JP2022060628A - Base-enlarged foundation structure, composite foundation structure of reinforced soil and construction method thereof - Google Patents

Abstract

To provide a foundation structure installed in soil improved in lifting resistance thereof.SOLUTION: A composite foundation structure comprises: a base-enlarged foundation structure having a columnar body 13 structured in an excavated hole 3 formed in soil 1 and a base-enlarged base plate 12 fixed to a lower end of the columnar body 13 with a larger cross sectional area than the columnar body 13 and provided at a bottom part of the excavated hole 3; earth retaining timbering 11 installed on a wall face of the excavated hole 3; back-filling sediment 4 back-filled into the excavated hole 3 after installing the base-enlarged foundation structure and compacted; multiple outside lock bolts 20 provided in a depth direction of the excavated hole 3 with intervals to each other and radially extended outward from the earth-retaining timber 11 and buried in the outside soil 1 around the earth-retaining timber 11, respectively; and multiple inside lock bolts 20 jointed to each of the outside lock bolts 20 with couplers, extended inward from the earth-retaining timber 11 and buried in the inside soil of the earth-retaining timber 11.SELECTED DRAWING: Figure 1

Description

The present invention relates to a composite foundation structure of a bottom-expanded foundation structure and a reinforced ground and a construction method thereof, and is mainly installed at a construction site where the location environment is limited such as a mountainous part or a mountainous part, for example, a steel tower or a bridge. It is related to the composite foundation structure for the purpose and its construction method. The composite foundation structure of the present invention is used to firmly fix steel towers, bridge columns, abutments, and other building structures to the ground.

A bottom-expanded foundation is a foundation with an enlarged diameter at the bottom of the foundation, and by providing a bottom-expanded foundation in the ground, the support resistance and lifting resistance of the foundation structure including the bottom-expanded foundation are greatly increased. It is possible to make it. Currently, the most efficient and large-scale method for constructing a bottom-expanding foundation is to excavate the ground using a dedicated bottom-expanding excavator while maintaining the stability of the excavated ground using a stabilizing liquid such as bentonite liquid or a casing. Construction method is being implemented. Such a construction method requires a large construction machine, and when the construction site is limited to a location environment such as a mountainous area or a mountainous area, specifically, a construction material or a dedicated excavator. Construction is not possible if there is no access lifeline such as public roads or railroads required for transportation.

Previous patent references related to the present invention are shown below.

Japanese Unexamined Patent Publication No. 2010-255212 Japanese Unexamined Patent Publication No. 5-179879 Japanese Unexamined Patent Publication No. 63-147011 Japanese Unexamined Patent Publication No. 52-89202

In Patent Document 1, while maintaining the ground stability of the vertical excavation hole wall and the bottom expansion hole wall with the casing and the stabilizing liquid, after excavating the conical bottom expansion part with the bottom expansion bucket, a reinforcing bar cage is installed and ready-mixed concrete by the tremie method. Disclose the invention of a method for constructing a cast-in-place concrete expansion pile to be driven. If the construction method according to Patent Document 1 is applied, since a stabilizing liquid such as bentonite is used in the excavation of the expanded bottom portion, the risk of collapse of the hole wall is small, and since the excavation is mechanical, the soil quality of the ground changes. It is possible to deal with a wide range of issues. In addition, since no worker is directly assigned to excavate the bottom of the expanded bottom, there is no danger of construction safety. However, the construction method of Patent Document 1 requires a huge excavation machine and a large crane for construction while lifting the huge excavation machine. Therefore, in a construction environment in a mountainous area where there is no access to carry in a large machine, Not applicable.

Patent Document 2 discloses that after vertical excavation to a predetermined depth, a hole is drilled horizontally in the excavation wall surface and a pipe is press-fitted to the outside thereof by a pressure propulsion machine. By press-fitting the pipe by the pressure propulsion mechanism and removing the earth and sand in the pipe, a plurality of bottom-expanded excavated parts are formed at the bottom of the foundation hole. Insert the lumber inside the pipe, connect and fix one end of the lumber to the lower end on the main pillar side, and place concrete. However, the bottom slab portion constructed by Patent Document 2 is not continuous in the circumferential direction, and the earth and sand of the local board is left between the pipes. Therefore, when a lifting axial force is generated on the bottom-expanded foundation having a discontinuous bottom-expanded portion, the slip surface (earth and sand fracture surface) generated in the field board in the case of the original expanded-bottom foundation continuous in the circumferential direction It is considered that the pulling resistance is reduced. In addition, considering the weight of the excavation drill, the mechanical device of the pressure propulsion mechanism, and the power machine that supports them, it is doubtful whether it is possible in the construction environment of the mountainous area.

The scale of the expanded foundation to which Patent Document 3 is applied is a scale of 100 m in depth, 6 m in diameter of the vertical foundation, 10 m in diameter of the expanded bottom, and 5 m in height of the expanded bottom, and the supporting ground is rock. Since the ground on which the expanded foundation is constructed is rock, there is no need for support work required for earth and sand ground. In order to vertically support the mountain retaining work constructed by the reverse winding method when excavating the vertical foundation, a horizontal shaft was excavated in 3 to 4 directions from the lowest end and constructed so that multiple concrete beams were piled up. , Construct a concrete structure that supports the load of the mountain retaining work. After that, the bedrock between the structures supported by the mountain retaining work is excavated without support to form an expanded space. However, in the construction method of Patent Document 3, excavation in the bedrock is carried out without support, so there is a risk of performing dome-shaped excavation with a diameter of 10 m without auxiliary support such as rock bolts. big. In addition, when excavating earth and sand, a large Yang heavy crane is required to use a small bucket, and it is difficult to carry in machinery in a mountainous construction environment. In addition, when the bottom expansion part is in the bedrock, as a design method of the withdrawal resistance, it is theoretically authorized to set the slip surface in terms of soil mechanics and to calculate the design withdrawal resistance value at that time. It is difficult to design because there is no such thing.

In Patent Document 4, the ground is excavated while providing earth retaining support to a predetermined depth, a drill hole is drilled diagonally downward at an inclination angle of 45 ° to 60 °, a lock bolt is inserted, and cement milk is poured into the ground void. Disclosed what is to construct a conical support by injecting. The ground on the lower surface of the support in the diagonal direction is further excavated, and a reinforced concrete structure is constructed by arranging reinforcements and placing concrete there to form an expanded bottom structure. However, since the tip of the lock bolt diagonally downward according to Patent Document 4 is arranged so as to be considerably wider than the casting interval inside the lock bolt, the tip is provided with the lock bolt and the cement milk injection. The work does not form a laterally continuous support structure. Therefore, when excavating the ground, there is a risk that the earth and sand at the tip of the lock bolt will come off, and the construction risk cannot be avoided.

The functions required of a foundation structure are the foundation for cross-sectional forces such as downward pushing axial force from the outside (superstructure), upward pulling axial force, horizontal shearing force, torsional moment, and bending moment. Structural resistance by the structure itself, the above-mentioned sectional force is effectively transmitted to the surrounding ground through the foundation structure, and the reaction force exerts resistance due to the coupled action of the foundation structure and the ground. And so on. It is required for the foundation structure to maintain the structure of the foundation structure and the stability of the ground.

Among the above-mentioned cross-sectional forces, the ground reaction force from the surrounding ground plays an important role in the downward pushing axial force and the upward pulling axial force from the superstructure. At the foundation of the transmission line tower, a large amount of pushing and pulling axial force acts due to the wind force acting on the transmission line tower and electric wires. Especially in the case of transmission tower foundations, the lifting axial force is often severe, and compared to the deep foundation foundations that do not have a bottom-expanded part, which has been overwhelmingly implemented in the past, the bottom-expanded foundations that have a bottom-expanded part have a pulling resistance. Due to the different geomechanical resistance mechanisms, increasing the withdrawal resistance is significantly effective.

However, in order to obtain the maximum lifting resistance by the expanded foundation, a cavity is excavated on the side of the foundation bottom without disturbing the ground above the expanded foundation, and the reinforced concrete foundation is formed in the expanded cavity constructed by excavation. You need to build a structure. In other words, in order to construct the bottom expansion part, in order to excavate sideways at the bottom of the foundation to construct the bottom expansion cavity, a roof-shaped (roof-shaped) and columnar support work that supports the earth and sand at the top of the bottom-expanding part is temporarily constructed. It is necessary to excavate the expanded bottom. Excavation work of the foundation expansion part is generally done by simple backhoe or hand digging, which requires a lot of construction time and construction cost, and there is a problem of construction risk such as landslide in addition to poor working environment. There is.

On the other hand, as a method of constructing a bottom-expanded foundation using a large machine, which is applied to large-scale buildings and bridge foundations, an earth drill that can maintain the stability of the excavated ground by using a casing and a stabilizing liquid and mechanically expand the bottom excavation. There is a method to construct the bottom expansion foundation efficiently and safely using the earth auger. These construction methods are economical and efficient because the excavation process of the expanded bottom is carried out not by human power but by a dedicated construction machine, but upfront investment of special machinery is required. Furthermore, in mountainous areas, it is impossible to apply such large-scale earth drills, earth augers, and lifting machines. In mountainous areas, there is often no access by public roads, so it is necessary to consider transportation means such as helicopters, ropeways, and monorails. On the other hand, in the case of a tower foundation on an accessible flat ground, it is possible to efficiently excavate the expanded ground using a large excavator, but excavation is carried out in muddy water and the excavation is carried out from the bottom so as to replace the muddy water. In order to construct a foundation body by placing tremie concrete, it is not possible to adopt the conventional construction method of fixing the foundation in the middle of the foundation body, so in the case of a steel tower foundation, the above-mentioned expanded foundation method Cannot be adopted.

(1) Repatriation resistance capacity and compression support resistance capacity of conventional foundations
1) The structural type of the foundation structure is the ground soil condition at the construction site, the position of the ground support layer, the position of the groundwater level, the transportation access conditions for construction materials, the structural type of the superstructure, the design load acting on the foundation structure, It is selected from such things.
2) As the foundation structural form of the steel tower foundation, the structural form of the deep foundation foundation and the inverted T-shaped foundation is often adopted. The main object of the present invention is to show the effect of the invention by having the bottom-expanded portion devised by the present invention for both the conventional deep foundation foundation and the inverted T-shaped foundation.
3) The standard shape of a deep foundation is a cylindrical cross section, and the position of the bottom of the foundation often reaches the supporting ground layer, and therefore is often deeper than the diameter. Assuming that the diameter of the column cross section = D and the depth of the deep foundation foundation = H, the ratio of the conventional deep foundation foundation is often H / D = 8-12.
4) The reason why the shape of the deep foundation is deepened is to increase the pulling resistance capacity and the compression support resistance capacity. As the excavation depth of the deep foundation increases, the amount of ground excavation and the volume of the structure increase, and the construction cost increases, such as excavation work at a deeper position, rebar assembly work, and concrete placing work, and the construction period becomes longer. Become.
5) As a structural type corresponding to such a situation, an expanded deep foundation foundation structural type having a widened bottom plate at the bottom of the foundation was proposed about 50 years ago, and there is also a construction example. In the deep foundation foundation structure with expanded bottom, the ground contact area of the bottom plate is 2 to 3 times larger than the cross-sectional area of the general column, so the compression support resistance capacity is greatly increased. On the other hand, regarding the withdrawal resistance ability, the slip surface of the surrounding ground at the time of withdrawal is completely different due to the presence of the widened bottom plate portion, so that the withdrawal resistance ability is significantly shown.
6) However, in order to adopt the bottom expansion foundation structure type, there are construction restrictions on the construction method of the bottom expansion part to be constructed at the bottom of the foundation, and it is possible to ensure economic and safety that solves the restrictions. At present, many ordinary deep foundation foundations are constructed due to the lack of various construction methods and structural types, and the adoption of wide-bottomed deep foundation foundations tends to decrease.
7) The standard shape of an inverted T-shaped foundation is literally an inverted T-shaped foundation, which is composed of a bottom plate at the bottom and a cylinder or prismatic foundation connected to it. This type of foundation is a type of foundation structure adopted when the supporting ground is located in a relatively shallow position.
8) Inverted T-shaped foundations include normal inverted T-shaped foundations and expanded inverted T-shaped foundations. Even in this case, in order to adopt the bottom-expanded inverted T-shaped foundation, there are construction restrictions and construction technical difficulties regarding the construction method of the bottom-expanded portion to be constructed on the bottom plate, and the constraints are economical and safe. There is no construction technology that can ensure the performance.

(2) Lifting resistance and construction method of the bottom expansion foundation structure
1) Regarding the lifting resistance of the bottom-expanded foundation, the soil mechanics theory development assuming that the slip surface at the time of lifting is a combination of the logarithmic spiral curve from the outer corner of the widened bottom slab and the straight line in the passive state of Rankine. The theoretical formula developed by is applied and incorporated into the Foundation Standards for Transmission Towers (JEC) of the Institute of Electrical Engineers of Japan.
2) The quotation resistance capacity of the bottom-expanded foundation may or may not be established for the logarithmic spiral curve and the sliding surface of the Rankine working state straight line, which can be expected to have a large lifting resistance, depending on the construction method. I know that.
3) The points of whether or not to form an ideal slip surface as a bottom-expanded foundation are (i) the excavation area setting and excavation method of the expanded-bottom foundation, and (ii) the degree of compaction of the backfill sediment, and the backfill sediment. It depends on whether or not the soil has soil strength characteristics (adhesive strength c and shear resistance angle φ) equal to or higher than those of the original ground originally existing around the ground.
4) There are two methods for classifying excavation areas and excavation methods. Excavation area method 1: With a cylindrical shape with a diameter equal to the width of the expanded bottom slab, vertical excavation is performed to the bottom of the foundation, a bottom plate is constructed, and a column is constructed on top of it. This is a method of backfilling the excavated earth and sand in the space with, and this is called the "vertical excavation backfilling method".
5) The second method, excavation area method 2: The space required for the bottom plate by excavating to the bottom of the foundation with a diameter shorter than the width of the bottom plate or a cylindrical shape equal to the width of the cylinder. Is a method of excavating from the lowermost end of the foundation in the lateral direction to construct an expanded bottom plate, and then backfilling the excavated earth and sand in the space between the outside of the column and the excavated surface. This is called the "expanded excavation method". The important point of the bottom expansion excavation method is that when excavating the cavity of the bottom expansion plate part, it will be safely excavated using an auxiliary method such as earth retaining support, but the original ground around the bottom expansion plate part will be loosened. Or it cannot be disturbed. Further, the bottom-expanded bottom plate portion needs to have a structure of the bottom-expanded bottom plate portion continuous in the circumferential direction.

(3) Evaluation of the lifting resistance of the bottom plate foundation
1) In the case of the "vertical excavation backfilling method" of the excavation area method 1, it is generally considered difficult to make the degree of compaction of the backfill soil equal to the degree of compaction of the original ground. .. Therefore, the soil strength characteristics of the backfill soil are reduced. The slip surface in such a case is a cylindrical surface along the side surfaces of the original ground and the bottom plate portion. That is, the pulling resistance is designed by the shearing method at the boundary surface which is the slip surface. Specifically, it is the sum of the slip surface shear resistance along the side surface of the bottom plate portion, the weight of the soil mass contained in this surface, and the weight of the foundation structure itself.
2) On the other hand, in the "expanded excavation method" of the excavation area method 2, the slip surface is not greatly affected by the compaction degree of the backfilled earth and sand, and the original ground around the expanded bottom plate is not disturbed. Is a composite of the logarithmic spiral curve from the outer corner of the widened bottom slab and the straight line in the active state of Rankine, and the amount of earth and sand that becomes the withdrawal resistance increases at once. It has been theoretically and experimentally confirmed that the withdrawal resistance increases or decreases under the influence of the protrusion width of the bottom expansion plate, but the withdrawal resistance by the expansion excavation method increases 3 to 4 times as much as the vertical excavation backfill method. There is.

The present invention considers a construction environment that is completely different from the methods conventionally tried by various methods for such a construction environment and a design environment, without using a special excavation machine, and also. It is the largest theoretically conceivable as a completed composite foundation structure, with the task of ensuring construction safety and providing an economical construction method for a composite foundation structure of a bottom-expanded foundation structure and reinforced ground. The task is to be able to have withdrawal resistance. The present invention cannot utilize its advantages only in a construction environment such as a mountainous area, and there are no restrictions on the construction environment even in flat land or urban areas with traffic access, and soil mechanics withdrawal. The resistance mechanism can be demonstrated.

In particular, it is an object to provide a new composite foundation structure and its construction method that can realize a significant cost reduction and shortening of the construction period as compared with the conventional bottom-expanded foundation structure even in a restricted environment of construction. ..

The basic role that the foundation structure of a tower or bridge should have is to provide structural stability to the various external loads that the so-called superstructure, such as the tower or bridge, receives. External load is mainly dead load, live load, wind load, snow load, seismic load, construction load and the like. Due to the load from these steel towers or superstructures, the foundation is subjected to the downward pushing axial force, the upward pulling axial force, the horizontal shearing force, the torsional moment, the bending moment, and other cross-sectional forces. The structural resistance of the structure itself and the above-mentioned sectional force are effectively transmitted to the surrounding ground through the foundation structure to maintain the structural stability of the foundation structure.

The foundation structure of the present invention is a soil mechanics of deep foundations and inverted T-shaped foundations that have already been proven in many places from the viewpoints of ground conditions, construction conditions, economic conditions, etc. in mountainous areas and mountainous areas. It relates to a bottom expansion foundation that can expand the pulling resistance capacity and the compression resistance capacity. In other words, although the present invention has many achievements, it improves the conventional construction risk and increase in construction cost in the deep foundation foundation and the bottom expansion foundation type in the inverted T-shaped foundation, and greatly enhances the pulling resistance capacity and the compression resistance capacity. It is related to the bottom expansion foundation that can be improved. Although various construction methods have been proposed for the bottom-expanded foundation, the present invention has increased the pulling resistance capacity and the compression resistance capacity based on a completely different idea from the conventional bottom-expanded foundation. It is a thing. Briefly, in the construction process of the bottom expansion foundation of the present invention, by performing economical and rational ground reinforcement for the weak part at the soil discontinuous boundary between the original ground and the backfill soil. This is a composite foundation structure of a bottom-expanded foundation structure and reinforced ground, in which the conventional mode of the fracture slip surface is changed to the mode of the fracture slip surface that can greatly increase the lifting resistance capacity.

If the "expanded excavation method" can be faithfully applied to the expanded foundation structure, the original ground around the expanded bottom plate will not be disturbed without being greatly affected by the degree of compaction of the backfilled soil. In that case, the slip surface is a combination of the logarithmic spiral curve from the outer corner of the widened bottom slab and the straight line in the active state of Rankine, and the amount of earth and sand that is the source of the withdrawal resistance increases at once. However, in actual construction, when excavating the cavity of the bottom plate, excavating with a simple construction method without disturbing the surrounding original ground and without using a special excavation machine may cause loosening of the original ground. There is a risk of collapse, and if safety is emphasized, a dedicated special excavation machine will be required, in which case the construction cost will increase and the construction environment will be limited.

The expanded foundation structure and the composite foundation structure of the reinforced ground according to the present invention are integrated with the columnar body constructed in the drilling hole formed in the ground and the lower end portion of the columnar body, and are cut off from the columnar body. A bottom-expanded foundation structure having a large area and having a bottom-expanded bottom plate provided at the bottom of the ground in the drilled hole, a retaining support provided on the side wall surface of the drilled hole, and the drilling hole after the bottom-expanded foundation structure is constructed. The backfilled earth and sand that are backfilled and compacted in, are provided at intervals in the depth direction of the excavation hole, and extend radially outward from the earth retaining support, each around the earth retaining support. A plurality of outer lock bolts buried in the outer ground of the above, and a plurality of outer lock bolts joined to each of the above outer lock bolts by using a coupler, extending inward from the above-mentioned earth retaining support, and buried in the inner ground of the above-mentioned earth retaining support. Equipped with an inner lock bolt.

In the construction method of the expanded foundation structure and the composite foundation structure of the reinforced ground according to the present invention, the ground is excavated, the earth retaining support is installed on the wall surface of the excavation hole formed by the excavation, and the earth retaining support is radially outside from the earth retaining support. A plurality of outer lock bolts are placed in the outer ground around the above-mentioned earth retaining support so as to extend in the direction, and the excavation of the above-mentioned ground, the installation of the earth retaining support, and the placement of the outer lock bolt are repeated to perform the earth retaining. An excavation hole is dug while reinforcing the outer ground around the support work, and the columnar body and the lower end of the columnar body are integrated into the excavation hole dug to a predetermined depth, and the cross-sectional area is larger than that of the columnar body. A bottom-expanded foundation structure with a large-sized bottom-expanded bottom slab is constructed, and earth and sand are backfilled and compacted between the drilled hole and the bottom-expanded foundation structure. By joining the inner lock bolts extending inward from the support work and repeating the backfilling of the earth and sand and the joining of the inner lock bolts, the excavation hole is backfilled while reinforcing the inner ground in the earth retaining support work.

An expanded foundation structure having a columnar body and an expanded bottom slab is provided in an excavation hole formed in the ground by excavating the ground. An expanded bottom slab of the expanded foundation structure is provided at the bottom of the excavation hole, and a columnar body is erected above the expanded bottom slab. The columnar body is constructed in the excavation hole and reaches the ground surface. Both the bottom-expanded bottom slab and the columnar body are preferably cylindrical, but they do not necessarily have to be cylindrical, and at least one of them may be prismatic. The columnar body and the expanded bottom slab are integrally formed by, for example, reinforced concrete.

The cross-sectional area of the expanded bottom slab (diameter if the expanded bottom slab is cylindrical) is larger than the cross-sectional area of the columnar body, and the bottom expanded foundation structure has a thick bottom (large diameter) and a thick bottom to thinner. The columnar body has an overall shape that extends upward. Since the expanded bottom slab is larger than the columnar body erected on the expanded bottom slab, the upper surface range of the expanded bottom slab in the range where the columnar body is not provided is exposed to the outside.

The drilled hole is formed so that the hole diameter (the size of the drilled hole) is approximately the same as or slightly larger than the cross-sectional area (diameter) of the bottom-expanded bottom slab. Generally, an excavation hole having the same cross-sectional shape as the cross-sectional shape of the bottom-expanded bottom slab is formed in the ground. The entire bottom-expanded foundation structure, including the expanded-bottom slab, can be accommodated in the excavation hole.

It is advisable to slightly project the upper end portion of the bottom-expanded foundation structure, that is, the upper end portion of the columnar body, from the opening (ground surface) of the excavation hole. That is, the height of the bottom-expanded foundation structure is made higher than the depth of the excavation hole (the depth of the excavation hole is made slightly shallower than the total height of the bottom-expanded foundation structure). For example, steel towers and bridge columns (legs) are fixed to the tip or inside of the columnar body of the expanded foundation structure, so by projecting the tip of the columnar body above the ground surface, this fixing work can be done. It will be easier to do.

After the bottom expansion foundation structure is installed, the excavation holes are backfilled with earth and sand and compacted.

A earth retaining support will be installed on the wall of the excavation hole. This prevents the ground around the excavation hole from collapsing into the excavation hole.

According to the present invention, a plurality of holes are provided at intervals in the depth direction of the excavation hole, and a plurality of pieces are radially outwardly extended from the earth retaining support and buried in the outer ground around the earth retaining work. There are a plurality of inner lock bolts that are joined to each of the outer lock bolts and the outer lock bolts by using a coupler, extend inward from the earth retaining support, and are buried in the inner ground of the earth retaining support. .. Multiple outer lock bolts and multiple inner lock bolts provide the boundary surface of the excavation hole and the ground around the expanded foundation structure (inside the earth retaining support where the outer ground and earth and sand of the earth retaining work are backfilled and compacted). Inner ground) is shear reinforced. That is, a "composite foundation structure" composed of an "expanded foundation structure" and a "reinforced ground" is constructed in the ground.

At first glance, the construction method of the composite foundation structure of the expanded foundation structure and the reinforced ground according to the present invention seems to be similar to the "vertical excavation backfilling method", but it is fundamentally different. That is, the excavation method required for constructing the bottom-expanded foundation structure is similar in that the ground is excavated so that the flat cross section (cross section) of the excavation fits in the flat cross section of the expanded bottom plate. However, according to the present invention, by repeating (1) excavation of the ground, (2) installation of earth retaining support, and (3) placement of outer lock bolts, while digging an excavation hole, earth retaining support is carried out. It reinforces the outer ground around the (excavation hole). This work is done on a small scale such as a back hoof for excavation, a liner plate or spray mortar machine as earth retaining support, a simple and compact rock bolt construction machine (for example, a compact construction machine such as a leg drill), and a small lifting machine. It is possible to construct using the construction equipment and construction machines of.

As described above, the excavation hole is dug while reinforcing the outer ground around the earth retaining support (excavation hole) by repeating excavation of the ground, installation of the earth retaining support, and placement of the outer lock bolt. After that, a bottom-expanded foundation structure including a columnar body and a bottom-expanded bottom slab is constructed in the excavation hole. Then, by repeating backfilling and compaction of earth and sand in the drilling hole and installation of the inner lock bolt (joining the inner lock bolt to the end of the outer lock bolt using a coupler), the boundary of the drilling hole is repeated. The excavation hole is backfilled while reinforcing the surface and the inner ground in the earth retaining support (excavation hole). These constructions can be easily carried out with small-scale construction equipment.

It has been theoretically and experimentally confirmed that the slip surface becomes a cylindrical surface along the sides of the original ground and the expanded bottom plate when the expanded foundation is constructed by the conventional "vertical excavation backfill method". There is. In other words, the lifting resistance when the bottom-expanded foundation is constructed by the "vertical excavation backfill method" is (1) shear resistance generated on the sliding surface along the side surface of the expanded bottom plate, and (2) sliding surface and columnar body. It is the sum of the weight of the soil mass existing between them and (3) the weight of the foundation structure.

On the other hand, in the present invention, the boundary surface of the earth retaining work and the outer ground around the earth retaining work and the inner ground inside the earth retaining work are shear-reinforced by a plurality of outer lock bolts and a plurality of inner lock bolts. , It does not have a slip surface as described above. The reason is that (i) the excavation boundary surface between the backfilled soil and the original ground is shear-reinforced by the outer lock bolt and the inner lock bolt provided so as to penetrate this boundary surface, and (ii) the excavation boundary surface. The outer ground (outer ground around the earth retaining work) is shear-reinforced by the outer rock bolt, and (iii) the backfilling earth and sand inside the excavation boundary surface (inner ground inside the earth retaining work) is inside. It is shear reinforced by rock bolts. Due to the above shear reinforcement effect, the shear slip that has occurred in the conventional "vertical excavation backfilling method" does not occur. This is the same as the case where the original ground near the expanded bottom slab is constructed without loosening by the "expanded bottom excavation method", and the slip surface is the logarithmic spiral curve from the outer corner of the widened bottom slab and the operation of Rankine. It is a composite of straight lines in the state. As a result, the combined foundation structure of the bottom-expanded foundation structure and the reinforced ground according to the present invention has at least 3 to 4 times the lifting resistance capacity as compared with the bottom-expanded foundation constructed by the above-mentioned "vertical excavation backfilling method". Increases to.

In one embodiment, the backfill sediment is a soil cement material in which cement or cement milk is added and agitated to the sediment discharged by the formation of the excavation hole. Compared with ordinary backfilling earth and sand, it is possible to easily improve the compaction degree and easily improve the ground strength (uniaxial compressive strength) of the backfilling earth and sand. As a result, it is possible to reduce the number of inner lock bolts buried in the inner ground of the earth retaining support.

Preferably, the outer lock bolt is composed of a core material and a grout filled around the core material. The reinforcement of the outer ground by the outer lock bolt can be strengthened.

The core material of the outer lock bolt is preferably formed in a hollow shape, and has a discharge hole for discharging the grout sent into the hollow of the core material to the outside. The grout sent into the hollow of the core material from the end of the outer lock bolt can be discharged from the discharge hole, and the grout can be filled around the core material.

In one embodiment, the inner lock bolt is composed of a core material and a wrapping concrete wrapped around the core material. Since it contributes to the increase in shear rigidity and strength of the inner ground, the number of inner lock bolts can be reduced.

In another embodiment, the bottom-expanded foundation structure including the columnar body and the bottom of the bottom slab is a precast prestressed concrete structure. In an environment where the location environment of the foundation structure is difficult to transport construction materials such as in mountainous areas and the transportation cost is high, the required amount of concrete, which is the main material for foundation construction, can be reduced, and as a result. , It is possible to reduce enormous transportation costs. In addition, it is possible to eliminate the need for rebar assembly at the construction site, solve quality control problems in the on-site placement of ready-mixed concrete, and significantly shorten the construction period at the construction site.

In another embodiment, the bottom-expanded foundation structure including the columnar body and the bottom-expanded bottom slab is a cast-in-place reinforced concrete structure. In an environment where the location environment of the foundation structure is such that it is easy to transport construction materials such as in the plains, concrete, which is the main material for foundation construction, is transported as ready-mixed concrete from the ready-mixed concrete plant to the construction site by a ready-mixed concrete vehicle. Concrete can be placed efficiently by placing a tremie or a bucket on the frame after installing the formwork and arranging the reinforcement. In other words, in areas where construction materials can be transported even in plain or mountainous areas where the location environment of the foundation structure is high, it is more advantageous to construct by casting concrete on site from the viewpoint of construction cost.

Normally, ground reinforcement using lock bolts is performed only on the ground around the outside of the drilling hole. If the ground area requiring reinforcement is large, long outer lock bolts are required. In the case of the present invention, the region to be shear-reinforced in the ground is relatively narrow. However, it is necessary to reinforce the area of the original ground and backfilled soil on both sides of the excavation boundary surface so as to be continuous. The construction method does not require special scaffolding during excavation or backfilling of earth and sand. In addition, since the required outer lock bolt length is short, it can be installed with a compact leg drill machine. That is, even in a mountainous area where a deep foundation foundation or an inverted T-shaped foundation is located, the composite foundation structure of the present invention does not require a special construction machine and does not bear a construction risk such as bottom expansion excavation. It can be constructed at low cost in a short period of time, and it is possible to increase the withdrawal resistance by 3 to 4 times compared to the withdrawal resistance of conventional deep foundations and inverted T-shaped foundations.

Other effects
From 1990 to 1999, the nationwide implementation rate of steel tower foundations was 39% for deep foundations and 49% for inverted T-shaped foundations. In other words, of all the basic forms, these two basic forms account for 88% of the total. The composite foundation structure of the bottom-expanded foundation structure and the reinforced ground of the present invention can be used in place of both of these foundation types. In the design of the tower foundation, the location conditions of the supporting ground are a major factor in determining the foundation type. In addition, although it acts on the tower foundation, as a design external force, the pulling force and the compression bearing force are large design factors.

In the conventional deep foundation foundation and inverted T-shaped foundation, in order to resist the pulling force, by increasing the diameter of the foundation and the depth of the foundation, the weight of the foundation is increased, and by increasing the shear resistance area, the shear resistance area is increased. I was trying to increase the withdrawal resistance. However, such a coping method results in an increase in the volume of the foundation structure itself, an increase in the excavation volume, and an increase in the excavation depth, resulting in an increase in construction cost and construction period.

Against this background, by using the composite foundation structure according to the present invention in place of the deep foundation foundation and inverted T-shaped foundation, which are currently the most popular as steel tower foundations, the size of the foundation shape can be reduced and the construction cost can be reduced. , Can contribute to shortening the construction period.

It is a vertical sectional view of a composite foundation structure including a bottom-expanded foundation structure and a reinforced ground. It is a vertical sectional view which shows the detail of the outer lock bolt. It is a vertical sectional view which shows the detail of the inner lock bolt. The state of construction of the composite foundation structure is shown. The state of construction of the composite foundation structure is shown. The state of construction of the composite foundation structure is shown. The state of construction of the composite foundation structure is shown.

FIG. 1 shows a so-called composite foundation structure of a so-called bottom expansion foundation structure and a reinforcement ground, which is composed of a concrete bottom expansion foundation structure and surrounding reinforcing ground according to the present invention. The composite foundation structure is installed at the bottom of the excavation hole 3 and the earth retaining support 11 provided on the wall surface (earth wall) of the excavation hole 3 formed by excavating the original ground 1 substantially vertically from the ground surface 2. 12 By a plurality of outer lock bolts 20 and inner lock bolts 30 extending outward and inward from each, and backfilling earth and sand 4 filling the gap between the excavation hole 3 (earth retaining support 11) and the bottom expansion slab 12 and the columnar body 13. It is composed. The set of the bottom-expanded bottom slab 12 and the columnar body 13 is the "expanded foundation structure". The ground is reinforced by the outer lock bolt 20 and the inner lock bolt 30 (reinforced ground).

The excavation hole 3 is formed in a cylindrical shape, and a low-height columnar expanded bottom slab 12 and a high-height columnar columnar body 13 are installed in the columnar excavation hole 3. The shape of the excavation hole 3, the bottom expansion slab 12, and the columnar body 13 is not limited to the cylindrical shape, and may be, for example, a prismatic shape. The drilling hole 3 has a diameter substantially equal to or slightly larger than the diameter of the bottom-expanded bottom slab 12, and the bottom-expanded bottom slab 12 is completely housed in the drilling hole 3 so that the bottom surface of the bottom-expanded bottom slab 12 touches the bottom surface of the drilling hole 3. The columnar body 13 erected on the upper surface of the expanded bottom slab 12 has a diameter smaller than that of the expanded bottom slab 12, and is erected in the center of the upper surface of the expanded bottom slab 12.

The earth retaining support 11 provided on the wall surface around the excavation hole 3 is composed of, for example, a liner plate or sprayed mortar (or sprayed concrete), and prevents the surrounding original ground 1 from collapsing toward the excavation hole 3. Mortar may be filled between the wall surface (side wall ground) of the excavation hole 3 and the liner plate. If the excavation hole 3 is cylindrical, the earth retaining support 11 is constructed in a cylindrical shape.

The outer lock bolt 20 and the inner lock bolt 30 extending outward and inward from the earth retaining support 11 are provided in a straight line so as to penetrate the earth retaining support 11. As shown in FIG. 1, a plurality of outer and inner lock bolts 20 and 30 are provided at intervals in the depth direction (vertical direction) of the excavation hole 3, and a plurality of outer and inner lock bolts 20 and 30 are also provided at equal angles in the circumferential direction. .. The outer and inner lock bolts 20 and 30 reinforce the boundary surface between the original ground 1 and the backfill earth and sand 4, and the ground of the original ground 1 and the backfill earth and sand 4, which is different from the conventional slip surface as described later. A new sliding surface 40 is defined, resulting in a significant improvement in withdrawal resistance. The detailed structure of the outer and inner lock bolts 20 and 30 and the details of the sliding surface 40 will be described later.

The columnar body 13 shown in FIG. 1 is a concrete structure corresponding to a conventional deep foundation. The bottom-expanded bottom plate 12 is the part corresponding to the bottom-expanded foundation. The composite foundation structure of the present invention may be a structure including the outer and inner lock bolts 20 and 30 constructed so as to penetrate the outer side and the inner side of the columnar body 13 and the excavation boundary surface (earth retaining support 11). ..

The withdrawal resistance of the expanded foundation structure and the composite foundation structure of the reinforced ground shown in FIG. 1 can be significantly improved as compared with the withdrawal resistance calculated in the conventional deep foundation or inverted T-shaped foundation. Explain the rationale.

(A) In the case of conventional columnar body + expanded bottom slab In the conventional columnar body and expanded bottom slab construction method, the foundation structure (conventional) has a width (diameter) equal to or slightly wider than the width (diameter) of the expanded bottom slab. The excavation of the ground and the installation of the earth retaining support are performed alternately to excavate the ground in order to construct the columnar body and the expanded bottom slab. After excavating the ground to a predetermined depth, foundation structures (columnar bodies and expanded bottom slabs) are constructed in the excavation holes formed in the ground by excavation. After that, the backfilled earth and sand are backfilled in the gap between the foundation structure and the earth retaining support.

In this way, when a deep foundation foundation or an inverted T-shaped foundation with an expanded bottom slab is constructed by the conventional construction method, if the lifting force 50 as shown in FIG. 1 acts, the original ground and backfilling earth and sand will be used. It has been proved by theoretical analysis and model experiments that slippage occurs at the boundary surface of. The main reason for this is that it is difficult to make the backfill soil into compacted soil similar to the original ground, and the excavation boundary surface is fundamentally discontinuous in terms of soil, so it is on the boundary surface. It is thought that the cause is that the shear resistance of Mohoroviči is lower than the shear resistance of the original ground.

When the slip surface is generated at the interface between the original ground and the backfilled soil due to the action of the lifting force, the lifting resistance is (i) the shear resistance generated at the sliding surface, (ii) the bottom plate and the columnar body. It is the sum of the weight of the backfilled soil on the difference in cross-sectional area with and (iii) the weight of the foundation structure.

(B) In the case of the columnar body + expanded bottom slab + shear reinforcing rock bolt of the present invention The excavation shape of the ground in the case of the present invention is the same as the conventional shape. However, in the process of excavation, the outer lock bolt 20 is installed from the inside of the earth retaining support 11 to the outside from the earth retaining support 11 at the design necessary place. By repeating the excavation of the ground 1, the installation of the earth retaining support 11, and the construction of the outer lock bolt 20, these constructions can be performed without temporary construction such as scaffolding. On the other hand, at the time of backfilling, the inner lock bolt 30 facing inward from the earth retaining support 11 is joined by nut joining using a long nut provided at the end of the outer lock bolt 20. This work can also be carried out without temporary installation of scaffolding or the like by alternately backfilling the earth and sand 4 and joining the inner lock bolt 30.

As described above, the resistance mechanism when the lifting force 50 as shown in FIG. 1 acts when a deep foundation foundation or an inverted T-shaped foundation having an expanded bottom slab is constructed by the construction method of the present invention is shown below. First, regarding the slip surface, the boundary surface between the original ground and the backfilled earth and sand as in the past does not become a slip surface. It is because the boundary surface between the original ground and backfilling earth and the earth and sand outside and inside the boundary surface are sheared at least above the original ground due to the presence of ground shear reinforcement by the outer lock bolt 20 and the inner lock bolt 30 that penetrated. This is because resistance and compaction can be obtained. It is considered that the state is equivalent to the case where only the expanded part of the expanded bottom slab constructed by the "expanded excavation method" is excavated without disturbing the surrounding ground. Therefore, the slip surface in this case is formed so as to spread from the bottom-expanded bottom slab 12 toward the ground surface 2 as shown by the alternate long and short dash line of reference numeral 40 in FIG. More specifically, the slip surface 40 has a mortar-like shape composed of a logarithmic spiral curve extending diagonally upward from the outer edge of the upper surface of the bottom-expanded bottom plate 12 and a straight line when Rankine passive earth pressure is applied. The formation of this slip surface 40 is theoretically guided, and is published by the Institute of Electrical Engineers of Japan, "Standard for Design of Supports for Power Transmission" (JEC-127) and by the Institute of Electrical Engineers of Japan. It is described as a design method for lifting resistance in "Design of Tower Foundation for Power Transmission". In addition, model experiments or FEM analysis applying the elasto-plastic constitutive law to the surrounding ground have proved that the fracture slip surface and lifting resistance by the "expanded excavation method" are appropriate for the above design method. ..

By executing the process for the composite shore structure according to the present invention for the conventional deep foundation foundation and inverted T-shaped foundation, the above slip surface 40 can be applied, and the shear resistance along the slide surface 40 can be applied. Since it can be calculated as the withdrawal resistance, it is considered that the withdrawal resistance will be 3 to 4 times higher than before, although it varies depending on the surrounding ground conditions and the shape of the foundation structure.

Next, the shear reinforcement of the ground performed on the excavation boundary surface of the present invention and the ground inside and outside the excavation boundary surface will be described. FIG. 2 is a vertical sectional view showing the structure of the outer lock bolt 20 in detail. As shown in FIG. 2, in order to perform shear reinforcement of earth and sand in the vicinity of the excavation boundary surface, a compact drilling drill (not shown) such as a leg drill from the inside of the earth retaining support 11 (inside the excavation hole 3). ) Is used to drill a hole in the original ground 1 sideways toward the outside of the earth retaining support 11 (outward in the normal direction from the peripheral surface of the excavation hole 3 (earth retaining support 11)). A lock bolt core material 21 is attached to the drill. A hollow deformed threaded reinforcing bar or the like is applied to the lock bolt core material 21, and a bit 22 for drilling is attached to the tip thereof. By rotating the bit 22, the original ground 1 is dug sideways. After drilling the original ground 1 to a predetermined position, the grout 23 is press-fitted into the lock bolt core material 21 from the end of the lock bolt core material 21. The lock bolt core material 21 is hollow, and a plurality of small discharge holes 24 are formed on the peripheral surface thereof. The grout 23 press-fitted into the lock bolt core material 21 is pushed out from the discharge hole 24 on the peripheral surface of the lock bolt core material 21 and is filled around the lock bolt core material 21. An outer lock bolt 20 composed of a lock bolt core material 21 and a grout 23 around it is provided on the peripheral ground of the excavation hole 3 (outer ground of the excavation boundary surface (earth retaining support 11)), and the peripheral ground is shear-reinforced. Will be done.

The end portion of the lock bolt core material 21 of the outer lock bolt 20 slightly extends to the inside of the earth retaining support 11 (inside the excavation hole 3). After the grout 23 develops a predetermined strength, the bearing plate 15 is attached to the lock bolt core material 21 of the outer lock bolt 20 extending inside the earth retaining support 11, and the long nut (coupler nut) 16 is attached via the bearing plate 15. It is tightened around the end of the lock bolt core 21. The long nut 16 serves as a coupling nut when constructing the inner lock bolt 30 described below.

FIG. 3 is a vertical cross-sectional view showing the structure of the inner lock bolt 30 together with the structure of the outer lock bolt 20 described with reference to FIG. After shear reinforcement with the outer lock bolt 20 to the ground outside the excavation interface is performed within a predetermined range, the inner lock bolt 30 is installed.

As shown in FIG. 3, the inner lock bolt 30 is composed of a lock bolt core material (such as a reinforcing bar with a deformed screw) 31 and a wound concrete 32 provided around the lock bolt core material 31. The construction of the inner lock bolt 30 is performed while backfilling the excavation hole 3 with the backfilling earth and sand 4, that is, forming a scaffolding with the backfilling earth and sand 4 in order to facilitate the construction of the inner lock bolt 30. At one end of the inner lock bolt 30, a part of the lock bolt core material 31 protrudes outward from the wound concrete 32, and as shown in FIG. 3, one end of the lock bolt core material 31 protruding to the outside is Screwed (joined) into the long nut 16. As a result, the outer lock bolt 20 and the inner lock bolt 30 are installed in a straight line in the direction connecting the outside and the inside of the earth retaining support 11. The inner lock bolt 30 may be only the lock bolt core material 31, but it is preferable to use a columnar body in which the concrete 32 is wound around the lock bolt core material 31 and integrated. In this case, as the shear rigidity of the inner lock bolt 30, the shear rigidity of the rock bolt core material 31 and the shear rigidity of the wound concrete 32 contribute to the ground shear reinforcement.

The shear reinforcement of the ground by the inner lock bolt 30 is different from the conventional construction method premised on drilling, but after the construction of the inner lock bolt 30, the earth and sand is backfilled while compacting the backfill earth and sand 4. Therefore, the shear reinforcement of the backfill earth and sand 4 can be surely carried out. Ultimately, the outer and inner ground, including the excavation interface, will be shear reinforced.

Although many construction results have been reported for rock bolts in the reinforcement of ground and bedrock, long nuts (coupler nuts) 16 were applied to the outside and inside of the excavation boundary surface for shear reinforcement of the ground as in the present invention. There are no cases.

Here, a numerical comparative calculation example of the effect of shear reinforcement of the ground by the outer and inner lock bolts 20 and 30 according to the present invention is shown using a standard ground as an example. It is a design act to determine the required specifications of the outer and inner lock bolts 20 and 30 according to the present invention. Here, the shear reinforcement effect when shear reinforcement with typical outer and inner lock bolts 20 and 30 is performed on typical ground is calculated.

First, the shear stress state generated in the earth and sand in the original ground 1 is described by the Mohr-Coulomb equation. The shear stress τ in the soil is expressed by the following equation by the viscous stress C in the ground, the direct stress in the soil σ, and the internal friction angle φ.

Shear stress in soil τ = C + σtanφ ・ ・ ・ Equation 1

Here, the soil direct stress σ is expressed by the following equation using the static earth pressure coefficient Ko, the unit volume weight γ of the soil, and the target ground depth h.

Soil direct stress σ ＝ Koγh ・ ・ ・ Equation 2

Therefore, from Equations 1 and 2, the shear stress τ in the soil is expressed by the following equation.
Shear stress in soil τ = C + Koγhtanφ ・ ・ ・ Equation 3

Here, standard data as shown below are applied to the soil characteristics of the ground.

Ground characteristic data: Adhesive stress of the ground: C = 10 kN / m ² , Internal friction angle: φ = 26 degrees, Unit volume weight: γ = 17.7 kN / m ³ , Target ground depth: h = 10 m, Static earth pressure coefficient : Ko = 0.4

Applying the above ground characteristic data to Equation 3, the shear stress τ in the soil of only the original ground 1 at a ground depth of 10 m is as follows.

Shear stress τ = 10 + 0.4x17.7x10xtan26 = 44.5 kN / m ² in the soil of the original ground 1 only. The shear stress τ obtained here is obtained by the Mohr-Coulomb fracture equation and indicates the limit shear stress at which the soil undergoes shear fracture at 10 m in the soil.

Next, the resistance shear stress that can be generated at a ground depth of 10 m by the outer lock bolt 20 (combination of the lock bolt core material 21 and the grout 23) is obtained. First, the resistance shear force Qs of the rock bolt core material 21 is obtained by the product of the cross-sectional area As of the rock bolt core material 21 and the shear stress τs (Qs = As × τs). Further, the resistance shear force Qg of the grout 23 filled around the lock bolt core material 21 is obtained by the product of the cross-sectional area Ag of the grout 23 and the shear stress τg of the grout 23 (Qg = Ag × τg).

The resistance shear stress of the outer rock bolt 20 can be considered to be the sum of the resistance shear force Qs of the rock bolt core material 21 and the resistance shear force Qg of the grout 23 (Qs + Qg). The characteristics of the outer lock bolt 20 are that the cross-sectional area of the rock bolt core 21 is As = 350 mm ² , the shear stress of the rock bolt core 21 is τs = 150 N / mm ² , the diameter of the glaut 23 is D = 200 mm, and the shear stress of the glaut 23 is τg. If = 3N / mm ² , the following values are calculated.

Total resistance shear force of outer lock bolt 20 Qs + Qg = 350x150 + 3.14x200x200 / 4x3 = 146.7 kN

Assuming that the vertical spacing (vertical construction pitch) of the outer lock bolts 20 is 1.5 m and the circumferential spacing (horizontal construction pitch) of the outer lock bolts 20 is 1.5 m, the average resistance shear stress due to the plurality of outer lock bolts 20 τrb is (Qs + Qg) / (1.5x1.5) = 65.2 kN / m ² .

The average resistance shear stress τrb = 65.2 kN / m ² due to the outer rock bolt 20, while the fracture shear stress τ = 44.5 kN / m ² of the outer ground. This means that the shear reinforcement of the outer lock bolt 20 has more than doubled the resistance shear stress of the ground.

On the other hand, the average shear resistance stress τrb can be calculated for the inner lock bolt 30 in the same manner. As for the inner backfill sediment 4, unlike the original ground, the internal friction angle of the soil is considered to be φ = 20 degrees due to the decrease in compaction, so the fracture shear stress τ = 35.8 kN / of the inner ground. It becomes m ² . In other words, the shear reinforcement of the inner lock bolt 30 more than doubles the resistance shear stress of the ground.

A method of constructing a composite foundation structure of a bottom-expanded foundation structure and a reinforced ground according to the present invention will be described with reference to FIGS. 4 to 7.

With reference to FIG. 4, at a predetermined position where the bottom-expanded foundation structure is to be constructed, the plan shape matches the plane (cross-section) shape of the bottom-expanded bottom slab 12, or the plan shape is slightly larger, and the original ground is downward from the ground surface 2. Excavate 1. An earth retaining support (liner plate or spray mortar) 11 is provided on the wall surface of the excavation hole 3 in order to prevent the ground from collapsing into the excavation hole 3 formed by vertically excavating the original ground 1. By alternately installing the earth retaining support 11 and excavating the original ground 1, the excavation hole 3 is gradually dug deeper while preventing the ground from collapsing.

With reference to FIG. 5, after excavation is completed to a predetermined depth, the construction of the outer lock bolt 20 is started. The outer lock bolt 20 is installed as described in FIG. When constructing the outer lock bolt 20, a separate scaffold is not required because the excavated bottom surface can be used as a scaffold when constructing the outer lock bolt 20. That is, excavation of the original ground 1, installation of the earth retaining support 11, and construction of the outer lock bolt 20 are carried out alternately. There is no need to use a special construction machine. The plurality of outer lock bolts 20 extend radially outward from the earth retaining support 11 and are buried in the outer ground of the earth retaining support 11.

With reference to FIG. 6, the construction of the outer lock bolt 20 ends at the section required by design. When the construction section of the outer lock bolt 20 is exceeded, the excavation of the original ground 1 and the installation of the earth retaining support 11 are alternately carried out to a predetermined position without constructing the outer lock bolt 20. Next, a bottom-expanded foundation structure including a bottom-expanded bottom slab 12 and a columnar body 13 is installed in the formed excavation hole 3. The bottom-expanded foundation structures 12 and 13 may basically have the bottom-expanded bottom plate 12 at the bottom of the foundation, regardless of the form of the deep foundation or the inverted T-shaped foundation. In addition, there are no restrictions on the structural type of the bottom-expanded foundation structures 12 and 13, such as RC structures using concrete materials and prestressed concrete structures. In addition, there are no restrictions on the construction method, whether it is cast-in-place concrete or precast concrete.

With reference to FIG. 7, after the bottom-expanded foundation structures 12 and 13 are constructed, the excavated earth and sand 4 is backfilled and tightened in the excavation hole 3 (the gap between the earth retaining support 11 and the bottom-expanded foundation structures 12 and 13). Harden. As described with reference to FIG. 3, the inner lock bolt 30 is installed while using the upper surface of the earth and sand 4 to be backfilled in the excavation hole 3 as a scaffold. The plurality of inner lock bolts 30 extend inward from the earth retaining support 11 and are buried in the inner ground (backfill earth and sand 4) of the earth retaining support 11. The construction sections of the outer and inner lock bolts 20 and 30 are sections that shear and reinforce the excavation boundary surface required by design. The upper edge of the expanded bottom plate 12 needs to be the starting point where the slip surface 40 (see FIG. 1) is formed, so that it is below the vicinity of the outer and inner lock bolts 20 and 30 at the lowermost end. The earth retaining support 11 is basically removed while the earth and sand 4 is backfilled and compacted.

As described with reference to FIG. 3, the inner lock bolt 30 is installed by screwing (joining) the lock bolt core material 31 into the long nut (coupling nut) 16 provided at the time of construction of the outer lock bolt 20. .. As described above, the upper surface of the backfill earth and sand 4 is used for the scaffolding when the inner lock bolt 30 is installed, and no special scaffolding erection is required. By alternately performing the backfilling work of the earth and sand 4 and the installation work of the inner lock bolt 30, the inner lock bolt 30 is provided in line with the outer lock bolt 20 provided in advance, and the excavation hole 3 is the earth and sand 4 It will be gradually backfilled by.

As for the backfill soil 4, basically, the excavated soil discharged when the original ground 1 is excavated to form the excavation hole 3 is used, but cement or cement milk is added to the soil discharged by the excavation. , Soil cement material produced by stirring may be used. By using the soil cement material, it is possible to easily improve the shear strength, the uniaxial compressive strength, and the shear rigidity and the compressive rigidity. A positive effect is exerted on the ground reinforcement using the inner lock bolt 30, and the slip surface 40 of the present invention is more reliably approached to the theoretical form.

Finally, as shown in FIG. 1, a composite foundation structure of a bottom-expanded foundation structure and a reinforced ground according to the present invention is completed. The specifications of the outer and inner lock bolts 20 and 30, the construction pitch and the construction range of the outer and inner lock bolts 20 and 30 are design matters.

1 Original ground 2 Ground surface 3 Excavation hole 4 Backfilling earth and sand
11 Dore support
12 Expanded bottom plate
13 Columnar body
16 long nut
20 Outer lock bolt
21 Lock bolt core material
23 grout
24 Discharge hole
30 Inner lock bolt
31 Lock bolt core material
32 Wrapped concrete

Claims (8)

A columnar body that is passed through a drilling hole formed in the ground, and a bottom-expanded bottom that is fixed to the lower end of the columnar body and has a larger cross-sectional area than the columnar body and has an expanded bottom plate provided at the bottom of the drilling hole. Foundation structure,
Earth retaining support provided on the wall of the above excavation hole,
Backfilled earth and sand that is backfilled and compacted in the excavation hole after the bottom expansion foundation structure is provided.
A plurality of outer lock bolts provided at intervals in the depth direction of the excavation hole and extending outward radially from the earth retaining support, each of which is buried in the outer ground around the earth retaining work. , And a plurality of inner lock bolts that are joined to each of the outer lock bolts using a coupler, extend inward from the earth retaining support, and are buried in the inner ground of the earth retaining work.
Composite foundation structure of expanded foundation structure and reinforced ground. The backfilling earth and sand is a soil cement material in which cement or cement milk is added to the earth and sand discharged by the formation of the excavation hole and the mixture is agitated.
The composite foundation structure of the expanded foundation structure and the reinforced ground according to claim 1. The composite foundation structure of the bottom-expanded foundation structure and the reinforced ground according to claim 1 or 2, wherein the outer lock bolt is composed of a core material and a grout filled around the core material. The inner lock bolt is composed of a core material and a wound concrete wound around the core material.
The composite foundation structure of the bottom-expanded foundation structure and the reinforced ground according to any one of claims 1 to 3. The bottom-expanded foundation structure including the columnar body and the bottom-expanded bottom slab is a precast prestressed concrete structure.
The composite foundation structure of the bottom-expanded foundation structure and the reinforced ground according to any one of claims 1 to 4. The bottom-expanded foundation structure provided with the columnar body and the bottom-expanded bottom slab is a cast-in-place reinforced concrete structure.
The composite foundation structure of the bottom-expanded foundation structure and the reinforced ground according to any one of claims 1 to 4. Excavate the ground,
Installed earth retaining support on the wall of the excavation hole formed by excavation,
A plurality of outer lock bolts are placed on the outer ground around the earth retaining work so as to extend outward radially from the earth retaining work.
By repeating the excavation of the ground, the installation of the earth retaining support, and the placement of the outer lock bolt, the excavation hole is dug while reinforcing the outer ground around the earth retaining support.
In the excavation hole dug to a predetermined depth, a bottom-expanded foundation structure having a columnar body and a bottom-expanded bottom plate fixed to the lower end of the columnar body and having a larger cross-sectional area than the columnar body is constructed.
Fill the excavation hole with earth and sand and compact it.
Using a coupler, join the inner lock bolt extending inward from the earth retaining support to the end of the outer lock bolt.
By repeating the backfilling of the earth and sand and the joining of the inner lock bolt, the excavation hole is backfilled while reinforcing the inner ground in the earth retaining support.
Construction method of composite foundation structure of expanded foundation structure and reinforced ground. Of the earth retaining works installed on the wall surface of the excavation hole, the earth retaining works below the outer and inner lock bolts at the lowermost end are removed.
The method for constructing a composite foundation structure of a bottom-expanded foundation structure and a reinforced ground according to claim 7.

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