RU2280267C1 - Method for seismic research of pile foundations - Google Patents

Abstract

FIELD: geo-physical research methods, namely, seismic prospecting, possible use during geo-engineering research.

SUBSTANCE: in accordance to proposed method, resilient oscillations are excited along external walls of building in the soil without direct access to piles by means of low power impact source. Registration of these is performed both on the side of excitation line and on the opposite side of building. Speeds and times of engagement of waves, reflected from geological boundaries, are determined. By means of comparative analysis of record form on temporal cuts, received separately along longitudinal and non-longitudinal profile line, diffraction effects are selected, caused by pile ends. Diffraction point times and their coordinates are determined, on basis of which, with consideration of resilient oscillations expansion speeds, depths of piles penetration into soil are calculated and their step is evaluated.

EFFECT: distribution of relation of depths of pile ends and root deposits directly below subject building, and also under conditions of active buildings and constructions within whole area of pile field without using direct access to piles and also decreasing laboriousness of drilling and digging operations.

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Description

The invention relates to geophysical research methods, namely to seismic exploration, and can be used in geotechnical surveys for previously constructed buildings and structures.

There is a method of determining the depth of immersion of a reinforced concrete pile in the soil when examining the pile foundation by measuring the distance from the soil surface to the lower end of the pile [1]. In this case, the pit is pumped out with the side surface of the pile exposed to its lower end.

The disadvantage of this method is the complexity and duration of determining the depth of immersion piles. In addition, when digging a pit, the stress state of the soil changes, which leads to the shutdown of the examined pile from work.

There is a method of determining the immersion depth of a reinforced concrete pile in the soil when examining a pile foundation, which consists in the fact that a well is drilled near the pile and an alternating electric current is passed through the reinforcement of the reinforced concrete pile [2]. In this case, the induction current is measured in the antenna of the receiving device lowered into the well, and the distance from the soil surface to the lower end of the pile is determined by changing the magnitude of the induction current.

The disadvantages of this method is the inability to access the reinforcement of each pile, the need for drilling near the pile of a special well and the implementation of measures to maintain its walls, which increases the complexity and cost of work.

A known method for determining the length of immersed in the medium of an electrically conductive pile [3]. It previously determines the vertical location of the specific conductivity of the medium by means of its electromagnetic sounding. After that, an alternating current of low frequency is passed through the medium between the pile and the grounding electrode and its value is measured in the pile. According to the magnitude of the current in the pile and the known distribution of the electrical conductivity of the medium, the length of the immersed part of the pile is judged.

The main disadvantages of this method are the significant background of domestic and industrial electrical noise, which leads to low reliability of the interpretation conclusions, as well as the need for access to the reinforcing base of the pile, which is not always possible. Moreover, it is unrealistic to determine the pitch of pile ends and conduct similar studies throughout the pile field. Also, the use of electromagnetic waves is limited by the wide distribution of clay, water-saturated soils, which are screens for them, which limits the possibilities of the method itself and does not allow determining the structural features of the base rocks.

There is a method of determining the depth of piles using the Pile length meter "IDS-1" [4], adopted by us as a prototype. This method consists in exciting vibrations in the pile head with a specialized hammer with an integrated force sensor and a piezoelectric transducer. Based on the value of the arrival time of the acoustic signal (waves) from the end of the pile and the known values of the speed of passage of elastic vibrations in the body of the pile, its length is judged.

The disadvantages of this method are the lack of reliable knowledge about the speed of propagation of waves in various types of piles. The excitation of vibrations in the pile head with a specialized hammer requires direct access to each of the piles, which leads to significant labor and financial costs. The method does not allow to determine the depth of piles, their pitch and structural features of the host soil in the framework of one method.

All known methods, including the prototype, provide only the determination of the depth of pile ends with direct access to each of the piles, and this practically does not allow the determination of the depth of pile ends over the entire area of the pile foundation in existing buildings and structures.

The objective of the present invention is to determine in one way the depth of pile ends, their pitch and structural features of the host deposits throughout the basement area, without direct access to piles. The technical result is the determination of the ratio of the depths of pile ends and primary deposits directly under the building under study, as well as in the conditions of existing buildings and structures within the entire area of the pile field without using direct access to piles and reducing labor costs for excavation and drilling.

The problem is achieved in that in the method of seismic inspection of the pile foundation, including the excitation of vibrations, the determination of the speed and time of arrival of waves, according to the invention, elastic vibrations are excited along the outer walls of the building in the ground using a low-impact source, both on the side of the excitation line and on the opposite side of the building and register them, then determine the speed and arrival times of waves reflected from geological boundaries, then by comparative analysis diffraction phenomena caused by pile ends are distinguished for recording forms in time sections obtained separately from longitudinal and non-longitudinal profile lines, the times of diffraction points and their coordinates are determined, based on which, taking into account the values of the propagation velocity of elastic vibrations, the depth of penetration of piles into the rocks is calculated and appreciate their step.

The claimed combination of signs "... excites elastic vibrations along the external walls of the building in the ground using a low-power shock source both on the side of the excitation line and on the opposite side of the building ..." allows you to determine the depths within the same method without direct access to piles pile endings, pitch piles and structural features of the host deposits. Such information allows us to solve the question of the ratio of the depths of pile ends and primary deposits directly under the building under study, as well as in the conditions of existing buildings and structures within the entire area of the pile field without using direct access to piles. As a result, the need for labor-intensive excavation and drilling is eliminated, which reduces both labor and financial costs for the inspection of the pile foundation.

The analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information, and the identification of sources containing information about analogues of the claimed invention, allowed to establish that the applicant did not find a source characterized by features identical to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototype, as the closest in the totality of the features of the analogue, allowed us to establish a set of significant distinguishing features in relation to the technical result perceived by the applicant in the claimed method set forth in the claims.

Therefore, the claimed invention meets the condition of "novelty."

To verify the compliance of the claimed invention with the condition "inventive step", the applicant conducted an additional search for known solutions in order to identify features that match the distinctive features of the claimed method from the prototype. The search results showed that the claimed invention does not follow explicitly from the prior art for the specialist, since the influence of the transformations provided for by the essential features of the claimed invention is not revealed from the prior art defined by the applicant.

Therefore, the claimed invention meets the condition of "inventive step".

Figure 1 presents a diagram of the formation of reflection points in the longitudinal and non-longitudinal variants of seismic profiling, where AB is the line of points of excitation and reception during longitudinal profiling; VG - line of points of reception for non-longitudinal profiling; DE - the line of formation of reflection points during longitudinal profiling; ZhZ - line of formation of reflection points for non-longitudinal profiling; PV - points of excitement; PP - points of reception; OGT - the general deep point of reflection; C - end of piles.

Figure 2 - selection in a temporary section of the ends of the piles at the diffraction points, where C are the diffraction points caused by the pile ends; K - line of reflections from the roof of bedrock.

Figure 3 is a diagram of observations, where N1 is a longitudinal profile; N2 - non-longitudinal profile; N3 - longitudinal profile.

Figure 4 - comparison of time sections along the longitudinal and non-longitudinal profiles, where C are the diffraction points caused by pile ends; OG1 - line of reflections from the roof of Quaternary clays; K is the line of reflections from the roof of indigenous sandstones.

The method is as follows.

Along the outer walls of the building under study, according to the method of multiple overlappings [5], elastic vibrations are excited in the ground and recorded on the side of the AB excitation line and on the opposite side of the VG building (Fig. 1). In the longitudinal profiling, the excitation points of the PV are on the same line (AB) with the reception points of the PP, and in the non-longitudinal variant, the line of the reception points (SH) is located on the side of the building opposite to the line of the points of excitation (AB). Such placement of the lines of reception and excitation of vibrations provides seismic transmission through the reflected waves of sediments underlying the building.

Longitudinal profiling is aimed at registering in the wave field the features of only the geological structure of the base rocks located in the plane of the AB and DE lines, without the influence of pile ends (C).

In non-longitudinal profiling, the reflection line (LC) is projected directly under the building at half the distance between the AB and the SH. Thus, along with geological features, reflection of pile ends (C) in the recorded wave field is also provided. In order to uniformly illuminate the entire width of the pile field, the distance between the lines of reception and excitation of oscillations is changed due to the displacement of the lines of reception and excitation along the Y axis, but in an interval not greater than the double width of the building.

The excitation of elastic vibrations is realized by directed impacts of a low power source (energy of a single action E = 500 J) sequentially at each point of excitation. The necessary intensity and regularity of the signal is achieved by summing up single effects. Seismic vibrations are recorded using a specialized computerized seismic station and electrodynamic seismic receivers [6]. The following recording parameters are most optimal: a sampling step of 0.1-0.2 ms, a recording length of 1000 samples, a low-pass filter - 1000-1400 Hz, a high-pass filter - 0-14 Hz, and a gain of 40 dB [7].

Reception points (PP) and excitation points (PV) are arranged as follows: the distance between the PS (Δx) is equal to the distance between the PS (Δ1) and is 0.5-1 m, the maximum distance of the PP from the PV (Lmax) is not more than 48 m, the distance of the PP from the PV (Lmin) is minimum - 0 m, the frequency of observations (n) should be in the range from 12 to 24.

The parameters of the observation systems, the source and recording equipment for the most common values of research depths of 5-20 m, characterized by the propagation velocity of elastic waves of 500-2000 m / s, provide registration of waves in the frequency range of 300-400 Hz.

The recorded seismic vibrations are digitally processed to determine the velocities and arrival times of waves reflected from geological or physical boundaries. The wave propagation velocity in the geological environment is determined by the traveltime curves of the reflected waves [8]. The final result of the processing process is the final total time sections along the longitudinal and non-longitudinal profile lines.

In accordance with the obtained velocity law, which describes the distribution of the values of the elastic wave propagation velocities in the studied time interval, a deep stratigraphic reference of the reflections recorded on time sections is performed. The depth of the reflecting horizon is defined as half the product of speed at the time of its registration [6]. When determining depths on a non-longitudinal profile, by amending the velocity law, the distance between the PP and PV lines is taken into account. Based on the definitions of the depths of the root deposits for all profile lines, an areal diagram of their roof is constructed within the entire pile field.

. Шаг свай определяют согласно масштабу оси абсцисс, то есть он равен разности координат Х двух близлежащих точек дифракции.The localization of diffraction phenomena associated with the ends of piles is carried out by a comparative analysis of the recording form on time sections obtained separately from longitudinal and non-longitudinal profile lines. Pile endings in a time section (Fig. 2) along a non-longitudinal profile line are distinguished in the form of overlapping diffraction zones, with characteristic diffraction triangles that are absent in a time section of a longitudinal profile. By the location in the time section of the diffraction points (C), the time of their registration (t) and the coordinate along the profile (X) are determined. Taking into account the values of the elastic vibration velocity (V) in the interval from the observation surface to the diffraction points fixed at time t, and taking into account the fact that the double passage time of the waves is plotted on the time section along the ordinate axis, the calculation of the depth of formation of the diffraction points (depth of pile ends ) is made according to the formula

. The pitch of the piles is determined according to the scale of the abscissa axis, that is, it is equal to the difference in the X coordinates of two nearby diffraction points.

An example illustrating the implementation of this method at a specific facility was obtained within the city of Perm when examining the western wing of a two-story building.

At this object without direct access to piles using a low-impact shock source (sledgehammer), seismic profiling was performed using the multiple overlap technique [5].

Longitudinal seismic profiling is carried out as follows. Along the southern side of the building (Fig. 3), at a distance of 1 meter from the wall with a pitch of PV = 1 m, a hammer was struck - profile N1. In this case, the oscillations were recorded using OYO SV-20 seismic receivers located on the same side of the building with a step of PP = 1 m. The oscillations were recorded using the IS-48 wide-range computerized digital seismic station [7].

In non-longitudinal profiling, the line of excitation of vibrations is aligned with the longitudinal profiles N1, and the line of receiving vibrations (pitch PP = 0.5 m) was located on the opposite north side of the building (profile N3). Thus, the line of reflection points is projected directly under the building and forms a non-longitudinal profile N2.

Further digital processing of recorded seismic data was performed using the Express-OGT software package [8]. During processing, a wide range of procedures was used: bandpass, inverse, fan, coherent filtering, recording form correction, check summation at each processing stage. The final result of digital processing of seismic data are the final time sections of the common deep point (sections of the CDP) along profiles N1 and N2, which are shown in figure 4 [9].

During processing using the ANVEL program, the law of the distribution of elastic wave velocities in rocks containing piles was obtained from the same package. The algorithm of the program is based on the analysis of hodographs of reflected waves. Since the hodograph, which is a function of the dependence of the travel time of the wave on the coordinates of the points of excitation and observation, is a hyperbola, then by selecting the curvature of this hyperbola from the CDP seismograms, an estimate of the velocity to one or another reflecting boundary is found [6, 9]. Thus, for the N2 non-longitudinal profile of interest to us, the law has the following form: 5 ms - 1000 m / s, 8 ms - 1050 m / s, 9 ms - 1100 m / s, 10 ms - 1100 m / s, 25 ms - 1150 m / s, 50 ms - 1500 m / s.

первый отражающий горизонт (ОГ1), соответствующий времени 9-11 мс, с учетом полученного скоростного закона находится на глубине 5-6 м и связан с кровлей четвертичных глин. Второй отражающий горизонт (К), соответствующий времени 19-25 мс, приурочен к кровле коренных песчаников на глубине в 11-14 м.At the next stage - interpretation - in time sections (Fig. 4) two reflecting horizons are distinguished. According to the formula

the first reflecting horizon (OG1), corresponding to a time of 9-11 ms, taking into account the obtained velocity law, is at a depth of 5-6 m and is associated with the roof of Quaternary clays. The second reflecting horizon (K), corresponding to a time of 19-25 ms, is confined to the roof of primary sandstones at a depth of 11-14 m.

After tying the main reflecting horizons, we carry out a comparative analysis of the recording form of temporary sections obtained by the longitudinal (N1) and non-longitudinal profile (N2). It shows the presence in the wave pattern of a non-longitudinal profile N2 in the interval of reflection from the roof of clays of a number of diffraction points (C) (Fig. 4), which are associated with pile ends.

On the X axis, the diffraction points have coordinates 1 m, 3.5 m, 6 m, 8.5 m, 11 m, 13.5 m, 16 m. On the time axis t, on which the travel time of the waves to the geological object and vice versa is plotted, all diffraction points are recorded in time limits 9-11 ms.

, находим глубины, на которых образовались точки дифракции. То есть глубина проникновения свай в породы равна произведению скорости упругих волн от поверхности наблюдений до точек дифракции на половину времени их регистрации.Further, given that the algorithm for approximating time values with the desired values is based on the formula

, we find the depths at which the diffraction points formed. That is, the penetration depth of the piles into the rocks is equal to the product of the speed of the elastic waves from the observation surface to the diffraction points by half the time of their registration.

So,

- point C ₁ (figure 4), having a coordinate X ₁ = 1.0 m, is fixed at a time t ₁ equal to 9.5 ms, or 0.0095 seconds, the propagation velocity of elastic waves up to a time of 9.5 ms according to the obtained velocity law is 1100 m / s, therefore, the penetration depth of the pile into the rocks will be

- point C ₂ (figure 4), having the coordinate X ₂ = 3.5 m, is fixed at a time t ₂ equal to 10 ms, or 0.010 seconds, the speed of propagation of elastic waves up to a time of 10 ms according to the obtained velocity law is 1100 m / s, therefore, the penetration depth of the pile into the rocks will be

- for other points C similarly.

The step between the diffraction points (dX) and, respectively, between the piles is determined from the difference in coordinates X ₂ and X ₁ . In our case, it will be dX = X ₂ -X ₁ = 3.5-1 = 2.5 m.

Thus, the use of this method provides a determination of the ratio of the depths of pile ends, their pitch and root deposits directly under the building under study (in the conditions of existing buildings and structures) within the entire area of the pile field in one way without using direct access to piles and using labor-intensive earthworks and drilling operations.

Information sources

1. Methods of inspection and design of foundations and foundations for overhaul, reconstruction and superstructure of buildings. - M., Stroyizdat, 1972, p. 14.

2. Copyright certificate of the USSR No. 861477, cl. E 02 D 33/00, 1979.

3. Patent of the Russian Federation No. 2190865, cl. G 01 V 3/06, G 01 B 7/02, 1996.

4. The meter length piles "IDS-1". http://logsys.ru/apparat/ids.htm

5. Meshbay V.I. Multiple overlap technique in seismic exploration. M .: Nedra, 1985.

6. Gurvich I.I., Boganik G.N. Seismic Intelligence: A Textbook for High Schools. - M .: Nedra, 1980.S. - 139, 234, 261, 411, 428, 442.

7. Shallow seismic station IS-48. User's manual. Latvia, Riga - 1997.

8. “Express-OGT” - a package of seismic data processing software using the OGT method. User's manual. Moscow Institute of Oil and Gas named after Gubkin. Moscow - 1990.

9. Hatton L., Werdington M., Makein J. Processing of seismic data. Theory and Practice / Transl. from English M .: Mir, 1989.S. - 10, 27.

Claims (1)

A method of seismic inspection of pile foundations, including the excitation of vibrations, the determination of the speed and time of arrival of waves, characterized in that the elastic vibrations excite along the outer walls of the building in the ground without direct access to the piles by means of an impact source of low power and register them as on the side of the excitation line, and on the opposite side of the building, determine the speeds and times of arrival of waves reflected from geological boundaries, then by comparative analysis of the shape records on time sections taken separately along longitudinal and non-longitudinal profile lines distinguish diffraction phenomena caused by pile ends, determine the times of diffraction points and their coordinates, based on which, taking into account the values of the propagation velocity of elastic vibrations, the depths of penetration of piles into the rocks are calculated and their pitch is estimated .

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