JPS6329047B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rational method and apparatus for measuring air permeability, water permeability, pore water pressure, spring water amount, etc. underground. For example, when implementing construction methods such as caissons or pressure shields in civil engineering work, the geology, water head, pore water pressure, and spring water volume of the excavated area are detected in advance, and the hydraulic conductivity coefficient is determined in order to implement various construction methods. Alternatively, it is important to determine the air permeability coefficient and set safe and reasonable construction conditions. Conventional methods for this purpose include, for example, inserting a test pipe vertically into the ground, pumping up the water stagnant in the pipe in a certain container, and lowering the water level in the pipe to a certain height, from which it takes a unit time to recover. The current water level was measured and the permeability coefficient was determined from this, but this was not always efficient and it was difficult to ensure the accuracy of the measurement results. Therefore, the inventor of the present invention made the water filled in the pipe inserted into the ground descend using pressure pressure, and after the descending speed or the water descended to a certain height below the natural water level, the pressure was released and the pipe We attempted to conduct various tests depending on the level and speed of recovery in the area.
In this case, there may be some inconveniences depending on the conditions of the location where the civil engineering work is being carried out, for example, in geological formations with low permeability, accurate measurements may not be possible unless a thin pipe is used. This led to the development of a geological testing method and equipment that can be applied to any location. The specific content of the present invention will be explained below based on an illustrated embodiment. In Fig. 1, 9 is a bore hole excavated to about 40 cm above the depth of the stratum to be tested, and 13 is a pipe. A porous point 11 and a cone 12 are attached to the tip, which are lowered to the bottom of the borehole 9 and then vertically driven to a depth of about 40 cm to set the porous point. In this case, the porous point portion is made of a special porous material, and a special cover is applied to the portion in advance to prevent it from being adversely affected by muddy water. Note that 10 indicates muddy water. Furthermore, a thin tube 14 is disposed coaxially inside the pipe 13, and its lower end communicates with the porous point 11 described above. Reference numeral 7 denotes a head that is airtightly connected to the upper end of the thin tube 14; however, when connecting airtightly to the upper end of the pipe 13, another head 7 corresponding to its diameter shall be prepared; things and tubules 1
Two types of pipes 13 and 14 are prepared, and the pipe 13 or the thin tube 14 can be freely switched to enclose the upper end part in an airtight manner. Furthermore, the head 7 is connected to an air pipe _P1 , which is fed under pressure from the compressor 1, to one side thereof, and an exhaust pipe _P2 , which is connected to the other side thereof. The compressor 1 described above may be replaced with a gas cylinder if necessary. 2 is a regulator valve, 3 is a pressure gauge, 4 is a flow meter, 5 is a water level gauge, 6 is a permeability gauge, and 8 is an exhaust valve. To explain an example in which the coefficient of permeability in the ground is to be determined in the above-mentioned state, first, the pipe 13 is sufficiently filled with water, and then the head 7 shown in FIG. After replacing the exhaust valve 8 with a new one, close the exhaust valve 8, open the regulator valve 2, and start the compressor 1 to generate a pressure of about half of the predicted pore water pressure. When water is supplied into the head 7, the water in the pipe 13 is forced into the ground by pressure, so that the water level gradually falls. Therefore, the falling status of this water level can be measured for each unit time, for example, 0, 30 seconds, 1 minute, 2 minutes, 3 minutes, 5 minutes, 7 minutes, etc.
Measurements are taken every 10 minutes, and every 5 minutes thereafter, and continuous measurements are taken until the water level reaches the equilibrium water level, which is the level at which the water level will no longer fall any further with the constant pressure mentioned above. Calculate the coefficients (hereinafter simply referred to as the first step). It is possible to set various construction conditions based on the lower cable permeability coefficient determined in this first step, but the problem with this step is the means for infiltrating the water in the pipe 13 into the ground. It is necessary to apply a constant pressure pressure, and the connections between the pipe 13, the head 7, and the air pipe _P1 must be kept completely airtight, and in order to maintain a constant pressure pressure, Various conditions must be met, such as the need to observe the pressure gauge 3, but it is difficult to ensure accuracy in field work. Therefore, the method of determining the final hydraulic conductivity obtained through the third step described below, which is corrected based on the descending hydraulic conductivity obtained in the first step described above, allows highly accurate measurement in practice. It is something that makes you familiar. That is, after passing through the first step, the pressure from the compressor 1 is further increased, and the water in the pipe 13 that has fallen to the equilibrium water level is transferred to the porous point 1.
1 (second step), and from that point, the exhaust valve 8 is opened to release the pressure inside the pipe 13, and the water level drops from the moment it becomes unpressurized (atmospheric pressure). The water recovers and begins to rise inside the pipe 13, so the rising water level per unit time is measured in the same manner as in the first step to determine the recovered hydraulic conductivity (third step). Then, the recovered hydraulic conductivity determined in the third step is determined by the descending hydraulic conductivity determined in the first step, or the descending hydraulic conductivity determined in the first step is determined by the recovered hydraulic conductivity determined in the third step. Accordingly, a method of correcting the coefficient by, for example, setting it at the midpoint between the coefficient differences between the two, and thereby obtaining the final hydraulic conductivity, makes it possible to measure the hydraulic conductivity with even higher precision. An example of applying the permeability coefficient determined by the above method to actual construction conditions is, for example, since the permeability coefficient and air permeability coefficient have the relationship shown in Table 1, it is converted to an air permeability coefficient and applied to the caisson. Alternatively, when carrying out a construction method such as a pressure air shield, it can be used to set conditions for supplying a necessary and sufficient amount of pressurized air to prevent spring water from entering the work room or the like from underground.

[Table] In the case of the above embodiment, the most common measurement was described in which the head 7 was connected to the upper end of the pipe 13 for relatively highly permeable strata, but especially for geological strata with low permeability. In this case, a capillary tube 14 which is extremely sensitive to the rise or fall of water is used, and a special head 7 is attached to the upper end of the capillary tube 14 (as shown in FIG. 1).
Measurement work shall be carried out in the same manner as when using 3. Furthermore, in the above embodiments, the case where the air permeability coefficient of the ground was particularly determined was explained, but it goes without saying that the scope of application of the present invention is not necessarily limited to this. As mentioned above, the present invention improves water permeability and air permeability underground by changing the water level in a pipe inserted underground.
Alternatively, when measuring the amount of spring water, the final hydraulic conductivity is obtained by mutually correcting the descending hydraulic conductivity and the recovery hydraulic conductivity, which makes it possible to obtain a highly accurate hydraulic conductivity. The pipe inserted into the pipe has a thin tube coaxially therein, and is equipped with a head that airtightly surrounds the upper end of the pipe so that it can be switched between the pipe and the thin tube alone, and a predetermined pressure is applied to the inside of the head. Therefore, when implementing various construction methods in civil engineering work, the geology, water head,
When measuring pore water pressure, spring water volume, etc., depending on the degree of permeability of the measurement location, for example, thick pipes should be used in normal locations with high permeability, and thin tubes should be used in locations with low permeability. This makes it possible to properly understand the rising or falling situation of water in the pipe and ensure accurate measurements.
Therefore, various inconveniences such as having to prepare a separate device depending on the measurement location can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view schematically showing a test device that is an embodiment of the present invention. 1... Compressor, 7... Head, 8... Exhaust valve, 9... Boring hole, 11... Porous point, 13... Pipe, 14... Thin tube.

Claims (1)

[Scope of Claims] 1. When measuring underground water permeability, air permeability, or spring water amount by changes in water level in a pipe inserted underground, the pipe is filled with water and then heated under a predetermined pressure. The first step is to measure the falling water level per unit time to determine the descending hydraulic conductivity, and the second step is to increase the pressure after the first step and completely drain the residual water in the pipe into the ground. After the completion of the second step, the pressure inside the pipe is released and the recovered hydraulic conductivity is calculated based on the change in the recovered water level per unit time. Third
A geological testing method characterized in that the final hydraulic conductivity is obtained by mutually correcting the recovered hydraulic conductivity obtained through the process. 2. For measuring underground water permeability, air permeability, or amount of spring water by changes in water level within a pipe inserted underground, a pipe inserted underground and a thin tube installed coaxially within the pipe. A geological testing device comprising: a head capable of airtightly enclosing the upper end of the head, which can be switched to either the pipe or the thin tube; and means capable of supplying a predetermined pressure into the head.