JPS6262203B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for measuring a pile support layer, which is used to reliably and quickly confirm the support layer of a pile.

(Prior Art) In order to confirm the support layer of a pile and measure its depth, it is necessary to know the N value determined by a standard penetration test as an engineering property of the support layer.

This standard penetration test is determined based on the number of blows required to penetrate 30 cm as a final blow, or the amount of penetration after 50 blows.

Conventionally, such standard penetration tests have been disclosed in, for example, Japanese Patent Publication No. 48-6893, or Japanese Patent Publication No. 1973-
Penetration testing equipment, such as that disclosed in No. 27989, has been widely used.

(Problem to be solved by the invention) However, when using the standard penetration test method described above, the number of blows required for penetration of 30 cm, or 50
Since the condition of the pile support layer is confirmed based on the amount of penetration (movement) due to repeated blows, it requires a considerable amount of time and the installation of large-scale testing equipment, and it is not only necessary to confirm the exact condition of the pile support layer. It is difficult to grasp the

Also, from a structural point of view, once the N value is measured, the sampler comes off each time, and since it cannot be duplicated underground, it has to be pulled up to the ground, assembled, and then excavated and measured again, which takes time. There were problems such as the length of the test and the cost required for measurement.

(Means for Solving the Problems) Therefore, in the present invention, when the N value can be continuously determined without the need to pull up the rod when measuring the N value, by using bare digging and a test cone built into the core chamber. The aim is to significantly shorten the measurement time and improve accuracy. Specifically, it measures the time required for each fixed excavation distance (Td value) by performing bare digging using the own weight of the hand feed and rod to a predetermined depth. After digging to the specified depth, the test cone built in the core cube is lowered to the bottom of the hole and the penetration value (Nd value) is measured using the same method as the standard penetration test.
The present invention relates to a method for confirming and measuring a pile support layer, which comprises a penetration measurement in which the N value in a standard penetration test is obtained by calculating the N value in a standard penetration test, and the values of both measurements are plotted to confirm the support layer.

In other words, the structure of the method for confirming and measuring the pile support layer of the present invention is to perform bare digging using hand feed and rod's own weight to a predetermined depth, and calculate the required digging time (Td value).
After measuring the excavation time and bare digging to the specified depth, the test cone built in the core cube is lowered to the bottom of the hole and the test is conducted in the same manner as the standard penetration test to determine the Nd value. It consists of a penetration measurement that converts into

The specific contents of the present invention will be explained below based on the illustrated embodiments. Fig. 2 shows a longitudinal section of the rotary type sounding used in the present invention in use, and 2 is a boring rod; 4 is a core tube, 7 is a penetrating rod, and 8 is a test cone. At the lower end of the boring rod 2, a core tube 4 is formed with the tip of the boring rod 2 protruding inward.
is detachably attached to the core tube 4.
Inside, a penetration rod 7 with a test cone 8 fitted to its lower end is built in, with its upper end connected to the threaded portion 3 provided at the tip of the boring rod 2 in a reverse threaded state. It is.

This boring rod 2 is rotated in the direction of arrow A by a boring machine (not shown) to perform normal boring, and a threaded portion 3 is provided on the periphery of the tip for connection to a core tube head 5, which will be described later. A core tube 4 has a metal crown 6 at its lower end, and is attached to the tip shaft of the boring rod 2 at a core tube head 5 with a predetermined diameter and a predetermined length.

That is, a threaded portion (not shown) that engages with the threaded portion 3 of the boring rod 2 is formed on the inner periphery of the opening of the core tube head 5, whereby the core tube 4 is connected to the boring rod. -ing

A penetration rod 7 has a test cone 8 at its lower end and is connected at its upper end to the lower end of the boring rod.

When the boring rod having the above configuration is turned in the direction opposite to the direction of rotation of the rod (in the direction of arrow B) after digging to a predetermined depth, the boring rod 2 separates from the core cube head.
The tip of the test cone touches the bottom of the hole.

This allows a penetration test to be performed.

(Function) First, the first measurement, which is the measurement of the time required for excavation for each fixed excavation distance (Td value), is carried out by installing a trident and a boring machine in the same way as in normal boring work, and by using a hand feed and a rod to a predetermined depth. The excavation time will be recorded for each meter of excavation.

If the excavation speed suddenly changes within 1 m, the depth should also be recorded.

Specifically, in order to determine whether or not the boring by bare digging is a supporting layer at the planned depth,
It is necessary to know the relative hardness of the strata along the way and compare them. As a material for this purpose, as shown in Figure 1, the numerical value expressed as the time required for excavation (the reciprocal of the speed) Td is calculated and plotted.

Here, Td (digging time) is △Z = distance from a certain depth to a certain depth (m) △T=Time required to excavate △Z (min) Then, It is determined by Td△T/△Z.

In Figure 1, the depth Z (m) is plotted on the Y axis and the Td value is plotted on the X axis.
The larger the value, the harder the stratum is, so if this is plotted, the support layer 1 can be confirmed and its depth can be measured.

In addition, if you want to determine the adhesive force of a clayey soil layer in this measurement, lower the test cone 8 built into the core tube 4 to the bottom of the hole, record the amount of penetration by scuttling, and calculate the adhesive force C from the weight of the rod and the amount of penetration. Calculate. This adhesive force C is obtained as follows.

W = Weight of Rod and Monken (subtracting buoyancy) (Kg) C = Adhesive force Nc = Coefficient Ap = Cross-sectional area of cone (cm ² ) Af = Circumferential area of cone (cm ² ), then W = CNcAp + CAf =C(NcAp+Af).

Next, after digging to the planned depth, a test cone 8 is lowered to the bottom of the hole, and a penetration test is performed in the same manner as a standard penetration test.

As mentioned above, in the penetration test, after bare digging to the planned depth in advance, the boring rod 2 is rotated in the direction opposite to the direction of rotation (A) of the boring rod 2 during excavation (in the direction of arrow B), and the boring rod 2 is rotated to the core cube head. 5 and thereby test cone 8
Start the standard penetration test by touching the tip of the hole to the bottom of the hole.

In this case, in the standard penetration test, the actual driving is
The N value is determined by recording the number of blows required to penetrate 30 cm or by recording the amount of penetration for 50 blows.This measurement also uses the same method to obtain the value (called the Nd value), and calculates the Nd value. N value in standard penetration test
Convert it to a value and record it.

Of course, it is also possible to calculate the number of blows required to penetrate 10 cm, which is less than the standard penetration test, or the amount of penetration for 20 blows, and convert it into the N value in the standard penetration test.

After the penetration measurement at one point is completed, the boring rod 2 is reversed and the penetration rod 7 with the test cone 8 fitted therein is stored in the core tube again.
Then, bare digging is carried out to the next scheduled depth, and when that point is reached, the Nd value is determined in the same manner as above.

FIG. 1 is a diagram showing the distribution of N values, with N values plotted on the X axis and depth plotted on the Y axis.

In other words, the Td value is measured up to point A, and from point A to N
The values are measured and plotted, thereby making it possible to confirm the existence of the support layer 1 and to measure its position.

Of course, it is also possible to measure the Td value at the same time as this Nd value measurement, and by simultaneously measuring both, it is possible to confirm the position of the support layer more accurately.

Finally, if it is desired to directly inspect the geology, it is also possible to replace the penetrating rod 7 with a Raymond sampler equipped with a normal shoe and penetrate the ground to extract the earth and sand.

(Effects of the Invention) As explained above, according to the present invention, digging time measurement is performed in which bare digging is performed to a predetermined depth using the own weight of the hand feed and rod, and the time required for each fixed excavation distance (Td value) is measured; After bare digging, the test cone built in the core cube is lowered to the bottom of the hole, and the penetration value (Nd value) is determined using the same method as the standard penetration test. This is converted to the N value in the standard penetration test. Since both measured values are plotted and the support layer is confirmed, the accuracy is not only significantly improved compared to the conventional penetration test method that only calculates the N value, but also the above Td value. Measurement time can be significantly shortened because measurements can be made while excavating.

Incidentally, as a result of comparing the measurements made by the present invention with the conventional method in a pile support layer of standard depth, it was confirmed that the measurements made by the method of the present invention were at least four times higher than those of the conventional method. Needless to say, the difference becomes larger as the depth of the pile support layer to be measured increases.

In general, in the case of the present invention, it is not necessary to replace the Raymond sampler and the core tube at each measurement time, but the test cone attached to the core tube is detached from the core tube at each point by detaching the penetrating rod fitted at the tip. It is economical, greatly improving work efficiency, and the penetration value can be expressed as the N value of the standard penetration test. In this case, it is not possible to confirm the underlying support layer, but according to the present invention, bare digging can be performed, so the position of the support layer can be reliably determined. Furthermore, the hard soil in the strata along the way is also displayed as the excavation time Td, which has various beneficial effects such as the ability to obtain information.

[Brief explanation of the drawing]

Fig. 1 is a distribution diagram of Td value and N value of one embodiment of the present invention, and Fig. 2-A and Fig. 2-B are longitudinal sectional views showing the usage state of the rotary type sounding used in the present invention. be. 1...support layer, 2...boring rod, 4...
... Core tube, 5 ... Core tube head, 7 ... Penetration rod, 8 ... Test cone.

Claims (1)

[Claims] 1 Excavation time measurement in which bare digging is carried out using the hand feed and the weight of the rod to a predetermined depth, and the time required for each fixed excavation distance (Td value) is measured.After bare digging to the predetermined depth, the test cone built in the core It consists of a penetration measurement in which the penetration value (Nd value) is determined by descending to the bottom of the hole using the same method as in the standard penetration test, and this is converted to obtain the N value in the standard penetration test, and the Td value and N value in both measurements are plotted. A method for confirming and measuring a pile support layer, which is characterized by confirming the support layer.