JPS6343526B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention targets soft ground such as sand layers, silt layers, clay layers, and softened weathered rocks, and directly causes ring-shaped shear failure at the bottom of a borehole. , from which the internal friction angle (φ) of the formation,
This relates to a test method aimed at determining the value of adhesive strength (C).

Traditionally, when constructing structures such as civil engineering and architecture, and when performing landslide and slope failure prediction, stability analysis, and countermeasure construction, the soil mechanical properties of the target ground strata have been an extremely important factor. However, especially the internal friction angle of each layer (hereinafter referred to as φ),
Knowing the values of shear strength constants such as adhesive force (hereinafter referred to as C) is absolutely necessary for design and construction.
Therefore, at present, standard penetration tests are performed in parallel with ○B geological survey boring to determine the N value, or the converted N value is determined from the cone bearing capacity value from static or dynamic cone penetration tests, and from this, the converted uniaxial compression Determine the strength qu value and converted C value, ○b Measure the shear strength τ using a vane test or pull-out test (Iskimeter, helical sounding borer, etc.) in ground mainly composed of clay strata, ○b) A commonly adopted method is to take a disturbed sample and conduct an indoor soil test (triaxial compression test, direct shear test, ring shear test, uniaxial compression test, etc.) to experimentally determine the values of φ and C. There is.

However, of the above, field tests can only determine the values of φ and C as indirect converted values, or the shear strength τ as their composite value, and indoor soil tests only allow undisturbed samples to be collected. However, there are drawbacks such as the inability to conduct sufficient tests on strata where it is impossible to test or areas with alternating layers where properties change frequently.

The method of the present invention can be applied to geological formations that are difficult to sample, such as soft sand layers, clayey soil layers, gravelly layers, soft or weathered rocks with developed cracks, or thin intercalated layers, in natural ground conditions. It has the great feature that it can be tested and the values of φ and C of the stratum can be directly determined. In addition, the test method of the present invention not only allows you to know the values in the horizontal direction of the strata, which are important for structure foundations and landslide surfaces, but also allows you to determine the values in any direction of the strata by changing the drilling direction of the borehole. It has the advantage that it is possible to obtain

The principles of the present invention, examples of test equipment, and test methods will be explained in detail below.

(1) Principle of the present invention Figure 1 is an explanatory diagram showing the basic principle of the present invention.

In Fig. 1A, 1 is a test cylindrical tube crimped to the bottom of a bored hole by an overburden load W, and its lower end crimped surface 3 is sufficiently roughened by cutting tooth profiles, grooves, etc. It is made to be non-slip by forming and crimping it to the strata surface. 2 is a rod for rotating this test cylindrical tube 1 by a moment M of external force.

FIG. 1B is an enlarged view of the stress state within the formation at the lower crimp surface of the test cylindrical tube.
Now, let us assume that the outer radius of the crimped surface of the test cylindrical tube is R, the circular radius is r, the area is A, and the overload is W, and if we consider the case where the test cylindrical tube is caused to undergo rotational displacement by an external force moment M, the hole bottom The vertical load stress σ _p generated in the stratum is approximately equal to the load p per unit area of the test cylindrical pipe, σ _p = p = W/A, and if the internal friction angle of the stratum is φ and the adhesive force is C, then , the shear stress τ with respect to rotational displacement is as follows.

τ=C+σ _p・tanφ=M/2/3π(R ³ −r ³ ) Here, the external load W is M ₁ , W ₂ ,
...If Wn is changed, the load stress in the formation becomes σ _p1 , σ _p2 , ...σ _po , so the magnitude of the external force moment that causes rotational displacement in this case is
Assuming M ₁ , M ₂ , ...Mn, the respective shear stress τ _o is τ _o = C + σ _po・tanφ = Mn/2/3π (R ³ − r ³ ) [However, n=1, 2, ... n]. That is, it is known that the shear stress τ _o or the external force moment Mn that gives a rotational displacement and the stratum load stress σ _po have a linear proportional relationship when φ and C of the stratum are constant values.

By the way, the shear stress τ _o =Mn/2/3π・(R ³ − r ³ ) and the rotational displacement (or rotation angle) of the test cylindrical tube
The relationship with θ is obtained experimentally as shown in Figure 2, and at each stage of the internal load stress σ _po , the shear stress (or external force moment) initially increases as the rotational displacement θ increases. It reaches a maximum value (shear fracture strength) at the value of θ, and as θ increases further, it gradually decreases to a certain value (residual shear strength).

Therefore, from this relationship diagram, it can be seen that the maximum value of τ _o corresponding to σ _po in each stage test, that is, the shear fracture strength τ _nax , and the residual shear strength τ _res that decreases to an almost constant value after fracture. , σ _po is the horizontal axis, and τ _o
By plotting on the vertical axis and connecting each point, a shear strength line as shown in Figure 3 is obtained. In this case, τ _nax . The inclination angle of the line is the internal friction angle φ of the stratum,
Further, the value of τ at the point where the extension of this straight line intersects with the vertical axis, that is, the τ _o axis, gives the adhesive force C. Similarly, τ _res .
The residual shear internal friction angle φ' is determined from the inclination angle of the line, and the residual shear adhesive force C' is determined from the value of τ at the intersection with the vertical axis.

In addition, in the above shear test, if necessary, the loaded state is maintained for a predetermined period of time selected from the soil properties at each loading stage where the overloading load is changed, and the lower ground near the crimping surface at the lower end of the test cylinder is It is carried out after compressing (consolidation).

(2) Example of Testing Apparatus FIG. 4 shows an example of the pressurization/rotation testing apparatus of the present invention.

1 in the figure is a test cylindrical tube, 9 and 10
Mounting coupling ring 8 with a small drainage hole
It is connected and fixed to. The crimping surface 3 at the lower end of 1 has appropriate tooth profiles and grooves 4 to prevent sliding on the contact surface with the ground during crimping. The cutting edge 5 of the test cylindrical tube was slightly tapered and protruded from the outer periphery (approximately 2 m/m), and was designed to minimize friction at the portion in contact with the hole wall. Also,
The test cylindrical tube, except for the cutting edge, is separated from the jacket tube 7 via a ball bearing 6, and has a structure that eliminates friction with the hole wall during rotation. A rod 2 is directly connected to the test cylindrical tube 1, has a piston 11 at the top, and is movable up and down within the cylinder 14. 12 is a piston ring or packing attached to the piston, which maintains airtightness (or watertightness) between the piston and the cylinder. Further, the rod 2 is provided with 13 cut grooves, and the protrusion 15 on the lower part of the cylinder 14 is inserted into these grooves.
Although it is free to move downward, it rotates in the left-right direction, that is, in the circumferential direction, integrally with the cylinder. 16 is a boring rod (or connecting shaft) connected from the ground, and its lower end is connected and fixed to the cylinder 14.
17 is a pressurizing chamber (gap) for pressurizing the piston 11 within the cylinder 14.

Figure 5 shows the pressurization system consisting of 1 to 15 above.
The rotation test equipment section and the ground operation equipment section are shown as one unit. 18 in the figure is a drive pipe (or casing pipe) for protecting the hole wall. A rotary torque meter 19 for measuring the magnitude of an external force moment is connected and fixed to the ground part of the boring rod 16, and is passed through the spindle case 22 of the boring machine 20 to the upper end in an airtight (or watertight) manner.
Attach a cap 23 to seal the inner hole of the boring rod from the outside. Numeral 21 is a spindle chuck (tightening screw) which is tightened onto the boring rod 16 to stop the vertical movement of the boring rod itself. However, in this case, the rotary drive gear of the boring machine is disengaged by the clutch, and the rotation of the spindle itself and the rotation of the boring rod fastened thereto are free. Reference numeral 24 denotes a compressed gas (for example, _N2 gas) cylinder, and a pressure reducing valve 25 sends air at a predetermined pressure into the boring rod through a nylon tube (or high pressure hose) 27. In addition, when water pressure or oil pressure is used, 24 can also be a liquid pump.

28 is a pedestal installed at the mouth of the borehole, and 29
A notch is provided to facilitate installation from the side. A dial gauge 30 is installed on this pedestal, and a measuring rod for measuring the rotational displacement (or rotation angle) of the boring rod is attached to the mounting part of the rotary torque meter which is fixed to the boring rod and rotates integrally with it. In addition to indicating the amount of displacement of 31 with a pointer, it can be connected to an external recorder using an electric converter and recorded manually.

Reference numeral 32 denotes a rotary arm for external force of the rotary torque meter, and by rotating this arm manually, a rotary torque is applied to the boring rod to cause rotational displacement.

33 is the output cable of the rotational torque meter, 34 is the output cable of the rotational displacement dial gauge, both of which are input to an electric amplifier (torque amplifier and displacement amplifier) 35, and the output thereof is - The relationship between the two is recorded on the recording paper 37 by the Y recorder as the rotational displacement on the X-axis and the rotational torque (or directly displaying the shear stress τ) on the Y-axis.

(3) Test method The test method using the test equipment described in (2) above is as follows.

Regarding Figs. 4 and 5, the pressurized/rotating test cylindrical tube consisting of 1 to 15 is connected to the boring rod 16 and lowered to the bottom of the hole, and the rotating torque meter 19 is connected to the aboveground part of the boring rod. After fixing and tightening the spindle chuck 21,
Pull the entire boring rod up about 3 to 5 cm and secure it in place. The purpose of this lifting operation was to release the pressure at the bottom of the hole before the test due to the boring rod, the rotating torque meter fixed to it, and other overload loads.

Next, an airtight cap 23 is placed at the top of the boring rod.
and connect the nylon tube 27 to the pressure reducing valve 25 attached to the compressed gas cylinder 24. After placing the mount 28 at the hole opening and arranging the spindle of the dial gauge 30 so as to be in contact with the rotational displacement measuring rod 31,
The electric converter output cables of the rotating torque meter 19 and the dial gauge 30 are connected to an electric amplifier 35, and the output thereof is connected to an XY recorder 36.

After the above preparation operations, perform the test according to the following steps.

(a) Open the valve of the compressed gas cylinder and use the pressure reducing valve to set the predetermined pressure for the first stage to the pressure chamber 1 through the nylon tube and the borehole of the boring rod.
7, and the piston 11 is pushed down to press and press the lower end crimping surface 3 of the test cylindrical tube to the hole bottom stratum. In this state, compression (consolidation) is performed for a predetermined time selected depending on the soil properties, and then the rotary arm 32 of the rotary torque meter is manually rotated in the direction of the arrow.
The speed of rotation in this case is controlled (strain control) while watching the pointer of the dial gauge so that the rotational displacement (or rotational angle) on the crimping surface is about 1%/min.

The process of this test is to record the relationship between rotational displacement and rotational torque (or shear stress) using an X-Y recorder 36.
It is drawn as a continuous curve on the paper 37 as shown in FIG. The first stage of the test is completed by increasing the rotational displacement until a curve showing a substantially constant residual shear strength exceeding the maximum shear strength is obtained.

(b) Next, close the valve of the compressed gas cylinder, open the pressure release valve, release the pressurized air in the boring rod and pressure chamber, and release the pressurization of the test cylindrical pipe, Gently rotate the test cylindrical tube connected to the hole several times to remove the crushed debris layer at the bottom of the hole near the lower end crimping surface, and attach the cutting edge crimping surface to the fresh stratum below.

(c) In the second stage test, the valve of the compressed gas cylinder is opened again in accordance with (a) above, and the pressure reducing valve sends air at a predetermined pressure through the inner hole of the boring rod into the pressure chamber to push down the piston. After pressing the lower end of the test cylindrical pipe against the hole bottom stratum and compressing (consolidation) in that state, the rotating arm of the rotating torque meter is rotated to determine the relationship between rotational displacement and rotational torque (or shear stress). Record.

(d) Perform the procedure described in (b) below and test each pressurization stage according to the procedure in (a) or (c).

The steps of pressurization in the above test operations are usually 4
~5 stages is appropriate. In addition, before and after this test operation, the rotational torque value with no pressurization was also measured, and the torque based on the frictional resistance of the rotating part and the contact part with the hole wall that occurs as the boring rod rotates was also determined. Then, this value is subtracted and corrected from the rotational torque value at each pressurization stage.

In actual test examples, the compression pressure σ _o in the pressing stage is in the range of 0.50 to 4.5 _Kg /cm ² for fine sand layers and clay layers. In addition, an example of the measured value of the fine sand layer is as follows, and φ
= 32.0°, and a shear strength constant of C = 0 to 0.03 Kg/cm ² was obtained.

σ _o (Kg/cm ² ) 0.5 1.2 2.1 3.0 4.1 τ _nax (Kg/cm ² ) 0.3 0.75 1.3 1.9 2.6

[Brief explanation of drawings]

FIGS. 1A and 1B are explanatory diagrams showing the basic principle of the present invention. Figure 2 shows the measured relationship between shear stress and rotational displacement of the test cylindrical tube, and Figure 3 shows the relationship between shear stress and rotational displacement of the test cylindrical tube.
FIG. 3 is a shear strength diagram diagrammatically drawn from the figure. FIG. 4 shows an example of the pressurization/rotation test device part of the present invention,
Figure 5 shows the pressurization/rotation test equipment section and the ground operation equipment section as one unit.

Claims (1)

[Claims] 1. A test cylindrical tube with teeth or grooves cut into the bottom end of a borehole drilled in the ground is crimped by a piston that is moved by a load from above or fluid pressure such as water pressure, oil pressure, or compression pressure. This test cylinder is characterized by applying an external force moment and rotating it to shear the strata at the bottom of the hole in a ring shape. A field test method in which the torque value is measured, and the internal friction angle (φ) and cohesive force (C), which are the shear strength constants of the strata, are determined from the relationship between the two in terms of fracture shear strength and residual shear strength.