New method for determining soil adfreezing strength patented by SPbGASU
Andrey Boyarintsev
A new method for determining the soil adfreezing strength has been patented by SPbGASU. Andrey Boyarintsev, a postgraduate student at the Department of Geotechnics, told us where this invention can be applied:
– Adfreezing strength is a mechanical characteristic that describes the interaction of soil with the foundations. It has to be determined for construction in the Arctic zone. The pile sinks into the ground with a temperature below zero degrees Celsius and it freezes to the ground. The force required to tear it off the ground is the adfreezing strength. This is the force that keeps all buildings in permafrost areas. By determining the adfreezing strength, we also determine the load-bearing capacity of the pile.
– Where else can your invention be used?
– When determining frost heaving forces. In winter, water in the upper layers of soil turns into ice and the soil increases in volume. Freezing to the foundation, the soil rises with it or slips through it. In the second case, it means that the ground peels away from the foundation or, in other words, that adfreeze forces are broken. The adfreezing strength affects the frost heave. Thus, understanding precise figures of the soil adfreezing strength and the foundation will make it possible to determine the exact value of the frost heave force and design the most efficient foundation.
It is worth noting that in St. Petersburg the ground freezes to 1.2 metres during cold winters. And the frost heaving forces occurring in such conditions can damage light structures: landscaping elements, single-storey buildings, overpasses and others. Therefore, determining frost heaving forces is utterly important for our city.
1. Schematic diagram of the experiment
2. Diagram of the experiment in process
The patent certificate
– What makes your invention different from other solutions?
– There are several methods for determining the soil adfreezing strength. The method I proposed is more economical as it does not require a lot of special equipment and operations. A ring made of the same material as the pile is used to model the foundation. The ring is placed on a hollow support that prevents it from moving when the pressure is applied. Soil is placed inside, which can be moved. This technique is good because it can be repeated quickly and easily.
– How accurate are the calculations?
– I compared the same material using the method approved by the state standard (‘GOST’) and my own one. The values are identical. Moreover, the scatter of values within one experiment under the GOST methodology is higher than mine. It means that my method is more accurate.
– Please tell us how you worked on the invention.
– The idea came to me when I was conducting experiments during my Master's degree studies. I had been thinking a lot about the dimensions of the foundation model, the trough, their ratio and whether these dimensions affect the test results, and decided to check this experimentally. But when I made up my work plan, I realized I wouldn't have enough time to complete the experiments during my Master's course. That's when I thought: is this model of the pile necessary at all, can we do without it?
– Who was helping you in your work?
– I formulated the idea myself. But I got a lot of help while discussing all the issues mentioned earlier with the staff of the Geotechnics Department: other postgraduate students and lecturers. Talking to them, I found the 'strings' I had to pull to arrive at this idea.
– Could you tell about your future plans?
– I am planning to write methodological guidelines and propose the invention for implementation in geotechnical engineering laboratories of Saint Petersburg.
Text: Tatyana Petrova
Photos: Andrey Boyarintsev, Sergey Klishis
✔ Find out more about the Department of Geotechnics at SPbGASU