KR101742110B1 - A method of Safety Maintenance only with Soil sheating work - Google Patents

Abstract

According to the present invention, a method for securing safety with only a soil sheathing wall in a section in which a support is dismantled comprises the following steps of excavating the ground, decompressing a portion of a pre-compression load, and dismantling a support having a lower portion to be dismantled. Therefore, construction costs and a construction period can be reduced, and further, stability of a soil sheathing wall and a surrounding structure can be maintained.

Description

[0001] The present invention relates to a method for maintaining stability by using an earth retaining wall alone,

The present invention relates to a method for maintaining the stability of an earth retaining wall after excavation is completed, particularly when the preceding load applied to the bracket is reduced during excavation before dismantling the bracket for installing an underground structure, horizontal displacement occurs in the retaining wall, The horizontal stress acting on the retaining wall is reduced. In addition, since the moment of the earth retaining wall is reduced due to the decrease of the pressure of the preload when the excavation is performed and the remaining pre-load acts in the direction opposite to the horizontal stress, the member force of the retaining wall is within the allowable range and the stability is maintained. Since the shear force of the retaining wall is increased by increasing the stiffness by two lines of wale, the preceding load in the concentrated load form changes to the distributed stress form and the transmission rate to be transmitted to the retaining wall becomes smaller. Therefore, it should be disassembled to eliminate the problem of construction by cutting the midway of the underground wall while maintaining the stability of the strut wall during the dismantling period of the strut disconnection section. The pre-load of the upper strut and the preceding load of the strut installed thereon, The present invention relates to a method for maintaining stability only by the use of a liquid.

Generally, the horizontal earth pressure acting on the earth retaining wall is the horizontal pressure in the ground, and it can be obtained from the vertical earth pressure and the horizontal earth pressure coefficient through the following equation.

Since the horizontal earth pressure (horizontal stress) is a function of depth, if the direction of maximum principal stress is not changed, it is linearly proportional to depth, and the distribution form of earth pressure becomes triangular distribution.

However, if the wall displaces horizontally as shown in [Figure 1], the direction of principal stress changes and the earth pressure factor decreases, so the magnitude and distribution of earth pressure acting on the back surface are different. That is, even if the wall rotates around the bottom, if the maximum principal stress does not change, the horizontal earth pressure shows a triangular distribution. However, when the displacement type is different, the direction of the principal stress changes. Therefore, the horizontal earth pressure does not become the earth pressure of the triangular distribution but varies depending on the kind of soil and displacement size.

In order for the ground to be in the equilibrium state of the primary and the passive, that is, when the ground is cut off, a displacement occurs to the cut-off surface and collapses or is pushed to the backside and the ground is to be destroyed.

) (단, :

수평변위,

:벽체높이)[Table 1] Wall displacement of limit state (

) (only, :

Horizontal displacement,

: Wall height)

[Fig.1] Relationship between wall displacement and earth pressure coefficient

(1) The earth pressure acting on the retaining walls (Soil Dynamics)

Figure 2 shows the distribution of active earth pressure with various wall displacements due to the horizontal displacement occurring in the earth retaining wall depending on the back ground conditions during excavation of the ground.

(b) Horizontal movement (c) Top center rotation (d) Center displacement

[Figure 2] Distribution of wall displacement and main earth pressure (Ohde, 1938)

The stiffness of the retained wall is a ductile wall with less stiffness than the reinforced concrete. Therefore, assuming that the earth pressure acting on the back surface is the same at the time of excavation, the horizontal displacement is larger than that of the reinforced concrete wall. Therefore, it can be assumed that the distribution of earth pressure changes as shown in [Figure 3].

(d) sand (Peck) (e) soft clay (Peck) (f) hard clay (Peck)

[Figure 3] Transition earth pressure distribution of excavated soil wall

(2) Increasing earth pressure

The increase earth pressure refers to the earth pressure acting on the earth retaining wall while increasing in proportion to the preceding load applied to the braces in each excavation step in order to suppress horizontal displacement of the earth retaining wall generated during excavation. Also, the increased earth pressure is greater than the main earth pressure and less than the stationary earth pressure.

More specifically, the increased earth pressure is applied when the displacement of the retaining wall is strongly suppressed by installing a brace or anchor to protect the surrounding structures sensitive to the settlement when excavating the ground. Especially, in case of near excavation in downtown area, the earth retaining structure is designed by applying the increased earth pressure instead of the main earth pressure to prevent deformation of the settlement close to the site.

)를 적용해서 구한다.Weissenbach (1976) proposed that the earth pressure is applied differently depending on the size of the wall displacement S based on the displacement Sa reaching the main earth pressure. The magnitudes of the main earth pressure and the manual earth pressure are the strength constants of the soil defined in the limit equilibrium state

).

: 주동토압,

: 정지토압)[Table 2] Increased earth pressure due to wall displacement (

: Main earth pressure,

: Static earth pressure)

Since the main earth pressure and the manual earth pressure act directly on the underground structure, the earth pressure acts as a load when examining the stability of the structure against earth pressure.

In addition, the distribution and size of the horizontal stress acting on the back of the retaining wall depends on the magnitude of horizontal displacement. That is, when the horizontal displacement occurs in the wall of the retaining wall, the horizontal earthquake pressure coefficient decreases and the horizontal stress decreases. As the horizontal displacement increases, the main earth pressure coefficient becomes smaller and the horizontal stress decreases.

Experiments and numerical analyzes have been carried out in order to suppress the deformation of the back ground by suppressing the horizontal displacement of the backing wall. As a result, when 50 ~ 100% of the design axial load is applied to the preceding load, deformation of the back ground is suppressed, And the settlement of the back ground can be reduced.

Here, the design axial force is an axial force acting on each brace installed to support the retained wall after completion of excavation. Since the axial force of each brace is a corresponding area of the horizontal stress distribution, the axial force of the braces becomes larger as the horizontal stress becomes larger. Therefore, the horizontal displacement of the retaining wall is suppressed by the increase of the preceding load in the braces, but the horizontal stress, which is proportional to the size of the preceding load, acts as the load on the back of the retaining wall.

More specifically, the earth pressure acting on the retaining wall increases as the depth of excavation increases, so that when the horizontal displacement of the retaining wall is suppressed by pressurizing the preceding load, Since the axial force of the braces increases gradually, the horizontal displacement of the retaining wall is larger due to the compression deformation, but the horizontal displacement due to compression deformation is smaller than expected.

Therefore, when earth excavation is completed by earthquake excavation, earth pressure is increased by preceding load, and after the earth excavation is completed, the braces are disassembled to construct the underground structure, so that the horizontal stress acts as load on the earthquake wall with long span, May be exceeded. In this case, in order to maintain the stability of the retaining wall, it is necessary to cut off the middle of the retaining wall to increase the stiffness of the retaining wall by combining the stiffness of the retaining wall and the rigidity of the concrete wall .

On the other hand, when the large preload is applied to the strut at design time, the moment acting on the strut wall is reduced by acting in the opposite direction to the horizontal stress, so that the vertical spacing of the strut can be widened by a reduced moment, , The horizontal displacement of the earth retaining wall caused by the excavation can be sufficiently suppressed, so that it is a basic common knowledge that can reduce the settlement occurring in the back ground.

However, in the case of the previous load method in the past, the braces are directly installed on the wale while using the general steel material (H-300x300) used for the retaining wall. Therefore, when the preceding load greater than 70 ton is applied, the band length exceeds the allowable shear stress, The horizontal displacement and the settlement of the back ground were more than expected in the retaining wall. In order to prevent this, the size of the H-beams used in the wales and the retaining walls must be greatly increased, but this increases the construction cost.

This problem has been solved by developing Korean Patent No. 10-0812338 entitled " Prior Loading Loading System of Earth Wall Walls "(hereinafter referred to as Patent Document 1).

Patent Document 1 discloses a structure in which a wedge wall 110 supporting a ground and two wales 120 arranged in a direction orthogonal to the wedge wall 110 are installed on the wale band 120 to install the preceding load carrying body 200. [ A front load distribution carrier 200 installed in front of the dead load wall body 110 to transmit the preceding load applied to the wedge wall 110 to the wale band 120 and a brace 140 installed at the center of the preceding load distribution carrier 200, A hydraulic jack 130 connected to the hydraulic jack 130, and a hydraulic jack 130 for pressing the preceding load.

Patent Document 1 having such a configuration greatly increases the rigidity by installing two rows of wales on the strut of the H-300x300 standard and distributes a large preceding load by installing sloped steel on both sides of the vertical steel, (Less than 200 tons), which is much larger than that of the existing wall (usually 50 ~ 60ton).

H-300x200x9x14 and H-300x300x10x15 steels are mainly used for the earth retaining walls and H-300x300x10x15 and H-300x300x15x15 steels are used for the braces and wale.

Since the allowable stress of steel is different according to the standard, the size of the preceding load that can be applied to the brace also depends on the steel specification. More specifically, as the size of the steel material increases, the cross-sectional properties become larger, so that the resistance against external force increases. Therefore, a large preceding load can be applied. As the steel material size becomes smaller, the resistance against external force becomes smaller. .

The effect of the 'Patent Document 1' will be described in more detail. Since the stiffness of the belt is greatly increased, the stress generated in the wristband becomes a distributed stress state even when a large leading load is applied, so that the transmission rate of the preceding load transmitted to the earth retaining wall is small Which is much larger than the existing forward load. Since the moment of the retaining wall is reduced, the vertical spacing of the braces can be widened and the horizontal displacement of the retaining wall caused by the excavation can be sufficiently suppressed.

Since the retaining structure of the 'Patent Document 1' is excavated step by step, the moment of the earth retaining wall is reduced because the horizontal stress is applied in the direction opposite to the horizontal stress even if the horizontal stress is increased in proportion to the preceding load applied to the braces. If the length is not long, the moment of the retaining wall is within the allowable range, so the stability of the retaining wall is maintained.

When 'Patent Document 1' is applied to the field, the following matters are greatly improved.

First, if the horizontal displacement of the retaining wall 11 is sufficiently suppressed by applying a large preceding load at each excavation stage, the deformation (loosening) of the backside ground is suppressed and the settlement of the backside ground is reduced. Therefore, (Subway tunnels, BOX, surrounding buildings, underground facilities, etc.).

Second, the vertical spacing of the braces 1 can be set to be 1.0 to 1.5 m more wider by the moment of the earth retaining wall 11, which is obtained by reducing the forward load applied to the braces in a direction opposite to the earth pressure (horizontal stress) The braces 1 can be installed at intervals of 3.5 to 4.5 m, which is wider than the conventional vertical installation spacing of 2.5 to 3.0 m. Therefore, in the past, there was often a case where two struts 1 were installed at one floor (slab average interval of 3.6 ~ 4.1m) in the ground. After the excavation of the ground was completed, The member of the earth retaining wall body 11 increases and exceeds the permissible range because the length of the earth retaining wall body 11 in the section where the braces are disassembled becomes longer. However, according to 'Patent Document 1', when a brace (1) is installed at 1.2 to 1.5 m above the underground slab and a large preceding load is applied, the brace (1) is disassembled when the brace (1) ), The forward load acts in a direction opposite to the horizontal stress to reduce the moment of the retaining wall 11, so that the stability of the retaining wall can be maintained even without interrupting the middle of the underground wall. Accordingly, not only the number of installation and disassembly steps of the brace 1 but also the number of construction materials required to install and dismantle the brace 1 are reduced, and the number of places where the construction is cut off is reduced or hardly occurred, The construction period was reduced.

Where the vertical spacing of the braces between 3.5 and 4.5 m is the net spacing between the braces and the braces. When excavating the ground, the earth retaining wall is displaced to the excavation side by the horizontal force acting on the back surface from the excavation surface, and this displacement no longer occurs at any depth. In this way, the point at which the displacement generated on the excavation side by the earth pressure (horizontal stress) at the lower part of the excavation surface becomes zero in the ground is called the virtual support point, and the vertical installation interval of 3.5 ~ 4.5m in the brace is pure The spacing is proximal.

On the other hand, the location where the virtual support points occur varies from 1.0 to 1.5 m on average, depending on the strength of the ground surface of the excavated soil. Therefore, the stiffener strand, which can maintain the stability of the retaining wall without increasing the stiffness of the retaining wall, can be from 4.5m to 5.5m in the safe side and from 5.0m to 6.0m within the allowable range.

Therefore, when the underground structure is constructed after the completion of the excavation of the ground, after curing the slab of the basement layer and disassembling the brace 1 on the slab, when the cured slab is 3.6 to 4.1 m, The stability of the retaining wall body 11 itself is maintained only by the rigidity of the retaining wall body 11 since the distance between the upper portion of the slab and the braces 1 to be dismantled is 4.8 to 5.3 m.

Third, since the spacing of the braces (1) is widened, it is possible to utilize the working space widely without over-excavation, thus facilitating the working space of the equipment and the steel work (fabrication and assembly).

Fourth, construction period (noise, vibration, dust) and environmental pollution (carbon dioxide) were reduced because the use period of equipment used for construction was reduced when construction period was decreased because of installation and disassembly stage of brace (1). Therefore, 'Patent Document 1' has shown that it is possible to reduce the environmental pollution more than the existing strut forward load method by reducing the construction cost, construction period and complaints.

As described above, Patent Document 1 suppresses the horizontal displacement of the retaining wall 11 as a result of performing a large number of experiments (large size, small size) and numerical analysis in order to make a much superior method than the existing strut pre-load method We have developed a preloading system to determine the range of large preloads that can be applied. Accordingly, in Patent Document 1, in order to reduce the number of strands of the strut and the back ground and to reduce the stiffness of the stratum corneum wall 11, and to maintain the stability of the stratum wall 11, To reduce the number of parts to be installed and to improve the stability, workability and economy.

However, it is more dangerous to dismantle the brace after excavation is completed than in the case of 'Patent Document 1' as well as when all the earth retaining walls are excavated.

The reason for this is that even if the horizontal displacement of the retaining wall is allowed when the brace (1) is dismantled, the horizontal stress is reduced and the horizontal stress increases due to the change of the back ground condition and the increase of groundwater level This is because the member force of the retaining wall body 11 is increased and the allowable stress can be exceeded.

More specifically, when the brace 1 is dismantled in a state where a horizontal stress enlarged in proportion to a large preceding load applied to the brace at the time of excavation acts as a load on the retaining wall body 11, ) Is longer. As a result, the stiffness of the retaining wall 11 is increased to increase the member force, but the horizontal displacement is increased, so that the horizontal stress acting on the back surface is decreased. However, since the horizontal displacement of the retaining wall has not reached the limit state, the earth pressure acting on the back surface of the retaining wall body 11 becomes the increased earth pressure between the main earth pressure and the manual earth pressure, which acts as a load on the back surface of the earth retaining wall body 11 do.

At this time, in order to construct an underground structure, if the brace is dismantled,

The member force of the earth retaining wall body 11 increases and becomes larger than the member force at the time of designing, which exceeds the allowable stress. In this case, it is practically impossible to reinforce the already-installed earth retaining wall 11 itself. Therefore, in the existing method, the middle portion of the wall of the underground structure is cut to maintain the stability of the retaining wall 11, and when the member force of the retaining wall 11 exceeds the allowable range, And the construction period was increased.

On the other hand, if the horizontal stress increases due to an increase in the groundwater level even if the spacing between the struts is increased, the member forces of the earth retaining walls may exceed the allowable range even if the preceding load applied to the strut decreases the moment of the earth retaining walls. In this case, it is necessary to cut off the middle part of the underground wall in order to maintain the stability of the earth retaining wall in the same way as the existing method.

On the other hand, Korean Patent No. 10-1222026 entitled " Stretch Boat Construction Method Using Length Control Press Strut "(hereinafter referred to as Patent Document 2) discloses a method of constructing a conventional retention structure.

In Patent Document 2, a strut is connected to one side of the support, and the operator rotates the first fixing nut in the second installation space through the opening to move the length-adjusting rod toward the wall to contact the wall The presser jack is installed in the first installation space through the opening portion and the presser jack is actuated to press the presser rod toward the wall so that the length adjusting rod is pressed toward the wall by the first retaining nut, Closing the length adjusting rod by rotating the second fixing nut on the length adjusting rod and pressing the second fixing nut on the other side of the supporting rod to prevent a change in the position of the length adjusting rod, And separating the pressure jack from the support through the opening after the position change prevention step.

This 'Patent Document 2' has a problem that the construction of the existing retaining structure can not be used as it is and new parts are required, which increases the cost and increases the construction period due to the assembling process of the additional parts.

On the other hand, Korean Patent No. 10-0648409 entitled " Suspended Retaining Structure Method "(hereinafter, " Patent Document 3 ") discloses an embodiment of a method for pressing a preceding load on a retaining wall.

Patent Document 3 discloses a structure in which a load corresponding to the side pressure of an earth wall acting on the outside of the vertical pile 10 is used in order to enlarge the installation space of the strut without using the existing structure of the earth retaining members, A load of a size corresponding to the side pressure of the earth wall acting on the outside of the vertical pile 10 between the vertical pile 10 and the reinforcing lateral valley 16 is pressed Is introduced in advance into the means (26), and the introduced load is continued by the gap retaining member (28) inserted around the pressing means (26).

This 'patent document 3' shows that the sagging occurs inside the reinforcement rib 16 due to the load introduced in advance between the vertical pile 10 and the reinforcement rib 16, whereas the vertical pile 10 Because it is going to be displaced outwardly, it is in close contact with the earth wall, so that the ground around the construction site can be prevented from sinking and the installation interval of the strut can be widened, so that the construction period can be shortened and the construction cost can be reduced.

The 'Patent Document 3' has the same problem as the 'Patent Document 1' since the size of the preceding load can not be adjusted when the strut is disassembled.

A prior load control technique for improving the above problems is disclosed in Chinese Patent Laid-Open Publication No. 2015-10194561 (hereinafter referred to as Patent Document 4).

[Patent Document 4] discloses a safety pile comprising a support protection pile which supports the soil without collapsing, a slant brace connected to support the support protection pile, a strain gauge installed on the slant brace to measure the amount of deformation and a strain gauge connected to the slant brace, And a smart control component connected to the hydraulic jack, the strain gauge and the hydraulic jack to adjust the magnitude of the preceding load when the difference between the calculation result in the design file and the monitoring data at the time of excavation is relatively large.

In the 'Patent Document 4', the reference values for adjusting the magnitude of the preceding load are the horizontal displacement of the supporting protective pile, the deformation amount of the slant brace, the surface settlement, the amount of rupture of the bottom of the pit (swelling) And the pore pressure of the pore.

This 'Patent Document 4' can protect the mud from falling out of the pit during the excavation by adjusting the size of the preceding load, but since a plurality of sloped pipes are inserted into the bottom of the pit and the bottom outside the pit, And when there is a building outside the pit, the inclined pipe can not be used, and there is a problem that the pore water pressure can not be measured.

Meanwhile, another technique of a pre-load control method for preventing the collapse of the soil when excavating the underground structure is disclosed in Korean Patent Laid-Open Publication No. 10-2006-0110130 (hereinafter referred to as Patent Document 5) have.

Patent Document 5 discloses a technique in which a vertical file is installed at regular intervals along a gravel excavation surface and a wale is installed horizontally at a predetermined interval inside the vertical file to support earth pressure or displacement generated when the gravel is vertically excavated And a rake girder is installed so as to be inclined so as to maintain a constant angle with respect to a wale installed on the upper side of the vertical pile, and a lower part of the rake girder is provided with a foundation on the excavation surface of the final wave guide , And a vertical member is installed on the laker girder at a position perpendicular to the wale installed transversely to the vertical pile installed in accordance with the stepwise excavation. The length of the vertical member is increased or decreased in proportion to the earth pressure, And a load displacement interlocking and fixing device is installed at the end of the vertical member, And the tension cable is fixed to a fixing device installed at both ends of the lacquer girder so that the installation shape of the tension cable is similar to that of the moment distribution diagram to provide a synchronizing support system, A load transmission bracket having a screw jack attached at right angles to the transverse wales and the vertical member installed on the girders of the system is hingedly connected to the transverse wales in a stepwise manner while the transverse wales are installed in each of the multistage excavation steps such as the Iceland method, A hydraulic jack is inserted into the load displacement interlocking and fixing device provided at the end of the vertical member, and the displacement and load design control values of the stroke of the jack and the measurement results of the displacement meter and the load meter attached to the girder and the vertical member are linked to the computer, And when the stroke of the hydraulic jack is interlocked with the tension cable The jack acts as a reaction force and acts on the tension wall to support the earth retaining wall.

This 'Patent Document 5' requires components such as a lacer girder and a tension cable, and requires a single tension cable to be connected to the entire vertical member, thereby increasing construction time and construction cost.

Meanwhile, in Korean Patent No. 10-1132640 (hereinafter referred to as "Patent Document 6"), evaluation of the collapse stability of the earthwork construction site where there is a risk of collapse when the retaining structures such as Patent Document 1 to Patent Document 3 are applied Technology has been published.

The stability evaluation (horizontal displacement, moment, shear force, etc.) of the earth retaining wall is to be applied by applying the horizontal stress (earth pressure + water pressure) acting on the back surface as a load. More specifically, as the horizontal stress acting on the back of the retaining wall increases, the horizontal displacement of the retaining wall increases and the member force (moment, shear force) increases, while the peripheral structure increases The stability is reduced. In other words, the member forces (moments, shear forces) of the retaining walls increase proportionally with the horizontal displacement, so it is very important to manage the horizontal displacement within the allowable range in order to maintain the stability of the retaining walls during excavation and demolition.

[Patent Document 6] acquires information on the site of the earth retaining walls, the ground, and various structures from a variety of measuring instruments installed on the construction site in order to prevent a collapse accident that may occur in the earth retaining construction site, To assess the safety of site collapse and to accurately predict collapse indications.

The 'Patent Document 6' discloses a method in which a) horizontal displacement data of an earth retaining wall measured by an in-ground inclinometer at another construction site is collected and accumulated and stored in a database, and horizontal displacement data of the accumulated earth retaining wall B) acquiring horizontal displacement data of the earth retaining wall measured by an in-ground inclinometer at each excavation step and axial force data of the support material measured by the axial force meter at the corresponding construction site to be subjected to the collapse safety evaluation; C) analyzing the correlation between the horizontal displacement data and the axial force data acquired at the construction site in real time, and analyzing the collapse risk grade indicating the collapse risk from the tendency according to the correlation between the horizontal displacement and the axial force, D) estimating a collapse weight index? From the estimated collapse risk grade; e) modifying the horizontal displacement control reference value of the corresponding soil film method calculated in step a) using the collapse weighted exponent b; f) modifying the horizontal displacement data measured in step b) And determining the collapse safety based on the comparison with the horizontal displacement management reference value.

In the 'Patent Document 6', data measured in real time is transmitted to the understanding / monitoring computer in the transmission / reception unit including the normal communication module. The surveillance computer processes data such as horizontal displacement and axial force received from the transmission / reception section into data usable for collapse safety evaluation and stores the data in a database. At the same time, the surveillance computer analyzes trends of measurement data (horizontal displacement and axial force) The safety assessment is carried out through stages such as calculation of collapse risk grade, calculation of weighted index of collapse, calculation of management standard value by construction method (correction of management standard value), comparison of measurement data and management standard value, and danger warning.

Korean Patent No. 10-0812338 Korean Patent No. 10-1222026 Korean Patent No. 10-0648409 Chinese Laid-Open Patent No. 2015-10194561 Korean Patent Laid-Open No. 10-2006-0110130 Korean Patent No. 10-1132640

The present invention is characterized in that, prior to dismantling a brace to construct an underground structure after completion of excavation by applying a large preceding load to the brace during excavation, a part of the preceding load applied to the brace provided on the brace to be dismantled is reduced, And the residual stress is applied in the direction opposite to the horizontal stress, so that the moment of the retaining wall is reduced, so that the stability of the retaining wall is maintained. Therefore, it is not necessary to cut off the middle part of the underground wall to reduce the construction cost and the construction period, and to provide a method of maintaining the stability of the earth retaining wall during the dismantling period.

Also, the present invention is characterized in that before the braces are dismantled, the braces provided on the braces to be disassembled or the braces provided on the braces are decompressed to relieve the preceding loads, so that the stability of the braces is improved. It is an object to provide a method for maintaining stability.

It is another object of the present invention to provide a method of maintaining the stability of a stranded wall during a strand disassembly period in which a preceding load of a strut pressed by a hydraulic jack per strand is decompressed to maintain stability even before disassembling the strut.

According to another aspect of the present invention, there is provided a method for maintaining the stability of an earth retaining wall in a disassembly zone during a disassembly period of a strut, the method comprising: completing a ground excavation by installing a plurality of struts for applying a preceding load to the earth retaining wall from top to bottom, Decompressing the preceding loads applied to the upper and the upper struts of the strut to be disassembled when the strut is disassembled from the lower strut in order to disassemble the strut in reverse order from the excavation floor.

According to another aspect of the present invention, there is provided a method for maintaining the stability of an earth retaining wall during a disassembly period of a disassembly zone, comprising steps of: decompressing a preceding load applied to a brace nearest to a disassembly brace, .

According to another aspect of the present invention, there is provided a method for maintaining stability of an earth retaining wall, comprising steps of: installing a bracket to which a hydraulic jack is attached at intervals as shown in the drawing, Is a brace installed on the upper part of the dismounting brace in accordance with the order of construction of the underground structure and the braces for reducing the preceding load.

In addition, the method for maintaining the stability of the retaining wall of the present invention is characterized in that, when designing the retaining structure, the stability of the retaining wall is determined in order to construct an underground structure after excavation is completed. The present invention relates to a method for adjusting the magnitude of a reduction in the amount of a preceding load applied to a bracing which is placed on a base, and a method for controlling the amount of bracing of the bracing member by adjusting the member force of the bracing wall caused by excavation of the bracing, Displacement, etc., and determine the appropriate decompression size of the preceding load so that each value can maintain the optimal safety condition of the retaining wall within the allowable range.

The present invention also relates to a method for maintaining the stability of an earth retaining wall during a disassembly period of a disassembly zone of the present invention, Based on the size of the load, the basis of the measurement is analyzed and compared with the numerical analysis results. In addition, numerical analysis of the measurement results is inversely analyzed to determine the appropriate decompression size of the preceding load so that the retained wall can maintain the optimal safety condition on the site condition, and then the preceding load of the strut is decompressed by the size, It is a method to maintain the stability only by the rigidity of the wall.

When disassembling the brace to construct the underground structure after excavation of the preceding load applied to the brace during excavation of the present invention, it is possible to maintain the stability of the brace by dismantling the preceding load of the brace to be disassembled and the upper brace The method has the following effect.

According to the present invention, there is provided a method for maintaining stability of an earth retaining wall, comprising: disposing a bracket for constructing an underground structure after completion of excavation; allowing a horizontal displacement of the earth retaining wall by reducing a part of a preceding load applied to the bracket; If the moment is within the permissible range, the magnitude of the horizontal stress acting on the load is reduced, and if the moment is within the permissible range, the remaining preload after the decompression acts in the opposite direction to the horizontal stress, The stability of the section retaining wall is maintained. Also, the tensile stress of the preloaded beam is smaller than that before the decompression, but the preload, which is much larger than the decompressed preload, restrains deformation of the backside so that the settlement of the backside ground is within the permissible range and the stability of the surrounding structure is maintained.

Therefore, in the dismounting step of the present invention, since the stability of the post-tensioning wall can be maintained only by the stiffness of the retaining wall, it is not necessary to cut off the middle of the underground wall or further install the reinforcing brace, And the cost of construction is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a floor chart of a method for maintaining the stability of an earth retaining wall of a strut disassembly period according to the present invention.
2 is a plan view of a conventional prior load carrying body.
3 is a side view of a conventional prior load carrier.

The same components as those of the conventional art will be described below with reference to the related art, and a detailed description thereof will be omitted.

When excavating the ground, stability is maintained because it installs the strut in stages from the top and applies the preceding load. However, in order to install an underground structure after completion of excavation, the horizontal stress, which is increased to the external force condition changing at the time of dismantling the strut, and the horizontal stress, which is increased by the preceding load applied to the strut during the excavation, Since the length of the stranded wall is longer, the strength of the wall of the stranded wall may exceed the allowable range.

The above external force condition means that when the groundwater level rises due to the rainstorm of guerrilla storms or water pipes during the construction, there is a tendency that horizontal stress is applied to the ground due to fluctuations in vibration conditions and back ground conditions, .

More specifically, the earth pressure increases in proportion to a large preceding load applied to the braces at the time of excavation, and when the braces are disassembled when the lateral stress further increased by the external force condition acts on the earth retaining wall, Since the horizontal stress, which is larger than that at the time of designing, is acting on the retaining walls of the strut breakage zone in the extended state, the member force of the retaining walls may increase and exceed the allowable range.

When the horizontal stress is equal to the design time or increased by the external force, the method of maintaining the stability of the earth retaining wall in the disengaging zone of the present embodiment increases the strength of the earth retaining wall when the supporting wall is disassembled, It is difficult to maintain the stability of the earth retaining walls and surrounding structures. In this case, it can be effectively applied.

The method of the present invention for securing stability of an earth retaining wall includes a ground excavation step for applying a preceding load while installing a plurality of braces from top to bottom on the earth retaining wall during excavation, Decompressing the preceding load of the strut located on the upper portion of the dismounting props, and dismounting the strut.

On the other hand, in order to maintain the stability of the earth retaining wall during the excavation of the ground, the braces with hydraulic jacks are installed sequentially from the top in the ground excavation step. At this time, the hydraulic jacks are installed parallel to each other with a wale band and a brace, and the excavation is completed while applying a preceding load to the braces at each excavation step.

The present invention provides a method for maintaining the stability of a retaining wall of a bracket during a dismantling of a bracket for installing an underground structure comprising a mat base and slabs for each basement after the excavation of the ground is completed, Therefore, the lateral stress increased by the preceding load acts as a load on the retaining wall of the braces. Therefore, when the stiffening wall of the disassembly section is extended and the member force exceeds the allowable range, the preceding load of the stiffener installed at the position where the member force of the retaining wall is maximized and the strut installed thereon are decompressed, Within the allowable range.

In more detail, according to the method for maintaining the stability of the stranded wall of the present invention, when the preceding load of the strand subjected to the preceding load is partially depressurized to permit horizontal displacement of the stranded wall, the horizontal stress acting on the back of the stranded wall That is, the reduced earth pressure acts as a load on the retaining wall, and the remaining pre-load acts in a direction opposite to the reduced horizontal stress so that the moment of the retaining wall is reduced, so that the moment of the retaining wall is within the allowable range. Therefore, according to the present invention, since the stability can be maintained only by the earth retaining walls during the disassembly period of the disassembly section, it is not necessary to cut off the middle of the underground wall for the stability of the disassembly section, thereby preventing the construction cost and the construction period from being increased.

On the other hand, if the braces are dismantled, horizontal strains of the retaining walls will become longer and the horizontal stress will act as loads on the retaining walls. If the member forces of the retaining walls are within the allowable range, the preceding loads applied to the upper braces will be decompressed no need.

The decompression size of the preceding load applied to the brace, which is the core of the method of maintaining the stability of the brace of the present invention, is a comprehensive decomposition of the brace, the ground condition, the back ground layer, the groundwater location, Should be considered.

At this time, the size of the decompression pressure is determined by the numerical analysis at the time of designing, and the final decompression size is determined by analyzing the measurement result measured in the horizontal horizontal displacement meter and the strut axial force meter during the construction and inverse analysis. That is, according to the present invention, there is provided a method for maintaining the stability of a stranded wall in a disassembly zone during a disassembly period of a strut, comprising the steps of: reducing a preload applied to the strut to reduce a horizontal stress, The load acts in a direction opposite to the horizontal stress to reduce the moment of the retaining wall so that the moment of the retaining wall exceeding the allowable range is within the allowable range.

More specifically, the present invention provides a method for maintaining the stability of an earth retaining wall in a disassembly zone during a disassembly period of the disassembly zone without disrupting the middle of the underground wall or installing additional reinforcing bars.

Hereinafter, a method for determining the magnitude of the reduced pressure of the preceding load will be described.

In the first method, numerical analysis is performed at the time of design, and when the braces are dismantled to construct an underground structure after excavation is completed, the decompression magnitude of the preceding load is determined on the disassembly upper brace or the braces on the upper brace .

This method is based on the analysis of the stiffness of the retained wall and the analysis of the member forces and horizontal displacements of the retained walls caused by the ground excavation conditions, such as the member forces and horizontal displacements of the retained walls that increase with the length of the earth retaining walls Compare and review.

At this time, based on the comparison and examination value, the preceding load applied to the brace installed on the brace to be disassembled is decompressed to an appropriate size so that the securing state of the retaining wall is kept optimal.

The second method is a method of adjusting the decompression magnitude of the preceding load applied to the braces installed on the braces, which are to be disassembled, at the stage where the braces are disassembled based on measurement results of the underground horizontal displacement meter and the strut axial force meter.

This method is first based on the numerical analysis results obtained in the structural calculation, and after the detailed analysis of the measurement results, it is compared with the numerical analysis results, and the results of measurement are inversely analyzed to determine the stable state of the earth retaining walls And the pressure of the front brace is reduced by the reduced pressure magnitude determined by a method of determining the reduced pressure of the preceding load so that the surrounding structure can be stabilized against the settlement while being maintained.

The common features of the above two methods are as follows.

Allowing lateral displacement of the retaining wall by reducing the forward load applied to the braces reduces the horizontal stress acting on the back of the retaining wall due to the smaller primary earth pressure coefficient. At this time, in the state where the horizontal stress is decreased [see Fig. 1], the moment load of the retaining wall is decreased because the preceding load of the supporter is partially decompressed and the remaining sup- ply load is applied to the securing wall in the direction opposite to the direction of the horizontal stress The member force of the retaining wall and the subsidence of the backside ground are within the permissible range.

If the force of the earth retaining wall exceeds the allowable range even when the preceding load of the supporter of the supporter to be dismantled is reduced, there is a method of further depressurizing the supporter of the supporter located on the supporter.

Hereinafter, the method of maintaining the stability of the earth retaining wall of the strut disassembly period of the present invention is described by taking the supposed site as an example, and the outline of the excavation work is as follows.

Excavation area: A = 3743 (m2) Excavation depth: GL -14.98 (m), 3 basement floors

Strut mounting step: 5 stages

Walls: CIP (D = 500), H-300x300x10x15 ctc 1500

Groundwater level: GL -5.0 (m) Order method: SGR method

Backward layer: buried soil, sediments 1, sediments 2, weathered soil, weathered rocks,

Surrounding building: 3 stories above the ground, 3m from the wall

The following is a cross-sectional view of the retaining wall with a plurality of braces in five stages [Figure 4] and a detailed view of the retaining wall [Figure 5].

In the following description, the uppermost brace is referred to as a first stage brace and the lowermost brace is referred to as a fifth stage brace in order to facilitate description.

[Figure 4] Sectioning of wall

[Figure 5] Details of the wall of the retaining wall

 [Table 3] shows that when the excavation is carried out at the site, the excavation is completed by pressing a suitable load on the brace in consideration of the horizontal stress acting on the back of the retained wall by the excavation step, and when the brace is dismantled, Since the moment exceeds the permissible range, the preceding load is gradually decreased at a certain rate for each case to reduce the moment load of the retaining wall within the allowable range.

[Table 3] Pressurization and decompression precedent load for each case

In Table 3, the leading load applied to the braces at excavation is 45, which is the smallest at the first stage, 110 which is larger than the first stage at the second stage, and 310, which is larger than the second stage, from the third stage to the fifth stage. The reason why the preceding loads in the first and second stages are small is that the earth pressure is small in proportion to the excavation depth, Since the earth pressure gradually increases from the three-stranded strut, the magnitude of the preceding load to be pressurized stepwise in order to further reduce the settlement of the back ground by suppressing the horizontal displacement of the earth retaining wall increases proportionally to the horizontal stress increased in proportion to the depth . However, the reason why the same-sized forward load is applied from the third stage to the fifth-stage strut is that the H-shaped steel, the wale and the strut which are the internal stress members of the earth retaining wall are subjected to a higher preceding load, This is because the allowable stress of steel is exceeded. Of course, the size of the preceding load is determined by considering the safety factor of each member.

On the other hand, if there is a structure susceptible to subsidence in the vicinity of the excavation site, increasing the size of the steel can increase the stability of the surrounding structure because it can press the larger preceding load and further reduce the settlement.

In the above-mentioned example site, when the four-strand brace is dismantled, the member force of the earth retaining wall is the largest. Therefore, when dismantling the 4-step brace, the part of the preceding load applied to the 3-step brace, which is expected to be dismantled next time, is decompressed so that the member force of the retained wall increases due to the increase of the stay of the retaining wall.

However, if the member force of the retaining wall is not within the permissible range only by decompressing the preceding load applied to the brace to be dismantled, if the shape of the building structure of the retaining wall, the condition of the back ground layer is changed, When a building or the like acts as an overhead load, the size of the reduced pressure of the preceding load and the number of the strut to be decompressed are different. In other words, not only only one prop is decompressed, but also a strut installed on a strut above the strut to be disassembled may be further depressurized by the preceding load, so that the member forces of the earth retaining walls may be satisfied with the force at the time of designing.

For this purpose, the numerical analysis at the time of design and the analysis of field measurements at the time of construction should be accurately analyzed to predict the behavior of the ground and the retained wall when the subsequent braces are dismantled. , You should understand the change in earth pressure. Therefore, if the forward load applied to the brace is unduly reduced without understanding the behavior of the back ground and the geotechnical theory at the dismantling of the brace, the member strength of the retained wall exceeds the allowable range or the peripheral structure near the back of the retained wall So that it is difficult to maintain the stability of the retaining walls and surrounding structures. That is, the retaining structure and the surrounding structure may be dangerous because of exceeding the allowable range. In this case, in order to stabilize the retained walls and surrounding structures, it is necessary to cut off the middle part of the underground wall or install the reinforcing brace, which increases the construction cost and construction period.

[Table 4] is the result of the first embodiment in which numerical analysis is performed under the conditions of [Table 3].

 [Table 4] Numerical analysis results for each case when decompressing only 3-stage leading load

As shown in [Table 4], when the ground is excavated, the same pre-load is applied to the braces in order to maintain the stability of the retaining wall. Therefore, the horizontal displacement, moment, shear force and settlement of the back- It is the same without.

However, the numerical analysis results from CASE 2 to CASE 5 were different when the excavation was completed after the excavation was completed because the successive loads of each prop unit were sequentially depressurized. As a result, the moments of the retained walls were decreased sequentially in each case, but the settlement of the backside ground gradually increased because the horizontal displacement of the retained wall was increased by depressurizing the preceding load.

Since the maximum moment of the earth retaining walls that can be used for the C29 axis reinforcement is about 260 kNm / m, the moments of the retaining walls are between 309.11 kNm / m and 279.68 kNm / m from Case 2 to Case 4 when the braces are dismantled. The CIP shaft reinforcement is safe until D29-8EA is used.

However, since the CIP reinforcing bar was constructed with D29-6EA, the member strength of the retaining wall located at the section where the brace is dismantled increases, and there is no way to reinforce the retaining wall itself even if the allowable range is exceeded. Therefore, in order to maintain the stability of the earth retaining wall located at the section where the four-strut bracket is dismantled, it is possible to maintain stability by cutting the middle of the underground wall or constructing the reinforcing brace, but this increases the construction cost and construction period.

On the other hand, in the case of the present example, when the forward load applied to the three-step brace is reduced from 310 to 220, the amount of the CIP axial reinforcement comes to an allowable value. That is, by decompressing 90.0 kN of the preceding load applied to the 3-step brace before disassembling the 4-step brace, it is possible to maintain the original construction state within the allowable range of the CIP axis reinforcement amount. Therefore, it is not necessary to cut off the middle part of the underground wall because the stability is maintained by the retaining wall alone.

When the preceding load applied to the 3-step strut was decompressed sequentially before disassembling the 4-strut strut from CASE 2 to CASE 5, the horizontal displacement of the earth retaining wall was increased to 0.79 mm, and the settlement of the back ground was slightly increased to 0.05 mm. That is, since both are within the allowable range, the stability of the retaining walls and surrounding structures is maintained.

If the part of the preceding load applied to the three-strand brace is decompressed, there are two reasons why the strength of the retained wall located in the section where the braces are dismantled is reduced.

First, if horizontal displacement is permitted by depressurizing the preceding load applied to the brace, the horizontal stress acting as a load on the back of the retaining wall is reduced.

Secondly, the member force of the earth retaining wall decreases due to the decrease of the horizontal stress, and does not fall within the allowable range. However, since the entire preceding load, which is pressed at the time of excavation, is not depressurized but only partially depressurized, it is necessary to reduce the pressure of the upstanding load applied to the three- And the moment of the earth retaining wall is reduced.

In summary, the method of maintaining the stability of the stranded wall in the dismantling zone of the present invention can satisfy the amount of reinforcing bars of the CIP wall because the strength of the wall of the retaining wall is reduced by the above two effects, The stability can be maintained without any other reinforcement.

On the other hand, in Table 3, when a part of the preceding load applied to the three-step brace was depressurized, only the CASE 5 could satisfy the conditions at the time of design.

However, if the horizontal displacement of the retaining wall and the settlement of the backside ground are within the allowable range, even if the member force of the reduced earth retaining wall is reduced by decreasing the preceding load applied to the three-stage braces to be disassembled, There is a method of dismantling the brace by further depressurizing the preceding load applied to the two-stage brace installed on the brace. This is often the case in real life situations.

Here, if the three-stage strut is an arbitrary strut, the strut closest to the arbitrary strut is a two-strut strut.

As shown in [Table 5], when the forward load of the 3-step strut is reduced and the forward load of the 2-step strut is further depressurized, the amount of reinforcement of the CIP wall is satisfied only in CASE5 in Table 4. However, in CASE4 and CASE5, It is possible to satisfy the CIP reinforcing amount which is applied, so that the stability can be maintained only by the earth retaining wall without any other reinforcement.

 [Table 5] Result of 3-stage strut forward load depressurization and 2-stage strut forward load depressurization

[Table 6] Results of three-stage forward load depressurization and two-stage forward load depressurization (three-stage: 250 kN / m standard)

As a result of [Table 6], it was found that reducing the previous load of the upper strut, that is, the three strut strut, to be dismantled does not affect the force of CIP.

[Table 7] Results of three-stage forward load depressurization and two-stage forward load depressurization (three-stage: based on 220 kN / m)

The results of Table 7 show that the stability of the three-stage braces to be dismantled was maintained within the allowable stress of the CIP when the two-stage braces were reduced by 10 by reducing the preceding load from 310 to 220 by 90.

[Table 8] Results of three-stage forward load depressurization and two-stage forward load depressurization (three-stage: based on 190 kN / m)

[Table 8] also shows that when the front load of the 3-stage strut is reduced from 310 to 190 by 120 as shown in [Table 7], when the 2-strut forward load is decreased by 10, the stability can be maintained within the allowable stress of the CIP there was. The horizontal displacement of the retaining wall increased from 16.14 to 16.46 by 0.32, and the settlement of the back ground was not increased by 0.11 from 5.85 to 5.74. As a result, it was shown that the retaining walls were allowed to stay within the allowable range even if the retaining walls were maintained only with the retaining walls by reducing the proximal load.

In general, the degree of safety δ / L of the surrounding structure against the settlement is set at 1/500, which is not permissible to crack, as the first criterion, and the limit of the first crack at the partition wall or the elevated crane The second criterion is 1/300, which is the expected limit of difficulty.

[Figure 6] Variations δ / L (Bjerrum, 1963)

The results of numerical analysis of Table 5, where 1) to 5) below are the largest occurrences of subsidence, were examined for the safety of surrounding buildings. The differential settlement is assumed to be 6.0 m.

[Unequal settlement calculation result]

1) CASE 1 - 0.50m Settlement: 5.17mm

- 6.50m Settlement amount: 3.65mm

- Uneven settlement (distance between pillars): 1.52mm (6.0m)

        Degree = 1.52 / 6000 = 1/3947 <1/500 OK

2) CASE 2 - 0.50m Settlement amount: 5.43mm

- 6.50m Settlement: 3.93mm

- Uneven settlement (distance between pillars): 1.50mm (6.0m)

Degree = 1.50 / 6000 = 1/4000 < 1/500 OK

3) CASE 3 - 0.50m Settlement: 5.48mm

- 6.50m Settlement amount: 4.17mm

- Uneven settlement (distance between pillars): 1.31mm (6.0m)

Degree = 1.31 / 6000 = 1/4255 <1/500 OK

4) CASE 4 - 0.50m Settlement: 5.57mm

- 6.50m Settlement amount: 4.42mm

- Uneven settlement (distance between pillars): 1.15mm (6.0m)

Degree = 1.31 / 6000 = 1/4580 <1/500 OK

5) CASE 5

- 0.50m Settlement: 5.70mm

- 6.50m Settlement: 4.66mm

- Uneven settlement (distance between columns): 1.04mm (6.0m)

Degree = 1.04 / 6000 = 1/5769 <1/500 OK

According to the numerical analysis results of CASE 1 to CASE 5 settlement 1) to 5), settlement problem occurred in the back ground due to the horizontal displacement of the retaining wall due to the decompression of the preceding load applied to the braces The stability of the retaining walls or surrounding structures is not a problem at all.

If the stability of the earth retaining wall is maintained by applying the method of maintaining the stability of the retaining wall of the present invention, it is not necessary to cut off the middle of the underground wall to reduce the construction period and the construction cost.

In this case, the construction time required to break the middle of the underground wall depends on the size of the site and the type of underground structure. Typically, a small site typically takes 15-20 days, and a large site usually can take 25-30 days less. Of course, the construction cost will also decrease accordingly.

In this case, the construction period refers to the time for cutting the reinforcing bars, the time for connecting the reinforcing bars, the time for installing the formwork, the time for pouring the concrete, the time for curing the concrete, and the time for dismantling the form after curing.

In addition, the method of maintaining the stability of the earth retaining walls of the brace disassembly section of the present invention reduces the construction costs such as the amount of reinforcing bar, the labor cost, and the mold use ratio added when the reinforcing bars are connected.

In addition, the method of maintaining the stability of the earth retaining wall of the strut disassembly section of the present invention is not a method used when excavating, but is a method used to disassemble a strut to construct an underground structure after completion of excavation.

Meanwhile, it should be noted that, in the method of maintaining the stability of the stranded wall of the present invention, when the horizontal displacement of the retained wall is excessively allowed, the backside ground is loosened and the settlement may be largely generated in the backside ground. In particular, since the permissible settlement varies depending on the type of structures around the construction site, only the member force of the retaining wall should not satisfy the permissible range, and the settlement caused for the safety of the surrounding structure must satisfy the permissible range.

To achieve this, it is necessary to fully understand the geotechnical theories and accurately analyze the field measurement results in order to reduce the pressure of the pressurized preloads within the allowable range of the structure while maintaining the stability of the retaining wall.

Hereinafter, a description will be made of a method for maintaining stability of an earth retaining wall according to a second embodiment of the present invention.

The method for maintaining the stability of the stranded wall in the disassembly zone of the second embodiment is characterized in that if the stranded wall of the stranded wall is extended and the member force of the stranded wall exceeds the allowable range, the upper part of the underground slab is to be dismantled, When the horizontal displacement of the retaining wall is allowed by sequentially depressurizing the preceding load applied to the braces exceeding the range, the main earth pressure coefficient becomes small as shown in [Figure 1] The momentum of the earth retaining wall is reduced by acting in a direction opposite to the horizontal stress acting on the earth retaining wall, so that the member force is within the allowable range.

Therefore, even if the length of the earth retaining wall located in the section where the braces are dismantled is long, the method of maintaining the stability of the earth retaining work site of the present embodiment can be carried out even if the middle portion of the underground wall is cut off or the reinforcing braces are not additionally installed. Stability can be maintained.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as set forth in the following claims Or modification of the invention.

Claims (3)

A ground excavation step in which a plurality of struts are installed from the upper part to the lower part to complete the excavation while applying a preceding load to the strut in each excavation step in order to maintain the stability of the earth retaining wall;
Decompressing a part of the preceding load applied to an arbitrary brace located on the upper part of the lower dismounting props before disassembling the lower dismounting props when disassembling the braces to construct an underground structure after completion of excavation;
And disassembling the lower disassembly target brace,
In the preceding load depressurization step, the optional strut is an optional strut positioned above the lower dismountable strut,
In the step of depressurizing the preceding load, the size of the preceding load decompression is determined by the stiffness of the earth retaining wall in designing the earth retaining wall, the analysis results of the member forces and the horizontal displacements of the earth retaining wall generated during the ground excavation, The comparison of the magnitude of the member force and the horizontal displacement value of the retaining wall increases with the lengthening of the span, and it is confirmed that even if the span of the retaining wall is long, it is within the permissible range. And the depressurization pressure applied during excavation of the brace located on the upper part of the dismantling proximal bracket is decompressed. Thus, by partially cutting off the underground wall, the rigidity of the retention wall is not reinforced, How to maintain stability with only.
A ground excavation step in which a plurality of struts are installed from the upper part to the lower part to complete the excavation while applying a preceding load to the strut in each excavation step in order to maintain the stability of the earth retaining wall;
Decompressing a part of the preceding load applied to the plurality of braces located on the upper portion of the lower dismounting props before disassembling the lower dismounting props to construct an underground structure after completion of excavation;
And disassembling the lower disassembly target brace,
In the preceding load depressurization step of the upper strut, the plurality of struts are a strut positioned on the upper part of the dismounting strut,
In the step of decompressing the preceding load, determination of the magnitude of the preload to be decompressed at the upper portion of the lower dismounting props is performed by the numerical analysis results obtained by performing the structural calculation on the measured results of the ground horizontal displacement meter and the strut axial force meter after completion of excavation And the reduced pressure of the preceding load is determined by the inverse analysis of the results of the measurement in the range of the size within the permissible range by the numerical analysis, Wherein a part of the underground wall is cut off to reinforce the rigidity.
The method of claim 2,
Wherein the plurality of braces is a brace closest to each other, wherein the plurality of braces are closest to each other.

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