JPS6033932B2 - Construction method of underground piles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel construction method for constructing piles while extremely simply and efficiently confirming the bearing capacity of piles driven into the ground.

To support above-ground structures such as power transmission towers,
It is known to reinforce and support the foundation by driving piles into the ground.

In this case, as buildings and other structures are constructed on very good footing, large, high-efficiency driving devices such as drop hammers, diesels, and hammers are used to drive the piles. In most cases, the location is remote, mountainous, rural, or wilderness, and it is impossible to bring in such large machinery. Therefore, as shown in FIG. 1, the process of attaching the screw 2 to the tip of the pile 1 and driving the pile 1 and screw 2 into the ground while simultaneously rotating them can be effectively operated.

According to this process, a simple rotation imparting device and a small driving device are sufficient.B Conventionally, in order to know the bearing capacity of this type of pile, boring is carried out at the point where the pile will be driven, and the The soil was taken back to the laboratory, the composition of its strata was examined in detail, the friction force between the pile surface and each stratum was calculated, and a rough estimate was obtained through theoretical reasoning.

However, this method requires extra work such as boring and strata analysis, and the time and geographical distance required for transporting the material to a separate laboratory cannot be avoided, making it unavoidably complicated. The present invention does not perform any such boring or strata analysis, and can be carried out as is while carrying out field work.
The present invention aims to provide an innovative construction method that enables construction by determining the frictional force between a pile and the stratum in which the pile is driven in situ'' and confirming the bearing capacity of the pile.

According to the method of the present invention, it is possible to know the bearing capacity of the pile at each depth where the pile is actually driven, and to check whether the pile has the bearing capacity as designed or not. The improvement in work efficiency and reliability is immeasurable. Examples of the present invention will be described in detail below.

In the present invention, the pile is divided into units of length in the longitudinal direction.

The unit length for this division is selected based not only on the length and diameter of the pile to be driven, but also on the composition of the strata at the point where it is driven. In other words, if the geological formation is expected to consist of a single layer of deep sediment, the unit length will be long, but if it is expected that different thin strata will appear one after another, it is better to choose a shorter unit length. Detection accuracy improves. The technical idea of the present invention is that during construction, the supporting force is determined by sequentially converting the changes in torque that occur each time a unit length is entered into the frictional force.

First, the theory of the present invention will be described.

Find the torque characteristics of the two screw parts of the pile.

The screw blade S is simulated as a disk approximately having a radius Rs as shown in FIG. The frictional force generated on one side of the blade S on the micro annular surface of the small radius r portion and the medium portion dr is expressed by the following formula: CX2rXdr where C is the frictional force of the soil per unit area.

Without considering the rotational axis of the screw here, and looking at the blade part, the total friction torque Qs on one side of the screw blade S is QS = 'Gan SPC 3p). ...[1' Next, find the torque characteristics of the first part of the pile.

If the pile 1 is divided into units of length L', the sheared surface of the soil is Ap, and the radius to the sheared surface is Rp as shown in Figure 4, then Apd2 is Rp・L. Determining the torque caused by surface friction, APXCXRp22R2pXLXC, . ,,． ，
{2} Through the above calculations, we have obtained the basic calculation formula for the frictional force per unit area between the screw and the pile.

Next, based on these, we will explain how to apply it to a practical size and specifically determine the supporting force.

As shown in Figure 5, the length of the sea bream section of the screw is 10 feet or 300 feet.

The unit segment length of the pile is therefore 10 feet or 30
0 enmity. The screw blades are respectively S,,S2
, S3, and S4. Determine the torque constant Ks of the screw portion from the previous equations [1-formula] and [2-formula].

Ks=2mR'2px3000 Tozuma tai {(R3S・1R'3p) 10 (R3s2-R3p) 10 (R3s3-R'p3)} x2 Tozuma light {(R3S4-Rp3) 10 (R is also 4-R3p) }
Similarly, the torque constant Kp of the pile portion is determined.

Kp Ni 2 R 2 p X 3000 Now Qn: Torque Cn when n feet deep. m: Average frictional force per unit area from depth n feet to depth m feet, Qn for each 10 feet drive is QI as shown in Figure 2.

NiKSXCM. Q20 KSXCI〇, dozens of KPXC〇, 10Q.

NiKSXC number, shame ten Kp (CM. ten C, small) Q. =K
SXC arc, node tens KPX (CO.1. tens C, decimal tens C20
, Cn. 30, 40 C minor rules) Summarized by m, Co. ,.

=Q stave C...Arc-Q20-QI.

-Co. 1. (Kp [KS) KSC Komatsu・Q30-Q2
0-CI〇, phantom melon p・KS) KSC3.

・Me-Q4. -Q3. -Number of C-Nobi p-K KSC Koisoji Q50-1Q40-1C. Carp (Kp/KS) KSC50
, arc; Q60-Q50-1C Yu, Rule (Kp-KS) KS If the torque when driving each unit length is found from the above, the actual frictional force between the soil and the pile at that time can be calculated. I understand that. Therefore, the final bearing force Pfu when the pile is driven to the required depth is the shear unit surface area Apn. m
and Cn. It can be found as the sum of the products of m.

That is, Pfu=ZApn. m×Cn. m becomes.

This method allows you to immediately determine the supporting capacity on-site by simply reading the rotational torque while actually driving a pile.Compared to conventional laboratory methods, it is much more convenient. I don't know.

When using this method, some error is unavoidable, but this is no different from the conventional example, and in practical use, there will be no problem if the actual value is taken based on the predetermined safety factor. be.

Also, for Ks, KP, etc., if you separately check the difference between the theoretical calculation value and the experimental value and use the correction value to find Cn4m>Pfu,
Furthermore, the accuracy can be increased.

As described above, by using the construction method according to the present invention, it is possible to confirm the bearing capacity at that time depending on the depth at which the pile is driven, and then drive the pile, which not only greatly improves reliability but also improves its practical performance. There is a tremendous amount of efficiency that can be achieved.

[Brief explanation of drawings]

Fig. 1 is an explanatory sketch of a pile targeted by the method according to the present invention, Fig. 2 is an explanatory drawing showing how the pile is driven to various depths, and Figs. 3 to 5 are illustrations of the guidance of the calculation formula. FIG. 1...Pile, 2...Screw. Ga' Zuzu 3 Zu Sai 4 Zu Ota Zu Juice Prisoner

Claims (1)

[Claims] 1 When driving piles into the ground using the screw rotation method, by dividing the piles into unit lengths in the longitudinal direction and detecting the torque applied to the piles when each unit length is driven into the ground, By determining the frictional force between the pile and the soil for each unit length, and determining the sum of the products of the outer peripheral surface of the pile at each unit length when the required length is driven and the frictional force there, An underground pile construction method characterized by detecting the bearing capacity of the entire pile at that time.