CN112577801B - Device and method for preparing physicochemical method improved soil sample containing directionally distributed fibers - Google Patents
Device and method for preparing physicochemical method improved soil sample containing directionally distributed fibers Download PDFInfo
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- CN112577801B CN112577801B CN202011547479.2A CN202011547479A CN112577801B CN 112577801 B CN112577801 B CN 112577801B CN 202011547479 A CN202011547479 A CN 202011547479A CN 112577801 B CN112577801 B CN 112577801B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/38—Diluting, dispersing or mixing samples
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/44—Sample treatment involving radiation, e.g. heat
Abstract
The invention discloses a device and a method for preparing a physicochemical method improved soil sample containing directionally distributed fibers, wherein the device comprises a detachable mould, a compaction positioning plate, a compaction hammer system and a fiber directional sieve; the detachable die comprises a bottom steel plate, two outer steel plates, two inner steel plates and a plurality of deformed steel bar pull rods; the bottom steel plate is matched with the self-tapping screw through the side screw hole to fix the side steel plate; the inner surface of the outer steel plate is provided with two fixing grooves for embedding the inner steel plate and a positioning groove for fixing a compaction positioning plate and a fiber directional screen; the inner surface of the inner steel plate is also provided with a positioning groove, and the size and the function of the positioning groove are the same as those of the positioning groove of the outer steel plate; the penetrating screw hole at the upper part of the outer steel plate is matched with the screw steel pull rod to fix the inner steel plate and the outer steel plate; the compaction positioning plate is used for assisting in positioning the compaction hammer system; the fiber orienting screen is used to distribute the fibers in a direction parallel to the deformed steel tie bar. The device has the advantages of convenient assembly, high sample preparation precision, accurate compaction control and the like.
Description
Technical Field
The invention belongs to the technical field of geotechnical engineering foundation treatment, and particularly relates to a device and a method for preparing a physicochemical method improved soil sample containing directionally distributed fibers.
Background
With the development of economic society, the engineering construction of high-rise buildings, high-speed railways, bridges, tunnels and the like gradually expands and extends to areas with unfavorable geological conditions. In order to make the physical and mechanical properties of the geotechnical materials in the areas with poor geological conditions meet the requirements of engineering construction, foundation treatment is often required. Common ground treatment techniques include physical, chemical, biological and combinations thereof. Among them, the physical and chemical methods, which combine physical and chemical methods, have received much attention from engineers and researchers due to their advantages such as remarkable improvement effect and convenience in operation.
In the existing technology of improving soil by physical and chemical methods, the combination of discrete short fibers and other materials is a commonly used effective means. The Chinese invention patent (application publication No. CN1932167) discloses a method for treating a short fiber reinforced lime soil foundation, which combines short fiber and lime and has the characteristics of low cost and simple construction. The Chinese invention patent (application publication No. CN104358198A) discloses a method for improving a heavy haul railway roadbed by fiber reinforced solidified soil, which combines monofilament-shaped fibers with a soil solidifying agent (composed of aluminosilicate, aluminoferrite, sulfate, sulfite, sulphoaluminate, chloride and oxide) and has good engineering characteristics of strength, deformation and the like. The Chinese invention patent (application publication No. CN104846807A) discloses a polypropylene fiber reinforced saline soil and a curing method thereof, wherein the method combines polypropylene fiber with lime and fly ash, and has the advantages of being widely applied to curing of saline soil and the like. The Chinese invention patent (application publication No. CN106436679A) discloses a reinforced earth containing basalt fibers and nano-silica and a preparation method thereof, and the method combines the basalt fibers and the nano-silica and can effectively improve the mechanical property of soft clay. The method has the common characteristic that the distribution of the fibers in the soil body is randomly dispersed.
However, it has been found that the distribution of the fibers in the fiber reinforced earth is non-uniform and tends to be horizontal or nearly horizontal due to the influence of the field construction or the preparation method of the sample in the room. The non-uniform distribution of the fibers causes the strength and deformation of the fiber reinforced soil to have anisotropic characteristics, so that the traditional fiber reinforced soil constitutive model and the stability analysis theory are not applicable any more. Aiming at the problem, related researches mainly adopt theoretical analysis or numerical simulation means to discuss the influence of fiber orientation on the strength and deformation characteristics of the fiber reinforced soil and the mechanical mechanism of the fiber reinforced soil. In addition, laboratory tests are important means for revealing rules, verifying theories and numerical models, but due to the difficulty in sample preparation, researches for exploring the influence effect and action mechanism of fiber orientation by adopting test means are rare. When the fiber is used in combination with other materials to modify the soil, the strength and deformation characteristics of the modified soil must be affected by the fiber orientation distribution, thereby further affecting the applicability or accuracy of constitutive models, numerical simulations, and theoretical analysis. However, studies related to this problem have not been reported. Therefore, there is a need to develop research on the influence effect of fiber orientation on the mechanical properties of the soil improved by combining fibers and other materials and the intrinsic mechanism thereof, which is of great significance for promoting the development and application of foundation treatment technology. One of the fundamental works of the research is a preparation device and a preparation method for improving soil samples by a physical and chemical method containing directionally distributed fibers.
Disclosure of Invention
The invention provides a preparation device and a preparation method of a physicochemical method improved soil sample containing directionally distributed fibers, the device and the method are simple to operate, low in cost and high in precision, and can be used for researching the influence effect of fiber orientation on the mechanical properties of the fibers and other materials combined improved soil and the internal mechanism of the fiber orientation.
The invention adopts the following technical scheme:
a preparation device for a physicochemical method improved soil sample containing directionally distributed fibers comprises a detachable mould, a compaction positioning plate, a compaction hammer system and a fiber directional screen;
the detachable die comprises a bottom steel plate, two outer steel plates, two inner steel plates and a plurality of deformed steel bar pull rods; each side surface of the bottom steel plate is provided with a plurality of screw holes which are used for being matched with self-tapping screws to fix the side steel plate; the inner surface of the outer steel plate is provided with two fixing grooves and positioning grooves, the fixing grooves are used for being embedded into the inner steel plate, and the positioning grooves are formed in the edge of the inner surface of the outer steel plate and used for fixing the compacting positioning plate and the fiber directional screen; the edge of the inner surface of the inner steel plate is provided with a positioning groove, and the size and the function of the positioning groove are the same as those of the positioning groove on the inner surface of the outer steel plate; the upper part of the outer steel plate is provided with a plurality of through screw holes which are used for being matched with the deformed steel pull rod to fix the outer steel plate and the inner steel plate; a soil sample is paved inside the detachable mould;
the compaction positioning plate is used for assisting in positioning the compaction hammer system, and the compaction hammer system is used for compacting the soil sample, so that the dry density of the improved soil sample is ensured to be uniform;
the fiber orientation screen is used for enabling the fibers to be distributed along the direction parallel to the threaded steel pull rod.
In the above technical solution, further, the compacting positioning plate includes an upper steel sheet and a lower steel sheet, and the height of the upper steel sheet and the lower steel sheet is greater than the length of the positioning groove on the inner surface of the outer steel sheet; the lower end of the upper steel sheet and the upper end of the lower steel sheet are provided with clamping grooves with the same size, and the upper steel sheet and the lower steel sheet are connected through the clamping grooves.
Furthermore, the compaction hammer system comprises a compaction hammer sleeve, a compaction hammer arranged in the compaction hammer sleeve and a sleeve cap arranged on the compaction hammer sleeve; the center of the sleeve cap is provided with a round hole for the striking hammer rod to pass through; the compaction hammer is formed by welding a compaction hammer head and a compaction hammer rod, the compaction hammer head and the compaction hammer rod are respectively of a cuboid and a cylinder (the section size of the compaction hammer rod is slightly smaller than the size of a round hole in the center of a sleeve cap), the cross section of the compaction hammer head is square (larger than the size of the round hole in the center of the sleeve cap), the side length of the compaction hammer head is larger than 1/3 of the net distance between two outer side steel plates or two inner side steel plates, and is smaller than 2/3 of the net distance between the two outer side steel plates or the two inner side steel plates; the inner edge of the cross section of the compaction hammer sleeve is square, the side length of the inner edge is larger than that of the cross section of the compaction hammer, and the larger amount of the inner edge is not more than 2 mm.
Furthermore, the fiber directional screen comprises four side aluminum plates and a plurality of bottom parallel fine aluminum wires arranged at the bottoms of the side aluminum plates; the side aluminum plates are connected with each other by welding, and the height of the side aluminum plates is the same as the depth of the detachable die; the clear distance between the bottom parallel aluminum filaments should be at least 5 times the fiber diameter but not more than 10 times the fiber diameter, and the distance between the bottom parallel aluminum filaments and the top surface of the soil sample is 1-2 cm.
Furthermore, the fiber directional screen also comprises a fixed steel plug, wherein a plurality of through holes with equal intervals are arranged at the vertical positions corresponding to the positioning grooves on the inner surfaces of the inner side steel plate and the outer side steel plate on the side aluminum plate, and the through holes are used for being matched with the fixed steel plug to adjust the vertical position of the fiber directional screen.
In the above apparatus, the cross-sectional shape of the base steel plate is square (in plan view). The depth and the width of the fixed groove on the inner surface of the outer steel plate and the depth and the width of the positioning groove are equal and are half of the thickness of the outer steel plate, the length of the fixed groove is equal to the height of the outer steel plate, the fixed groove is used for embedding the inner steel plate, the length of the positioning groove is 2 times of the thickness of the outer steel plate, and the positioning groove is used for fixing and compacting a positioning system and a fixed fiber directional screen. The length of the deformed steel bar pull rod is slightly greater than the sum of the length of the inner steel plate and the thickness of the outer steel plate; the function of the deformed steel bar pull rod is to tightly connect the outer steel plate, the inner steel plate and the bottom steel plate. The thickness of an upper steel sheet and a lower steel sheet of the compaction positioning plate is half of that of an outer steel sheet and an inner steel sheet, and the length is the sum of the clear distance between the two outer steel sheets and the thickness of the outer steel sheets; the heights of the upper steel sheet and the lower steel sheet are 2 times of the lengths of the positioning grooves on the inner surfaces of the inner steel sheet and the outer steel sheet; the size of the clamping groove of the upper steel sheet and the lower steel sheet is the same as that of the positioning groove on the inner surface of the inner steel sheet and the outer steel sheet; the compaction positioning plate can be clamped into or pulled out of the positioning grooves on the inner surfaces of the outer steel plate and the inner steel plate as required. The mass and the falling height of the compaction hammer are respectively 4.5kg and 45 cm; the side length of the square of the cross section of the compaction hammer head is slightly larger than 1/3 of the net distance between two outer side steel plates or two inner side steel plates, so that the matching between the compaction hammer system and the size of the detachable die is ensured; the sleeve cap can be mounted on or dismounted from the top end of the compaction hammer sleeve as required, and the maximum drop height of the compaction hammer can be limited to a set value by combining the sleeve cap and the compaction hammer sleeve. In the fiber directional screen, the diameter of the part of the fixed steel plug inserted into the through hole of the side aluminum plate is slightly smaller than that of the through hole, and the width of the part of the fixed steel plug inserted into the positioning grooves on the inner surfaces of the inner side steel plate and the outer side steel plate is slightly smaller than that of the positioning grooves.
The invention also provides a method for preparing the physicochemical method improved soil sample containing directionally distributed fibers, which is realized based on the device and comprises the following steps:
(1) naturally air-drying the soil body taken from the site or drying the soil body by adopting an oven to obtain dry soil, then grinding the dry soil, and sieving the dry soil by a standard sieve (such as a 2mm sieve) with the aperture required by relevant specifications; weighing chemical additives according to a predetermined mass percentage; preparing fibers according to the preset fiber length and the fiber mass percentage;
(2) uniformly mixing a chemical additive and the screened dry soil, then scattering a small amount of purified water with preset quality for multiple times while stirring, uniformly mixing, then maintaining for a plurality of periods, and obtaining the chemically-modified soil after the maintenance is finished;
(3) assembling a detachable mould and a compaction hammer system; uniformly brushing a layer of vaseline on the inner surface of the detachable mould, sticking a layer of preservative film on the inner surface of the detachable mould, and uniformly brushing a layer of vaseline on the preservative film, so as to ensure that the quick detachment of the detachable mould after compaction is finished and the surface disturbance of the compacted block in the detachable mould detachment process are minimized; the bottom of a compaction hammer head of the compaction hammer system is coated with a layer of transparent adhesive tape for preventing the bottom surface of the compaction hammer head from being bonded with a soil sample in the compaction process;
(4) dividing the fiber and the chemical method improved soil required by the primary preparation process into 9 parts and 10 parts respectively;
(5) uniformly paving a part of chemically-improved soil at the bottom of the detachable mould and troweling the surface of the soil layer;
(6) adjusting the position of a fixed steel plug on the fiber directional screen to enable the distance between the bottom parallel fine aluminum wires of the fiber directional screen and the surface of the soil layer in the detachable mold to be 1-2cm as an adjustment standard, and then assembling the fiber directional screen on the detachable mold;
(7) uniformly scattering a part of fibers into a fiber directional sieve, and stirring the fibers to enable the fibers to fall on the surface of a soil layer in a detachable mold;
(8) pulling out the fiber directional screen from the detachable mold, uniformly paving a part of chemically-modified soil on the surface of the fibers in the detachable mold, and trowelling the surface of a soil layer;
(9) repeating the steps (6), (7) and (8) until an interbedded structure containing three layers of fibers and four layers of chemically modified soil is formed;
(10) assembling the compaction positioning plate and the detachable die together, compacting the mutual-layer structure obtained in the step (9) by using a compaction hammer system 27 times, wherein the compaction sequence is that the periphery is performed first and then the interior is performed at intervals of one compaction, so that the compaction hammer sleeve is ensured to be in close contact with the inner wall of the detachable die or the side surface of the compaction positioning system from top to bottom; after compaction, interlayer napping treatment is carried out;
(11) pulling out the compaction positioning plate, repeating the steps (6), (7), (8), (9) and (10) until all the fibers required in the one-time preparation process and the chemically modified soil are blended and compacted to obtain a physically and chemically modified soil compaction block;
(12) disassembling the detachable mould, taking out the soil compaction block improved by the physical and chemical method, placing the soil compaction block in a fresh-keeping bag for sealed cool storage, cleaning the soil sample and vaseline on the surface of the detachable mould, wiping, assembling and returning for subsequent tests;
(13) placing the physical and chemical modified soil compaction blocks stored in the fresh-keeping bag in a refrigerator for freezing for a plurality of cycles, wherein the cycle is 24 h;
(14) dividing a cutting auxiliary line on the surface of the frozen physical and chemical method improved soil compaction block according to the included angle between the preset fiber orientation and the horizontal plane, and cutting the physical and chemical method improved soil compaction block into small blocks along the cutting auxiliary line to obtain the physical and chemical method improved soil compaction block containing the preset directionally distributed fibers;
(15) and (3) trimming and forming the physical and chemical method improved soil compaction block containing the preset directionally distributed fibers according to the requirements of different tests on the size of the sample, and unfreezing the physical and chemical method improved soil compaction block in a normal-temperature light-shielding environment for 24 hours to obtain the physical and chemical method improved soil sample containing the directionally distributed fibers.
The fiber can be natural fiber such as jute fiber, palm fiber, coconut fiber, sisal fiber, flax fiber, straw fiber, bamboo fiber, bagasse and the like, can also be artificial fiber such as polypropylene fiber, polyester fiber, polyethylene fiber, glass fiber, nylon fiber, polyvinyl alcohol fiber and the like, and can also be fiber with enhanced physical and mechanical properties such as durability, corrosion resistance, strength and the like. The chemical additive can be one of different materials such as cement, lime, fly ash, nano silicon dioxide, coal slag, road fluid, lignin, high polymer materials and the like, and can be a combination of two or more different materials.
Compared with the prior art, the invention has the following beneficial effects:
(1) the device for preparing the physicochemical method improved soil sample containing directionally distributed fibers has the advantages of detachability, convenient assembly, easy manufacture, low cost, high sample preparation precision, accurate compaction control and the like, overcomes the defect that the traditional compaction instrument can only prepare a cylindrical compaction block, and can conveniently prepare the physicochemical method improved soil sample containing any fiber orientation (the included angle between the axial direction of the fibers and the horizontal plane) between 0 and 90 degrees.
(2) The invention provides a fiber orienting sieve which can quickly and effectively distribute fibers along a preset direction on a horizontal plane, and compared with the traditional manual fiber arranging operation, the fiber orienting sieve has the advantages of high efficiency and uniform and consistent fiber orientation; in addition, the fiber directional screen is assembled with the detachable mould by adopting the fixed steel plug with adjustable position, and the parallel fine aluminum wires at the bottom of the fiber directional screen can be conveniently and accurately adjusted to the position 1-2cm away from the surface of the soil layer in the detachable mould, so that the orientation is basically not changed in the falling process of the fibers.
(3) The invention adopts the compaction hammer with the square cross section to compact the improved soil by the physical and chemical method to the preset dry density, and the side length of the cross section of the compaction hammer is slightly larger than 1/3 of the internal dimension of the detachable mould, thereby overcoming the problem of dead angle which can not be compacted when the cylindrical compaction hammer is adopted in the mould with the rectangular cross section, ensuring that a certain lap joint exists at the adjacent compaction positions and effectively avoiding the problem of rugged compaction surface.
(4) The invention adopts the processes of freezing, drawing auxiliary lines, cutting, natural melting and the like to prepare the physicochemical method improved soil sample containing directionally distributed fibers, can achieve the aim of reducing the disturbance of the cutting process to the fibers as much as possible on the premise of ensuring that the fiber orientation accurately meets the preset requirement, and overcomes the defect that the fibers can be pulled or pulled out by the operation of trimming and compacting blocks under the traditional non-freezing condition.
(5) The device and the method for preparing the soil sample improved by the physical and chemical method containing directionally distributed fibers have the advantages of strong applicability, multiple purposes and wide accommodation range, and can be used for preparing samples with different fiber lengths, different fiber contents and different chemical additive mixing amounts.
(6) The physicochemical method modified soil sample containing directionally distributed fibers prepared by the device and the method can be used for various tests, including a triaxial compression test, an unconfined compressive strength test, a direct shear test and the like.
Drawings
FIG. 1 is a schematic view of a removable mold;
FIG. 2 is a schematic view of the compacting positioning plate, wherein FIG. 2 a is an assembled state and FIG. 2 b is an unassembled state;
FIG. 3 is a schematic view of a compaction hammer system, with FIG. 3 a in an assembled state and FIG. 3 b in an unassembled state;
FIG. 4 is a schematic view of a fiber orienting screen, with FIG. 4 a in an assembled state and FIG. 4 b in an unassembled state;
FIG. 5 is a schematic view of the apparatus when the tamping positioning plate is assembled with the detachable mold;
FIG. 6 is a schematic view of the apparatus when the fiber orienting screen is assembled with the removable mold;
FIG. 7 is a flow chart of sample preparation;
FIG. 8 is a schematic view of the compaction sequence;
FIG. 9 is a schematic view of a physicochemical method modified soil compacting block cutting auxiliary line at different preset fiber orientations;
in the figure: the device comprises a detachable die 1, a compaction positioning plate 2, a compaction hammer system 3, a fiber directional screen 4, a bottom steel plate 1-1, an outer steel plate 1-2, an inner steel plate 1-3, a screw steel pull rod 1-4, a hexagon nut 1-5, a self-tapping screw 1-6, an outer steel plate fixing groove 1-2-1 and an outer steel plate positioning groove 1-2-2, the steel plate compaction device comprises 1-3-1 parts of inner side steel plate positioning grooves, 2-1 parts of upper steel plates, 2-2 parts of lower steel plates, 3-1 parts of compaction hammers, 3-2 parts of compaction hammer sleeves, 3-3 parts of sleeve caps, 3-1-1 parts of compaction hammers, 3-1-2 parts of compaction hammer rods, 4-1 parts of side aluminum plates, 4-2 parts of bottom parallel fine aluminum wires, 4-3 parts of fixed steel plugs and 4-1-1 parts of through-penetration holes.
Detailed Description
The invention will be further described with reference to the following drawings and specific embodiments.
Fig. 1-6 show an apparatus for preparing a physicochemical method modified soil sample containing directionally distributed fibers according to the present invention. The device includes: the device comprises a detachable die 1, a compaction positioning plate 2, a compaction hammer system 3 and a fiber directional screen 4.
The detachable die 1 consists of a bottom steel plate 1-1, two outer steel plates 1-2, two inner steel plates 1-3, four threaded steel pull rods 1-4, eight hexagon nuts 1-5 and eight self-tapping screws 1-6; each side surface of the bottom steel plate 1-1 is provided with two screw holes which are used for being matched with self-tapping screws 1-6 to fix side steel plates (comprising outer side steel plates 1-2 and inner side steel plates 1-3); the cross section of the bottom steel plate 1-1 is square (overlook), the side length is 15cm, and the thickness is 1 cm; the outer steel plate 1-2 is provided with six through screw holes along the thickness direction, and the inner surface is provided with two outer steel plate fixing grooves 1-2-1 and an outer steel plate positioning groove 1-2-2 (the horizontal clear distance between the positioning groove and the outer steel plate vertical to the central section of the bottom steel plate is 1/2 of the outer diameter of the compaction hammer sleeve); the bottom of the inner steel plate 1-3 is provided with two through screw holes along the thickness direction, and the through screw holes are used for being matched with self-tapping screws 1-6 to connect the bottom steel plate 1-1 and the outer steel plate 1-2; the top of the inner surface of the inner steel plate 1-3 close to the edge is provided with an inner steel plate positioning groove 1-3-1 (the horizontal clear distance between the positioning groove and the inner steel plate, which is perpendicular to the central section of the bottom steel plate, is 1/2 of the outer diameter of the compaction hammer sleeve), and the size and the effect of the groove are the same as those of the outer steel plate positioning groove 1-2-2; the length of the deformed steel bar pull rod 1-4 is slightly larger than the sum of the length of the inner steel plate 1-3 and the thickness of the outer steel plate 1-2.
The compacting positioning plate 2 consists of an upper steel sheet 2-1 and a lower steel sheet 2-2; the thickness of the upper steel sheet 2-1 and the lower steel sheet 2-2 is half of the thickness of the outer steel sheet 1-2 and the inner steel sheet 1-3, and the length is the sum of the clear distance between the two outer steel sheets 1-2 and the thickness thereof; the heights of the upper steel sheet 2-1 and the lower steel sheet 2-2 are 2 times of the lengths of the positioning grooves on the inner surfaces of the inner steel sheet 1-3 and the outer steel sheet 1-2.
The compaction hammer system 3 consists of a compaction hammer 3-1, a compaction hammer sleeve 3-2 and a sleeve cap 3-3; the compaction hammer 3-1 is 4.5kg and 45cm in mass and drop height respectively and is formed by welding a compaction hammer head 3-1-1 and a compaction hammer rod 3-1-2; the compaction hammer head 3-1-1 and the compaction hammer rod 3-1-2 are respectively rectangular and cylindrical in shape; the cross section of the compaction hammer head 3-1-1 is square, and the side length of the compaction hammer head is slightly larger than 1/3 of the net distance between two outer side steel plates or two inner side steel plates.
The fiber directional screen 4 consists of four side aluminum plates 4-1, a plurality of bottom parallel fine aluminum wires 4-2 and four fixed steel plugs 4-3; the side aluminum plates 4-1 are connected with each other by welding, and the height of the side aluminum plate 4-1 is the same as the depth of the detachable die 1; the side aluminum plate 4-1 is provided with a plurality of through holes 4-1-1 with equal intervals at the vertical positions corresponding to the positioning grooves on the inner surfaces of the inner side steel plate 1-3 and the outer side steel plate 1-2, and the through holes are used for being matched with the fixed steel plugs 4-3 to adjust the vertical position of the fiber directional screen 4; the clear distance between every two aluminum filaments of the bottom parallel fine aluminum filaments 4-2 should be at least 5 times the fiber diameter, but should not be larger than 10 times the fiber diameter.
Example (b):
a preparation method of a triaxial compression sample of directionally distributed jute fiber reinforced lime solidified expansive soil with the included fiber orientation of 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees.
Schematic diagrams of sample preparation procedures and methods are shown in fig. 7-9.
Step 1: the material is prepared. The soil body needing to be improved is weak potential expansive soil taken from a deep and large foundation pit of a certain station of a first-grade line of a combined-fertilizer subway, and the basic physical and mechanical properties of the soil body are as follows: the natural density is 2.69g/cm3The natural water content is 21.3 percent, the specific gravity is 2.69, the free expansion rate is 53 percent, the plastic limit is 20.1 percent, the liquid limit is 42.7 percent, the optimal water content is 18 percent, and the maximum dry density is 1.72g/cm3. The selected reinforcement material is jute fiber which is one of the most cheap and widely used natural fibers and is called gold fiber. Among all natural fiber types, jute fiber has the highest tensile strength and is resistant to crushing and high temperature. The excellent characteristics of jute fiber make jute fiber play more and more important role in the field of soil improvement. The basic physical mechanical parameters (average values) of the adopted jute fiber are as follows: the length of the fiber is 12mm, the fiber content (in dry soil mass percent) is 0.6 percent, the diameter is 55 mu m, and the density is 1.38g/cm3Elongation of 1.65%, tensile strength of 596.5MPa, Young's modulus of 20GPa, specific tensile strength of 424.5MPa/g.cm-3Specific Young's modulus of 14.25GPa/g.cm-3. The adopted lime is slaked lime, and the components and the mass percent of the lime are calcium hydroxide (90%), calcium carbonate (1.8%), aluminum oxide (0.4%), ferric oxide (0.3%), magnesium oxide (0.7%), silicon dioxide (1.2%) and impurities (5.9%). Before the lime is added, the lime is sieved through a 2mm sieve to remove impurities. The mixing amount of the lime is 4 percent (accounting for the mass percent of the dry soil).
Step 2: preparing the soil improved by a chemical method. Uniformly mixing the sieved lime with dried, scattered and sieved dry soil by adopting a manual method, then scattering purified water accounting for 18 percent of the mass of the dry soil for a few times while stirring, uniformly mixing, placing in a constant-temperature (25 +/-1 ℃) and constant-humidity (humidity 95%) environment for curing for 14 days, and obtaining the lime-cured expansive soil after the curing is finished.
And step 3: a device is prepared. Uniformly coating a layer of vaseline on the inner surface of the detachable mould 1, then pasting a layer of preservative film on the inner surface of the detachable mould 1 coated with the vaseline, uniformly coating a layer of vaseline on the preservative film, and then wrapping a layer of transparent adhesive tape on the bottom surface of a compaction hammer 3-1-1 of the compaction hammer system 3.
And 4, step 4: the preparation physical and chemical method improves the soil compaction block. According to the parameters of the volume of the detachable mould 1, the maximum dry density required to be compacted, the content of the preset material and the like, the mass of the dried expansive soil required in the primary preparation process is 5805g, the mass of the jute fiber is 34.83g, and the mass of the lime is 232.2 g. Dividing the jute fiber and lime solidified expansive soil required in the primary preparation process into 9 parts and 10 parts respectively, wherein the mass of each part is 3.87g and 30.12 g; paving a part of lime cured expansive soil on the bottom surface of the detachable mold 1 and trowelling the surface, installing a fiber directional sieve 4 and adjusting the position of the fiber directional sieve to be 1-2cm away from the surface of the soil layer, scattering a part of jute fiber into the fiber directional sieve 4, and stirring the fiber to enable the jute fiber to fall into the surface of the soil layer in a fixed direction; repeating the above operations until an interbedded structure comprising three parts of jute fiber and four parts of lime-cured expansive soil is formed; using a compaction hammer system 3 to compact the above-mentioned interlayer structure 27 times in the order shown in fig. 8 (the numbers in the figure represent compaction sequence, and the shaded parts are compaction overlapped regions), and then performing surface "napping" treatment; and repeating the operation until obtaining the jute fiber reinforced lime solidified expansive soil compaction block with the horizontal fiber orientation.
And 5: and (5) disassembling the device. And placing the taken out jute fiber reinforced lime solidified expansive soil compaction block with the fiber orientation being horizontal in a fresh-keeping bag, sealing, storing in shade, cleaning the detachable mould 1, and wiping, assembling and returning the detachable mould.
Step 6: the freezing physical and chemical method improves the soil compaction block. And (3) placing the jute fiber reinforced lime solidified expansive soil compaction block which is wrapped in the sealed fresh-keeping bag and has the fiber orientation of the horizontal fiber reinforced lime solidified expansive soil compaction block in a refrigerator for freezing for 24 hours.
And 7: and improving the soil compaction block according to a physicochemical method after cutting and freezing according to the preset fiber orientation. As shown in fig. 9, cutting auxiliary lines were defined with an oil marker on the surface of the frozen jute fiber reinforced lime solidified expansive soil compacted cake with the fiber orientation horizontal. Wherein the cutting auxiliary line at the fiber orientation of 0 ° is parallel or perpendicular to the horizontal plane (fig. 9 (a)); the cutting auxiliary line when the fiber orientation is 15 ° or 75 ° is parallel to the horizontal plane, and forms an included angle of 15 ° or 75 ° with the horizontal plane (fig. 9 (b)); the cutting auxiliary line when the fiber orientation is 30 ° or 60 ° is parallel to the horizontal plane, and forms an included angle of 30 ° or 60 ° with the horizontal plane (fig. 9 (c)); the cutting auxiliary line when the fiber orientation is 45 ° is parallel to the horizontal plane or forms an angle of 45 ° with the horizontal plane (fig. 9 (d)); the cutting auxiliary line at the fiber orientation of 90 ° is parallel or perpendicular to the horizontal plane (fig. 9 (e)).
And 8: and (3) trimming the soil compaction block containing the directionally distributed fibers according to the size requirement of the sample by a physical and chemical method. And slowly and finely trimming the directionally distributed jute fiber reinforced lime solidified expansive soil compaction block containing the preset fiber orientation obtained in the previous step into a freezing cylinder sample with the diameter of 39.1mm and the height of 80mm by using tools such as a long ring cutter, an art designing cutter and the like.
And step 9: and (3) putting the obtained frozen cylinder sample in a normal-temperature light-shielding environment for melting for 24h, and finally obtaining a triaxial compression sample of the directionally-distributed jute fiber reinforced lime solidified expansive soil with the included fiber orientations of 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees.
Claims (3)
1. A device for preparing a physicochemical method improved soil sample containing directionally distributed fibers is characterized by comprising a detachable die, a compaction positioning plate, a compaction hammer system and a fiber directional screen;
the detachable die comprises a bottom steel plate, two outer steel plates, two inner steel plates and a plurality of deformed steel bar pull rods; each side surface of the bottom steel plate is provided with a plurality of screw holes which are used for being matched with self-tapping screws to fix the side steel plate; the inner surface of the outer steel plate is provided with two fixing grooves and positioning grooves, the fixing grooves are used for being embedded into the inner steel plate, and the positioning grooves are formed in the edge of the inner surface of the outer steel plate and used for fixing the compacting positioning plate and the fiber directional screen; the edge of the inner surface of the inner steel plate is provided with a positioning groove, and the size and the function of the positioning groove are the same as those of the positioning groove on the inner surface of the outer steel plate; the upper part of the outer steel plate is provided with a plurality of through screw holes which are used for being matched with the deformed steel pull rod to fix the outer steel plate and the inner steel plate; a soil sample is paved inside the detachable mould;
the compaction positioning plate is used for assisting in positioning the compaction hammer system, and the compaction hammer system is used for compacting the soil sample, so that the dry density of the improved soil sample is ensured to be uniform;
the fiber directional screen is used for enabling fibers to be distributed along the direction parallel to the deformed steel bar pull rod;
the compaction positioning plate comprises an upper steel sheet and a lower steel sheet, and the height of the upper steel sheet and the height of the lower steel sheet are greater than the length of a positioning groove on the inner surface of the outer steel sheet; the lower end of the upper steel sheet and the upper end of the lower steel sheet are provided with clamping grooves with the same size, and the upper steel sheet and the lower steel sheet are connected through the clamping grooves;
the fiber directional screen comprises four side aluminum plates and a plurality of bottom parallel fine aluminum wires arranged at the bottoms of the side aluminum plates; the side aluminum plates are connected with each other by welding, and the height of the side aluminum plates is the same as the depth of the detachable die; the clear distance between the bottom parallel aluminum filaments is at least 5 times of the fiber diameter, but not more than 10 times of the fiber diameter, and the distance between the bottom parallel aluminum filaments and the top surface of the soil sample is 1-2 cm;
the fiber directional screen also comprises a fixed steel plug, wherein a plurality of equidistant through holes are formed in the vertical positions, corresponding to the positioning grooves in the inner surfaces of the inner side steel plate and the outer side steel plate, of the side aluminum plate, and the vertical positions are used in cooperation with the fixed steel plug to adjust the fiber directional screen.
2. The apparatus for preparing the physicochemical modified soil sample containing directionally distributed fibers according to claim 1, wherein the compaction hammer system comprises a compaction hammer sleeve, a compaction hammer arranged in the compaction hammer sleeve and a sleeve cap arranged on the compaction hammer sleeve; the center of the sleeve cap is provided with a round hole for the striking hammer rod to pass through; the compaction hammer is formed by welding a compaction hammer head and a compaction hammer rod, the compaction hammer head and the compaction hammer rod are respectively rectangular and cylindrical, the cross section of the compaction hammer head is square, the side length of the compaction hammer head is greater than 1/3 of the net distance between two outer side steel plates or two inner side steel plates, and is less than 2/3 of the net distance between the two outer side steel plates or the two inner side steel plates; the inner edge of the cross section of the compaction hammer sleeve is square, the side length of the inner edge is larger than that of the cross section of the compaction hammer, and the larger amount of the inner edge is not more than 2 mm.
3. A method for preparing a physicochemical modified soil sample containing directionally distributed fibers, which is realized based on the device of claim 1 or 2, and comprises the following steps:
(1) naturally air-drying the soil body taken from the site or drying the soil body by using an oven to obtain dry soil, then grinding the dry soil, and sieving the dry soil by using a standard sieve with the required aperture according to relevant specifications; weighing chemical additives according to a predetermined mass percentage; preparing fibers according to the preset fiber length and the fiber mass percentage;
(2) uniformly mixing a chemical additive and the screened dry soil, then scattering a small amount of purified water with preset quality for multiple times while stirring, uniformly mixing, then maintaining for a plurality of periods, and obtaining the chemically-modified soil after the maintenance is finished;
(3) assembling a detachable mould and a compaction hammer system; uniformly brushing a layer of vaseline on the inner surface of the detachable mould, sticking a layer of preservative film on the inner surface of the detachable mould, and uniformly brushing a layer of vaseline on the preservative film, so as to ensure that the quick detachment of the detachable mould after compaction is finished and the surface disturbance of the compacted block in the detachable mould detachment process are minimized; the bottom of a compaction hammer head of the compaction hammer system is coated with a layer of transparent adhesive tape for preventing the bottom surface of the compaction hammer head from being bonded with a soil sample in the compaction process;
(4) dividing the fiber and the chemical method improved soil required by the primary preparation process into 9 parts and 10 parts respectively;
(5) uniformly paving a part of chemically-improved soil at the bottom of the detachable mould and troweling the surface of the soil layer;
(6) adjusting the position of a fixed steel plug on the fiber directional screen to enable the distance between the bottom parallel fine aluminum wires of the fiber directional screen and the surface of the soil layer in the detachable mold to be 1-2cm as an adjustment standard, and then assembling the fiber directional screen on the detachable mold;
(7) uniformly scattering a part of fibers into a fiber directional sieve, and stirring the fibers to enable the fibers to fall on the surface of a soil layer in a detachable mold;
(8) pulling out the fiber directional screen from the detachable mold, uniformly paving a part of chemically-modified soil on the surface of the fibers in the detachable mold, and trowelling the surface of a soil layer;
(9) repeating the steps (6), (7) and (8) until an interbedded structure containing three layers of fibers and four layers of chemically modified soil is formed;
(10) assembling the compaction positioning plate and the detachable die together, compacting the mutual-layer structure obtained in the step (9) by using a compaction hammer system 27 times, wherein the compaction sequence is that the periphery is performed first and then the interior is performed at intervals of one compaction, so that the compaction hammer sleeve is ensured to be in close contact with the inner wall of the detachable die or the side surface of the compaction positioning system from top to bottom; after compaction, interlayer napping treatment is carried out;
(11) pulling out the compaction positioning plate, repeating the steps (6), (7), (8), (9) and (10) until all the fibers required in the one-time preparation process and the chemically modified soil are blended and compacted to obtain a physically and chemically modified soil compaction block;
(12) disassembling the detachable mould, taking out the soil compaction block improved by the physical and chemical method, placing the soil compaction block in a fresh-keeping bag for sealed cool storage, cleaning the soil sample and vaseline on the surface of the detachable mould, wiping, assembling and returning for subsequent tests;
(13) placing the physical and chemical modified soil compaction blocks stored in the fresh-keeping bag in a refrigerator for freezing for a plurality of cycles, wherein the cycle is 24 h;
(14) dividing a cutting auxiliary line on the surface of the frozen physical and chemical method improved soil compaction block according to the included angle between the preset fiber orientation and the horizontal plane, and cutting the physical and chemical method improved soil compaction block into small blocks along the cutting auxiliary line to obtain the physical and chemical method improved soil compaction block containing the preset directionally distributed fibers;
(15) and (3) trimming and forming the physical and chemical method improved soil compaction block containing the preset directionally distributed fibers according to the requirements of different tests on the size of the sample, and unfreezing the physical and chemical method improved soil compaction block in a normal-temperature light-shielding environment for 24 hours to obtain the physical and chemical method improved soil sample containing the directionally distributed fibers.
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| CN113235669B (en) * | 2021-04-14 | 2022-03-29 | 吉林建筑大学 | Assembled pre-buried half-pile remolded soil consolidation model box |
| CN113668502A (en) * | 2021-07-13 | 2021-11-19 | 中铁十九局集团第五工程有限公司 | Method for improving expansive soil |
| CN114197444A (en) * | 2021-11-09 | 2022-03-18 | 河南大学 | Method for improving expansive soil |
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