CN113237773A - Mechanical test device and method for simulating pile end resistance and neutral point change - Google Patents
Mechanical test device and method for simulating pile end resistance and neutral point change Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- 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
- G01N3/14—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by dead weight, e.g. pendulum; generated by springs tension
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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
- G01N2203/0001—Type of application of the stress
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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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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Abstract
The invention discloses a mechanical test device and a method for simulating resistance of a pile end and change of a neutral point, wherein the test device comprises a loading system, a rectangular model box, a support system, a pile foundation with side wings, a pile end soil simulation device and a measuring system; when the loading mechanism adopts a pile foundation pressurizing device, the pile foundation generates positive frictional resistance; when the loading mechanism adopts a pile loading pressurizing device, the pile foundation generates negative friction resistance. The side wing bends upwards and downwards along with the soil body around the pile, a displacement field of the soil around the pile can be obtained according to the bending of the side wing, and the position of a neutral point is analyzed according to an interpolation method; the pile end spring is deformed, and the pile end axial force, namely the end resistance, can be measured according to the deformation. The mechanical test device provided by the invention is simple and high in precision, and can simulate the pile end resistance and the soil deformation around the pile of positive and negative frictional resistance and the change of the neutral point position in the process of negative frictional resistance.
Description
Technical Field
The invention relates to the technical field of civil engineering, in particular to a mechanical test device and a method for simulating pile end resistance and neutral point change.
Background
The main effect of pile foundation is with upper portion load transmission to lower part soil layer, and its vertical bearing capacity is that pile soil combined action provides, and pile body can carry out the interact with pile week and pile end soil in the transmission course and form frictional resistance and end resistance. When the soil sinking displacement around the pile is smaller than that of the pile body, the positive frictional resistance in the upward direction is generated around the pile to prevent the pile foundation from sinking; when the soil subsidence displacement around the pile is larger than the pile body, negative friction resistance in the downward direction is generated around the pile, the pile foundation subsidence is increased, and the building is unevenly subsided. The method is influenced by factors such as load size, pile body rigidity, pile soil surrounding and pile end soil property, the interaction and load transfer mechanism of the pile soil are complex, and the current related research theory is still incomplete.
When the soil property around the pile is not changed, the influence of the pile end soil rigidity on the proportion of the frictional resistance and the end resistance to the total bearing capacity is great: when the rigidity of the pile end soil is small, the frictional resistance is fully exerted, and the end resistance ratio is small; on the contrary, the frictional resistance cannot be fully exerted, and the end resistance ratio is large. When the negative frictional resistance is generated, the frictional resistance at the position where the settlement of the soil around the pile is equal to that of the cross section of the pile and no relative displacement occurs is zero, namely the neutral point of the pile. The frictional resistance above this position is a negative frictional resistance and the frictional resistance below this position is a positive frictional resistance, at which point the shaft force of the pile body reaches a maximum. The neutral point is an important parameter in the stress analysis and the bearing capacity design of the pile foundation, and the change of the position of the neutral point directly influences the magnitude of the negative frictional resistance of the pile foundation.
Neutral point depth ratio specified in the current specificationln/l 0(whereinl nThe depth of the neutral point is the depth of the neutral point,l 0lower limit depth of a soft soil layer around the pile) is obtained from engineering experience, estimation is carried out according to the characteristics of a soil bearing layer at the pile end, and the situation of overlarge error often exists in the actual design. The conventional experimental research method is to calculate the relative displacement of the pile soil by measuring the soil pressure around the pile and the stress distribution of the pile body, and calculate the displacement zero point as the depth of the neutral point. The neutral point position can not be directly measured, the interaction of the pile and the soil can not be directly observed, and the mechanism error is difficult to control.
Chinese patent publication No. CN108181180A discloses a test apparatus and method for simulating the change of the neutral point of negative frictional resistance of a pile caused by ground stacking. The testing device obtains settlement of different depths of soil around the pile and pile-soil relative displacement through the colored gravel and the pile side marks so as to determine the position change of a neutral point. But has the following disadvantages: the used material only can be transparent soil, and the colored gravel used as the marking is easy to mix with the transparent soil; drainage is needed, and drainage conditions are not consistent with actual conditions; the settlement and the deformation are determined by adopting the image processing of the camera, and the data is difficult to keep accurate; the loading mechanism is relatively complex to manufacture and relatively high in cost.
The mechanical test device provided by the invention is simple and high in precision, and can simulate the pile end resistance and the soil deformation around the pile of positive and negative frictional resistance and the change of the neutral point position in the process of negative frictional resistance. The device can be used as a teaching aid in class, so that students can understand the concept of the bearing capacity of the pile foundation clearly; and important application reference can be provided for pile foundation design, and higher theoretical and application values are achieved.
Disclosure of Invention
The invention aims to solve the technical problem of providing a mechanical test device and a method for simulating the resistance of a pile end and the change of a neutral point.
In order to solve the technical problems, the invention adopts the following technical means:
the mechanical test device for simulating the resistance magnitude of the pile end and the change of the neutral point comprises a loading mechanism, a rectangular model box, a support mechanism, a pile foundation with a side wing, a pile end soil simulation mechanism and a measuring mechanism, wherein the loading mechanism comprises a pile top load pressurizing device, a ground pile loading pressurizing device and a weight; the rectangular model box comprises a left side wall, a right side wall, a transparent front side wall and a transparent rear side wall; the rectangular model box contains pile foundation and experimental soil; the bracket mechanism comprises a bracket upper plate, a bracket lower plate and bracket columns; a bracket column is arranged in front of the bracket upper disc and the bracket lower disc; the support upper wall supports the rectangular model box, and a pile foundation socket is arranged at the center of the support upper wall; the pile foundation with the side wings comprises a pile foundation and the side wings; the pile soil-holding simulation mechanism comprises an upper bearing plate, a lower bearing plate, a guide rod and a spring, wherein the spring is sleeved on the guide rod, two ends of the spring are respectively abutted against the upper bearing plate and the lower bearing plate, the upper bearing plate moves along the guide rod when stressed, and the pile soil-holding simulation mechanism is used for simulating the vertical deformation of pile soil-holding; the pile foundation is vertically arranged in the rectangular model box, the top end of the pile foundation extends outwards from the rectangular model box, the bottom end of the pile foundation penetrates through the pile foundation socket and then abuts against the upper surface of the upper bearing plate, and the left side and the right side of the part, located in the box body, of the pile foundation are provided with side wings which are arranged at intervals; the side wing is made of semi-flexible material and deforms along with the deformation of the soil body; the weights are directly placed on the pile top load pressurizing device or the ground stacking pressurizing device; when the pile foundation pressurizing device is adopted, the pile foundation can generate positive frictional resistance; when the pile loading pressurizing device is adopted, the pile foundation can generate negative frictional resistance; the measuring mechanism comprises a ruler and scales arranged on the front transparent side wall.
The loading mechanism comprises a pile foundation pressurizing device and a pile loading pressurizing device, and can respectively enable the pile foundation to generate positive frictional resistance and negative frictional resistance; the transparent front and back side walls of the rectangular model box are convenient for observation; the side wing part of the pile foundation is made of semi-flexible materials, can be bent and deformed along with the deformation of soil, and can obtain a displacement field of the soil around the pile according to the bending of the side wing; the pile end soil simulation mechanism comprises a guide rod, an upper bearing plate, a lower bearing plate, a spring and an anti-deviation plate and is used for simulating the vertical deformation of pile end soil; the measuring mechanism comprises a transparent side wall with scales and a ruler.
The working principle of the invention is as follows:
when the loading mechanism adopts a pile foundation pressurizing device, the pile foundation generates positive frictional resistance. The side wing bends upwards along with the soil body around the pile, and a displacement field of the soil around the pile can be obtained according to the bending of the side wing. The pile end spring deforms, and the pile end axial force, namely the end resistance, can be measured according to the deformation; when the loading mechanism adopts a pile loading pressurizing device, the pile foundation generates negative friction resistance. The side wings are bent upwards and downwards along with the soil body around the pile, a displacement field of the soil around the pile can be obtained according to the bending of the side wings, and the position of a neutral point is analyzed according to an interpolation method. The pile end spring is deformed, and the pile end axial force, namely the end resistance, can be measured according to the deformation.
The positive frictional resistance and the negative frictional resistance working condition of the pile foundation can be simulated only by replacing the pile foundation pressurizing device and the ground pile loading pressurizing device, other internal test equipment does not need to be used, the displacement field of the soil around the pile during positive frictional resistance can be obtained through deformation and displacement of the side wings and the springs, the side resistance and the end resistance of the pile foundation, the displacement field of the soil around the pile during negative frictional resistance, and the neutral point and the end resistance of the pile foundation.
The device of the invention is simple and high in precision, can simulate the pile end resistance and the soil deformation around the pile of the positive and negative frictional resistance, and can also simulate the change of the neutral point position during the negative frictional resistance.
The further preferred technical scheme is as follows:
the pile foundation pressurizing device and the pile loading pressurizing device are both provided with a pressing block and a pressing block support, and the pressing block support of the pile foundation pressurizing device is clamped at the top end of the pile foundation so that the gravity of the pile foundation pressurizing device acts on the top end of the pile foundation; the bottom of a pressing block support of the pile loading pressurizing device is provided with a pressing plate, the top end of the pile foundation upwards penetrates through the pressing plate and has no friction with the pressing plate, and the gravity of the pile loading pressurizing device only acts on the upper surface of experimental soil filled in the rectangular model box through the pressing plate.
Through setting up the briquetting support, be convenient for make pile foundation pressure device or pile through the briquetting support carry pressure device's gravity to act on the upper surface of the experimental soil of packing in pile foundation or the rectangular mold case.
The pile foundation pressurizing device and the pile loading pressurizing device are made of light materials.
The left side wall and the right side wall are rigid side walls, the front side wall and the rear side wall are transparent side walls, and the front side and the rear side of each rigid side wall are provided with vertically arranged caulking grooves.
By the arrangement, the front and rear transparent side walls can be conveniently nested and arranged in the caulking grooves of the rigid side walls or pulled out from the caulking grooves of the rigid side walls.
The upper tray of the bracket is bonded with the bottom end of the rigid side wall to form a rectangular model box.
Through the arrangement, a part of the upper tray of the bracket serves as the bottom surface of the rectangular model box, and the upper tray of the bracket also plays a role in supporting the rectangular model box. The number of the components is reduced, so that the device has a simpler structure.
The four support columns are vertically arranged at four corners of the lower support plate respectively, and the bottom ends of the support columns are fixedly connected with the lower support plate respectively; the support upper disc is provided with a support jack corresponding to the support column, and the support upper disc is sleeved on the support column through the support jack.
Through setting up the support jack, be convenient for the support hanging wall cup joints on the support post through the support jack.
The top of four support posts all be equipped with bearing bolt, bearing bolt sets up at same height, bearing bolt supports support hanging wall.
And a support bolt is arranged on the support column to limit and support the support upper disc. The support column can also be provided with a limit platform or a limit protrusion instead of a bolt.
Two side connection around lower bearing plate be provided with prevent inclined to one side board, prevent vertical setting of inclined to one side board and bottom and lower bearing plate fixed connection.
The width of the upper bearing plate corresponds to the interval between the two anti-deviation plates, and no friction exists between the upper bearing plate and the anti-deviation plates, so that the upper bearing plate and the pile foundation butted on the upper bearing plate are prevented from moving vertically and not being inclined.
A mechanical test method for simulating the resistance of the pile base end and the change of a neutral point comprises the following steps:
the first step is as follows: inserting the pile foundation into a model box to penetrate through the support upper disc, placing the pile end soil simulation mechanism on the lower bearing plate, enabling the lower end of the pile foundation to be just contacted with the pile end soil simulation mechanism, and positioning the position of the pile foundation at the moment;
the second step is that: weighing the soil amount required by filling the model box according to the density of the soil to be tested, horizontally placing the model box at the edge of a test bed, adhering the upper support plate to the bottom of the model box in a high-altitude state, and uniformly filling the soil into the model box; the model box is horizontally placed, the front transparent side wall is drawn out, the pile foundation is horizontally placed at the moment, and the side wings are vertical; the purpose of this is to allow even loading of the soil and to avoid bending of the flanks during loading of the soil.
The third step: erecting a model box, inserting four support columns into the upper support disc, stabilizing the support disc on the bearing bolts, and enabling the lower end of a pile foundation to be just in contact with a pile end soil simulation mechanism; recording the initial position of the side wing, and measuring the distance between the upper bearing plate and the lower bearing plate by using a ruler, namely the initial length of the spring;
the fourth step: when the positive frictional resistance of the pile foundation is simulated, the pile foundation pressurizing device is installed at the top end of the pile foundation, and weights are loaded on the loading device; when pile foundation negative frictional resistance simulation is carried out, the pile loading pressurizing device is installed at the top end of soil, and weights are loaded on the loading device;
the fifth step: after the deformation is stable, reading the displacement deformation of the pile foundation and the side wings, measuring the final length of the spring to obtain the deformation and displacement field of the pile foundation and the side wings, calculating the deformation of the spring, defining the downward bending of the side wings as a negative value and the upward bending as a positive value, and taking the average sedimentation value of each side wing as the sedimentation value of the layer of soil;
when the positive frictional resistance working condition of the pile foundation is simulated, the known pile top load, namely the sum of the weights and the gravity of the pressurizing device isQThe resistance of the pile base end can be calculated according to Hooke's law through the deformation of the springN l The pile foundation frictional resistance isQ s =Q-N l ；
When the negative frictional resistance working condition of the pile foundation is simulated, the known ground stacking load is that the sum of the gravity of the weight and the pressurizing device is equal toQSetting pile foundation frictionResistance isQ n The resistance of the pile base end can be calculated according to Hooke's law through the deformation of the springN l The total frictional resistance of the pile foundation isQ n -Q s =Q-N l ；
And a sixth step: the rigidity of the pile foundation, the compression modulus of soil, the load size of a weight or the elastic modulus of a spring are changed, and the positive and negative frictional resistance stress characteristics of the pile foundation under different working conditions are simulated.
The invention has the advantages that:
(1) utilize the deformation of the flexible flank of pile foundation to confirm displacement and the deformation of soil around the stake, its deformation and displacement value can accurately be read out through the scale on the transparent lateral wall, need not be with the help of other auxiliary assembly, be convenient for directly perceived and qualitative analysis, easy operation, and the influence factor is few, and the error is little.
(2) By replacing the loading device, simulation of the positive frictional resistance working condition and simulation of the negative frictional resistance working condition of the pile foundation can be realized, and a corresponding displacement field and pile end resistance are obtained.
(3) The material of the pile foundation can be changed, namely the rigidity of the pile foundation is changed, and the relation between the rigidity of the pile foundation and a displacement field is searched.
(4) The soil around the pile can be adjusted, namely the compression modulus of the soil is changed, and the relation between the soil strength and the displacement field is searched.
(5) The load size of the weight can be changed conveniently, and the relation between the load size and the displacement field is searched.
(6) The pile end soil simulation mechanism can change the rigidity of the pile end soil simulation mechanism by replacing the spring, and the relation between the pile end soil strength and a displacement field is searched.
(7) The test device has small volume, convenient operation and convenient carrying, can be used as a demonstration teaching aid in classroom teaching, and enables students to intuitively understand the working principle of the pile foundation and the concept of a neutral point; and important application reference can be provided for pile foundation design, and higher theoretical and application values are achieved.
Drawings
FIG. 1 is a view showing a state of use of the present invention in stacking and pressurizing.
Fig. 2 is a view showing the state of the pile base of the present invention in use.
FIG. 3 is a perspective view of a rectangular mold box of the present invention (with the transparent front side wall removed).
FIG. 4 is a perspective view of the transparent front side wall and scale of the rectangular mold box of the present invention.
Fig. 5 is a perspective view of the pile foundation and the side wings of the present invention.
Fig. 6 is a perspective view of the bracket mechanism of the present invention.
Fig. 7 is a perspective view of the pile tip soil simulation mechanism of the present invention.
Fig. 8 is a perspective view of the pile foundation pressing device of the present invention.
Fig. 9 is a perspective view of the stacking and pressurizing device of the present invention.
Description of reference numerals: 1-pile foundation, 2-side wing, 3-soil, 4-pile end soil simulation mechanism, 4.1-guide rod, 4.2-upper bearing plate, 4.3-spring, 4.4-deviation prevention plate, 4.5-lower bearing plate, 5-bracket lower plate, 6-bracket column, 7-bearing bolt, 8-bracket upper plate, 9-fixing bolt, 10-rigid side wall, 11-transparent side wall, 12-stacking loading pressurizing device, 13-pile foundation pressurizing device, 14-weight, 15-scale and 16-ruler.
Detailed Description
The present invention will be further described with reference to the following examples.
Referring to fig. 1-5, the mechanical test device for simulating the resistance of the pile end and the change of the neutral point of the pile end of the invention comprises a loading mechanism, a rectangular model box, a support mechanism, a pile foundation with side wings, a pile end soil simulation mechanism and a measuring mechanism; the loading mechanism comprises a pile top load pressurizing device 12, a ground stacking pressurizing device 13 and weights 14; the rectangular model box comprises a left side wall, a right side wall, a transparent front side wall and a transparent rear side wall; the rectangular model box contains a pile foundation 1 and experimental soil 3; the bracket mechanism comprises a bracket upper plate 8, a bracket lower plate 5 and a bracket column 6; a bracket column 6 is arranged in front of the bracket upper plate 8 and the bracket lower plate 5; the support upper plate 8 supports the rectangular model box, and a pile foundation socket is arranged at the center of the support upper plate 8; the pile foundation with the side wings comprises a pile foundation 1 and side wings 2, wherein the side wings 2 are made of semi-flexible materials and can deform along with the deformation of a soil body; the pile end soil simulation mechanism comprises an upper bearing plate 4.2, a lower bearing plate 4.5, guide rods 4.1 and springs 4.3, wherein two springs 4.3 with the same length and elastic modulus are respectively sleeved on the two guide rods 4.1, two ends of each spring are respectively abutted against the upper bearing plate 4.2 and the lower bearing plate 4.5, the upper bearing plate 4.2 moves along the guide rods when stressed, and the pile end soil simulation mechanism is used for simulating vertical deformation of pile end soil; the pile foundation 1 is vertically arranged in the rectangular model box, the top end of the pile foundation 1 extends outwards from the rectangular model box, the bottom end of the pile foundation 1 penetrates through a pile foundation socket and then abuts against the upper surface of the upper bearing plate 4.2, and the left side and the right side of the part of the pile foundation 1 in the box body are respectively provided with side wings 2 which are arranged at intervals; the side wing 2 is made of semi-flexible materials, and the side wing 2 deforms along with the deformation of the soil body; the weight 14 is directly placed on the pile top load pressurizing device 12 or the ground stacking pressurizing device 13; when the pile foundation pressurizing device 13 is adopted, the pile foundation 1 can generate positive frictional resistance; when the pile loading pressurizing device 12 is adopted, the pile foundation 1 can generate negative frictional resistance; the measuring mechanism comprises a ruler 16 and scales 15 arranged on the front transparent side wall 11.
The side wings 2 are made of semi-flexible material such as bamboo skin; during the preparation with 1 both sides of pile foundation cutting with the electric saw, insert the cut groove with flank 2 and fixed with glue, can sensitively warp when making its atress. The spring 4.3 bears the weight of the upper bearing plate 4.2, and the bearing plate 4.2 moves up and down freely along with the spring 4.3.
The loading mechanism of the embodiment comprises a pile foundation pressurizing device and a pile loading pressurizing device, and can respectively enable the pile foundation to generate positive frictional resistance and negative frictional resistance; the transparent front and back side walls of the rectangular model box are convenient for observation; the side wing part of the pile foundation is made of semi-flexible materials, can be bent and deformed along with the deformation of soil, and can obtain a displacement field of the soil around the pile according to the bending of the side wing; the pile end soil simulation mechanism comprises a guide rod, an upper bearing plate, a lower bearing plate, a spring and an anti-deviation plate and is used for simulating the vertical deformation of pile end soil; the measuring mechanism comprises a transparent side wall with scales and a ruler.
The working principle of the embodiment is as follows:
when the loading mechanism adopts a pile foundation pressurizing device, the pile foundation generates positive frictional resistance. The side wing bends upwards along with the soil body around the pile, and a displacement field of the soil around the pile can be obtained according to the bending of the side wing. The pile end spring deforms, and the pile end axial force, namely the end resistance, can be measured according to the deformation; when the loading mechanism adopts a pile loading pressurizing device, the pile foundation generates negative friction resistance. The side wings are bent upwards and downwards along with the soil body around the pile, a displacement field of the soil around the pile can be obtained according to the bending of the side wings, and the position of a neutral point is analyzed according to an interpolation method. The pile end spring is deformed, and the pile end axial force, namely the end resistance, can be measured according to the deformation.
The positive frictional resistance and the negative frictional resistance working condition of the pile foundation 1 can be simulated only by replacing the pile foundation pressurizing device 13 and the ground pile loading pressurizing device 12, other internal test equipment does not need to be used, the displacement field of the pile soil around the pile during the positive frictional resistance can be obtained through the deformation and the displacement of the side wings 2 and the springs 4.3, the side resistance and the end resistance of the pile foundation 1, the displacement field of the pile soil around the pile during the negative frictional resistance, and the neutral point and the end resistance of the pile foundation 1.
The device of the embodiment is simple and high in precision, can simulate the pile end resistance and the pile surrounding soil deformation of positive and negative frictional resistance, and can also simulate the change of the neutral point position in the process of negative frictional resistance.
As can be seen from fig. 8 and 9, the pile foundation pressurizing device 13 and the pile loading pressurizing device 12 are both provided with a pressing block and a pressing block support, and the pressing block support of the pile foundation pressurizing device 13 is clamped at the top end of the pile foundation 1 so that the gravity of the pile foundation pressurizing device 13 acts on the top end of the pile foundation 1; the bottom end of the pressing block support of the stacking pressurization device 12 is provided with a pressing plate, the top end of the pile foundation 1 upwards penetrates through the pressing plate and has no friction with the pressing plate, and the gravity of the stacking pressurization device 12 only acts on the upper surface of the experimental soil filled in the rectangular model box through the pressing plate.
Through setting up the briquetting support, be convenient for make pile foundation pressure device 13 or pile load pressure device 12's gravity act on the upper surface of the experimental soil who fills in pile foundation 1 or the rectangular mold case through the briquetting support.
The pile foundation pressurizing device 13 and the pile loading pressurizing device 12 are made of light materials.
The lateral wall is rigidity lateral wall 10 about, and the front and back lateral wall is transparent lateral wall 11, and the front side of rigidity lateral wall 10, rear side all are equipped with the caulking groove of vertical setting, and caulking groove border department is equipped with fixing bolt 9, and transparent lateral wall 11 plays the fixed action around fixing bolt 9 is to preventing outwards to drop, and transparent lateral wall 11 is taken out or is inserted from the caulking groove around the permission simultaneously.
The arrangement is such that the front and rear transparent side walls 11 can be conveniently nested in or withdrawn from the slots of the rigid side walls 10.
The upper tray 8 and the rigid side walls 10 of the bracket are bonded together to form a rectangular model box.
Through the arrangement, a part of the upper bracket disc 8 serves as the bottom surface of the rectangular model box, and meanwhile, the upper bracket disc 8 also serves as the support of the rectangular model box. The number of the components is reduced, so that the device has a simpler structure.
As can be seen from fig. 6, four support columns 6 are arranged, the four support columns 6 are respectively vertically arranged at four corners of the support lower disc, and the bottom ends of the support columns 6 are respectively connected and fixed with the support lower disc 5; the support upper disc 8 is provided with a support jack corresponding to the support column, and the support upper disc 8 is sleeved on the support column 6 through the support jack.
Through setting up the support jack, the support hanging wall 8 of being convenient for cup joints on support post 6 through the support jack.
The top ends of the four bracket columns 6 are all provided with bearing bolts 7, the bearing bolts 7 are arranged at the same height, and the bearing bolts 7 support the bracket upper disc 8.
And a support bolt 7 is arranged on the support column 6 to limit and support the support upper disc 8. The support column 6 can also be provided with a limit table or a limit projection instead of the bolt 7.
Referring to fig. 7, the front side and the rear side of the lower bearing plate 4.5 are connected to form an anti-deviation plate 4.4, the anti-deviation plate 4.4 is vertically arranged, and the bottom end of the anti-deviation plate is fixedly connected to the lower bearing plate 4.5. The width of the upper bearing plate 4.2 corresponds to the interval between the two deviation-preventing plates 4.4, so that the upper bearing plate 4.5 and the pile foundation 1 abutted against the upper bearing plate are prevented from being kept vertically and not being deviated.
A mechanical test method for simulating the resistance of the pile base end and the change of a neutral point comprises the following steps:
the first step is as follows: the pile foundation 1 is inserted into a model box and penetrates through the support upper disc 8, the pile end soil simulation device 4 is placed on the lower bearing plate 5, the lower end of the pile foundation 1 is just contacted with the pile end soil simulation device 4, and the position of the pile foundation 1 at the moment is positioned through the scale 15 on the transparent side wall 11.
The second step is that: weighing the soil amount required by filling the model box according to the density of the soil 3 to be tested, horizontally placing the model box at the edge of a test bed, adhering the upper bracket disc 8 to the bottom of the model box in a high-altitude state, and uniformly filling the soil 3 into the model box; when the model box is to be horizontally placed and the transparent side wall on the model box is drawn out, the pile foundation 1 is also horizontally placed at the moment, and the side wing 2 is vertical; the purpose of this is to allow uniform loading of the soil and to avoid bending of the lateral wings 2 during loading of the soil.
The third step: erecting the model box, inserting four support columns 6 into a support upper disc 8, stabilizing the support upper disc on a bearing bolt 7, and enabling the lower end of the pile foundation 1 to be just in contact with a pile end soil simulation device 4; the initial position of the wing 2 is recorded by means of a scale 15 on the transparent side wall and the distance between the upper bearing plate 4.2 and the lower bearing plate 4.5, i.e. the initial length of the spring 4.3, is measured with a straight edge 16.
The fourth step: carry out loading
(1) When carrying out the simulation of pile foundation positive frictional resistance operating mode, install pile foundation pressure device 13 the top of pile foundation 1, load weight 14 on loading device 13, wait to warp stable back, read out the displacement deflection of pile foundation 1 and flank 2, measure the final length of spring 4.3.
(2) When the pile foundation negative friction resistance working condition is simulated, the pile loading pressurizing device 12 is installed at the top end of the soil 3, the weight 14 is loaded on the pile loading pressurizing device 12, after the pile foundation 1 and the side wing 2 are stably deformed, the displacement deformation of the pile foundation 1 and the side wing 2 is read out, and the final length of the spring 4.3 is measured.
The fifth step: and (6) carrying out data processing.
(1) The deformation and displacement fields of the pile foundation 1 and the side wing 2 are obtained, the deformation amount of the spring 4.3 is calculated, and the downward bending of the side wing is defined as a negative value, and the upward bending is defined as a positive value. The average sedimentation value of each flank 2 is taken as the sedimentation value of the layer of soil. When the positive frictional resistance working condition of the pile foundation is simulated, the known pile top load, namely the sum of the gravity of the weight 14 and the pressurizing device 13 is equal toQDisclosure of the inventionThe over-spring 4.3 deformation can calculate the resistance of the pile base end according to Hooke's lawN l The pile foundation frictional resistance isQ s =Q-N l 。
(2) The deformation and displacement fields of the pile foundation 1 and the side wing 2 are obtained, the deformation amount of the spring 4.3 is calculated, and the downward bending of the side wing is defined as a negative value, and the upward bending is defined as a positive value. Taking the average sedimentation value of each flank 2 as the sedimentation value of the soil layer, and finding out the position-neutral point with zero relative displacement through linear interpolation comparison. When the pile foundation negative friction resistance working condition simulation is carried out, the known ground stacking load, namely the sum of the gravity of the weight 14 and the pressurizing device 12 is thatQThe negative frictional resistance of the pile foundation is set asQ n The resistance of the pile base end can be calculated according to Hooke's law through the deformation of the spring 4.3N l The total frictional resistance of the pile foundation isQ n -Q s =Q-N l 。
And a sixth step: the rigidity of the pile foundation 1, the compression modulus of the soil 3, the load size of the weight 14 or the elastic modulus of the spring 4.3 are changed, and the positive and negative frictional resistance stress characteristics of the pile foundation under different working conditions are simulated.
The advantages of this embodiment are:
(1) utilize the deformation of the flexible flank of pile foundation to confirm displacement and the deformation of soil around the stake, its deformation and displacement value can accurately be read out through the scale on the transparent lateral wall, need not be with the help of other auxiliary assembly, be convenient for directly perceived and qualitative analysis, easy operation, and the influence factor is few, and the error is little.
(2) By replacing the loading device, simulation of the positive frictional resistance working condition and simulation of the negative frictional resistance working condition of the pile foundation can be realized, and a corresponding displacement field and pile end resistance are obtained.
(3) The material of the pile foundation can be changed, namely the rigidity of the pile foundation is changed, and the relation between the rigidity of the pile foundation and a displacement field is searched.
(4) The soil around the pile can be adjusted, namely the compression modulus of the soil is changed, and the relation between the soil strength and the displacement field is searched.
(5) The load size of the weight can be changed conveniently, and the relation between the load size and the displacement field is searched.
(6) The pile end soil simulation mechanism can change the rigidity of the pile end soil simulation mechanism by replacing the spring, and the relation between the pile end soil strength and a displacement field is searched.
(7) The test device has small volume, convenient operation and convenient carrying, can be used as a demonstration teaching aid in classroom teaching, and enables students to intuitively understand the working principle of the pile foundation and the concept of a neutral point; and important application reference can be provided for pile foundation design, and higher theoretical and application values are achieved.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, which is defined in the appended claims.
Claims (9)
1. Pile tip soil analog mechanism and measurement mechanism, its characterized in that:
the loading mechanism comprises a pile top load pressurizing device (12), a ground stacking pressurizing device (13) and weights (14);
the rectangular model box comprises a left side wall, a right side wall, a transparent front side wall and a transparent rear side wall; the rectangular model box is internally provided with a pile foundation (1) and experimental soil (3);
the bracket mechanism comprises a bracket upper plate (8), a bracket lower plate (5) and bracket columns (6); a bracket column (6) is arranged in front of the bracket upper disc (8) and the bracket lower disc (5); the support upper disc (8) supports the rectangular model box, and a pile foundation socket is arranged at the center of the support upper disc (8);
the pile foundation with the side wings comprises a pile foundation (1) and side wings (2), wherein the side wings (2) are made of semi-flexible materials and can deform along with the deformation of a soil body;
the pile end soil simulation mechanism comprises an upper bearing plate (4.2), a lower bearing plate (4.5), a guide rod (4.1) and a spring (4.3), wherein the spring (4.3) is sleeved on the guide rod (4.1), two ends of the spring are respectively abutted against the upper bearing plate (4.2) and the lower bearing plate (4.5), the upper bearing plate (4.2) moves along the guide rod when stressed, and the pile end soil simulation mechanism is used for simulating vertical deformation of pile end soil;
the pile foundation (1) is vertically arranged in the rectangular model box, the top end of the pile foundation (1) extends outwards from the rectangular model box, the bottom end of the pile foundation (1) penetrates through a pile foundation socket and then abuts against the upper surface of the upper pressure bearing plate (4.2), and the left side and the right side of the part, located in the box body, of the pile foundation (1) are respectively provided with side wings (2) which are arranged at intervals; the side wing (2) is made of semi-flexible material, and the side wing (2) deforms along with the deformation of the soil body; the weights (14) are directly placed on the pile top load pressurizing device (12) or the ground stacking pressurizing device (13); when the pile foundation pressurizing device (13) is adopted, the pile foundation (1) can generate positive frictional resistance; when the pile loading pressurizing device (12) is adopted, the pile foundation (1) can generate negative frictional resistance;
the measuring mechanism comprises a ruler (16) and scales (15) arranged on the front transparent side wall (11).
2. The mechanical test device for simulating the pile tip resistance and the neutral point change according to claim 1, characterized in that: the pile foundation pressurizing device (13) and the pile loading pressurizing device (12) are both provided with a pressing block and a pressing block support, and the pressing block support of the pile foundation pressurizing device (13) is clamped and sleeved at the top end of the pile foundation (1) so that the gravity of the pile foundation pressurizing device (13) acts on the top end of the pile foundation (1); the bottom end of a pressing block support of the stacking pressurization device (12) is provided with a pressing plate, the top end of the pile foundation (1) penetrates through the pressing plate upwards and has no friction with the pressing plate, and the gravity of the stacking pressurization device (12) only acts on the upper surface of experimental soil filled in the rectangular mold box through the pressing plate.
3. The mechanical test device for simulating the pile tip resistance and the neutral point change according to claim 1, characterized in that: the pile foundation pressurizing device (13) and the pile loading pressurizing device (12) are made of light materials.
4. The mechanical test device for simulating the pile tip resistance and the neutral point change according to claim 1, characterized in that: the left side wall and the right side wall are rigid side walls (10), the front side wall and the rear side wall are transparent side walls (11), and the front side and the rear side of each rigid side wall (10) are provided with vertically arranged caulking grooves.
5. The mechanical test device for simulating pile tip resistance and neutral point change according to claim 4, characterized in that: the upper tray (8) of the bracket is bonded with the bottom end of the rigid side wall (10) to form a rectangular model box.
6. The mechanical test device for simulating the pile tip resistance and the neutral point change according to claim 1, characterized in that: the four support columns (6) are vertically arranged at four corners of the lower support disc respectively, and the bottom ends of the support columns (6) are fixedly connected with the lower support disc (5) respectively; the support upper disc (8) is provided with a support jack corresponding to the support column, and the support upper disc (8) is sleeved on the support column (6) through the support jack.
7. The mechanical test device for simulating pile tip resistance and neutral point change according to claim 6, wherein: the top ends of the four bracket columns (6) are respectively provided with a bearing bolt (7), the bearing bolts (7) are arranged at the same height, and the bearing bolts (7) support the bracket upper disc (8).
8. The mechanical test device for simulating the pile tip resistance and the neutral point change according to claim 1, characterized in that: two side connection in front and back of lower bearing plate (4.5) be provided with anti-inclined to one side board (4.4), anti-inclined to one side board (4.4) vertical setting and bottom and lower bearing plate (4.5) fixed connection.
9. A mechanical test method for simulating the resistance of the pile base end and the change of a neutral point is characterized by comprising the following steps:
the first step is as follows: inserting the pile foundation (1) into a model box to penetrate through a support upper disc (8), placing a pile end soil simulation mechanism (4) on a lower bearing plate (5), enabling the lower end of the pile foundation (1) to be just contacted with the pile end soil simulation mechanism (4), and positioning the position of the pile foundation (1) at the moment;
the second step is that: weighing the soil amount required by filling the model box according to the density of the soil (3) to be tested, horizontally placing the model box at the edge of the test bed, adhering the support upper plate (8) to the bottom of the model box in a high altitude state, and uniformly filling the soil (3) in the model box;
the third step: erecting a model box, inserting four support columns (6) into a support upper disc (8), stabilizing the support upper disc on a bearing bolt (7), and enabling the lower end of a pile foundation (1) to be just in contact with a pile end soil simulation mechanism (4); recording the initial position of the side wing (2), and measuring the distance between the upper bearing plate (4.2) and the lower bearing plate (4.5), namely the initial length of the spring (4.3), by using a ruler;
the fourth step: when pile foundation positive frictional resistance simulation is carried out, a pile foundation pressurizing device (13) is installed at the top end of a pile foundation (1), and a weight (14) is loaded on a loading device (12); when pile foundation negative friction resistance simulation is carried out, a pile loading pressurizing device (12) is installed at the top end of the soil (3), and a weight (14) is loaded on a loading device (13);
the fifth step: after the deformation is stable, reading the displacement deformation of the pile foundation (1) and the side wings (2), measuring the final length of the spring (4.3), obtaining the deformation and displacement fields of the pile foundation (1) and the side wings (2), calculating the deformation of the spring (4.3), defining the downward bending of the side wings as a negative value, defining the upward bending as a positive value, and taking the average sedimentation value of each side wing (2) as the sedimentation value of the soil layer;
when the positive frictional resistance working condition of the pile foundation is simulated, the known pile top load, namely the sum of the gravity of the weight (14) and the pressurizing device (13), is equal toQThe resistance of the base end of the pile can be calculated according to Hooke's law through the deformation of the spring (4.3)N l The pile foundation frictional resistance isQ s =Q-N l ；
When the pile foundation negative frictional resistance working condition is simulated, the known ground stacking load, namely the sum of the gravity of the weight (14) and the pressurizing device (12), is thatQThe negative frictional resistance of the pile foundation is set asQ n The resistance of the base end of the pile can be calculated according to Hooke's law through the deformation of the spring (4.3)N l The total frictional resistance of the pile foundation isQ n -Q s =Q-N l ；
And a sixth step: the rigidity of the pile foundation (1), the compression modulus of the soil (3), the load of the weight (14) or the elastic modulus of the spring (4.3) are changed, and the positive and negative frictional resistance stress characteristics of the pile foundation under different working conditions are simulated.
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