JP2014134065A - Soil determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil determination method for allowing easy soil determination from a testing parameter acquired in penetration test.SOLUTION: In penetration test for, when rotating a penetration rod 1 having a penetration body at the front end to penetrate into a ground, measuring rotation torque T and a penetration amount St of the penetration rod 1 while stepwise changing load W applied onto the penetration rod 1, the soil determination method allows soil determination on the basis of a testing parameter dT/dΣSt showing the rate of change of the rotation torque T to change of a cumulative penetration amount ΣSt. Since the testing parameter used for the soil determination shows tendency to significantly increase in connection with sandy soil, the soil determination is allowed at one view.

Description

  The present invention relates to a method for determining soil quality on the basis of various measurement data obtained by a test of rotating a screw point into the ground.

Conventionally, in a penetration test using a rotary percussion drill, a method of measuring a load and torque acting on a rod and investigating soil properties based on these measured values is known (Patent Document 1). This soil investigation uses a torque increase gradient At (At = rotational torque increment / load increment) as a test parameter, and obtains a distribution of the torque increase gradient At for each predetermined depth and obtains a boundary value for soil determination. It is intended to distinguish between viscous soil and sandy soil.

Japanese Patent Laid-Open No. 11-200355

However, the test parameters from the penetration test show an increasing gradient in both viscous and sandy soils. For this reason, since the boundary value (reference value) for soil determination must be obtained, the determination procedure is complicated.

The soil quality determination method of the present invention was created in view of the above problems, and an object thereof is to provide a soil quality determination method capable of easily determining soil quality from test parameters acquired by an penetration test.

The present invention is a penetration test in which a penetrating rod having a penetrating body at the tip is rotationally penetrated into the ground, and the rotational torque T and penetration amount St of the penetrating rod are measured while changing the load W applied to the penetrating rod in stages. The soil quality is determined based on the test parameter dT / dΣSt indicating the ratio of the change in the rotational torque T to the change in the cumulative penetration amount ΣSt.

  Since the test parameters used in the soil quality determination method of the present invention show a significant increase tendency in sandy soil, the soil quality can be determined at a glance.

First, FIG. 1 thru | or FIG. 3 shows the penetration test for acquiring the test parameter (rotation torque T) used for this invention. In this penetration test, the penetration rod 1 provided with a screw point 3 as an example of a penetration body at the tip of the rod 2 is rotated and penetrated into the ground, and a maximum of seven stages with respect to a test depth section of 0.25 m. (250N, 375N, 500N, 625N , 750N, 875N, 1kN) while loading by weight 4 a load W of, measuring the torque T and the penetration amount _{S t} per one rotation of the penetration rod 1. Specifically, as shown in FIGS. 1 and 3, first, the initial load 250N is made to penetrate once in a state of being loaded on the penetration rod 1 (S01). In this case, if the penetration amount S _t has not reached the 25 cm (S02), and loading the next load 375N to penetration rod 1 rotated once penetration (S03). Adds a load 125N for each rotation, the cumulative penetration amount [sigma] s _t is rotated penetrate until it reaches the 0.25 m.

Further, as shown in FIGS. 2 and 3, in a state where the loading of the maximum load 1kN (S04), the cumulative penetration amount [sigma] s _t does not reach the 0.25m, the cumulative while loading the maximum load 1kN penetration amount [sigma] s _t is repeated rotation penetration to reach the 0.25 m (S05). Then, when the measurement of the first test depth section (depth 0 m to 0.25 m) is completed, the rotation penetration is stopped (S06), and the next test depth section (depth 0.25 m to 0.5 m) is measured. In such a case, there are seven or more measurement points in the test section. Conversely, if the cumulative penetration amount [sigma] s _t before loading the maximum load 1kN reaches 0.25m, as shown in FIG. 1, the measurement point is 1 to 6 places.

By the way, since the measured value by the penetration test is influenced by the circumferential friction of the rod 2, the load W and the rotational torque acting on the screw point 3 cannot be measured. Therefore, every time 0.25 m penetrates, the penetrating rod 1 is pulled up by 1 cm and rotated (S07), and the rotational torque Tm at this time is measured (S08) and returned to the original position (S09). This rotational torque Tm is used for calculating the circumferential friction of the rod 2. As a calculation method, assuming that the vertical and horizontal circumferential friction acting on the rod 2 is Wf and Tf, respectively, the load W and the rotational torque T acting on the screw point 3 are the load Wa acting on the entire penetration rod 1. And Ta are used to express the following equation.
Wa = Wf + W, Ta = Tf + T
Therefore, the load W and the rotational torque T acting on the screw point 3 are expressed by the following equations.
W = Wa-Wf, T = Ta-Tf
In the following description, it is assumed that the rotational torque T of the penetrating rod 1 takes into account the circumferential friction of the rod 2. In the penetration test, the maximum value T _max , the minimum value T _min, and the average value T (−) are also measured for the rotational torque T per rotation of the penetration rod 1.

In the soil determination method of the present invention, dT / dΣSt is set as a test parameter based on the measured value by the penetration test. This test parameter dT / dΣSt indicates the ratio of the change in the rotational torque T to the change in the cumulative penetration amount ΣSt. Specifically, as shown in FIG. 4, the test parameter dT / dSt is an inclination of an approximate line shown in a graph in which the vertical axis indicates the rotational torque T and the horizontal axis indicates the total penetration amount ΣSt in the test section. For viscous soils, loams and humus soils, the test parameter dT / dΣSt shows a constant or slight increase trend, whereas sandy soils show a significant increase trend. For this reason, sandy soil can be determined at a glance.

It is a 1st example of the penetration test for acquiring the test parameter concerning the soil quality judging method of the present invention. It is the 2nd example of the penetration test for acquiring the test parameter concerning the soil quality judging method of the present invention. It is a flowchart which shows the procedure of the penetration test for acquiring the test parameter which concerns on the soil quality determination method of this invention. It is a graph which shows the test parameter dT / dΣSt which concerns on the soil quality determination method of this invention.

1 Intrusion rod 2 Rod 3 Screw point 4 Weight

Claims (1)

In the penetration test to measure the rotational torque T and the penetration amount St of the penetration rod while changing the load W applied to the penetration rod step by step through the penetration rod having a penetration body at the tip.
A soil determination method characterized by determining soil quality based on a test parameter dT / dΣSt indicating a rate of change in rotational torque T with respect to change in cumulative penetration amount ΣSt.