CN114047078B - Dynamic excavation unloading test device and test method under true three-dimensional stress state - Google Patents
Dynamic excavation unloading test device and test method under true three-dimensional stress state Download PDFInfo
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- CN114047078B CN114047078B CN202111211157.5A CN202111211157A CN114047078B CN 114047078 B CN114047078 B CN 114047078B CN 202111211157 A CN202111211157 A CN 202111211157A CN 114047078 B CN114047078 B CN 114047078B
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- G—PHYSICS
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- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/18—Performing tests at high or low temperatures
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
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Abstract
The invention provides a dynamic excavation unloading test device and a test method under a true three-dimensional stress state, which comprise a temperature control heating circuit, an electric heating rod, a filling body, a loading sample and a true triaxial test system; six surfaces of the cuboid loading sample are respectively clung to an upper pressure head, a lower pressure head, a left pressure head, a right pressure head, a front pressure head and a rear pressure head of the true triaxial test system; the electric heating rod is positioned at the center of the prefabricated excavation hole in the loading sample; filling the filling body between the electric heating rod and the prefabricated excavation hole; one end of a lead of the temperature control heating circuit penetrates through a lead hole of the front side pressure head and then is connected with the electric heating rod. The unloading device can realize the unloading of stepwise excavation and excavation at various speeds, can realize the unloading of excavation with different excavation sections (rectangular, elliptical, horseshoe-shaped and the like) and excavation sizes, and is suitable for single-shaft and double-shaft loading excavation unloading tests.
Description
Technical Field
The invention belongs to the technical field of indoor rock mechanical tests, and relates to a dynamic excavation unloading test device and a test method under a true three-dimensional stress state.
Background
Before underground spaces such as underground tunnels, roadways, chambers and the like are excavated, underground rocks are in a stress balance state, and the excavation of the underground spaces breaks through the original stress balance state, changes the original stress state of rock masses and degrades the original three-dimensional stress state into a two-dimensional or even one-dimensional stress state. This unbalanced stress condition results in, on the one hand, a reduction in the stress experienced by the portion of the surrounding rock and, on the other hand, an increase in the stress experienced by the portion of the surrounding rock. The unbalanced stress state easily causes great deformation and even instability damage of surrounding rocks, seriously threatens the life safety of underground constructors, delays the construction progress and causes huge economic loss. Therefore, the research on the excavation unloading influence of the underground space excavation process on the surrounding rock is very important. Compared with field tests, the indoor development of excavation unloading test research is a feasible, economic and easy-to-realize scheme.
At present, the invention patents in the aspect of the unloading test device for underground space excavation are as follows: the invention name is as follows: the test device and the test method for simulating blasting excavation unloading under the three-dimensional loading condition (application number: 201711185344.4, published as 2018.03.16) disclose the test device and the test method for simulating blasting excavation unloading under the three-dimensional loading condition, but the device needs 45 jacks to apply load, only monitors the deformation of surrounding rock through strain gauges, has complex operation procedures, is difficult to ensure that different jacks apply the same and stable load synchronously, and cannot monitor the load change of the surrounding rock in the loading process; the invention name is as follows: the test device and the test method (application number: 201711185343.X, published: 2018.03.06) for simulating the excavation unloading under the deep three-dimensional loading condition disclose the test device and the test method for simulating the excavation unloading under the deep three-dimensional loading condition, but the device increases the disturbance influence of the self vibration of a drilling machine on a sample in the test, can only excavate a circular hole, does not consider the influence of the actual hole section shapes such as rectangle, ellipse, horseshoe, circular arch and the like, needs a larger installation space, is limited by the size of a press machine, needs to specially customize a high-strength drilling machine installation frame, is provided with central holes in two pressing plates, and is not really totally closed; patents that suffer from the above-mentioned disadvantages also include: the invention relates to a test device and a test method for simulating mechanical excavation unloading of a deep circular tunnel (application number: 201711185208.5, published: 2018.02.16) and a Chinese invention patent named as a test device (application number: 201910053947.1, published: 2019.06.21) for simulating an unloading mechanical response process of underground rock-soil body excavation; the invention relates to a rock internal excavation unloading simulation experiment device and an application method thereof (application number: 201811331853.8, published: 2019.01.25), and does not consider that the characteristic difference between a polyester material and a rock material is large, so that the experiment result is greatly influenced.
In summary, the currently published technical schemes have the problem that the difference between the excavation process of the actual engineering and the loading process, the two-dimensional stress loading excavation process, the mechanical unloading excavation process, the hydraulic unloading excavation process and the like is large, the mechanical properties of the filling material for filling, heating, excavating and unloading are far from the mechanical properties of the surrounding rock, and the existing related technologies have complicated operation processes and limited application conditions.
Disclosure of Invention
In order to overcome the problems in the prior art, the invention provides a dynamic excavation unloading test device and a test method under a true three-dimensional stress state, which can realize step-by-step excavation unloading and excavation unloading at various rates, can realize excavation unloading of different excavation sections (rectangles, ellipses, horseshoe shapes and the like) and excavation sizes, and are simultaneously suitable for single-shaft and double-shaft loading excavation unloading tests.
In order to realize at least one of the technical purposes, the invention adopts the technical scheme that the dynamic excavation unloading test device under the true three-dimensional stress state is provided, and comprises a temperature control heating circuit, an electric heating rod, a filling body, a loading sample and a true triaxial test system; six surfaces of the cuboid loading sample are respectively clung to an upper pressure head, a lower pressure head, a left pressure head, a right pressure head, a front pressure head and a rear pressure head of the true triaxial test system; the electric heating rod is positioned at the center of the prefabricated excavation hole in the loading sample; filling the filling body between the electric heating rod and the prefabricated excavation hole; one end of a lead of the temperature control heating circuit penetrates through a lead hole of the front side pressure head and then is connected with the electric heating rod.
Furthermore, the temperature control heating circuit comprises an alternating current power supply, a lead, a digital display intelligent temperature regulator, an alternating current contactor and a high-temperature thermocouple temperature sensor; the other end of the lead is connected with an alternating current contactor; the digital display intelligent temperature regulator is respectively connected with the alternating current contactor and the high-temperature thermocouple temperature sensor; the output end of the alternating current power supply is respectively connected with the alternating current contactor and the digital display intelligent temperature regulator.
Further, the electric heating rod comprises an internal thermal resistor and an external shell, and the shell is wrapped outside the thermal resistor; the external diameter of electrical heating rod is less than the internal diameter of prefabricated excavation hole, and the axial depth in prefabricated excavation hole is not exceeded to electrical heating rod's length.
Furthermore, the filling body is a mixture formed by mixing sand, polylactic acid and acetyl tributyl citrate, and is manufactured by heating and solidifying; the loading sample is prepared by proportioning cement, sand and water; or the material is prepared by further adding other materials for preparing the rock-like material according to the mixture ratio; the natural rock mass can also be drilled on site and then cut indoors through water power to manufacture the rock mass; the mechanical properties of the filling body are consistent with those of the loaded sample.
The invention also provides a dynamic excavation unloading test method under the true three-dimensional stress state, which comprises the following steps:
step S1: the method comprises the following steps of (1) preparing a loading sample for pouring a rock-like rectangular block body containing a prefabricated excavation hole through cement, sand and water;
step S2: a filling body which is consistent with the mechanical property of the loading sample prepared in the step S1 is prepared from sand, polylactic acid and acetyl tributyl citrate and is used for filling the prefabricated excavation hole in the prefabricated loading sample; embedding the electric heating rod in the filling body filled in the prefabricated excavation hole while filling the prefabricated excavation hole with the filling body;
and step S3: connecting the temperature control heating circuit and an electric heating rod embedded in the filling body;
and step S4: placing the fabricated rock-like body loading sample filled by the filling body and containing the prefabricated excavation hole in a true triaxial test system, starting to apply initial stress to the loading sample, and loading the rock-like body loading sample to an initial three-dimensional stress state according to a preset loading path by adjusting six pressure heads of the true triaxial loading system;
step S5: after the initial stress applied to the rock-like body loading sample is consistent with the original rock stress state of the actual engineering and is stable for 0.5-1.5 hours, the temperature-controlled heating circuit starts to be powered on, the temperature of the electric heating rod is firstly adjusted to be the melting or thermal decomposition temperature of the filling body through a digital display intelligent temperature regulator in the circuit after the power supply is switched on, the electric heating rod starts to heat, melt or thermally decompose the filling body filled in the prefabricated excavation hole, the purpose of dynamically excavating and unloading the sample hole surrounding rock containing the filling hole in the true triaxial stress state is achieved, and relevant excavation unloading influence research is carried out after the test is finished.
Further, in the step S1, the prefabricated excavation hole passes through the pre-buried hole mold during the process of pouring the loading sample, and the hole mold pre-buried in the cement mortar is taken out after the cement mortar is completely solidified, so that the prefabricated excavation hole is formed.
Further, the manufacturing method of the filling body in the step S2 includes: uniformly mixing sand, polylactic acid and acetyl tributyl citrate, heating and melting to prepare mixed molten slurry, pouring the mixed molten slurry into a gap between the prefabricated excavation hole and the electric heating rod, and pouring the mixed molten slurry while vibrating and loading a sample to avoid bubbles generated inside the poured mixed molten slurry, wherein the electric heating rod is required to be kept parallel to the prefabricated excavation hole and be positioned at the central position of the prefabricated excavation hole when the mixed molten slurry is poured; forming a filling body after the mixed molten slurry poured between the prefabricated excavation hole and the electric heating rod is completely cooled; the raw material proportion of the filling body is determined by an orthogonal test according to the mechanical parameters of a natural rock body sampled on site.
Further, the connection method of the temperature-controlled heating circuit in step S3 is as follows: the alternating current contactor is connected with the digital display intelligent temperature regulator; a high-temperature thermocouple temperature sensor is connected to the digital display intelligent temperature regulator; connecting the alternating current contactor and the digital display intelligent temperature regulator to an alternating current power supply; the lead wire is connected with an electric heating rod embedded in the filling body, passes through a lead wire hole of the front side pressure head and is then connected with an alternating current contactor.
The invention has the beneficial effects that:
the method can realize stepwise excavation in a true triaxial stress environment, can realize excavation unloading of different excavation unloading rates, different excavation section shapes (such as rectangles, ellipses, horseshoe shapes, circular arches and the like) and different excavation sizes, is simultaneously suitable for excavation unloading tests in uniaxial loading, biaxial loading and true triaxial stress environments, is suitable for excavation unloading tests of true triaxial compression testing machines of any size, can realize synchronous or asynchronous excavation of single holes and multiple holes, can realize fine control of excavation parameters, provides a pre-filling material which is easy to realize excavation and has mechanical properties very close to rock masses, and reproduces the actual underground engineering excavation process to the maximum extent. The device has wide application range, and the needed equipment is simpler, and is easy to obtain and economical.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an excavation unloading test apparatus according to an embodiment of the present invention.
Fig. 2 is a front structural view of the excavation unloading test apparatus according to the embodiment of the present invention.
Fig. 3 is a structural right side view of the excavation unloading test apparatus according to the embodiment of the present invention.
Fig. 4 is a schematic diagram of a true triaxial indenter including wire guides in an embodiment of the present invention.
FIG. 5 is a schematic view of a sample loaded with a single pre-formed hole according to an embodiment of the present invention.
Fig. 6 is a schematic view of loading samples of different cross-sectional shapes of excavated holes according to an embodiment of the present invention.
Fig. 7 is a schematic view of loading samples with different numbers of excavated holes according to an embodiment of the present invention.
FIG. 8 is a sample loading schematic of coplanar orthogonal apertures in an embodiment of the present invention.
FIG. 9 is a sample loading schematic diagram of a spatially orthogonal aperture in an embodiment of the invention.
In the drawing, 1, an alternating current power supply, 2, an alternating current contactor, 3, a digital display intelligent temperature regulator, 4, a high-temperature thermocouple temperature sensor, 5, a lead, 6, a lead hole, 7, a thermal resistor, 8, an electric heating rod, 9, a filling body, 10, a prefabricated excavation hole, 11, a loading sample, 121, an upper pressure head, 122, a lower pressure head, 123, a left pressure head, 124, a right pressure head, 125, a front pressure head and 126, a rear pressure head.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1-5, the invention provides a dynamic excavation unloading test device under a true three-dimensional stress state, which comprises a temperature control heating circuit, an electric heating rod 8, a filling body 9, a loading sample 11 and a true triaxial test system; six surfaces of the cuboid rock-like loading sample 11 are respectively attached to an upper pressure head 121, a lower pressure head 122, a left pressure head 123, a right pressure head 124, a front pressure head 125 and a rear pressure head 126 of the true triaxial test system; the electric heating rod 8 is positioned at the center of the prefabricated excavation hole 10 in the loading sample 11; the filling body 9 is filled between the electric heating rod 8 and the prefabricated excavation hole 10; one end of a lead 5 of the temperature control heating circuit passes through the lead hole 6 of the front side pressure head 125 and then is connected with the electric heating rod 8.
Further, the temperature control heating circuit comprises an alternating current power supply 1, a lead 5, a digital display intelligent temperature regulator 3, an alternating current contactor 2 and a high-temperature thermocouple temperature sensor 4; the other end of the lead 5 is connected with the alternating current contactor 2; the digital display intelligent temperature regulator 3 is respectively connected with the alternating current contactor 2 and the high-temperature thermocouple temperature sensor 4; the output end of the alternating current power supply 1 is respectively connected with the alternating current contactor 2 and the digital display intelligent temperature regulator 3. Specifically, the temperature is controlled through digital display intelligent temperature regulator 3 to electric heating rod 8, and electric heating rod 8 measures the temperature through high temperature thermocouple temperature sensor 4, and digital display intelligent temperature regulator 3 chooses to purchase or the customization according to the temperature control scope of experimental demand.
Further, the electric heating rod 8 includes an inner thermal resistor 7 and an outer housing, and the outer housing is wrapped outside the thermal resistor 7.
Further, the filling body 9 is a mixture formed by mixing sand, polylactic acid and acetyl tributyl citrate, and is manufactured by heating and solidifying; the mechanical properties of the filling 9 are consistent with those of the loaded sample 11.
Further, the loading sample 11 is prepared by proportioning cement, sand and water; or the material is prepared by further adding other materials for preparing the rock-like material according to the mixture ratio; or the natural rock mass can be drilled on site and then manufactured indoors through hydraulic cutting. The loaded sample 11 corresponds to the surrounding rock in the actual site engineering in the present invention.
In a specific embodiment, the raw material proportion of the filling body 9 is determined by an orthogonal test according to the mechanical parameters of a natural rock body sampled on site;
in a specific embodiment, the power of the electrical heating rod 8 is determined according to the melting temperature or the thermal decomposition temperature of the filling body 9, the outer diameter of the electrical heating rod 8 is smaller than the inner diameter of the prefabricated excavation hole 10, and the length of the electrical heating rod 8 does not exceed the axial depth of the prefabricated excavation hole 10.
In one embodiment, the size of the loaded sample 11 is determined according to research requirements, but must not exceed the maximum sample size that can be loaded by the rock triaxial test system.
In one embodiment, the cross-sectional shape and cross-sectional dimensions of the prefabricated excavation hole 10 in the loading sample 11 are determined by scaling down according to the project site hole parameters.
The invention also provides a dynamic excavation unloading test method under the true three-dimensional stress state, the embodiment takes the rock-like body loading sample which is formed by pouring cement mortar by using cement, sand and water as an example for explanation, but the technical scheme of manufacturing the rock-like body sample by using natural rock or other materials also comprises the technical scheme.
Step S1: the method comprises the steps that cement, sand and water are used for pouring a rock-like rectangular block body loading sample 11 containing a prefabricated excavation hole 10;
step S2: a filling body 9 which is consistent with the mechanical property of the loading sample 11 manufactured in the step S1 is prepared in advance from sand, polylactic acid and acetyl tributyl citrate and is used for filling a prefabricated excavation hole 10 in the prefabricated loading sample 11; when the prefabricated excavation hole 10 is filled with the filling body 9, the electric heating rod 8 is embedded in the filling body 9 filled in the prefabricated excavation hole 10;
and step S3: connecting the temperature control heating circuit which is connected in advance with an electric heating rod 8 which is embedded in a filling body 9;
and step S4: placing a fabricated rock-like body loading sample 11 filled by a filling body 9 and containing a prefabricated excavation hole 10 in a true triaxial test system, starting to apply initial stress to the loading sample 11, adjusting six pressure heads of the true triaxial loading system, and loading to an initial three-dimensional stress state according to a preset loading path;
step S5: after the initial stress applied to the rock-like body loading sample 11 is consistent with the surrounding rock stress state of the actual engineering and is stable for 0.5-1.5 hours, the temperature control heating circuit starts to be powered on, the temperature of the electric heating rod 8 is adjusted to be the melting or thermal decomposition temperature of the filling body 9 through the digital display intelligent temperature adjusting instrument 3 in the circuit after the power is switched on, the electric heating rod 8 starts to heat, melt or thermally decompose the filling body 9 filled in the prefabricated excavation hole 10, the purpose of dynamically excavating and unloading the surrounding rock of the sample hole containing the filling hole in the true triaxial stress state is achieved, and related excavation unloading influence research is carried out after the test is finished. Under the same condition of the filling body 9, the excavation unloading rate is related to the heating temperature of the electric heating rod, the excavation unloading rate is faster when the power is higher, and therefore the excavation unloading rate can be controlled by controlling the temperature of the electric heating rod; the length of the stable time is related to the lithology, the stress level during loading and the experimental scheme, if the rock mass is a complete rock mass, the stable time is short, and if the rock mass is a fractured rock mass, the stable time is long, and the stable state can be considered to be reached within the elastic stage range of the uniaxial compression strength of the rock mass within 1 hour.
Further, in the step S1, the prefabricated excavation hole 10 passes through the pre-buried hole mold during the process of pouring the loading sample, the hole mold pre-buried in the cement mortar is taken out after the cement mortar is completely solidified, and the prefabricated excavation hole 10 is formed, and the shape and the size of the section of the prefabricated excavation hole 10 are determined according to the research purpose.
Further, the manufacturing method of the filling body 9 in the step S2 includes: uniformly mixing sand, polylactic acid and acetyl tributyl citrate, heating and melting to prepare mixed molten slurry, pouring the mixed molten slurry into a gap between the prefabricated excavation hole 10 and the electric heating rod 8, and when pouring the mixed molten slurry, vibrating and loading the sample 11 while pouring to avoid bubbles generated inside the poured mixed molten slurry, wherein the electric heating rod 8 and the prefabricated excavation hole 10 are required to be kept parallel and positioned at the central position of the prefabricated excavation hole 10 when pouring the mixed molten slurry; and forming the filling body 9 after the mixed melted slurry poured between the prefabricated excavation hole 10 and the electric heating rod 8 is completely cooled.
Further, the connection method of the temperature-controlled heating circuit in step S3 is as follows: the alternating current contactor 2 is connected with the digital display intelligent temperature regulator 3; a high-temperature thermocouple temperature sensor 4 is connected to the digital display intelligent temperature regulator 3; then connecting the AC contactor 2 and the digital display intelligent temperature regulator 3 to the AC power supply 1; the lead wire 5 is connected to an electric heating rod 8 embedded in the packing 9, and the lead wire 5 is passed through a lead wire hole 6 of the front side head 125 and then connected to the ac contactor 2.
In a specific embodiment, as shown in fig. 6, the prefabricated excavation hole 10 according to the present invention has a cross-section schematically shown in a circular, elliptical, rectangular and dome shape, and in this embodiment, other technical solutions of this embodiment are completely identical to the above-described embodiment except that the cross-section of the prefabricated excavation hole 10 has a different shape.
In a specific embodiment, as shown in fig. 7, which is a schematic diagram of excavation unloading of single-hole, double-hole, and three-hole loading samples 11 according to the present invention, an excavation method of each loading sample 11 in this embodiment is completely consistent with the process in the foregoing embodiment, and according to different excavation sequences, the double-hole loading samples can be used for excavating one hole first and then another hole, or can be used for excavating double holes simultaneously; the three-hole loading sample of the embodiment can realize that the middle hole is firstly excavated and then the holes on the two sides are excavated, the holes on the two sides are firstly excavated and then the holes in the middle are excavated, or the holes can be excavated from left to right or from right to left in sequence.
In one embodiment, as shown in fig. 8 and 9, which are schematic diagrams of coplanar orthogonal holes and spatial orthogonal holes of the present invention, respectively, wherein, if coplanar orthogonal holes are required, a long electrical heating rod and two short electrical heating rods are required, and the length of the short electrical heating rod is half of that of the long electrical heating rod; or four electric heating rods with the same length are needed, and the length of each electric heating rod is half of the depth of the excavated hole 10; if the holes are orthogonal in space, two identical electric heating rods 8 are needed; the remaining test methods were the same as described in the above examples to achieve the cross-hole excavation unloading test.
In particular, in the present invention, all devices not described are commercially available devices, all circuit connections not described are connections that are conventional in the art, and all operation methods not described are operation methods that are conventional in the art.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrases "comprising 8230; \8230;" comprises 8230; "does not exclude the presence of additional like elements in a process, method, article, or apparatus that comprises the element.
All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (7)
1. A dynamic excavation unloading test device in a true three-dimensional stress state is characterized by comprising a temperature control heating circuit, an electric heating rod (8), a filling body (9), a loading sample (11) and a true triaxial test system; six surfaces of a cuboid loading sample (11) are respectively attached to an upper pressure head (121), a lower pressure head (122), a left pressure head (123), a right pressure head (124), a front pressure head (125) and a rear pressure head (126) of a true triaxial test system; the electric heating rod (8) is positioned at the center of the prefabricated excavation hole (10) in the loading sample (11); the filling body (9) is filled between the electric heating rod (8) and the prefabricated excavation hole (10); one end of a lead (5) of the temperature control heating circuit penetrates through a lead hole (6) of the front side pressure head (125) and then is connected with an electric heating rod (8);
the filling body (9) is a mixture formed by mixing sand, polylactic acid and acetyl tributyl citrate and is manufactured by heating and solidifying; the loading sample (11) is prepared by proportioning cement, sand and water; or the material is prepared by further adding other materials for preparing the rock-like material according to the mixture ratio; the natural rock mass can also be drilled on site and then cut indoors by water power to manufacture the rock mass; the mechanical properties of the filling body (9) are consistent with those of the loaded sample (11).
2. The dynamic excavation unloading test device under the true three-dimensional stress state according to claim 1, wherein the temperature control heating circuit comprises an alternating current power supply (1), a lead (5), a digital display intelligent temperature regulator (3), an alternating current contactor (2) and a high-temperature thermocouple temperature sensor (4); the other end of the lead (5) is connected with the alternating current contactor (2); the digital display intelligent temperature regulator (3) is respectively connected with the alternating current contactor (2) and the high-temperature thermocouple temperature sensor (4); the output end of the alternating current power supply (1) is respectively connected with the alternating current contactor (2) and the digital display intelligent temperature regulator (3).
3. The dynamic excavation unloading test device under the true three-dimensional stress state according to claim 1, characterized in that the electric heating rod (8) comprises an internal thermal resistor (7) and an external shell, and the external shell is wrapped outside the thermal resistor (7); the external diameter of electrical heating rod (8) is less than the internal diameter of prefabricated excavation hole (10), and the axial depth of prefabricated excavation hole (10) is not exceeded to the length of electrical heating rod (8).
4. A dynamic excavation unloading test method under a true three-dimensional stress state is characterized by comprising the following steps:
step S1: the method comprises the steps that a rock-like rectangular block body loading sample (11) containing a prefabricated excavation hole (10) is poured through cement, sand and water;
step S2: a filling body (9) which is consistent with the mechanical property of the loading sample (11) manufactured in the step S1 is prepared from sand, polylactic acid and acetyl tributyl citrate and is used for filling the prefabricated excavation hole (10) in the prefabricated loading sample (11); when the prefabricated excavation hole (10) is filled with the filling body (9), the electric heating rod (8) is embedded in the filling body (9) filled in the prefabricated excavation hole (10);
and step S3: after the temperature control heating circuit is connected, the temperature control heating circuit is connected with an electric heating rod (8) embedded in a filling body (9);
and step S4: placing a fabricated rock mass loading sample (11) filled by a filling body (9) and containing a prefabricated excavation hole (10) in a true triaxial test system, starting to apply initial stress to the loading sample (11), and loading to an initial three-dimensional stress state according to a preset loading path by adjusting six pressure heads of the true triaxial loading system;
step S5: after the initial stress applied to the rock-like body loading sample (11) is consistent with the original rock stress state of the actual engineering and is stable for 0.5-1.5 hours, power supply is started to be supplied to the temperature-controlled heating circuit, after the power supply is switched on, the temperature of the electric heating rod (8) is adjusted to be the melting or thermal decomposition temperature of the filling body (9) through the digital display intelligent temperature adjusting instrument (3) in the circuit, the electric heating rod (8) starts to heat, melt or thermally decompose the filling body (9) filled in the prefabricated excavation hole (10), the purpose of dynamically excavating and unloading surrounding rocks of the sample hole containing the filling hole in the true triaxial stress state is achieved, and relevant excavation unloading influence research is developed after the test is finished.
5. The dynamic excavation unloading test method under the true three-dimensional stress state according to claim 4, wherein in the step S1, the prefabricated excavation hole (10) passes through the pre-buried hole die during the process of pouring the loading sample, and the hole die pre-buried in cement mortar is taken out after the cement mortar is completely solidified, so that the prefabricated excavation hole (10) is formed.
6. The dynamic excavation unloading test method under the true three-dimensional stress state according to claim 4, wherein the manufacturing method of the filling body (9) in the step S2 comprises the following steps: uniformly mixing sand, polylactic acid and acetyl tributyl citrate, heating and melting to prepare mixed melted slurry, pouring the mixed melted slurry into a gap between the prefabricated excavation hole (10) and the electric heating rod (8), and pouring and vibrating the loading sample (11) when pouring the mixed melted slurry to avoid bubbles in the mixed melted slurry, wherein the electric heating rod (8) and the prefabricated excavation hole (10) are ensured to be parallel and positioned at the central position of the prefabricated excavation hole (10) when pouring the mixed melted slurry; forming a filling body (9) after the mixed melted slurry poured between the prefabricated excavation hole (10) and the electric heating rod (8) is completely cooled; the raw material proportion of the filling body (9) is determined by an orthogonal test according to the mechanical parameters of a natural rock body sampled on site.
7. The dynamic excavation unloading test method under the true three-dimensional stress state according to claim 4, wherein the connection method of the temperature control heating circuit in the step S3 is as follows: the alternating current contactor (2) is connected with the digital display intelligent temperature regulator (3); the digital display intelligent temperature regulator (3) is connected with a high-temperature thermocouple temperature sensor (4); then connecting the alternating current contactor (2) and the digital display intelligent temperature regulator (3) to the alternating current power supply (1); the lead (5) is connected with an electric heating rod (8) embedded in the filling body (9), and the lead (5) passes through a lead hole (6) of the front side pressure head (125) and then is connected with the alternating current contactor (2).
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