CN111441399B - Method for detecting strength of beaded karst cave after grouting - Google Patents
Method for detecting strength of beaded karst cave after grouting Download PDFInfo
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- CN111441399B CN111441399B CN202010385248.XA CN202010385248A CN111441399B CN 111441399 B CN111441399 B CN 111441399B CN 202010385248 A CN202010385248 A CN 202010385248A CN 111441399 B CN111441399 B CN 111441399B
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D15/00—Handling building or like materials for hydraulic engineering or foundations
- E02D15/02—Handling of bulk concrete specially for foundation or hydraulic engineering purposes
- E02D15/04—Placing concrete in mould-pipes, pile tubes, bore-holes or narrow shafts
Abstract
The invention discloses a method for detecting strength of a beaded karst cave after grouting, which comprises the steps of lowering a detection electrode by using a pilot borehole, detecting by adopting a cross-hole high-density resistivity method, and inverting based on a sparse regularization method to achieve visualization and accuracy of a detection result, so that grouting strength conditions of the karst cave are obtained, and subsequent construction safety is ensured. Therefore, the invention proposes the relationship between the compressive strength and the resistivity by testing the resistivity of the concrete test blocks with different mud contents in advance; and (3) after concrete is injected, detecting the resistivity, and obtaining whether the injected grout meets the expected strength requirement from the resistivity inversion diagram, so as to guide whether the strength grade of the grouted grout concrete should be enhanced or grouting should be increased.
Description
Technical Field
The invention relates to a method for detecting strength of a beaded karst cave after grouting, and belongs to the technical field of karst cave grouting strength detection.
Background
In recent years, with the rapid progress of the foundation construction, the land occupation is relatively tense, so that engineering construction personnel have to process various bad landforms so as to meet the construction requirements. The most common of them is the karst landform, and the defects of the karst area must be overcome to build buildings in the karst area. A large number of karst landforms exist in the Guangdong area of China, and the flower community in the northern part of Guangzhou is obvious, so that how to properly process the cavern is very important. At present, the most common method is to carry out grouting treatment on the soil karst cave. However, in the existing engineering, a forming method is not adopted to carry out professional detection on the grouting condition of the karst cave, for example, the filling degree of grouting and the strength of concrete after grouting and the like, due to the fact that the underground part in the depth of the soil karst cave is originally difficult to detect, whether the grouting effect meets the expectation or not can not be ensured after the soil karst cave is grouted, once the grouting effect cannot be ensured, if engineering construction is carried out again, the consequences can not be imagined. At present, the lack of strength detection of karst cave grouting in engineering causes that many operators can only perform grouting according to experience or feeling, so that the controllability and the accuracy of the karst cave grouting are greatly reduced, the engineering construction and the development of karst areas are not facilitated, and if the strength of the grouting in the karst cave does not meet the requirements and cannot be detected in advance, the damage to the engineering is great. And moreover, the size of the beaded karst cave is difficult to estimate, so that the control of the grouting amount is particularly important, unnecessary loss of materials is avoided, and better economic benefit is achieved.
Disclosure of Invention
The invention aims to provide a method for detecting the strength of a beaded cave after grouting, which is simple to implement, low in cost and reliable in detection result.
In order to achieve the purpose, the invention adopts the following technical scheme: a method for detecting strength of a beaded karst cave after grouting comprises the following steps:
firstly, performing advanced drilling on a region to be detected, preliminarily determining the position of a karst cave and preliminarily judging the size of the karst cave by combining geological data so as to prepare the grouting amount;
step two, the advanced drilling holes are properly protected to serve as grouting holes and detection holes, and the advanced drilling holes are prevented from being blocked;
placing a resistivity test electrode group in the detection hole, and carrying out resistivity measurement on the karst cave before grouting to obtain the position and size information of the karst cave;
before grouting, measuring the resistivity of the concrete test blocks with different mud contents 7d after the grout is solidified in a laboratory, and testing the compressive strength of the concrete test blocks by adopting a universal testing machine so as to establish the relationship between the compressive strength and the resistivity of the concrete with different mud contents;
fifthly, drilling grouting holes according to the construction specification of grouting, and then grouting into the karst cave through the grouting holes;
after grouting is completed, placing a resistivity test electrode group in the detection hole again 7d after the grout is solidified, connecting the resistivity test electrode group with a direct-current resistivity tester, and then carrying out electrode running test;
and seventhly, performing resistivity inversion calculation by adopting the electrode-running test result to obtain the resistivity of the karst cave area, and inquiring the relation between the compressive strength and the resistivity of each group of concrete test blocks established in a laboratory to confirm the strength of the karst cave after grouting so as to determine whether the grouting strength in the karst cave meets the engineering requirements.
In the method, the geological data is a geological report of a non-rainy season within 1 month recently.
In the method, a plurality of the advance drill holes are selected, two or more adjacent advance drill holes are selected as detection holes, a PVC pipe is placed in each detection hole, the bottom of each PVC pipe is sealed by a waterproof adhesive tape, a group of mounting holes are formed in the side wall of each PVC pipe at certain intervals, and resistivity test electrodes are embedded in the mounting holes.
In the method, a sleeve valve pipe is embedded in the grouting hole, and the intersection of the sleeve valve pipe and the ground is blocked in advance.
In the method, the distance of the advance drilling is controlled to be between 5 and 10 m.
In the method, the concrete test blocks are divided into 7 groups, each group comprises 3 test blocks, the total determination is carried out for 21 times, wherein the mud content of each group of concrete test blocks is respectively 0%, 5%, 10%, 15%, 20%, 25% and 30%.
In the method, the inversion calculation is to solve an inverse problem according to a sparse iteration method by using sparse regularization processing on the measurement result:
where S is sensitivity, R is the measurement set of potentials, c is apparent resistivity, c is0For initial resistivity values, λ is a given sparse regularization parameter.
Due to the adoption of the technical scheme, the invention has the following advantages: the method utilizes the advanced drilling to lower the detection electrode, adopts a cross-hole high-density resistivity method to detect, and then carries out inversion based on a sparse regularization method to achieve visualization and accuracy of detection results, thereby obtaining the grouting strength condition of the karst cave, and being used for guiding whether the strength grade of the grouting slurry concrete should be enhanced or increasing the grouting slurry to ensure the subsequent construction safety.
Drawings
FIG. 1 is a schematic diagram of the structure in the practice of the present invention;
FIG. 2 is a schematic diagram of the structure of a PVC pipe and a resistivity test electrode;
FIG. 3 is a graph showing the relationship between compressive strength and resistivity of concrete test blocks with different amounts of slurry according to the example of the present invention.
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.
The embodiment of the invention comprises the following steps: geological exploration in a place in northern Guangzhou can basically confirm that the geological condition of the area with beaded karst caves exists, and the geological exploration result of the area is the following soil layer condition:
A. filling soil with impurities, wherein the average layer thickness is 1.8 m; B. mucky soil with an average layer thickness of 2.9 m; C. fine sand with an average layer thickness of 3.25 m; D. coarse sand with an average layer thickness of 4.5 m; E. powdery clay with an average layer thickness of 2.38 m; F. the method comprises the steps of drilling a core soil sample at one position of a strongly weathered limestone, a moderately weathered limestone and a slightly weathered limestone, wherein the core soil sample at one position is discontinuous and is a typical soil sample of a karst cave, grouting treatment is needed, and the grouting treatment result of the karst cave is detected by using the method.
Before grouting, due to the existence of underground karst caves, underground water or slurry exists frequently, so that the change of electrical property is complicated; after grouting, the concrete forms a whole body with the soil body or rock body in the karst cave range, so that the electrical property change is relatively stable. The amount of mud in the concrete affects its resistivity. The resistivity of concrete test blocks with different mud contents is tested in advance, and the relation between the compressive strength and the resistivity is suggested; and (3) after concrete is injected, detecting the resistivity, and obtaining whether the injected grout meets the expected strength requirement from the resistivity inversion diagram, so as to guide whether the strength grade of the grouted grout concrete should be enhanced or grouting should be increased.
Referring to fig. 1 to 3, the method for detecting the strength of the beaded cave after grouting according to the present invention includes the following steps:
firstly, adding advanced drilling holes at the periphery of a drilling hole with a discontinuous soil core according to a distance of 5-10 m, wherein the advanced drilling holes are distributed in a quincuncial pile shape, and the diameter of each advanced drilling hole is 95 mm;
step two, the advanced drilling holes are properly protected to serve as grouting holes 1 and detection holes 2, and the advanced drilling holes are prevented from being blocked; the method comprises the following steps that a plurality of pilot drill holes are selected, two adjacent pilot drill holes are selected as detection holes 2, a PVC pipe 5 is placed in each detection hole 2, the bottom of each PVC pipe 5 is sealed by a waterproof adhesive tape 7, a group of mounting holes are formed in the side wall of each PVC pipe 5 at intervals of 300mm, and resistivity test electrodes 6 are embedded in the mounting holes; a sleeve valve pipe 4 with the thickness of 45mm is embedded in the grouting hole 1, and the intersection of the sleeve valve pipe 4 and the ground is blocked in advance.
Placing a PVC pipe 5 provided with a resistivity test electrode group in the detection hole 2, connecting the resistivity test electrode group with a multifunctional digital direct current method instrument with the model of WDJD-4, carrying out cross-hole resistivity test on the existing drill hole by using the multifunctional digital direct current method instrument, and determining the size and the position of a beaded first karst cave, a beaded second karst cave and a beaded third karst cave in the area by combining geological data (geological report in a non-rainy season within 1 month recently) to prepare grouting amount;
and step four, before grouting, carrying out resistivity measurement on the concrete test blocks with different mud contents 7d after the grout is solidified in a laboratory, and testing the compressive strength of the concrete test blocks by adopting a universal testing machine so as to establish the relationship between the compressive strength and the resistivity of the concrete with different mud contents. The specific implementation mode is as follows: the concrete test blocks are divided into 7 groups, and each group of 3 test blocks is tested 21 times, wherein the mud content of each group of concrete test blocks is 0%, 5%, 10%, 15%, 20%, 25% and 30%, and the mud with the proportions is respectively mixed with grouting material P.O32.5 ordinary portland cement and fine aggregate sand, so that the concrete test blocks with different mud contents can be obtained, wherein the test blocks are standard concrete test blocks with the mud contents of 150mm to 150 mm; and respectively carrying out resistivity test and compression test of a universal testing machine on each concrete test block after curing for 7d under the same condition, and respectively taking the average values of the resistivity value and the compression strength after each group of concrete test blocks are measured as the final result. Experiments show that the magnitude of the compressive strength of the concrete test blocks with different mud contents is related to the change of the mud contents, specifically, the concrete with higher mud content has lower compressive strength and is easy to be compressed and damaged, so that the relationship between the compressive strength and the resistivity of the concrete test blocks with different mud contents can be established, as shown in fig. 3.
Fifthly, drilling grouting holes according to the construction specification of grouting, and then grouting into the karst cave through the grouting holes; during grouting, the grouting sequence from bottom to top must be observed, the lower karst cave is processed first, and then the upper karst cave is processed, and the injection rate of grouting and the pressure change of grouting are noticed.
After grouting is completed, placing a resistivity test electrode group in the detection hole 2 again after the grout is solidified for 7d, connecting the resistivity test electrode group with a multifunctional digital direct current method instrument with the model of WDJD-4, and then carrying out electrode running test;
and seventhly, performing resistivity inversion calculation by adopting the electrode-running test result to obtain the resistivity of the karst cave area, and inquiring the relation between the compressive strength and the resistivity of each group of concrete test blocks established in a laboratory to confirm the strength of the karst cave after grouting so as to determine whether the grouting strength in the karst cave meets the engineering requirements. The inversion calculation is to solve an inverse problem according to a sparse iteration method by utilizing sparse regularization processing on a measurement result:
where S is sensitivity, R is the measurement set of potentials, c is apparent resistivity, c is0For initial resistivity values, λ is a given sparse regularization parameter.
In conclusion, the invention utilizes the advanced drilling to lower the detection electrode, adopts the cross-hole high-density resistivity method to detect, and then carries out inversion based on the sparse regularization method to achieve visualization and accuracy of detection results, thereby obtaining the grouting strength condition of the karst cave, and being used for guiding whether the strength grade of the grouting slurry concrete should be enhanced or increasing the grouting to ensure the subsequent construction safety.
Claims (6)
1. A method for detecting strength of a beaded karst cave after grouting is characterized by comprising the following steps:
firstly, performing advanced drilling on a region to be detected, preliminarily determining the position of a karst cave and preliminarily judging the size of the karst cave by combining geological data so as to prepare the grouting amount;
step two, the advanced drilling holes are properly protected to serve as grouting holes and detection holes, and the advanced drilling holes are prevented from being blocked;
placing a resistivity test electrode group in the detection hole, and carrying out resistivity measurement on the karst cave before grouting to obtain the position and size information of the karst cave;
before grouting, measuring the resistivity of the concrete test blocks with different mud contents 7d after the grout is solidified in a laboratory, and testing the compressive strength of the concrete test blocks by adopting a universal testing machine so as to establish the relationship between the compressive strength and the resistivity of the concrete with different mud contents;
fifthly, drilling grouting holes according to the construction specification of grouting, and then grouting into the karst cave through the grouting holes;
after grouting is completed, placing a resistivity test electrode group in the detection hole again 7d after the grout is solidified, connecting the resistivity test electrode group with a direct-current resistivity tester, and then carrying out electrode running test;
step seven, performing resistivity inversion calculation by adopting the running pole test result to obtain the resistivity of the karst cave area, and inquiring the relation between the compressive strength and the resistivity of each group of concrete test blocks established in a laboratory to confirm the strength after the karst cave grouting so as to determine whether the grouting strength in the karst cave meets the engineering requirements; the inversion calculation is to solve an inverse problem according to a sparse iteration method by utilizing sparse regularization processing on a measurement result:
where S is sensitivity, R is the measurement set of potentials, c is apparent resistivity, c is0And (3) taking the initial resistivity value, wherein lambda is a given sparse regularization parameter, and k is the iteration number.
2. The method for detecting the strength of the beaded cave after grouting according to claim 1, which is characterized in that: the geological data is a geological report during a non-rainy season within 1 month recently.
3. The method for detecting the strength of the beaded cave after grouting according to claim 1, which is characterized in that: the method comprises the following steps that a plurality of pilot holes are selected, two or more adjacent pilot holes are selected as detection holes, a PVC pipe is placed in each detection hole, the bottom of each PVC pipe is sealed by a waterproof adhesive tape, a group of mounting holes are formed in the side wall of each PVC pipe at certain intervals, and resistivity testing electrodes are embedded in the mounting holes.
4. The method for detecting the strength of the beaded cave after grouting according to claim 1, which is characterized in that: and sleeve valve pipes are embedded in the grouting holes, and the intersection of the sleeve valve pipes and the ground is blocked in advance.
5. The method for detecting the strength of the beaded cave after grouting according to claim 1, which is characterized in that: the distance of the advanced drilling hole is controlled to be 5-10 m.
6. The method for detecting the strength of the beaded cave after grouting according to claim 1, which is characterized in that: the concrete test blocks are divided into 7 groups, 3 test blocks in each group are tested for 21 times, wherein the mud content of each group of concrete test blocks is 0%, 5%, 10%, 15%, 20%, 25% and 30% respectively.
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