Abstract:
A penetration-type pipe strain gauge easily transportable and easily installable in various places at low cost in a short period of time to measure strain produced in a shallow layer of the ground. Strain gauges are attached to the outer peripheral surface of an inner pipe, and a pipe strain gauge body is formed by integrally incorporating the inner pipe in an outer pipe. A boring screw is provided at the forward end of the pipe strain gauge body. A rotary tool mounting part for mounting a tool for rotating the pipe strain gauge body is formed at the rear end of the strain gauge body. The pipe strain gauge body is buried in the shallow layer of the ground by using the rotary tool.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to an art of detecting a ground strain caused by a land slide on a slope or caused by a collapse of subsurface ground or mudflow after a heavy rain by means of strain gauges mounted inside the body of a penetrated tubular strainmeter in the ground and evaluating the ground strains by a measuring instrument on the ground, and more particularly, to a penetration-type tubular strainmeter for detecting a ground strain developed in a shallow ground layer. 
       BACKGROUND ART 
       [0002]    A conventional tubular strainmeter is disclosed in, for example, the patent document 1 cited below. The conventional tubular strainmeter is laid deeply in the ground of a hazardous area, as shown in  FIG. 11 , to detect and measure strains developed in tubes by means of internal strain gauges installed in the tubes, and to confirm the position of a landslide and to assess the landslide. 
         [0003]    The conventional tubular strainmeter is installed as follows. First, an installation hole is pre-bored for the tubular strainmeter with a boring machine to a depth in the range from 20 to 30 m. Next, a strain gauge  5  is stuck on the outer peripheral surface of each steel tube ( 1   a ,  1   b ,  1   c , . . . ). Each gauge is covered with a protective material. These steel tubes are connected together by fitting one end of a tube into another end of another tube using a joint tube  2  and fastening the joint tube  2  with a rivet  3 , thereby forming a measuring tube  1 , which is then inserted into the installation hole. Finally, cement milk is poured into the installation hole to fill the space in the hole and firmly fix the tube in the ground to improve the detection accuracy of the tubular strainmeter. 
         [0000]    Patent document 1: Japanese Utility Model Registration No. 2514095. 
       PROBLEMS TO BE SOLVED BY THE INVENTION 
       [0004]    Installation of a conventional tubular strainmeter requires a considerable amount of labor. First, it is not easy to carry the measurement tube  1 , since it consists of many steel tubes and has a length of more than 20 m. 
         [0005]    Second, installation of the strainmeter requires two separate works, one for pre-boring an installation hole that exceeds 20 m with a boring machine, and another for setting up a measurement tube  1  in the ground. In addition, each of the strain gauges  5  stuck on the steel tube must be covered with a protective material  6  to prevent it from being peeled off during installation when it comes into contact with the wall of the installation hole. Further, the measurement tube  1  must be assembled from many tubes. Additionally, injection of cement milk into the installation hole is necessary after the strainmeter is placed in the installation hole to improve the detection accuracy of the strainmeter. Thus, installation of a conventional tubular strainmeter requires tremendous amounts of time, labor, and cost preventing the strainmeter from easy installation. 
         [0006]    Conventional tubular strainmeters are buried deep in the ground to detect positions of landslides. It should be noted, however, that a ground strain develops in a shallow ground layer of a slope prior to the landslide, that is, there can be a premonitory phenomenon indicative of the landslide. Therefore, it is possible to make an assessment of time and degree of a possible landslide based on the premonitory ground strain detected in the shallow ground layer say, provided that it is accurately measured and evaluated. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the prior art problems as mentioned above, the present invention seeks to provide an improved penetration-type tubular strainmeter that can be easily carried to various sites by a person to measure a ground strain in a shallow ground layer and conveniently installed in the ground in a short period of time with much less work and cost. 
       Means for Solving the Problem 
       [0008]    To this end, there is provided in accordance with one aspect of the invention, a tubular strainmeter for measuring a ground strain by means of strain gauges mounted on a tubular member penetrated in the ground, the tubular strainmeter comprising: 
         [0009]    a body having a double-tube structure that includes an inner tube housed in an outer tube, the inner tube mounted, on the outer surface thereof, with a multiplicity of strain gauges; 
         [0010]    a drilling screw mounted on the leading end of the body of the strainmeter; and a tool mount provided at the rear end of the body for attaching thereto a tool for rotating the body. 
         [0011]    The tubular strainmeter has a total length shorter than the shoulder height of an average adult. 
       (Function) 
       [0012]    The tubular strainmeter has the following functions: (a) it can be compact in size and lightweight, since it has a total length shorter than the shoulder height of an average adult; (b) It can be installed in the ground without using a large-scale boring machine, since its total length is short. (c) The tubular strainmeter is self-equipped with a drilling screw at its leading end, and can be coupled at its rear end with a tool for rotating the tubular strainmeter, thereby boring an installation hole and installation of the strainmeter in the hole can be done simultaneously. (d) The strain gauges will not be peeled off by the ground during installation if they are not covered with protective materials, since they are attached to the inner tube of a double-tube system and covered with the outer tube. (e) There is no need of assembling many steel tubes to form the tubular strainmeter, since the tubular strainmeter has a compact size. (f) The soil removed radially outwardly by the drilling screw during penetration of the strainmeter will be pushed back radially inwardly by the ground pressure to fill the gap between the tubular strainmeter and the ground. 
         [0013]    The drilling screw is firmly fixed in the ground after the strainmeter is penetrated. Thus, the tubular strainmeter is firmly fixed in a shallow ground layer without filling the installation hole with cement milk. 
         [0014]    In addition, the penetration-type tubular strainmeter may be provided at the rear end portion of the body with a multiplicity of radially extending pressure receiving plates that are spaced apart at equal circumferential intervals. 
       (Function) 
       [0015]    As the pressure receiving plates are penetrated in the ground, the rear end portion of the tubular strainmeter is firmly fixed in the ground. Moreover, the movement of nearby sediment results in an earth pressure acting on the fixed pressure receiving plates, which is properly coupled to the rear end portion of the strainmeter. 
         [0016]    In the penetration-type tubular strainmeter defined herein, the tips of the pressure receiving plates may be acutely angled. 
       (Function) 
       [0017]    Being acutely angled, the tips of the pressure receiving plates can cut into the ground, thereby facilitating burial of the whole pressure receiving plates in the ground. 
         [0018]    The penetration-type tubular strainmeter defined herein may be provided with an aforementioned rotating tool in the form of a portable electric rotating tool. 
       (Function) 
       [0019]    The portable electric rotating tool provides readiness and convenience to the penetration and installation of the tubular strainmeter. 
         [0020]    The results of the invention may be summarized as follows. 
         [0021]    Particularly, the invention provides a tubular strainmeter having the following features. 
         [0000]    (a) The tubular strainmeter is so compact and lightweight that it can be easily carried by a human to a desired installation site. (b) It can be installed in a short period of time with a reduced cost and labor, since its installation is easy, requiring only a little work. (c) The tubular strainmeter can accurately measure strain in a shallow ground layer, since it can be firmly fixed in the shallow ground layer. 
         [0022]    By providing the strainmeter with pressure receiving plates, strain in a shallow ground layer can be accurately detected. 
         [0023]    With the tips of the pressure receiving plates being sharply angled, the pressure receiving plates can be entirely penetrated in the ground easily by pushing them with a foot or by striking them with a hammer. 
         [0024]    The inventive tubular strainmeter is adapted to be installed with a portable electric tool mounted on the rear portion of the strainmeter, so that it can be quickly installed at various places (including slopes) where no electricity is available or no favorable staging ground is available. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Preferred embodiments (Embodiments 1 and 2) of the invention will now be described in detail by way of example with reference to  FIGS. 1 through 10 . 
           [0026]      FIG. 1  is an exploded perspective of a penetration-type tubular strainmeter in accordance with Embodiment 1. 
           [0027]      FIG. 2  is a partly cutaway perspective of the tubular strainmeter equipped with pressure receiving plates. 
           [0028]      FIG. 3  is a partial axial-cross section of the body of the tubular strainmeter, showing the internal structure of the strainmeter. 
           [0029]      FIG. 4(   a )-(b) are cross sections of the tubular strainmeter taken along line A-A′ of  FIG. 3 , when two strain gauges are circumferentially arranged ( FIG. 4(   a )) and when four strain gauges are circumferentially arranged ( FIG. 4(   b )). 
           [0030]      FIG. 5  is an enlarged perspective of the rear end portion of the tubular strainmeter. 
           [0031]      FIG. 6  is an axial cross section of a jig for mounting a rotating tool. 
           [0032]      FIG. 7  is an exploded perspective of an electric rotating tool to be mounted on the jig. 
           [0033]      FIG. 8  shows how the penetration-type tubular strainmeter is installed in the ground. More particularly,  FIG. 8(   a ) shows the tubular strainmeter before it is installed;  FIG. 8(   b ) shows a process of mounting pressure receiving plates on the body of the strainmeter; and  FIG. 8(   c ) shows the tubular strainmeter installed in the ground. 
           [0034]      FIG. 9  is an exploded perspective of a penetration-type tubular strainmeter in accordance with Embodiment 2. 
           [0035]      FIG. 10  is a perspective of a T-shaped manual rotating tool  21 . 
           [0036]      FIG. 11  is a front elevation of a conventional tubular strainmeter installed in the ground. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    As shown in  FIG. 8(   c ), a tubular strainmeter  10  in accordance with a first embodiment (Embodiment 1) is penetrated in the ground when in use. The tubular strainmeter  10  has a multiplicity of strain gauges  27 , which are stuck inside the body  11  of the tubular strainmeter and spaced apart at equal intervals in the axial direction of the tubular strainmeter. The strain gauges can detect a ground strain caused by, for example, a landslide, and output an electric signal indicative of the strain detected. The electric signal generated by the strain gauges  27  is sent to a measuring instrument  24  on the ground via a connecting cable  26  and read by the instrument  24 . 
         [0038]    Referring again to  FIGS. 1 through 5 , the structure of the tubular strainmeter  10  will be described in more detail. The strainmeter has a body  11 , a drilling screw  18  provided on the leading end of the strainmeter, and slits  13   b  formed in the rear end of the strainmeter for receiving a rotating tool. As shown in  FIG. 3 , the body  11  comprises a cylindrical inner tube  12  that is mounted, on the outer surface thereof, with a multiplicity of strain gauges  27  spaced apart at equal intervals in the axial direction (e.g. located at  4  axial positions), and is covered with a concentric outer tube  13 . The inner and outer tubes  12  and  13 , respectively, are integrally bonded to each other with a solidified epoxy resin  14  filling the gap between them. The slits  13   b  are formed in the rear end periphery of the opening  13   e  of the outer tube  13 , to thereby receive therein a rotating tool for rotating the whole tubular strainmeter  10 . 
         [0039]    Lead wires  28  connected to the respective strain gauges  27  enter the inner tube  12  via holes (not shown) formed in the inner tube  12  and extend therein to the female connector  15  fixed at the rear end of the inner tube  12 . The female connector  15  closes the rear opening of the inner tube  12 , and protrudes from the rear opening  13   e  of the outer tube  13 . 
         [0040]    In the example shown herein two strain gauges  27 , are stuck on the outer surface of the inner tube  12  to face each other across the inner tube  12  (i.e. spaced apart at equal circumferential intervals), as shown in  FIG. 4(   a ). In this case, the circumferential positions of the strain gauges  27  on the inner tube  12  may be identified by ticking off certain marks on the peripheral edge of the rear opening  13   e  of the outer tube  13 . Alternatively, in place of ticking off marks, circumferential positions of the strain gauges  27  may be aligned with the position of the slits  13   b.    
         [0041]    The tubular strainmeter  10  is installed in the ground such that the circumferential positions of the two strain gauges  27  (i.e. the line passing through the two strain gauges  27 ) are aligned with the gradient of the slope of the ground or the direction of an anticipated mudflow (from upstream to downstream). Arranged in this manner, the strain gauges  27  will be subjected to a maximum stress under a landslide and detect the strain with the highest accuracy. 
         [0042]    The tubular strainmeter is provided on the rear end of its body  11  (or on the rear end of the outer tube  13 ) with detachable pressure receiving plates  19 . In Embodiment 1, the pressure receiving plates  19  have planar pressure-receiving sections  19   a  that extend from a central cylindrical section  19   b  to opposite radial directions. Formed on the upper end of the cylindrical section  19   b  is an inner flange  19   c  to form a circular hole  19   d . The rear end portion  13   a  of the outer tube  13  constituting the body  11  of the tubular strainmeter is made thicker than the rest portions of the tube  13 . Formed on the outer circumferential surface of the leading end of the outer tube  13  are a male screw  13   c  and an annular step  13   d.    
         [0043]    Each of the pressure receiving plates  19  is configured such that the inner flange  19   c  can be seated on the step  13   d  of the outer tube  13  when the cylindrical section  19   b  is fitted on the rear end of the tubular strainmeter  10 . The inner flange  19   c  is firmly fixed between the step  13   d  and the front edge  17   b  of a cap  17  having a female thread when the cap  17  is threaded onto the male thread section  13   c  that projects from the circular hole  19   d . When the strainmeter is penetrated in the ground, an earth pressure caused by a ground movement will adequately act on the planar pressure-receiving sections  19   a , which pressure in turn acts as a stress on the rear end portion of the body  11  of the tubular strainmeter. It is noted that in order to maximize the load (pressure) applied to the planar pressure-receiving section  19   a , pressure receiving plates  19  are mounted on the body  11  in such a way that their planar surfaces, i.e. the pressure receiving sections  19   a , are perpendicular to the gradient of the slope, that is, perpendicular to the orientation of the strain gauges  27 , as shown in  FIGS. 4(   a ) and  8 ( b ). A male connector  25  at one end of the connecting cable  26 , connected at the other end thereof to the measuring instrument  24  ( FIG. 8(   c )), is connected to the female connector  15  projecting from the circular hole  17   a.    
         [0044]    It is noted that a tubular strainmeter  10  not equipped with pressure receiving plates  19  can still measure ground strain well, with a little lower detection accuracy in comparison with the one equipped with the pressure receiving plates  19 . 
         [0045]    Referring to  FIGS. 6 and 7 , the structure of a jig for connecting a rotating tool  20  with the strainmeter  10  will now be described.  FIG. 6  shows a cross section of a metal jig  30  for fixing an electric rotating tool  20  to the rear end of the tubular strainmeter  10 . The jig  30  is formed of a thick-cylindrical shaft  30   a  and a thin cylindrical shaft  30   e , coaxially connected to each other as shown. The thick shaft  30   a  has at the front end (lower end) thereof a cylindrical hole (or opening)  30   b  that can entirely encompass the female connector  15  at the rear end of the tubular strainmeter  10 . Formed at the front end of the thick shaft  30   a  are pawls  30   c  that can engage with slits  13   b  formed in the rear end of the tubular strainmeter  10 , and a step  30   d  to be secured between the rear flange section  17   c  of the cap  17  and the rear open end  13   e  ( FIG. 1 ) of the strainmeter  10 . The thin shaft  30   e  is grabbed by the chuck  20   a  of the rotating tool. The thin shaft  30   e  is provided on the outer surface thereof with three chamfers  30   f  spaced at equal circumferential intervals. 
         [0046]    The tool fixing jig  30  is placed from above on the female connector  15  formed at the rear end of the tubular strainmeter so as to engage the pawls  30   c  with the tool mounting slits  13   b . Then, the cap  17  is put on the thin shaft  30   e  and screwed to press, via the step  30   d , the jig  30  against the circumferential edge of the rear opening  13   e  of the strainmeter  10 . Finally, the chuck  20   a  of the electric rotating tool  20  is manipulated to grab the thin shaft  30   e  that extends from the circular hole  17   a.    
         [0047]    Next, referring to  FIG. 8 , a method of installing the penetration-type tubular strainmeter in the ground in accordance with Embodiment 1 will be described. When, for example, it is necessary to measure the ground strain in a slope where there can be a hazardous landslide, a tubular strainmeter  10  of the invention equipped on the rear end thereof with the electric rotating tool  20  is erected upright on the ground (with the drilling screw  18  placed on the ground), as shown in  FIG. 8(   a ). Then, the strainmeter is screwed into the ground by rotating the tool  20  until the step  13   d  of its thick rear end portion  13   a  comes to almost the same level as the ground surface, as shown in  FIG. 8(   b ). In installing the strainmeter  10  in the ground, the rotational position of the strainmeter is adjusted so that the circumferential positions of the strain gauges  27  (or the line passing through the strain gauges  27 ) is aligned with the gradient of the slope. 
         [0048]    Then, the electric rotating tool  20  is removed from the rear end portion of the tubular strainmeter  10 . The jig  30  is also removed by loosening the cap  17 . Subsequently, the cylindrical section  19   b  of the pressure receiving plates  19  is fitted from above on the male thread section  13   c  at the rear end of the strainmeter  10 , as shown in  FIG. 8(   b ), and then forced into the ground so as to penetrate the acute-angled tips of the planar pressure-receiving sections  19   a  in the ground by pounding or pushing the pressure receiving plates  19 . Then, the rotational positions of the pressure receiving plates  19  are adjusted so that the flat planes of planar pressure-receiving sections  19   a  become perpendicular to the gradient of the slope (or perpendicular to the line passing through the strain gauges  27 ). The pressure receiving plates  19  are securely fixed by screwing the cap  17 . 
         [0049]    Finally, the connecting cable  26  having the male connector  25  and extending from the measuring instrument  24  near the penetrated tubular strainmeter  10  in the ground is connected to the female connector  15  provided at the rear end of the strainmeter  10 , as shown in  FIG. 8(   c ), thereby enabling measurement of the ground strain by the measuring instrument  24 . 
         [0050]    It is noted that the total length L of the tubular strainmeter  10  (L being the length from the tip of the screw  18  to the female connector  15  at the rear end) is shorter than the shoulder height of an average adult to make it easy for a worker to carry the strainmeter  10 , mount the tool  20  on the rear end of the strainmeter, and penetrate the strainmeter  10  in the ground. For this reason, the total length L is preferably in the range from 60 centimeters (cm) to about 1 meter (m). Dimensions of the strainmeter may be conveniently chosen. For example, for a tubular strainmeter having a total length of about 1 m, a preferred length of the drilling screw is about 10 cm, a preferred diameter of the outer tube  13  (except for the thick rear end portion) is about 15 millimeters (mm). The width of the pressure receiving plates  19  (as measured in the diametrical direction of the tubular strainmeter) is about 15 cm, while their heights (as measured in the longitudinal direction of the tubular strainmeter) is about 10 cm. 
         [0051]    The inner tube  12 , outer tube  13 , and drilling screw  18  are preferably made of a metal such as a stainless steel having sufficient rigidity not to yield to the torque (as large as 140 Newtonmeters (Nm) or so when a 12-Volt electric drill or an electric driver is used) applied thereto by the electric rotating tool and undergo a plastic deformation when driving them into the ground. On the other hand, from the point of reducing the weight of the tubular strainmeter, use of appropriate plastics and/or resin materials such as high-strength polymers having sufficient rigidity deserves consideration. For example, the inner tube  12  may be made of an appropriate resin material while the outer tube  13  is made of a highly rigid and non-corrosive metal, thereby simultaneously achieving sufficient rigidity, non-corrosiveness, and a light weight of the tubular strainmeter. 
         [0052]    The thick rear portion  13   a  may be integrally formed with the outer tube  13 . Alternatively, it may be fabricated from a separate member having tool mounting slits  13   b  and then integrally welded to the rear end of the outer tube  13 . 
         [0053]    The drilling screw  18  may be fabricated from a solid rod and integrally jointed (by welding for example) to the open front end of the outer tube  13 . The leading end of the inner tube  12  is closed (by filling and solidifying an epoxy resin for example) before the drilling screw is jointed to the outer tube  13 . 
         [0054]    The pressure receiving plates  19  are preferably made of a material having sufficient rigidity and strength to withstand pushing and hammering during installation of the plates. The material is also preferred to have corrosive resistance because they are buried. A sufficiently rigid plastic material, such as a polymer material, may be also used. 
         [0055]    Four or more planar pressure-receiving sections  19   a  can be provided equally well on the cylindrical section  19   b  to extend therefrom radially outwardly, and spaced apart at equal circumferential intervals. By doing so, the rear end of the tubular strainmeter  10  is fixed more firmly in the ground. In addition, the accuracy of the measurement of the ground strain is improved due to the fact that the pressure receiving sections  19   a  can receive more fully the load of a ground strain if the planar surfaces of the pressure receiving sections  19   a  are not exactly perpendicular to the gradient of the slope. 
         [0056]    In the embodiments shown herein, there are four strain gauges  27  stuck at four different axial (or longitudinal) positions on the outer surface of the inner tube  12  (only two of them shown in  FIG. 3 ), though at least one strain gauge  27  needs be stuck in the axial direction. 
         [0057]    Although it is shown that two strain gauges  27  are stuck on the inner tube  12  and at two opposing circumferential positions in Embodiment 1 ( FIG. 4(   a )), four strain gauges may be stuck at four, equally spaced, circumferential positions of the inner tube  12 , as shown in  FIG. 4(   b ). In this case, if two facing strain gauges  27  are not aligned with the gradient of the slope, i.e. if the lines passing through two facing strain gauges are not aligned with the gradient, the ground strain can be accurately determined from the differential strains of two gauges  27  arranged across the inner tube  12 . Hence, orientations of the strain gauges  27  can be advantageously chosen rather arbitrarily at the time of installation. It would be understood that the number of the strain gauges  27  to be circumferentially stuck on the inner tube  12  at equal intervals can be increased to 6, 8, or more. Odd number of strain gauges  27  (e.g. 3 gauges) can be also arranged at equal intervals. 
         [0058]    Referring to  FIG. 9 , a further penetration-type tubular strainmeter  10 ′ in accordance with Embodiment 2 will now be described. The tubular strainmeter  10 ′ has a thick rear end portion  13 ′ a  of a length of L 1  and a male thread section  13 ′ c  of a length of L 2 , which are longer than the lengths of the corresponding portion and section of Embodiment 1 shown in  FIG. 1 . The cylindrical section  19 ′ b  of pressure receiving plates  19 ′ has an inner flange section  19 ′ c  that forms a round hole  19 ′ d . The inner flange section  19 ′ c  protrudes rearward from the bent portions  19 ′ e  by a length of L 3 . A cap  17 ′ has at least one tool insertion hole  17 ′ d  for receiving therein a rod-shaped tool. The cap  17 ′ has a length of L 4  slightly longer than the length of L 2  of the male thread section  13 ′ c.    
         [0059]    The tubular strainmeter  10 ′ is penetrated in the ground until the thick rear end portion  13 ′ a  is exposed in the air by a length equal to the protruding length L 3  of the cylindrical section  19 ′ b . As a consequence, the planar pressure-receiving sections  19 ′ a  are buried in the ground, but the inner flange  19 ′ c , supported by the step  13 ′ d , remains at the level of L 3  above the ground surface. Thus, the lower end of the female thread section is located at a level of L 3  above the ground, so that dirt is less likely to enter the female thread section. On the other hand, in installing the pressure receiving plates  19 ′, acutely angled tips of the respective planar pressure-receiving sections  19 ′ a  are inserted to a certain depth of the ground by striking or pushing the bent portion  19 ′ e  in the same manner as in Embodiment 1 until the rear end portion of the thread section  13 ′ c  protrudes from the circular hole  19 ′ d  sufficiently to allow the cap  17 ′ to be screwed on the thread section  13 ′ c . Then, a rod-like tool (e.g. a hexagonal wrench) is inserted in the tool insertion hole  17 ′ d  (configured to receive the hexagonal wrench for example) and levered to rotate the cap  17 ′. 
         [0060]    Since the front end  17 ′ b  of the cap  17 ′ pushes the inner flange section  19 ′ c  in response to the torque applied to the cap, the planar pressure-receiving sections  19 ′ a , partly exposed in the air, can be further penetrated in the ground by a length of L 2  equal to the length of the male thread section  13 ′ c . By forming a tool insertion hole  17 ′ d  in the cap  17 ′ in this way, the remaining exposed portions of the planar pressure-receiving sections  19 ′ a  can be easily penetrated in the ground by screwing the cap  17 ′ even when a large force is otherwise needed to penetrate the exposed portion. In place of the tool insertion hole  17 ′ d , the cap  17 ′ may be provided with a quadrangular or hexagonal outer surface to thereby rotate the cap  17 ′ with a spanner for example. 
         [0061]    In penetrating the tubular strainmeter, a T-shaped manual rotating tool  21  having a jig  30 ′ ( FIG. 10 ) may be used in place of the electric rotating tool  20 . 
         [0062]    As shown and described above, the penetration-type tubular strainmeter of the invention can be conveniently installed at various places in a simple manner at low cost. Thus, by installing the tubular strainmeters quickly in those places where hazardous landslides are anticipated, analyses and assessments of soil deformation phenomena from a precursory landslide to a ground collapse are made possible. Therefore, the invention is highly significant in this regard.