CN108797554B - Reinforcement test and optimization method based on compaction effect - Google Patents
Reinforcement test and optimization method based on compaction effect Download PDFInfo
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 44
- 239000004568 cement Substances 0.000 claims description 24
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Abstract
The invention discloses a reinforcement test and optimization method based on compaction effect. The invention measures the stable compaction force around the pile and the compaction force at the bottom of the pile through the soil pressure cell, thereby solving the problem of how to measure the compaction effect of the rammer; by the relationship among the compaction force, the compaction coefficient of soil and the tamping energy, a method for optimizing the shape of the tamping hammer, the tamping times and the drop distance of the tamping hammer is provided, and the problem of obtaining the optimal tamping effect under the minimum tamping energy by a tamping tool with any shape is solved; the method for measuring the pile body compaction coefficient by the penetration resistance is provided, the disturbance to the rammed pile is reduced, and the energy loss in the ramming process is reduced. According to the principle that the compaction energy is minimum and the compaction force is not increased basically when the tamping times exceed a certain tamping time, the optimal combination suitable for the existing railway is provided.
Description
Technical Field
The invention relates to the technical field of buildings, in particular to a reinforcement testing and optimizing method based on compaction effect.
Background
At present, many existing railways in China cannot meet the requirement of rapid increase of passengers and goods and need to be improved at an increased speed, but the bearing capacity of the existing railway roadbed is possibly insufficient, and the roadbed is reinforced by cement soil compaction piles commonly used at present. The cement-soil compaction pile is a strengthening method which adopts mechanical hole forming in the existing railway bed, the diameter of the formed hole is slightly smaller than the distance between sleepers, and then the mixture of cement and plain soil is tamped in the hole layer by layer. After the reinforcement is finished, the mixture of cement and plain soil is solidified into cement soil piles with better uniformity and high strength, meanwhile, in the tamping process, the soil between the piles is compacted, and the bearing capacity of the soil between the piles is also improved. The road bed soil cement stake after consolidating and the stake soil between bear upper portion railway roadbed, track, sleeper and train load jointly, and its bearing capacity can carry out quantitative description through the bearing capacity formula of composite foundation, and its formula is:
fsp＝mfp+(1-m)fs(1)
in the formula fsp-the composite foundation bearing capacity of the consolidated subgrade;
fpthe bearing capacity of the cement-soil pile formed after reinforcement is related to the pile length, the pile body compactness and the cement mixing amount;
fs-the bearing capacity of the soil between the piles after reinforcement;
m-area replacement rate of the pile;
generally, the bearing capacity of the composite foundation can be improved from the following aspects 3:
(1) the bearing capacity of the piles is multiple times of the bearing capacity of soil among the piles, so that the bearing capacity of the composite foundation can be improved by improving the area replacement rate of the piles, but the construction space of the existing railway is limited, and the quantity of the piles is increased if the area replacement rate is increased, which is basically unrealistic in the existing railway.
(2) According to the formula (1), the bearing capacity of the composite foundation is improved, the bearing capacity of the pile is improved, the length of the pile can be increased, the compactness of the pile can be increased, the cement mixing amount is increased, and the diameter of the pile is increased. However, excessive increase of the cement mixing amount greatly increases the cost, and the bearing capacity of the pile is not remarkably improved, so that the cement mixing amount commonly used in engineering is 5-10%. The compactness of the pile can be increased by increasing the bearing capacity of the pile, and the compactness of the pile is required to reach 97 percent in general engineering.
(3) Increase fspThe bearing capacity of the soil between the piles can be increased, and the method is to tamp and expand the pile body through the tamping hammer, and the pile body compacts the surrounding soil between the piles, so that the bearing capacity of the soil between the piles is increased.
There are many factors that can be seen to affect the bearing capacity after consolidation, but it is most economical to increase the bearing capacity of the soil between piles and the compaction factor of the piles themselves. The pile body is tamped by the tamping hammer, so that the bearing capacity of soil between piles and the compactness of the pile body are improved simultaneously, and the existing defects are as follows:
1) in the tamping process, manual tamping is generally carried out on site through an olive hammer, the weight of the hammer is generally 20kg, and factors influencing the tamping effect include tamping times, the drop distance of the hammer and the shape of the hammer. At present, in the process of tamping by using the olive hammer, the shape of the bottom of the olive hammer is generally elliptical, circular, conical and flat, the manufacture is totally dependent on experience, the drop distance of the hammer and the tamping times are generally determined according to the experience in the tamping process, and the optimal design is not considered.
2) In terms of compaction effect evaluation: in the conventional compaction evaluation, the compaction coefficient is usually determined according to the compaction coefficient of soil around the pile, namely the ratio of the average dry density of the soil around the pile after compaction to the average dry density of the soil around the pile before compaction. The problems in the evaluation by this method are: the compaction of soil around the pile is gradually reduced from the pile to the soil between the piles, the compaction effect of the soil is good when the soil is close to the pile, and the compaction effect of the soil is basically not good when the soil is far away from the pile. Where the soil is taken to determine the dry density of the soil and replacing the average dry density of the soil around the pile with it is artificially subjective. When the compaction effect of the soil around the pile is measured, the result measured by the traditional sampling method is related to the selected position, is greatly influenced by human factors, and greatly excavates the soil around the pile, so that the soil around the pile is likely to laterally move towards the sampling direction in the continuous tamping process, and the experimental result is certainly influenced. Secondly, in the process of tamping, the tamping effect cannot be dynamically mastered, and only the dry density at a certain point at a certain moment can be taken as evaluation.
The compaction effect of the pile is measured by the dry density of the pile body at present, the compaction coefficient of the pile body is measured by taking a cutting ring sample after the tamping is finished, the dry density at intervals of certain tamping times cannot be measured, and the compaction effect cannot be dynamically reflected.
3) The optimization aspects of the shape of the rammer, the ramming times and the falling distance of the rammer are as follows: at present, only the compaction coefficient of the pile body of the cement soil is used as an evaluation index, and when the compaction coefficient does not reach the specified standard, the tamping times are increased until the dry density of the pile body reaches the relevant standard. In the existing railway cement soil compaction pile reinforcement, construction is usually carried out by means of railway skylight time, the time is generally short and is only 3 hours, and all trains of the existing railway are stopped in the time, so that the time is particularly precious, optimization of each part needs to be considered, the roadbed reinforcement is completed by using the minimum tamping energy and the minimum tamping time, and the best reinforcement effect is achieved. At present, no optimization method aiming at the aspects is proposed.
4) Method for testing experimental density: at present, a sand filling method, a water filling method and a cutting ring method are commonly used, wherein the soil sampling volume of the sand filling method and the water filling method is large and does not conform to the test of the density in a small model. The cutting ring method needs to dig a cutting ring sample in the middle of the pile body, and the volume of the cutting ring sample is 200cm3The density of the pile body is seriously influenced, the pits of the cutting ring must be filled before next tamping, and the method has great influence on the compaction coefficient of the pile body after 10-time or 20-time tamping. The ring cutter method is relatively small in size, inconvenient to operate in a test pit, capable of damaging the rammed face of the last time, incapable of guaranteeing the continuity of the test, long in test time and not suitable for experimental research and use, and the water content of soil needs to be measured after the test.
Disclosure of Invention
The invention aims to provide a reinforcing test and optimization method based on compaction effect, which measures the stable compaction force around a pile and the compaction force at the bottom of the pile through a soil pressure cell and solves the problem of how to measure the compaction effect of a rammer; by the relationship among the compaction force, the compaction coefficient of soil and the tamping energy, a method for optimizing the shape of the tamping hammer and the tamping times is provided, and the problem that the tamping tool with any shape can obtain the optimal tamping effect at the minimum tamping energy is solved; the relation between the pile body compaction coefficient and the miniature penetrometer is established, a method for measuring the pile body compaction coefficient by the penetration resistance is provided, the disturbance to the rammed pile is reduced, and the energy loss caused by the annular knife method pits in the ramming process is reduced; according to the principle that the compaction energy is minimum and the tamping times are not increased basically when exceeding a certain impacting time, the combination suitable for the existing railway is provided.
In order to achieve the aim, the invention provides a strengthening test and optimization method based on compaction effect, which comprises the following steps:
(1) design of test model
The compaction pile is formed by drilling a first hole in the existing railway roadbed, filling cement soil into the first hole and tamping by using a tamping hammer, the compaction pile is compacted under the action of the tamping hammer, meanwhile, the original soil around the pile is compacted towards two sides, one layer is tamped in the first hole every 30cm, the compaction pile has repeatability, and only the lowest layer is selected as a research object;
(1.1) drilling design: drilling 9 holes I with the diameter of 25cm and the depth of 60cm and the distance of more than 1m, and virtually paving cement soil with the thickness of 40cm and the mass of 35kg in each hole I;
(1.2) rammer shape design: the hammer bottom with the diameter of 24cm is designed into three types of rammers, namely a flat bottom, a spherical bottom and a conical bottom, and the weight of the rammer is 20 kg;
(1.3) the arrangement design of the soil pressure cell: respectively drilling a hole II with the diameter of 9cm on two sides of the diameter direction of the hole I, wherein the two holes are symmetrically arranged, the hole II is 15cm away from the bottom of the hole I, soil pressure boxes with the diameter of 8cm and the height of 2cm are respectively placed at the center of the bottom of the hole I and the center of the bottom of the two holes II, the hole II is plugged by soil, each soil pressure box is connected to a dynamic and static strain analysis system through a test data line penetrating out of the soil, and the dynamic and static strain analysis system is connected to a display terminal;
(1.4) design of tamping parameters: the drop distance of a rammer between the bottom of the rammer and the pile surface of the compacted pile is 30cm, 60cm and 90cm, the rammer is a flat bottom hammer, a ball bottom hammer and a cone bottom hammer, and the pile bottom compaction force and the pile body penetration resistance of 5, 10, 20, 30 and 40 times of ramming are respectively measured;
(2) data acquisition and arrangement
(2.1) collecting compaction force data: the soil rammer is used for ramming the cement soil in the first hole to generate compaction force on the soil pressure cell, and the soil pressure cell transmits the received compaction force to the dynamic and static strain analysis system through the test data line and displays the compaction force through the display terminal;
(2.2) the pile body compaction coefficient data acquisition and calibration method comprises the following steps: after 5, 10, 20, 30 and 40 times of tamping, uniformly penetrating the pile top surface by using a miniature penetrometer, recording the penetration resistance at the peak value, measuring 6 test points by tamping each time, performing penetration in 6 areas, and separating the next test point from the last test point by more than 3 cm;
calibrating the relation between the penetration resistance and the pile body compaction coefficient: preparing a cement soil sample under the optimal water content, putting 1.8kg of mixed materials into a light compaction cylinder, compacting the mixed materials in three layers, respectively compacting each layer of different samples for 5, 10, 15, 20, 25, 30, 35 and 40 times, respectively measuring the penetration resistance after each group of compacting times, then pushing out the sample by a soil pusher, measuring the density and the water content of the sample by a circular cutting method, and calculating the dry density of the sample, wherein the calculation formula is shown as the formula (1):
in the formula: rhodDry density at each hit
rho-Density of samples measured by Ring knife method at each hit
w is the water content of the compacted sample, in percentage;
the unit of penetration resistance of the penetrometer is N, the compaction coefficient is the ratio of the dry density of the sample to the maximum dry density, and the calculation formula is shown in formula (2):
where rhodmaxMaximum dry density
The penetration resistance is measured on the samples under different compaction, the dry density of the samples is measured at the same time, the compaction coefficient K of the pile body is calculated, the compaction coefficient K and the penetration resistance F have a power function relationship, and the mathematical expression relation is shown as the formula (3):
K＝28.917F0.2635(3)
(3) compaction force-based binary optimization method
(3.1) the compaction force, the drop distance of the rammer and the ramming times are in logarithmic function relationship, the compaction force is increased to a small extent after the ramming times exceed 30 strokes, so the ramming times are not suitable to exceed 30 strokes, and the relationship between the compaction force, the drop distance of the rammer and the ramming times is shown in formula (4):
P＝Alog(N)+Blog(D)+C (4)
in the formula (4), P is the compaction force generated by the rammer at the bottom or side of the pile;
n is the number of tamping times (times);
d is the drop distance (cm) of the rammer;
log is a logarithmic function with a base 10;
the expression of the pile bottom and pile side compaction force is obtained by using the regression analysis function of Excel and is respectively shown as the formula (5) and the formula (6):
P＝92.309log(N)+41.729log(D)+77.895 (5)
P＝110.212log(N)+47.880log(D)+16.338 (6)
(3.2) according to the data calibrated by the micro penetrometer, the pile body compaction coefficient K of a certain drop distance and a certain tamping frequency can be obtained, and the functional relation of the pile body compaction coefficient, the drop distance of the tamping hammer and the tamping frequency is obtained by utilizing the regression analysis function of Excel and is shown as (7):
K＝23.729log(N)+10.301log(D)+41.963 (7)
(4) optimization method
(4.1) rammer shape optimization based on compaction force: taking the three rammers with the falling distance of 30cm and the ramming frequency of 30 as an example, the ramming method is optimized according to the compaction force. Bottom compaction force: the compaction force of the flat bottom hammer is 295.31kPa, the compaction force of the ball bottom hammer is 247.94kPa, and the cone bottom hammer is 280.15 kPa; the pile bottom compaction force of the flat-bottom hammer is set to be 1, the round-bottom hammer is 84% of the flat-bottom hammer, and the cone-bottom hammer is 95% of the flat-bottom hammer. Pile side compaction force: a flat bottom hammer of 209.32kPa, a ball bottom hammer of 223.97kPa, and a cone bottom hammer of 247.05 kPa; if the pile side compaction force of the flat-bottom hammer is 1, the ball bottom hammer is 108 percent of that of the flat-bottom hammer, and the cone bottom hammer is 116 percent of that of the flat-bottom hammer. If only the pile body is tamped, a flat-bottom hammer is adopted; if the soil mass around the pile is compacted, adopting a cone bottom hammer; the existing railway needs to strengthen the compactness of a pile body and simultaneously squeeze the soil around the pile to improve the bearing capacity, so that a flat bottom hammer is not suitable for selection, and compared with a round bottom hammer and a conical bottom hammer, the pile bottom squeezing capacity and the pile side squeezing capacity of the conical bottom hammer are better than those of the round bottom hammer, so that the conical bottom hammer is adopted.
(4.2) based on the relation between the pile body compaction coefficient, the tamping times of the tamping energy and the drop distance of the tamping hammer: when the tamping times exceed 30 strokes, the increase range of the compaction force is small, so the tamping times are not suitable to exceed 30 strokes, the construction optimization aims at achieving the specified pile body compaction coefficient by using the minimum tamping energy, and the tamping energy is calculated according to the formula (8):
m is the mass of the rammer, kg;
w is the tamping energy when each layer of the pile body reaches the compaction coefficient of 97 percent, and N.m.
As a further improvement of the invention, the soil pressure box in the step (1.3) adopts a resistance strain dual-mode soil pressure box with the diameter of 8 cm.
As a further improvement of the present invention, the soil pressure cell in step (1.3) is sleeved with a hollow iron sheet cylinder with a diameter of 9cm and a height of 3cm, a layer of cotton cloth is first laid on the ground glass, the hollow iron sheet cylinder is laid at the center of the cotton cloth, then 0.5cm of standard sand is laid, then the soil pressure cell is placed, the soil pressure cell is arranged at the center of the hollow iron sheet cylinder, then 0.5cm of standard sand is laid on the soil pressure cell, then the test data line is led out from the side hole of the hollow iron sheet cylinder, and finally the soil pressure cell is wrapped with the cotton cloth and placed at the center of the bottom of the first hole and the center of the bottoms of the second holes.
As a further improvement of the invention, the rammer in the step (1.2) is composed of a wood handle inserted into the iron sheet mould and a concrete hammer which is poured into the iron sheet mould and is integrated with the wood handle, the sum of the dry weight of the concrete hammer and the weight of the wood handle is 20kg, and the concrete hammer and the wood handle are further connected into a whole through three rows of iron nails.
As a further improvement of the invention, the display terminal in the step (2.1) is a computer, the model of the dynamic and static strain analysis system is JM3841, the single-channel sampling rate is 512Hz, and three channels are 170Hz, so that the continuous acquisition of data can be realized.
Compared with the prior art, the reinforcing test and optimization method based on compaction effect has the following beneficial effects:
1) a mathematical model among the pile body compaction coefficient, the tamping times and the drop distance of the tamping hammer is established. The pile body compaction coefficients under different drop distances and different tamping times of the rammers can be determined through a mathematical model.
2) Based on the relationship between the compaction energy, the compaction force and the tamping times, the optimization method of the shape of the rammer, the drop distance of the rammer and the tamping times is provided. Firstly, mathematical models of compaction force and tamping times are respectively established, then a mathematical relation model of the compaction force and the drop distance of the rammer is established, and then the mathematical relation of the compaction force, the drop distance of the rammer and the tamping times is comprehensively established according to the two models, so that unified quantitative description is facilitated. According to the principle that the compaction energy is minimum and the tamping times are not increased basically when exceeding a certain impacting time, the combination suitable for the existing railway is provided.
3) By adopting the optimized rammer, the ramming work can be completed under the condition of less ramming energy, and the ramming effect of the soil around the pile is good. The main body is as follows:
a) the effect of tamping the soil around the pile by adopting the conical rammer is better than that of tamping by adopting a circular bottom hammer, the side compaction force of the pile is averagely improved by 7.4 percent and the bottom compaction force of the pile is improved by 13.1 percent when the ramming times are the same (30 strokes and 30cm drop distance). According to the analysis, the flat bottom hammer did not suit the tamping of the soil cement in the hole, because its lateral compaction force was much smaller.
b) In the selection of the drop distance, the drop distance of 60cm is selected for 30 times, so that the tamping requirement cannot be met, and the tamping times are increased to make small contribution to the pile body compaction coefficient and the pile side compaction force. When the pile body reaches the compaction coefficient of 97 percent, the energy is saved by 4.75 percent, 11.56 percent and 17.17 percent respectively when the drop distance of 64cm is adopted compared with the drop distances of 70cm, 80cm and 90 cm.
4) The method for measuring the pile body compaction coefficient by the penetration resistance is provided, and the pile body compaction coefficient can be converted by the penetration resistance according to the calibration value method. The method for detecting the pile body compaction coefficient by adopting the penetrometer has higher efficiency than that of a ring cutter method, has small disturbance on the pile body, and reduces the energy loss caused by the pits of the ring cutter method in the tamping process. Through the penetrating instrument survey pile body compaction coefficient, only need evenly insert the pile body 6 times, every diameter of inserting the hole is about 6mm, so little to the soil body disturbance, the survey time is fast, and does not have the influence to pile body density, does not harm the ramming face of last time, can guarantee the continuity of test.
5) The compaction effect is evaluated by measuring the compaction force around the pile and the compaction force at the bottom of the pile through the soil pressure cell, the compaction effect is more visual compared with the traditional sampling and density measuring method, the soil around the pile does not need to be excavated, and the accuracy of the experimental result is ensured. The compaction force of the soil between the piles can be quantitatively and dynamically measured, and the compaction force with any tamping times can be measured. By adopting a real-time data acquisition system, under the condition of three channels, data acquisition can be carried out every 1s/170, and the method is accurate enough for the quasi-static test of tamping.
The invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, which illustrate embodiments of the invention.
Drawings
FIG. 1 is a schematic view of a rammed hole during actual consolidation;
FIG. 2 is a detailed layout of the tamping model;
FIG. 3 is a schematic view of an assembled earth pressure cell;
FIG. 4 is a schematic representation of the shape of the ram participating in optimization;
FIG. 5 is a schematic view of the arrangement of the penetration point positions at each number of times of tamping;
FIG. 6 is a graph showing the correlation between K and F;
FIG. 7 is a graph showing the relationship between the compaction force and the number of times of tamping when the drop distance is 30cm, (a) the compaction force and the number of times of tamping at the bottom of the pile, and (b) the compaction force and the number of times of tamping at the side of the pile;
FIG. 8 is a graph of the impact of conical hammer drop distance on compaction force;
FIG. 9 is a graph of W, N versus D for a compaction factor of 97%;
FIG. 10 is a graph of regression analysis set parameters.
Detailed Description
Embodiments of the present invention will now be described with reference to the drawings, wherein like element numerals represent like elements.
Referring to fig. 1-9, the consolidation testing and optimizing method based on compaction effect includes the following steps:
1. design of test model
In the existing railway reinforcement, a cement-soil compaction pile is formed by drilling a first hole in an existing railway roadbed, filling a mixture of cement and plain soil in the first hole, and tamping the cement-soil compaction pile by using a tamping hammer. The pile is compacted under the action of the rammer, and the original soil around the pile is compacted at the two sides, so that the bearing capacity of the soil around the pile is improved, the compaction coefficient of the pile body is improved, and the bearing capacity of the pile is improved.
The invention provides a method for evaluating the compaction effect of a pile body and the compaction effect of soil mass around the pile by using compaction force, and the method has repeatability in the consideration that one layer is compacted every 30cm above a drill hole, so that only the lowest layer can be selected as a research object.
1.1) drilling design: according to the objective of field consolidation, the diameter of the ram is 24cm, the diameter of the drilled hole is typically 25cm, and the model is also designed to be 25 cm. Considering repeatability, only the lowest layer is taken as a research object, the compacted thickness of the cement soil is considered to be 30cm, the general virtual pavement thickness reaches 40-50cm, and the test pit is designed to be 60cm deep. In summary, the drilled hole one 1 is a cylindrical hole with a diameter d of 25cm and a depth of 60cm (as shown in fig. 2, the position a is a virtual earth-filling surface, and the position b is a tamped earth-filling surface). Considering that the test pit can not be used repeatedly, 9 identical holes 1 can be arranged at the same time, and the sizes are as same as possible. The distance between the first holes and the second holes is required to be more than 1m so as to prevent the tamping effects of all the drill holes from being superposed.
1.2) rammer shape design: the existing commonly used hammer bottom shapes comprise a flat bottom hammer, a spherical bottom hammer and a conical bottom hammer, an iron sheet mould designed according to the size and a wood handle 3 inserted in the iron sheet mould are adopted, then concrete is poured in the iron sheet mould to be combined with the wood handle 3 into a whole, and the weight of the poured concrete is controlled to be dry weight and the weight of the wood handle is 20 kg. For the conical bottom hammer, different inclination angles can be considered, so that the influence of the shape of the hammer on the tamping effect is optimized. In order to prevent the wooden handle from falling off from the rammer during ramming, three rows of iron nails can be nailed around the wooden handle, so that the wooden handle 3 and the concrete hammer 2 are integrated (the shape of the bottom of the rammer is designed as shown in figure 4).
1.3) soil pressure arrangement design: the soil pressure cell adopts a resistance strain dual-mode soil pressure cell with the diameter of 8cm, the real-time change of the measured soil pressure can be displayed on a display terminal, namely a computer screen, and the change of the compaction force in the tamping process can be conveniently recorded. The pile bottom soil pressure box is arranged in the center of the first hole 1, the pile side soil pressure boxes are arranged at the height of 15cm from the pit bottom, and the pile side soil pressure boxes are symmetrically arranged in the diameter direction, so that the influence caused by occasional tamping deviation of the rammers is prevented (the arrangement of the soil pressure boxes is shown in figure 2). The soil pressure cell 4 is sleeved by an iron sheet hollow cylinder 41 with the diameter of 9cm and the height of 3cm, a layer of cotton cloth 42 is paved on the ground glass, the iron sheet hollow cylinder 41 is flatly placed in the center of the cotton cloth 42, 0.5cm of standard sand 43 is paved, then the soil pressure cell 4 is placed, and the soil pressure cell 4 must be arranged in the center of the iron sheet hollow cylinder 41. And (3) paving 0.5cm of standard sand 43 on the soil pressure cell 4, then leading the test data line 5 out of the side hole of the iron sheet hollow cylinder 41, and wrapping the soil pressure cell 4 by cotton cloth 42. Bore a diameter respectively and be two 8 in the hole of 9cm in the diameter direction both sides in hole 1, two 8 symmetrical arrangement in hole, hole two 8 are apart from hole 1 bottom 15cm height, it is 8cm respectively to place a diameter at the bottom center in hole 1 and two hole two 8 bottom centers, highly be 3cm by the soil pressure cell 4 of cotton cloth parcel, and carry out the shutoff to hole two 8 with earth, accomplish the installation of soil pressure cell 4, each soil pressure cell 4 is connected to dynamic and static strain analysis system 6 through wearing out the outer test data line 5 of earth, dynamic and static strain analysis system 6 is connected to display terminal 7 and is computer screen.
1.4) design of tamping parameters:
the drop distance D of the rammer, namely the distance between the bottom of the rammer and the pile surface, is always changed in the ramming process, but the change amount is not large, and the initial drop distance is taken as the measurement. In order to study the influence of the drop distance of the rammer, the ram is easy to be skewed due to the too high drop distance of the rammer according to the physiological characteristics of people, and only three conditions of 30cm, 60cm and 90cm are considered in the optimization method.
The tamping times are as follows: in order to determine the influence of the number of times of tamping on the tamping effect, the pile bottom compaction force and the pile body penetration resistance were determined 5, 10, 20, 30 and 40 times, respectively.
The shape of the ram influences: the three conditions of a flat bottom hammer, a spherical bottom hammer and a conical bottom hammer are adopted respectively.
2. Data acquisition and arrangement
2.1) compaction force data acquisition
Data acquisition adopts JM3841 dynamic and static strain test analytic system, and this system can realize the sampling rate of single channel 512Hz, and this experiment adopts 3 passageway tests, is a passageway (the soil pressure cell of hole one bottom) respectively, and 2 passageways (the soil pressure cell of two hole two bottoms) of stake side can realize 170H's sampling rate, and the change of compaction force in the record tamping process that can be complete basically.
Data are adopted: when the rammer is rammed, the soil pressure box generates a very large compaction force, the received compaction force is transmitted to the dynamic and static strain analysis system by the soil pressure box through the test data line and is displayed by the display terminal, but when the rammer stops ramming, the impacted compaction force is rapidly reduced, and a stable compaction force is formed. According to the field situation, the real long-term compaction force is the compaction force after the compaction force is stabilized, so the compaction force after the stabilization is measured in the test.
2.2) pile body compaction coefficient data acquisition and calibration method
After 5, 10, 20, 30 and 40 times of tamping, the pile top surface after tamping is penetrated by a micro penetrometer, and the penetration resistance at the peak value is recorded. Since the mini-penetrometer is greatly affected by the penetration speed, it is recommended to perform uniform penetration, 6 points are measured, the maximum value and the minimum value are removed, and the average value of the penetration resistance of the remaining 4 times is taken as a representative value of the penetration resistance. Penetration should be performed in 6 zones, and the map of the measurement points is shown in FIG. 5. The next test point is required to be more than 3cm from the last test point.
Calibrating the relation between the penetration resistance and the pile body compaction coefficient: preparing cement soil under the optimal water content, putting 1.8kg of mixed material into a light compaction cylinder, compacting by three layers, compacting each layer for 5 times, measuring the penetration resistance, then pushing out a sample by a soil pusher, measuring the density and the water content of the sample by a circular knife method, and calculating the dry density of the sample. The calculation formula is shown as formula (1):
in the formula: rhodDry density at each hit
rho-Density of samples measured by Ring knife method at each hit
w-water content of the compacted sample, in percent.
The penetration resistance of the compacted samples was measured in three layers, with the number of compaction times per layer being 10, 15, 20, 25, 30, 35, 40 for different samples measured in the above procedure.
In the case of blending some red clay with cement, the maximum dry density is 1.75g/cm3The optimum water content was 17.8%, the ash incorporation ratio was 7% of the dry mass, and the penetration resistance at the optimum water content was measured. The unit of penetration resistance of the penetrometer is N, the ratio of the measured dry density of the sample to the maximum dry density is a compaction coefficient, and the calculation formula is shown as formula (2):
where rhodmaxTesting the maximum dry density of the red clay, 1.75g/cm in this example3.
And (3) measuring the penetration resistance of the samples under different compaction conditions, measuring the dry density of the samples, and calculating the compaction coefficient of the pile body. Mathematical statistics as shown in fig. 6, K is a power function of penetration resistance F, and the fitted correlation coefficient is 0.9419, which shows that K is highly correlated with F when the water content is fixed.
The above relation is expressed mathematically as shown in formula (3).
K＝28.917F0.2635(3)
According to the formula (3), the compaction coefficient and the penetration resistance have a monotonic function relation when the water content is the optimal water content, and then the compaction coefficient of the pile body can be calculated according to the penetration resistance.
3. Compaction force-based binary optimization method
3.1) Effect of number of hits
The pile-side compaction force is logarithmically and significantly related to the number of strikes, so the compaction force can be expressed as a logarithmic function of the number of strikes. Figure 7 is a 30cm drop distance with a pile side compaction force versus number of rams fitted as shown in figure 7 (b). According to FIG. 7(b), it can be seen that the average pile-side compaction force of the three types of hammers is increased by 9.86%, 8.44% for 20-30 times and 3.01% for 30-40 times for 10 times of increase in the number of tamping. It can be seen that when the number of times of tamping is increased to more than 30 times, the increase in compaction force is not already significant, and therefore it is recommended that the number of times of tamping be controlled to less than 30 times.
The pile bottom compaction force can also be expressed in terms of the logarithm of the number of rammings, as shown in fig. 7 (a). The rule of the pile bottom compaction force and the tamping times is similar to the relation between the pile side compaction force and the tamping times, and the relation can be obtained through calculation: the pile bottom compaction of the three hammers is increased by 12.17 percent in 10-20 times, increased by 7.43 percent in 20-30 times and increased by 2.39 percent in 30-40 times. The data show that more than 30 strokes contribute very little to the compaction force.
3.2) influence of the drop distance on the compaction force
Taking a cone bottom hammer as an example, when the tamping times are 20 times, the data are collated as shown in fig. 8. According to fig. 8, the compaction force is also logarithmically related to the ram drop distance.
3.3) mathematical relationship between compaction force and drop distance of rammer and ramming frequency
Considering that the compaction force, the drop distance of the rammer and the ramming frequency are in logarithmic function relationship and are closely related, the relationship between the compaction force, the drop distance of the rammer and the ramming frequency can be set as shown in the formula (4).
P＝Alog(N)+Blog(D)+C (4)
In the formula (4), P is the compaction force generated by the rammer at the bottom or side of the pile;
n is the number of tamping times (times);
d is the drop distance (cm) of the rammer;
log is a logarithmic function with a base 10;
here, taking a cone bottom hammer as an example, the fitting method is explained:
the data was first collated and logarithmized for N and D, as shown in Table 1, column A, B, E:
TABLE 1 relationship between compaction force and number of tamping times and distance between impact and impact
Note: the first row A, B, C, D in the table, etc., represents the column number of Excel, and the first column 1, 2, 3 of the table represents the Excel row number.
Inputting the data of table 1 into Excel, solving the logarithm of the hit number N and the drop distance D in columns C and D, the function of which is in the form of "═ Log (number, 10)", for the solution of table 1, inputting "═ Log (a1, 10)" in the cell C1, inputting "═ Log (B1, 10)" in the cell D1, and then copying the cells C1 and D1 to C2: d13 cells, and the above steps complete logarithmic solution.
The specific operation method of the regression analysis function of Excel is that a selection menu "tool" - > "analysis tool …" selects "regression" in a popped up dialog box as shown in fig. 10. The Y value is selected from the pile bottom compaction force column (E2: E13), and the X value is selected from the log (N) and the log (D) columns (B2: C13). The output area selects H1 (or any other blank cell). Regression data statistics are generated where rsquad values represent correlation coefficients, Intercept represents the constant term of the fit, X Variable 1 represents the coefficients of the log (n) after the fit, and X Variable 2 represents the coefficients of the log (d) after the fit. Similarly, if the Y value is F2: f13, the return condition of the pile side compaction force is obtained.
The expression of the pile bottom and pile side compaction force is obtained as shown in the formula (5) and the formula (6).
P＝92.309log(N)+41.729log(D)+77.895 (5)
P＝110.212log(N)+47.880log(D)+16.338 (6)
Pile bottom compaction force calculated according to the formula (5), correlation coefficient R2The average error of the fit is 2.008% and the maximum error is 5.5% when the fitting is 0.911; calculating the pile side compaction force according to the formula (6)Coefficient of correlation R2The average error of the fit was 2.925%, with a maximum error of 9.9%, at 0.906. From the fitting error, the expression can reflect the relationship between the compaction force and the tamping times and the falling distance more truly.
3.4) relationship between pile body compaction coefficient and drop distance and tamping frequency of tamping hammer
According to the data calibrated by the micro penetrometer, the pile body compaction coefficient K of a certain drop distance and a certain tamping frequency can be obtained, the summarizing method is similar to the compaction force method, and the analysis is still carried out by adopting a binary regression method. The pile body compaction coefficient has uniformity on three hammer type regression equations. The analytical fit of the functional relationship is shown in (7).
K＝23.729log(N)+10.301log(D)+41.963 (7)
K calculated according to equation (7) fit, correlation coefficient 0.893, maximum error is produced by a flat-bottom hammer hitting a 30cm drop, maximum error 6.6%. The average error was 1.7%. According to the fitting result, the relation between the compaction coefficient and the ramming frequency and the drop distance of the rammer can be reflected more truly by the formula (7).
4. Optimization method
4.1) rammer shape optimization based on compaction force
Taking the three rammers with the falling distance of 30cm and the ramming frequency of 30 as an example, the ramming method is optimized according to the compaction force. Bottom compaction force: the compaction force of the flat bottom hammer is 295.31kPa, the compaction force of the ball bottom hammer is 247.94kPa, and the cone bottom hammer is 280.15 kPa; the pile bottom compaction force of the flat-bottom hammer is set to be 1, the round-bottom hammer is 84% of the flat-bottom hammer, and the cone-bottom hammer is 95% of the flat-bottom hammer. Pile side compaction force: a flat bottom hammer of 209.32kPa, a ball bottom hammer of 223.97kPa, and a cone bottom hammer of 247.05 kPa; if the pile side compaction force of the flat-bottom hammer is 1, the ball bottom hammer is 108 percent of that of the flat-bottom hammer, and the cone bottom hammer is 116 percent of that of the flat-bottom hammer. If only the tamping purpose is to tamp the pile body, the flat bottom hammer is best; the conical bottom hammer is best when the aim of compacting the soil around the pile is fulfilled. However, the density of the pile body of the existing railway needs to be enhanced, and meanwhile, soil mass around the pile needs to be compacted, so that the flat-bottom hammer is not suitable for selecting. Compared with a round bottom hammer and a conical bottom hammer, the pile bottom compaction force and the pile side compaction force of the conical bottom hammer are better than those of a round bottom hammer, so that the conical bottom hammer is better than the round bottom hammer, and is preferable.
4.2) optimization of the number of tamping times and the drop distance of the tamping hammer based on the pile body compaction coefficient and the tamping energy
As mentioned above, the increase of the compaction force is small after the number of tamping strokes exceeds 30 strokes. Taking a conical hammer as an example, the increment of the compaction force of 30-40 strokes is only 5.2 percent and is less than the increment of the compaction force (more than 10 percent) of two stages of 10-20 strokes and 20-30 strokes, and excessive tamping times have poor effect on increasing the compaction force, so the tamping times are not suitable to exceed 30 strokes.
The purpose of construction optimization is to achieve a specified pile body compaction coefficient by using the minimum tamping energy, and the tamping energy is calculated according to the formula (8).
m is the mass of the rammer, kg;
w is the tamping energy when each layer of the pile body reaches the compaction coefficient of 97 percent, and N.m.
In the case of the preferred conical bottom hammer, to achieve a predetermined compaction factor of 97% (here, the data obtained in the light weight compaction test), the predetermined number of tamping times is first calculated according to equation (7), and then the tamping energy at which the pile body compaction factor is achieved is calculated according to equation (8), the calculation result being shown in fig. 9. As can be seen from fig. 9, the larger the drop distance, the smaller the number of times of tamping is required, but the greater the tamping energy when a specified compaction factor is reached. Theoretically, a scheme of small drop distance and multiple tamping times should be adopted for tamping, but according to the explanation of compaction force, when the tamping times are more than 30 times, the compaction force is not basically increased, so that the tamping times are recommended to be controlled at 30 times, the drop distance is 64cm according to linear insertion calculation, and the tamping energy is required to be 3772.8 N.m. Therefore, an optimized scheme can be calculated, when the mass of the rammer is 20kg, and the pile body compaction coefficient reaches 97%, D is 64cm, and N is 30 times.
The present invention has been described in connection with the preferred embodiments, but the present invention is not limited to the embodiments disclosed above, and is intended to cover various modifications, equivalent combinations, which are made in accordance with the spirit of the present invention.
Claims (5)
1. A strengthening test and optimization method based on compaction effect is characterized by comprising the following steps:
(1) design of test model
The compaction pile is formed by drilling a first hole in the existing railway roadbed, filling cement soil into the first hole and tamping by using a tamping hammer, the compaction pile is compacted under the action of the tamping hammer, meanwhile, the original soil around the pile is compacted towards two sides, one layer is tamped in the first hole every 30cm, the compaction pile has repeatability, and only the lowest layer is selected as a research object;
(1.1) drilling design: drilling 9 holes I with the diameter of 25cm and the depth of 60cm and the distance of more than 1m, and virtually paving cement soil with the thickness of 40cm and the weight of 35kg in each hole I;
(1.2) rammer shape design: the hammer bottom with the diameter of 24cm is designed into three types of rammers, namely a flat bottom, a spherical bottom and a conical bottom, and the weight of the rammer is 20 kg;
(1.3) the arrangement design of the soil pressure cell: respectively drilling a hole II with the diameter of 9cm on two sides of the diameter direction of the hole I, wherein the two holes are symmetrically arranged, the hole II is 15cm away from the bottom of the hole I, soil pressure boxes with the diameter of 8cm and the height of 2cm are respectively placed at the center of the bottom of the hole I and the center of the bottom of the two holes II, the hole II is plugged by soil, each soil pressure box is connected to a dynamic and static strain analysis system through a test data line penetrating out of the soil, and the dynamic and static strain analysis system is connected to a display terminal;
(1.4) design of tamping parameters: the drop distance of a rammer between the bottom of the rammer and the pile surface of the compacted pile is 30cm, 60cm and 90cm, the rammer is a flat bottom hammer, a ball bottom hammer and a cone bottom hammer, and the pile bottom compaction force and the pile body penetration resistance of 5, 10, 20, 30 and 40 times of ramming are respectively measured;
(2) data acquisition and arrangement
(2.1) collecting compaction force data: the soil rammer is used for ramming the cement soil in the first hole to generate compaction force on the soil pressure cell, and the soil pressure cell transmits the received compaction force to the dynamic and static strain analysis system through the test data line and displays the compaction force through the display terminal;
(2.2) the pile body compaction coefficient data acquisition and calibration method comprises the following steps: after 5, 10, 20, 30 and 40 times of tamping, uniformly penetrating the pile top surface by using a miniature penetrometer, recording the penetration resistance at the peak value, measuring 6 test points by tamping each time, performing penetration in 6 areas, and separating the next test point from the last test point by more than 3 cm;
calibrating the relation between the penetration resistance and the pile body compaction coefficient: preparing a cement soil sample under the optimal water content, putting 1.8kg of mixed materials into a light compaction cylinder, compacting the mixed materials in three layers, respectively compacting each layer of different samples for 5, 10, 15, 20, 25, 30, 35 and 40 times, respectively measuring the penetration resistance after each group of samples are compacted, then pushing out the samples by a soil pusher, measuring the density and the water content of the samples by a circular cutting method, and calculating the dry density of the samples, wherein the calculation formula is shown as the formula (1):
in the formula: rhodDry density at each hit
rho-Density of samples measured by Ring knife method at each hit
w is the water content of the compacted sample, in percentage;
the unit of penetration resistance of the penetrometer is N, the compaction coefficient is the ratio of the dry density of the sample to the maximum dry density, and the calculation formula is shown in formula (2):
where rhodmaxMaximum dry density
The penetration resistance of the sample is measured under different compaction times, the dry density of the sample is measured at the same time, the compaction coefficient K of the pile body is calculated, the compaction coefficient K and the penetration resistance F have a power function relationship, and the mathematical expression relation is shown as a formula (3):
K＝28.917F0.2635(3)
(3) compaction force-based binary optimization method
(3.1) the compaction force, the drop distance of the rammer and the ramming times are in logarithmic function relationship, the compaction force is increased to a small extent after the ramming times exceed 30 strokes, so the ramming times are not suitable to exceed 30 strokes, and the relationship between the compaction force, the drop distance of the rammer and the ramming times is shown in formula (4):
P＝Alog(N)+Blog(D)+C (4)
in the formula (4), P is the compaction force generated by the rammer at the bottom or side of the pile;
n is the number of tamping times (times);
d is the drop distance (cm) of the rammer;
log is a logarithmic function with a base 10;
the expression of the pile bottom and pile side compaction force is obtained by using the regression analysis function of Excel and is respectively shown as the formula (5) and the formula (6):
P＝92.309log(N)+41.729log(D)+77.895 (5)
P＝110.212log(N)+47.880log(D)+16.338 (6)
(3.2) according to the data calibrated by the micro penetrometer, the pile body compaction coefficient K of a certain drop distance and a certain tamping frequency can be obtained, and the functional relation of the pile body compaction coefficient, the drop distance of the tamping hammer and the tamping frequency is obtained by utilizing the regression analysis function of Excel and is shown as (7):
K＝23.729log(N)+10.301log(D)+41.963 (7)
(4) optimization method
(4.1) rammer shape optimization based on compaction force: taking three types of rammers with a drop distance of 30cm and ramming times of 30 as an example, optimizing according to compaction force, wherein the bottom compaction force is as follows: the compaction force of the flat bottom hammer is 295.31kPa, the compaction force of the ball bottom hammer is 247.94kPa, and the cone bottom hammer is 280.15 kPa; setting the pile bottom compaction force of the flat-bottom hammer to be 1, setting the round-bottom hammer to be 84 percent of the flat-bottom hammer, setting the cone-bottom hammer to be 95 percent of the flat-bottom hammer, and setting the pile side compaction force to be two: a flat bottom hammer of 209.32kPa, a ball bottom hammer of 223.97kPa, and a cone bottom hammer of 247.05 kPa; if the pile side compaction force of the flat-bottom hammer is set to be 1, the ball bottom hammer is 108 percent of the flat-bottom hammer, the cone bottom hammer is 116 percent of the flat-bottom hammer, and according to the data, if only the pile body is tamped, the flat-bottom hammer is adopted; if the soil mass around the pile is compacted, adopting a cone bottom hammer; the existing railway not only needs to strengthen the compactness of the pile body, but also needs to compact the soil around the pile, thereby improving the bearing capacity, so the flat bottom hammer is not suitable for selecting, the round bottom hammer is compared with the conical bottom hammer, the pile bottom compaction force and the pile side compaction force of the conical bottom hammer are both better than those of the round bottom hammer, and the conical bottom hammer is adopted;
(4.2) based on the relation between the pile body compaction coefficient, the tamping times of the tamping energy and the drop distance of the tamping hammer: when the tamping times exceed 30 strokes, the increase range of the compaction force is small, so the tamping times are not suitable to exceed 30 strokes, the construction optimization aims at achieving the specified pile body compaction coefficient by using the minimum tamping energy, and the tamping energy is calculated according to the formula (8):
m is the mass of the rammer, kg;
w is the tamping energy when each layer of the pile body reaches the compaction coefficient of 97 percent, and N.m.
2. The compaction effect based reinforcement test and optimization method of claim 1, wherein: and (4) adopting a resistance strain dual-mode soil pressure cell with the diameter of 8cm for the soil pressure cell in the step (1.3).
3. The compaction effect based reinforcement test and optimization method of claim 2, wherein: the soil pressure cell in the step (1.3) is sleeved by an iron sheet hollow cylinder with the diameter of 9cm and the height of 3cm, a layer of cotton cloth is firstly paved on the ground glass, the iron sheet hollow cylinder is flatly placed in the center of the cotton cloth, then 0.5cm of standard sand is paved, then the soil pressure cell is placed, the soil pressure cell is arranged in the center of the iron sheet hollow cylinder, 0.5cm of standard sand is paved on the soil pressure cell, then a test data line is led out from a side hole of the iron sheet hollow cylinder, finally the soil pressure cell is wrapped by the cotton cloth and placed in the center of the bottom of the hole I and the centers of the bottoms of the two holes II.
4. The compaction effect based reinforcement test and optimization method of claim 1, wherein: the rammer in the step (1.2) is composed of a wood handle inserted into the iron sheet mould and a concrete hammer poured into the iron sheet mould and combined with the wood handle into a whole, the sum of the dry weight of the concrete hammer and the weight of the wood handle is 20kg, and the concrete hammer and the wood handle are further connected into a whole through three rows of iron nails.
5. The compaction effect based reinforcement test and optimization method of claim 1, wherein: the display terminal in the step (2.1) is a computer, the model of the dynamic and static strain analysis system is JM3841, and the sampling rate is 512 Hz.
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