The soil under the foundation will often be compacted during foundation construction and then further loaded and compacted as the installation ages and MACHINES are run. So the finished installation is often very different from when the site was just a PLANT floor or an open field. Foundation NATURAL Frequency (Fn) can be determined by dropping a mass and recording the ground vibrations. 

Two types of tests can be done by Civil Engineers to determine the soils present at unimproved SITES:

1. The simplest is a penetration test where a pipe is driven into the ground and the number of blows and the given distance traveled are recorded. More blows equal harder, more compact soil. Core samples are retrieved and inspected to determine the type of soils present. The soil is analyzed and a chart of blows and soil type per depth is commonly supplied.
2. Another common and fairly simple test is a cross-hole measurement of the soils. Two holes are bored and a transducer is lowered into one and a seismometer in the other hole. By MEASURING the velocity of the waves passed between the holes, an estimate of the soil stiffness (elastic modulus) is obtained.

A Red Flag is when the soil is found to be very poor with high amount of fine clays and high water table. The foundation will tend to have a lower natural frequency and lower bearing capacity if the soil is poor. In these cases, Vibro/Dynamics advises a larger foundation and "foot print" with the softest isolators permissible to avoid settling and to improve isolator effectiveness. If the foundation is under-sized, the isolators will have reduced effectiveness regardless of their stiffness.

The soil under the foundation will often be compacted during foundation construction and then further loaded and compacted as the installation ages and machines are run. So the finished installation is often very different from when the site was just a plant floor or an open field. Foundation Natural Frequency (Fn) can be determined by dropping a mass and recording the ground vibrations. 

Two types of tests can be done by Civil Engineers to determine the soils present at unimproved sites:

A Red Flag is when the soil is found to be very poor with high amount of fine clays and high water table. The foundation will tend to have a lower natural frequency and lower bearing capacity if the soil is poor. In these cases, Vibro/Dynamics advises a larger foundation and "foot print" with the softest isolators permissible to avoid settling and to improve isolator effectiveness. If the foundation is under-sized, the isolators will have reduced effectiveness regardless of their stiffness.