JP4066196B2 - Construction method of foundation using calcareous ground as support layer - Google Patents

Description

  The present invention relates to a construction method for a construction structure foundation using a calcareous ground as a support layer.

  In the tropical and subtropical regions on the earth, calcareous ground is widely distributed along the coastline. In Japan, there is a representative calcareous ground called Ryukyu limestone layer composed of coral reef deposits.

  When constructing a foundation structure in the construction field, the foundation layer that supports the foundation is naturally required to have a supporting force capable of resisting all external loads including the overload of the foundation.

  Here, the calcareous ground is characterized by the fact that the soil particles themselves are relatively easy to disintegrate, but the ground is strong, and has a hollow portion and a weak portion of various sizes in the ground. Because it has a very complicated formation state that the consolidated part and the unconsolidated part form a mutual layer, the dispersion of ground strength is large, and it is considered inappropriate to evaluate as a support layer until now, It is also difficult to calculate the support capacity.

  In the case where such calcareous ground exists, according to the conventional method, the ground that provides stable strength existing in the lower layer position of the calcareous ground is used as the base layer and has been used as the supporting ground for the foundation.

  At present, it is difficult to use the calcareous ground as the supporting layer, and in Japan, the foundation structure will be designed using the lower mudstone layer as the supporting ground, but the layer thickness of the calcareous ground is 20-50m. Because it is very large, the mudstone layer support design has the problem that the physical scale of the foundation structure is enlarged, which causes an excessive cost burden during construction, and is also implemented on the facility side as the depth increases This leads to restrictions on construction.

  In this way, because it is difficult to evaluate the ground as a ground that transmits supporting force due to special properties, there are few examples of supporting the foundation with calcareous ground at present, and in the sense of ensuring the reliability of the foundation However, the amount of construction has become large, accompanied by an overall improvement of the ground.

  On the other hand, if the depth of the foundation structure can be suppressed up to the middle layer of the calcareous ground, the construction scale, construction period and construction cost can be significantly reduced, and it will lead to effective use of the limited land. Bring effect.

  As described above, the present inventor is proceeding with numerical analysis for the characteristics and calculation method of bearing capacity for calcareous ground containing the cavity, or verification of ground constants that are one of the ground evaluation conditions. Has reached the view that foundation construction is possible (for example, Non-Patent Documents 1 to 4).

Masatoshi Ouchi et al., “About the basic form with the Ryukyu limestone layer as a supporting layer”, 15th Okinawa Geotechnical Research Presentation Summary, 2002, pp. 51-54 Masatoshi Ouchi et al., “Numerical analysis of bearing capacity considering variation in N value”, 16th Okinawa Geotechnical Research Presentation Summary, 2003, pp. 23-26 Ouchi Masatoshi et al., “Numerical analysis of bearing capacity of foundation with Ryukyu limestone layer as support layer”, 15th Okinawa Geotechnical Research Presentation, 2002, pages 55-58 Ouchi Masatoshi et al., “On the bearing capacity characteristics of the belt foundation on the ground with a cavity”, 16th Okinawa Geotechnical Research Presentation Summary, 2003, pp. 19-22

  In order to solve such a problem, the present invention searches for an internal state of calcareous ground to be constructed by a physical exploration method before foundation construction, and if necessary, an injection material having a strength equivalent to the surrounding ground in a cavity in the calcareous ground. The main purpose is to provide a construction method for supporting the foundation structure on the calcareous ground by efficiently combining the filling of the soil. It is another object of the present invention to provide a construction method for selecting and supporting the foundation structure on the calcareous ground.

  In order to achieve the above object, the present invention is configured as follows.

In the foundation construction method using the calcareous ground of the first invention as a support layer,
It is a construction method for foundations using calcareous ground as a support layer,
Before foundation construction , insert the electrodes that will be the transmitting and receiving points in the borehole and explore the geological condition of the construction ground by the physical exploration method,
Identify the calcareous ground that can support the foundation after investigating the internal condition of the ground and the dispersion or deviation of the ground strength,
The foundation to be built in the specified calcareous ground is a rigid foundation consisting of a caisson foundation constructed by a pneumatic caisson method,
In addition, the geological condition of the caisson sedimentation ground by the physical exploration method from the transmission / reception point of the electrode below the caisson and the transmission / reception point of the electrode installed in the excavation ground inserted in the boring hole installed in advance from the caisson work room Exploration and construction of cavities and weak parts scattered in the construction ground, and the filling work of the injection material into the cavity or weak parts that require filling of the hollow part or weak part by design It is characterized by doing.

In the second invention,
In the construction method of the foundation using the calcareous ground of the first invention as a support layer,
The geophysical survey method, characterized seismic method, Electrical Prospecting, by any one or more combinations of the underground radar method or Jiotomogura Fi to improve the precision and accuracy of the survey.

In the third invention,
In constructing the foundation construction method using the calcareous ground of the first or second invention as a support layer,
(1) Preliminary design of foundation based on field survey, (2) Examination using calcareous ground as support layer, examination of foundation structure and selection of foundation structure, (3) Details of foundation based on results of geophysical exploration Design, (4) verify the superiority of each detail designed foundation structure, (5) determine the foundation structure and foundation method,
The foundation is constructed after the foundation design including the selection of the foundation method is performed according to the series of steps (1) to (5) above.

According to the present invention, the following effects can be obtained.
(A) When constructing a foundation with a calcareous ground as a support layer, it is possible to confirm the dispersion or deviation of ground strength by exploring the internal state of the ground by physical exploration methods before foundation construction. The result will be the identification of calcareous ground that can support the foundation, enabling safe and reliable construction, and filling the cavity or weak part scattered in the calcareous ground from the ground with the strength equivalent to the surrounding ground. Thus, the foundation can be supported on the calcareous ground which forms a homogeneous ground with high strength and uses the homogeneous ground as a supporting ground, so that an absolute stable base layer can be secured.
(B) In the case of calcareous ground in the geological state with poor support capacity of the foundation, the foundation structure is a rigid foundation, so that stress propagation to the surrounding ground of the foundation is achieved, the internal stress level of the support ground is reduced, and By increasing the support strength of the support ground, the support force influence range for the foundation support ground can be expanded, so the support force influence range for the support ground is increased and stress propagation to the surrounding ground is also included. Because the internal stress level can be reduced, small-scale cavities or weak parts existing in the construction ground can be ignored in the design calculation, and the filling work of the cavities or weak parts can be omitted. This leads to labor saving in construction.
(C) Furthermore, by using the caisson foundation constructed by the pneumatic caisson method with the foundation structure as a rigid foundation, the geological condition of the caisson-sinked ground and surrounding ground by the geophysical exploration method and scattered in the construction ground The filling work of the injection material into the cavity or weak part can be performed from the caisson work room in the caisson setting process, so observation work can be performed according to the construction situation, and further safety and reliability are obtained. It becomes possible.
(D) methods in geophysical exploration performed prior basic construction is seismic method, Electrical Prospecting, by utilizing the underground radar method or Jiotomogura Fi, it is possible to carry out the foundation ground outside, in performing basic design Detailed data can be grasped, and moreover more detailed information can be obtained by evaluating the construction ground by combining multiple types of physical exploration methods as necessary, thereby improving the accuracy and accuracy of exploration. Since it can be obtained, it is possible to eliminate uncertainties in the design.
(E) Procedures of design method including selection of foundation construction method, (1) Preliminary design of foundation based on field survey, (2) Examination using calcareous ground as support layer, examination of foundation structure and selection of foundation structure (3) Perform detailed design of the foundation based on the results of geophysical exploration, (4) Verify the superiority of each of the detailed designed foundation structures, (5) Determine the foundation structure and foundation construction method, (1 ) To (5), the complicated basic design of the calcareous ground support can be easily clarified.
Due to the effects (A) to (E) described above, it is possible to bring about effective utilization of a limited land.
In addition, when constructing a rigid foundation using the pneumatic caisson method, it is possible to collect detailed data on the vicinity of the excavated ground surface (ground surface) even if the accuracy of geophysical exploration is reduced. In the investigation stage, high-detail exploration can be eliminated.

  Hereinafter, with regard to the implementation of the present invention, with the Ryukyu limestone layer as the calcareous ground, the case where the foundation structure is a pile foundation and a rigid foundation is taken as an example, and in the rigid foundation, an example of construction by the open-cut method and the pneumatic caisson method Based on the above, it will be described in detail with reference to the drawings.

As shown in FIG. 1, first, the Ryukyu limestone layers 2c and 2d are characterized by the fact that the soil particles themselves are relatively easy to collapse. This alone is expected to form a weak ground with a small N value. Actually, the ground has such a strong characteristic that it can contain many hollow portions 4 of various sizes, such as uniaxial compressive strength reaching 50 N / mm ² in the ground. Here, the cavity portion 4 includes a void portion such as a crack generated in the layer boundary and a weak portion that does not cause cavitation, and the representative of the places where the ground property changes rapidly in the ground 2 is referred to as the cavity portion. Will be described under the description of “cavity 4”. In the drawing, the Ryukyu limestone layers 2c and 2d will be described as being in a simple state. However, for example, it is impossible to distinguish between the Ryukyu limestone layer 2c and the Ryukyu limestone layer 2d. For example, there are cases where the Ryukyu limestone layer 2d is surrounded by the inside of the Ryukyu limestone layer 2c, and naturally there are cases where the ground is very complicated and chaotic.

  However, in the examples up to now, as shown in FIG. 1, the foundation structures 1 and 5 having the Ryukyu limestone layers 2c and 2d as the supporting ground are scarce, and the Ryukyu limestone layers 2c and 2d exist in the ground 2. In this case, there are only a few examples in which the foundation construction is performed by using the base layer, that is, the supporting layer, which is superior in the supporting capacity performance of the foundation including the Shimajiri mudstone layer 2e located in the lower layer.

  Another reason why the examples are scarce is that not only the properties of the Ryukyu limestone itself but also the ground 2 in the region where the Ryukyu limestone is likely to deposit often form a mutual layer, and the consolidated layer 2c of the calcareous ground and the unconsolidated The complicated overlapping of the layers 2d is also a large uncertainty factor in the calculation of the bearing capacity of the ground. Therefore, in order to remove these unclear factors and perform a safe design, conventionally, the calcareous grounds 2c and 2d are avoided. It was an inevitable idea to construct the foundation.

  Of course, the foundation structure that penetrates the Ryukyu limestone layers 2c and 2d and uses the Shimajiri mudstone layer 2e as the supporting layer is long and deep regardless of the type of structure such as the pile foundation 1 or the rigid foundation 5 Will lead to loss of economic efficiency.

  Of course, as the construction scale of the foundation increases, not only does it become difficult to secure the construction site with an increase in the number of various facilities, but also a corresponding increase in the construction period is required.

  As described above, the greatest reason for incorporating the pile foundation 1 while avoiding the Ryukyu limestone layers 2c and 2d is the presence of the cavity 4 in the ground 2, and the vicinity of the lower end of the pile after the foundation pile 1b is placed. This is because if the construction is completed without confirming the presence of the hollow portion 4, the support force is greatly affected, and the pile foundation 1 main body is concerned about a very dangerous state in which the design support force cannot be exhibited.

  That is, this is a case where all or part of the cavity 4 is present in the range of the pressure bulb 3 that indicates the bearing force influence range acting on the pile foundation 1. This is because such a foundation pile 1b cannot be included in the calculation as a structural element of the pile foundation 1 because the force needs to be evaluated as zero.

  In addition, as shown in FIG. 2, one of the management methods used when constructing the pile foundation 1 is “stop management” of the foundation pile 1b, but the supporting force such as the N value of the ground 2 is used as a management standard. When the foundation pile 1b is laid, the presence of the cavity 4 where the supporting force is zero, the pressure bulb 3 does not contact the cavity 4, and it is necessary to have a depth and position that satisfies the design. Therefore, the phenomenon that the pile length of the foundation pile 1b has to be much longer than the design depth also occurs, and the pile length of each foundation pile 1b (depth at the lower end of the foundation pile 1b) is extremely large. There is a big problem that the construction plan developed from the design stage cannot actually be reflected, such as being forced to be irregular, and it is necessary to raise the capital not only for the construction amount but also for the economy.

  Therefore, the embodiment of the present invention is divided into the case of the pile foundation 1 structure shown in FIG. 3 and the case of the rigid foundation 5 structure shown in FIG. The construction method of the foundation that is safe and reliable will be described. Of course, the foundation structure may be other than this.

  First, the ground survey stage and the design stage starting from the site reconnaissance will be explained as the stage before foundation construction.

  First, in order to consider the foundation construction using the Ryukyu limestone layers 2c and 2d as the foundation layer, it is essential to grasp the geological condition in the construction ground 2 including the cavity 4 in detail and with accuracy. In the invention, it is necessary to efficiently use the geophysical exploration method to obtain information on the ground condition before the foundation design and construction, and to enable the exploration of the ground as necessary in the foundation construction process. To do.

  Here, the types of geophysical exploration methods include seismic exploration method, electrical exploration method, underground radar method, gravity exploration method, magnetic / radioactive exploration method, geotomography, or acoustic exploration method. By using the resistivity imaging method from among the exploration methods and the resistivity tomography method from the geotomography at the same time, all the exploration data for the same signal path with these multiple electrode arrangements with different sensitivity characteristics The method of increasing the amount of information necessary for analysis and taking the same exploration means for high-density electric exploration (hereinafter referred to as hybrid high-density electric exploration) is shown, but there are also parts that depend on the geology including the surroundings. Any of the above-described exploration methods may be adopted depending on the appropriateness of the target ground, and a combination of these two or more may be selected as appropriate in order to improve accuracy. It is. That is, if necessary conditions such as measurement accuracy are satisfied, for example, only Rayleigh wave exploration which is one of the seismic exploration methods from the ground surface 2a may be used.

  Specifically, as shown in FIG. 5, electrodes 7a and 7b, which are transmission / reception points, are installed in the ground surface 2a and a boring hole 6 for obtaining a minimum soil sample required in the preliminary stage. Then, a physical exploration is performed to measure the specific resistance distribution in the ground 2 over the transmission / reception path 7d of all the electrodes 7a, 7b. Of course, this is not the case if the ground 2e capable of supporting a stable foundation exists in a shallow depth region and it is determined in the preliminary survey stage such as boring data that detailed exploration is not required.

  In this illustration, the state of the electrodes 7a and 7b, the boring hole 6 and the transmission / reception path 7d is easy to understand, and an arbitrary one section is cut out and expressed, but the actual basic structures 1 and 5 are three-dimensional objects. As shown in FIG. 6, a plurality of exploration surfaces in a form surrounding the foundation structures 1 and 5 (not shown) planned by utilizing a plurality of boring holes 6 together with the electrodes 7 a installed on the ground surface 2 a. It is desirable to perform three-dimensional exploration and evaluation of measurement results with the (cut surface) 7e, and more specifically, the installation of the exploration surface 7e and the electrodes 7a and 7b serving as transmission and reception points can be increased according to the required accuracy. What is necessary is just to increase the actual number of measurement points by moving the electrodes 7a and 7b and then performing measurement again.

  After the analysis of the data obtained from the specific resistance value by the hybrid high-density electrical exploration method is completed, the evaluation using one exploration surface 7e as one two-dimensional information is finally processed and obtained as an image such as an image image. It becomes possible, and by grasping the three-dimensional coordinate value about the geological state of the foundation ground 2 including the cavity 4 scattered inside the ground 2 by comprehensively evaluating this by combining the necessary cross sections, It becomes possible to make a three-dimensional image.

  These exploration technologies and technologies applied to the Ryukyu limestone layers 2c and 2d have become possible with the recent advancement of high precision and high speed due to the development of analysis processing technology represented by computers. In the exploration technique, the state inside the ground 2 could not be confirmed with high accuracy.

  In this way, the analysis results of the hybrid high-density electric exploration method and the data based on preliminary surveys such as boring data and test digging results are used as design data in the basic design at the same time. In addition, it becomes possible to determine the optimum base layer for transmitting the supporting force from the ground 2 to the foundation structures 1 and 5, and to specify the depth and horizontal position of the foundation.

  However, because the location of the foundation structures 1 and 5, especially the horizontal position, cannot be designed freely because of the limited use of the national land, etc. It is necessary to impose from the design stage.

  Therefore, as shown in FIG. 7, the large and small cavities 4 mixed within the bearing force influence range of the ground 2 expressed by the pressure bulb 3 generated at the assumed position 10 of the foundation structures 1 and 5 based on the design. By performing the cavity filling 8 of the cavity 4a that affects the supporting force of the ground 2 in the ground from the ground, effective use of the land is achieved with the minimum necessary ground improvement, but the supporting force is not affected. If it is found from the analysis results of the geophysical exploration that the ground 2 is composed only of the cavities 4 of a scale, these cavities 4 can be left as they are, and are more suitable in terms of workability and economy. Ground conditions. For example, the small-diameter pressure bulb 3 generated in the substructure 1 or the hollow portion 4 in the large-diameter pressure bulb 3 generated in the substructure 5 or in the vicinity thereof, which can be ignored in design, can be left as it is. It becomes possible.

  In practice, however, the cavity 4a that has a relatively large scale impact on the support force is often searched, so that the drilling and injection machine 8a having the drilling hole and the injection rod 8b is used from the ground. For the cavity 4a based on the exploration result, the person 9 improves the cavity 4a to a state where the ground strength equivalent to that of the surrounding ground is ensured with a cement-based injection material or the like at a pinpoint to constitute a strong homogeneous ground. This is possible. At this time, it goes without saying that the filling amount of cement-based injection material and the amount of material used for cement-based injection material are minimized, and permanent grouting is also applied to voids and weak areas such as cracks. It is effective to use a chemical injection material as described above, and as a filling method for the weak portion, it is preferable to perform construction while appropriately selecting replacement filling or compaction filling. The same applies to the filling of the cement-based injection material described below.

  Here, the present invention is described by taking examples of typical pile foundations 1 and rigid foundations 5 as foundation structures, but the ground 2 includes many hollow portions 4 and 4a, and the calcareous ground 2c. , 2d itself has a complicated alternate layer state, and the foundation design has to be performed for the place that is the ground 2 with poor homogeneity, the rigid foundation 5 becomes more effective.

  This is because the pressure bulb 3 generated in the foundation structures 1 and 5 has a scale, and generally the diameter of the pressure bulb 3 does not depend on the foundation structure and is approximately 1.5 times the foundation width. .

  That is, in this example, the pressure bulb 3 generated in the rigid foundation 5 becomes a larger pressure bulb 3 as compared with the pressure bulb 3 generated in the pile foundation 1, and the support force transmission of the ground 2 is spread over a wider range. It is possible to cause the structure 5 to act, and to reduce the internal stress level of the supporting ground by propagation of stress to the surrounding ground, thereby increasing the supporting strength of the supporting ground. Here, when the pile foundation 1 takes the form of a group pile with respect to the bearing capacity characteristics acting on the pile foundation 1, it is possible to calculate the bearing capacity based on the virtual caisson foundation in consideration of the effect. However, under ground conditions such as the Ryukyu limestone layers 2c and 2d, the situation that the pile lengths are uneven as described in the paragraph 0027 is threatened, and the foundation pile 1b including the lower end of the foundation pile 1b It is necessary to expect the pressure bulb 3 on a scale based on the base width of the virtual caisson foundation. In this case, the search accuracy of the ground 2 is further improved, and the search range required for the design of the pile foundation 1 is set wider (not shown). ing).

  Even if the cavity 4 where the supporting force is zero exists in the pressure bulb 3, this phenomenon is that the supporting force of the ground 2 acting on the foundation structures 1, 5 is the cavity 4 with respect to the pressure bulb 3. This is because the small-sized cavity 4 can be ignored because it is related to the volume ratio.

  In other words, when designing with a pile foundation 1 structure, it is conceivable that even a very small cavity 4 may affect the bearing capacity. It is necessary to carry out in detail centering on the position of the lower end of the pile 1b. Conversely, when designing with the rigid foundation 5 structure, it is necessary to investigate by enlarging the range even if the accuracy of the physical exploration 7 is lowered.

  Next, paying attention to the observation construction at the time of the foundation construction of the present invention, the invention carried out at the foundation construction stage will be described.

  As mentioned above, the rigid foundation 5 is advantageous depending on the conditions of the ground 2, but the caisson foundation by the pneumatic caisson method that does not require a deadline is effective in consideration of both construction and cost, especially when the groundwater level is high It is.

  As shown in FIG. 8, the presence of the caisson working chamber 11a, which is the greatest feature of the pneumatic caisson method, is very effective for the non-homogeneous ground 2 in the caisson 11 setting or flooring stage. The operator 9 in the caisson working room 11a uses a transmission / reception point of the electrode 7b below the caisson 11 inserted into the boring hole 6 installed in the investigation stage in the caisson 11 setting stage, and uses a portable measuring instrument (electrode) 7a. It is possible to carry out observation construction that implements hybrid high-density electrical exploration as necessary, with the transmission / reception point of the ground surface (excavated ground) as necessary.

  As a result, it is possible to grasp the internal state of the excavated ground thereafter, and to collect detailed data about the vicinity of the excavated ground surface (the ground surface 2a), in addition to visual confirmation of the local ground. As a result, there are cases where high-detail exploration can be dispensed with in the survey stage.

  The same applies to the caisson 11 flooring stage, and it is of course effective in observing the state of the most important caisson landing ground. Of course, Rayleigh waves are not necessary for hybrid high-density electric exploration. Since the used physical exploration may be performed from the excavated ground surface (the ground surface 2a), the exploration method may be appropriately selected according to the required measurement accuracy.

  Thus, based on the exploration results performed from the caisson working chamber 11a, as shown in FIG. 9, it becomes possible to carry out the work for the supplementary cavity filling 8, which is very reliable, In addition, the foundation construction can be performed on the complicated and special ground 2 by a very safe method.

  Furthermore, the advantage of the caisson foundation 5b employing the pneumatic caisson method is that, as shown in FIG. 10, it is necessary to pay special attention to the existence of the ground 2 having special properties in which the cavity 4 is scattered when the caisson foundation 5b is constructed. For the hollow portion 4b circumscribing the caisson, the buried concrete work in the normal construction (after caisson 11 flooring, the concrete placing pipe 12a and the concrete placing pump 12b are buried in the caisson working chamber 11a. And filling the cavity 4b by contact grouting (filling the contact grout 13 from the inlet installed in the side wall of the caisson 11 to the ground loosening portion 14 by the grout pipe 13a and the grout pump 13b). It is said that the work is completed halfway automatically It is, this is intended to act effectively as a labor-saving measures for safety and the safety of the foundation construction.

  On the other hand, as shown in FIG. 11, in the case where the design is possible with the foundation structure of the pile foundation 1 type, in the placing stage of the foundation pile 1b by the pile driving machine 15, the bore hole 6 installed in the investigation stage is provided. Using the transmission / reception point of the electrode 7b below the foundation pile 1b to be inserted, the electrode 7c serving as an underground transmission / reception point is installed on the foundation pile 1b to be placed, or the function of the electrode 7c is provided on the foundation pile 1b itself. By mounting, it is possible to perform an observation construction in which hybrid high-density electric exploration is necessary and carried out in accordance with the placement depth of the foundation pile 1b.

  Of course, by using a management method based on the ground support force such as the N value of the ground 2 by general stop management, it is possible to perform construction management with higher accuracy and safety.

  Further, in the case where the structure of the rigid foundation 5 is adopted in the design, and the ground water level of the foundation ground 2 is low and the ground 2 is dug down by light construction, there is no concern about water discharge as shown in FIG. Thus, it is also possible to construct the foundation 5a directly by the open-cut method.

  In this case, it is typical that the steel pipe sheet pile 5d, the erection material 5e and the cutting beam 5f are used to perform a mountain stay, and a natural ground excavation is performed by an excavating machine such as the backhoe 16, but even with such a construction method, Hybrid high density using portable measuring instrument (electrode) 7a as the transmission / reception point of the ground surface (excavation ground) using the transmission / reception point of the electrode 7b directly below the foundation 5a inserted in the borehole 6 installed in the survey stage. The observation construction that carries out the electric exploration as needed becomes possible.

  As a result, it is possible to grasp the internal state of the excavated ground thereafter, and to collect detailed data about the vicinity of the excavated ground surface (the ground surface 2a), in addition to visual confirmation of the local ground. Therefore, the case where high-detail exploration can be made unnecessary at the survey stage is the same as the case where the above-described pneumatic caisson method is adopted.

  Similarly, the same can be said for the floor foundation excavation stage of the foundation 5a, which is effective in observing the state of the most important foundation landing ground.

  Furthermore, similarly, as shown in FIG. 13, it is possible to carry out a supplementary cavity filling 8 operation based on the results of exploration performed directly from the excavated ground surface (ground surface 2a) of the foundation 5a. The foundation construction can be performed in a very safe and very safe manner on the complicated and special ground 2.

  FIG. 14 shows a flowchart for designing the foundation structure represented by the pile foundation 1 and the rigid foundation 5 as described above using the calcareous ground 2c and 2d as the foundation layer.

  The design flowchart shown in FIG. 14 clarifies a series of design procedures from the investigation stage to the determination of the basic structure, detailed design, and risk countermeasures with uncertain elements. Hereinafter, description will be made in order from the [Start] terminal.

  First, [start] the foundation design, and in preparation for the ground to be the foundation construction work, including a field survey for surveying natural and artificial objects that obstruct the geological literature and the construction work, [Investigation] is conducted by boring and test digging to collect soil samples.

  Next, based on the results of the investigation, the preliminary bearing capacity of the foundation for the calcareous ground will be [preliminarily designed] and a design calculation document will be created and examined. As a result of this preliminary design, if it is determined that the calcareous ground does not have the ability to support the foundation at all, the foundation construction method by the conventional method will be adopted, resulting in the [Termination] terminal and even a slight possibility exists. If so, go to the next step.

  Furthermore, it is desirable to examine [applicability of calcareous ground support] for applicable foundation structures and evaluate the suitability of all types of foundations that satisfy the functions as foundations established in the preliminary design. .

  At this time, for each of the foundation structures selected above, the respective construction methods are included in the study, and the stability, reliability, site conditions in the construction, surrounding environment and necessary site are compared and examined. Inferring safety based on the degree of [effect] as an absolute condition. Here, the standard index is the conventional construction method, excluding the combination of the foundation structure and construction method that results in a significant increase in cost or the expectation of the effect compared to the conventional construction method, and again , Repeat the examination of [Applicability of support of calcareous ground] for the foundation structure and its construction method with different patterns (NG) to study the results to obtain the cost-effectiveness over the conventional construction method (Good) .

  Next, based on the results of detailed ground surveys such as adding boring data, collecting undisturbed samples, or conducting more detailed geophysical surveys, [Detailed Design] is performed. However, if the results here do not satisfy the various conditions in the foundation design, re-select a different foundation structure, consider [applicability of calcareous ground support], and also consider the construction method [cost-effectiveness] (NG), and various conditions such as the ground, foundation structure, construction method, environment, construction period and construction cost are combined to narrow down the foundation structure with more effective superiority (Good).

  From this, [determine] the foundation structure of the foundation using the calcareous ground as the support layer and the construction method of the foundation.

  In addition, as a response to unforeseen circumstances at the time of construction or to an unclear matter at the design level, the foundation construction should be conducted by ground investigation, filling with cement-based injection material in the cavity, or ground improvement. Consider the construction method of observation construction in synchronization as [risk countermeasures] in advance of foundation construction. Here, the process [construction method] that flows to [risk countermeasure] is positioned as an auxiliary means for the basic foundation construction method including observation construction.

  Finally, the design ends after returning to the [End] terminal, and the complex basic design of the calcareous ground support can be easily clarified by arranging the design procedure in this order.

  Based on the above explanation, when constructing a foundation with a calcareous ground as the foundation layer, the type and scale of the foundation structure and the design depth are determined by grasping the internal state of the construction ground from the physical exploration conducted before the foundation construction. In addition to using the technology to homogenize the cavities scattered in the calcareous ground, it is possible to observe and construct both the exploration and filling of the cavities, and the design method procedure is shown simply and clearly. It became possible to sublimate the foundation structure to a level where it was possible to build the calcareous ground that was difficult to obtain as a layer.

  In the case of carrying out the present invention, it may be applied to a rigid foundation, an elastic foundation, a foundation located in the middle thereof, and an independent or continuous foundation regardless of various types of foundations. If it is, it is applicable even if it is a container structure such as a basement without being limited to the foundation, and it is within the scope of the present invention to appropriately change the design shown in the embodiment and implement it. .

It is sectional drawing of the pile foundation which shows the general conventional construction method in case the ground which can support a foundation is used as a foundation layer (support layer). It is sectional drawing of the pile foundation which shows the general conventional construction method in the case of using calcareous ground as a base layer (support layer). It is sectional drawing of embodiment which shows the pile foundation structure in the case of using the calcareous ground by this invention as a foundation layer (support layer). It is sectional drawing of embodiment which shows the rigid basic structure in the case of making the calcareous ground by this invention into a base layer (support layer). It is sectional drawing of the physical exploration method which shows the combination exploration method with the resistivity imaging method in the electrical exploration method which abbreviate | omitted illustration of a part of ground condition, and the resistivity tomography method in geotomography. It is the permeation | transmission perspective view which showed the physical exploration result obtained by the exploration method in FIG. 5 in one exploration surface inside the ground. It is sectional drawing which shows the filling operation | work of the cavity part which affects the supporting force of the ground in the stage before foundation construction which abbreviate | omitted illustration of some ground conditions. It is sectional drawing of observation construction which shows the physical exploration state in the caisson foundation caisson sedimentation or caisson flooring stage by the pneumatic caisson method. It is sectional drawing of observation construction which shows the filling work of the cavity part which affects the bearing capacity of the ground in the caisson foundation or caisson flooring stage of a caisson foundation by a pneumatic caisson method. It is sectional drawing which shows the filling operation | work of the cavity part circumscribed to the caisson by the filling concrete work or the contact grout work in the caisson flooring stage of the caisson foundation by the pneumatic caisson method. It is sectional drawing of the observation construction which shows the physical exploration situation in the foundation pile placement stage of a pile foundation. It is sectional drawing of the observation construction which shows the physical exploration state in the foundation ground excavation of the rigid foundation by the open-cut method or the ground excavation completion stage. It is sectional drawing of the observation construction which shows the filling work of the cavity part which influences the bearing capacity of the ground in the foundation ground excavation of a rigid foundation by the open-cut method or the ground excavation completion stage. It is a design flowchart of the foundation which uses a calcareous ground as a base layer (support layer).

Explanation of symbols

1 Pile foundation (foundation structure)
1a footing 1b foundation pile 2 ground 2a ground surface 2b surface layer 2c calcareous ground (consolidated Ryukyu limestone layer)
2d calcareous ground (unconsolidated Ryukyu limestone layer)
2e Ground that can support the foundation (Shimojiri mudstone layer)
3 Pressure bulb 4 Cavity (including void or weak part)
4a Cavity 4b that affects the bearing capacity of the ground 4b Cavity 5 that circumscribes the caisson 5 Rigid foundation (foundation)
5a Foundation structure (direct foundation)
5b Foundation structure (Caisson foundation)
5c Virtual line 5d showing assumed position of rigid foundation 5d Steel pipe sheet pile 5e Raised material 5f Cut beam material 6 Boring hole 7 Geophysical exploration 7a Electrode (ground transmission / reception point) or portable measuring instrument 7b Electrode (transmission / reception point in hole)
7c Electrode (transmission / reception point in the ground)
7d Transmission / reception path 7e Exploration surface 8 Cavity filling 8a Drilling and injection machine 8b Drilling and injection rod 9 Worker 10 Virtual line 11 showing design scale and position of foundation based on results of physical exploration 11 Caisson 11a Caisson working room 12 Filling Concrete 12a Concrete placing pipe 12b Concrete placing pump 13 Contact grout 13a Grout pipe 13b Grout pump 14 Ground loosening part 15 Pile driver 16 Backhoe

Claims (3)

It is a construction method for foundations using calcareous ground as a support layer,
Before foundation construction , insert the electrodes that will be the transmitting and receiving points in the borehole and explore the geological condition of the construction ground by the physical exploration method,
Identify the calcareous ground that can support the foundation after investigating the internal condition of the ground and the dispersion or deviation of the ground strength,
The foundation to be built in the specified calcareous ground is a rigid foundation consisting of a caisson foundation constructed by a pneumatic caisson method,
In addition, the geological condition of the caisson sedimentation ground by the physical exploration method from the transmission / reception point of the electrode below the caisson and the transmission / reception point of the electrode installed in the excavation ground inserted in the boring hole installed in advance from the caisson work room And survey of filling work of injection material into the cavity or weak part that needs to be filled in the cavity or weak part by design. A foundation construction method using a calcareous ground as a support layer. The geophysical survey method, seismic methods, Electrical Prospecting, according to claim 1, characterized in that to improve the precision and accuracy of the search by any one or more combinations of the underground radar method or Geotomography Construction method for foundations using calcareous ground as a support layer. In constructing a foundation construction method using the calcareous ground according to claim 1 or 2 as a support layer,
(1) Preliminary design of foundation based on field survey, (2) Examination using calcareous ground as support layer, examination of foundation structure and selection of foundation structure, (3) Details of foundation based on results of geophysical exploration Design, (4) verify the superiority of each detail designed foundation structure, (5) determine the foundation structure and foundation method,
A foundation construction method using a calcareous ground as a support layer, wherein the foundation is constructed after foundation design including foundation construction method selection according to the series of steps (1) to (5) above.

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