JP7499093B2 - Liquefaction resistance evaluation method - Google Patents

Description

The present invention relates to a method for evaluating the liquefaction resistance of ground containing garbage.

Traditionally, reclaimed land on the bay coast is loosely deposited and is known to have a high probability of liquefaction during an earthquake. For this reason, it is important to thoroughly consider the possibility of liquefaction and its effects when designing buildings (see, for example, Patent Document 1). On the other hand, there are also reclaimed land areas where waste is buried without being incinerated, and there is no established method for evaluating the liquefaction resistance of such waste-mixed ground.

Figure 6 shows a schematic diagram of the effect of garbage in the ground on liquefaction strength. As shown in Figure 6(a), in ground without garbage, soil particles are loosely piled below the groundwater level, and as water pressure increases due to earthquake force, the soil particles separate, leading to liquefaction. On the other hand, in ground containing garbage, as shown in Figure 6(b), the garbage mixed in the soil exerts a binding effect on the soil particles, acting like fiber reinforcement and preventing liquefaction. In other words, by accurately assessing the effect of garbage in the ground, it is possible to increase the liquefaction strength and reduce costs by making it possible to reduce the diameter of piles erected in the ground.

JP 2011-79951 A

The Geotechnical Society has prescribed a method for directly investigating the liquefaction strength of on-site ground, in which soil samples are taken, specimens are prepared, and cyclic triaxial tests are performed. However, this liquefaction strength test is based on the premise that the soil itself is the subject, and no test method is provided for soil that contains foreign matter. For this reason, current designs rely on a simplified judgment in which a grain size analysis is performed after removing the debris, and the FL value (safety factor against liquefaction) is calculated based on the Building Foundation Design Guidelines. However, this method ignores the effect of debris mixed in the ground, and cannot be said to accurately evaluate the impact of liquefaction.

The present invention has been made in consideration of the above, and aims to provide a method for evaluating the liquefaction strength of ground that is suitable for evaluating the liquefaction strength of ground that contains garbage.

In order to solve the above problems and achieve the objectives, the liquefaction strength evaluation method of the present invention is a method for evaluating the liquefaction strength of garbage-mixed ground, and is characterized by having the steps of collecting soil samples from the ground to be evaluated, sifting the collected soil samples to prepare soil specimens that do not contain garbage of a predetermined size or larger, and garbage-mixed specimens that contain garbage, conducting liquefaction tests on each specimen, and evaluating the liquefaction strength of the ground to be evaluated based on the results of the liquefaction tests.

Another method for evaluating liquefaction strength according to the present invention is characterized in that, in the above-mentioned invention, a soil sample that passed through a 40 mm sieve is used to prepare a test specimen containing rubbish, and a soil sample that passed through a 9.5 mm sieve is used to prepare a test specimen of soil alone.

In addition, another liquefaction strength evaluation method according to the present invention is characterized in that, in the above-mentioned invention, the liquefaction strength of the target ground is evaluated as the liquefaction strength of the garbage-mixed specimen, the average value of the liquefaction strengths of the garbage-mixed specimen and the soil specimen, or the ratio of the liquefaction strengths of the garbage-mixed specimen and the soil specimen corrected by the liquefaction resistance ratio.

The liquefaction strength evaluation method according to the present invention is a method for evaluating the liquefaction strength of garbage-mixed ground, and includes the steps of collecting soil samples from the ground to be evaluated, sifting the collected soil samples to prepare soil specimens that do not contain garbage of a predetermined size or larger, and garbage-mixed specimens that contain garbage, conducting liquefaction tests on each specimen, and evaluating the liquefaction strength of the ground to be evaluated based on the results of the liquefaction tests, thereby achieving the effect of being able to evaluate the liquefaction strength of garbage-mixed ground.

In addition, according to another method for evaluating liquefaction strength according to the present invention, a soil sample that passed through a 40 mm sieve is used to create a test specimen containing rubbish, and a soil sample that passed through a 9.5 mm sieve is used to create a test specimen of soil alone, which has the effect of allowing appropriate liquefaction tests to be performed on each test specimen.

In addition, according to another method of evaluating liquefaction strength of the present invention, the liquefaction strength of the test specimen containing garbage, the average value of the liquefaction strengths of the test specimen containing garbage and the test specimen containing only soil, or the ratio of the liquefaction strengths of the test specimen containing garbage and the test specimen containing only soil corrected by the liquefaction resistance ratio is evaluated as the liquefaction strength of the ground to be evaluated, which has the effect of making it possible to evaluate the liquefaction strength taking into account the garbage contamination status of the ground to be evaluated, etc.

FIG. 1 is a diagram showing an embodiment of a method for evaluating liquefaction resistance according to the present invention. Figure 2 is a photograph of the sieving process, where (1) is the 40 mm sieve, (2) is the residue after the 40 mm sieve, (3) is the portion that passed the 40 mm sieve (already dried), (4) is the 9.5 mm sieve, and (5) is the portion that passed the 9.5 mm sieve. Figure 3 shows photographs of the test specimens; (1) is a soil specimen, and (2) is a specimen containing rubbish. FIG. 4 is a schematic diagram of a cyclic triaxial testing device, (1) being a small device and (2) being a large device. FIG. 5 is a diagram showing a liquefaction strength curve. FIG. 6 is a diagram showing the effect of garbage in the ground on liquefaction strength.

Below, an embodiment of the method for evaluating liquefaction strength according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment.

As shown in FIG. 1, the method for evaluating liquefaction resistance according to an embodiment of the present invention is a method for evaluating the liquefaction resistance of garbage-mixed ground. In this method, first, an in-situ density measurement is performed on the garbage-mixed ground to be evaluated as an index for creating a test specimen (step S1).

Next, a ground sample is collected from the garbage-mixed ground (steps S21 and S22).
The process of sampling is shown in Figure 2 (1) to (5). First, the excavated soil is sieved through a 40 mm sieve using a sieving machine to remove excess debris (Figure 2 (1) to (3)). The sample that passes through the 40 mm sieve is used to prepare a test specimen containing debris (Figure 2 (2)). Next, the sample that passes through the 40 mm sieve is sieved manually through a 9.5 mm sieve (Figure 2 (4)). The sample that passes through the 9.5 mm sieve is used to prepare a soil specimen (Figure 2 (5)).

Next, two types of specimens are prepared: a soil specimen and a soil-mixed specimen (steps S22 and S32).
The specifications of the specimen and the required soil volume are shown below.

a. Soil specimen: Collected samples were sieved through a 9.5 mm sieve.
- Test piece dimensions: diameter φ5cm, height h10cm
Number of specimens: 4 specimens for 1 sample + 1 spare specimen = 5 specimens. Amount of soil required: 2.5 x 2.5 x 10 x π = 200 cc/body, 200 x 5 = 1000 cc = 1 liter x 2 = about 2 liters.

b. Test specimens containing debris: Remove any debris larger than 40 mm from the collected sample.
・Test piece dimensions: diameter φ30cm, height h60cm
Number of specimens: 4 specimens for 1 sample + 1 spare specimen = 5 specimens. Required soil volume: 15 x 15 x 60 x π = 42411 cc/body = 43 liters/body, 43 x 5 = 215 liters x 1.5 = 323 liters.

For the soil specimen, a small specimen with a diameter of 5 cm and a height of 10 cm is used, the same as for the liquefaction strength test specified by the Geotechnical Society. For the specimen containing garbage, a large specimen with a diameter of 30 cm and a height of 60 cm is used, since it is thought that a normal size specimen would not be able to perform a normal test due to the large dimensional ratio of the contaminants.
Examples of the test specimens prepared are shown in Figures 3 (1) and (2).

Next, a liquefaction test is carried out on each test specimen (steps S23, S33).
The liquefaction test is conducted based on the "Undrained Soil Cyclic Triaxial Test" (Geotechnical Society Standard JGS0541-2009). Four specimens are used per sample. The test equipment used is, for example, the stress-controlled cyclic triaxial test equipment shown in Figures 4 (1) and (2). For soil specimens, the small-scale cyclic triaxial test equipment shown in Figure 4 (1) is used, and for specimens containing rubbish, the large-scale cyclic triaxial test equipment shown in Figure 4 (2) is used.

An example of the test results is shown in Figure 5. In the example of the liquefaction strength curve in the figure, the liquefaction strength ratio at N = 15 repeated loadings is R _{L15 for soil alone, 0.21 for soil alone} , and R _{L15 for garbage mixed soil, 0.26 for garbage mixed soil} , confirming that the inclusion of garbage increases the liquefaction strength.

Next, the liquefaction strength of the garbage-mixed ground is evaluated based on the test results (step S4). The liquefaction strength of the garbage-mixed ground can be evaluated, for example, by any of the following methods 1 to 3. Note that the present invention is not limited to these methods, and any method that evaluates the liquefaction strength based on the test results may be used.

(Method 1)
R _{L15, a method of directly using dust mixed} in. In the example shown in Figure 5, the value is 0.26.

(Method 2)
Considering the possibility that garbage may not be uniformly mixed within the site being evaluated, this method uses the average value of R _{L15, soil alone} and R _{L15, garbage mixed in} . In the example shown in Figure 5, avg[0.21, 0.26] = 0.235.

(Method 3)
This is a method for correcting the liquefaction resistance ratio R = τ _L /σ _z ' calculated by the simplified judgment in the Guidelines for Designing Foundation Structures, based on liquefaction tests. The correction formula is shown in Equation (1).

R' = (R _{L15, garbage mixed} / R _{L15, soil only} ) · R ... (1)
Here, R' is the corrected liquefaction resistance ratio for the garbage-mixed ground, and R is the liquefaction resistance ratio calculated from the corrected N-value Na based on the architectural foundation structure design guidelines.

In the example shown in Figure 5, R' = [0.26/0.21] R = 1.24R, resulting in a 1.24-fold increase in liquefaction strength.

According to this embodiment, the liquefaction strength of garbage-mixed ground can be evaluated based on the above method.

In order to verify the effects of this invention, a simplified liquefaction assessment method was used to assess liquefaction before conducting liquefaction tests on actual garbage-mixed ground. It was found that liquefaction occurred over an area of 10 m or more above the ground surface even with level 1 earthquake motion, and that the piles needed to be reinforced. When the liquefaction strength of this ground was evaluated using this embodiment, it was found that liquefaction would hardly occur with level 1 earthquake motion, and that the costs of reinforcing the piles could be reduced. In this way, by applying this embodiment to assess the liquefaction strength of garbage-mixed ground, the costs of erecting piles can be reduced.

As explained above, the liquefaction strength evaluation method of the present invention is a method for evaluating the liquefaction strength of garbage-mixed ground, and includes the steps of collecting soil samples from the ground to be evaluated, sifting the collected soil samples to create soil specimens that do not contain garbage larger than a predetermined size, and garbage-mixed specimens that contain garbage, conducting liquefaction tests on each specimen, and evaluating the liquefaction strength of the ground to be evaluated based on the results of the liquefaction tests, thereby making it possible to evaluate the liquefaction strength of garbage-mixed ground.

In addition, according to another method for evaluating liquefaction strength according to the present invention, a soil sample that passed through a 40 mm sieve is used to create a test specimen containing rubbish, and a soil sample that passed through a 9.5 mm sieve is used to create a test specimen of soil alone, so that a liquefaction test can be appropriately performed on each test specimen.

In addition, according to another method of evaluating liquefaction strength according to the present invention, the liquefaction strength of the test specimen containing garbage, the average value of the liquefaction strengths of the test specimen containing garbage and the test specimen containing only soil, or the ratio of the liquefaction strengths of the test specimen containing garbage and the test specimen containing only soil corrected by the liquefaction resistance ratio is evaluated as the liquefaction strength of the ground to be evaluated, so that the liquefaction strength can be evaluated taking into account the amount of garbage mixed into the ground to be evaluated, etc.

As described above, the liquefaction strength evaluation method of the present invention is useful for considering ground liquefaction in building design, and is particularly suitable for evaluating the liquefaction strength of ground containing garbage.

Claims (3)

A method for evaluating the liquefaction strength of garbage-containing ground, comprising:
A method for evaluating liquefaction strength comprising the steps of: collecting soil samples from the ground to be evaluated; sifting the collected soil samples to prepare soil specimens that are simply soil and do not contain debris larger than a predetermined size; and soil-mixed specimens that contain debris; conducting cyclic undrained triaxial tests on the soil for each specimen; and evaluating the liquefaction strength of the ground to be evaluated based on the liquefaction strength curve obtained by the tests. The method for evaluating liquefaction strength described in claim 1, characterized in that soil samples that passed through a 40 mm sieve are used to prepare a test specimen containing garbage, and soil samples that passed through a 9.5 mm sieve are used to prepare a test specimen of soil alone. The method for evaluating liquefaction strength according to claim 1 or 2, characterized in that the liquefaction strength of the ground to be evaluated is evaluated based on the liquefaction strength ratio of the garbage-mixed test specimen obtained by the test, the average value of the liquefaction strength ratios of the garbage-mixed test specimen and the soil test specimen, or the liquefaction resistance ratio calculated from the corrected N value based on the architectural foundation structure design guidelines and corrected by the ratio of the liquefaction strength ratios of the garbage-mixed test specimen and the soil test specimen.

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