Numerical Simulation Analysis Of Ground Bearing Capacity Test Of The Hammer Impact Loading

There exists some disadvantages of immense scale equipment (with the back-forcing devices), time consuming resulting and expensive cost of the traditional ways of subgrade performance detection testing, including plate load test, CBR and Benkelman beam test. With the development of technology of detection method, great attention is gained to the new equipment like PFWD based on the principle of the response of falling weight impacting hammer to plate, which is heavy greatly improved the traditional ways of testing. However, with the inherent shortcomings of the devices like PFWD with such heavy plate at the bottom, which is not that portable and obtains only simple index, the more portable, convenient, efficient and detection results-reliable equipment "CASPOL" with more detecting indexes gets popular. The "CASPOL" detects the peak acceleration of falling hammer with acceleration sensor to in it, then converting it to the impacting value Ia to calculate the soil parameter of CBR, K30, cohesion c and internal friction angle Φ.At present, in the process of the verifying the detection precision, and optimizing the testing equipment, due to limited test conditions, influencing factors, such as different soil type, degree of compaction, different hammer weight, different hammer head shape, different hammer-soil contact area and so on, are time consuming and expensive. Yet the essence of the above problem is a kind of sensitivity analysis, a reasonable numerical analysis platform could provide an effective tool for such issue.The main contents of this paper include:1) the response model of clay and sandy soil under impacting load is established, utilizing the FEM software ABAQUS, and the applicability of the model is analyzed.2) the established response model has been used to calculate the tendency of CBR, K30, cohesion and internal friction angle, and the impact value of Ia, with the existing test results were compared and analyzed.3) by controlling the variables of the model, such as the different falling weight, falling height, different hammer head shape, different hammer-soil contact area, the sensitivity analysis is undertaken, after observing the ranging tendency of the impacting value Ia, the optimization of the testing equipment "CASPOL" is made for reference.Accodding to the above research, the applicability of the established model is verified; the results demonstrate that the obtained tendency of the impacting value Ia with the variables ranging is reliable, except that the value Ia of CBR and K30 is of low correlation; also, it can be possible to optimize Caspol by reducing the hammer weight, cutting down the falling height, changing the shape of the head of the hammer, or increasing in the hammer-soil contact area.