KR20210071137A - Method for evaluating the embedment depth and ground bearing capacity of unknown bridge foundation - Google Patents

Abstract

The present invention relates to a method for calculating the penetration depth and ground bearing power of a ballastless foundation underneath a bridge which can improve the reliability of measurements. The method for calculating the penetration depth and ground bearing power of a ballastless foundation underneath a bridge comprises: a first step of drilling a receiving hole in the ground within a prescribed distance from a ballastless foundation for measurement, and installing an elastic wave reception sensor; a step of positioning a medium cone penetration tester at a position opposite to the receiving hole around the ballastless foundation; a third step of generating an elastic wave signal while driving the medium cone penetration tester into the ground; and a fourth step of receiving an elastic wave signal generated by the third step by the elastic wave reception sensor, and analyzing the received signal to calculate the penetration depth of the ballastless foundation.

Description

{METHOD FOR EVALUATING THE EMBEDMENT DEPTH AND GROUND BEARING CAPACITY OF UNKNOWN BRIDGE FOUNDATION}

The present invention relates to a technique for calculating the rooting depth and the ground bearing capacity of a free foundation under a bridge.

There are shallow foundations and deep foundations for bridge foundations. Shallow foundation is a type of foundation that directly transmits the load of the superstructure to the ground through the bottom of the foundation. There are independent foundations, continuous foundations, composite foundations, and front foundations. A deep foundation is a type of foundation that transmits the load of the superstructure into the ground through the tip and main surface of the foundation. There are pile foundations and caisson foundations.

The design ground surface of the bridge foundation structure should be stable over a long period of time and the bearing capacity should be expected. In addition, resistance to consolidation settlement, freezing and thawing, and scouring must be secured. For this, the stress generated in the foundation ground must be sufficiently small compared to the shear fracture stress of the ground.

The effective insertion depth of the bridge foundation is an important factor in calculating the vertical bearing capacity, and the ground in the case of obtaining the effective insertion depth can generally take the design ground plane in the normal state.

The current state of the railroad bridge's substructure is being comprehensively evaluated through foundation damage, pile damage and defects, and unequal settlement of the foundation due to the depth of penetration of the foundation, lateral flow, and scour.

The evaluation of the condition of an unknown foundation for a railway bridge with a long service life (a foundation structure that is difficult to grasp due to the lack of design data) must be preceded in implementing the recent and frequent pole railing.

In order to evaluate the condition of the free foundation of a railway bridge with a long service life, a method of excavating the constructed surrounding ground and evaluating the depth, type, and ground conditions of the foundation of the railway bridge through visual inspection and various field test methods can be used. However, this method is complicated and uneconomical, and may cause problems such as damage to the railroad bridge foundation.

Accordingly, the inventor of the present invention has researched for a long time a method for estimating the embedding depth of the free foundation under the bridge and the bearing capacity of the ground, and after trial and error, he has completed the present invention.

An object of the present invention is to provide a method for calculating the depth of penetration and ground bearing capacity of a free foundation under a bridge that can improve the reliability of the measured values by maintaining the striking energy constant by using a medium-sized cone penetration tester that strikes pneumatically.

The purpose of this study is to provide a method for calculating the penetration depth and ground bearing capacity of an immature foundation under a bridge, which can estimate the phase velocity change of the received seismic wave to calculate the penetration depth of the immature foundation.

The purpose of this study is to provide a method for calculating the penetration depth and ground bearing capacity of the free foundation under the bridge that can calculate the bearing capacity of the ground using the correlation with the standard penetration test.

On the other hand, other objects not specified in the present invention will be additionally considered within the range that can be easily inferred from the following detailed description and effects thereof.

According to an embodiment of the present invention, it relates to a method for calculating the depth of rooting and the ground bearing capacity of the free foundation under the bridge,

A first step of drilling a receiving hole in the ground within a certain distance from the free foundation for measurement, and installing an elastic wave receiving sensor;

a second step of positioning a medium cone penetration tester in a position opposite to the receiving hole with respect to the free base;

a third step of driving the medium cone penetration tester and generating an elastic wave signal while penetrating the ground;

and a fourth step of receiving, by the elastic wave receiving sensor, the elastic wave signal generated by the third step, and calculating the penetration depth of the imperfect base by analyzing the received signal;

It provides a method for calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge.

According to an embodiment of the present invention, the first step is

After drilling, inserting a tube to prevent collapse of the hole wall and installing the acoustic wave receiving sensor in the tube.

According to an embodiment of the present invention, the second step is

The distance between the receiving hole and the medium cone penetration tester may include setting within 10m.

According to an embodiment of the present invention, the third step is

It may include pneumatic driving.

According to an embodiment of the present invention, the third step is

A free-falling hammer with a weight of 30 kgf strikes a detachable rod with an outer diameter of 32 mm and a length of 1000 mm from 500 mm to generate a ground seismic signal as the detachable rod penetrates.

According to an embodiment of the present invention, the third step is

It may include measuring the number of hits (N' value) required to penetrate the detachable rod by 100 mm, and calculating the ground bearing capacity of the free foundation based on the correlation with the standard penetration test.

According to an embodiment of the present invention, the fourth step is

The method may include estimating a phase velocity change for each depth of the received acoustic wave signal to calculate the impingement depth of the imperfect base.

Reliability of the received seismic wave measurement value can be improved by using the method for calculating the rooting depth and ground bearing capacity of the free foundation under the bridge according to the present invention.

In addition, by using the present invention, it is possible to easily calculate the rooting depth and the ground bearing capacity of the free foundation.

On the other hand, even if it is an effect not explicitly mentioned herein, it is added that the effects described in the following specification expected by the technical features of the present invention and their potential effects are treated as described in the specification of the present invention.

1 is a view showing a medium-sized cone penetration tester according to the present invention.
FIG. 2 is a view showing that an elastic wave signal is generated using the medium cone penetration tester according to the present invention, the geophone sensor installed in the receiving hole is received, and the received signal is analyzed and displayed.
3 to 5 are diagrams showing that the mid-sized cone penetration tester is extended according to the present invention to generate an elastic wave signal while penetrating into the ground, and the position of the geophone sensor is changed in response to the penetrating medium-sized cone penetration tester.
Figure 6 (a) shows the change of the phase velocity value according to the frequency in the case where there is a foundation pile between the elastic wave signal generator and the geophone sensor, and Figure 6 (b) is the case where there is no foundation pile between the elastic wave signal generator and the geophone sensor It is a diagram showing the change of the phase velocity value according to the frequency.
7 is a flowchart of a process showing a method for calculating the depth of rooting and the ground bearing capacity of the bridge lower free foundation according to the present invention.
It is revealed that the accompanying drawings are exemplified by reference for understanding the technical idea of the present invention, and the scope of the present invention is not limited thereby.

In the description of the present invention, if it is determined that the subject matter of the present invention may be unnecessarily obscured as it is obvious to those skilled in the art with respect to related known functions, the detailed description thereof will be omitted.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, an embodiment of the method for calculating the rooting depth and ground bearing capacity of the free foundation under the bridge according to the present invention will be described in detail with reference to the accompanying drawings, and in the description with reference to the accompanying drawings, the same or corresponding components are the same Reference numerals are given, and overlapping descriptions thereof will be omitted.

Although there is a dynamic cone penetration test to evaluate the condition of compacted soil, it is suitable for application to the completed upper subgrade, and it is reliable in the very irregular and mixed ground with materials such as gravel or crushed stone, such as the ground constituting the lower foundation of a railway bridge. It is difficult to calculate the measurements.

In addition, there is a standard penetration test to calculate the ground bearing capacity, etc., but the standard is large, it takes a lot of manpower and time, and it is not suitable for the field conditions of the railway bridge in use.

Accordingly, the present invention is to calculate the penetration depth of the free foundation and the bearing capacity of the ground using a medium cone penetration tester.

7 is a flowchart of a process showing the method for calculating the depth of insertion and the ground bearing capacity of the bridge lower free foundation according to the present invention.

1 is a view showing a medium-sized cone penetration tester according to the present invention.

As shown in FIG. 1 , the present invention generates an elastic wave by a medium cone penetration tester 10, and the medium cone penetration tester 10 according to the present invention includes a pneumatic motor (M), a detachable rod 11, and an inserted cone. (12), and a hammer (13).

The medium cone penetration tester 10 secures high striking energy by increasing the standard to compensate for the shortcomings of the dynamic cone penetration test, and increases the rigidity of the separate rod 11 and the inserted cone 12, and the separate rod 11 ), it is possible to achieve a maximum penetration depth of 10 m.

The detachable rod 11 has an outer diameter of 32mm and a length of 1000mm, and may extend the length by combining several in the longitudinal direction. An insertion cone 12 having a pointed end is coupled to the end of the detachable rod 11 to facilitate insertion into the ground. The insertion cone 12 and the detachable rod 11 may be separated and coupled to each other. As such, the separable rod 11 is freely coupled and separated from the insertion cone 12, and it is easy to combine and separate the separable rods 11 so that a plurality of the separable rods 11 are long coupled to the deep depth of the ground. (11) can be penetrated.

The hammer 13 is free-falling with a weight of 30 kgf hammer 13 and free-falling from 500 mm to strike the detachable rod.

At this time, the blow of the hammer 13 is driven pneumatically. As the hammer 13 is pneumatically driven, the striking energy can be kept constant, and as the striking energy becomes constant, the signal generated by the striking energy is also constant, and the reliability of various measured values calculated therefrom is increased. .

The pneumatic pressure from the pneumatic motor (M) is transferred to the lift part of the hammer 13 through the hose with the valve in the guide part of the medium cone penetration tester 10, and the hammer 13 is raised to a certain drop. After that, the hammer 13 will fall free and hit the detachable rod.

FIG. 2 shows that an acoustic wave signal is generated using the medium cone penetration tester 10 according to the present invention, the geophone sensor 20 installed in the receiving hole H receives it, and the received signal is analyzed and displayed. It is a drawing.

As shown in FIG. 2 , when an elastic wave is generated in the ground using the medium cone penetration tester 10 according to the present invention, the generated elastic wave rides on the ground and is transmitted to the geophone sensor 20 of the receiving hole (H). do.

In this case, the phase velocity value of the elastic wave received by the geophone sensor 20 may be calculated differently in the case where there is a gratuitous basis (P) on the path through which the elastic wave passes and in the case where there is no imperfect basis (P). From this, the rooting depth of the impermanent foundation (P) can be estimated, which will be described later in detail.

A signal at the moment (trigger) when the hammer 13 strikes the detachable rod 11 is transmitted through communication, and an elastic wave signal received from the geophone sensor 20 is received and the elastic wave velocity can be calculated through the time difference. have. The seismic velocity can be calculated as distance/time.

In this way, the shear modulus of the ground may be calculated by calculating the seismic velocity.

The time-frequency analyzer 30 communicates with the geophone sensor 20 of the signal unit and the receiving hole H of the medium cone penetration tester 10 and analyzes the information transmitted from both sides. When the analyzed information is delivered to the indicator 40 , the indicator 40 may display it as a graph or the like so that the user can check it.

As shown in Figure 7, the method for calculating the penetration depth and ground bearing capacity of the free foundation under the bridge according to the present invention is the first step of drilling the receiving hole (H) and installing the geophone sensor 20, the medium cone penetration tester ( The second step of positioning 10), the third step of generating an elastic wave signal by driving the medium cone penetration tester 10, the geophone sensor 20 receives the elastic wave signal, and the and calculating the ground bearing capacity and the like.

As shown in FIG. 2 , a receiving hole (H) is drilled in the ground within a predetermined distance from the free foundation (P) for measurement, and an elastic wave receiving sensor can be installed. In this case, the elastic wave receiving sensor includes a geophone sensor 20 .

The step of drilling the receiving hole (H) and installing the elastic wave receiving sensor includes inserting a pipe to prevent collapse of the hole wall after drilling the ground, and installing the elastic wave receiving sensor in the inserted pipe. At this time, the tube may be formed of a PVC tube so as not to interfere with the reception of acoustic waves.

And the medium cone penetration tester (10) is positioned in a position opposite to the receiving hole (H) around the free base (P). As described above, a signal is sent from one side to the other centering on the imperfect base (P) to determine the depth of insertion of the imperfect base (P), and the process of generating and receiving a signal along the depth is repeated.

On the other hand, the distance between the medium cone penetration tester 10 and the receiving hole (H) may be formed within 10m. Preferably, both the medium cone penetration tester 10 and the receiving hole (H) are located within a radius of 3 m from the free foundation (P). This is for more accurate transmission and measurement of seismic signals.

At this time, while extending 1 m (1000 mm) of the detachable rod 11 of the medium cone penetration tester 10, the detachable rod 11 can be extended to a deep depth to penetrate and generate a signal.

On the other hand, the position of the geophone sensor 20 installed in the receiving hole (H) is also changed according to the depth into which the detachable rod 11 is penetrated. As the penetration depth increases, the location of the geophone sensor 20 is also installed to correspond to the depth.

In the present invention, when the detachable rod 11 reflects 1m and penetrates 1m by one detachable rod, the geophone sensor 20 is also located at a depth of 1m in the receiving hole (H) accordingly, and the detachable rod 11 ) can be combined and penetrated to a depth of 2m, the location of the geophone sensor 20 may also be located at a depth of 2m from the receiving hole (H).

3 to 5 show the position of the geophone sensor 20 in response to the medium cone penetration tester 10 being extended to generate an elastic wave signal while penetrating into the ground by extending the medium cone penetration tester 10 according to the present invention. It is a diagram showing that is changed.

Referring to FIG. 3 , while one detachable rod, that is, a 1 m detachable rod is inserted into the ground, an elastic wave signal is continuously generated, and the geophone sensor 20 of the receiving hole H receives a signal for this.

Referring to FIG. 4 , it can be seen that one detachable rod 11 is coupled to the other detachable rod 11 ′ and penetrates to a depth of 2 m. The geophone position in the receiving hole (H) is also deepened corresponding to the insertion depth of the coupled detachable rods (11, 11').

Referring to FIG. 5 , one detachable rod 11 is coupled to another detachable rod 11 ′, and another detachable rod 11” is coupled to the other detachable rod 11 ′ to be attached to the ground. You can check what has been inserted.

The geophone position in the receiving hole (H) is also deepened in response to the insertion depth of the coupled detachable rods (11, 11', 11”).

3 to 5, while changing the position of one geophone sensor 20 in response to the insertion depth of the detachable rod, rather than installing a plurality of geophone sensors 20 in the receiving hole (H) It is to receive the elastic wave generated by the detachable rod.

When a plurality of geophone sensors are installed, all of the seismic waves generated by the separable rod are measured by each geophone sensor 20, and accordingly, the amount of data not only increases, but also the rooting of the impermanent basis (P) from these numerous data. It is also not easy to select valid data for estimating depth.

Therefore, the present invention installs only one geophone sensor 20 at a position corresponding to the penetration depth of the separable rod and analyzes the elastic wave signal received from one geophone sensor 20 to determine the penetration depth of the free foundation (P). can be easily derived.

Figure 6 (a) shows the change of the phase velocity value according to the frequency in the case where there is a foundation pile between the elastic wave signal generator and the geophone sensor, and Figure 6 (b) is the case where there is no foundation pile between the elastic wave signal generator and the geophone sensor It is a diagram showing the change of the phase velocity value according to the frequency.

As shown in FIGS. 6(a) and 6(b), the change in the phase velocity value according to the frequency can be confirmed in the case where there is a foundation pile between the elastic wave signal generator and the geophone sensor and when there is no foundation pile.

Using this, in the present invention as well, it is possible to check the change in the phase velocity value in the case where there is a gratuitous basis between the seismic signal generated from the insertion cone coupled to the end of the detachable rod and the geophone sensor located in the receiving hole. Therefore, it is possible to estimate the rooting depth of the imperfect foundation.

On the other hand, the present invention can calculate the ground force, such as the ground bearing force, the internal friction angle, the adhesive force, the deformation coefficient, etc. using a medium-sized cone penetration tester. It is possible to measure the number of blows (N' value) required to penetrate the detachable rod according to the present invention by 100 mm, and calculate the ground bearing capacity of the free foundation based on the correlation with the standard penetration test.

Several formulas have been proposed to calculate the ground bearing capacity, internal friction angle, adhesion force, and strain coefficient, etc. through the N value measured according to the conventional standard penetration test. Therefore, the present invention corrects the N' value obtained through the test using a medium cone penetration tester to the standard penetration test, and applies it to the equation for calculating the conventional ground bearing capacity, internal friction angle, adhesion force, deformation coefficient, etc. will be calculated

In order to consider the correlation with the standard penetration test, the measured N' value can be corrected by considering the penetration energy, the surcharge of the ground, and the groundwater level.

First, the method of correcting the N' value using the penetration energy is as follows.

In consideration of the weight, drop, cone cross-sectional area, and penetration depth of the standard penetration test and the medium cone penetration test, apply to the theoretical formulas suggested below, respectively.

Penetration Energy (Q) =

where, M: weight of the striking hammer

H: falling

A : Cone cross-sectional area

δ: penetration depth.

For example, the number of blows may be inversely proportional to the difference in penetration energy between the standard penetration test and the medium cone penetration test. Therefore, the N' value measured by the medium cone penetration test can be corrected in consideration of the penetration energy of the standard penetration test and the medium cone penetration test. can be saved

Next, the measured N' value may be corrected in consideration of the groundwater level.

When performing a medium penetration test on fine particles and silt layers, the N' value, which is underestimated due to the effect of excessive pore water pressure generated during striking, can be corrected by the following formula.

Here, N: Corrected N value

N' : measured value

In this way, the ground bearing capacity, internal friction angle, adhesion force, deformation coefficient, etc. can be obtained using the N value corrected in consideration of the groundwater level.

Furthermore, it is possible to correct the N' value through the correction of the overhead load.

Overload correction is affected by depth, and it is corrected using a generalized constant based on an effective vertical stress of 100kPa.

Here, CN: Corrected N value

P: 100 kPa

: 유효연직응력

: effective vertical stress

In this way, the N' value measured through the medium cone penetration test is corrected in consideration of the correlation with the standard penetration test, and then the bearing capacity of the ground, internal friction angle, adhesion force, and deformation coefficient are obtained.

As a specific method for obtaining the bearing capacity of the ground, the internal friction angle, the adhesive force, the deformation coefficient, etc., various methods proposed in the prior art may be used, and a detailed description thereof will be omitted.

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the protection scope of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention pertains.

10: Medium cone penetration tester
11, 11', 11”: Detachable Rod
12: insert cone
13: Hammer
M: pneumatic motor
20: geophone sensor
30: time-frequency analyzer
40: indicator
P: free basics
H: receiver

Claims (7)

It relates to a method for calculating the penetration depth and ground bearing capacity of the free foundation under the bridge,
A first step of drilling a receiving hole in the ground within a certain distance from the free foundation for measurement, and installing an elastic wave receiving sensor;
a second step of positioning a medium cone penetration tester in a position opposite to the receiving hole with respect to the free base;
a third step of driving the medium cone penetration tester and generating an elastic wave signal while penetrating the ground; and
and a fourth step of receiving, by the elastic wave receiving sensor, the elastic wave signal generated by the third step, and calculating the penetration depth of the imperfect base by analyzing the received signal;
A method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge. According to claim 1,
The first step is
After drilling, inserting a tube to prevent collapse of the hollow wall and installing the acoustic wave receiving sensor in the tube,
A method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge. According to claim 1,
The second step is
The distance between the receiving hole and the medium cone penetration tester, characterized in that it comprises setting within 10m,
Method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge. According to claim 1,
The third step is
characterized in that it comprises pneumatically driven,
A method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge. According to claim 1,
The third step is
It is characterized in that it falls freely with a 30kgf hammer and strikes a detachable rod with an outer diameter of 32mm and a length of 1000mm from 500mm to generate an acoustic wave signal of the ground as the detachable rod penetrates,
A method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge. 6. The method of claim 5,
The third step is
Measuring the number of hits (N' value) required to penetrate the detachable rod by 100 mm, and calculating the ground bearing capacity of the free foundation based on the correlation with the standard penetration test,
A method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge. According to claim 1,
The fourth step is
and estimating the phase velocity change for each depth of the received acoustic wave signal, and calculating the impingement depth of the imperfect base.
A method of calculating the depth of penetration and ground bearing capacity of the free foundation under the bridge.

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