JP5421165B2 - Earth retaining structure and its construction method - Google Patents

Description

  The present invention relates to a retaining wall applied to a ground having a viscous soil at least deeper than a floor and a method for constructing the retaining wall.

  In the construction of underground structures and semi-underground structures, a construction method is generally applied in which the foundation is excavated to form a flooring surface, the bottom plate is constructed, and then the frame is raised upward. Has been.

  And when excavating the original ground, prior to this, steel sheet piles, main pile side sheet piles, steel pipe sheet piles, column row continuous walls (soil cement column wall, muddy water solidified wall, mortar column wall, etc.), underground A retaining wall consisting of continuous walls, etc. is constructed, and the excavation from the surface layer raises and cuts to a desired level, and supports such as retaining anchors are constructed to secure a stable excavation space. .

  By the way, when constructing the earth retaining wall described above on soft ground, various ground improvements have been made to ensure the stability of the earth retaining wall within the range of the depth of floor retaining and deeper than flooring. The so-called “passive reaction force” is increased deeper than the floor.

  For earth pressure from the back of the retaining wall (including earth and water pressure), the rigidity of the retaining wall itself (bending rigidity, shear rigidity, etc.) and the above-mentioned support work reaction force (self-supporting type without support work) Excavation space is stably secured by the resistance force consisting of the above-mentioned passive reaction force deeper than the flooring. And this passive reaction force is extremely important to ensure the stability of the earth retaining wall against the working earth pressure over the entire construction period from the ground excavation to the flooring and the construction of the structure. Is an element.

  Here, the passive reaction force is forced to increase, and the “soft ground” where the ground improvement is often carried out deeper than the flooring means that the N value of the boring survey is about 5 or less, and the possibility of consolidation There is a lack of bearing capacity, such as clay soil, clay soil, humus soil, peat soil, etc., and sandy ground that has a high groundwater level and can be liquefied. It means the ground where consolidation settlement and liquefaction are concerned.

  The ground improvement described above includes a method of excavating the original ground and forming a flooring surface, and a method of performing a desired depth range of the original ground from the ground prior to excavation. In addition, as an improved form, a form in which a columnar or block-like improved body is formed by injecting chemicals or cement into the ground (consolidation method), sand is pressed into the ground and compacted, Examples include a method of forming a sand pile to consolidate the ground and forcibly drain pore water (consolidation methods such as a vibro-floating method, a sand drain method, a paper drain method, etc.).

  Here, FIGS. 4 and 5 show a conventional earth retaining structure composed of an earth retaining wall, a supporting work, and a ground improvement body deeper than the floor, and FIG. 4 is a longitudinal sectional view thereof, and FIGS. Are both VV arrow views of FIG. 4 and show two representative forms of ground improvement bodies, respectively.

  On the soft ground G, a retaining wall Y is constructed in a frame shape (endless shape), for example, in a rectangular shape in a plan view, and between the opposing retaining walls Y and Y, the cut beams S2 are erected via the upsets S1 and S1. A ground improvement body K consisting of a large number of columnar improvement piles K1, ... is created in the range of the depth of the retaining wall Y deeper than the flooring T that is supported and excavated by D is formed.

  With respect to this earth retaining structure D, the conventional ground improvement body is constructed so as to connect the opposite earth retaining walls Y, Y like a ground beam deeper than the floor as shown in FIGS. 5a and 5b. This structure is based on the design philosophy of taking reaction force from both earth retaining walls Y and Y by the underground beam by this ground improvement body and securing the stability of the earth retaining wall Y.

  Specifically, as shown in FIG. 4, the beam reaction force Q1, the rigidity of the retaining wall Y, and the passive reaction force of the ground improvement body K against the earth pressure Pa acting from the back surface of the retaining wall Y. Resist at Q2. In order to make full use of this passive reaction force Q2, it is necessary to form an underground beam by connecting the earth retaining walls Y, Y facing each other with a ground improvement body K. It is.

  Here, regarding the form of the ground improvement body, the ground improvement body K shown in FIG. 5a is a form in which the columnar improvement piles K1 are densely arranged below the entire flooring, and the ground improvement body K shown in FIG. The improved pile K1 is formed in a lattice shape, and a part of the lattice is an underground beam connecting the earth retaining walls Y and Y (reaction force Q2 'acts from the central beam in each place).

  As shown in the drawing, the ground improvement body forming the conventional earth retaining structure is formed as an underground beam straddling between the earth retaining walls, all or a part of which is opposed. Therefore, when the excavation range becomes wide and the distance between the retaining walls becomes long, the ground improvement range naturally increases, which directly leads to an increase in construction cost. In addition, when the distance between the retaining walls is 50 m or more, for example, the ground improvement piles are continuously formed so as to connect the retaining walls and the underground beam is created. Beam function as expected of the beam, that is, the effect of suppressing the deformation of the retaining wall by connecting the retaining walls firmly and transmitting the reaction force received from the retaining walls into the underground beam It is extremely questionable whether or not it can be used.

  As described above, the form of the ground improvement body forming the conventional earth retaining structure can cause the above-mentioned increase in construction cost, and the underground that is actually expected especially when the distance between the earth retaining walls is long. In response to problems such as the possibility that the beam function is not sufficiently exhibited, the present inventors have come up with an earth retaining structure that can solve these problems.

  Here, in order to turn to the conventional public technique relating to the structure of the retaining wall and the construction method, the public technique is wide-ranging, and one of them is the mountain fastening method disclosed in Patent Document 1.

  In this earth retaining method, a plurality of retaining walls perpendicular to the retaining wall are provided at intervals on the excavation surface side of the retaining wall, and the retaining wall is a column constructed in an unsettled state against the hard ground. It is formed from a row of ground improvement bodies, and the unimproved original ground and the retaining wall left between the opposing retaining walls are integrated by an uneven surface provided on the surface of the retaining wall. The retaining wall is provided in a non-bonded state with respect to the retaining wall.

  According to this construction method, the retaining wall made of the ground improvement body can suppress the deformation of the retaining wall. However, when the ground improvement body is constructed on a soft viscous ground, it is considered that the opposite retaining wall and the soft original ground between them will behave integrally when the uneven wall surface is provided on the surface of the retaining wall. Absent. In addition, since the ground improvement body is formed away from the retaining wall, the initial deformation of the retaining wall cannot be suppressed, and therefore it is very doubtful whether a sufficient deformation suppressing effect can be obtained.

JP 2001-355237 A

  The present invention has been made in view of the above-described problems, and has a high effect of suppressing deformation of the retaining wall, and even when the planar scale of the retaining wall is wide, the ground improvement range in deeper than the flooring is wide. Therefore, the purpose of the present invention is to provide a retaining structure and its construction method, which do not require the problem of increasing the construction cost.

  In order to achieve the above object, the earth retaining structure according to the present invention is an earth retaining structure applied to a ground having viscous soil at least deeper than an excavation floor, and includes an earth retaining wall and an excavation floor attachment of the earth retaining wall. A ground improvement body formed deeper, and in a plan view, the ground improvement body abuts against the retaining wall and extends in a direction along the earth retaining wall, and from the belt part to the excavation side A plurality of projecting portions projecting, and a reactive reaction force that resists earth pressure from the back surface of the retaining wall is at least a ground reaction force that the belt portion receives from clay soil deeper than a floor, and the projecting portion and the floor It consists of the frictional force with the cohesive soil deeper than the attachment.

  The earth retaining structure of the present invention is applied to the ground having the viscous soil deeper than the flooring, and the frictional force or adhesive force between the viscous soil deeper than the flooring and the projecting portion constituting the ground improvement body. The ground improvement range is set by reflecting this frictional force or adhesive force in the passive reaction force at the time of design. The improvement range is to be reduced as compared with the retaining structure.

  The distribution mode of the viscous soil deeper than the flooring is not limited to the ground where the soil is deeper than the flooring and the clay wall exists in the entire range of the depth of the retaining wall (such as the ground where the viscous soil spreads uniformly from the surface layer) ), A clay soil may exist only in a part of the range. For example, when a clay soil layer and a sandy soil layer are laminated in the depth of the retaining wall, the frictional force between the soil improvement body and the clay soil layer is within the thickness range. Is taken into account as a passive reaction force at the time of design.

  Here, "passive reaction force" is a reaction force that acts on the retaining wall from the ground deeper than the flooring on the excavation side of the retaining wall. The ground improvement body which contacts is directly subjected to a passive reaction force from the original ground, and this acts as an earth pressure resistance reaction force against the earth retaining wall.

  In addition, “viscous soil” means a ground that has at least an adhesive force and can take into account frictional force with the ground improvement body, regardless of whether it is soft ground or hard ground. ~ Soft clay, silt, humus soil, peat soil, etc. are the targets. However, in view of trying to reinforce the earth retaining wall by improving the ground, the clay soil mentioned here is generally applied to the soft ground.

  The earth retaining wall may have a linear shape with a long extension, or may have a frame shape (endless shape) such as a rectangle, a rectangle, a circle, or an ellipse in plan view.

  The ground improvement body which forms the earth retaining structure of the present invention is composed of a belt part which abuts the earth retaining wall and extends in a direction along the earth retaining wall, and a plurality of projecting parts which project from the belt part to the excavation side. It has a so-called comb-tooth shape in plan view.

  And, the belt portion and the projecting portion constituting the ground improvement body are formed by, for example, injecting chemicals or cement into the ground to form an improvement body formed in a columnar shape or a block shape in an adjacent posture, or The entire structure is formed by forming an improved body formed in a columnar shape or block shape in an adjacent posture by press-fitting sand into the ground and compacting.

  The diameter and height (improvement height) of the above-mentioned band part, the protrusion length and height of the protrusion part, and the spacing between adjacent protrusion parts (this is related to the base number of the protrusion part) is the magnitude of the working earth pressure. Depending on the specifications of the improved pile, the adhesive strength of the clay, the required frictional force, etc.

  In the main earth retaining structure, as a passive reaction force against the earth pressure acting on the earth retaining wall from the back of the earth retaining wall, the belt part of the ground improvement body that directly contacts the earth retaining wall starts from the viscous soil deeper than the flooring. In addition to the ground reaction force to be received, the frictional force acting between the protruding portion and the clay soil deeper than the floor is taken into consideration. That is, at least the ground reaction force and the friction force become the passive reaction force against the applied earth pressure.

  The inventors of the present invention have designed the conventional earth retaining structure, that is, a design in which the reaction force of the earth retaining wall can be obtained by connecting the earth retaining walls with underground beams made of ground improvement bodies. Instead of this idea, the ground improvement body has a structure consisting of a belt and a protrusion, and a rational design concept has been devised, in which the frictional force between the protrusion and the viscous soil is added to the passive reaction force. The earth retaining structure of the present invention has been achieved on the premise of the design concept (technical concept).

  According to the earth retaining structure of the present invention, in particular, when the earth retaining scale is wide, the reactive reaction force of the earth retaining wall root is increased while making the ground improvement range as small as possible. Therefore, the deformation of the retaining wall due to the working earth pressure can be effectively suppressed. This also leads to the realization of construction in consideration of the surrounding environment by shortening the construction period and reducing noise and vibration.

  Further, as a more preferable form of the earth retaining structure according to the present invention, as a passive reaction force against the earth pressure from the rear surface of the earth retaining wall, the ground reaction force received from the viscous soil whose tip area is deeper than the flooring is further increased. Mention may be made of the earth retaining structure to be added.

  For example, in the case of an improved pile made of viscous soil with a uniform depth after flooring, and the projecting portion constituting the ground improvement body improved into a columnar shape of φ: Rcm, it is determined by the width Rcm and the improved pile length: Lcm The area to be subjected to the ground reaction force from the clay soil deeper than the flooring.

  Therefore, this ground reaction force is also reflected in the design, that is, the ground reaction force that the belt receives from the clay soil deeper than the floor, the friction force between the protruding portion and the clay soil deeper than the floor, and The ground improvement range can be further reduced by making the ground reaction force that the tip area of the protrusion receives from the clay soil deeper than the floor and the reaction force against the working soil pressure, which is necessary for ground improvement. This leads to a reduction in construction costs.

  Further, the earth retaining structure construction method according to the present invention constructs an earth retaining wall for the ground having viscous soil at least deeper than the excavated floor, excavates the ground to the floor, and precedes the excavation of the ground. In the construction method of the earth retaining structure in which the ground improvement body is created at least deeper than the excavation floor after the excavation of the ground, the ground improvement body is composed of a belt portion and a projecting portion, and the soil from the rear surface of the earth retaining wall. The passive reaction force that resists pressure comprises at least the ground reaction force that the belt portion receives from the viscous soil deeper than the flooring, and the friction force between the protruding portion and the viscous soil deeper than the flooring, The belt portion that contacts the retaining wall and extends in a direction along the retaining wall is constructed, and a plurality of the projecting portions projecting from the belt portion to the excavation side are constructed.

  Here, the plurality of projecting portions after the belt portion is constructed may be constructed all at once or sequentially.

  According to the construction method of the present invention, especially when the planar scale of the earth retaining wall is wide, the ground improvement range can be greatly narrowed compared to the conventional construction method, and both the shortening of the construction period and the reduction of the construction cost can be achieved. Can be realized.

  As can be understood from the above description, according to the earth retaining structure and its construction method of the present invention, at least along the ground having a clay soil deeper than the excavated floor, in contact with the earth retaining wall and along the direction. A ground improvement body composed of an extending belt portion and a plurality of projecting portions projecting from the belt portion to the excavation side is created, and the frictional force between the projecting portion and the viscous soil is applied to the reactive soil pressure. By considering the force, it is possible to effectively suppress the earth retaining wall from being deformed by the applied earth pressure while reducing the ground improvement range. Moreover, as the passive reaction force, the ground improvement range can be further reduced by further expecting the ground reaction force received from the viscous soil whose tip area is deeper than the flooring.

It is a top view of one embodiment of the earth retaining structure of the present invention. (A) is the IIa-IIa arrow directional view of FIG. 1, (b) is the IIb-IIb arrow directional view of FIG. (A) is the top view which demonstrated typically the working earth pressure and the passive reaction force resisting this in the III section of FIG. 1, (b) is the longitudinal section. It is a longitudinal cross-sectional view explaining the conventional earth retaining structure. (A), (b) is a VV arrow directional view of FIG. 4, respectively, Comprising: It is the top view which showed embodiment of the ground improvement body which comprises the conventional earth retaining structure.

  Embodiments of the present invention will be described below with reference to the drawings. In the illustrated example, the earth retaining wall is formed in a rectangular frame shape in plan view, but the planar outline of the earth retaining wall to be created has an endless shape such as a square, a circle, an ellipse, etc. In addition to this, it also includes straight lines that are applied in the case of revetment work. Moreover, although the illustrated example shows the earth retaining structure having a relatively wide earth retaining range, the earth retaining structure of the present invention can naturally be applied to a small earth retaining area, and the effect can be enjoyed. .

  1 is a plan view of an embodiment of the earth retaining structure of the present invention, FIG. 2a is a view taken along the arrow IIa-IIa in FIG. 1, and FIG. 2b is a view taken along the arrow IIb-IIb in FIG.

  The earth retaining structure 100 shown in the figure has a earth retaining wall 10 formed in a rectangular frame shape with respect to the ground G in which viscous soil spreads uniformly from the surface layer, and a ground improvement body deeper than the flooring T on the excavation side. 40.

  The earth retaining wall 100 shown in the figure has a large plane scale with a longitudinal length L of 50 m or more, and its form is a steel sheet pile, a main pile sheet pile, a steel pipe sheet pile, a columnar continuous wall, It consists of one kind of underground continuous walls.

  Further, according to the excavation of the ground, a support work such as a cut beam as shown by the dotted arrow 50 in FIGS. 2a and 2b is constructed at a desired level, but the rigidity of the retaining wall 10 is high, and the ground properties are If self-supporting earth retaining is possible, installation of support works will be unnecessary.

  The ground improvement body 40 formed deeper than the flooring T on the excavation side of the retaining wall 10 has a band portion 20 that abuts the retaining wall 10 and extends in a direction along the retaining wall 10 in a plan view shown in FIG. The plurality of projecting portions 30 projecting from the belt portion 20 to the excavation side.

  And these belt | band | zone part 20 and the protrusion part 30 inject | pour a chemical | medical agent, cement, etc. in a ground, and the several columnar improvement piles 2 and 3 which can be stirred with the ground are formed in the row | line | column form in the adjacent attitude, and they comprise Has been. In addition to this, other well-known improvements such as a form that forms a block-like improvement body, a form that presses and compacts sand into the ground, and forms a sand pile are applied. can do.

  As is clear from FIG. 1, the projecting portion 30 constituting the ground improvement body 40 is not a long form straddling the opposing retaining walls 10, 10, but is compared to the planar side length of the retaining wall 10. It is extremely short. And in any of the four sides of the rectangular outline which comprises the earth retaining wall 10, in those excavation sides, it is what is called a comb-tooth shape which consists of the belt | band | zone part 20 and the some protrusion part 30 which protrudes from this. A ground improvement body 40 is created.

  Here, with reference to FIG. 3, the passive reaction force by the ground improvement body 40 and the design concept at the time of designing the earth retaining structure 100 are demonstrated. FIG. 3A is a plan view schematically illustrating the working earth pressure and the passive reaction force against this in the III part of FIG. 1, and FIG. 3B is a longitudinal sectional view thereof.

  Since the ground improvement body 40 is formed in the viscous ground G, although the adhesive force differs depending on the soil properties of the viscous soil, the friction force with the viscous soil G can be expected.

  As shown in FIG. 3a, first, the earth retaining wall 10 receives the ground reaction received from the clay soil G on the back surface thereof as one of the reactive reaction forces. Force Pp1 acts.

  Further, as another passive reaction force, a frictional force Pf between the side surface of the projecting portion 30 of the ground improvement body and the viscous soil G acts on the retaining wall 10.

  Furthermore, as another passive reaction force, a ground reaction force Pp2 that the tip area of the protrusion 30 receives from the clay soil G acts.

  That is, as the passive reaction force against the earth pressure Pa acting on the earth retaining wall 10, in addition to the ground reaction force Pp1 that the belt portion 20 receives from the viscous soil G on the back surface, the side surface of the protruding portion 30 and the viscous soil G This is a design philosophy that includes the friction force Pf between them and the ground reaction force Pp2 that the tip area of the projecting portion 30 receives from the viscous soil G in the passive reaction force. The planar shape of the ground improvement body 40 illustrated on the assumption of this design philosophy is Is formed.

  In addition, the cross-sectional diameter and improved height of the columnar improved piles 2 and 3, the protruding length and improved height of the protruding portion 30, the spacing between adjacent protruding portions 30 and 30 (this is related to the radix of the protruding portion 30), etc. Is appropriately adjusted according to the size of the working earth pressure, the specifications of the improved pile, the adhesive strength of the cohesive soil and the necessary frictional force.

  According to the earth retaining structure 100 shown in the figure, a belt part 20 that abuts the earth retaining wall 10 and extends in a direction along the earth retaining wall 10, and a plurality of projecting parts 30 projecting from the belt part 20 to the excavation side, The ground improvement body 40 is comprised from the frictional force Pf between the side surface of the protrusion part 30 and the viscous soil G, and the ground reaction force Pp2 which the front-end | tip area of the protrusion part 30 receives from the viscous soil G is included in a passive reaction force. Thus, even when the earth retaining scale is large, the ground improvement range can be significantly narrowed as compared with the conventional earth retaining structure. In addition, along with the narrowing of the ground improvement range, the construction cost will be reduced and the construction period will be shortened. Further, since the belt portion 20 is formed in a posture in contact with the earth retaining wall 10, the initial deformation of the earth retaining wall 10 due to the working earth pressure can be sufficiently suppressed, and thus the earth retaining due to the earth pressure acting is applied. The total amount of deformation of the wall 10 can be reduced.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  2, 3 ... Columnar improvement piles, 10 ... Earth retaining wall, 20 ... Belt, 30 ... Projection, 40 ... Ground improvement body, 100 ... Earth retaining structure, G ... Cohesive soil (ground), T ... Flooring

Claims (4)

A soil retaining structure applied to the ground having viscous soil at least deeper than the excavated floor,
A retaining wall,
A ground improvement body formed deeper than the excavation floor of the earth retaining wall,
In plan view, the ground improvement body comprises a band portion that contacts the retaining wall and extends in a direction along the retaining wall, and a plurality of protrusion portions that protrude from the band portion to the excavation side,
The passive reaction force that resists earth pressure from the back of the retaining wall is at least the ground reaction force that the belt part receives from the viscous soil deeper than the flooring, and the frictional force between the protruding part and the viscous soil deeper than the flooring, Tona is,
The earth retaining structure in which the creation range of the ground improvement body is set by the design based on the passive reaction force, and the earth retaining wall and the ground improvement body are set .   The earth retaining structure according to claim 1, wherein a ground reaction force received from viscous soil having a deeper area than the flooring is further applied as a passive reaction force against earth pressure from the back surface of the earth retaining wall.   The earth retaining structure according to claim 1 or 2, wherein the earth retaining wall has an endless shape in a plan view. Build a retaining wall on the ground that has cohesive soil at least deeper than the excavated floor, excavate the ground until flooring, and prior to or after excavating the ground, at least deeper than the excavated floor In the construction method of earth retaining structure to create ground improvement body in
The ground improvement body is composed of a belt portion and a protruding portion, and the reaction force against the earth pressure from the back of the retaining wall is at least the ground reaction force that the belt portion receives from the clay soil deeper than the floor, and the protrusion. parts and the friction force between the cohesive soil floor with deeper, Ri Tona, the design based on receiving働反force, sets the Establishment range of the soil improvement material, set the soil retaining wall and該地Edition improved body ,
The ground improvement body band set on the basis of the design is constructed so as to contact the retaining wall and extend in a direction along the retaining wall, and the ground improvement body protrusion portion set on the basis of the design. A method for constructing the earth retaining structure, in which a plurality of constructions are constructed so as to protrude from the belt portion to the excavation side.

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