EP1295994B1 - 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 by means of Rütteldruckverdichtung using a suitable computer or processor unit. In this case, a deep vibrator with a rotating about a vertical axis imbalance on a rod hanging, if necessary, with the supply of water and / or air, shaken into the ground and pulled in height steps mostly given size and kept shaking in shaking intervals in individual depths. The vibrator performs this tumbling movements around a zero movement, which is close to its elastic suspension on the rod, while the Rüttlerspitze performs a circular path with maximum amplitude. This soil improvement process is carried out repeatedly in a denser or wider grid over a total area depending on the requirement, in order to achieve a desired soil carrying capacity and / or to hinder liquefaction conditions of the soil in the event of earthquakes. The problem here is to check the result of Rütteldruckverdichtung. In the previous practice it is assumed that the monitoring of the power consumption and thus the soil compaction performance of the vibrator provides a sufficient indication of the result of compaction work in the individual altitude levels. Final certainty about the storage density D achieved so far are for example pressure probing here. If the result is insufficient, the soil improvement process must be improved by supplementing the vibrating pressure compaction, which may be set after a first superimposed grid.

In DE 198 59 962 A1, a method is described in addition, in which the so-called advance angle between the phase position of the deep vibrator and the phase position of its imbalance mass is used as a parameter for determining the degree of compaction. Device technology for this purpose, a pulse generator for determining a zero position of the imbalance and at least two arranged in mutually perpendicular vertical planes acceleration sensor provided on the vibrator.

From DE 199 28 692 C1 a method for on-line compression control of a deep vibrator is known, in which soil dynamic characteristics and therefrom the storage density of the soil from the measurements Penetration depth of the vibrator, tilt angle of the vibrator axis, forward angle of imbalance and at least one horizontal deflection (amplitude) of the vibrator. In this case, one or more sensors on the vibrator should provide the required measured values, which may be acceleration sensors 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 is used directly as a significant quantity for the compaction success, in the second-mentioned document the storage density is calculated from the stated number of measured values, whereby it remains unclear how these measured values are used to monitor the power consumption of the jogger.

The object of the present invention is to control the storage density online during the individual vibrating intervals with reduced measuring effort in the case of the vibrating pressure compression method of the aforementioned type. The solution consists in a method for determining the storage density D of the soil during soil improvement by means of Rütteldruckverdichtung, a deep vibrator shaking with a rotating about a vertical axis imbalance on a rod suspended in the ground, pulled in individual height steps and shaking in Rüttelintervallen in individual depths is held and the depth of each t of the vibrator is detected, which is characterized in that the storage density D is determined as a function of the depth-dependent horizontal stress σ _{H of} the soil and the amplitude s of the vibrator, wherein the amplitude s from the radial acceleration s̈ of the vibrator is calculated, wherein the Rüttlerdrehzahl n be detected by an accelerometer with the appropriate Drehzahlmeßtechnik and the radial acceleration s̈. In this case, the storage density D is thus calculated from the amplitude s of the vibrator taking into account voltage-dependent soil characteristics by means of the computer or processor unit. Hereby, the required measurement is considerably simplified, in particular, the detection or calculation of the feed angle of the vibrator (phase position of the vibrator unbalance relative to the phase position of the vibrator jacket) is completely dispensed with. Rather, only the radial acceleration s̈ of the vibrator for determining the amplitude s of the vibrator, the vibrator speed n and the depth position t of the vibrator is measured. Thus, a radial acceleration s̈, which is detected at a suitable point of the vibrator between the Rüttlerspitze and the zero motion of the vibrator, essentially used as the only measured variable to be detected, it is assumed that the Rüttlerdrehzahl n is detected in each case with appropriate measurement technology on the drive motor , In this way, from the radial acceleration s̈, which can be measured via a single accelerometer attached to the vibrator, and the vibrator frequency or vibrator speed n, the vibrator amplitude s are determined, from which then the storage density D according to the invention is calculated in the computer or processor unit , A number of device characteristics and a number of soil characteristics to be obtained from previous digestion wells are first read into the computing or processing unit.

In concrete execution, the storage density D is determined as a function of the depth-dependent horizontal stress σ _{H of} the soil and of the radial acceleration s̈ (D = f (σ _H , s̈).) It is simplifiedly assumed that the horizontal stress of the soil in the horizontal plane of the vibrating work substantially independent of the direction is the same. Here, the horizontal stress is σ _H as the product of the depth-dependent vertical stress σv and the earth pressure coefficient K ₀ is calculated (σ _H = K ₀ · σ _V). This can again be said that the vertical stress σ _V of the soil is determined as a function of storage density D and depth position t (σ _v = f (D, t)), so that the calculation of the storage density D must be done by means of 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), where the weight is a function of the storage density D (γ = f (D)), so that it becomes more apparent how the calculation of the vertical stress σ _V must be done by iteration.

The Erddruckbeiwert K ₀ , which also enters into the calculation of the horizontal stress is to be determined as an exponential function of the storage density D (K ₀ = a · 10 ^{b · D} ). This makes it possible to detect a further occurrence of the storage density D in the calculation approach, so that the iterative calculation of the storage density D is also required from this point of view.

definiert ist, wobei e die Porenzahl des Bodens, e_max die maximale Porenzahl und e_min die minimale Porenzahl ist, üblicherweise auf Werte der Porenzahlen an der Bodenoberfläche bezogen ist, ist das Ergebnis der Lagerungsdichte gemäß dem vorliegenden Verfahren spannungsabhängig normiert, d.h. die Berechnung der Lagerungsdichte bezieht sich auf maximale bzw. minimale Porenzahlen in entsprechender Tiefe. Die Lagerungsdichte ist gemäß vorstehendem ein Verhältniswert. Die Porenzahl e ist hierbei eine Funktion der Wichte γ [ e = f (γ)].While the storage density, with $$\mathrm{D}\mathrm{=}\frac{{\mathrm{e}}_{\mathrm{Max}}\mathrm{-}\mathrm{e}}{{\mathrm{e}}_{\mathrm{Max}}\mathrm{-}{\mathrm{e}}_{\min }}$$

where e is the pore number of the soil, e _{max is} the maximum pore number and e _{min is} the minimum pore number, usually based on values of pore numbers at the soil surface, the result of the storage density according to the present method is normalized by stress, ie the calculation of Storage density refers to maximum or minimum pore numbers in appropriate depth. The storage density is a ratio according to the above. The pore number e is a function of the weight γ [e = f (γ)].

As in previous methods, the determination of the storage density primarily serves to limit the duration of corresponding Rüttelintervalle, ie when a predetermined target value of the storage density is reached in the appropriate depth, the respective Rüttelintervall is terminated and the vibrator by a predetermined height increment, in particular by 50 cm, after pulled up. At constant or sinking amplitude s is a predetermined rotational frequency, z. B. 30 Hz, maintained, since it can be assumed that an increasing compaction of the soil. However, if the amplitude s increases, this indicates a loosening of the soil or a resonance phenomenon of the vibrator-soil system due to the shaking. In this case, the rotational frequency is to be changed, preferably reduced. Alternatively, a maximum of the amplitude s can be sought and maintained via a change in the rotational frequency n.

In order to obtain a significant averaged characteristic value of the acceleration measurement and thus of the amplitude determination, it is proposed that the accelerometer be arranged at half the height increment of the lower vibrator tip on the deep vibrator used to carry out the above method, ie in particular by 25 cm at a height increment of 50 cm.

The sole drawing shows an example of a depth vibrator suitable for carrying out the method. Here, a linkage 11, a flexible coupling 12 and a deep vibrator 13 are shown; At the latter, an imbalance 15 and a Beschleunigsaufnehmer 16 are marked. The movement zero point of the vibrator is indicated by 17, around which a wobbling movement of the vibrator axis takes place, with small amplitudes s12 in the region of the elastic coupling 12 and with large amplitudes s 14 in the region of the vibrator tip 14. Measured and denoted by s in the above is the amplitude in Area of the acceleration pickup 16.

Claims (11)

1. A method of determining the density D of a soil in the course of a soil improving operation, using vibro-compaction,
   wherein a depth vibrator (11) with an unbalanced mass (15) which rotates around a vertical axis, which depth vibrator (11) is suspended on a rod assembly, is vibrated into the soil, optionally with water and/or air being added, is lifted in individual lifting stages and vibratingly held at vibration intervals in individual depth positions, wherein the depth position t of the vibrator is recorded at each stage,
   and wherein the density D is determined as a function of the depth-dependent horizontal stress σ_H of the soil and as a function of the amplitude s of the vibrator, wherein the amplitude s is calculated on the basis of the radial acceleration s̈ of the vibrator, wherein the rotation frequency n is recorded by a respective speed measuring technology and the radial acceleration s̈ is recorded via an acceleration recording device (16).
2. A method according to claim 1,
   wherein the horizontal stress σ_H is calculated as the product of the depth-dependent vertical stress σ_ν and of the earth pressure coefficient K₀ [σ_H = K₀ x σ_ν].
3. A method according to claim 2,
   wherein the vertical stress σ_ν of the soil is determined as the function of the density D and the depth position t [σ_ν = f(D,t)], wherein the density D is calculated by iteration.
4. A method according to claim 3,
   wherein the vertical stress σ_ν is determined as the product of the specific gravity γ and the depth position t [σ_ν = γ x t], wherein the specific gravity γ is a function of the density D [γ = f(D)], wherein the vertical stress σ_ν is calculated by iteration.
5. A method according to any one of claims 2 to 4,
   wherein the earth pressure coefficient K₀ is determined as the exponential function of the density D [K₀ = a x 10^bD x ^D ], wherein the density D is calculated by iteration.
6. A method according to any one of claims 1 to 5,
   wherein the density which is defined by $$\mathit{D}\mathrm{=}\frac{{\mathit{e}}_{\max }\mathrm{-}\mathit{e}}{{\mathit{e}}_{\max }\mathrm{-}{\mathit{e}}_{\min }}$$

   

   
   with e being the number of pores, e_max being the maximum number of pores and e_min being the minimum number of pores, is calculated by stress-dependent values for e_max and for e_min, wherein e is a function of the specific gravity γ [e = f(γ)].
7. A method according to any one of claims 1 to 6,
   wherein the vibrator, with a constant or decreasing amplitude s, is driven at a constant rotation frequency n.
8. A method according to any one of claims 1 to 7,
   wherein the vibrator, with an increasing amplitude s, is driven at a reduced rotation frequency n.
9. A method according to any one of claims 1 to 8,
   wherein, by changing the rotation frequency n, a maximum of the amplitude s is searched and set.
10. A method according to any one of claims 1 - 9.
    wherein the vibration intervals are ended as a function of reaching a nominal value for the density D.
11. A method according to any one of claims 1 to 10,
    wherein an acceleration recording device (16) is arranged so as to be distant from the lower vibrator point (14) by half the increment between the lifting stages, more particularly by 25cm at an increment of 50 cm between the lifting stages.

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