JP6656724B2 - Liquefaction determination method - Google Patents

Description

  The present invention relates to a liquefaction determination method capable of easily and accurately determining a safety factor for liquefaction of an investigation ground.

  Conventionally, as a method of determining liquefaction of the ground, a safety factor (FL) is obtained as a value obtained by dividing a liquefaction resistance ratio (RL) by an external force of an earthquake. A way to be taken.

That is, if the liquefaction resistance ratio (RL) can be determined, liquefaction determination can be performed. As a method of obtaining the liquefaction resistance ratio, the ground is sampled, a liquefaction test is performed on the sampled ground sample, and a method of obtaining the liquefaction resistance ratio, and N value, particle size and A method of obtaining the index from the plasticity index of the ground has been used.
However, such a liquefaction determination method requires a high survey cost, and for example, it is very difficult to use the method on a residential land.

  For this reason, a simple method for calculating the liquefaction resistance ratio so that it can be investigated at a low cost is to perform a Swedish sounding test (penetration test) and determine the liquefaction resistance ratio using the parameters obtained in this test. ing.

For example, Patent Literature 1 discloses a ratio of a dynamic shear strength ratio R, which is an index indicating the strength of the ground, and an earthquake shear stress ratio L, which is an index indicating the strength of a side on which liquefaction occurs in the ground. In the liquefaction determination method for determining the resistivity FL of the ground against liquefaction from R / L and determining the degree of risk of liquefaction based on the FL value, the method for calculating the dynamic shear strength ratio R The rotational torque T and the amount of penetration St of the penetrating rod are measured by a penetrating test in which the penetrating rod is rotationally penetrated into the ground while the load W applied to the penetrating rod having the penetrating body is changed stepwise, and based on these measured values, , Cp obtained by the following equation as an index indicating the hardness of the soil,
Cp = (D · nht / δSt) / (πT / WD)
Here, nht is the half rotation number of the penetrating rod, D is the maximum diameter of the penetrating rod, δE obtained as the energy accompanying the rotational penetration of the penetrating rod, and:
δE = πT · δnht + W · δSt
ΔT / δWD, which is the ratio of the increase amount of the load W to the increase amount of the rotation torque T, and δT / δSt, which is the ratio of the increase amount of the penetration amount St to the increase amount of the rotation torque T, are defined as test parameters. At least one of these test parameters is used as an explanatory variable, and the dynamic shear strength ratio R is estimated by a regression equation obtained by executing a multiple regression analysis with the objective variable being the dynamic shear strength ratio R. A liquefaction determination method, wherein a resistivity FL against liquefaction of ground is determined from a ratio R / L of a dynamic shear strength ratio R and the shear stress ratio L during earthquake. (Patent Document 1). In this patent document 1, the dynamic shear strength ratio R corresponds to the liquefaction resistance ratio (RL) according to the present invention, and the shear stress ratio during earthquake corresponds to the external force according to the present invention.

However, in such a liquefaction determination method, the number of parameters (constants) for obtaining the liquefaction resistance ratio increases, and the liquefaction determination cannot be performed easily.
In addition, since the liquefaction resistance ratio is obtained by combining many parameters, it is not possible to judge whether the error in the estimated ground discrimination, mechanical characteristics, and liquefaction characteristics is an effect of a constant or a variation in the ground itself. Liquefaction determination with accuracy could not be performed.

JP 2015-21355 A

  In view of the above-described conventional disadvantages, the present invention can obtain a high-precision liquefaction resistance ratio with a small number of constants without performing a boring survey, sampling, and the like, and can easily determine liquefaction. It is intended to provide a method for determining liquefaction.

In order to achieve the above object, the liquefaction determination method of the present invention is to drill a survey hole in the survey ground by rotating a drilling tool provided at the tip of a rod of a drilling machine, A drilling measurement step of measuring the load, torque and half-revolution applied to the drilling tool, and the load, torque and half-revolution applied to the drilling tool measured in the drilling measurement step and the effective earth covering of the survey ground seeking liquefaction resistance ratio from pressure, Ri Do from liquefaction determining step of determining the safety factor for the liquefaction, the liquefaction determining step, multiplied load torque and the half speed effective soil the absolute value of the value The liquefaction resistance ratio is calculated based on the value obtained by dividing by the overburden pressure, the liquefaction resistance ratio is divided by an external earthquake force, a safety factor is obtained, and liquefaction determination is performed .

As is clear from the above description, the following effects can be obtained in the present invention.
(1) According to the first aspect of the present invention, the liquefaction resistance ratio can be calculated from the load, torque, and half-rotation applied to the drilling tool, and the effective overburden pressure of the surveyed ground.
Therefore, the safety factor can be easily obtained.
(2) Since the safety factor can be obtained simply by performing a penetration test, liquefaction determination can be performed at low cost.
(3) The invention according to claim 2 can provide the same effects as the above (1) and (2), and can also specify the ground that is liable to be liquefied (the ground to be liquefied).

FIG. 1 to FIG. 5 are explanatory diagrams showing a first embodiment of the present invention.
FIG. 6 is an explanatory view showing a second embodiment of the present invention.
FIG. 4 is a process chart of the first embodiment. Explanatory drawing which shows a drilling measurement process. Explanatory drawing which shows the measurement result of a drilling measurement process, etc. FIG. 4 is a distribution diagram showing a determination result of a soil determination step. FIG. 4 is a distribution diagram illustrating a determination result of a liquefaction determination step. Process drawing of 2nd Embodiment.

  Hereinafter, the present invention will be described in detail with reference to the drawings for carrying out the present invention.

  In the first embodiment for carrying out the present invention shown in FIGS. 1 to 5, reference numeral 1 denotes a liquefaction determination method of the present invention.

  In this liquefaction determination method 1, as shown in FIG. 1, a drilling tool 6 (for example, a screw) provided at the tip of a rod 8 of a drilling machine 5 is rotated to drill a survey hole 7 in a survey ground. A drilling measurement step 2 for measuring the load, torque and half-rotation applied to the drilling tool 6 during drilling, and increasing and decreasing and half of the load and torque applied to the drilling tool measured in the drilling measurement step 2 Soil quality determination step 3 for determining the soil quality of the survey ground at a predetermined depth from the increase and decrease in the number of revolutions and the effective earth covering pressure of the research ground, and a formation determined to be liquefied by the soil determination step 3 In some cases, the liquefaction resistance ratio is calculated from the load applied to the drilling tool measured in the drilling measurement step 2, the torque and the half-revolution, and the effective overburden pressure of the surveyed ground. And a liquefaction determination step 4 for determining the safety factor.

  In the drilling measurement step 2, as shown in FIG. 2, a drilling hole 7 is drilled in the investigation ground using a drilling machine 5, and data at the time of drilling are measured. The screw (drilling tool) 6 provided at the tip of the rod 8 of the drilling machine 5 is penetrated into the survey ground while rotating, and the load W, torque T, half-rotational speed Nsw, and penetration time S at the time of penetration are measured. I do. In the present embodiment, as shown in FIG. 3, the measurement results penetrate 13.5 m from the ground surface, and the data was measured every 5 cm.

As the drilling machine 5 to be used, any drilling machine can be used as long as it can measure the load W, torque T, half-rotational speed Nsw, and penetration time S at the time of penetration. In the embodiment, a drilling machine for a Swedish sounding test is used.
The N values and the like in FIG. 3 are measured by sampling or the like for comparison.
The soil determination step 3 is a step of determining which soil layer is the liquefaction target soil layer from the data measured in the drilling measurement step 2.

First, the liquefaction target soil layer is a soil layer that is likely to be liquefied. In the fields of construction and civil engineering, a soil layer having a fine particle content FC of 65% or less is often referred to as a target soil layer. It has established.
The fine-grain content indicates the so-called cohesive soil content. When the fine-grain content is 65%, the cohesive soil content is 65%, and the sandy soil is 35%.
In the determination of the soil layer to be liquefied, conventionally, the soil layer was sampled, and the fine particle content FC was determined from an indoor particle size test.

In the soil determination step 3 of the present invention, a value obtained by multiplying the change in load and torque ΔT and the change in half-rotation speed ΔNsw, and dividing the absolute value of the value by the effective overburden pressure σv ′ (a value considering buoyancy). It is determined whether or not the liquefaction target soil layer. As can be seen from FIG. 2, when the screw is penetrated into the survey ground while rotating, the sandy soil is characterized by the fact that the torque and the half-revolution increase and decrease as the soil becomes sandy. Since the torque and the half rotation speed are affected by the constraint pressure, the influences are excluded by dividing the torque and the effective rotation by the effective earth covering pressure.
| W · △ T · △ Nsw | / σv '
FIG. 4 shows a distribution diagram comparing the value calculated by this calculation formula with the actually measured fine particle content FC. As can be seen from FIG. 4, if it exceeds 0.1, it can be confirmed that the fine particle content is less than 65%.
That is, if | W · △ T · △ Nsw | / σv ′> 0.1, it can be determined that the soil layer is a liquefaction target soil layer.

  The liquefaction determination step 4 calculates the liquefaction resistance ratio RL of the liquefaction strength of the soil layer determined to be the liquefaction target soil layer from the data measured in the drilling measurement step 2, and performs liquefaction. Make a decision.

  In the liquefaction determination step 4 of the present invention, the liquefaction resistance ratio is calculated by multiplying the load, the torque T and the half-rotation speed Nsw, and dividing the absolute value of the multiplied value by the effective overburden pressure σv ′ (a value considering buoyancy). RL is calculated, the liquefaction resistance ratio RL is divided by the external force of earthquake, a safety factor FL is obtained, and liquefaction determination is performed. This focuses on the fact that there is a good correlation between the N value and the torque, the half-rotation speed and the penetration time, as can be seen from FIG. Since the torque and the half rotation speed are affected by the constraint pressure, the influences are excluded by dividing the torque and the effective rotation by the effective earth covering pressure.

WT Nsw / σv '
FIG. 5 shows a distribution diagram comparing the value of each soil layer calculated by this calculation formula with the actually measured liquefaction resistance ratio RL of each soil layer. As can be seen from FIG. 5, there is a good correlation between the value calculated from the above formula and the liquefaction resistance ratio RL, and it is possible to estimate the liquefaction resistance ratio RL with high accuracy from the value obtained by the formula. is there.

  If the liquefaction resistance ratio RL can be estimated, the safety factor FL can be obtained by dividing this value by the external force. As described above, if the safety factor FL> 1.0, it can be evaluated that liquefaction does not occur.

[Different modes for carrying out the invention]
Next, a different embodiment for carrying out the present invention shown in FIG. 6 will be described. In the description of these different embodiments for carrying out the present invention, the same components as those in the first embodiment for carrying out the present invention will be denoted by the same reference numerals, and redundant description will be omitted.

  In the second embodiment for carrying out the present invention shown in FIG. 6, the main difference from the first embodiment for carrying out the present invention is that a liquefaction determination method 1A in which the soil determination step 3 is not performed. In this regard, in the liquefaction determination method 1A as well, when the liquefaction target soil layer is clear in advance or when liquefaction determination is performed on all soil layers, the liquefaction determination should be performed appropriately and with high accuracy. Can be.

  INDUSTRIAL APPLICABILITY The present invention is used in industries such as civil engineering and construction where liquefaction determination for designing and constructing structures is required.

1, 1A: liquefaction determination method, 2: drilling measurement step,
3: soil determination process 4: liquefaction determination process
5: drilling machine, 6: drilling tool,
7: hole for investigation, 8: rod.

Claims (2)

A drilling hole is drilled in the survey ground by rotating a drilling tool provided at the tip of a rod of a drilling machine, and a drilling hole, which measures the load, torque and half-rotation applied to the drilling tool during drilling. A liquefaction resistance ratio is determined from a measurement step, a load applied to the drilling tool measured in the drilling measurement step, a torque and a half rotation and an effective earth covering pressure of the surveyed ground, and a safety rate against liquefaction is determined. Ri Do from liquefaction determining step,
In the liquefaction determination step, the liquefaction resistance ratio is calculated by multiplying the load, the torque and the half-rotation speed, and the absolute value of the value is divided by the effective cover pressure, and the liquefaction resistance ratio is divided by the external force. A liquefaction determination method comprising: determining a safety factor; and performing liquefaction determination. A drilling hole is drilled in the survey ground by rotating a drilling tool provided at the tip of a rod of a drilling machine, and a drilling hole, which measures the load, torque and half-rotation applied to the drilling tool during drilling. The soil quality of the survey ground at a predetermined depth is determined from the measurement process, the load applied to the drilling tool measured in the drilling measurement process, the increase / decrease of the torque and the increase / decrease of the half rotation speed, and the effective cover pressure of the survey ground. In the soil determination step to be performed, in the geological layer determined to be liquefied by the soil determination step, the load applied to the drilling tool measured in the drilling measurement step, the torque and the half-revolution and the Liquefaction resistance ratio is determined from the effective overburden pressure of the surveyed ground, and the liquefaction determination process determines the safety factor against liquefaction.
In the liquefaction determination step, the liquefaction resistance ratio is calculated by multiplying the load, the torque and the half-rotation speed, and the absolute value of the value is divided by the effective cover pressure, and the liquefaction resistance ratio is divided by the external force. Safety factor, liquefaction judgment,
The soil determination step is to determine whether or not the liquefaction target soil layer by a value obtained by multiplying the load, the change in the torque and the change in the half revolution, and dividing the absolute value of the value by the effective overburden pressure. Liquefaction determination method characterized by the above-mentioned.

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