JPH0451640B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method of fixing reinforcing anchors in the ground by injecting an improved fixing material into insertion holes for reinforcing anchors drilled in the ground. . [Prior Art and Problems] Recently, during tunnel construction, methods have been frequently used to reinforce the ground or prevent collapse of the slope of the ground by driving reinforcing anchors such as lock bolts and earth anchors. These methods include injecting cement mortar into the insertion hole together with reinforcing anchors and fixing it, and using resin instead of cement mortar.More recently, the fixing material for cement mortar has been given expandability. A method has been proposed to improve the adhesion between the rock hole wall and cement mortar in rock insertion holes. (Unexamined Japanese Patent Publication No. 1983-
(No. 62216, Japanese Unexamined Patent Publication No. 156398/1982) However, in either method, there was no way to establish the necessary pull-out strength of the ground itself, so it was difficult to use cement resin or It was used in the production of common cement-concrete products by simply mixing expansive admixtures. As a result, there are many cases in which the required quality is not satisfied for the pull-out strength of cement mortar after hardening, and to compensate for this, methods such as increasing the length of reinforcing anchors are taken, making the construction work more complicated and the construction period longer. It became uneconomical. Also, in the method of mixing expansion materials, whether it is increasing the frictional force with the rock or suppressing the bulge of soft rock into the insertion hole, it is important to ensure that the expansion pressure of cement mortar matches the physical properties of the ground. Because they were not satisfied, they were not able to achieve satisfaction. [Object of the Invention] The object of the present invention is to improve the shortcomings of the conventional anchoring methods as described above, and to fix reinforcing anchors that reliably exhibit the necessary pull-out strength in accordance with the physical properties of the ground to be constructed. The purpose is to provide a method. [Structure of the Invention] The present invention measures the physical properties of the ground on which reinforcing anchors are installed, and determines the minimum value that the anchoring material injected into the insertion hole must exhibit based on the physical property values and the required pull-out strength. The critical expansion pressure is determined by the following equation, and the fixing material is mixed with an expansion material that exhibits an expansion pressure higher than the critical expansion pressure. That is, in the method of anchoring reinforcing anchors to the ground where the physical properties of the ground are C≧0.1 φ≠0 C: Adhesive force of the ground (Kgf/cm ² ) φ: Angle of internal friction of the ground (degrees) P ₀ = (T /2πa-C) tanφ (Kgf/cm ² ) P ₀ : Critical expansion pressure of injection fixing material (Kgf/cm ² ) a: Insertion hole radius of reinforcing anchors (cm) T: Required pull-out strength of reinforcing anchors ( Kgf/
Reinforcing anchors are anchored in the ground using an anchoring material mixed with an expanding material at a mixing ratio of 12.5 to 100% so as to exert an expansion pressure higher than the critical expansion pressure determined by cm). [Description of the invention] The conventional method of fixing rock bolts to the ground, earth anchors, etc. to the ground using cement mortar assumes that the ground or rock itself is a strong and rigid body with great strength. Therefore, the main function of cement mortar is to exert a strong adhesion force to the ground, and improvements have been made to improve its bonding ability with the ground and its resistance through frictional force with the ground. Therefore, in cases where the ground is soft, long bolts or the like must be driven to obtain the required anchoring force, or if it is determined that the anchoring force cannot withstand the problem, other construction methods have been used. The present invention is based on an idea fundamentally different from the conventional idea as described above. In other words, the core technical idea of the present invention is to "improve the ground to increase the strength of the ground while also increasing the adhesion force with cement mortar," and the conventional idea was to use reinforcing anchors. This enables reliable and economical reinforcing bolt construction even on soft ground where it is difficult to install reinforcement bolts. Next, the present invention will be specifically explained. Figure 1 is a diagram illustrating the stress state of the ground when a tensile force is applied by constructing a reinforcing anchor using an anchoring material that generates expansion pressure in the ground.
is the ground, 2 is the anchoring material, 3 is the lock bolt, τ is the shear failure strength of the ground (Kgf/cm ² ), σ _r is the compressive stress perpendicular to the ground failure surface (Kgf/cm ² ), and a is the reinforcement anchor insertion hole diameter (cm), r indicates the diameter to the ground failure surface (cm), and P indicates the expansion pressure of the anchoring material (Kgf/cm ² ), respectively. Further, FIG. 2 is a diagram showing a state in which cracks have occurred in the ground, FIG. 3 is a diagram illustrating a Mohr-Coulomb stress circle, and FIG. 4 is a diagram illustrating a state of pull-out strength. In FIG. 1, the shear fracture strength, which mainly affects the pull-out strength of the lock bolt, is expressed by the following equation. τ=C+σ _r tanφ (Kgf/cm ² ) C: Adhesive force of the ground (Kgf/cm ² ) φ: Internal friction angle of the ground (degrees) Here, inject the fixing material into the reinforcing anchor insertion hole. Assume an inflated state. In other words, in soft ground such as a sandy mountain due to the expansion pressure applied to the wall of the insertion hole, cracks with a depth of r ₀ occur in the ground as shown in Figure 2, and the reinforcing anchor The stress relationship in the ground changes at the wall of the insertion hole and at the crack end on the horizontal axis shown in the representative example. Considering this from a soil engineering perspective, it is as follows. (Prerequisites) The physical properties of the ground are C: Same as above φ: Same as above _σt : Tensile strength of the ground (Kgf/cm ² ). It is assumed that there is no initial ground pressure. (Ground condition) Cracked area (a≦r≦r ₀ ) σ _r =A×1/r (Kgf/cm ² ) (Curve a in Figure 2) σ=0 However, P=A×1/a Crack (r ₀ ≦ r) σ _r = B×1/r ² (Kgf/cm ² ) (Curve b in Figure 2) σ = −σ _r = −B×1/r ² (Kgf/cm ² ) However, σ _t =−σ〓=B×1/r ₀ ^2Since σ _r in the above is also in a continuous state at the point r ₀ , the following relationship occurs. A×1/r ₀ =B×1/r ₀ ² Therefore, each of A, B, and r ₀ is determined as follows. A=P・a B=(P・a) ² /σ _t r ₀ =P・a/σ _t From the above, the pull-out strength T per unit length is
As shown in Figure 1, T=2πr×(C+σ _r tanφ) T ₍₁₎ =2πCr+2πPa tanφ ...(1) (a≦r<r ₀ ) T ₍₂₎ = _2πCr +2π Pa) ² ×tanφ×1/r ……(2) (r ₀ ≦r), and equations (1) and (2) are continuous at r=r ₀ . Then, the minimum values of equations (1) and (2) without considering the range of r are as follows. T _(1)nio =2πr _a (C+Ptanφ) (rT _(1)nio =a) Here, if we compare r ₀ and r _(2)nio , we find that r ₀ = Pa/σ _t due to the ground condition. become. Therefore, if there is no initial ground pressure, the stress in the ground due to expansion pressure alone is always σ _r =
-σ〓 (see curve c in Figure 2) becomes a state of pure shear stress, and the so-called tensile strength σ _t is obtained from the Mohr-Coulomb stress circle shown in Figure 3: σ _t = -σ〓 _y = σ _ry = C cosφ However, σ〓 _y : Stress in the circumferential direction at the time of pure shear failure σ _ry : Expressed as the stress in the radial direction at the time of pure shear failure. Therefore, (rT _(2)nio /r ₀ ) ² = sinφ≦1 ∴r _(2)nio ≦r ₀ , and as shown in Figure 4, the state of the pull-out strength T is the weakest near the insertion hole wall. As a result, it turns out that you can pull it out from there. That is, from equation (1), T _nio = 2πa (C + P tanφ) (r = a) ∴P ₀ = (T/2πa - C) / tanφ (Kgf/cm ² )...(3
), and the minimum expansion pressure (critical expansion pressure) required for the filling material when the necessary pull-out strength T is given.
P ₀ is obtained by equation (3). As is clear from the above, according to the present invention, which improves the ground by applying a compressive force that matches the physical properties of the target ground to the ground using the expansion pressure of the anchoring material, the physical properties of the ground, C, φ, reinforcing anchor. If you know the pull-out strength, T, required for the reinforcing anchor, and the radius, a, of the hole into which the reinforcing anchor is inserted, you can very easily select an anchoring material that produces the required expansion force, and you can create an economical and reliable reinforcing anchor. Retention can be carried out. Once the target ground is determined, the procedure for selecting the expandable material to be mixed into the fixing material is as follows. The adhesion force C and internal friction angle φ of the target ground are determined by investigating the ground. Determine the pull-out strength T required of the ground and the size a of the reinforcing anchor insertion hole to be constructed in the ground. The critical expansion pressure P ₀ is calculated using the above equation (3). An intumescent material is selected that generates an inflating pressure equal to or higher than the critical inflating pressure after curing. [Embodiments of the Invention] Examples of the present invention will be described below. Example 1 FIG. 5 is a diagram illustrating the measurement results of the pull-out strength in a demonstration experiment on the ground. Ground: Diluvial sandy soil C: 0.25 (Kgf/cm ² ) φ: 35 (degrees) Required pull-out strength of lock bolt: 50 (Kgf/cm) Lock bolt insertion hole diameter: 5 (cm) ∴P ₀ = (50/ 2π×2.5−0.25)/0.700=4.2 (Kgf/cm ² ) It was decided to use an expansion material that generates an expansion pressure higher than the above critical expansion pressure P ₀ .

【table】

[Table] In the demonstration experiment on the ground, a lock bolt hole with a diameter of 5 cm and a depth of 2 m was drilled in the ground, a irregularly shaped lock bolt with a diameter of 2.5 cm was inserted, and a fixing material mixed with each of these samples was injected and hardened. Attach the board,
The pull-out strength was measured by pulling with a jack. The results are shown in Table 2 and Figure 4.

[Table] As the results show, even when using the same sample, the physical properties of the ground differ slightly depending on the position where the lock bolt is inserted, so there is considerable variation in the pull-out strength. In addition, in Fig. 5, the × mark indicates the original data;
The circle indicates the average value. However, in terms of average values, existing commercially available products do not meet the required pull-out strength at all, regardless of whether expansion material is mixed in or not. In contrast, samples A ₁ to _{A 3} mixed according to the present invention showed the expected results. That is, sample A ₁ : Although the expansion pressure was close to the critical expansion pressure, since the expansion pressure was lower than that, the required pull-out strength was slightly insufficient. Sample A ₂ : Since an expansion pressure higher than the critical expansion pressure was generated, the required pull-out strength was satisfied. Sample A ₃ : Since the expansion pressure was generated much higher than the critical expansion pressure, the area below the required pull-out strength was extremely small. However, because the filler itself became brittle due to expansion, the pull-out strength was lower than that of sample _A2 . From the above results, by employing the intumescent material according to the present invention, it has become possible to use reinforcing anchors even on soft ground, where the application of reinforcing anchors has not been considered at all until now. Example 2 The condition of the ground around the Kanto region is as shown in Table 3, so
The expansion pressure of the fixing material applied here under the same requirements as in the example is shown in the same table.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, in the ground where the physical properties of the ground are 0.1≦C and φ≠0, P ₀ = (T/2πa−C)/tanφ (Kgf/cm ² ). This method involves fixing reinforcing anchors while improving the ground by adding pressure to the ground by mixing an inflatable material that exerts an inflation pressure higher than the critical inflation pressure determined by the anchoring material. It is economical because it allows the mixing of an appropriate expansion material that corresponds to the physical properties of the ground, and it also has the effect of reliably securing the required pull-out strength. Furthermore, the application range of the reinforcing anchors is wide-ranging, from soft ground such as alluvial sandy soil to soft rock, which has not been considered in the past.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the stress state of the ground when a tensile force is applied by constructing a reinforcing anchor using an anchoring material that generates expansion pressure in the ground, and Figure 2 shows the state of stress in the ground when cracks have occurred in the ground. Figure 3 is a diagram to explain the Mohr-Coulomb stress circle, Figure 4 is a diagram to explain the state of pull-out strength, and Figure 5 is a diagram to explain the state of pull-out strength.
The figure is a diagram illustrating the measurement results of the pull-out strength in a demonstration experiment on the ground. 1...Ground, 2...Fixing material, 3...Lock bolt.

Claims (1)

[Claims] 1. A method for fixing reinforcing anchors to the ground where the physical properties of the ground are C≧0.1 φ≠0 C: Adhesive force of the ground (Kgf/cm ² ) φ: Angle of internal friction of the ground (degrees) P ₀ = (T/2πa-C) tanφ (Kgf/cm ² ) P ₀ : Critical expansion pressure of injection fixing material (Kgf/cm ² ) a: Radius of insertion hole of reinforcement anchors (cm) T: Reinforcement anchors Required pulling strength (Kgf/
A method of anchoring reinforcing anchors in the ground using an anchoring material mixed with an expansion material at a mixing ratio of 12.5 to 100% so as to exert an expansion pressure higher than the critical expansion pressure determined by cm).