KR20170051710A - Apparatus for measuring shear strength of soil in ground subsidence envirinment - Google Patents

Abstract

The present invention provides a measurement device, simulating generation of a sink hole and locating an aspect of change of a shear stress of soil during a generation process of the sink hole. More specifically, the present invention is able to comprehend a maximum shear stress and the remaining shear stress of the soil during a generation process of the sink hole to quantitatively comprehend a relation between the generation of the sink hole and the shear stress. The present invention comprises: a chamber unit storing soil therein; a retraction guide unit having a connection rod; and a load cell installed in a lower portion of the chamber unit to support the chamber unit.

Description

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to an apparatus for measuring soil shear strength of a soil-

The present invention relates to a test apparatus or a measuring apparatus for grasping the behavior of geology and ground, and more particularly, to an apparatus for measuring the shear strength of a soil in a ground subsidence environment such as a sink hole.

The sinkhole is becoming an issue.

A sinkhole is one of the subsurface phenomena that occurs when the inside of the ground becomes soft or empty and the upper ground sinks. If the ground is weak or the ground is changed and rain is repeated in the state of cavity formation, the cavity is diffused and finally the sink hole is formed due to the collapse of the ground on the cavity top. For example, limestone grounds may dissolve in groundwater over a long period of time, or may be caused by rapid drainage of groundwater that has stayed at a certain level. The sinkholes due to this natural phenomenon are sometimes found to have a diameter of several tens of meters and a depth of more than one hundred meters. In the past, sinkholes were not classified as major catastrophic disasters because they occurred mainly in the limestone or mining areas. However, in recent years, sinkholes have occurred in urban areas where people and facilities are concentrated.

Downtown sinkholes are classified as either naturally occurring or due to poor engineering work. Especially, in the urban engineering works, groundwater excavation without sufficient investigation changes the groundwater level of the surrounding ground, which causes stability of the artificial structure built in the ground and weakens the ground supporting the underground facilities. For this reason, it is necessary to constantly monitor the stability of the ground considering the characteristics of geologic and groundwater in the dangerous areas in order to investigate the downtown sink hole disasters and construct a maintenance system.

Currently, disaster safety measures for sinkholes are being conducted in order to resolve the risk of sinkhole risk itself and to relieve social uneasiness. Recently, as part of a preliminary investigation of a downtown sink hole, a project has been conducted to detect underground cavities beneath urban pavements through vehicles equipped with Ground Penetrating Radar (GPR). However, the ground penetrating radar is not the perfect equipment for investigating the ground deformation near underground structures, only sensing information about strata within a few meters of the surface (up to 1 to 5 meters). This is also the opinion of experts who analyze video. Therefore, it is practically difficult to accurately detect ground loosening areas and underground cavities in various sizes even in the case of a new technology called surface transmission radar. Therefore, a systematic and scientific approach is needed to identify the mechanism of the sink hole and establish a sink hole alarm system.

In order to prepare for sinkholes, it is necessary to quantify the risk of occurrence of sinkholes and to monitor the stability of the ground on a daily basis, starting with identifying causes of sinkholes. Although the physical causes of sinkholes have been identified at present, there are limits to assessing and predicting risks by quantifying the risk of occurrence. Research to quantify sinkhole risk should be preceded.

One of the most important factors in quantifying the risk of sinkholes is the shear strength of soil. Since the sinkholes sink into the upper ground with cavities in the ground, the relationship between the gravity (shear stress) acting on the upper ground and the shear resistance (shear strength) between the sinkhole and the surrounding ground is very important Do. When the shear stress exceeds the threshold value, a depression occurs. Therefore, it is very important to quantitatively evaluate the shear stress and shear strength of the ground in case of the ground subsidence in order to quantify the risk and safety of the sink hole.

The present invention solves the above-mentioned problems, and it is possible to grasp the change of the shear strength of the soil during the generation of the sinkholes while simulating the sinkholes, and particularly, to measure the shear strength of the soil submerged soil to be able to grasp the maximum shear strength and residual shear strength The purpose of the device is to provide.

In order to achieve the above object, according to the present invention, there is provided an apparatus for measuring a soil shear strength of a ground subsidence soil, comprising: a soil receiving unit for receiving soil gypsum to simulate a soil body, a first penetrating part on the upper surface, ; A second panel sandwiched between the first penetration portion and the second penetration portion; a second panel sandwiched between the first penetration portion and the second penetration portion; A recessed guiding portion having a connecting rod for connecting thereto; And a load cell installed at a lower portion of the tilting portion to support the tilting portion so that when the tilting guide portion is pulled to the lower side of the tilting portion to slide the tilting body between the first panel and the second panel, The working shear stress is measured in the load cell.

In one embodiment of the present invention, a plurality of water inlets are formed on one side surface of the toe portion to adjust the water level of the water to be filled in the soil.

According to an embodiment of the present invention, a bag portion capable of being held by the user is formed below the second panel of the recess guide portion.

In another embodiment of the present invention, annular first slits and second slits are formed between the outer circumferential surface of the first panel and the inner circumferential surface of the first penetrating portion, and between the outer circumferential surface of the second panel and the inner circumferential surface of the second penetrating portion And an annular ring formed in a ring shape so as to form a separation surface between the first body and the second body, the second body being inserted into the first slit and passing through the second slit, do. Particularly, teeth are continuously formed in the lower portion of the incision ring, so that the body can be easily separated.

In addition, it is preferable that a handle is formed on an upper portion of the incision ring so that the user can grasp the incision ring to rotate the incision ring.

Also, in one embodiment of the present invention, a ring-shaped channel for receiving water is formed in the inside of the incision ring, and a plurality of water discharge holes may be formed in the lower portion of the incision ring.

In another embodiment of the present invention, the incision ring may be formed in a cylindrical shape.

According to another aspect of the present invention, there is provided a torsion bar, comprising: a torsion bar which receives a gravel inside to simulate a torsion bar, has a first penetrating part on an upper surface thereof and a second penetrating part on a lower surface thereof; A pedestal portion for supporting the toe portion at a lower portion of the toe portion; A first panel sandwiched between the penetrating portions of the upper surface of the touched portion and a connecting rod connecting the first panel and the receiving portion to each other through the inside of the touched portion; And a load cell installed at a lower portion of the receiving portion to raise the toe portion so that a shearing stress acting on the sliding surface when the toe body between the first panel and the receiving portion slides causes the load cell .

The apparatus for measuring the soil shear strength of the ground depression ground according to the present invention has an advantage in that it can accurately grasp the change in the shear stress of the soil in a time series manner while simulating the process of generating the sink hole. More specifically, there is an advantage that residual shear stress and maximum shear stress, which are important quantitative indicators relating to the occurrence of sinkholes, can be measured.

In particular, it is the measurement of residual shear stress, which is the most important factor in the occurrence of sinkholes. The residual shear stress of the soil is formed by an external force, and a sliding surface is formed. The frictional force existing between the soil particles and the soil particles is reduced and the soil particles are completely rearranged along the already formed shear surface. . It is therefore regarded as the minimum shear stress for a given strain. The residual shear stress is mainly determined by a ring shear test device or an indirect shear test device capable of infinite rotation. However, the two test devices can not take into account the resistance of the soil to the vertical direction and have the disadvantage that the shear section can not be formed in advance. Therefore, it is possible to measure the residual shear stress more reliably because it can be measured by two methods depending on whether the shear section is formed in advance in this test apparatus.

The data accumulated through the present invention is expected to provide an opportunity to evaluate and prepare for sink hole occurrence in comparison with the shear strength of the observed soil in the area of the ground subsidence.

On the other hand, even if the effects are not explicitly mentioned here, the effect described in the following specification, which is expected by the technical features of the present invention, and its potential effects are treated as described in the specification of the present invention.

1 is a schematic perspective view of a main portion of an apparatus for measuring soil shear strength of a soil depression ground according to an embodiment of the present invention.
2 is a schematic cross-sectional view taken along the line aa in Fig.
3 is a schematic cross-sectional view of the state in which the recess inducing portion is lowered in the state of FIG.
4 is a graph showing the relationship between shear stress and strain.
5 is a view for explaining the configuration and action of the incision ring.
Fig. 6 is a schematic cross-sectional view of Fig. 5, illustrating the cutting process of the incision ring.
7 is a schematic perspective view of an apparatus for measuring the soil shear strength of a ground subsidence according to another embodiment of the present invention.
8 is a schematic cross-sectional view taken along the line bb in Fig.
* The accompanying drawings illustrate examples of the present invention in order to facilitate understanding of the technical idea of the present invention, and thus the scope of the present invention is not limited thereto.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.

In the present invention, the term 'depression of the ground' refers to a phenomenon in which cavities are formed in the ground including a so-called 'sink hole'. In this specification, all phenomena in which cavities are formed in the ground regardless of their size or cause are defined as 'subsidence'.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, with reference to the accompanying drawings, a detailed description will be made of an apparatus for measuring soil shear strength of a ground subsidence soil according to an embodiment of the present invention.

FIG. 1 is a schematic perspective view of a main portion of a soil shear strength measuring apparatus of a soil depression ground according to an embodiment of the present invention, FIG. 2 is a schematic sectional view taken along line aa of FIG. 1, Fig.

1 to 3, an apparatus 100 for measuring soil shear strength of a ground subsidence soil soil according to an embodiment of the present invention includes a trench 10, a recess guide 20 And a load cell 30.

The trough 10 is in the form of a box with an empty interior to accommodate the soil sample g.

When the soil sample (g) is filled, a soil mass is formed, which simulates the soil in the area where the sink hole is generated. The soil sample (g) may be transferred without disturbance at the site of the sinkhole hazardous area, or samples with controlled composition or particle size may be used for elaborate experiments. It is also possible to use methods such as consolidating and filling the soil sample (g) so as to accurately simulate the ground conditions on the site.

A plurality of water inlets (13, 14) are formed on one side of the trough (10). Water is supplied to the soil sample (g) through the water inlet (13, 14). Water fills the pores of the soil, which replicates the groundwater level in the body. The reason why the plurality of water inlets 13 and 14 are formed in the vertical direction is to facilitate the adjustment of the water level. However, even if there is only one water inlet in the lower part, the groundwater level can be adjusted by installing sensor inside the soil part. It is preferable that the soil portion 10 is made of a transparent material so that the behavior of the soil sample g can be visually confirmed or photographed by a photographing device.

The upper surface of the trough 10 may be removably engaged to fill the soil sample g with the upper surface thereof open.

The first penetrating portion 11 and the second penetrating portion 12 are formed in the upper surface and the lower surface center of the trench 10, respectively. The recessed guiding portion 20 is provided from the first penetrating portion 11 to the second penetrating portion 12 through the inside of the tacking portion 10.

The recess guide portion 20 includes a first panel 21, a second panel 22, and a connecting rod 23. The first panel 21 has a plate shape corresponding to the first through-hole 11 and is fitted to the first through-hole 11. Similarly, the second panel 22 is formed in a plate shape corresponding to the second through-hole 12 and is fitted in the second through-hole 12. The connecting rod 23 connects between the first panel 21 and the second panel 22 and is installed long inside the tiller 10. Therefore, the soil sample g is placed in the trench 10 and the first panel 21 and the second panel 22 are installed at the respective positions of the tiller, and then the connecting rod 23 is joined to the two panels, The area can be determined. A bar-shaped bag portion 24 is provided at the lower portion of the second panel 22. The user can hold the bag portion 24 and pull the depression inducing portion 20 downward. 3, when the depression inducing portion 20 is pulled out in the initial state as shown in FIG. 2, the body disposed between the first panel 21 and the second panel 22 is pushed by the second penetration portion 12 As shown in FIG.

That is, the depressed inducing portion 20 is for artificially depressing the ground or simulating a sinkhole. The ground subsidence is a phenomenon in which the bottom of the cavity is depressed downward while a cavity is formed at the bottom of the ground, as described above. In this apparatus, the lower cavity is not simulated, but simulates the stress acting on the body of the cavity top by pulling the recessed induction portion 20 downward.

A plurality of load cells 30 are installed on the lower side of the trench 10 to measure the shear stress acting on the soil body during the soil depression process and the corresponding shear strength.

2, when the user pulls the depression inducing portion 20, the force pulling downward is applied to the torsion between the first panel 21 and the second panel 22 with reference to the sliding surface s (P) acts on the lower body, and a force (Q) against the lower pulling force acts on the surrounding body. Resistance is about the nature of the material, so it is called a kind of frictional force, or shear strength. When the pulling force (P) exceeds the maximum shear strength of the soil sample, sliding occurs rapidly.

In Fig. 4, the relationship between the shear stress and the strain rate is shown in a graph. In the initial stage, elastic deformation occurs even though the stress is increased. However, when the stress exceeds the critical point, that is, when the force exceeds the maximum shear stress, a rapid deformation occurs and then a displacement occurs. Only a smaller residual stress is required.

Returning to the present measuring apparatus, when the user initially applies force to pull the recessed guiding portion 20 slowly, the toe body receives the force but only the minute deformation occurs, and the breaking point of the soil is not reached. When the force is increased, The shear stress of the soil increases and reaches the fracture eventually through the elastic zone of the soil. When a larger force is applied, the toe body slides downward, which means that the shear section is forced in the direction of pulling, and thereafter displacement occurs even with a smaller force. In the load cell 30, the force acting on the sliding surface can be continuously measured. That is, when the initial pulling force starts to generate displacement, and after the displacement occurs, the force can be measured. As the pulling force increases, the force acting on the sliding surface becomes larger, so that the value measured by the load cell becomes larger. At the moment of collapse, the value measured at the load cell is the maximum shear stress. In other words, it becomes the maximum shear strength of the body. After the shear section, only residual stresses less than the maximum shear stress act on the sliding surface (s, front section) and can be measured on the load cell.

As described above, when the soil sample (g) is subjected to an artificial depression experiment using a recessed induction portion, the maximum shear stress and residual shear stress of the corresponding soil can be obtained.

On the other hand, when evaluating the occurrence and risk of sinkholes, a more important factor than the maximum shear stress is residual shear stress.

The present invention provides a method and an apparatus capable of more precisely measuring the residual shear stress in addition to the measuring method described above. These additional devices are disclosed in Figures 5 and 6.

FIG. 5 is a view for explaining the construction and action of the incision ring, and FIG. 6 is a schematic sectional view of FIG. 5, illustrating the incision process of the incision ring.

Referring to FIGS. 5 and 6, the present embodiment 110 may further include a cutout ring 50. FIG. The cutting ring 50 is intended to artificially form a shear section s on the tongue received in the tongue section 10. The first slit 27 and the second slit 28 are thinly formed on the upper surface and the lower surface of the tilting portion 10 along the first panel 21 and the second panel 22, respectively. And the cutting ring 50 may be formed in a ring shape thinner than the slits 27 and 28 and inserted into the slits 27 and 28. [ A knob 52 is vertically formed on the cutout ring 50 to rotate the cutout ring 50 inserted in the first slit 27.

That is, when the incision ring 50 is inserted into the first slit 27 as shown in FIGS. 6A, 6B and 6C according to the order of time, The ring 50 bisects the soil sample g and forms a shear section s and is discharged through the second slit 28. In this embodiment, the teeth 51 are continuously formed in the lower part of the cutting ring 50 so that the cutting of the soil sample g can be more easily performed. In particular, since the plant sample is often mixed with the roots of the plant, the teeth 51 are very useful.

In addition, although not shown, a channel for receiving water is formed in the incision ring 50, and a plurality of water discharge holes are formed in the lower portion of the channel. When water is supplied through the cutting ring 50 when the cutting ring 50 forms a shear surface in the soil sample, a shear surface can be formed on the soil sample g more easily through a kind of lubricating action. Here, even if the front end face is made through the cutout ring 50 in the trench 10, the first panel and the second panel are connected to the trench 10 so that the ground bottom recessed guiding portion 20 does not fall down spontaneously.

As described above, when the front end surface s is formed through the cutting ring 50, the torsion between the first panel 21 and the second panel 22 causes the displacement to be suddenly generated with only a slight force, . At this time, the force acting on the cylindrical shear section, that is, the resistance against the deformation of the soil, can be regarded as the residual shear stress. In other words, if a displacement is generated by pulling downward the depression inducing portion 20 in a state where the incision surface is formed, the moment when the displacement starts to occur can be regarded as the residual shear stress.

In case of not forming the incision plane, the instantaneous moment of the movement becomes the maximum shear stress, but it can be seen as the residual shear stress after forming the incision plane.

When we look at the actual sinkhole generation process, if the bottom of the ground is loosened, the upper ground becomes increasingly stronger downward. Gravity always works the same, but the bearing capacity of the lower part gradually weakens. When the force is continuously applied, the top surface of the loosened soil body forms a shear section and eventually collapses downward. As a result, the shear stress of the soil immediately before the sink hole is generated is directly related to the occurrence of the sink hole.

Using the present invention, the residual shear stress can be measured under various conditions such as type of soil, degree of consolidation, water level and environmental factors such as rainfall, and based on the measured data, the shear strength of the soil just before the occurrence of the sink hole The perception can be grasped on a case-by-case basis and converted into a database.

These databases provide a basis for quantitatively assessing the risk of occurrence of sinkholes. For example, the soil shear strength can be measured by using a vane tester widely used in the civil engineering industry for a soil with a high risk of subsidence. And the measured shear strength can be compared with the residual shear stress just before the occurrence of the sinkhole on the database secured by the present invention. If the shear strength of the soil measured through the vane tester is similar to the residual shear stress on the database, it can be prepared for sink hole occurrence or emergency site investigation by preliminary alarm. Conversely, if the measured shear strength is close to the maximum shear stress on the database, it can be evaluated as a safe hole occurrence area.

Thus, in the present invention, the change in the shear strength of the soil during the generation of the sinkholes can be grasped in a time-wise manner. It is also possible to construct a database on the maximum shear stress and residual shear stress under the conditions under repeated measurements in various samples and conditions. As the number of measurements increases, the reliability of the database will increase.

As described above, the present invention simulates soil depression and can grasp the change in shear stress of the soil over time. Therefore, not only can the dynamics in the sinkhole generation process be ascertained academically, but also utilized as a practical safety measure .

Although the depressed induction portion 20 has been pulled down to simulate the depression of the ground up to now, in another embodiment of the present invention, the depression of the depression can be simulated by pulling up the inverted portion.

An embodiment of this type is shown in Figs.

Referring to FIGS. 7 and 8, unlike the above-described embodiment, the lower surface of the saw tooth 10 is opened in the present embodiment 200, and the second penetration portion is not formed. However, a pedestal 40 is provided below the trench 20. The load cell 30 is installed at a lower portion of the pedestal 40. The present embodiment is different from the previous embodiment in that the trowel portion 10 is lifted upward to simulate the depression of the ground. However, the result is the same in that a shear surface s is generated between the toe disposed in the recessed inducing portion 20 and the surrounding toe. It is also the same in that a shear ring can be used to form the shear section in advance. Among the reference numerals shown in FIGS. 7 and 8, the same elements as those shown in FIGS. 1 to 6 have already been described above, so a detailed description thereof will be omitted.

A reference numeral T, which is not shown, is for supporting the toe portion as a table, and the central portion of the table is penetrated so as to pull downward the depression inducing portion 20.

The scope of protection of the present invention is not limited to the description and the expression of the embodiments explicitly described in the foregoing. It is again to be understood that the present invention is not limited by the modifications or substitutions that are obvious to those skilled in the art.

100,200: Soil shear strength measurement device of ground subsidence
10: toe portion, 11: first penetrating portion, 12: second penetrating portion
20: recessed guiding portion, 21: first panel, 22: second panel
30: Load cell
40: Base
50: cutting ring, 51: tooth, 52: handle
s: front section (sliding surface), g: soil sample

Claims (10)

A trench section for receiving the gravel inside to simulate the body, a first penetrating section on the upper surface, and a second penetrating section on the lower surface;
A second panel sandwiched between the first penetration portion and the second penetration portion; a second panel sandwiched between the first penetration portion and the second penetration portion; A recessed guiding portion having a connecting rod for connecting thereto; And
And a load cell installed at a lower portion of the tiller portion and supporting the tiller portion,
Wherein the shearing stress acting on the sliding surface when sliding the soil between the first panel and the second panel is measured by the load cell by pulling the recessed guiding portion to the lower side of the trough portion, Measuring device. The method according to claim 1,
Wherein a plurality of water inlets are formed in one side surface of the toe portion so that the water level of the water to be filled in the soil can be adjusted. The method according to claim 1,
Wherein a bag portion capable of being held by a user is formed in a lower portion of the second panel of the recess guide portion. The method according to claim 1,
Wherein an annular first slit and a second slit are formed between the outer circumferential surface of the first panel and the inner circumferential surface of the first penetrating portion and between the outer circumferential surface of the second panel and the inner circumferential surface of the second penetrating portion,
And a cutting ring formed in an annular shape so as to form a separation surface between the first body and the second body, the second body being inserted between the first and second slits and passing through the second slit, An apparatus for measuring soil shear strength of ground subsidence soil. 5. The method of claim 4,
And a sawtooth is continuously formed in a lower portion of the cutting ring. 5. The method of claim 4,
Wherein an upper portion of the incision ring is formed with a handle for grasping by a user to rotate the incision ring. 5. The method of claim 4,
A ring-shaped channel for receiving water is formed inside the cut-out ring,
And a plurality of water discharge holes are formed in the lower portion of the incision ring. 5. The method of claim 4,
Wherein the incision ring is formed in a cylindrical shape. A trench section for receiving the gravel inside to simulate the body, a first penetrating section on the upper surface, and a second penetrating section on the lower surface;
A pedestal portion for supporting the toe portion at a lower portion of the toe portion;
A first panel sandwiched between the penetrating portions of the upper surface of the touched portion and a connecting rod connecting the first panel and the receiving portion to each other through the inside of the touched portion; And
And a load cell installed at a lower portion of the receiving unit,
Wherein the shear stress acting on the sliding surface is measured by the load cell when the soil body between the first panel and the receiving unit is lifted by sliding the surrounding soil body. Device. 10. The method of claim 9,
Wherein a plurality of water inlets are formed in one side surface of the toe portion so that the water level of the water to be filled in the soil can be adjusted.

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