CN115492177B - Method for determining optimal fly ash mixing amount of CFG pile - Google Patents

Abstract

The invention belongs to the technical field of foundation treatment and pile foundation engineering, and relates to a method for determining the optimal fly ash mixing amount of a CFG pile, which comprises the following steps: curing the initial cementing material with the initial fly ash to prepare a first CFG pile, and carrying out field load test; monitoring the vertical ultimate bearing capacity of the first CFG pile and observing the damage mode of the pile body; changing the total doping amount of the cementing material and the doping amount of the fly ash through the destruction mode of the first CFG pile, re-piling to prepare a second CFG pile, and carrying out field load test to change the destruction mode; drawing by taking the unconfined compressive strength of the CFG pile test block as an x axis and the vertical ultimate bearing capacity of the CFG pile as a y axis, and determining the optimal fly ash doping amount; the invention provides a determination method aiming at the optimal mixing amount of the fly ash in the CFG pile, so that the vertical bearing capacity of the pile meets engineering requirements and realizes reasonable utilization of the fly ash.

Description

A method for determining the optimal fly ash content for CFG piles

Technical field

The invention belongs to the technical fields of foundation treatment and pile foundation engineering, and relates to a method for determining the optimal amount of fly ash incorporated into CFG piles.

Background technique

With the development of industrialization and urbanization, resource consumption in my country's industrial sector is further increasing; at the same time, with the rapid development of the power industry, coal is used as the main fuel for power production, resulting in a rapid increase in fly ash emissions. If a large amount of fly ash is not treated, it will cause flying and cause serious pollution to the environment; how to handle and use fly ash is a matter of great concern.

CFG piles are variable-strength piles with a certain strength made of gravel, sand, fly ash mixed with cement and water, and made by various pile forming machines. The vertical bearing capacity of CFG piles is affected by many factors, and the amount of fly ash incorporated is one of the main influencing factors. If the amount of fly ash is too high, the strength of the pile body will not meet the design requirements. If the amount of fly ash is too low, cement will be wasted and the economic cost will be increased. At present, there is no effective and reasonable method to determine the amount of fly ash incorporated. If the amount of fly ash added to CFG piles can be scientifically and reasonably determined, waste fly ash will be consumed and cement will be saved, and the strength of the pile body can be ensured, which has important practical value and economic benefits.

Contents of the invention

The present invention overcomes the shortcomings of the existing technology and proposes a method for determining the optimal amount of fly ash incorporated into CFG piles, thereby solving the problem of uncertainty in the amount of fly ash incorporated into CFG piles in actual engineering applications.

In order to achieve the above objects, the present invention is achieved through the following technical solutions.

A method for determining the optimal amount of fly ash added to CFG piles, including the following steps:

1) Preset the total amount of initial cementing material and the initial amount of fly ash in the CFG pile. The cementing material includes cement and fly ash. According to the preset total amount of initial cementing material The test pile was designed and cured under the initial fly ash mixing amount to make the first CFG pile.

2) Test the vertical ultimate bearing capacity of the first CFG pile body, and observe the failure mode of the pile body to determine whether the failure mode is pile-soil interface failure or pile body failure.

3) Based on the failure mode observed in step 2, adjust the total cementitious material mixing amount and fly ash mixing amount based on the initial cementitious material mixing amount and fly ash mixing amount. , re-pile the second CFG pile, and conduct on-site load tests, so that the pile-soil interface failure or pile body failure of the first CFG pile changes to the pile body failure or pile-soil interface failure of the second CFG pile; The unconfined compressive strength and vertical ultimate bearing capacity of CFG piles whose failure mode is pile body failure are recorded as N ₁ and N ₂ respectively; the unconfined compressive strength and vertical ultimate bearing capacity corresponding to CFG piles whose failure mode is pile-soil interface failure are The compressive strength and vertical ultimate bearing capacity are recorded as M ₁ and M ₂ respectively.

4) According to the total amount of cementitious material and the amount of fly ash in the first and second CFG piles, prepare CFG pile test blocks with different amounts of fly ash and perform maintenance. The curing time is the same as The curing time of the first and second CFG piles is consistent. After the curing of the CFG pile test block is completed, the unconfined compressive strength of the CFG pile test block is measured, and the unconfined compressive strength and the amount of fly ash are plotted. relationship graph.

5) Draw the unconfined compressive strength as the x-axis and the vertical ultimate bearing capacity as the y-axis. Draw a straight line L ₁ parallel to the x-axis through the points (M ₁ , M ₂ ), passing through the origin O and the point (N ₁ , N ₂ ) draw a straight line L ₂ , and record the intersection of straight line L ₁ and straight line L ₂ as point P. Then the unconfined compressive strength corresponding to the abscissa Q of point P is the optimal fly ash content. Calculate the unconfined compressive strength of the CFG pile under the input amount, and then determine the optimal fly ash blending of the CFG pile through the relationship between the unconfined compressive strength and the amount of fly ash obtained in step 4. quantity.

Preferably, step 1 is to preset the total amount of initial cementitious material and the initial amount of fly ash based on the geological survey of the construction site and based on the stratigraphic structure and soil type.

Preferably, in step 3, when the first CFG pile suffers pile body failure, the amount of fly ash added is further reduced until the second CFG pile fails at the pile-soil interface in the field load test; if the second CFG pile fails For the second CFG pile, pile-soil interface failure did not occur under all fly ash mixing amounts. Based on the initial total cementing material mixing amount, the total cementing material mixing amount was increased and the initial fly ash mixing amount was maintained. The amount of ash added remains unchanged, and the second CFG pile is prepared again until pile-soil interface failure occurs; when the pile-soil interface failure occurs in the first CFG pile, the amount of fly ash is further increased until the second CFG pile is destroyed. The CFG pile suffered pile body failure during the field load test.

More preferably, the amount of fly ash added or reduced each time is increased or decreased by 1% to 2%, and the total amount of cementitious materials added is increased or decreased by 4% to 6% each time.

Preferably, in step 4, if the total amount of cementitious material mixed in the first CFG pile and the second CFG pile is equal, then the total amount of cementitious material mixed in the CFG pile test block is equal to that of the first CFG pile and the second CFG pile. The total cementitious material incorporated into the pile remains consistent;

Select the fly ash content of 3 or more CFG pile test blocks, and select the fly ash content of the first CFG pile and the second CFG pile as the fly ash content of the CFG pile test block. between, including the amount of fly ash mixed in the first CFG pile and the second CFG pile; the amount of fly ash added each time increases or decreases by 1% to 2%, and the CFG pile test block is measured. Unconfined compressive strength, and plot the relationship between unconfined compressive strength and fly ash content.

Preferably, in step 4, when the pile body failure of the first CFG pile occurs and the total amount of cementitious material in the second CFG pile where pile-soil interface failure occurs is not equal to the total amount of the first CFG pile, prepare first The first CFG pile test block with the same total cementitious material content and fly ash content as the first CFG pile, and measure the unconfined compressive strength of the first CFG pile test block;

Then prepare a second CFG pile test block with a total cementing material content equal to that of the second CFG pile where pile-soil interface failure occurred. The fly ash content of the second CFG pile test block is selected between the first CFG pile and the first CFG pile. The amount of fly ash added to the second CFG pile where pile-soil interface failure occurred is equal to the amount of fly ash incorporated into the first CFG pile and the second CFG pile where pile-soil interface failure occurred, and is selected 3 or more types of fly ash are mixed in. The amount of fly ash is increased or decreased by 1% to 2% each time. Measure the unconfined compressive strength of the second CFG pile test block and draw it. The relationship between unconfined compressive strength and fly ash content.

The beneficial effects produced by the present invention compared with the existing technology are:

The present invention provides a method for determining the optimal amount of fly ash in CFG piles, which can make the vertical bearing capacity of the pile meet the engineering requirements while achieving rational utilization of fly ash, and is more It scientifically ensures that the amount of fly ash incorporated into CFG piles is the optimal value, so that fly ash can work with other ingredients to ensure the strength of the CFG pile body, while also avoiding the waste of raw materials such as cement, and saving project costs. It also protects the environment and provides a practical solution for determining the amount of fly ash incorporated into CFG piles in actual projects.

Description of the drawings

Figure 1 is the coordinate diagram of point P obtained through on-site load testing.

Figure 2 is a graph of the unconfined compressive strength described in Example 1.

Figure 3 is a coordinate diagram of point P1 in Embodiment ₁ .

Figure 4 is a graph of the unconfined compressive strength described in Example 2.

Figure 5 is a coordinate diagram of point P2 in Embodiment ₂ .

Figure 6 is a graph of the unconfined compressive strength described in Example 3.

Figure 7 is a coordinate diagram of point P3 in Embodiment ₃ .

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear, the present invention will be further described in detail with reference to the embodiments and drawings. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention. The technical solution of the present invention will be described in detail below with reference to the embodiments and drawings, but the scope of protection is not limited by this.

Example 1

A method for determining the optimal amount of fly ash added to CFG piles. The specific steps are as follows:

Step 1) According to the "Geotechnical Engineering Survey Code" GB50021-2001, the soil quality of a construction site was surveyed. The results are shown in Table 1. From Table 1, it can be seen that the soil type is silty clay.

Step 2) Based on local construction experience, determine the total amount of initial cementitious materials in the CFG pile to be 18% and the initial amount of fly ash to be 7%. Prepare the first CFG pile and conduct an on-site load test after 28 days of curing. , it was found that the failure mode was pile body failure, and the vertical ultimate bearing capacity was 490 kN;

Step 3) Further reduce the amount of fly ash and prepare a second CFG pile. It was found that when the fly ash content was reduced to 4%, the failure mode of the second CFG pile was pile-soil interface failure, and the vertical ultimate bearing capacity was 540 kN.

Step 4) According to the "Cement-Soil Mix Ratio Design Regulations" JGJ/T 233-2011, prepare a cement material with a total mixing amount of 18% and fly ash mixing amounts of 4%, 5%, 6% and 7%. CFG pile test block and cured for 28 days. The unconfined compressive strength of the CFG pile test block was measured to be 25.32 MPa, 23.43 MPa, 21.17 MPa and 20.21MPa respectively. The unconfined compressive strength and fly ash incorporation were plotted. The quantity relationship curve is shown in Figure 2.

Step 5) Take the unconfined compressive strength of the CFG pile test block as the x-axis and the vertical ultimate bearing capacity of the CFG pile as the y-axis. Draw a straight line parallel to the x-axis through the point (25.32, 540). L ₁₁ , draw a straight line L ₂₁ through the origin O and point (20.21, 490). The intersection of straight line L ₁₁ and straight line L ₂₁ is recorded as point P ₁ . Then the corresponding value of the abscissa of point P ₁ is 22.27 MPa, which is the maximum The unconfined compressive strength of CFG piles under optimal fly ash content is shown in Figure 3. Further through the relationship curve between the unconfined compressive strength of the CFG pile test block and the fly ash content obtained in step 4) (Figure 2), it can be determined that the optimal fly ash content of the CFG pile is 5.51%. .

Example 2

A method for determining the optimal amount of fly ash added to CFG piles. The specific steps are as follows:

Step 1) According to the "Code for Geotechnical Engineering Investigation" GB50021-2001, the soil quality of a construction site was investigated. The results are shown in Table 2. From Table 2, it can be seen that the soil type is clay.

Step 2) Based on local construction experience, determine the total amount of initial cementitious materials in the CFG pile to be 15% and the initial amount of fly ash to be 6%. Prepare the first CFG pile and conduct an on-site load test after 28 days of curing. , it was found that the failure mode was pile body failure, and the vertical ultimate bearing capacity was 460 kN;

Step 3) Further reduce the amount of fly ash to 1%, 3% and 5%, and find that the failure mode of the second CFG pile is pile failure; then increase the total amount of initial cementitious material to 20 %, keep the initial fly ash mixing amount at 6%, prepare the second CFG pile again, and find that the failure mode is pile body failure, then further reduce the fly ash mixing amount; when the fly ash mixing amount is reduced When the minimum is 3%, the failure mode is found to be pile-soil interface failure, and the vertical ultimate bearing capacity is 590 kN.

Step 4) According to the "Cement-Soil Mix Ratio Design Regulations" JGJ/T 233-2011, prepare a CFG pile test block with a total cementing material content of 15% and a fly ash content of 6%, and maintain it for 28 days. , the unconfined compressive strength of the CFG pile test block was measured to be 18.82 MPa. CFG pile test blocks with a total cementing material content of 20% and fly ash content of 3%, 4%, 5% and 6% were prepared and cured for 28 days. The lateral strength of the CFG pile test block was measured. The limited compressive strengths are 27.12 MPa, 25.88 MPa, 23.46 MPa and 21.63MPa respectively. The relationship between the unconfined compressive strength and the amount of fly ash is drawn, as shown in Figure 4.

Step 5) Take the unconfined compressive strength of the CFG pile test block as the x-axis and the vertical ultimate bearing capacity of the CFG pile as the y-axis. Draw a straight line parallel to the x-axis through the point (27.12, 590). L ₁₃ , draw a straight line L ₂₃ through the origin O and point (18.82, 460). The intersection of straight line L ₁₃ and straight line L ₂₃ is recorded as point P ₃ . Then the corresponding value of the abscissa of point P ₃ is 24.14 MPa, which is the maximum The unconfined compressive strength of CFG piles under optimal fly ash content is shown in Figure 5. Further through the relationship curve between the unconfined compressive strength of the CFG pile test block and the fly ash content obtained in step 4) (Figure 4), it can be determined that the optimal fly ash content of the CFG pile is 4.71%. .

Example 3

A method for determining the optimal amount of fly ash added to CFG piles. The specific steps are as follows:

Step 1) According to the "Geotechnical Engineering Survey Code" GB50021-2001, the soil quality of a construction site was surveyed. The results are shown in Table 3. From Table 3, it can be seen that the soil type is silty clay.

Step 2) Based on local construction experience, determine the total amount of initial cementitious material in the CFG pile to be 25% and the initial amount of fly ash to be 5%. Prepare the first CFG pile and conduct an on-site load test after 28 days of curing. , it was found that the failure mode was pile-soil interface failure, and the vertical ultimate bearing capacity was 810 kN.

Step 3) Further increase the amount of fly ash to prepare a second CFG pile. It was found that when the fly ash mixing amount increased to 8%, the failure mode of the second CFG pile was pile failure, and the vertical ultimate bearing capacity was 730 kN.

Step 4) According to the "Cement-Soil Mix Ratio Design Regulations" JGJ/T 233-2011, prepare a mixture with a total cementitious material content of 25% and fly ash content of 5%, 6%, 7% and 8%. CFG pile test block and cured for 28 days. The unconfined compressive strength of the CFG pile test block was measured to be 28.93 MPa, 26.48 MPa, 25.37 MPa and 22.61MPa respectively. The unconfined compressive strength and fly ash incorporation were plotted. The quantity relationship curve is shown in Figure 6.

Step 5) Take the unconfined compressive strength of the CFG pile test block as the x-axis and the vertical ultimate bearing capacity of the CFG pile as the y-axis. Draw a straight line parallel to the x-axis through the point (28.93, 810). L ₁₂ , draw a straight line L ₂₂ through the origin O and point (22.61, 730). The intersection of straight line L ₁₂ and straight line L ₂₂ is recorded as point P ₂ . Then the corresponding value of the abscissa of point P ₂ is 25.09 MPa, which is the maximum The unconfined compressive strength of CFG piles under optimal fly ash content is shown in Figure 7. Further through the relationship curve between the unconfined compressive strength of the CFG pile test block and the fly ash content obtained in step 4) (Figure 6), it can be determined that the optimal fly ash content of the CFG pile is 7.08%. .

The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be concluded that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the premise of the present invention, Below, several simple deductions or substitutions can be made, which should all be deemed to belong to the patent protection scope of the present invention as determined by the submitted claims.

Claims (3)

1. The method for determining the optimal fly ash doping amount of the CFG pile is characterized by comprising the following steps of:

1) Presetting the total mixing amount of initial cementing materials and the mixing amount of initial fly ash in the CFG pile, wherein the cementing materials comprise cement and the fly ash, and designing a test pile and curing to prepare a first CFG pile according to the preset total mixing amount of the initial cementing materials and the preset mixing amount of the initial fly ash;

2) Testing the vertical ultimate bearing capacity of the first CFG pile body, observing the damage mode of the pile body, and determining the damage mode as pile-soil interface damage or pile body damage;

3) Adjusting the total doping amount of the cementing material and the doping amount of the fly ash based on the total doping amount of the initial cementing material and the initial doping amount of the fly ash through the damage mode observed in the step 2, re-piling to prepare a second CFG pile, and performing a field load test to change the pile-soil interface damage or the pile body damage of the first CFG pile into the pile body damage or the pile-soil interface damage of the second CFG pile; the unconfined compressive strength and the vertical ultimate bearing capacity corresponding to the CFG pile with the failure mode of pile body failure are respectively recorded as N ₁ And N ₂ The method comprises the steps of carrying out a first treatment on the surface of the The unconfined compressive strength and the vertical ultimate bearing capacity corresponding to the CFG pile with the failure mode of pile-soil interface failure are respectively recorded as M ₁ And M ₂ The method comprises the steps of carrying out a first treatment on the surface of the When the first CFG pile occurs, the pile bodyThe coal ash doping amount is further reduced until the second CFG pile is damaged at the pile-soil interface in the field load test; if the second CFG pile is not damaged at the pile-soil interface under all the fly ash doping amounts, increasing the total doping amount of the cementing material on the basis of the total doping amount of the initial cementing material, keeping the initial fly ash doping amount unchanged, and preparing the second CFG pile again until the pile-soil interface is damaged; when the first CFG pile is damaged by the pile-soil interface, the fly ash doping amount is further increased until the second CFG pile is damaged by the pile body in the field load test;

4) According to the total doping amount of the cementing materials and the doping amount of the fly ash in the first CFG pile and the second CFG pile, preparing CFG pile test blocks with different doping amounts of the fly ash, maintaining the CFG pile test blocks, keeping the maintenance time consistent with the maintenance time of the first CFG pile and the second CFG pile, measuring the unconfined compressive strength of the CFG pile test blocks after the CFG pile test blocks are maintained, and drawing a relation graph of the unconfined compressive strength and the doping amount of the fly ash;

if the total doping amount of the cementing materials in the first CFG pile and the second CFG pile is equal, the total doping amount of the cementing materials of the CFG pile test block is consistent with the total doping amount of the cementing materials in the first CFG pile and the second CFG pile;

the method comprises the steps of selecting the mixing amount of fly ash of more than 3 CFG pile test blocks, wherein the mixing amount of the fly ash of the CFG pile test blocks is selected between the mixing amounts of the fly ash in a first CFG pile and a second CFG pile, and the mixing amount of the fly ash in the first CFG pile and the second CFG pile is equal to the mixing amount of the fly ash in the first CFG pile and the second CFG pile; the increasing or decreasing amplitude of the fly ash doping amount is 1% -2% each time, the unconfined compressive strength of the CFG pile test block is measured, and a relation graph of the unconfined compressive strength and the fly ash doping amount is drawn;

when the first CFG pile is damaged by the pile body, the total doping amount of the cementing material in the second CFG pile with the damaged pile-soil interface is unequal to that of the first CFG pile, firstly preparing a first CFG pile test block with the total doping amount of the cementing material and the doping amount of the fly ash equal to that of the first CFG pile, and measuring the unconfined compressive strength of the first CFG pile test block;

then preparing a second CFG pile test block with the total mixing amount of the cementing material being equal to that of a second CFG pile with the broken pile-soil interface, wherein the mixing amount of the fly ash of the second CFG pile test block is selected between the mixing amounts of the fly ash of the first CFG pile and the second CFG pile with the broken pile-soil interface, the mixing amount of the fly ash of the second CFG pile with the broken pile-soil interface is equal to that of the fly ash of the first CFG pile and the second CFG pile with the broken pile-soil interface, more than 3 fly ash mixing amounts are selected, the increasing or decreasing amplitude of the fly ash mixing amount is 1% -2% each time, measuring the unconfined compressive strength of the second CFG pile test block, and drawing a relation graph of the unconfined compressive strength and the fly ash mixing amount;

5) Plotting is performed with unconfined compressive strength as x-axis and vertical ultimate bearing capacity as y-axis, and the cross point (M ₁ ，M ₂ ) To a straight line L parallel to the x-axis ₁ Crossing the origin O and the point (N ₁ ，N ₂ ) Straight line L ₂ Will be straight line L ₁ And straight line L ₂ And (3) marking the intersection point of the CFG pile as a point P, wherein the unconfined compressive strength corresponding to the abscissa Q of the point P is the unconfined compressive strength of the CFG pile under the optimal fly ash doping amount, and then determining the optimal fly ash doping amount of the CFG pile through the relation graph of the unconfined compressive strength and the fly ash doping amount obtained in the step 4.

2. The method for determining the optimal fly ash mixing amount of the CFG pile according to claim 1, wherein the step 1 is to preset the total mixing amount of the initial cementing material and the initial fly ash mixing amount according to the stratum structure and the soil type through geological investigation of a construction site.

3. The method for determining the optimal fly ash mixing amount of the CFG pile according to claim 1, wherein the increasing or decreasing range of the fly ash mixing amount is 1% -2% each time, and the increasing or decreasing range of the total cementing material mixing amount is 4% -6% each time.