JP6914780B2 - How to drill a hole for burying a ground anchor - Google Patents

Description

The present invention relates to a method of drilling a hole for embedding a ground anchor in a support layer of the ground on which a structure is constructed by using a drilling machine using a double pipe drilling method.

Conventionally, when a lifting force acts on a structure, as shown in FIG. 4, a hole 1 that reaches the inside of a support layer G2 having a high N value in the lower layer of the surface layer G1 of the ground G is drilled. After burying the fixing body 3 of the ground anchor 2 in this hole (ground anchor burying hole 1), the fixing body 3 and the structure 20 are connected by a tension material 4 such as a wire, and are opposed to the structure 20 side. A force member 5 is provided to apply a tensile force between the fixing body 3 and the structure 20 to prevent the structure 20 from being lifted by groundwater or the like (see, for example, Patent Document 1). ).
The ground anchor burial hole 1 is generally drilled by using a drilling machine using a double pipe drilling method including a drilling casing and an inner rod.

Japanese Unexamined Patent Publication No. 2011-144558

By the way, when burying the ground anchor 2, a survey is conducted in advance by boring at a plurality of locations, and the depth at the time when the N value becomes large is defined as the depth to the support layer G2 (support layer position). After excavating from the position of the support layer to a predetermined depth, the anchoring body 3 was buried.
However, since the number of surveys by boring is limited and the support layer G2 is not necessarily flat but uneven, the actual support layer position may differ from the presumed support layer position, and as a result, There are problems that the burial depth of the fixing body 3 becomes shallow, and in the worst case, the fixing body 3 protrudes into the surface layer G1 and a sufficient frictional force cannot be obtained with the ground. rice field.

The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a method for drilling a ground anchor burial hole capable of reliably burying a fixed body of a ground anchor in a support layer. ..

In the present invention, a structure is constructed by using a drilling machine using a double pipe drilling method (hereinafter referred to as a double pipe drilling machine) provided with a drilling casing and an inner rod. This is a method of drilling a hole for burying a ground anchor in the support layer of the ground. After double pipe drilling to a predetermined depth, only the inner rod is penetrated into the ground at the time of penetration. The striking pressure, the rotational pressure, and the feed pressure (pushing pressure) are measured, and the above-mentioned is based on the magnitude of the drilling energy calculated from the measured striking pressure, the rotational pressure, and the feed advancing pressure. It is determined whether or not the tip of the inner rod has reached the inside of the support layer, and if it is determined that the tip of the inner rod has not reached the inside, the inner rod is pulled up and then the depth at which the inner rod is penetrated is reached. After drilling and discharging the soil for the portion by double pipe drilling, the work of penetrating only the inner rod into the ground again to determine whether or not the inner rod has reached the inside of the support layer is performed. It is repeated until the inner rod reaches the inside of the support layer, and when it is determined that the inner rod has reached the inside, the support layer is drilled by double pipe drilling to a depth at which the ground anchor is embedded. It is a feature.
In this way, since the position (depth) of the support layer is confirmed before the support layer is drilled, the anchored body of the ground anchor can be reliably embedded in the support layer.
In addition, when only the inner rod is intruded, water is not supplied so that the energy that depends on the water supply pressure and the amount of water supply, which has low energy calculation accuracy, is excluded from the drilling energy calculation. Therefore, the calculation accuracy of the drilling energy can be improved, and the position of the support layer can be confirmed with high accuracy.
Needless to say, when performing double pipe drilling, drilling is performed while supplying water (drilling water) to the ground to be excavated from the tip side inside the inner rod.
Further, by configuring the double pipe drilling machine to supply water from the side surface on the tip side of the inner rod, it is possible to prevent clogging of the tip of the inner rod when the inner rod is penetrated. Therefore, the inner rod can be easily penetrated.

The outline of the present invention does not list all the necessary features of the present invention, and a subcombination of these feature groups can also be an invention.

It is a figure which shows the drilling method (first half) of the ground anchor buried hole. It is a figure which shows the drilling method (the latter half) of the ground anchor buried hole. It is a figure which shows the structure of the tip part of the double pipe drilling type drilling machine. It is a figure which shows the support method of the structure using the ground anchor.

The method of drilling the ground anchor buried hole according to the present embodiment will be described with reference to the drawings.
First, as shown in FIG. 1A, a double pipe drilling machine 10 provided with a drilling casing 11, an inner rod 12, a rotary drive device 13 and a water supply device 14 is installed on the ground surface G0. Then, double pipe drilling is performed to a predetermined depth.
The ground G on which the structure is constructed generally includes a surface layer G1 having a small N value and low strength, and a support layer G2 having a large N value and high strength in the lower layer of the surface layer G1. "Predetermined depth" refers to the depth H to the surface (estimated support layer position) of the support layer G2 previously obtained by boring or the like, which is indicated by the alternate long and short dash line in the figure.
The drilling casing 11 is a cylindrical member having a drilling bit 11a at the tip, and inside the drilling casing 11, an inner bit 12a and a ejection hole 12b are provided at the tip, and is coaxial with the drilling casing 11. A cylindrical inner rod 12 is installed.
The rotation drive device 13 includes a rotation mechanism that rotates the drilling casing 11 and the inner rod 12, a propulsion mechanism that pushes the drilling casing 11 and the inner rod 12 into the ground G, and the drilling casing 11 and the inner rod. and having a striking mechanism which gives striking force to the 12, pushing force T _V of drilling the casing 11 and the inner rod 12, the striking force B _f, hit number B _n, drilling speed V _d, the rotational speed R _p and, It is provided with a plurality of sensors (not shown) that measure the rotational torque T _q.
Further, the water supply device 14 supplies cutting water to the inside of the inner rod 12.
As shown in FIG. 3A, the drilled water supplied to the inside of the inner rod 12 is ejected into the excavated ground surface from the ejection hole 12b provided on the side surface on the tip end side of the inner rod 12. As shown in FIG. 3, the ejection hole 12b may be in a direction perpendicular to the side surface of the inner rod 12, or may be in a direction obliquely upward as shown in FIG. 3 (b). The hole diameter of the ejection hole 12b is 10 to 20 mm, and 2 to 4 locations are provided at positions 30 to 100 mm from the tip of the inner rod 12.
In this example, as will be described later, since the inner rod 12 has a step of penetrating into the ground G without sending water, as shown in FIG. 3C, the inner rod 12 is formed on the tip side surface. This is because if the ejection hole 12c is provided on a certain bottom surface, the ejection hole 12c may be clogged at the time of penetration, and water may not be supplied at the time of double pipe drilling.
On the other hand, in double pipe drilling, as shown by the downward arrow in FIG. 1A, the drilling water is sent from the inside of the inner rod 12 by the water supply device 14, and the drilling casing 11 and the inner rod 12 are used. While rotating at the same time, push it into the ground G to drill holes in the ground, discharge earth and sand, and wash with water. At this time, the earth and sand are discharged to the ground surface from the space surrounded by the drilling casing 11 and the inner rod 12, as shown by the upward arrow in the figure.
In the double pipe drilling, the drilling casing 11 and the inner rod 12 are pushed into the ground G while adding pipes having a predetermined length (for example, 1.5 m), respectively.

When the drilling to a predetermined depth is completed, as shown in FIG. 1 (b), a pipe of, for example, 50 cm is added only to the inner rod 12, and water is supplied only to the inner rod 12 without water supply. The _{drilling energy E is calculated while giving the advancing pressure P v} , the striking pressure P _s , and the rotational pressure P _k and penetrating only the inner rod 12 into the ground G, and based on the magnitude of the drilling energy E. Therefore, it is determined whether or not the tip of the inner rod 12 has reached the inside of the support layer G2.
Specifically, the excavation velocity V _d is measured every 10 cm, and the drilling energy E is calculated every 10 cm from the applied striking pressure P _s and rotational pressure P _k. Then, the data of the first and last 10 cm is used as a reference value, the average value between the middle 30 cm is set as E _ave , and if this average value E _{ave exceeds the set value E 2} corresponding to the support layer G2, the figure is shown. As shown in 2 (a), it is considered that the tip of the inner rod 12 has reached the inside of the support layer G2.
The drilling energy E is the energy for excavating the ground per 1 m and is given by the following formula.
_{E = E V + E R +} E P + E W (MN · m / m)
_{= T V · V d / V} d + 2πT q · R p / V d + B p · B n / V d + P · Q / V d
Here, _{E V = T V · V d} / V d in pushing energy (MN · m / m), the T _V pushing force (MN), V _d is a drilling speed (m / min).
E _R = 2π T _q · R _p / V _d is the rotational energy (MN · m / m), T _q is the rotational torque ( _{MN m), R p} is the rotational speed (r / min), and V _d is the excavation speed. (M / min).
E _P = B _p・ B _n / V _d is the striking energy (MN ・ m / m), B _p is the striking energy per striking _{(MN m / time), B n} is the number of striking (times / min), V _d is the excavation speed (m / min).
The _{E W = P · Q / V} d Promoting by drilling water energy (MN · m / m), P is water supply pressure (MN / m ^2), Q is water flow rate ^{(m 3 / min), V} d is drilled The speed (m / min).
In this example, when penetrating only the inner rod 12 to the ground G is not subjected to water (P = Q = 0), so an E _W = 0.

On the other hand, when the average value E _ave is equal to _{or less than the set value E 2} , the tip of the inner rod 12 does not reach the inside of the support layer G2 as shown in FIG. 1 (b). ) And FIG. 3A, for example, after pulling up the inner rod 12 by 50 cm, the drilling casing 11 is added by 50 cm, and the soil K between 50 cm when the inner rod 12 is penetrated is a double pipe. Drilling, discharging earth and sand, and washing with water are performed.
When the double pipe drilling for 50 cm is completed, another 50 cm pipe is added to the inner rod 12, and only the inner rod 12 is placed in the ground G as in the case of FIG. 1 (b) without water supply. Calculate the average value of drilling energy E _{ave while penetrating 50 cm.} Then, the calculated average value E _ave of the drilling energy and the set value E ₂ are compared to determine whether or not the tip of the inner rod 12 has reached the inside of the support layer G2.
The above operation is repeated until the tip of the inner rod 12 reaches the inside of the support layer G2.
When the tip of the inner rod 12 reaches the inside of the support layer G2, as shown in FIG. 2B, after pulling up the inner rod 12 by 50 cm, the drilling casing 11 is added by 50 cm, and the inner rod 12 is penetrated for 50 cm. The soil is drilled, discharged with earth and sand, and washed with water using a double-tube drilling hole. Next, as shown in FIG. 2C, the support layer G2 is drilled by a double pipe drilling to a predetermined depth h, and then the drilling casing 11 and the inner rod 12 are pulled up to obtain FIG. The ground anchor burial hole 1 is formed as shown in.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the claims that such modified or modified forms may also be included in the technical scope of the invention.

For example, in the above-described embodiment, only the inner rod 12 is penetrated to confirm whether or not the ground G is the support layer G2, but even within the support layer G2, only the inner rod 12 is penetrated. The drilling energy E may be calculated, and it may be confirmed that _{the average value E ave} of the calculated drilling energy exceeds the set value E _2.
Further, in the above-described embodiment, the predetermined position is the estimated support layer position obtained in advance by boring or the like, but the predetermined position is about 0.5 to 1.5 m deeper than the estimated support layer position. May be.
Further, the predetermined position may be shallower than the estimated support layer position.
Further, in the above-described embodiment, it is determined whether or not the tip of the inner rod 12 has reached the inside of the support layer G2 by using the drilling energy E. However, assuming that the bottom area of the inner rod 12 is S, the striking pressure _{P P = E P / S (} MN / m 2) , the rotation pressure _{P R = E R / S (} MN / m 2), KyuSusumu圧is _{P V = E V / S (} MN / m 2) since given, with reference to drilling pressure _{P = P V + P R +} P P, the tip of the inner rod 12 may determine whether the host vehicle has reached the supporting layer G2.

1 Ground anchor burial hole, 10 Double pipe drilling machine, 11 Drilling casing,
11a drilling bit, 12 inner rod, 12a inner bit,
12b ejection hole, 13 rotary drive device, 14 water supply device,
G ground, G0 ground surface, G1 surface layer, G2 support layer.

Claims (3)

A method of drilling a hole for embedding a ground anchor in the support layer of the ground on which a structure is constructed using a drilling machine using a double pipe drilling method equipped with a drilling casing and an inner rod. And
After double-tube drilling to a predetermined depth
Only the inner rod is penetrated into the ground to measure the impact pressure, the rotational pressure, and the feed pressure at the time of penetration, and the cutting calculated from the measured impact pressure, the rotational pressure, and the feed pressure. Based on the magnitude of the hole energy, it is determined whether or not the tip of the inner rod has reached the inside of the support layer.
If it is determined that it has not been reached,
After pulling up the inner rod, the soil for the depth of the inner rod is drilled and discharged by double pipe drilling, and then only the inner rod is penetrated into the ground again to penetrate the inner rod. The operation of determining whether or not the rod has reached the inside of the support layer is repeated until the inner rod reaches the inside of the support layer.
A method for drilling a ground anchor burial hole, which comprises drilling the support layer to a depth at which the ground anchor is embedded by double pipe drilling when it is determined that the ground anchor has been reached. The method for drilling a hole for burying a ground anchor according to claim 1, wherein water is not supplied when only the inner rod is penetrated. The method for drilling a hole for burying a ground anchor according to claim 2, wherein the drilling machine using the double pipe drilling method has a configuration in which water is supplied from the side surface on the tip end side of the inner rod.

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