DE102012104009B4 - Quality assurance process for creating piles and open profile for it - Google Patents

Abstract

Quality assurance method for creating piles in the subsurface (U) with a leading, open profile and inward removal of the soil or bottom closure of the profile displacement of the soil, characterized in that at the foot (11) of the open profile (1) on the inside along a chord the cross section of the profile (1) a compression wave velocity (vp) of the substrate (U) is measured.

Description

The invention relates to a quality assurance method for creating piles in the ground with a leading, open profile and inside promotion of the soil or at the bottom closure of the profile displacement of the soil. Furthermore, the invention relates to an open profile for the creation of foundation piles.

Open profile means a component with a self-contained, in the longitudinal direction along the profile substantially the same cross-section. The profile is open at the bottom and top. Accordingly, open profiles in addition to circular casings and square tubes, box sections, shafts, caissons and the like can be. A pile is any form of foundation created by such an open profile.

Piles are known for foundations in difficult subsoil. They serve to remove loads in greater depths. In particular, bored piles are known for vibration-free production of pile foundations for buildings on insufficiently stable ground. When creating bored piles, for example, an open profile having a circular cross-section is pressed into the ground here as piping with an oscillating movement. At the same time the soil contained in the interior of this casing is removed as cuttings with a guided in the piping gripper or rinsing process. Subsequently, a probation basket is inserted into the exposed interior of the casing and concreted, whereby the casing is removed again.

It is critical of this process that if the tubing is too far ahead of the cuttings, soil loosening occurs near the bottom of the well. In particular, it may happen unnoticed in drilled piles that the soil at the Bohrpfahlfuß is relaxed or significantly loosened by the drilling process. In the groundwater, a bottom hydraulic fracture can result in loosening or transport of soil particles. Furthermore, inexperienced device drivers a deeper excavation than the piping happen. The piping must actually be leading to ensure the lateral support of the soil. A loosening of the bottom hole leads to a deteriorated pile behavior.

So far, it was known to counteract a hydraulic groundbreaking by a sufficient water level in the casing and a soulful sinking and discharging the cuttings by the machine operator. The actually achieved quality of this experience-based, sensitive machine guidance can not be assessed parallel to the production.

Furthermore, it is known to use a plug formation in open subfloors introduced in the underground in order to use the entire bottom surface of the introduced open profile as a load-bearing surface can. A plug forms when the soil within the profile tightens sufficiently. If, therefore, a foundation with an open profile driven into the subsurface with plug formation is desired or expected, its quality can hitherto not be assessed in parallel with production.

Furthermore, it is known in the so-called Franki pile to bring a closed with a plug of dry concrete bottom profile with a so-called Rammbären in the underground. The soil is displaced by the profile closed with the concrete plug below. Upon reaching the viable ground, the propulsion of the profile comes to a standstill and the dry concrete plug is expelled from the ram on the foot with further displacement of the soil and stomped to a cross-sectional widened foot, the groundwater then leads to hydraulic curing of the widened foot.

Even with this already 100-year-old foundation method, no production-parallel verification of the concrete foot education is given.

Methods and apparatus for measuring the compression wave velocity of earth formations are known in the field of well logging in different designs. For example, on the DE 31 06 345 A1 in which a borehole probe is equipped with a sound transmitter and a sound receiver, the records being obtained as a function of depth in the borehole.

The object of the invention is to provide a quality assurance method for creating bored piles and a correspondingly prepared piping, in which the quality of the pile production can be monitored.

This object is achieved with a quality assurance method according to claim 1 and a profile according to claim 6.

By measuring a compressional wave velocity of the ground at the foot of the profile on the inside along a chord of the cross-section of the profile, the compression wave velocity in the area of the subsurface near the bottom of the hole is measured, on which the concreted pile is later deposited. Because the Wave velocity is equal to the root of the quotient of the pressure and soil-dependent modulus of elasticity to density, indicates a decrease in the wave velocity on a relaxation or loosening of the soil in the interior of the foot of the profile. On the other hand, an increase in wave velocity indicates the achievement of a viable soil layer. Thus, the device driver receives by the information from the sound measurement a reading to assess the manufacturing quality of the pile foundation. According to the device, this is made possible by providing at least one sound transmitter on the inside of the profile and at least one sound receiver along a chord in the cross section of the profile. As a sound transmitter and receiver piezoelectric sensors, in particular ultrasonic sensors can be used, for example. In order to achieve a representative measuring section, the measuring section should be designed along a chord of the profile, for example over the circular cross section in a casing, in particular over its diameter. In the case of several sound transmitters and receivers, it is possible, for example, to measure crosswise over two substantially diametrically perpendicular measuring sections. Of course, other geometric distributions are possible.

Likewise, in the case of a pile foundation with plug formation, it is possible to detect the solidification in the region of the plug by means of a correspondingly increased compression wave velocity via the transmitter / receiver at the foot of the profile. Conversely, an unachieved plug formation can be detected by a too low compression wave velocity.

When placing Franki piles, the location of the dry concrete can be monitored by measuring the compression wave velocity.

Furthermore, when submitting such profiles into the ground by means of arranged on the profile sound transmitter and receiver a subsoil exploration take place in which the almost undisturbed compression wave velocity of the ground when lowering the profile is measured.

In order to be able to penetrate the particularly critical region from the bottom of the hole to the foot of the profile, the transceivers are arranged 5 cm to 40 cm, preferably 10 cm to 30 cm, particularly preferably about 20 cm above the lower end of the profile. Thus, the transmitter / receiver are in the field of overfeed of the profile opposite the Bohrgutentnahme. Thus, the determined compressional wave velocity of the subsurface provides a measure of the load bearing capacity or loosening of the subsurface at the bottom of the hole.

When a wave reflected off the bottom of the hole is measured from the foot of the profile, the height difference between the exposed bottom hole and the bottom edge of the profile can be determined. Thus, loosening caused by loosening or hydraulic foundation fracture in the area of the bottom hole can be seen. In particular, it is concluded on the basis of the measured compression wave velocity from the transit time of the reflected wave on the advance of the foot of the profile to the borehole bottom. When the profile is closed at the bottom by a dry concrete foot, the wave reflected from the lower edge of the dry concrete foot is measured. From the determined early strength development, the ultimate strength can then be estimated after pulling the casing (profile) via correlation.

If, after reaching the final depth or an intermediate depth, the temporal change of the overfeed is measured, in the case of cohesive soils the change in the bottom hole position can be measured indirectly as a result of relaxation elevations. From this, it is possible to deduce the toughness index and the "over-consolidation rate" (OCR), which can be used to determine important ground-mechanical parameters for the foundation.

According to the device, the transmitter / receiver are embedded in the profile to avoid damaging the transmitter / receiver when oscillating impressions and / or pulling the profile.

If a cable connection for voltage and signal transmission, which is protected in the profile, is provided for each transmitter / receiver, the measuring devices can be controlled directly by the device driver and the measured values can be displayed and evaluated directly.

Alternatively, each transmitter / receiver has a power supply, in particular accumulator, to be used for a pile foundation use. In this case, the measurement data is transmitted wirelessly via data transmission means, for example by radio or ultrasound transmission, whereby a simultaneous measurement data evaluation is also possible. Alternatively, a signal logger can be provided on the transmitter / receiver, which is read after creation of the pile foundation. Although simultaneous quality control is not possible in this embodiment, the recorded values can be used to secure the stability of the pile foundation created. It is advantageous in this embodiment, the lack of any, possibly disturbed and sensitive transmission means in the drilling situation.

Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings.

It shows:

1 a pressed in the ground piping with the forming bottom hole in a schematic cross section and

2 in detail, the lower portion of the casing with a forming reflected wave.

In 1 is a schematic cross-section through an area of the substrate U a depressed by a casing machine profile, here a piping 1 with a substantially cleared interior 10 shown. The piping 1 is pressed starting from the earth's surface O at the desired location by a piping machine, not shown here by oscillating motion. At the same time it is doing with a gripper, also not shown, the interior 10 the piping 1 freed from cuttings. It thus creates a borehole 2 in the underground U, passing through the piping 1 kept open. The removal of the cuttings is done so that the bottom hole 21 about 0.5 m above the foot 11 the piping is located. To a hydraulic ground fault in the area of the bottom hole 21 to avoid is in the borehole 2 (Inner space 10 the piping 1 ) filled with a counter-pressure supporting fluid, such as water.

Near the foot 11 the piping 1 are transmitter / receiver 3 , here consisting of a sound transmitter 31 and an on the diameter opposite arranged sound receiver 32 arranged. The sound transmitter 31 and the sound receiver 32 are in exceptions 12 , about 20 cm above the foot 11 the piping 1 are inserted, used. The sound transmitter 31 sends in on activation 1 represented sound signal from the sound receiver 32 is taken opposite. Due to the measurable transit time of the sound signal through the ground in the area below the borehole bottom 21 Thus, the compression wave velocity v _p can be determined. Since the wave velocity is equal to the root of the quotient of the pressure- and soil-dependent modulus of elasticity to density, v _p = √E / _ρ , where E = modulus of elasticity and ρ = density of the soil, the soil-carrying capacity can be derived from the measured velocity ,

In a further embodiment of the invention is also by suitable control and measurement recording of the sound transmitter 31 and the sound receiver 32 one at the bottom of the hole 21 So the transition between the still fixed floor in the interior 10 the piping 1 and the borehole created 2 reflected wave measured ( 2 ). Based on the measured transit time and the underlying compression wave velocity from the measurement according to 1 can thus the height of the bottom hole 21 over the foot 11 the piping 1 be determined.

With the quality assurance method according to the invention and the piping according to the invention, it is thus possible to detect the quality of the foundation already when drilling down the piping and conveying the cuttings and immediately counteract any risks due to hydraulic ground failure and / or loosening of the soil can. In this case, loosening due to hydraulic ground failure or extreme ground relaxation can be verified by a significantly reduced compression wave velocity. Furthermore, by the features according to the invention when creating bored piles always the lead of the piping, so the measure between the foot 11 the piping 1 and the bottom hole 21 by evaluating the wave reflected at the bottom of the hole. Further, the in-depth desirable soil layer can be verified by measuring the compression speed (high compression wave velocity feature). Possibly. can thus be stopped at a lower depth with the setting of the bored pile, which means a significant cost savings. Furthermore, the viscosity index or the earth pressure coefficient can be determined for over-consolidated soil.

Thus, the quality assurance method according to the invention and the piping according to the invention is a measure for work-parallel quality control when depositing bored piles in the underground. Due to the simultaneously determined measurement results can u. U. a saving in pile length can be achieved or improved quality, ie higher carrying capacity can be verified. Furthermore, the accompanying measurement can also serve as an indirect subsoil digestion of undisturbed soil with regard to storage density and stress state.

LIST OF REFERENCE NUMBERS

1

open profile, piping

10

inner space

11

foot

12

exception

2

well

21

bottomhole

3

Transmitter-receiver

31

sound transmitter

32

sound receiver

O

earth's surface

U

underground

v _p

Compressional wave velocity

Claims (10)

Quality assurance procedure for the creation of piles in the subsurface (U) with a leading, open profile and internal removal of the soil or at lower closure of the profile displacement of the soil, characterized in that the foot ( 11 ) of the open profile ( 1 ) inside along a chord of the cross section of the profile ( 1 ) a compression wave velocity (v _p ) of the subsurface (U) is measured. Quality assurance method according to claim 1, characterized in that the determined compression wave velocity (v _p ) of the substrate (U) is a measure of the load capacity or loosening of the substrate (U) on the foot ( 11 ) of the profile ( 1 ). Quality assurance method according to claim 1 or 2, characterized in that the foot ( 11 ) of the profile ( 1 ) one at a bottom of the hole ( 21 ) reflected wave or at lower closure of the profile by a dry concrete foot the wave reflected from the lower edge of the dry concrete foot is measured. Quality assurance method according to claim 3, characterized in that on the basis of the measured compression wave velocity (v _p ) from the transit time of the reflected wave on the advance of the foot ( 11 ) of the profile ( 1 ) to the bottom of the hole ( 21 ) is closed. Quality assurance method according to claim 4, characterized in that after reaching the final depth or an intermediate depth, the temporal change of the overfeed is measured. Profile ( 1 for the production of piles in the subsurface (U), for carrying out a quality assurance procedure according to one of claims 1 to 5, characterized in that on the foot ( 11 ) of the profile ( 1 ) inside at least one sound transmitter ( 31 ) and along a chord in the cross section of the profile opposite at least one sound receiver ( 32 ) are provided. Profile ( 1 ) according to claim 6, characterized in that the transmitter / receiver ( 3 ) 5 cm to 40 cm, preferably 10 cm to 30 cm, more preferably about 20 cm above the lower end of the profile ( 1 ) are arranged. Profile ( 1 ) according to claim 6 or 7, characterized in that the transmitter / receiver ( 3 ) In profile ( 1 ) are admitted. Profile ( 1 ) according to claim 6, 7 or 8, characterized in that for each transmitter / receiver ( 3 ) one in profile ( 1 ) Protected cable connection for supply voltage and signal transmission are provided. Profile ( 1 ) according to claim 6, 7 or 8, characterized in that each transmitter / receiver ( 3 ) have a power supply, in particular accumulator, and a signal logger or wireless data transmission means.

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