# Experimental Study on Mechanical Properties of Cement-Solidified Remolded Soil Reinforces by Polyvinyl Alcohol Fiber

Authors: Ling Mei; Xin Dong; Shuyan Yang; Jie Deng
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

As a reusable resource, remolded soils are often not utilized on a large scale due to their high water content and low bearing capacity. By using polyvinyl alcohol fiber (PVA) as reinforcing material and cement as cementing material, the remolded soil was improved into a usable consolidated remolded soil, and the effects of different fiber content, fiber length modulus, and conservation age on the static and dynamic characteristics of the consolidated remolded soil were investigated by conducting triaxial consolidated undrained shear tests and dynamic triaxial tests on the consolidated remolded soil. The results show that the use of PVA fiber reinforced cement can effectively improve the shear strength and dynamic strength of the remolded soil and reduce the water content of the remolded soil; the best effect on the static strength of the remolded soil was achieved when 0.1% of PVA fibers with a length of 6 mm were incorporated into the specimens at a conservation age of 28 d; the best effect on the dynamic strength of the remolded soil was achieved when 0.3% of PVA fibers with a length of 12 mm were incorporated into the specimens at a conservation age of 7 d.


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## Body

## 1. Introduction

China’s remolded soil is widely present in the middle and lower reaches of the Yangtze River waterway, from the water transport projects of various coastal ports, which produces a large amount of remolded soil every year, currently ranking first in the world, and according to the current situation of ports in coastal cities, China’s port construction is still developing rapidly, and the amount of remolded soil brought will definitely continue to expand, however, remolded soil, because of its high water content, low permeability, low bearing capacity, and other characteristics However, due to its high water content, low permeability and low bearing capacity, remolded soil is currently dumped at will, which not only causes waste of resources but also has a negative impact on the ecological environment and does not have its proper value for use. In fact, remolded soil is a reusable resource, and its reasonable comprehensive use can effectively reduce its water content and improve its carrying capacity, thus achieving the effect of saving resources and protecting the ecological environment [1].The methods commonly used to reinforce remolded soils are mainly chemical materials such as cement and lime, but these methods are gradually failing to meet the needs of the project, while available research shows that the use of fibers can reinforce concrete materials [2], the use of combined fiber and cement curing can effectively strengthen the soil [3]. However, research in this area is incomplete with regard to the reinforcement of remolded soils [4–6]. Lin et al. [7] conducted a study on the improvement of mechanical properties of limestone soils by polypropylene fibers, and the results showed that when the fiber admixture was 0.5%, a large amount of gel material hydrated calcium silicate attached to the fiber surface, which improved the cementation force and compactness between polypropylene fibers and limestone particles. Sen [8] studied the effect of improving the unconfined compressive strength and shear strength of sea-coated silt with polypropylene fiber through indoor tests, and then proposed the most fiber content and fiber length. Maher and Ho [9] carried out uniaxial compressive tests and splitting tests on plain soils incorporated with glass fibers, and the results showed that the incorporation of glass fibers was effective in increasing the unconfined peak compressive and tensile strengths of the plain soils.In this paper, a series of triaxial consolidation undrained shear tests and dynamic triaxial tests were carried out with polyvinyl alcohol fiber (PVA) as reinforcing material and cement as curing material on a large volume of remolded soil in China. The effects of different fiber content, fiber length modulus, and conservation age on the cohesion, internal friction angle, water content, and dynamic strength of cemented remolded soil were investigated, and the optimum dosing and length modulus were then derived.


## 2. Method

### 2.1. Test Materials

#### 2.1.1. Soil Material

The remolded soil used in this test was taken from the middle and lower reaches of the Yangtze River, Zhenjiang Jiang Xijindu section of the channel, the soil was in a flow plastic state, its mineral composition is mainly based on ilmenite and montmorillonite, the basic physical and mechanical properties of the soil samples are shown in Table1. The liquidity index of the remolded soil is calculated to be greater than 1 according to (1), so the remolded soil can be judged to be in a fluid-plastic state.(1)IL=ω−ωLωp−ωL.Table 1
Basic mechanical properties of remolded soil.
Water content (%)Specific gravityLiquid limit (%)Plasticity index (%)Density (g·cm−3)Organic matter content (%)37.52.383736.31.871.5The test soil specimen is a remodeling soil. The remolded soil is first air-dried and passed through a 2 mm sieve, then dried and cooled in an oven. Based on natural moisture content, the remodeling soil is prepared at a moisture content of 37.5%, and finally, the prepared remodeling soil is sealed and left to stand for 24 h before the specimen is prepared to the required size for the test.


#### 2.1.2. Fiber Material

The fiber reinforcement material used for the test is polyvinyl alcohol fiber (PVA) (shown in Figure1), which has a slightly yellow appearance and is a synthetic fiber material that is nontoxic and nonhazardous to humans and the environment. This fiber material has high strength, high modulus, low elongation, and other characteristics, the main thing is that it can dissolve in water and has a good affinity with cement materials. The basic physical and mechanical properties of the PVA material are shown in Table 2.Figure 1
Polyvinyl alcohol fiber.Table 2
Basic mechanical properties of polyvinyl alcohol fiber.
Dry fracture strength (MPa)Dry elongation at break (%)Modulus of elasticity (GPa)Heat and water resistance (°C)Length (mm)Dispersion≥12006.0∼8.0≥35≥104M ± 0.51∼3Note: M is for 3 mm, 6 mm, 9 mm, and 12 mm.


#### 2.1.3. Cement Material

P.O 42.5 (Yangchun cement), a normal silicate cement from Shanghai, was used as the consolidating agent.


### 2.2. Test Contents

Triaxial consolidated undrained shear and dynamic triaxial tests were carried out on PVA fiber reinforced cement cured remolded soils to investigate the static and dynamic properties of the improved remolded soils through single control of PVA fiber content and fiber length modulus. The PVA fiber dose was 0%, 0.1%, 0.2%, and 0.3%, the fiber length modulus was 3 mm, 6 mm, 9 mm, and 12 mm, the age of the triaxial consolidation undrained shear test specimens was 1 d, 3 d and 7 d, the age of the dynamic triaxial test specimens was 1 d, 3 d, and 7 d and the cement dose was 6%.


#### 2.2.1. Triaxial Consolidated Undrained Shear Test

In order to determine the stress-strain relationship of the remolded soil under the conditions of different PVA fiber admixture and fiber length modulus, and thus to obtain its static strength parameters, and considering that the remolded soil cured by PVA fiber reinforced cement has significantly improved permeability, this test was carried out using the cemented undrained triaxial shear test (CU) with a cylindrical specimen, 39.1 mm in diameter and 80 mm in height. The test shear rate was set at 0.08 mm/min and tests were carried out at consolidation envelope pressures of 100, 200, and 300 kPa, respectively. The specific static triaxial tests carried out are shown in Table3.Table 3
Static triaxial test scheme for solidification of remolded soil.
TestFiber dose (%)Fiber length modulus (mm)Conservation age (d)S10127/14/28S20.1S30.2S40.3S50.33S66S79S812


#### 2.2.2. Dynamic Triaxial Test

The strength of soil is always linked to a certain limit of strain, so the dynamic strength should be discussed for the corresponding number of vibration cycles. The lower the number of vibration cycles, the higher the dynamic strength; the higher the number of vibration cycles, the lower the dynamic strength. In order to determine the effect of varying PVA fiber admixture and fiber length modulus on the dynamic strength of the remolded soil (i.e., the number of cycles of vibration of the specimen at a specific dynamic strength), a dynamic triaxial test study was carried out. The specimens were cylinders of 50 mm in diameter and 100 mm in height, and the dynamic stress was set at 50 kPa. The specific dynamic triaxial tests carried out are shown in Table4.Table 4
Dynamic triaxial test scheme for solidification of remolded soil.
TestFiber dose (%)Fiber length modulus (mm)Conservation age (d)S90121/3/7S100.1S110.2S120.3S130.33S146S159S1612


## 2.1. Test Materials

### 2.1.1. Soil Material

The remolded soil used in this test was taken from the middle and lower reaches of the Yangtze River, Zhenjiang Jiang Xijindu section of the channel, the soil was in a flow plastic state, its mineral composition is mainly based on ilmenite and montmorillonite, the basic physical and mechanical properties of the soil samples are shown in Table1. The liquidity index of the remolded soil is calculated to be greater than 1 according to (1), so the remolded soil can be judged to be in a fluid-plastic state.(1)IL=ω−ωLωp−ωL.Table 1
Basic mechanical properties of remolded soil.
Water content (%)Specific gravityLiquid limit (%)Plasticity index (%)Density (g·cm−3)Organic matter content (%)37.52.383736.31.871.5The test soil specimen is a remodeling soil. The remolded soil is first air-dried and passed through a 2 mm sieve, then dried and cooled in an oven. Based on natural moisture content, the remodeling soil is prepared at a moisture content of 37.5%, and finally, the prepared remodeling soil is sealed and left to stand for 24 h before the specimen is prepared to the required size for the test.


### 2.1.2. Fiber Material

The fiber reinforcement material used for the test is polyvinyl alcohol fiber (PVA) (shown in Figure1), which has a slightly yellow appearance and is a synthetic fiber material that is nontoxic and nonhazardous to humans and the environment. This fiber material has high strength, high modulus, low elongation, and other characteristics, the main thing is that it can dissolve in water and has a good affinity with cement materials. The basic physical and mechanical properties of the PVA material are shown in Table 2.Figure 1
Polyvinyl alcohol fiber.Table 2
Basic mechanical properties of polyvinyl alcohol fiber.
Dry fracture strength (MPa)Dry elongation at break (%)Modulus of elasticity (GPa)Heat and water resistance (°C)Length (mm)Dispersion≥12006.0∼8.0≥35≥104M ± 0.51∼3Note: M is for 3 mm, 6 mm, 9 mm, and 12 mm.


### 2.1.3. Cement Material

P.O 42.5 (Yangchun cement), a normal silicate cement from Shanghai, was used as the consolidating agent.


## 2.1.1. Soil Material

The remolded soil used in this test was taken from the middle and lower reaches of the Yangtze River, Zhenjiang Jiang Xijindu section of the channel, the soil was in a flow plastic state, its mineral composition is mainly based on ilmenite and montmorillonite, the basic physical and mechanical properties of the soil samples are shown in Table1. The liquidity index of the remolded soil is calculated to be greater than 1 according to (1), so the remolded soil can be judged to be in a fluid-plastic state.(1)IL=ω−ωLωp−ωL.Table 1
Basic mechanical properties of remolded soil.
Water content (%)Specific gravityLiquid limit (%)Plasticity index (%)Density (g·cm−3)Organic matter content (%)37.52.383736.31.871.5The test soil specimen is a remodeling soil. The remolded soil is first air-dried and passed through a 2 mm sieve, then dried and cooled in an oven. Based on natural moisture content, the remodeling soil is prepared at a moisture content of 37.5%, and finally, the prepared remodeling soil is sealed and left to stand for 24 h before the specimen is prepared to the required size for the test.


## 2.1.2. Fiber Material

The fiber reinforcement material used for the test is polyvinyl alcohol fiber (PVA) (shown in Figure1), which has a slightly yellow appearance and is a synthetic fiber material that is nontoxic and nonhazardous to humans and the environment. This fiber material has high strength, high modulus, low elongation, and other characteristics, the main thing is that it can dissolve in water and has a good affinity with cement materials. The basic physical and mechanical properties of the PVA material are shown in Table 2.Figure 1
Polyvinyl alcohol fiber.Table 2
Basic mechanical properties of polyvinyl alcohol fiber.
Dry fracture strength (MPa)Dry elongation at break (%)Modulus of elasticity (GPa)Heat and water resistance (°C)Length (mm)Dispersion≥12006.0∼8.0≥35≥104M ± 0.51∼3Note: M is for 3 mm, 6 mm, 9 mm, and 12 mm.


## 2.1.3. Cement Material

P.O 42.5 (Yangchun cement), a normal silicate cement from Shanghai, was used as the consolidating agent.


## 2.2. Test Contents

Triaxial consolidated undrained shear and dynamic triaxial tests were carried out on PVA fiber reinforced cement cured remolded soils to investigate the static and dynamic properties of the improved remolded soils through single control of PVA fiber content and fiber length modulus. The PVA fiber dose was 0%, 0.1%, 0.2%, and 0.3%, the fiber length modulus was 3 mm, 6 mm, 9 mm, and 12 mm, the age of the triaxial consolidation undrained shear test specimens was 1 d, 3 d and 7 d, the age of the dynamic triaxial test specimens was 1 d, 3 d, and 7 d and the cement dose was 6%.


### 2.2.1. Triaxial Consolidated Undrained Shear Test

In order to determine the stress-strain relationship of the remolded soil under the conditions of different PVA fiber admixture and fiber length modulus, and thus to obtain its static strength parameters, and considering that the remolded soil cured by PVA fiber reinforced cement has significantly improved permeability, this test was carried out using the cemented undrained triaxial shear test (CU) with a cylindrical specimen, 39.1 mm in diameter and 80 mm in height. The test shear rate was set at 0.08 mm/min and tests were carried out at consolidation envelope pressures of 100, 200, and 300 kPa, respectively. The specific static triaxial tests carried out are shown in Table3.Table 3
Static triaxial test scheme for solidification of remolded soil.
TestFiber dose (%)Fiber length modulus (mm)Conservation age (d)S10127/14/28S20.1S30.2S40.3S50.33S66S79S812


### 2.2.2. Dynamic Triaxial Test

The strength of soil is always linked to a certain limit of strain, so the dynamic strength should be discussed for the corresponding number of vibration cycles. The lower the number of vibration cycles, the higher the dynamic strength; the higher the number of vibration cycles, the lower the dynamic strength. In order to determine the effect of varying PVA fiber admixture and fiber length modulus on the dynamic strength of the remolded soil (i.e., the number of cycles of vibration of the specimen at a specific dynamic strength), a dynamic triaxial test study was carried out. The specimens were cylinders of 50 mm in diameter and 100 mm in height, and the dynamic stress was set at 50 kPa. The specific dynamic triaxial tests carried out are shown in Table4.Table 4
Dynamic triaxial test scheme for solidification of remolded soil.
TestFiber dose (%)Fiber length modulus (mm)Conservation age (d)S90121/3/7S100.1S110.2S120.3S130.33S146S159S1612


## 2.2.1. Triaxial Consolidated Undrained Shear Test

In order to determine the stress-strain relationship of the remolded soil under the conditions of different PVA fiber admixture and fiber length modulus, and thus to obtain its static strength parameters, and considering that the remolded soil cured by PVA fiber reinforced cement has significantly improved permeability, this test was carried out using the cemented undrained triaxial shear test (CU) with a cylindrical specimen, 39.1 mm in diameter and 80 mm in height. The test shear rate was set at 0.08 mm/min and tests were carried out at consolidation envelope pressures of 100, 200, and 300 kPa, respectively. The specific static triaxial tests carried out are shown in Table3.Table 3
Static triaxial test scheme for solidification of remolded soil.
TestFiber dose (%)Fiber length modulus (mm)Conservation age (d)S10127/14/28S20.1S30.2S40.3S50.33S66S79S812


## 2.2.2. Dynamic Triaxial Test

The strength of soil is always linked to a certain limit of strain, so the dynamic strength should be discussed for the corresponding number of vibration cycles. The lower the number of vibration cycles, the higher the dynamic strength; the higher the number of vibration cycles, the lower the dynamic strength. In order to determine the effect of varying PVA fiber admixture and fiber length modulus on the dynamic strength of the remolded soil (i.e., the number of cycles of vibration of the specimen at a specific dynamic strength), a dynamic triaxial test study was carried out. The specimens were cylinders of 50 mm in diameter and 100 mm in height, and the dynamic stress was set at 50 kPa. The specific dynamic triaxial tests carried out are shown in Table4.Table 4
Dynamic triaxial test scheme for solidification of remolded soil.
TestFiber dose (%)Fiber length modulus (mm)Conservation age (d)S90121/3/7S100.1S110.2S120.3S130.33S146S159S1612


## 3. Test Results

### 3.1. Static Triaxial Test

#### 3.1.1. Effect of Fiber Dose

PVA fibers with a length modulus of 12 mm were selected and dosed at 0%, 0.1%, 0.2%, and 0.3% to conduct static triaxial shear test studies on cured remolded soils to obtain the changes in cohesion, angle of internal friction, and water content of the soils at different curing times, with the following results.(1) Cohesion. Figure 2 shows the relationship between the fiber dose and the cohesion of the soil sample at different ages. As shown in the figure, As the modulus of fiber length increases, the cohesion of the soil sample increases and tends to stabilize at 1 d and 3 d; at 7 d, the cohesion of the soil sample had a maximum value at 0.1 mm of fiber content, and the cohesion of the soil sample stabilized with the further increase of fiber content. The influence of the fiber content decreases, mainly due to the reduction of the water content of the soil. Therefore, the more fibers are used, the better the reinforcement effect is, but the optimum value exists.Figure 2
Variation of cohesion of cured remolded soils with fiber admixture at different curing times.(2) Internal Friction Angle. Figure 3 shows the variation of the internal friction angle of the soil sample with the amount of fiber content at different curing times. This is due to the adsorption of free water by the fibers after incorporation into the remolded soil, which increases the slip effect in the soil particles, and the higher the fiber dose, the more obvious the slip effect. In addition, by comparing the test results of specimens at the same dosing level and different curing times, it can be seen that the greater the curing time, the smaller the internal friction angle of the specimens.Figure 3
Variation of the angle of internal friction of cured remolded soil with fiber admixture at different curing times.(3) Water Content. Figure 4 shows the variation of the moisture content of the specimens with the fiber admixture at different curing times. It can be seen from the graph that the water content of the specimens changed less with the increase of fiber admixture at the same fiber admixture, but there was a certain difference in the water content of the soil samples at different curing ages at the same fiber admixture, which was mainly due to the hydration reaction between the admixture and water after the specimens were made, which was also the main reason for the decrease of the water content. It can be seen that the effect of fiber admixture on the moisture content of the specimens is small and the age of maintenance has a greater effect on the moisture content of the specimens.Figure 4
Variation of the water content of cured remolded soil with fiber admixture at different curing times.From the analysis of the above results, the optimum fiber dose is 0.1% and the conservation age is 28 d.


#### 3.1.2. Effect of Fiber Length Modulus

The remolded soil cured with 0.3% PVA fiber was selected and studied in static triaxial shear tests at modulus of fiber lengths of 3 mm, 6 mm, 9 mm, and 12 mm to obtain the changes in cohesion, angle of internal friction, and water content at different ages of maintenance, with the following results.(1) Cohesion. Figure 5 shows the relationship between the modulus of fiber length and the cohesion of the soil sample at different ages. As shown in the figure, the cohesion of the soil samples increased with the increase of the fiber length modulus at 1 and 3 d. At 7 d, the cohesion of the soil samples was greatest at the fiber length modulus of 6 mm, and the cohesion of the soil samples decreased with the further increase of the fiber length modulus, but the decrease was not significant. It can be seen that the increase of fiber length modulus has a positive effect on the growth of cohesion of soil samples; however, as the age of maintenance increases, the contribution of fiber length modulus to the growth of cohesion of soil samples becomes smaller and smaller, and there is an optimal value of the length modulus of incorporated fibers.Figure 5
Diagram of the variation of cohesion of remolded soil with fiber length modulus at different conservation ages.(2) Internal Friction Angle. Figure 6 shows the relationship between the modulus of fiber length and the angle of internal friction of the soil sample at different ages. As shown in the graph, the internal friction angle of the soil sample gradually decreases and stabilizes as the modulus of fiber length increases. The internal friction angle of the soil sample decreases more with the increase of the modulus of fiber length at 1 d and 3 d, and less with the increase of the modulus of fiber length at 7 d. This is because the fibers have the ability to adsorb free water after being incorporated into the remolded soil, which increases the sliding effect in the soil particles to a certain extent, thus reducing the sliding friction between the fibers and the soil particles, and the larger the modulus of fiber length, the more obvious the sliding effect.Figure 6
Diagram of variation of internal friction angle of remolded soil with fiber length modulus at different conservation ages.(3) Water Content. Figure 7 shows the variation of fiber length modulus in relation to the moisture content of the soil samples at different ages of maintenance. As shown in the figure, with the increase of length modulus, the water content of the specimens changed very little under the same age, but still showed a decreasing trend in general, except for the hydration reaction between cement and water, which absorbed a lot of water, PVA also has hydrophilic and adsorption properties, but its effect was not particularly obvious under the length of the fibers, for example, the water content of the specimens changed from 30.2% corresponding to 3 mm to 29.3% corresponding to 12 mm under 7 d of curing, which showed a minimal decreasing trend. For example, the water content of the specimens went from 30.2% corresponding to 3 mm to 29.3% corresponding to 12 mm with a negligible decrease, indicating that the influence of the length modulus of the fibers on the variation of the water content is not the main reason.Figure 7
Diagram of variation of the water content of remolded soil with fiber length modulus at different conservation ages.From the analysis of the above results, the optimum fiber dose is 0.1%, the age of conservation is 28 d and the modulus of fiber length is 6 mm.


### 3.2. Dynamic Triaxial Test

#### 3.2.1. Effect of Fiber Dose

PVA fibers with a length modulus of 12 mm were selected and the cured remolded soil was dosed at 0%, 0.1%, 0.2%, and 0.3% in dynamic triaxial tests to obtain the number of vibrations of the cured remolded soil at different curing ages, the results are shown in Figure8. It can be seen that the number of vibrations of the specimens is positively correlated with the fiber dose and the curing time, that is, as the fiber dose increases and the curing time increases, the number of vibrations of the specimens increases, which indicates that the strength of the specimens has been greatly improved. As shown in Figure 9, the increase in the number of vibrations of the specimens with the fiber content was 115.4%, 53.6%, and 51.2% for 1 d; 66.7%, 91.1%, and 48.8% for 3 d; 59.5%, 50.8%, and 50.6% for 7 d. 50.8% and 50.6%, respectively. It can be seen that the magnitude of the increase is greater at 1 d and 0.1% and at 3 d and 0.2%, while the slope of change k is 150 for the former and 410 for the latter. The specimens showed a better state of stress and achieved the best dynamic strength.Figure 8
Variation of the number of vibrations of consolidated remolded soils with fiber content at different conservation ages.Figure 9
Change rate of the vibration number with fiber dose for cured remolded soils.


#### 3.2.2. Effect of Fiber Length Modulus

The remolded soil cured with 0.3% PVA fiber was selected and the number of vibrations of the cured remolded soil with different length modulus of PVA fiber was studied in dynamic triaxial tests at 3 mm, 6 mm, 9 mm, and 12 mm, respectively, and the results are shown in Figure10. It can be seen that the number of vibrations of the specimens is positively correlated with the modulus of fiber length and the curing time, that is, as the modulus of fiber length increases and the curing time increases, the number of vibrations of the specimens increases, which indicates a significant increase in the strength of the specimens. As shown in Figure 11, the increase in the number of vibrations of the specimens with the fiber admixture was 58.8%, 44.4%, and 51.3% for 1 d; 41.9%, 79.5%, and 50.6% for 3 d; 79.4%, 44.3%, and 62.5% for 7 d. At 7 d, the increase in the number of vibrations with the amount of fibers was 79.4%, 44.3%, and 62.5%, respectively. It can be seen that, in terms of growth, the variation in the number of vibrations of the specimens with the modulus of fiber length was greater when the maintenance time was 3 d and the modulus of fiber length was 9 mm and when the maintenance time was 7 d and the modulus of fiber length was 6 mm, both reaching more than 79%, while in terms of the slope of change k, the former k was 11.7 and the latter k was 9. Therefore, after considering the variation and the rate of change, it is concluded that, with the same amount of fiber doping, the number of vibrations of the specimens with the modulus of fiber length The best dynamic strength of the specimens was achieved at a modulus of 9 mm and a maintenance time of 3 d.Figure 10
Variation of the number of vibrations of consolidated remolded soils with fiber length modulus at different conservation ages.Figure 11
Change rate of the vibration number with fiber length modulus for cured remolded soils.


### 3.3. Combined Comparison Analysis of Dynamic and Static Strength

From the static triaxial tests carried out, it was determined that the shear strength of the cured remolded soil improved significantly better and the water content decreased significantly when the maintenance time was 27 d, the PVA fiber length modulus was 6 mm and the admixture was 0.1%; the dynamic strength characteristics of the cured remolded soil improved significantly when the maintenance time was 3 d, the PVA fiber length modulus was 9 mm and the admixture was 0.2%. The reason for the difference in the situation of PVA fibers required for the optimum increase in static and dynamic strength is mainly due to the fact that when the fibers are mixed with the remolded soil, chemical bonds between molecules similar to cement cementation are produced during the preconsolidation process, making the compressive strength of the specimens higher than the tensile strength; and when the fiber admixture is increased, a fiber network is formed under the attachment between the remolded soil particles, making the specimens have excellent compressive properties and are During the tensile process of the specimen, although many soil particles are adsorbed around the fibers, they still move with the specimen and cannot bear the axial pressure, so more fiber doping and length modulus are required to ensure that it bears the axial pressure, thus showing that less PVA is required to improve the static strength of the remolded soil than the dynamic strength.


## 3.1. Static Triaxial Test

### 3.1.1. Effect of Fiber Dose

PVA fibers with a length modulus of 12 mm were selected and dosed at 0%, 0.1%, 0.2%, and 0.3% to conduct static triaxial shear test studies on cured remolded soils to obtain the changes in cohesion, angle of internal friction, and water content of the soils at different curing times, with the following results.(1) Cohesion. Figure 2 shows the relationship between the fiber dose and the cohesion of the soil sample at different ages. As shown in the figure, As the modulus of fiber length increases, the cohesion of the soil sample increases and tends to stabilize at 1 d and 3 d; at 7 d, the cohesion of the soil sample had a maximum value at 0.1 mm of fiber content, and the cohesion of the soil sample stabilized with the further increase of fiber content. The influence of the fiber content decreases, mainly due to the reduction of the water content of the soil. Therefore, the more fibers are used, the better the reinforcement effect is, but the optimum value exists.Figure 2
Variation of cohesion of cured remolded soils with fiber admixture at different curing times.(2) Internal Friction Angle. Figure 3 shows the variation of the internal friction angle of the soil sample with the amount of fiber content at different curing times. This is due to the adsorption of free water by the fibers after incorporation into the remolded soil, which increases the slip effect in the soil particles, and the higher the fiber dose, the more obvious the slip effect. In addition, by comparing the test results of specimens at the same dosing level and different curing times, it can be seen that the greater the curing time, the smaller the internal friction angle of the specimens.Figure 3
Variation of the angle of internal friction of cured remolded soil with fiber admixture at different curing times.(3) Water Content. Figure 4 shows the variation of the moisture content of the specimens with the fiber admixture at different curing times. It can be seen from the graph that the water content of the specimens changed less with the increase of fiber admixture at the same fiber admixture, but there was a certain difference in the water content of the soil samples at different curing ages at the same fiber admixture, which was mainly due to the hydration reaction between the admixture and water after the specimens were made, which was also the main reason for the decrease of the water content. It can be seen that the effect of fiber admixture on the moisture content of the specimens is small and the age of maintenance has a greater effect on the moisture content of the specimens.Figure 4
Variation of the water content of cured remolded soil with fiber admixture at different curing times.From the analysis of the above results, the optimum fiber dose is 0.1% and the conservation age is 28 d.


### 3.1.2. Effect of Fiber Length Modulus

The remolded soil cured with 0.3% PVA fiber was selected and studied in static triaxial shear tests at modulus of fiber lengths of 3 mm, 6 mm, 9 mm, and 12 mm to obtain the changes in cohesion, angle of internal friction, and water content at different ages of maintenance, with the following results.(1) Cohesion. Figure 5 shows the relationship between the modulus of fiber length and the cohesion of the soil sample at different ages. As shown in the figure, the cohesion of the soil samples increased with the increase of the fiber length modulus at 1 and 3 d. At 7 d, the cohesion of the soil samples was greatest at the fiber length modulus of 6 mm, and the cohesion of the soil samples decreased with the further increase of the fiber length modulus, but the decrease was not significant. It can be seen that the increase of fiber length modulus has a positive effect on the growth of cohesion of soil samples; however, as the age of maintenance increases, the contribution of fiber length modulus to the growth of cohesion of soil samples becomes smaller and smaller, and there is an optimal value of the length modulus of incorporated fibers.Figure 5
Diagram of the variation of cohesion of remolded soil with fiber length modulus at different conservation ages.(2) Internal Friction Angle. Figure 6 shows the relationship between the modulus of fiber length and the angle of internal friction of the soil sample at different ages. As shown in the graph, the internal friction angle of the soil sample gradually decreases and stabilizes as the modulus of fiber length increases. The internal friction angle of the soil sample decreases more with the increase of the modulus of fiber length at 1 d and 3 d, and less with the increase of the modulus of fiber length at 7 d. This is because the fibers have the ability to adsorb free water after being incorporated into the remolded soil, which increases the sliding effect in the soil particles to a certain extent, thus reducing the sliding friction between the fibers and the soil particles, and the larger the modulus of fiber length, the more obvious the sliding effect.Figure 6
Diagram of variation of internal friction angle of remolded soil with fiber length modulus at different conservation ages.(3) Water Content. Figure 7 shows the variation of fiber length modulus in relation to the moisture content of the soil samples at different ages of maintenance. As shown in the figure, with the increase of length modulus, the water content of the specimens changed very little under the same age, but still showed a decreasing trend in general, except for the hydration reaction between cement and water, which absorbed a lot of water, PVA also has hydrophilic and adsorption properties, but its effect was not particularly obvious under the length of the fibers, for example, the water content of the specimens changed from 30.2% corresponding to 3 mm to 29.3% corresponding to 12 mm under 7 d of curing, which showed a minimal decreasing trend. For example, the water content of the specimens went from 30.2% corresponding to 3 mm to 29.3% corresponding to 12 mm with a negligible decrease, indicating that the influence of the length modulus of the fibers on the variation of the water content is not the main reason.Figure 7
Diagram of variation of the water content of remolded soil with fiber length modulus at different conservation ages.From the analysis of the above results, the optimum fiber dose is 0.1%, the age of conservation is 28 d and the modulus of fiber length is 6 mm.


## 3.1.1. Effect of Fiber Dose

PVA fibers with a length modulus of 12 mm were selected and dosed at 0%, 0.1%, 0.2%, and 0.3% to conduct static triaxial shear test studies on cured remolded soils to obtain the changes in cohesion, angle of internal friction, and water content of the soils at different curing times, with the following results.(1) Cohesion. Figure 2 shows the relationship between the fiber dose and the cohesion of the soil sample at different ages. As shown in the figure, As the modulus of fiber length increases, the cohesion of the soil sample increases and tends to stabilize at 1 d and 3 d; at 7 d, the cohesion of the soil sample had a maximum value at 0.1 mm of fiber content, and the cohesion of the soil sample stabilized with the further increase of fiber content. The influence of the fiber content decreases, mainly due to the reduction of the water content of the soil. Therefore, the more fibers are used, the better the reinforcement effect is, but the optimum value exists.Figure 2
Variation of cohesion of cured remolded soils with fiber admixture at different curing times.(2) Internal Friction Angle. Figure 3 shows the variation of the internal friction angle of the soil sample with the amount of fiber content at different curing times. This is due to the adsorption of free water by the fibers after incorporation into the remolded soil, which increases the slip effect in the soil particles, and the higher the fiber dose, the more obvious the slip effect. In addition, by comparing the test results of specimens at the same dosing level and different curing times, it can be seen that the greater the curing time, the smaller the internal friction angle of the specimens.Figure 3
Variation of the angle of internal friction of cured remolded soil with fiber admixture at different curing times.(3) Water Content. Figure 4 shows the variation of the moisture content of the specimens with the fiber admixture at different curing times. It can be seen from the graph that the water content of the specimens changed less with the increase of fiber admixture at the same fiber admixture, but there was a certain difference in the water content of the soil samples at different curing ages at the same fiber admixture, which was mainly due to the hydration reaction between the admixture and water after the specimens were made, which was also the main reason for the decrease of the water content. It can be seen that the effect of fiber admixture on the moisture content of the specimens is small and the age of maintenance has a greater effect on the moisture content of the specimens.Figure 4
Variation of the water content of cured remolded soil with fiber admixture at different curing times.From the analysis of the above results, the optimum fiber dose is 0.1% and the conservation age is 28 d.


## 3.1.2. Effect of Fiber Length Modulus

The remolded soil cured with 0.3% PVA fiber was selected and studied in static triaxial shear tests at modulus of fiber lengths of 3 mm, 6 mm, 9 mm, and 12 mm to obtain the changes in cohesion, angle of internal friction, and water content at different ages of maintenance, with the following results.(1) Cohesion. Figure 5 shows the relationship between the modulus of fiber length and the cohesion of the soil sample at different ages. As shown in the figure, the cohesion of the soil samples increased with the increase of the fiber length modulus at 1 and 3 d. At 7 d, the cohesion of the soil samples was greatest at the fiber length modulus of 6 mm, and the cohesion of the soil samples decreased with the further increase of the fiber length modulus, but the decrease was not significant. It can be seen that the increase of fiber length modulus has a positive effect on the growth of cohesion of soil samples; however, as the age of maintenance increases, the contribution of fiber length modulus to the growth of cohesion of soil samples becomes smaller and smaller, and there is an optimal value of the length modulus of incorporated fibers.Figure 5
Diagram of the variation of cohesion of remolded soil with fiber length modulus at different conservation ages.(2) Internal Friction Angle. Figure 6 shows the relationship between the modulus of fiber length and the angle of internal friction of the soil sample at different ages. As shown in the graph, the internal friction angle of the soil sample gradually decreases and stabilizes as the modulus of fiber length increases. The internal friction angle of the soil sample decreases more with the increase of the modulus of fiber length at 1 d and 3 d, and less with the increase of the modulus of fiber length at 7 d. This is because the fibers have the ability to adsorb free water after being incorporated into the remolded soil, which increases the sliding effect in the soil particles to a certain extent, thus reducing the sliding friction between the fibers and the soil particles, and the larger the modulus of fiber length, the more obvious the sliding effect.Figure 6
Diagram of variation of internal friction angle of remolded soil with fiber length modulus at different conservation ages.(3) Water Content. Figure 7 shows the variation of fiber length modulus in relation to the moisture content of the soil samples at different ages of maintenance. As shown in the figure, with the increase of length modulus, the water content of the specimens changed very little under the same age, but still showed a decreasing trend in general, except for the hydration reaction between cement and water, which absorbed a lot of water, PVA also has hydrophilic and adsorption properties, but its effect was not particularly obvious under the length of the fibers, for example, the water content of the specimens changed from 30.2% corresponding to 3 mm to 29.3% corresponding to 12 mm under 7 d of curing, which showed a minimal decreasing trend. For example, the water content of the specimens went from 30.2% corresponding to 3 mm to 29.3% corresponding to 12 mm with a negligible decrease, indicating that the influence of the length modulus of the fibers on the variation of the water content is not the main reason.Figure 7
Diagram of variation of the water content of remolded soil with fiber length modulus at different conservation ages.From the analysis of the above results, the optimum fiber dose is 0.1%, the age of conservation is 28 d and the modulus of fiber length is 6 mm.


## 3.2. Dynamic Triaxial Test

### 3.2.1. Effect of Fiber Dose

PVA fibers with a length modulus of 12 mm were selected and the cured remolded soil was dosed at 0%, 0.1%, 0.2%, and 0.3% in dynamic triaxial tests to obtain the number of vibrations of the cured remolded soil at different curing ages, the results are shown in Figure8. It can be seen that the number of vibrations of the specimens is positively correlated with the fiber dose and the curing time, that is, as the fiber dose increases and the curing time increases, the number of vibrations of the specimens increases, which indicates that the strength of the specimens has been greatly improved. As shown in Figure 9, the increase in the number of vibrations of the specimens with the fiber content was 115.4%, 53.6%, and 51.2% for 1 d; 66.7%, 91.1%, and 48.8% for 3 d; 59.5%, 50.8%, and 50.6% for 7 d. 50.8% and 50.6%, respectively. It can be seen that the magnitude of the increase is greater at 1 d and 0.1% and at 3 d and 0.2%, while the slope of change k is 150 for the former and 410 for the latter. The specimens showed a better state of stress and achieved the best dynamic strength.Figure 8
Variation of the number of vibrations of consolidated remolded soils with fiber content at different conservation ages.Figure 9
Change rate of the vibration number with fiber dose for cured remolded soils.


### 3.2.2. Effect of Fiber Length Modulus

The remolded soil cured with 0.3% PVA fiber was selected and the number of vibrations of the cured remolded soil with different length modulus of PVA fiber was studied in dynamic triaxial tests at 3 mm, 6 mm, 9 mm, and 12 mm, respectively, and the results are shown in Figure10. It can be seen that the number of vibrations of the specimens is positively correlated with the modulus of fiber length and the curing time, that is, as the modulus of fiber length increases and the curing time increases, the number of vibrations of the specimens increases, which indicates a significant increase in the strength of the specimens. As shown in Figure 11, the increase in the number of vibrations of the specimens with the fiber admixture was 58.8%, 44.4%, and 51.3% for 1 d; 41.9%, 79.5%, and 50.6% for 3 d; 79.4%, 44.3%, and 62.5% for 7 d. At 7 d, the increase in the number of vibrations with the amount of fibers was 79.4%, 44.3%, and 62.5%, respectively. It can be seen that, in terms of growth, the variation in the number of vibrations of the specimens with the modulus of fiber length was greater when the maintenance time was 3 d and the modulus of fiber length was 9 mm and when the maintenance time was 7 d and the modulus of fiber length was 6 mm, both reaching more than 79%, while in terms of the slope of change k, the former k was 11.7 and the latter k was 9. Therefore, after considering the variation and the rate of change, it is concluded that, with the same amount of fiber doping, the number of vibrations of the specimens with the modulus of fiber length The best dynamic strength of the specimens was achieved at a modulus of 9 mm and a maintenance time of 3 d.Figure 10
Variation of the number of vibrations of consolidated remolded soils with fiber length modulus at different conservation ages.Figure 11
Change rate of the vibration number with fiber length modulus for cured remolded soils.


## 3.2.1. Effect of Fiber Dose

PVA fibers with a length modulus of 12 mm were selected and the cured remolded soil was dosed at 0%, 0.1%, 0.2%, and 0.3% in dynamic triaxial tests to obtain the number of vibrations of the cured remolded soil at different curing ages, the results are shown in Figure8. It can be seen that the number of vibrations of the specimens is positively correlated with the fiber dose and the curing time, that is, as the fiber dose increases and the curing time increases, the number of vibrations of the specimens increases, which indicates that the strength of the specimens has been greatly improved. As shown in Figure 9, the increase in the number of vibrations of the specimens with the fiber content was 115.4%, 53.6%, and 51.2% for 1 d; 66.7%, 91.1%, and 48.8% for 3 d; 59.5%, 50.8%, and 50.6% for 7 d. 50.8% and 50.6%, respectively. It can be seen that the magnitude of the increase is greater at 1 d and 0.1% and at 3 d and 0.2%, while the slope of change k is 150 for the former and 410 for the latter. The specimens showed a better state of stress and achieved the best dynamic strength.Figure 8
Variation of the number of vibrations of consolidated remolded soils with fiber content at different conservation ages.Figure 9
Change rate of the vibration number with fiber dose for cured remolded soils.


## 3.2.2. Effect of Fiber Length Modulus

The remolded soil cured with 0.3% PVA fiber was selected and the number of vibrations of the cured remolded soil with different length modulus of PVA fiber was studied in dynamic triaxial tests at 3 mm, 6 mm, 9 mm, and 12 mm, respectively, and the results are shown in Figure10. It can be seen that the number of vibrations of the specimens is positively correlated with the modulus of fiber length and the curing time, that is, as the modulus of fiber length increases and the curing time increases, the number of vibrations of the specimens increases, which indicates a significant increase in the strength of the specimens. As shown in Figure 11, the increase in the number of vibrations of the specimens with the fiber admixture was 58.8%, 44.4%, and 51.3% for 1 d; 41.9%, 79.5%, and 50.6% for 3 d; 79.4%, 44.3%, and 62.5% for 7 d. At 7 d, the increase in the number of vibrations with the amount of fibers was 79.4%, 44.3%, and 62.5%, respectively. It can be seen that, in terms of growth, the variation in the number of vibrations of the specimens with the modulus of fiber length was greater when the maintenance time was 3 d and the modulus of fiber length was 9 mm and when the maintenance time was 7 d and the modulus of fiber length was 6 mm, both reaching more than 79%, while in terms of the slope of change k, the former k was 11.7 and the latter k was 9. Therefore, after considering the variation and the rate of change, it is concluded that, with the same amount of fiber doping, the number of vibrations of the specimens with the modulus of fiber length The best dynamic strength of the specimens was achieved at a modulus of 9 mm and a maintenance time of 3 d.Figure 10
Variation of the number of vibrations of consolidated remolded soils with fiber length modulus at different conservation ages.Figure 11
Change rate of the vibration number with fiber length modulus for cured remolded soils.


## 3.3. Combined Comparison Analysis of Dynamic and Static Strength

From the static triaxial tests carried out, it was determined that the shear strength of the cured remolded soil improved significantly better and the water content decreased significantly when the maintenance time was 27 d, the PVA fiber length modulus was 6 mm and the admixture was 0.1%; the dynamic strength characteristics of the cured remolded soil improved significantly when the maintenance time was 3 d, the PVA fiber length modulus was 9 mm and the admixture was 0.2%. The reason for the difference in the situation of PVA fibers required for the optimum increase in static and dynamic strength is mainly due to the fact that when the fibers are mixed with the remolded soil, chemical bonds between molecules similar to cement cementation are produced during the preconsolidation process, making the compressive strength of the specimens higher than the tensile strength; and when the fiber admixture is increased, a fiber network is formed under the attachment between the remolded soil particles, making the specimens have excellent compressive properties and are During the tensile process of the specimen, although many soil particles are adsorbed around the fibers, they still move with the specimen and cannot bear the axial pressure, so more fiber doping and length modulus are required to ensure that it bears the axial pressure, thus showing that less PVA is required to improve the static strength of the remolded soil than the dynamic strength.


## 4. Conclusion

By conducting a series of triaxial consolidation undrained shear tests and dynamic triaxial tests on remolded soils cured by the PVA fiber reinforced cement method, the effects of different fiber admixtures, fiber length modulus, and age of maintenance on the cured remolded soils were investigated from both static and dynamic strength perspectives, with the following main findings:(1)
Curing the remolded soil by using PVA fiber reinforced cement can effectively improve the shear strength and dynamic strength of the remolded soil and reduce the moisture content of the remolded soil, and the internal friction angle of the soil sample gradually decreases and stabilizes with the increase of the fiber modulus and fiber admixture.(2)
The cohesion of the cured remolded soil increases with the increasing modulus of fiber length and fiber admixture at curing ages of 1 d and 3 d, and the maximum cohesion and internal friction angle exist at the curing age of 7 d.(3)
The specimens cured the remolded soil best in terms of static strength when 0.1% of PVA fibers of 6 mm in length were incorporated at a curing age of 7 d.(4)
The number of vibrations of the specimens under the dynamic triaxial test increased with the increasing modulus of fiber length and admixture, with the specimens curing best in dynamic strength of the remolded soil at 7 d of service age when 0.3% of PVA fiber of 12 mm in length was admixed.(5)
The reason for the difference in the situation of PVA fibers required for the optimum increase in static and dynamic strength is mainly due to the fact that when the fibers are mixed with the remolded soil, chemical bonds between molecules similar to those used for cement cementation are created during the preconsolidation process, making the compressive strength of the specimens higher than the tensile strength, so more fiber admixture and a longer length modulus are required to increase the tensile strength. [10–19].



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*Source: 5169404-2022-07-30.xml*