Method for preventing fracture along end face of rock sample

Abstract

The invention discloses a method for preventing fracture along the end face of a rock sample, relates to a rock tensile test technology, is applied to a rock direct tensile test, and comprises the following steps: estimating the deformation modulus of rock according to the density and ultrasonic propagation velocity of the rock sample; according to the estimated deformation modulus of the rock, a pull head with the adaptive height is determined; the puller and the rock sample are bonded together through the structural adhesive, and it is guaranteed that the structural adhesive layer at least has the specified thickness after bonding; and adding a circle of structural adhesive around the bonding interface. According to the method, the structural adhesive layer is kept to have a certain thickness, the height of the stainless steel pull head is increased, and a circle of structural adhesive is added around the bonding interface, so that the tensile stress of the end face of the rock sample can be reduced to be smaller than an average value, early fracture along the end face is avoided, and the accurate rock tensile strength can be tested.

Description

Technical Field

[0001] The invention relates to a rock uniaxial direct tensile test method, in particular to a test method for preventing premature fracture along the end face of a rock sample during a rock uniaxial direct tensile test. Background Art

[0002] During the excavation of rock slopes, foundation pits, and underground caverns, tensile stress will be generated in the rocks at some locations (such as the top of the slope, the top of the pit, and the top of the arch). Rocks have strong compressive strength but weak tensile strength. Their tensile strength is generally 1 / 4 to 1 / 25 of their compressive strength, with an average of 1 / 10. Therefore, tensile stress can easily cause tensile failure of rocks and lead to geotechnical engineering disasters. In order to ensure the safety of the project, surveyors need to test the tensile modulus and tensile strength of rocks to provide accurate tensile mechanical parameters for engineering design and construction.

[0003] The most accurate method to test the tensile modulus and tensile strength of rock is the uniaxial direct tensile test of rock. Before the tensile test, the upper and lower end faces of the rock sample are respectively bonded to two stainless steel pull heads by structural adhesive, and then the stainless steel pull heads are connected to the testing machine for tensile test. However, during the test, fractures often occur along the end faces of the rock sample, resulting in the inability to accurately test the tensile strength of the rock. There are two reasons for this fracture: one is the stress concentration at the end face of the rock sample, and the other is the relatively weak rock at this location caused by the cutting and grinding of the end face when making the cylindrical sample. Some papers propose the use of dumbbell-shaped or dog-bone-shaped rock samples to ensure that fractures do not occur at the end face, but the production cost of such rock samples is very high, so they cannot be widely used in engineering practice. Summary of the invention

[0004] The embodiment of the present application provides a method for preventing fracture along the end face of a rock sample, thereby ensuring that premature fracture does not occur along the end face, and achieving accurate testing of the tensile strength of the rock.

[0005] The embodiment of the present application provides a method for preventing fracture along the end face of a rock sample, which is applied in a direct tensile test of rock, and includes:

[0006] The deformation modulus of rock is estimated based on the density of rock sample and the ultrasonic wave propagation velocity;

[0007] According to the estimated deformation modulus of the rock, the pull head with suitable height is determined;

[0008] The pull head is bonded to the rock sample by means of structural adhesive, and after bonding, the structural adhesive layer is ensured to have at least a specified thickness;

[0009] Add a circle of structural adhesive around the bonding interface.

[0010] Optionally, the deformation modulus of the rock is estimated to satisfy the following condition based on the density of the rock sample and the ultrasonic wave propagation velocity:

[0011] E r =0.233ρν 2

[0012] Among them, E r is the estimated deformation modulus of rock, ρ represents the density of rock sample, and ν is the ultrasonic propagation velocity.

[0013] Optionally, according to the estimated deformation modulus of the rock, determining the pull head of the appropriate height includes:

[0014] In E r When the height is ≤2.5, use a 3cm high slider;

[0015] In 2.5 <E r When the height is ≤10.0, use a 5cm high slider;

[0016] In E r If the height is >10.0, use a slider that is higher than 7cm.

[0017] Optionally, the pull head is bonded to the rock sample by structural adhesive, including:

[0018] During bonding, the structural adhesive layer is ensured to be full by extrusion, and the extrusion distance is controlled to ensure that the structural adhesive layer after bonding has a thickness of at least 1 mm.

[0019] Optionally, adding a circle of structural adhesive around the bonding interface includes: aligning the maximum thickness of the structural adhesive added around the bonding interface with the middle line of the structural adhesive layer.

[0020] The method of the present application can reduce the tensile stress on the end face of the rock sample to less than the average value by maintaining a certain thickness of the structural adhesive layer, increasing the height of the stainless steel pull head, and adding a circle of structural adhesive around the bonding interface, thereby ensuring that premature fracture will not occur along the end face, thereby achieving accurate testing of the tensile strength of the rock.

[0021] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0023] Figure 1 The basic process diagram of the method for preventing fracture along the end face of a rock sample according to the present embodiment is shown;

[0024] Figure 2 Schematic diagram of pull heads at different heights in the method of this embodiment;

[0025] Figure 3 It is a schematic diagram of bonding the pull head to the rock sample in the method of this embodiment;

[0026] Figure 4 The method of this embodiment is to add a circle of structural adhesive around the bonding interface. DETAILED DESCRIPTION

[0027] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0028] The present application embodiment provides a method for preventing fracture along the end face of a rock sample, which is applied in a direct tensile test of a rock. Figure 1 As shown, the following steps are included:

[0029] In step S101, the deformation modulus of the rock is estimated according to the density of the rock sample and the ultrasonic propagation velocity. In a specific example, the deformation modulus of the rock estimated according to the density of the rock sample and the ultrasonic propagation velocity satisfies:

[0030] E r =0.233ρν 2

[0031] Among them, E r is the estimated deformation modulus of rock (unit: GPa), ρ represents the density of rock sample (unit: g / cm 3 ), ν is the ultrasonic propagation speed (unit: m / s).

[0032] In step S102, the suitable height of the slider 1 is determined according to the estimated deformation modulus of the rock.

[0033] In step S103, the pull head is bonded to the rock sample by means of structural adhesive, and after bonding, it is ensured that the structural adhesive layer has at least a specified thickness.

[0034] In step S104, a circle of structural adhesive is added around the bonding interface.

[0035] In some embodiments, Figure 2 As shown, according to the estimated deformation modulus of the rock, the slider 1 for determining the adapted height includes:

[0036] In E r When the height is ≤2.5, use a 3cm high slider;

[0037] In 2.5 <E r When the height is ≤10.0, use a 5cm high slider;

[0038] In E r If the height is >10.0, use a slider that is higher than 7cm.

[0039] In some embodiments, the structural adhesive is epoxy resin adhesive or acrylic adhesive.

[0040] In some embodiments, bonding the pull head and the rock sample together by structural adhesive includes:

[0041] During bonding, the structural adhesive layer is ensured to be full by extrusion, and the extrusion distance is controlled to ensure that the thickness of the structural adhesive layer after bonding is at least 1mm. Figure 3 As shown, the pull head 1 and the rock sample 2 are bonded together in the center. During bonding, on the one hand, the structural adhesive layer 3 is ensured to be full by slow extrusion. On the other hand, the extrusion distance should be controlled so that the structural adhesive cannot be completely squeezed out. The thickness of the structural adhesive layer 3 should be at least about 1 mm.

[0042] In some embodiments, adding a circle of structural adhesive around the bonding interface includes: aligning the maximum thickness of the structural adhesive added around the bonding interface with the middle line of the structural adhesive layer. Adding a circle of structural adhesive 4 around the bonding interface, the thickness of the circle of structural adhesive 4 varies as follows Figure 4 As shown, the maximum thickness is about 2.5 mm, and the maximum thickness is basically aligned with the middle line of the structural adhesive layer 3. The height of a circle of structural adhesive 4 is about 15 mm, and the attachment height on the slider 1 is relatively small, and the attachment height on the rock sample 2 is relatively large.

[0043] The method of the present application maintains a certain thickness of the structural adhesive layer, increases the height of the stainless steel pull head, and adds a circle of structural adhesive around the bonding interface, which can reduce the tensile stress on the end face of the rock sample to less than the average value, thereby ensuring that premature fracture does not occur along the end face, and fracture only occurs in the middle of the sample, thereby testing the accurate tensile strength of the rock.

[0044] In addition, although exemplary embodiments have been described herein, the scope includes any and all embodiments based on the present disclosure with equivalent elements, modifications, omissions, combinations (e.g., various embodiments intersecting schemes), adaptations or changes. It is not limited to the examples described in this specification or during the implementation of this application, and its examples will be interpreted as non-exclusive.

[0045] The above description is intended to be illustrative rather than restrictive. For example, the above examples (or one or more of them) can be used in combination with each other. For example, those of ordinary skill in the art may use other embodiments when reading the above description.

[0046] The above embodiments are merely exemplary embodiments of the present disclosure. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present disclosure, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present invention.

Claims

1. A method for preventing fracture along the end face of a rock specimen, applied in a direct tensile test of rock, characterized in that: include: The deformation modulus of rock is estimated based on the density of rock sample and the ultrasonic wave propagation velocity; According to the estimated deformation modulus of the rock, the pull head with suitable height is determined; The pull head is bonded to the rock sample by means of structural adhesive, and after bonding, the structural adhesive layer is ensured to have at least a specified thickness; Add a circle of structural adhesive around the bonding interface.

2. The method for preventing fracture along the end face of a rock sample according to claim 1, characterized in that: According to the density of the rock sample and the ultrasonic propagation velocity, the deformation modulus of the rock is estimated to satisfy: E r =0.233ρν 2 Among them, E r is the estimated deformation modulus of rock, ρ represents the density of rock sample, and ν is the ultrasonic propagation velocity.

3. The method for preventing fracture along the end face of a rock sample according to claim 1, characterized in that: According to the estimated deformation modulus of the rock, the pull head with suitable height is determined to include: In E r When the height is ≤2.5, use a 3cm high slider; In 2.5 <E r When the height is ≤10.0, use a 5cm high slider; In E r If the height is >10.0, use a slider that is higher than 7cm.

4. The method for preventing fracture along the end face of a rock sample according to claim 1, characterized in that: The pull head and the rock sample are bonded together by structural adhesive, including: During bonding, the structural adhesive layer is ensured to be full by extrusion, and the extrusion distance is controlled to ensure that the structural adhesive layer after bonding has a thickness of at least 1 mm.

5. The method for preventing fracture along the end face of a rock sample according to claim 1, characterized in that: Adding a circle of structural adhesive around the bonding interface includes: aligning the maximum thickness of the structural adhesive added around the bonding interface with the middle line of the structural adhesive layer.

Images