earthwork.
Disadvantage of alcohol combustion method: This method must reserve a large amount of 95% pure alcohol, the operation process is cumbersome, and it takes a lot of time, manpower and material resources. Moreover, there may be large errors in human error caused by different test results. At the same time, when the flame is extinguished, it will be found that the slurry formed by the adsorption of alcohol by soil sometimes can not complete combustion and volatilization. All of these make us wonder whether the data obtained from this method can accurately reflect the actual situation.