LU500778B1 - Device for Determining Fracture Toughness of Soil by Self-weight and Use Method thereof - Google Patents

Abstract

The invention discloses a device for determining the fracture toughness of soil by self-weight and use method thereof. The device comprises a fixing unit, a sliding unit and a sliding control unit. The fix unit and that sliding unit are arrange in parallel and are vertically arranged on a horizontal test bench, the bottom of the fixed unit is fixedly connected with the horizontal test bench, and the bottom of the sliding unit is slidably connected with the horizontal test bench, the sliding unit is electrically connected with the sliding control unit for controlling the movement of the sliding unit. According to the method, the fracture toughness of different soil types can be determined, and important mechanical parameters are provided for studying the disaster mechanism of geological disasters such as soil landslide, ground collapse, initial debris flow, ground fissures and the like.

Description

DESCRIPTION LUS00778 Device for Determining Fracture Toughness of Soil by Self-weight and Use Method thereof

TECHNICAL FIELD The invention relates to the technical field of geological disaster reduction, in particular to a device for determining the fracture toughness of soil by self-weight and using method thereof.

BACKGROUND Mountainous hills are one of the five basic land terrains in the world, and many countries in the world have such terrains. With the establishment of large-scale engineering projects in various countries and the rapid development of mountain town construction, the number of geological disasters such as landslide, land subsidence and land subsidence is increasing, the geological disasters are becoming more and more serious, and the geological safety problems are becoming increasingly prominent. Ground fissures formed by landslide, land subsidence and land subsidence are common associated geological disasters at present, which are characterized by large number, wide coverage area, large penetration depth, long crack extension and large crack width. For example, in 2001, the Taping landslide occurred with a volume of millions of cubic meters. Once it collapsed, it would seriously affect the river channel. Four obvious tension and shear cracks occurred in the landslide area (Figure 1), with the cracks being 10-22 m long, 1-5 m wide and 0.2 m deep. In 2009, the Liangshuijing landslide in Yunyang County, the boundary cracks of the landslide have all penetrated and extended to the middle of the river. The cracks are 5-30 cm wide, exceeding 1.0 m locally, 10-45 cm high and exceeding 1.5m locally. In 2010, many ground collapses occurred, with a maximum diameter of more than 80 meters. From January to February 24th, 2012, a large-scale karst collapse geological disaster occurred in Yuejiagiao town (Figure 2), which affected the generation and life of thousands of local villagers. Therefore, it is particularly important to study the formation mechanism and effective prevention of soil cracks.

At present, soil cracks can be divided into three types according to their causes: HUS00778 structural cracks, non-structural cracks and mixed causes cracks, which reflect the macroscopic factors of soil cracks. But now more and more scholars begin to transform from macro mechanism to micro mechanism, and study the stress characteristics and parameters of soil, the most important of which is fracture mechanics mechanism. Fracture mechanics can effectively explain the scientific problems such as soil cracking, expansion, opening degree and depth estimation from the micro angle, and effectively evaluate the development of ground fissures. Therefore, the parameter test of fracture toughness KIC, which can effectively characterize soil properties, is an important link in analyzing the formation of soil cracks. At present, the standard three-point bending test is commonly used for testing the fracture toughness KIC of materials, and the three-point bending test is aimed at brittle materials such as steel bars, concrete and rocks. However, in view of the loose medium of soil, which is a non-tensile material in engineering, the sample is easy to be destroyed, and it is difficult to accurately test and obtain the fracture toughness of soil.

SUMMARY The purpose of the invention is to provide a device for determining the fracture toughness of soil by self-weight and a using method thereof, so as to solve the problems existing in the prior art. By using the device, the fracture toughness of different soil types can be determined, and important mechanical parameters are provided for studying the disaster mechanism of geological disasters such as soil landslide, ground collapse, initial debris flow, ground fissures and the like.

In order to achieve the above purpose, the present invention provides the following scheme: the present invention provides a device for determining the fracture toughness of soil by self-weight, which comprises a fixing unit, a sliding unit and a sliding control unit. The fix unit and that sliding unit are arrange in parallel, and are vertically arranged on a horizontal test bed; the bottom of the fixed unit is fixedly connected with the horizontal test bench, and the bottom of the sliding unit is in sliding connection with the horizontal test bench; the sliding unit is electrically connected with the sliding control unit, and the sliding control unit is used for HUS00778 controlling the horizontal movement of the sliding unit.

Optionally, the fixing unit adopts a fixed support.

Optionally, the sliding unit adopts a sliding support.

Optionally, the sliding support comprises a plurality of rectangular columns, and a plurality of first rolling units are arranged between the bottom of each rectangular column and the horizontal test bench; a plurality of second rolling units are arranged on the top of each rectangular upright post, and the length of the rectangular upright post is the same as the width of the test object.

Optionally, the first rolling units have the same diameter and equal spacing between them, and the second rolling units have the same diameter and equal spacing between them.

Optionally, the sliding control unit adopts a displacement controller, and the displacement rate of the displacement controller is not more than 3mm/ min, and the horizontal displacement is not more than 30 cm.

The invention also provides an application method of the device for determining the fracture toughness of the soil by self-weight, which comprises the following steps: S1, prefabricating a test object; S2, horizontally placing test object on the top of the fixed unit and the sliding unit; S3, starting the sliding control unit, so that the distance between the fixed unit and the sliding unit is gradually increased, and under the action of self-weight, the lower part of the mid-span test object is gradually in a tensile stress state; S4, observing and shooting the deformation and cracking of the lower part of the test object until a tensile crack appears; SS, when the tensile crack expands to a certain critical depth ao, the test object suddenly breaks, and the sliding control unit is closed, and the effective length S and the critical depth ao of the test object when breaking are recorded,

S6, according to the effective length s and the critical depth ao, calculate the HUS00778 fracture toughness of the test object according to the method shown in formulas (D-2): K, = 3.975M{h— ag) "> (I) M = 2 yhS? 8 2) in which, Ki is the fracture toughness of soil kKN.m7*5; y is the weight of soil (KN/m°); h is the thickness of soil beam (m); ao is the critical cracking depth (m) when the soil beam is broken; § is the effective length (m) when the soil beam is damaged.

Optionally, the length of the test object is 0.30-0.50 m, the width is 0.05 m, and the thickness is 0.02-0.08 m.

Optionally, S2 further comprises laying a smooth film on the top of the sliding unit.

Optionally, a high-definition camera is adopted in the process of observing and shooting the deformation and cracking of the lower part of the test object.

The invention discloses that following technical effect: According to the device for determining the fracture toughness of soil by self-weight and the using method thereof provided by the invention, aiming at the failure characteristics of soil, the fracture toughness of soil is determined by self-weight of soil under the condition of not applying external load, and the basic theoretical key of the research on the disaster mechanism of geological disasters such as soil landslide, ground collapse, initial debris flow, ground fissures and the like is solved.

BRIEF DESCRIPTION OF THE FIGURES In order to explain the embodiment of the present invention or the technical scheme in the prior art more clearly, the following will briefly introduce the drawings used in the embodiment. Obviously, the drawings in the following description are only some embodiments of the present invention, for those skilled in the art, other drawings can be obtained according to these drawings without paying creative labor.

Fig. 1 is a schematic diagram showing four tensile and shear cracks in landslide HUS00778 range in the present invention; Fig. 2 is a schematic diagram of large-area karst collapse geological disaster in the present invention; Fig. 3 is a structural schematic diagram of a soil fracture toughness testing device in an embodiment of the present invention; Fig. 4 is a flow chart of the using method of the soil fracture toughness testing device in the embodiment of the present invention.

Among them, 1 is a horizontal test bench, 2 is a fixed bearing, 3 is a sliding bearing, 4 is a sliding bearing displacement controller, 5 is an soil beam, 6 is a smooth film, and 7 is a ball at the bottom of the sliding bearing, 8 is the ball at the top of sliding bearing, 9 is the tensile crack of soil beam, a is the length (m) of soil beam, S is the effective length (m) when the soil beam breaks, h is the thickness (m) of soil beam, and ao is the critical cracking depth when the soil beam breaks.

DESCRIPTION OF THE INVENTION The following will clearly and completely describe the technical scheme in the embodiment of the present invention with reference to the drawings in the embodiment of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative labor belong to the scope of protection of the present invention.

In order to make the above objects, features and advantages of the present invention more obvious and easy to understand, the present invention will be further explained in detail with reference to the drawings and specific embodiments.

The invention provides a device for determining the fracture toughness of soil by self-weight, as shown in Figure 3. The device comprises a fixing unit, a sliding unit and a sliding control unit. The fixed unit and the sliding unit are arranged in parallel and vertically on the horizontal test bench 1, and the bottom of the fixed unit is fixedly connected with the horizontal test bench 1. The bottom of the sliding unit is in sliding connection with the horizontal test bench 1, and the sliding unit is electrically 7500778 connected with a sliding control unit for controlling the horizontal movement of the sliding unit.

In this embodiment, the fixed unit adopts the fixed support 2, and the sliding unit adopts the sliding support 3, wherein the sliding support 3 is a small rigid structure, including three rectangular columns which are arranged in parallel and perpendicular to the horizontal test bench 1. Top balls 8 of sliding bearings with the same diameter are uniformly arranged on the tops of the three rectangular columns, and bottom balls 7 of sliding bearings with the same diameter are uniformly arranged on the bottoms of the three rectangular columns. The diameters of the sliding bearing bottom ball 7 and the sliding bearing top ball 8 can be selected according to different experimental objects. In this embodiment, the diameters of the sliding bearing bottom ball 7 and the sliding bearing top ball 8 are both 5 mm. The length of the rectangular column is the same as the width of the test object, which is indicated by b. in this embodiment, the length of the rectangular column is 5 cm.

In this embodiment, the sliding control unit adopts a sliding support displacement controller 4, which is connected with the sliding support 3 in a wired way and is used for regulating the horizontal displacement of the sliding support 3. The sliding bearing displacement controller 4 adopts an electric control mode, the displacement rate is within 3mm/ min, and the maximum horizontal displacement is cm.

As shown in fig. 4, the application method of the device for determining the fracture toughness of soil by self-weight includes the following steps: S1, prefabricating a soil beam 5; as shown in fig. 3, the test objects are soil beam 5, with length a, width b and thickness A, with values of a=0.30-0.50 m, b=0.05 m and h=0.02-0.08 m respectively. Soil beam 5 can be collected in situ, or it can be prepared manually through the combination of clay type, soil-rock ratio, water content, compactness and other parameters.

S2, horizontally placing the soil beam 5 on the top of the fixed support 2 and the HUS00778 sliding support 3; in this embodiment, a smooth film 6 is laid on the surface of the top ball 8 of the sliding support 3 to reduce the friction between the sliding support 3 and the soil beam 5.

S3, starting the sliding support displacement controller 4, so that the distance between the fixed support 2 and the sliding support 3 is gradually increased, and under the action of self-weight, the lower part of the mid-span soil beam 5 is gradually in a tensile stress state; S4, observing and photographing the deformation and cracking of the lower part of the soil beam 5 between the fixed support 2 and the sliding support 3 until a tensile crack 9 appears at the lower part of the soil beam 5; in this embodiment, a high-definition camera is used for high-precision continuous shooting.

SS, when the tensile crack 9 extends to a certain critical depth ao, the soil beam 5 suddenly breaks, and the sliding support displacement controller 4 is closed, and the effective length S and the critical depth ao of the soil beam 5 at that moment are recorded; S6, according to the effective length S and the critical depth ao, calculate the fracture toughness of the soil beam 5 according to the method shown in formulas (D-2): K, =3975M(h— ag) *° (I) M = -yhs? 8° 2) in which, Ki is the fracture toughness of soil kKN.m7*5; y is the weight of soil (KN/m°); h is the thickness of soil beam (m); ao is the critical cracking depth (m) when the soil beam is broken; § is the effective length (m) when the soil beam is damaged, M is the maximum bending moment in the middle of the soil beam (kN.m).

The working principle of the device provided by the invention is as follows: HUS00778 After the soil beam is prepared, it is placed on the upper part of the fixed support 2 and the sliding support 3 on the horizontal test bench 1 of the invention. The sliding support 3 is slowly moved outwards by the sliding support displacement controller 4, and the suspended length of the soil beam between the fixed support 2 and the sliding support 3 is increased. Under the action of self-weight, the bending moment m in the middle of the suspended soil beam gradually increases, so that the lower end of the middle of the suspended soil beam is in a state of tensile stress. With the increase of the length of the suspended soil beam, the soils at the maximum tensile stress in the middle of the soil beam cracks first, forming tensile cracks. When the tensile crack reaches the critical value ao, the suspended soil beam breaks, and the effective length of the soil beam is S. By bringing ao and S into formula (1) and formula (2), the fracture toughness Ki of the soil can be obtained.

The fracture toughness of different soil types can be determined by using the device provided by the invention, and important mechanical parameters are provided for studying the disaster mechanism of geological disasters such as soil landslide, ground collapse, initial debris flow, ground fissures and the like.

In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner" and "outer" etc. are based on the orientations or positional relationships shown in the drawings, only for the convenience of describing the present invention, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed and operated in a specific orientation.

The above-mentioned embodiments only describe the preferred mode of the invention, and do not limit the scope of the invention. On the premise of not departing from the design spirit of the invention, various modifications and improvements made by ordinary technicians in the field to the technical scheme of the invention shall fall within the protection scope determined by the claims of the invention.

Claims (10)

CLAIMS LU500778

1. A device for determining the fracture toughness of soil by self-weight, characterized by comprising a fixing unit, a sliding unit and a sliding control unit, the fix unit and that sliding unit are arrange in parallel, and are vertically arranged on a horizontal test bed (1); the bottom of the fixed unit is fixedly connected with the horizontal test bench (1), and the bottom of the sliding unit is in sliding connection with the horizontal test bench (1); the sliding unit is electrically connected with the sliding control unit, and the sliding control unit is used for controlling the horizontal movement of the sliding unit.

2. The device for determining the fracture toughness of soil by self-weight according to claim 1, characterized in that the fixing unit adopts a fixed support (2).

3. The device for determining the fracture toughness of soil by self-weight according to claim 1, characterized in that the sliding unit adopts a sliding support (3).

4. The device for determining the fracture toughness of soil by self-weight according to claim 3, wherein the sliding support (3) comprises a plurality of rectangular columns, and a plurality of first rolling units are arranged between the bottom of each rectangular column and the horizontal test bench (1); a plurality of second rolling units are arranged on the top of each rectangular upright post, and the length of the rectangular upright post is the same as the width of the test object.

5. The device for determining the fracture toughness of soil by self-weight according to claim 4, characterized in that the first rolling units have the same diameter and equal spacing between them, and the second rolling units have the same diameter and equal spacing between them.

6. The device for determining the fracture toughness of soil by self-weight according to claim 5, wherein the sliding control unit adopts a displacement controller (4), and the displacement rate of the displacement controller (4) is not more than 3mm/ min, and the horizontal displacement is not more than 30 cm.

7. The use method of the device for determining the fracture toughness of soil by self-weight according to any one of claims 1-6, which is characterized by comprising the following steps:

sl, prefabricating a test object; 7500778 s2, horizontally placing the test object on the top of the fixed unit and the sliding unit; s3, starting the sliding control unit, so that the distance between the fixed unit and the sliding unit is gradually increased, and under the action of self-weight, the lower part of the test object is gradually in a tensile stress state; s4, observing and shooting the deformation and cracking of the lower part of the test object until a tensile crack (9) appears; s5, when the tensile crack (9) expands to a certain critical depth ao, the test object suddenly breaks, and the sliding control unit is closed, and the effective length S and the critical depth ao of the test object when breaking are recorded, s6, according to the effective length S and the critical depth ao, calculate the fracture toughness of the test object according to formulas (1)-(2): K | = 3.975M(h — ag) "> (I) M = *yhs? 2) in which, Ki is the fracture toughness of soil kKN.m7*5; y is the weight of soil (KN/m°); h is the thickness of soil beam (m); ao is the critical cracking depth (m) when the soil beam is broken; § is the effective length (m) when the soil beam is damaged.

8. The use method of the device for determining the fracture toughness of soil by self-weight according to claim 7, characterized in that the length of the test object is

0.30-0.50 m, the width is 0.05 m, and the thickness is 0.02-0.08 m.

9. The use method of the device for determining the fracture toughness of soil by self-weight according to claim 7, characterized in that S2 further comprises laying a smooth film (6) on the top of the sliding unit.

10. The use method of the device for determining the fracture toughness of soil by self-weight according to claim 7, characterized in that a high-definition camera is adopted in the process of observing and shooting the deformation and cracking of the lower part of the test object.