Study On Desk Test Method For Coefficient Of Subgrade Reaction

This paper summarized the results of coefficient of subgrade reaction studies, and analyzed the test principles and test methods of coefficient of subgrade reaction. Judging from the existing research results and the engineering applications, the results of situ testing is reasonable and widely used. But the situ testing requires harsh conditions, complex equipment and procedures. In addition, it needs a high cost. The desk test tried to simulate the situ testing, but it lacks of the analysis of stress conditions, the results of the desk test needs to be amended before being used in engineering.This paper set about from this issue, and put forward a new method of desk test by analyzing the stress conditions, the differences between laboratory test and situ testing of the sample size, the changes in the timing characteristics of deformation strength, and the laboratory equipment. The first thing to do is to determine the depth influenced by the load plate’s stress. Stratify the soil body influenced by the load plate’s stress, using the laws of additional stress with depth to calculate the stress value of each layer of the soil body. Doing laboratory test with the use of consolidometer and creep apparatus, and add up all the settlements measured by each test, then we will get the final P-S curve, from which the coefficient of subgrade reaction can be calculated. Taking the Xiashu loess in Nanjing as the research object, to discuss the coefficient of subgrade reaction in different consistency status, and comparing these results and the recommended values in relevant specifications, and we found that the new method was feasible. Several research results were made by this paper as follows:(1) This paper introduced the coefficient of subgrade reaction test methods which commonly used in engineering. Including K30site load test, pressure test, flat dilatometer test, consolidation test, and triaxial test, and detailed introductions were given to the principle, instruments, operation steps and technical requirements of each test method;(2) This paper put forward a new method of laboratory test. Aiming at the disadvantages of the methods which now commonly used in engineering, we analyzed the sample size and the stress state in detail, and had made the testing schemes with the use of consolidometer and creep apparatus;(3) This paper described the engineering geology of the study area. Including the distribution, material composition, physical properties, water properties of the Xiashu loess, based on which we studied the mechanical property of the Xiashu loess. This paper laid the foundation for the test method of the coefficient of subgrade reaction;(4) This paper studied the coefficient of subgrade reaction of Xiashu loess in Nanjing with the new test method. Comparing these results and the recommended values in (Code for geotechnical investigations of urban rail transit)(GB50307-2012), we found that the new method was feasible. The results also provided a scientific basis for the construction of the study area;(5) The test data was analyzed, and the law was summarized. Then the formulas were given, with which the workload could be reduced to a large degree.