A prediction method for the strength of seaweed fiber-reinforced silt-cement soil

Abstract

The present invention belongs to the field of marine engineering construction, and particularly relates to a method for predicting the strength of seaweed fiber reinforced silt cement soil. The present invention uses seaweed fiber in the field of silt solidification for the first time, which can improve its early strength in a short time, has good applicability and durability, and the seaweed fiber is degradable and will not pollute the environment, featuring environmental friendliness. The present invention prepares specimens under the conditions of cement mixing ratio, seaweed fiber length, and seaweed fiber mixing ratio, and conducts unconfined compressive tests after curing to the specified age respectively. Through the back-inference of test data, a strength evaluation model that can simultaneously reflect the influence of water-cement ratio, seaweed fiber mixing ratio, seaweed fiber length, and curing age is established. This model can predict the unconfined compressive strength values of seaweed fiber reinforced cement soil under different working conditions.

Description

Technical Field

[0001] The present invention belongs to the field of ocean engineering construction, and particularly relates to a method for predicting the strength of seaweed fiber-reinforced silt cement soil. Background Art

[0002] The unconfined compression test is a special case of the undrained shear test under confining pressure. The strength measured therefrom can reflect the overall strength index of the soil mass, and is an important index for calculating the characteristic value of the foundation bearing capacity in engineering. It is also often used as a reference index for the mix design of indoor tests and the design value of the compressive strength of on-site projects.

[0003] By incorporating randomly dispersed fibers into cement-solidified soil, it is found that the fibers can effectively improve the unconfined compressive strength of cement-solidified soil, and it is also found that the improvement of the compressive strength by fibers is different under different cement incorporation ratios and curing ages. However, the existing fibers are non-degradable and cause certain pollution to the environment.

[0004] In addition, for cement-solidified soil, domestic and foreign scholars have conducted a large number of studies on its strength development law and proposed different strength estimation formulas. However, these strength prediction formulas have limitations such as few parameters, and the prediction accuracy is poor. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for predicting the strength of seaweed fiber-reinforced silt cement soil to solve at least one of the technical problems in the background art. The adopted technical solution is as follows:

[0006] A method for predicting the strength of seaweed fiber-reinforced silt cement soil specifically includes the following steps:

[0007] Step 1: For the soil samples transported back from the engineering site, measure their natural moisture content, and then measure their air-dried moisture content after natural air-drying; then mechanically crush them and pass them through a 5-mm standard copper sieve for soil to make them into a powdery state; place the air-dried soil samples in a vacuum drying oven for 8 hours to remove moisture, and place them in a shaded and cool place for material piling.

[0008] Step 2: Sequentially add cement and seaweed fibers to the piled soil material, and use a cement paste mixer to stir; then pour the evenly stirred soil material into the experimental mold, place the experimental mold on the experimental vibrating table for vibration, shave off the cement soil above the upper edge of the mold along the top surface of the mold, immediately level the test piece and cover the surface with plastic wrap for sealing.

[0009] Step 3: Use different cement incorporation ratios, seaweed fiber lengths, and seaweed fiber incorporation ratios, and repeat Step 2 to prepare multiple groups of seaweed fiber-reinforced solidified soil specimens.

[0010] Step 4: Place the specimen in a thermo-hygrostat curing cabinet and cure it until the specified age. Then take it out, immediately wipe off the visible free water on the surface of the specimen, and measure the size and weight of the specimen.

[0011] Step 5: Use a universal testing machine to measure the unconfined compressive strength of the seaweed fiber-reinforced solidified soil specimen.

[0012] Step 6: Conduct curve fitting on the obtained unconfined compressive strength, and then obtain the prediction formula for the strength of seaweed fiber-reinforced silt cement soil:

[0013]

[0014] where the seaweed fiber incorporation ratio cement incorporation ratio

[0015] In the formula, q u —unconfined compressive strength of seaweed fiber-reinforced solidified soil, unit is kPa, ω n —water content of silt, unit is %, ρ f —seaweed fiber incorporation ratio, unit is %, ρ c —cement incorporation ratio, unit is %, L—length of seaweed fiber, unit is mm, T—curing age, unit is d, T0—standard curing age, taken as 28 d; W f —weight of incorporated seaweed fiber, unit is g; W s —dry weight of silt, unit is g; W c —weight of incorporated cement, unit is g.

[0016] Further verify the rationality of the prediction formula.

[0017] Preferably, in Step 1, the blanking time is 24 hours, and the curing age time is 7 d - 60 d.

[0018] Preferably, in Step 2, the stirring and preparation of the specimen are completed within 1 hour after adding cement.

[0019] Preferably, in Step 3, the cement incorporation ratio is 6% - 12%, the incorporation length of seaweed fiber is 3 - 9 mm, and the seaweed fiber incorporation ratio is 0.3% - 0.9%.

[0020] Preferably, in Step 4, the curing age time is 7 d - 60 d.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention first introduces seaweed fiber as an additive to co-cure silt with cement. Seaweed fiber has strong moisture absorption performance and can improve the early strength of silt in a short time when used for silt curing, verifying the applicability and durability of seaweed fiber-reinforced solidified soil. In addition, as a new type of biological fiber, seaweed fiber has the advantages of being green, environmentally friendly, highly moisture-absorbing, degradable, and renewable. After the seaweed fiber completes the curing effect in the silt-cement soil, it will degrade and will not pollute the environment, featuring environmental friendliness.

[0023] (2) The present invention proposes a formula that can predict the unconfined compressive strength of seaweed fiber-reinforced cement soil. The parameters of this formula include silt moisture content, cement mixing ratio, seaweed fiber length, seaweed fiber mixing ratio, curing age, and other parameters. Through these parameters, researchers can fully predict the unconfined compressive strength values of seaweed fiber-reinforced cement soil under different working conditions, greatly reducing the test process for various working conditions and the long-term curing time. Description of the Drawings

[0024] Figure 1 Flow chart of a method for predicting the strength of seaweed fiber-reinforced silt-cement soil according to the present invention;

[0025] Figure 2 Point graph and prediction curve of the strength of seaweed fiber-reinforced silt-cement soil with the change of water-cement ratio at 0.3% mixing ratio according to the present invention;

[0026] Figure 3 Point graph and prediction curve of the strength of seaweed fiber-reinforced silt-cement soil with the change of water-cement ratio at 0.6% mixing ratio according to the present invention;

[0027] Figure 4 Point graph and prediction curve of the strength of seaweed fiber-reinforced silt-cement soil with the change of water-cement ratio at 0.9% mixing ratio according to the present invention. Detailed Embodiments

[0028] The drawings are only for illustrative purposes; it should be understood that the cases mentioned below are only used to explain the present invention, for the convenience of describing the present invention and simplifying the description. Therefore, it cannot be construed as a limitation of the present invention.

[0029] The principles and features of the present invention are described below in conjunction with embodiments. The embodiments cited are only used to explain the present invention and are not intended to limit the scope of the present invention. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0030] The present invention is described in detail below in conjunction with the drawings and specific embodiments.

[0031] Embodiment 1

[0032] Taking silt and seaweed fiber as examples, this embodiment illustrates the applicability of the prediction method of the present invention and the specific calculation and analysis steps.

[0033] As Figure 1 shown, a method for predicting the strength of seaweed fiber reinforced silt cement soil specifically includes the following steps:

[0034] Step 1: Determine the natural moisture content of the soil sample transported back from the construction site, and then determine its air-dried moisture content after natural air-drying; then mechanically crush it and pass it through a 5-mm standard copper sieve for soil to make it into a powder; place the air-dried soil sample in a vacuum drying oven for 8 hours to remove moisture, and place it in a shaded and cool place for material storage.

[0035] Step 2: Add cement and seaweed fiber to the stored soil material in sequence and stir it using a cement paste mixer; then pour the evenly stirred soil material into the experimental mold, place the experimental mold on the experimental vibrating table for vibration, shave off the cement soil that is higher than the upper edge of the mold along the top surface of the mold, immediately level the test piece and cover the surface with plastic wrap for sealing;

[0036] The basic property indexes of the used cement, silt, and seaweed fiber are shown in Table 1, Table 2, and Table 3.

[0037] Table 1 Physical property indexes of silt

[0038]

[0039] Among them, the organic matter is measured by the ignition method to measure the organic matter content.

[0040] Table 2 Physical property indexes of cement

[0041]

[0042] Table 3 Physical property indexes of seaweed fiber

[0043]

[0044] Step 3: Using different cement incorporation ratios, seaweed fiber lengths, and seaweed fiber incorporation ratios, repeat Step 2 to prepare multiple groups of seaweed fiber reinforced solidified soil specimens.

[0045] The present invention defines two concepts, the seaweed fiber incorporation ratio

[0046]

[0047] wherein, W f —— the weight (g) of the incorporated seaweed fiber; W s —— the dry weight (g) of the silt.

[0048] Cement incorporation ratio

[0049]

[0050] Among them, W c —— The weight of cement incorporated (g); W s —— The dry weight of the silt (g).

[0051] In this example, 40 groups of seaweed fiber reinforced solidified soil specimens were prepared based on three cement incorporation ratios, three seaweed fiber lengths, and three seaweed fiber incorporation ratios. The specific situation is shown in Table 4:

[0052] Table 4 Grouping of seaweed fiber reinforced solidified soil specimens

[0053]

[0054] Step 4: Place the specimen in a constant temperature and humidity curing box and cure it until the specified age, then take it out. Immediately wipe off the visible free water on the surface of the specimen and measure the size and weight of the specimen.

[0055] Step 5: Use a universal testing machine to measure the unconfined compressive strength of the seaweed fiber reinforced solidified soil specimen; among them, the parameters set for the universal testing machine are a loading rate of 1 mm / min and other parameters. The test can be stopped when the axial stress reaches the peak or when the strain reaches 8%.

[0056] Step 6: Perform curve fitting on the obtained unconfined compressive strength, and then obtain the prediction formula for the strength of seaweed fiber reinforced silt-cement soil, specifically:

[0057]

[0058] Among them, the seaweed fiber incorporation ratio The cement incorporation ratio

[0059] In the formula, q u — The unconfined compressive strength of seaweed fiber reinforced solidified soil (kPa), ω n — The water content of the silt (%), ρ f — The seaweed fiber incorporation ratio (%), ρ c — The cement incorporation ratio (%), L — The length of the seaweed fiber (mm), T — The curing age (d), T0 — The standard curing age, taken as 28 d; W f — The weight of the seaweed fiber incorporated (g); W s — The dry weight of the silt (g); W c — The weight of the cement incorporated (g).

[0060] Such as Figures 2 - 4As shown, software is used to process the unconfined compressive strength data of specimens with different seaweed fiber incorporation ratios and curing ages, and the analysis results of the unconfined compressive strength varying with the water-cement ratio under three seaweed fiber incorporation ratios and four curing ages are given.

[0061] It can also be found from Figures 2 - 4 that the variation range of parameter B is between 1.38 and 1.62, and it is basically not affected by the changes in curing age, seaweed fiber incorporation ratio, and seaweed fiber length.

[0062] Its theoretical basis is the Abrams equation commonly used to predict the unconfined compressive strength of concrete:

[0063]

[0064] In the formula, q u —Unconfined compressive strength under specific age conditions; ζ—Water-cement ratio, the mass ratio of water content to cement content; A, B—Test constants independent of the water-cement ratio.

[0065] Therefore, in this embodiment, when predicting the unconfined compressive strength of seaweed fiber-reinforced solidified soil, parameter B is taken as 1.50, and formula (3) is expressed as:

[0066]

[0067] The above strength data analysis results based on the Abrams equation show that parameter A is not only related to the curing age T, but also varies with the seaweed fiber incorporation ratio and seaweed fiber length. Therefore, in order to obtain an effective unconfined compressive strength prediction formula, it is first necessary to determine the relationship between parameter A and the curing age T, seaweed fiber incorporation ratio, and seaweed fiber length. Table 5 shows the parameter A corresponding to different curing ages and different seaweed fibers.

[0068] Table 5 Parameter A corresponding to different curing ages and different seaweed fibers

[0069]

[0070] For seaweed fiber-reinforced solidified soil, it is found in this paper that parameter A obtained based on the Abrams equation approximately satisfies a power relationship with the curing age T, and this relationship is expressed as:

[0071]

[0072] Among them, T0—Reference age for dimensionlessization, taken as a fixed value of 28 days; M and N—Empirical constants independent of the curing age, and the values are shown in Table 6.

[0073] Table 6 M values and N values corresponding to different seaweed fiber ratios

[0074]

[0075] As can be seen from Table 6 above, M varies with the incorporation ratio and fiber length of seaweed fiber, while N does not change much with the incorporation ratio and fiber length of seaweed fiber, remaining between 0.27 and 0.30 all the time. In the later calculation, N is taken as 0.285 in this paper.

[0076] Therefore, formula (5) is written as:

[0077]

[0078] By fitting the experimental data curve with software, it is obtained that:

[0079] M = (-22167×ρ f + 640)×Ln(L)+1050×Ln(L)+8110 (7);

[0080] Substituting formula (7) and N = 0.285 into formula (4), we get

[0081]

[0082] In the formula, q u —Unconfined compressive strength of seaweed fiber reinforced solidified soil (kPa), ω n —Water content of silt (%), ρ f —Incorporation ratio of seaweed fiber (%), ρ c —Incorporation ratio of cement (%), L—Length of seaweed fiber (mm), T—Curing age (d), T0—Standard curing age, taken as 28 d. Table 7 shows the comparison between the experimental values and calculated values of unconfined compressive strength calculated by formula (8).

[0083] Table 7 Comparison between experimental values and calculated values of unconfined compressive strength

[0084]

[0085]

[0086] As can be seen from Table 7, by comparing the calculated values of unconfined compressive strength obtained by formula (8) with the experimental values of indoor unconfined compressive strength, it is found that the maximum error is 19.60% < 20%. Therefore, formula (8) has good applicability and can provide reference value for the indoor test formula design and engineering strength inspection of seaweed fiber reinforced solidified soil.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the specification of the present invention.

Claims

1. A method for predicting the strength of seaweed fiber-reinforced silt-cement soil, characterized in that, The specific steps include: Step 1: Determine the natural moisture content of the soil sample brought back from the project site, and then determine its air-dried moisture content after natural air drying; Then the soil sample was crushed mechanically and passed through a 5 mm standard copper sieve to form a powder; the air-dried soil sample was placed in a vacuum drying oven for 8 hours to remove moisture and then placed in a dark and cool place to keep the material dry; Step 2: Add cement and seaweed fiber to the soil material in sequence, and stir with a cement slurry mixer; then pour the evenly stirred soil material into the experimental mold, place the experimental mold on an experimental vibration table for vibration, and cut off the cement soil that is higher than the upper edge of the mold along the top surface of the mold, immediately smooth the test piece and cover the surface with plastic wrap to seal it; Step 3: using different cement incorporation ratios, seaweed fiber lengths and seaweed fiber incorporation ratios, repeat step 2 to prepare multiple groups of seaweed fiber reinforced soil samples; Step 4: Place the sample in a constant temperature and humidity curing box and cure it to the specified age, then take it out, immediately wipe off the visible free water on the surface of the sample, and measure the size and weight of the sample; Step 5: Use a universal testing machine to measure the unconfined compressive strength of the seaweed fiber reinforced soil sample; Step 6: Perform curve fitting on the obtained unconfined compressive strength to obtain the prediction formula of the strength of seaweed fiber reinforced silt cement soil: Among them, the incorporation ratio of seaweed fiber Cement incorporation ratio where q u — unconfined compressive strength of seaweed fiber reinforced solidified soil, unit: kPa, ω n — water content of silt, unit: %, ρ f — incorporation ratio of seaweed fiber, unit: %, ρ c — incorporation ratio of cement, unit: %, L — length of seaweed fiber, unit: mm, T — curing age, unit: d, T0 — standard curing age, taken as 28 d; W f — weight of incorporated seaweed fiber, unit: g; W s — Dry weight of the sludge, in g; W c — Weight of cement incorporated, in g.

2. The method for predicting the strength of seaweed fiber-reinforced silt-cement soil according to claim 1, characterized in that, In the step 1, the stuffing time is 24 hours, and the curing period is 7 days to 60 days.

3. The method for predicting the strength of seaweed fiber-reinforced silt-cement soil according to claim 1, characterized in that, In the step 2, the stirring and preparation of the sample is completed within 1 hour after the cement is added.

4. The method for predicting the strength of seaweed fiber-reinforced silt-cement soil according to claim 1, characterized in that, In the step three, the cement blending ratio is 6%-12%, the blending length of the seaweed fiber is 3-9 mm, and the seaweed fiber blending ratio is 0.3%-0.9%.

5. The method for predicting the strength of seaweed fiber-reinforced silt-cement soil according to claim 1, characterized in that, In the step 4, the curing period is 7d-60d.

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