EP1295994A2 - Method to determine the degree of compaction of a foundation - Google Patents

Abstract

The sub-surface vibrator (13), suspended on a rod (11), has an unbalanced weight (15) rotating about a vertical axis. With a supply of water and/or air if appropriate, it is vibrated into the ground. It is drawn up in a series of stages. It is held vibrating in individual strata. Compaction is calculated from the vibration amplitude, taking into account stress-dependent ground parameters.

Description

The invention relates to a method for determining the storage density of the soil during soil improvement using Vibration pressure compression using a suitable computer or processor unit. Here, a deep vibrator is used an imbalance on a linkage rotating around a vertical axis hanging, if necessary with the addition of water and / or air, shaken into the ground and in increments of height mostly given size and in vibrating intervals in held at individual depths shaking. The vibrator leads staggering movements around a zero point of motion, which is close to its elastic suspension on the frame, while the jogger tip is a circular path with maximum amplitude performs. This soil improvement method is used in one upon request denser or further grid over a total area spread repeatedly executed to a desired To achieve load capacity of the soil and / or liquefaction conditions of the ground in the event of earthquakes. Problematic it is the result of the vibration compression to check. In previous practice it is assumed that monitoring power consumption and thus the soil compaction performance of the vibrator is sufficient Clue for the result of the compression work in the offers individual levels. Ultimate certainty about the achieved Storage density D are given here, for example CPTs. If the result is insufficient, the soil improvement method must be used through additional implementation of the Vibration compression, possibly after one of the first overlaid grid can be set, improved.

DE 198 59 962 A1 also describes a method at which the so-called lead angle between the phase position of the deep vibrator and the phase position of its unbalanced mass used as a parameter to determine the degree of compaction becomes. In terms of equipment, a pulse generator is used on the vibrator to determine a zero position of the unbalance and at least two arranged in vertical planes perpendicular to each other Accelerometer provided.

DE 199 28 692 C1 describes a method for online compaction control known a deep vibrator, in which Soil dynamic parameters and the storage density of the Bottom from the measured values penetration depth of the vibrator, tilt angle the vibrator axis, lead angle of the unbalance and at least one horizontal deflection (amplitude) of the vibrator be determined. One or more sensors should be used deliver the required measured values to the vibrator, the accelerometers and / or angle sensors and / or compasses and / or displacement transducers.

While it becomes clear in the first-mentioned document that the Lead angle itself as a significant quantity for the success of compaction is used in the second Scripture from the number of measured values mentioned Storage density is calculated, whereby it remains unclear how these measured values for monitoring the power consumption of the vibrator should be related.

des Rüttlers zur Bestimmung der Amplitude s des Rüttlers, die Umlauffrequenz n und die Tiefenlage t des Rüttlers gemessen. Damit wird eine Rüttleramplitude s, die an geeigneter Stelle des Rüttlers zwischen der Rüttlerspitze und dem Bewegungsnullpunkt des Rüttlers erfaßt wird, im wesentlichen als einzige zu erfassende Meßgröße herangezogen, wobei vorausgesetzt wird, daß die Rüttlerdrehzahl n in jedem Fall mit entsprechender Meßtechnik am Antriebsmotor erfaßt wird. Auf diese Weise kann aus der Radialbeschleunigung

, die über einen einzigen am Rüttler befestigten Beschleunigungsaufnehmer gemessen werden kann, und die Rüttlerfrequenz bzw. Rüttlerdrehzahl n die Rüttleramplitude s ermittelt werden, aus der dann die Lagerungsdichte D erfindungsgemäß in der Rechner- bzw. Prozessoreinheit berechnet wird. Eine Anzahl von Gerätekennwerten und eine Anzahl von Bodenkennwerten, die aus vorhergehenden Aufschlußbohrungen zu erhalten sind, sind in die Rechner- bzw. Prozessoreinheit zunächst einzulesen.The present invention has for its object to control the bearing density online during the individual vibration intervals with reduced measurement effort in the vibration compression compression method of the type mentioned. The solution to this is that the bearing density D is calculated from the amplitude s of the vibrator, taking into account voltage-dependent soil parameters, using the computer or processor unit. This considerably simplifies the required measurement, in particular the detection or calculation of the lead angle of the vibrator (phase position of the vibrator imbalance compared to the phase position of the vibrator jacket) is completely dispensed with. Rather, only the radial acceleration

of the vibrator to determine the amplitude s of the vibrator, the rotational frequency n and the depth t of the vibrator. A vibrator amplitude s, which is detected at a suitable point on the vibrator between the vibrator tip and the zero point of motion of the vibrator, is essentially used as the only measurement variable to be recorded, provided that the vibrator speed n is recorded in each case with appropriate measuring technology on the drive motor , In this way, radial acceleration can

, which can be measured using a single accelerometer attached to the vibrator, and the vibrator frequency or vibrator speed n, the vibrator amplitude s are determined, from which the bearing density D is then calculated according to the invention in the computer or processor unit. A number of device parameters and a number of soil parameters that can be obtained from previous digestion holes must first be read into the computer or processor unit.

ermittelt (D = f(σ_H ,

). Hierbei wird vereinfacht davon ausgegangen, daß die Horizontalspannung des Bodens in der Horizontalebene der Rüttlerarbeit im wesentlichen richtungsunabhängig gleich ist. Hierbei wird die Horizontalspannung σ_H als Produkt aus der tiefenabhängigen Vertikalspannung σ_V und dem Erddruckbeiwert K₀ berechnet (σ_H = K₀ · σ_V). Hierbei kann wiederum gesagt werden, daß die Vertikalspannung σ_V des Bodens als Funktion von Lagerungsdichte D und Tiefenlage t ermittelt wird (σ_V = f (D, t)), so daß die Berechnung der Lagerungsdichte D mittels der Horizontalspannung durch Iteration erfolgen muß. Konkret kann die Vertikalspannung σ_V als Produkt aus Wichte γ und Tiefenlage t ermittelt werden (σ_V = γ t), wobei die Wichte eine Funktion der Lagerungsdichte D ist (γ = f (D)), so daß näher erkennbar wird, wie die Berechnung der Vertikalspannung σ_V durch Iteration erfolgen muß.In a concrete version, the bearing density D is a function of the depth-dependent horizontal stress σ _{H of} the soil and the radial acceleration

determined (D = f (σ _H ,

). It is assumed here in a simplified manner that the horizontal tension of the soil in the horizontal plane of the vibrator work is essentially the same regardless of the direction. The horizontal stress σ _{H is} calculated as the product of the depth-dependent vertical stress σ _V and the earth pressure coefficient K ₀ (σ _H = K ₀ · σ _V ). Here again it can be said that the vertical stress σ _{V of} the soil is determined as a function of the bearing density D and depth t (σ _V = f (D, t)), so that the bearing density D must be calculated using the horizontal stress by iteration. Specifically, the vertical stress σ _V can be determined as the product of the weight γ and the depth t (σ _V = γ t), the weight being a function of the bearing density D (γ = f (D)), so that it can be seen in more detail how the Vertical stress σ _V must be calculated by iteration.

The earth pressure coefficient K ₀ , which is also included in the calculation of the horizontal stress, is to be determined as an exponential function of the bearing density D (K ₀ = a · 10 ^{b · D} ). With this, a further occurrence of the bearing density D can be seen in the calculation approach, so that the iterative calculation of the bearing density D is also necessary from this point of view.

While the storage density that with D = e Max - e e Max - e min is defined, where e is the pore number of the soil, e _{max is} the maximum pore number and e _{min is} the minimum pore number, is usually related to values of the pore numbers on the surface of the soil, the result of the storage density is normalized according to the present method, i.e. the calculation of the Storage density refers to the maximum or minimum number of pores in the corresponding depth. The storage density is a ratio value according to the above. The pore number e is a function of the weight γ [e = f (γ)].

As with previous methods, the determination of the bearing density is used primarily to limit the corresponding time Jogging intervals, d. H. if a given setpoint the Storage density is reached at the appropriate depth the respective jogging interval ends and the jogger by one predetermined height increment, in particular by 50 cm pulled up. With constant or decreasing amplitude s a predetermined circulation frequency, for. B. 30 Hz, maintained, since an increasing compaction of the soil is assumed can be. However, if the amplitude s increases, this indicates this is due to loosening of the soil or a resonance phenomenon of the vibrator-floor system as a result of the vibrations. In this case, the rotation frequency should be changed, preferably to reduce. Alternatively, a change in the circulation frequency n searched for and maintained a maximum of the amplitude s become.

A significant averaged characteristic of the acceleration measurement and thus to get the amplitude determination, it is proposed that the deep vibrator used for Carrying out the above method of accelerometers by half the step from the bottom Jogger tip is arranged away, especially around 25 cm with a step width of 50 cm.

The only drawing shows an example of one to perform suitable deep vibrator. Here are a linkage 11, an elastic coupling 12 and a deep vibrator 13 shown; on the latter are an imbalance 15 as well an accelerometer 16 marked. At 17 is the zero point of movement of the jogger, around which a wobble motion the vibrator axis takes place with low amplitudes s12 in the area of the elastic coupling 12 and with large amplitudes s 14 in the area of the vibrator tip 14. Measured and in the above denoted by s is the amplitude in the range of Accelerometer 16.

Claims (14)

Method for determining the storage density D of the soil during soil improvement by means of vibration compression,
wherein a deep vibrator with an unbalance rotating about a vertical axis hanging on a rod, possibly with the addition of water and / or air, shaken into the ground, pulled in individual height steps and shaking in individual deep positions at vibrating intervals and
the bearing density D is calculated from the amplitude s of the vibrator taking into account voltage-dependent soil properties. The method of claim 1, wherein the orbital frequency n and the depth position t of the vibrator are measured. Method according to one of claims 1 or 2, wherein the radial acceleration

of the vibrator to determine the amplitude s of the vibrator is measured directly. A method according to claim 3, wherein the bearing density D as a function of the depth-dependent horizontal stress σ _{H of} the soil and the radial acceleration

of the vibrator is determined [D = f (σ _H ,

)]. Method according to Claim 4, in which the horizontal stress σ _{H is} calculated as the product of the depth-dependent vertical stress σ _V and the earth pressure coefficient K ₀ [σ _H = K ₀ · σ _V ]. Method according to Claim 5, in which the vertical stress σ _{V of} the soil is determined as a function of the bearing density D and depth position t [σ _V = f (D, t)], so that the bearing density D is calculated by iteration. Method according to claim 6, in which the vertical stress σ _{V is determined} as the product of the weight y and the depth t [σ _V = γ t)], the weight γ being a function of the bearing density D [γ = f (D)], so that the vertical stress σ _{V is} calculated by iteration. Method according to one of Claims 5 to 7, in which the earth pressure coefficient K _{0 is determined} as an exponential function of the bearing density D [K ₀ = a · 10 ^{b · D} ], so that the bearing density D is calculated by iteration. Method according to one of claims 1 to 8, wherein the storage density, the with D = e Max - e e Max - e min is defined, where e is the pore number, e _{max is} the maximum pore number and e _{min is} the minimum pore number, is calculated with voltage-dependent values for e _max and e _min , where e is a function of the weight γ [e = f (γ)]. Method according to one of claims 1 to 9, wherein the Vibrator with constant or decreasing amplitude s is driven with a constant rotational frequency n. Method according to one of claims 1 to 10, wherein the Vibrator with increasing amplitude s with reduced circulation frequency n is driven. Method according to one of claims 1 to 9, in which over a change in the rotational frequency n a maximum in the amplitude s is searched and set. Method according to one of claims 1 to 12, wherein the Vibration intervals depending on reaching a setpoint for the storage density D can be ended. Method according to one of claims 1 to 11,
characterized in that an accelerometer (16) is arranged at half the height increment from the lower vibrator tip (14), in particular by 25 cm with a height increment of 50 cm.

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