Determination of soil stiffness levels

An apparatus which propels itself on a soil surface for determination of soil stiffness levels of a soil area having a vibration unit being part of a so-called vibration plate, which can be moved into contact with the soil surface, whereas the vibration unit (5) can preferably also be used for soil compaction, comprising:

• a vibration plate having a force production unit by means of which a periodic first excitation force and a second excitation force, which is not the same as the first and which act on the vibration unit (5), can be produced, whereas
• the first excitation force can be adjusted by means of the force production unit in such a way that a maximum oscillation amplitude of the first excitation force can be directed at right angles against the soil surface, whereas the period of the first excitation force can be adjusted in such a way that resonance of an oscillating system formed from the vibration unit and a predetermined soil subarea of the soil area can be achieved, and the vibration unit (5) never loses contact with the soil subarea of the soil area under the influence of the first excitation force, and whereas
• the second excitation frequency can be adjusted by means of the force production unit in such a way that the maximum oscillation amplitude of the second excitation force can be directed obliquely with respect to the soil surface and the excitation force is sufficiently large than the vibration unit loses soil contact in a jumping manner;
• a measuring device with which oscillation data of the excitation force as well as oscillation data of the vibration unit can be determined as an oscillation response;
• and
• an evaluation unit by means of which at least one absolute value of a soil stiffness of a predetermined soil subarea can be determined by means of the first excitation force from the oscillation data of the excitation force and the data of an oscillation response of the vibration unit (5), whereas a plurality of relative values of soil stiffnesses of predetermined soil subareas of the soil area can be determined by means of the second excitation force.

A method for determination of soil stiffness levels of a soil area, in which case one and the same self-propelled apparatus (1) is used not only to determine the absolute soil stiffness level (kB) when located on at least one predetermined soil subarea (3) of the soil area but also to determine a plurality of relative soil stiffness levels(s) while crossing over a plurality of soil subareas of the soil area, comprising:

• moving a vibration unit (5) into a predetermined soil subarea (3), in order to determine an absolute soil stiffness level (kB), a first time-variable excitation force is applied by means of the vibration unit (5) in permanent contact with the soil surface, whereas the vibration unit (5) and the predetermined soil subarea (3) represent a single oscillating system, and first data items of a first oscillation response of the oscillating system and second data items of the first time-variable excitation force are determined, and an absolute soil stiffness level (kB) of the predetermined soil subarea (3) is determined from the first and second data items;
• and
• moving the vibration unit (5) to the soil of one of the soil subarea of the soil area, in order to determine a plurality of relative soil stiffness levels(s) of a plurality of soil subarea, a second time-variable excitation force acts on the vibration unit (5) in such a way that the vibration unit (5) is lifted off the soil surface (2) and can thus be moved in a jumping manner to a plurality of the soil subareas, third data items of a second oscillation response of the oscillation of the vibration unit (5), caused by the second excitation force, and fourth data items of the oscillation of the second excitation force are determined, and relative soil stiffness levels (kB) of the soil subarea are determined successively and continuously over the soil area from the third and fourth data items, whereas
• the amplitude of the first harmonic and of subharmonics during periodic excitation of the vibration unit (5) by the second excitation force are determined as third data items of the second oscillation response, preferably third data items are determined in soil subarea, which are located at different points, in a soil area together with the relevant absolute values, and are stored in order to carry out a calibration process which allows measured relative values to be represented as absolute values, whereas
• the soil area has the same soil composition, except for a tolerance, the amplitude values of the third data items with respect to the maximum oscillation level of the excitation oscillation with individual weighting factors to be determined forming a sum, whereas the sum value is the respective location-specific absolute value, and the individual weighting factors are determined from a plurality of measurements, and whereas the numbers of measurements corresponds to the number of weighting factors, and the magnitude of the sum after a calibration process is a measure of an absolute soil compaction level or of an absolute soil stiffness of a soil subarea which is just been moved over.

A method for determination of soil stiffness levels of a soil area, in which case one and the same self-propelled apparatus (1) is used not only to determine the absolute soil stiffness level (kB) when located on at least one predetermined soil subarea (3) of the soil area but also to determine a plurality of relative soil stiffness levels(s) while crossing over a plurality of soil subareas of the soil area, comprising:

• moving a vibration unit (5) into a predetermined soil subarea (3), in order to determine an absolute soil stiffness level (kB), a first time-variable excitation force is applied by means of the vibration unit (5) in permanent contact with the soil surface, whereas the vibration unit (5) and the predetermined soil subarea (3) represent a single oscillating system, and first data items of a first oscillation response of the oscillating system and second data items of the first time-variable excitation force are determined, and an absolute soil stiffness level (kB) of the predetermined soil subarea (3) is determined from the first and second data items;
• and
• moving the vibration unit (5) to the soil surface of one of the soil subarea of the soil area, in order to determine a plurality of relative soil stiffness levels(s) of a plurality of soil subareas, a second time-variable excitation force acts on the vibration unit (5) in such a way that the vibration unit (5) is lifted off the soil surface (2) and can thus be moved in a jumping manner to a plurality of the soil subareas, third data items of a second oscillation response of the oscillation of the vibration unit (5), caused by the second excitation force, and fourth data items of the oscillation of the second excitation force are determined, and relative soil stiffness levels (kB) of the soil subarea are determined successively and continuously over the soil area from the third and fourth data items, whereas
• the first time-variable excitation force is produced as a periodic first force with a maximum first oscillation level, which is directed at right angles (with the exception of an adjustment tolerance) against the soil surface (2), and the periodicity is adjusted in such a manner that the oscillating system is at resonance, and the first and second data items include the resonant frequency and a phase angle between a time sequence of maximum oscillation values of the first excitation force and of the first oscillation response, whereas
• the amplitude of the first harmonic and of subharmonics during periodic excitation of the vibration unit (5) by the second excitation force are determined as third data items of the second oscillation response, preferably third data items are determined in soil subareas, which are located at different points, in a soil area together with the relevant absolute values, and are stored in order to carry out a calibration process which allows measured relative values to be represented as absolute values, whereas
• the soil area has the same soil composition, except for a tolerance, the amplitude values of the third data items with respect to the maximum oscillation level of the excitation oscillation with individual weighting factors to be determined forming a sum, whereas the sum value is the respective location-specific absolute value, and the individual weighting factors are determined from a plurality of measurements, and whereas the numbers of measurements corresponds to the number of weighting factors, and the magnitude of the sum after a calibration process is a measure of an absolute soil compaction level or of an absolute soil stiffness of a soil subarea which is just been moved over.

A method for determination of soil stiffness levels of a soil area, in which case one and the same self-propelled apparatus (1) is used not only to determine the absolute soil stiffness level (kB) when located on at least one predetermined soil subarea (3) of the soil area but also to determine a plurality of relative soil stiffness levels(s) while crossing over a plurality of soil subareas of the soil area, comprising:

• moving a vibration unit (5) into a predetermined soil subarea (3), in order to determine an absolute soil stiffness level (kB), a first time-variable excitation force is applied by means of the vibration unit (5) in permanent contact with the soil surface, whereas the vibration unit (5) and the predetermined soil subarea (3) represent a single oscillating system, and first data items of a first oscillation response of the oscillating system and second data items of the first time-variable excitation force are determined, and an absolute soil stiffness level (kB) of the predetermined soil subarea (3) is determined from the first and second data items;
• and
• moving the vibration unit (5) to the soil surface of one of the soil subarea of the soil area, in order to determine a plurality of relative soil stiffness levels(s) of a plurality of soil subareas, a second time-variable excitation force acts on the vibration unit (5) in such a way that the vibration unit (5) is lifted off the soil surface (2) and can thus be moved in a jumping manner to a plurality of the soil subareas, third data items of a second oscillation response of the oscillation of the vibration unit (5), caused by the second excitation force, and fourth data items of the oscillation of the second excitation force are determined, and relative soil stiffness levels (kB) of the soil subarea are determined successively and continuously over the soil area from the third and fourth data items, whereas
• the second time-variable excitation force is produced with a second periodic force, the second force has a maximum oscillation level which is greater than a first maximum oscillation level of a first periodic force of the first excitation force in such a way that the vibration unit (5) is lifted off the soil surface (2), whereas
• the second maximum oscillation level of the second periodic force is directed obliquely to the rear with respect to the vibration unit towards the soil surface (20, in order that the vibration unit (5) can be moved in the forward direction, and a lowest determined subharmonic frequency is determined, as the third data items of the second oscillation response, as a measure for a relative soil stiffness(s) with a relative soil stiffness(s) becoming greater, the lower of the lowest determined subharmonic oscillation is, whereas
• the amplitude of the first harmonic and of subharmonics during periodic excitation of the vibration unit (5) by the second excitation force are determined as third data items of the second oscillation response, preferably third data items are determined in soil subarea, which are located at different points, in a soil area together with the relevant absolute values, and are stored in order to carry out a calibration process which allows measured relative values to be represented as absolute values, whereas
• the soil area has the same soil composition, except for a tolerance, the amplitude values of the third data items with respect to the maximum oscillation level of the excitation oscillation with individual weighting factors to be determined forming a sum, whereas the sum value is the respective location-specific absolute value, and the individual weighting factors are determined from a plurality of measurements, and whereas the numbers of measurements corresponds to the number of weighting factors, and the magnitude of the sum after a calibration process is a measure of an absolute soil compaction level or of an absolute soil stiffness of a soil subarea which is just been moved over.