I need to estimate the settlement of 7 m by 14 m concrete footing supporting a Gas Insulated Switchgear (GIS) Plant due to vibration caused by installation of sheetpiles at 1.5 to 2 m from the footing edge. The footing is founded at 0.5 m depth on loose to medium dense sand (electric cone tip resistance between 4 to 5 MPa)about 5 m in thickness overlying medium dense to dense sand. The sheetpile will be installed using ICE vibratory hammer ICE-428.
I tried to use Prof Massarsch' Method outlined in a paper 'Settlements and damage caused by construction-induced vibrations'. Int Workshop Wave 2000, Bochum, 2000.
Can anybody or Prof Massarsch advise on how to calculate the 'number of equivalent cycles' for such a continuous vibratory hammer. I also have a problem on how to calculate the parameter 'f1' in the settlement formulae.
thank you for your question which I hope to answer as follows:
1. During vibratory driving, the number of vibration cycles will be very large. You should assume a value at, or above the curve for 100 cycles in Fig. 9.
2. The factor f1 gives the relationship between vertical and shear strain. The curves in Fig. 9 were determined based on the laboratory tests by Seed and Youd.
You can start with estimating the shear strain level due vertical oscillation (shear strain = vertical particle velocity divided by the shear wave velocity). Alternatively, you can make a prediction using say 1% shear strain..
If you wish to avoid settlements, you should prescibe a vibration level (particle velocity) which is lower than 0.01% shear strain.
You should verify the settlement estimate by making vibration measurements.