An important parameter is the water pressure.

Everyone has at least once walked along a wet beach and noticed how the wet sand spreads out like jelly if you step on it a few times.

On the beach, this can be amusing, but on a construction site or during an earthquake, it is no joke. Houses and streets built on drained swampy land or on unconsolidated soil can settle in certain situations, making their use short-lived. This phenomenon is called soil liquefaction, and it can be countered by compacting the soil in places where new structures are being built.

Soil liquefaction occurs when the water in the ground, usually groundwater, cannot drain quickly enough. This leads to a significant increase in hydrostatic pressure in the soil, which in turn causes soil movement, and in many cases, the structures on it.

Even minor vibrations can cause this effect.

The earthquake that occurred in Christchurch (New Zealand) in 2011 showed how sandy soil filled with water can turn, so to speak, into mush. The earthquake itself, with a magnitude of 6.2, was quite weak, but its epicenter was within the city limits and relatively close to the surface. The resulting soil liquefaction made much of the city uninhabitable. The reason for this is that the center of Christchurch is located on sandy soil saturated with water, which formed from an alluvial fan—a cone-shaped deposit of sedimentary rocks created by three rivers.

March 10, 2011: Soil liquefaction in Christchurch after a powerful earthquake.

Such liquefaction can also occur in loamy or clay soils. This type of hazardous soil is found, for example, in the Rhine-Rhone valley. There are historical records of what happened in Visp (Valais, Switzerland) and its surroundings in 1855, when an earthquake of the same strength as in Christchurch occurred in this area. Fortunately, no one died, but the destruction of buildings was enormous. However, it seems no lessons were learned from this experience, as the areas destroyed then are now densely populated again.

Sloping areas, as well as areas located near rivers and lakes, can also slide on the liquefied soil layer and lead to the formation of large cracks or faults. This damages not only buildings, bridges, and roads but also water supply, gas supply, sewage, electricity, and telecommunications networks, and underwater tanks and wells can end up on the surface.

Christchurch 2011: The ground turns to mush.

Cone Penetration Tests.

To prevent the scenarios described above, the soil at construction sites must be thoroughly analyzed before work begins. The cone penetration test method was developed in the Netherlands in the late 1950s and has since been used as a cost-effective method of soil investigation. This method provides a good understanding of the soil structure and its various layers. It is used everywhere in fields where significant changes in soil bearing capacity may occur during drilling and construction work, etc.

The cone penetration test involves pushing a conical tip into the soil at a constant speed. A specially equipped truck is used to conduct the tests. The test results are illustrated by a graph showing the cone resistance depending on the depth of cone penetration. Along with soil resistance, the cone sensors used in the tests measure cone inclination, friction coefficient, soil temperature, electrical conductivity, and pore water pressure. The latter parameter is measured using a pressure transducer 21Y from KELLER.

Cone penetration test report and test cone.

 Piezo-resistive pressure transducer series 21Y.

The Y-line transducers have very low temperature error, achieved through an additional circuit with a temperature sensor that divides the temperature range into fields of 1.5 Kelvin (K) each. Compensation values are calculated for each temperature field, which, depending on the current temperature in each specific case, are fed into the analog signal path during operation. With this approach, it can be said that these transducers always operate at calibration temperature. High vertical integration, modular design, and programmable electronics allow for mass production tailored to individual orders.

Series 21Y also features exceptional resistance to electromagnetic fields. For example, in the case of conductive and radiated fields, the devices show values ten times lower than the limits set by the CE standard. The transducers are also extremely insensitive to external voltages between the housing and electrical connection, which is especially important when used with frequency converters. High insulation voltage of 300 V also makes this product ideal for use in the most adverse conditions.

Have questions or need advice on selecting equipment for your production? Contact the specialists at «Izmerkon» — we will help find the optimal solution for your needs.