Method and Arrangement for Producing a Foundation Element in the Ground

The invention relates to a method for producing a foundation element in the ground by means of a jet grouting device, wherein a jet grouting rod of the jet grouting device is introduced into the ground, and a hardenable suspension is injected under pressure into the surrounding ground, wherein the foundation element is produced in the ground, and spaced apart from a place of introduction of the jet grouting rod at least one elongate measuring element is introduced into the ground, by which measurement values are detected when producing the foundation element by the jet grouting device, in accordance with the preamble of claim.

The invention further relates to an arrangement for producing a foundation element in the ground with a jet grouting device having a jet grouting rod with which, by injecting a hardenable suspension into the ground, the foundation element can be produced in the ground, and spaced apart from a place of introduction of the jet grouting rod at least one elongate measuring element is introduced into the ground, by which measurement values can be detected when producing the foundation element by the jet grouting device, in accordance with the preamble of claim.

A generic prior art can be taken from EP 2 843 137 B1. In this known method a pendulum rod is introduced as a measuring element into the ground such that it is spaced apart from a ground column produced in the jet grouting process. The distance of the pendulum rod to the jet grouting rod provided is smaller than a set maximum range of the jet stream. Through a rotating movement of the jet grouting rod the generated jet stream thus passes pendulum rod regularly. As a result, the pendulum rod is set into vibrations which are detected as measurement signals.

With this known method the processes in the ground that are generally not visible when producing a foundation element in a jet grouting process can be detected and observed. This is implemented in that a rigid pendulum rod is set into vibration when the jet stream passes. The frequency and amplitude of the vibration allow conclusions as to the size, intensity and direction of the jet stream.

However, the provision and introduction of a continuous pendulum rod proves to be difficult in the case of drilling depths of 5 meters and more and is altogether impossible as from a certain depth. Basically, a pendulum rod can also be composed of several segments. However, the number and type of connections of the individual segments change the vibration behavior of the entire pendulum rod so that a detection and evaluation of measurement signals is rendered more difficult and barely possible in certain cases. Moreover, in the case of a rigid pendulum rod the vibration behavior is generally also still affected by ambient conditions, e.g. whether such a pendulum rod is arranged in a matching borehole or one of oversize. If a pendulum rod rests over its entire surface against the surrounding ground, this generally results in a different vibration behavior as compared to a pendulum rod that only partially or discontinuously makes contact over the length of the borehole. All this can lead to a more difficult evaluation of vibration signals in the known measuring arrangement.

The invention is based on the object to provide a method and an arrangement, with which a foundation element can be produced in a particularly efficient way in the ground in a jet grouting process.

The object is achieved on the one hand by a method having the features of claimand on the other hand by an arrangement having the features of claim.

The method according to the invention is characterized in that as measuring element a deformable hose is used which is filled with a measuring liquid and in that as measurement value changes of state of the measuring liquid, in particular a pressure and/or a filling level in the hose, are detected.

A basic idea of the invention resides in the fact that as measuring element a deformable hose, in particular an elastically deformable one, is used which is filled with a measuring liquid. Compared to a rigid measuring stick a hose of almost any length can be transported on a drum and introduced into a borehole in the ground. Hence, a measuring element can also be used without any difficulty for the measurement of foundation elements that have a length or depth in the ground amounting to 10 meters up to 30 meters and more. Especially after introduction of the hose in the ground the hose is filled with an incompressible measuring liquid, preferably water. The hose is closed at its lower end and can preferably be provided with an introduction tip.

The flexible measuring hose thus formed is arranged in the ground by being spaced apart in a defined manner to the place of introduction of a jet grouting rod. The distance is chosen such that a generated jet stream, when passing the hose, causes a deformation of the hose, more particularly causing a dent in the hose. This preferable impact of the jet stream on the measuring hose can be detected by a change of state of the measuring liquid. In particular, this impact or passing-by can lead to and be detected as a pressure change in the measuring liquid and/or a change of the filling level, especially a temporary limited increase of the filling level of the measuring liquid in the narrowed hose. Such changes of state of a generally incompressible measuring liquid can be detected reliably. In particular, the measuring hose can also be guided along the ground surface still to a desired place of measurement so that the measurement with a sensitive measuring means does not have to be carried out directly at the place where the foundation element is produced.

All in all, by way of the method according to the invention the production of a foundation element in a jet grouting process can be checked and monitored particularly accurately, thereby allowing a foundation element to be produced reliably and precisely in an efficient way.

In principle, the hose can be introduced in any arrangement into the ground. According to a further development of the invention it is particularly preferred that the hose is introduced into the ground approximately parallel to the foundation element to be produced. Advantageously, one or several vertically extending bores are introduced approximately parallel to the foundation element to be produced. A measuring element can then be inserted into the at least one bore thus produced.

According to an embodiment variant of the invention it is especially advantageous that initially a bore to introduce the hose is produced in the ground and that subsequently the foundation element is produced. Thus, right from the start of production of the foundation element a checking and monitoring of the jet stream and of the foundation element produced thereby can take place.

Furthermore, it is particularly expedient that the distance between the hose and the jet grouting rod is chosen such that the foundation element reaches close up to the hose. In particular, the distance can be chosen to correspond approximately to a radius of the foundation element to be produced. This ensures that when the jet passes the measuring hose or brushes past it a temporary deformation or physical change is generated that can be detected by way of the measuring liquid. The distance of the hose can be slightly smaller or slightly larger than a radius of the foundation element or the expected range of the jet.

Basically, the foundation element can be produced in the ground with any circumferential contour, for instance oval-shaped or polygonal. According to an embodiment of the invention a particularly efficient method variant results from the fact that the jet grouting rod of the jet grouting device is rotated and displaced vertically to produce a pile-shaped foundation element. This results in a substantially cylindrical foundation element in the ground, in which case diameter expansions can also be provided in specific places, in particular in a base region of the foundation element. By way of a suitable injection device a hardenable suspension, in particular a concrete or cement suspension, can be injected under pressure into the ground, whereby the foundation element is formed in situ by the mixture composed of the loosened ground material and the injected hardenable suspension.

Especially for the production of foundation elements with greater depths it is advantageous according to a further development of the invention that the hose is unwound from a hose drum and introduced into the ground and that subsequently the hose is filled under pressure with the measuring liquid. The filling of the measuring liquid under pressure also ensures that the hose rests well against the surrounding ground so that a passing-by of the jet stream can generally also be ascertained even if this does not fully reach as far as the measuring hose. After filling the hose with the measuring liquid a calibration step can be carried out in conjunction with a measuring means so that a defined initial state without the effect of a jet stream is established. Based on this calibrated state the impact of a jet stream and the change of state in the measuring liquid caused thereby can be ascertained particularly accurately.

Furthermore, it is especially advantageous that at an upper end of the hose a measuring means is arranged, by which at least one change of state of the measuring liquid is detected. The measuring means can be provided directly at the place where the hose emerges from the ground or, if the hose is extended, at a place spaced apart therefrom.

In conjunction with this it is particularly expedient that a measuring means comprising a pressure sensor and/or a filling level sensor is used. By way of a sight glass the filling level sensor can provide optical detection or a float gauge or detect a filling level via electrical conductivity. By preference, the measuring means can be directly connected to a control means of the jet grouting device so that, depending on the measurement values detected, direct control of the jet grouting device can take place. In particular, an injection pressure and/or a feed quantity of suspension to the jet grouting rod can be controlled.

The object is furthermore achieved by an arrangement for producing a foundation element in the ground which is characterized in that as measuring element a deformable hose is used which is filled with a measuring liquid, and in that a measuring means is provided, with which changes of state of the measuring liquid, in particular a pressure and/or a filling level in the hose, can be detected.

The arrangement according to the invention can in particular be used to carry out a previously described method. The advantages described previously can be achieved thereby.

A particularly advantageous embodiment of the invention resides in the fact that the measuring means is connected to a computer unit in which the detected measurement values are stored and/or can be analyzed. For this the computer unit, more particularly a computer, is provided with a corresponding analysis software. The detected measurement values can be evaluated such that based on these a statement can be made as to the direction and intensity of the jet in the ground and thus with regard to the design of the foundation element in the ground.

Another advantageous embodiment of the invention resides in the fact that the measuring means and/or the computer unit is connected to a control means for controlling the jet grouting device. In this way, a feedback to the jet grouting device is brought about, thereby making it possible to achieve a desired intensity and direction of the generated jet stream and thus a defined design of the foundation element in the ground.

The invention is described further hereinafter by way of a preferred exemplary embodiment illustrated schematically in the drawing.

In the single FIGURE a generally known jet grouting devicewith a preferably mobile carrier implementis illustrated schematically. On the carrier implementa jet grouting rodis supported such that it can be displaced vertically and introduced into ground. The jet grouting rodcan, in particular comprise a drilling means and be driven in a rotating manner in order to be drilled down into the ground.

In a lower end region of the jet grouting rodone or several nozzlesare arranged. From the nozzlea hardenable suspensioncan be injected under predetermined pressure into the surrounding groundto form a foundation element. The hardenable suspensioncan loosen surrounding groundor penetrate into a loose ground formation in order that in the region of the injected suspensiona foundation element is formed in the groundafter hardening.

According to the invention a measuring elementis introduced approximately parallel to and at a distance A to the jet grouting rodintroduced into the ground. In the illustrated exemplary embodiment the distance A is chosen slightly smaller than a radial range of the rotating jet stream of suspensionfrom the nozzle.

The elongate measuring elementcomprises a flexible or elastic hosethat is filled with a measuring liquid. A lower endof the hoseis closed and can be designed with a penetration tip for easier penetration of the hoseinto an introduction bore in the ground.

At the upper end of the hosea measuring meansis arranged which can preferably comprise a pressure sensor for measuring a pressure of the measuring liquidin the hose. When the jet stream of suspensionfrom the nozzlethat rotates about a vertical axis of rotation of the jet grouting rodpasses by or brushes past, a deformation of the flexible hoseis brought about. This leads to a pressure increase in the measuring liquidwhich can be detected with high reliability by the measuring means.

Hence, by the measuring meansthe passing-by or progressing-past of the rotating jet can be detected reliably. Moreover, based on the level of the pressure detected a statement can be made by way of a non-depicted analysis unit as to the intensity and range of the jet stream. This also allows a corresponding statement to be made as to the foundation element designed in the ground. The measuring meanscan preferably be coupled with a control means of the jet grouting deviceso that depending on the detected measurement values of the measuring meansa control regarding the setting of supply of suspensionand of the injection pressure can take place.