JP2009138435A - Method of constructing foundation structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of constructing a foundation structure capable of efficiently constructing a highly reliable foundation structure. <P>SOLUTION: This method of constructing a foundation structure of a structure having a direct foundation part 2 for placing the load of a building 1 thereon and a pile foundation part 30 formed of steel pipe piles 3 includes a pile reaction force calculation step of calculating a reaction on the direct foundation part and pile reactions supported by the steel pipe piles, respectively, a pile selection step of calculating a minimum pipe length L1 and selecting a steel pipe pile 3 capable of securing a maximum pile length L2 allowing the estimated error of an estimated bearing force P1 to be absorbed, and a pile driving step of confirming the bearing force after the steel pipe pile is driven to the minimum pile length, continuously driving the steel pipe pile until a bearing force equal to or higher than the pile reaction force can be confirmed, and removing the excess part 31 of the steel pipe pile, if any, when the bearing force equal to or higher than the pile reaction force is confirmed before the overall length of the steel pipe pile is driven. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for constructing a foundation structure for constructing a foundation structure of a structure such as a building with steel pipe piles.

  Conventionally, when a pile such as a steel pipe pile is placed, a construction management method is known in which measurement is performed and the supporting force of the pile is confirmed (see Patent Documents 1 and 2).

  For example, in the pile driving construction management system disclosed in Patent Document 1, the deformation and wave near the pile head due to pile driving are measured, the support force of the pile is estimated in real time, and the hammer driving force is based on the result. Is controlled so that excessive stress is not generated in the pile.

Patent Document 2 discloses a dynamic pile support capacity estimation method for estimating a support capacity of a pile by measuring a resistance at the time of hitting when placing a steel pipe pile with a diesel hammer. .
Japanese Patent No. 3173719 JP-A-5-25826

  However, the conventional pile construction management method described above uses a method for estimating the bearing capacity of a pile that can be carried out more easily than the static loading test, and whether or not the bearing capacity of the pile to be built has reached the design bearing capacity. I have only confirmed that.

  For this reason, there is a risk that the pile length will be insufficient if the pile is continuously driven without confirming the design support capacity, or if a uniform long pile is prepared to prevent the pile length shortage, the waste of removing most of the pile may occur. There is.

  In addition, the pile disclosed in the above-mentioned literature is not a structure calculation as a composite foundation of a direct foundation part and a pile foundation part. It is only a construction management method for checking whether or not the power is satisfied.

  Therefore, an object of the present invention is to provide a foundation structure construction method capable of efficiently constructing a highly reliable foundation structure.

  In order to achieve the above object, the foundation construction method according to the present invention is a construction method of a foundation structure of a structure including a direct foundation portion on which a load of an upper structure is loaded and a pile foundation portion made of a steel pipe pile. Calculating the reaction force of the direct foundation, setting the installation position of the steel pipe pile in plan view, and setting the control area shared by the steel pipe pile at each pile position from the set pile position. The pile reaction force calculation step of calculating the pile reaction force borne by each pile position excluding the reaction force borne by the direct base from the load acting on the dominant area, and the pile reaction force calculation step was calculated. While calculating the combination of the pile diameter and the minimum pile length that has an estimated bearing capacity equal to or greater than the pile reaction force, it is possible to absorb the estimation error of the estimated bearing capacity, and to strike the steel pipe pile with a pile length longer than the minimum pile length. Pile selection process to select piles so that it can be installed The steel pipe pile selected in the pile selection step is penetrated into the ground, the support force is confirmed after penetrating to the minimum pile length, and the steel pipe pile is penetrated until a support force greater than the pile reaction force can be confirmed. And a pile driving step of removing the steel pipe pile when there is a surplus of the steel pipe pile when a supporting force equal to or greater than the pile reaction force is confirmed.

  Here, it is preferable that the minimum pile length is set to such a length that the estimated settlement amount is not more than an allowable value.

  In the construction method of the foundation structure of the present invention configured as described above, steel pipe piles that can be easily added, cut and removed at the site are used, and each pile is taken into account after considering the reaction force directly borne by the foundation. The pile reaction force at the position is calculated, and the combination of the minimum pile diameter and the pile length that satisfies the pile reaction force is calculated. And, if an estimation error occurs in the estimated bearing capacity due to the difference in physical properties of the local ground from the estimation, a steel pipe pile that can be adjusted to such a length that the length of the steel pipe pile will not be insufficient is rational. Select to use for construction. Also, at the time of construction, the support capacity of the steel pipe pile actually placed is confirmed, and the penetration of the steel pipe pile is continued until the required support capacity is reached.

  For this reason, the reliable foundation structure provided with the steel pipe pile from which the actual bearing capacity was confirmed can be constructed. Moreover, since the steel pipe pile of a reasonable length that can absorb the estimation error of the estimated bearing force is prepared and constructed, the length of the steel pipe pile does not become insufficient on the way. Further, when the necessary supporting force is satisfied, the placement is finished, and if there is an excess, the projecting steel pipe pile can be easily removed by cutting, so that the foundation structure can be constructed efficiently.

  Moreover, if the minimum pile length is set to such a length that the estimated settlement is less than the allowable value, a foundation structure having a predetermined settlement or less can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  First, with reference to FIG. 2, the structure of the structure provided with the foundation structure constructed | assembled by the construction method of the foundation structure of this Embodiment is demonstrated.

  In this structure, the upper structure is a building 1 such as a detached house, and is in contact with the ground 4 via a direct foundation 2 formed by a reinforced concrete floor slab or the like.

  And the ground reaction force 4a which the lower surface of this direct foundation part 2 receives from the ground 4 becomes the reaction force which the foundation part 2 bears directly. In addition, when the surface layer is improved by the reason that the ground 4 is soft and the ground strength is low, the reaction force directly received by the lower surface of the foundation part 2 from the improvement of the surface layer is the reaction force directly borne by the foundation part 2 It becomes.

  This ground reaction force 4a is calculated based on various parameters obtained from the ground investigation such as the N value of the ground 4, the internal friction angle, the adhesive force, and the uniaxial compressive strength. For example, the spring value of the ground 4 is set from one or more values of various parameters, and the ground reaction force 4a is calculated directly from the displacement of the lower surface of the base portion 2 and its spring value.

  On the other hand, when surface ground improvement is performed, parameters based on the improvement effect such as strength after improvement by surface ground improvement are set, and the increased reaction force is calculated using the set parameters.

  Further, below the direct foundation portion 2, a pile foundation portion 30 including a plurality of steel pipe piles 3 is provided. Here, the head of the pile foundation 30 is directly joined to the foundation 2 and constructed as an integral foundation structure.

  The steel pipe piles 3,... Calculate the pile reaction force required after setting which position of the building 1 to be placed in plan view. That is, which steel pipe pile 3 bears the load which acts from the building 1 which is a superstructure changes with the positions and number of placing the steel pipe piles 3.

  Here, the lower surface of the foundation portion 2 is directly divided into areas where the steel pipe piles 3,... Share the load, and the divided area is referred to as a control area of the steel pipe piles 3,. And the pile reaction force which each pile position bears is calculated by deducting the reaction force according to the control area which the base part 2 bears directly from the load which acts on this domination area.

  On the other hand, the loading load 1a-1c of the building 1 varies depending on the position of the building 1 as shown in FIG. 2 and the reaction force directly borne by the foundation 2 is uniform regardless of the position. The pile reaction force borne by the steel pipe piles 3,... Obtained by subtracting the reaction force of the foundation portion 2 directly from the load 1a-1c will differ depending on the position, and the pile length will be different if the pile diameter is the same. Become.

  Here, the steel pipe pile 3 of this Embodiment is the sum of the front-end support force 3a which is the reaction force of the ground 4 with respect to a pile front-end surface, and the peripheral friction force 3b based on adhesion with the surrounding surface of a pile and the ground 4. Is the reaction force borne by the pile, that is, the support force of the pile, and it is not always necessary to penetrate the tip of the pile into the hard support ground 41.

  Further, since the tip support force 3a is a product of the bottom area and the reaction force of the ground 4, it is proportional to the pile diameter, and the peripheral friction force 3b is a product of the pile peripheral area and the adhesion force of the ground 4, so the pile diameter And proportional to pile length. For this reason, steel pipe piles 3 with the same peripheral frictional force 3b include large pile diameters and short pile lengths, small pile diameters and long pile lengths, and intermediate pile diameters and pile lengths. There will be multiple types.

  Moreover, when surface processing, such as a groove | channel and an unevenness | corrugation, is given to the surrounding surface of the steel pipe pile 3, since the adhesive force with the ground 4 can be estimated highly compared with the case where there is no processing, surface processing of the pile surrounding surface The combination of pile diameter and pile length varies depending on the presence or absence and type of processing.

  Next, the flow of the basic structure construction method of the present embodiment will be described.

  FIG. 1 is a flowchart showing the flow of the foundation construction method.

  First, the building 1 as an upper structure is designed (step S1). Here, when the building 1 is composed of building units, the data of the load table created in advance can be used, so that the design can be simplified. Then, after determining the outer shape, floor plan, arrangement position, etc. of the building 1 in the design of the building, the structural calculation of the superstructure and the calculation of the upper load 1a-1c are performed (step S2).

  Further, in parallel with or separately from the design of the building, a ground survey is performed on the ground 4 for constructing the pile foundation portion 30 (step S3).

  This ground survey can be conducted by standard penetration tests or Swedish sounding tests. For example, various parameters such as an internal friction angle, adhesive force, and uniaxial compressive strength are calculated by an N value obtained in a standard penetration test or a loading test on a collected sample. Also, various parameters can be calculated by obtaining a converted N value from the measured value of the Swedish sounding test.

  FIG. 7A is a diagram showing a relationship between the N value obtained in the Swedish sounding test and the long-term allowable stress qa calculated from the uniaxial compressive strength of the flat plate loading test. The points plotted in a distributed manner are measured values, and the solid line is a general design estimated line RD that is generally used as an estimated value that can be used for design.

  However, as can be seen from the measured values plotted in FIG. 7 (a), some actual grounds may be lower than or higher than the strength of the general design estimation line RD. Therefore, an estimated value that envelopes these measured values at the upper limit is defined as an upper limit estimated line R1, and an estimated value that is enveloped at the lower limit is defined as a lower limit estimated line R2.

  In addition, this ground survey can also use the result of the ground survey conducted on the ground 4 in the past or the result of the ground survey conducted in the surrounding area.

  Further, from the ground survey result and the arrangement conditions of the building 1 set in the building design, the reaction force acting directly on the lower surface of the foundation portion 2 that is a reaction force required for the entire building 1 is calculated ( Step S4).

  On the other hand, after the reaction force acting on the upper load 1a-1c and the lower surface of the foundation part 2 is calculated, the direct foundation part 2 on which the building 1 is placed is designed (step S5). In the design of the direct foundation 2, the strength and the amount of reinforcement used for the construction of the reinforced concrete slab are determined.

  And it is determined whether the load calculated by the design of the building 1 and the design of the direct foundation part 2 is less than the reaction force of the direct foundation part 2 calculated in step S4 (step S6).

  If the reaction force directly under the direct foundation part 2 is greater than the load calculated in steps S2 and S5, the calculation is terminated assuming that the direct foundation part 2 can sufficiently support the building 1. On the other hand, if the reaction force of the direct foundation portion 2 is below the upper load, the pile foundation is considered (step S7). In addition, when surface layer ground improvement is performed, the surface layer ground improvement is examined first, and the reaction force increased by the surface layer ground improvement is compared with the overlay load.

  If it is determined that the load condition cannot be satisfied with the direct foundation part 2 alone, the subsequent design is performed as a composite foundation (pile-raft foundation) of the direct foundation part 2 and the pile foundation part 30. .

  First, in order to calculate the pile reaction force, the pile position is set so that the pile is arranged directly in the base portion 2 in plan view. The load borne by one pile varies depending on the pile position and the number of piles arranged around the pile position.

  The pile reaction force required at each pile position is obtained by subtracting the reaction force corresponding to each control area of the foundation portion 2 directly from the load acting on each control area at each pile position.

  Thus, after calculating the required pile reaction force in each pile position, the preliminary | backup design of a pile is performed by step S8. In the preliminary design of this pile, a combination of the minimum pile length and the pile diameter necessary to satisfy the required pile reaction force and the pile length of the steel pipe pile 3 actually used for placing are selected.

  For example, when one pile diameter is determined in order to extract a pile type satisfying a certain pile reaction force, the tip support force 3a is calculated from the pile diameter, and the tip reaction force 3a is subtracted from the pile reaction force. This is a share of the surface friction force 3b. Since this peripheral surface friction force 3b is calculated by the product of the circumference calculated from the pile diameter, the pile length and the adhesion force of the ground 4, the adhesion force depends on the pile diameter and the presence or absence of surface treatment of the pile peripheral surface. Is determined, the minimum required minimum pile length L1 is automatically calculated.

  Moreover, when calculating the minimum pile length L1, the subsidence amount estimated when a load acts is also checked. In other words, even if it is a supporting force that satisfies the pile reaction force as the magnitude of the force, if the subsidence amount exceeds the allowable value, it may cause unacceptable ground subsidence or uneven subsidence. Is set as the minimum pile length L1.

  The minimum pile length L1 calculated in this way is the reaction force of the ground 4 when calculating the tip support force 3a and the adhesion force between the ground 4 and the pile peripheral surface (hereinafter simply referred to as “ground strength”). However, it is estimated from the results of the ground survey, and the actual bearing capacity PR obtained when the steel pipe pile 3 is actually placed and the minimum pile length L1 estimated from the ground survey results There is a possibility that the estimated support force P1 is different.

  That is, the length of the steel pipe pile 3 satisfying the required pile reaction force P differs depending on whether the ground strength is determined by the upper limit estimation line R1 or the lower limit estimation line R2 as shown in FIG. Come.

  FIG. 7B shows an estimated supporting force P1 obtained from the ground strength calculated based on the upper limit estimated line R1, and an estimated supporting force P2 obtained from the ground strength calculated based on the lower limit estimated line R2. And the general design bearing capacity PD obtained from the ground strength calculated based on the general design estimation line RD.

  And if the length of the steel pipe pile 3 which satisfy | fills the required pile reaction force P is calculated | required from the estimated support force P1, the minimum pile length L1 will be calculated, and if it calculates | requires from the estimated support force P2, the longest pile length L2 will be calculated.

  That is, when the length of the steel pipe pile 3 is calculated from the general design bearing capacity PD, it becomes the general design pile length LD, but if the actual ground strength is larger than the ground strength estimated by the general design estimation line RD, the minimum pile length L1 is reached. There is a possibility that the steel pipe pile 3 can be shortened, and if the actual ground strength is small, the steel pipe pile 3 may become long up to the longest pile length L2.

  Therefore, a steel pipe pile 3 having a minimum pile length L1 as a minimum pile length and an additional steel pipe that can secure the longest pile length L2 by adding it are prepared, and the required pile reaction force P is satisfied at the minimum pile length L1. If not, the steel pipe can be extended. Moreover, the steel pipe pile 3 of the longest pile length L2 is prepared in advance, and when it is confirmed that the necessary pile reaction force P is satisfied, the surplus portion can be cut and removed.

  Thus, the steel pipe pile 3 required for construction can be rationally selected by calculating the minimum pile length L1 and the longest pile length L2.

  Furthermore, when selecting the steel pipe pile 3 used for placing, check its stress, and if the generated stress is not less than the allowable value, increase the thickness, increase the pile diameter, Make adjustments such as increasing the pile length.

  And the steel pipe pile 3 of the longest pile length L2 calculated by this preliminary design is prepared, for example, and the pile foundation part 30 is constructed.

  First, as shown in FIG. 4, a pile that penetrates the steel pipe pile 3 into the local ground 4 is placed until the minimum pile length L1 is reached (step S9).

  At this time, the penetration of the steel pipe pile 3 is temporarily interrupted, and the support capacity of the pile piled up is confirmed (step S10). Here, the confirmation of the actual bearing capacity PR of the pile is performed based on the measured value measured by the load cell when the load cell is installed on the weight that strikes the pile head of the steel pipe pile 3, for example. Can do.

  The graph shown on the right side of FIG. 4 shows the actual bearing force PR measured when the steel pipe pile 3 is penetrated to the minimum pile length L1. Here, the actual support force PR does not reach the required pile reaction force P, and the determination in step S11 is “insufficient support force”, which requires further driving of the steel pipe pile 3 (step S12). ).

  In this way, if the actual bearing force PR is not confirmed until the minimum pile length L1 is reached, the work is not interrupted and the steel pipe pile 3 can be efficiently constructed. In addition, even if the actual support force PR exceeds the required pile reaction force in the first confirmation, there is no problem because the support force increases from the design and only becomes safer.

  Further, horizontal lines drawn at equal intervals on the ground 4 in the left side of FIG. 4 are driving unit lines H,... Indicating unit depths for driving the steel pipe piles 3. When it is determined in step S11 that the supporting force is insufficient, in step S12, the construction unit for one stage of the driving unit line H is driven, and in step S13, the actual supporting force PR of the pile is measured again.

  Driving of the steel pipe pile 3 for the construction unit (step S12) and confirmation of the actual support force PR (step S13) are repeated until it is confirmed in step S14 that the actual support force PR exceeds the required pile reaction force P. It is.

  Next, FIG. 5 is a diagram showing a state in which the actual support force PR has reached the required pile reaction force P. From this figure, it can be seen that the length of penetration of the steel pipe pile 3 was longer than the minimum pile length L1 but shorter than the longest pile length L2.

  On the other hand, the steel pipe pile 3 that has been driven in at a depth shallower than the longest pile length L2 is divided into a surplus portion 31 protruding from the ground 4 and a placement portion 32 embedded in the ground 4. If the surplus portion 31 is left as it is, it will directly hinder the construction of the foundation 2 and the construction of the building 1, and therefore, if the surplus portion 31 exists, it is removed (steps S15 and S16).

  FIG. 6 is a diagram for explaining an operation for removing the surplus portion 31. Since the steel pipe pile 3 can easily cut a desired portion with a burner or the like, the steel pipe pile 3 is cut at a position protruding from the ground 4 and an unnecessary portion is removed as a surplus portion 31.

  Next, the operation of the foundation structure construction method of the present embodiment will be described.

  In the construction method of the foundation structure of the present embodiment configured as described above, the steel pipe pile 3 that can be easily added, cut and removed at the site is used, and the reaction force directly borne by the foundation portion 2 is taken into consideration. Then, the pile reaction force at each pile position is calculated, and the combination of the minimum pile diameter and the minimum pile length L1 that satisfies the pile reaction force is calculated.

  Then, when an estimation error occurs in the estimated bearing force because the physical properties of the local ground 4 are different from the estimation, the steel pipe pile 3 having the longest pile length L2 so that the length of the steel pipe pile 3 is not short or The steel pipe pile 3 which is combined with the minimum pile length L1 and combined with the steel pipe is rationally selected and used for construction.

  Moreover, at the time of construction, the actual supporting force PR of the actually placed steel pipe pile 3 is confirmed, and the penetration of the steel pipe pile 3 is continued until the actual supporting force PR reaches the required pile reaction force P.

  For this reason, a highly reliable foundation structure provided with the steel pipe piles 3, ... in which the actual supporting force is confirmed can be constructed. Moreover, since the reasonable length steel pipe pile 3 which can absorb the estimation error of the estimated supporting force P1 is prepared and constructed, the length of the steel pipe pile 3 does not become insufficient on the way.

  Furthermore, when the necessary supporting force is satisfied, the placing is finished, and if there is an excess 31, it can be easily removed by cutting the protruding steel pipe pile 3, so that the foundation structure can be constructed efficiently. . That is, since the ratio of the placement extension during construction to the construction cost of the pile foundation 30 is large, if the construction of the pile can be completed halfway, the construction period can be shortened and the cost can be reduced.

  Moreover, if the minimum pile length L1 is set to a length at which the estimated settlement amount is equal to or less than an allowable value, a foundation structure having a predetermined settlement amount or less can be obtained.

  Although the best embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes that do not depart from the gist of the present invention are possible. Are included in the present invention.

  For example, in the above embodiment, the first actual bearing force PR was measured after reaching the minimum pile length L1, but this is not a limitation, and even if shallower than the minimum pile length L1, The bearing capacity of the pile can be confirmed.

  Moreover, although the said embodiment demonstrated the method of confirming the supporting force of the steel pipe pile 3 based on the measured value of the load cell attached to the weight which hits a pile, it is not limited to this, Other well-known The bearing capacity of the steel pipe pile 3 may be confirmed by a static loading test, a rapid loading test, a dynamic loading test, or the like.

  Furthermore, in the said embodiment, although the case where the steel pipe pile 3 of the longest pile length L2 was prepared and there was a surplus part was cut and removed, it was not limited to this, The minimum pile length L1 The construction method which prepares the steel pipe pile 3 and extends until the required pile reaction force P is satisfied may be used. Such a steel pipe pile 3 can be easily added by welding or the like.

It is a flowchart explaining the construction method of the foundation structure of the best embodiment of this invention. It is explanatory drawing explaining the structure of a foundation structure. It is explanatory drawing explaining the relationship between the pile length and support force which are determined by preliminary design. It is explanatory drawing explaining the relationship between the support force confirmed in the field during the placement of a steel pipe pile, and an estimated support force. It is explanatory drawing explaining the relationship between the supporting force of the steel pipe pile confirmed on the spot, and an estimated supporting force. It is explanatory drawing explaining the operation | work which removes the surplus part of a steel pipe pile. (A) is a diagram explaining the variation in ground strength from the relationship between the N value obtained in the Swedish sounding test and the long-term allowable stress qa based on the flat plate loading test, and (b) is calculated from each estimated value of ground strength. It is the figure which showed each supporting force.

Explanation of symbols

1 Building (superstructure)
1a-1c Overload 2 Direct foundation 30 Pile foundation 3 Steel pipe pile 31 Surplus 3a Tip support force 3b Surface friction force 4 Ground 4a Ground reaction force P Required pile reaction force P1 Estimated support force PR Actual support force L1 Minimum pile Long L2 longest pile length

Claims (2)

A method for constructing a foundation structure of a structure having a direct foundation part for loading a load of a superstructure and a pile foundation part made of a steel pipe pile,
Calculate the reaction force of the direct foundation, set the installation position in plan view of the steel pipe pile, set the control area shared by the steel pipe pile at each pile position from the set pile position, A pile reaction force calculation step for calculating a pile reaction force borne by each pile position by removing a reaction force borne by the foundation directly from a load acting on the control area;
While calculating the combination of the pile diameter and the minimum pile length which have the estimated support force more than the said pile reaction force calculated by the said pile reaction force calculation process, the said minimum pile which can absorb the estimation error of the estimated support force A pile selection process for selecting a pile so that a steel pipe pile having a longer pile length can be placed;
The steel pipe pile selected in the pile selection step is penetrated into the ground, the support force is confirmed after penetrating to the minimum pile length, and the steel pipe pile is penetrated until a support force greater than the pile reaction force can be confirmed. And a pile driving step for removing the steel pipe pile when there is a surplus of the steel pipe pile when a supporting force equal to or greater than the pile reaction force is confirmed. Method.   The method for constructing a foundation structure according to claim 1, wherein the minimum pile length is set to a length at which an estimated settlement amount is equal to or less than an allowable value.

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