A method for testing the tensile strength of the interface of traditional rammed earth ruins

Abstract

The present invention relates to a method for testing the tensile strength of the interface of a rammed earth sample layer. Silicone acrylic emulsion and epoxy resin are applied to both end surfaces of the sample, respectively, the two ends of the sample are reinforced, and the two ends are tightly adhered to the tensile sheet through an adhesive. The tensile sheet with a handle is pasted and connected to a universal testing machine. The tensile rate of the universal testing machine is adjusted. After stress-strain calculation, the tensile strength of the sample σ=F / S and the interfacial strain of the sample layer ε=△L / L0 are obtained. The method is simple to operate, easy to apply, and low in cost. It has a wide range of application scenarios in measuring the tensile strength of the interface of rammed earth layers.

Description

Technical Field

[0001] The present invention relates to the field of earthen site protection test research and protection reinforcement, and is an important method for studying the internal force of the interface of traditional rammed earth site layers, and is particularly important for studying the internal force distribution characteristics of the weak area of ​​the interface of the rammed earth structure layer under the action of static force, seismic force, etc. The method can also be applied to related fields such as geotechnical engineering. Background Art

[0002] There are many ancient earthen building sites in Xinjiang, Gansu, Ningxia and Shaanxi in the northwest of my country, including the Great Wall winding in the north, the pass and beacon towers on the vast Gobi Desert in the northwest, and the Jiaohe, Gaochang, Loulan and Niya sites in Xinjiang. They are thousands of years old and spread across China. These earthen building sites have a long history. Some have been listed as world cultural heritage sites with high archaeological and historical value. Affected by the construction technology, the interface of the rammed earth layer is relatively fragile. Under the influence of long-term natural and human factors, the interface of the layer first suffers from various diseases such as surface weathering, erosion, and development of transverse cracks. Under the action of the gravity of the site body, local cracks or crushing are formed, forming through-layered cracks until collapse. This disease is one of the main factors threatening the long-term preservation of the site body. The investigation found that the flat-bottomed rammed earth layer and shallow rammed earth pits make the site more prone to layered collapse and destruction.

[0003] In general, soil strength mainly refers to shear and compressive strength, while tensile strength is often ignored. However, a large number of experiments have found that the tensile damage of rammed earth sites is the main factor in the overall damage of rammed earth bodies. Because the contact between the layers of the rammed earth body is relatively weak, its tensile strength is much lower than the compressive strength of the soil body. Under the action of external forces, it is often the first to be torn apart. Therefore, studying the tensile strength of the rammed earth body interface has important engineering practical significance. However, the commonly used laboratory soil compressive strength test methods include soil beam bending method, radial splitting method and axial fracturing method. These methods are not practical for testing the tensile strength of the interface of traditional rammed earth sites, especially they cannot truly reflect the tensile strength of the interface. In view of this, through a large number of experiments, it is found that the tensile strength test of rammed earth using uniaxial tension is the most effective and direct method. Summary of the invention

[0004] Tensile strength is an important indicator for evaluating the integrity of clay bodies, but there are relatively few engineering practices and studies on it. Problems such as local compression and tension of ruins soil, weathering and erosion of layer interfaces, layered peeling in suspended areas, and interlayer sliding collapse are closely related to the tensile strength of the rammed earth layer interface. In order to overcome the limitations of existing testing machines in testing the tensile damage of reshaped soil samples, it is especially difficult to test the bite force of the interface of traditional rammed layers. To this end, the purpose of the present invention is to provide a method for testing the tensile strength of the interface of traditional rammed ruins layers. This method uses a chemical reinforcement to reinforce the two ends of the reshaped soil sample, and sticks a tensile sheet on the sample to be tested, and then connects it to the WDW-200 microcomputer-controlled electronic universal testing machine through the tensile sheet hook to achieve the full process of tensile damage of the sample, thereby effectively measuring the maximum tensile strength of the sample interface.

[0005] The purpose of the present invention is to be achieved through the following technical solutions:

[0006] A method for testing the tensile strength of the interface of a traditional rammed earth ruins layer, the steps of which are:

[0007] 1. Production of tension sheet

[0008] (1) Sample preparation: A non-interface tensile strength sample with a diameter of 61.8 mm and a height of 41.7 mm was prepared. The test sample was a two-layer compacted sample with a single-layer compacted thickness of 41.7 mm and a double-layer compacted thickness of 83.4 mm. The sample was naturally dried in the shade. The actual tensile sample thickness was 20 mm and the moisture content of the sample was 2±0.5%.

[0009] (2) The specimen is centered and 10% silicone-acrylic emulsion is applied to the upper and lower ends of the specimen for reinforcement. The reinforcement depth is strictly controlled within the range of 5±1mm, and the penetration amount of silicone-acrylic emulsion at both ends of the specimen is controlled to be no less than 3ml;

[0010] (3) After the reinforced silicone-acrylic emulsion is completely dry for 48 hours, evenly apply epoxy resin on both ends of the silicone-acrylic emulsion with a thickness of 2 mm. Then, a 70 mm × 70 mm × 5 mm square tension sheet with a handle is bonded and buckled on the epoxy resin and squeezed;

[0011] (II) Test of tensile strength of sample interface

[0012] (1) Effectively connect the tensile plates with handles at both ends of the specimen to the clamps of the electronic universal testing machine;

[0013] (2) Adjust the tensile rate of the universal testing machine to 0.5 mm / min, apply an initial load of 0.001 KN to the specimen, and then reset the force and displacement to zero;

[0014] (3) Click the Start Test button to start the tensile test until the sample is completely destroyed. Click the Stop Test button to end the tensile test of the sample and obtain the tensile force F.

[0015] (4) Save test data;

[0016] (5) The test results are calculated to obtain the tensile strength of the sample σ = F / S and the interface strain of the sample layer ε = △L / L0, and the tensile strength curve of the sample layer interface is drawn:

[0017] Where:

[0018] σ represents the uniaxial tensile strength of the specimen;

[0019] F represents the maximum tensile force, the maximum tensile force at which the specimen breaks;

[0020] S represents the cross-sectional area of ​​the specimen;

[0021] ε represents the strain corresponding to the maximum tensile stress;

[0022] △L represents the displacement corresponding to the maximum tensile stress;

[0023] L0 represents the effective length of the sample.

[0024] The advantages and beneficial effects of the present invention are:

[0025] (1) The present invention uses 10% silicone acrylic emulsion to reinforce the two ends of the sample to be tested, and tightly adheres to the tensile sheet through an adhesive to avoid deformation of the sample caused by the sample fixture and crushing by confining pressure, thereby achieving a good direct test of the tensile strength of the layer interface; the tensile sheet is adhered to the two ends of the sample by epoxy resin, and a uniform force of 0.5 mm / min is achieved through the tensile sheet with the help of a universal testing machine.

[0026] (2) It can achieve a relatively stable testing process with high test accuracy and can adapt to the measurement of soil tensile strength under a variety of complex soil conditions.

[0027] (3) The present invention can be applied to the testing of the tensile strength of rocky, porous, and fragile materials that cannot meet the pressure requirements of the universal testing machine clamp.

[0028] (5) The present invention is simple to operate, convenient to apply, and low in cost, and has a wide range of application scenarios in measuring the tensile strength of the interface of rammed earth layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the tension sheet;

[0030] Figure 2 Schematic diagram of the assembly of the tensile sheet and the testing machine. DETAILED DESCRIPTION

[0031] The universal testing machine used in the present invention is a WDW-200 microcomputer-controlled electronic universal testing machine produced by Tianshui Hongshan Testing Co., Ltd. for tensile strength testing. The tensile rate is 0.5 mm / min, and the moisture content of the sample during the experiment is 2±0.5%.

[0032] The present invention will be further described below in conjunction with the accompanying drawings:

[0033] A method for testing the tensile strength of the interface of a traditional rammed earth ruins layer, the steps of which are:

[0034] 1. Production of tension sheet

[0035] (1) Sample preparation: Jiaohe soil was collected to prepare a tensile strength sample without interface with a diameter of 61.8 mm and a height of 41.7 mm. Sample 1 was directly compacted and formed into a two-layer compacted sample with smooth, rough and tamped surfaces. The single-layer compacted thickness was 41.7 mm and the double-layer compacted thickness was 83.4 mm. The sample was naturally dried in the shade. To meet the requirements for the end reinforcement height of the tensile strength sample, the actual tensile sample thickness was ensured to be 20 mm. The sample was dried in the shade for 36-48 hours, and the moisture content of the sample was 2±0.5%;

[0036] (2) The sample is centered and 10% concentration of silicone-acrylic emulsion 2 is used to smear and reinforce the upper and lower ends of the sample. The reinforcement depth is strictly controlled within the range of 5±1mm, and the penetration amount of silicone-acrylic emulsion 2 reinforced sample is controlled to be no less than 3ml;

[0037] (3) After the reinforced silicone-acrylic emulsion is completely dry for 48 hours, the strength of the two ends of the sample 1 reinforced by the silicone-acrylic emulsion 2 is higher than that of the sample in the middle area. The epoxy resin 3 is evenly applied on both ends of the silicone-acrylic emulsion 2 with a thickness of 2 mm. Then, a 70 mm × 70 mm × 5 mm square pull tab 4 with a handle is bonded and pressed on the epoxy resin 3. Appropriate force is applied to ensure that the pull tab is completely and tightly in uniform contact with the sample 1 to prevent the epoxy resin from flowing to the middle area of ​​the sample and affecting the test results.

[0038] (II) Test of tensile strength of sample interface

[0039] (1) Effectively connect the tensile plates 4 with handles at both ends of the specimen to the clamps of the electronic universal testing machine 5;

[0040] (2) Adjust the tensile rate of the universal testing machine 5 to 0.5 mm / min, apply an initial load of 0.001 KN to the specimen, and then reset the force and displacement to zero.

[0041] (3) Click the start test button of the universal testing machine 5, and the tensile test begins until the sample is completely destroyed. Click the stop test button to end the tensile test of the sample and obtain the tensile force F.

[0042] (4) Save the test data.

[0043] (5) The test results show that the tensile strength of the sample is σ = F / S and the interface strain of the sample layer is ε = △L / L0.

[0044] Where:

[0045] σ represents the uniaxial tensile strength of the specimen;

[0046] F represents the maximum tensile force, the maximum tensile force at which the specimen breaks;

[0047] S represents the cross-sectional area of ​​the specimen;

[0048] ε represents the strain corresponding to the maximum tensile stress;

[0049] △L represents the displacement corresponding to the maximum tensile stress;

[0050] L0 represents the effective length of the sample.

[0051] In order to determine the tensile strength of the interface of the traditional rammed earth ruins, samples of different interfaces were collected during the actual operation. In order to reduce the influence of density and moisture content on the results, the density of each group of samples was similar (the difference in density was no more than ±0.01g / cm 3 ), the difference in moisture content of each group of samples is no more than ±1%. Finally, the influence of different layer interface treatment methods and ramming layer increase on tensile strength is comprehensively evaluated.

Claims

1. A method for testing the tensile strength of the interface of a traditional rammed earth site layer, comprising the following steps:

1. Production of tension sheet (1) Preparation of samples (1) Prepare a non-interface tensile strength sample with a diameter of 61.8 mm and a height of 41.7 mm. The test sample is a two-layer compacted sample with a single-layer compacted thickness of 41.7 mm and a double-layer compacted thickness of 83.4 mm. Naturally dry in the shade. The actual tensile sample thickness is 20 mm. The moisture content of the sample is 2±0.5%; (2) The specimen (1) is centered and a 10% silicone-acrylic emulsion (2) is applied to the upper and lower ends of the specimen for reinforcement. The reinforcement depth is strictly controlled within the range of 5±1 mm, and the penetration amount of the silicone-acrylic emulsion (2) into the specimen (1) is controlled to be no less than 3 ml; (3) After the reinforced silicone-acrylic emulsion (2) is completely dry for 48 hours, epoxy resin (3) is evenly applied to both ends of the silicone-acrylic emulsion (2) with a thickness of 2 mm. Then, a 70 mm×70 mm×5 mm square tension sheet with a handle (4) is bonded and pressed onto the epoxy resin (3) and squeezed with force; (II) Test of tensile strength of sample interface (1) Effectively connect the tensile plates with handles at both ends of the specimen to the clamps of the electronic universal testing machine (5); (2) Adjust the tensile rate of the universal testing machine (5) to 0.5 mm / min, apply an initial load of 0.001 kN to the specimen, and then reset the force and displacement to zero; (3) Click the Start Test button to start the tensile test until the sample is completely destroyed. Click the Stop Test button to end the tensile test of the sample and obtain the tensile force F. (4) Save test data; (5) The test results are calculated to obtain the tensile strength of the sample σ = F / S and the interface strain of the sample layer ε = △L / L0: Where: σ represents the uniaxial tensile strength of the specimen; F represents the maximum tensile force, the maximum tensile force at which the specimen breaks; S represents the cross-sectional area of ​​the specimen; ε represents the strain corresponding to the maximum tensile stress; △L represents the displacement corresponding to the maximum tensile stress; L0 represents the effective length of the sample.

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