Study on the Interface Reinforcement Effect of Bamboo Grid in Filled Loess Embankment in a High and Steep Gully PDF

Citation: Chen, G.; Tian, H.; Du, Z.;

Zhang, J.; Guo, Y.; Wang, J. Study on

the Interface Reinforcement Effect of

Bamboo Grid in Filled Loess

Embankment in a High and Steep

Gully. Buildings 2024, 14, 3423.

https://doi.org/10.3390/

buildings14113423

Academic Editors: Bjorn Birgisson

and Antonio Caggiano

Received: 19 September 2024

Revised: 4 October 2024

Accepted: 14 October 2024

Published: 28 October 2024

Licensee MDPI, Basel, Switzerland.

This article is an open access article

distributed under the terms and

conditions of the Creative Commons

Attribution (CC BY) license (https://

creativecommons.org/licenses/by/

4.0/).

buildings

Article

Study on the Interface Reinforcement Effect of Bamboo Grid in

Filled Loess Embankment in a High and Steep Gully

Guozhou Chen

1,2,3

, Haodong Tian

*, Zibo Du

, Jingwei Zhang

, Yuancheng Guo

and Julong Wang

School of Civil Engineering, Zhengzhou University, Zhengzhou 450001, China; [email protected] (G.C.);

[email protected] (Z.D.); [email protected] (J.Z.); [email protected] (Y.G.);

[email protected] (J.W.)

Huanghe S & T University, Zhengzhou 450006, China

Henan Urban Planning and Design Institute Co., Ltd., Zhengzhou 450044, China

* Correspondence: [email protected]

Abstract: A bamboo grid is a new type of reinforcement material, which can replace traditional

geogrids in the reinforcement of embankments. In this study, the reinforcement effect of the bamboo

grid that is only set at the interface between the filled and undisturbed soils of the filled loess

embankment in a high and steep gully was investigated. The influence of reinforcement position

and grid spacing on the reinforcement effect was studied by carrying out a large-scale direct shear

test, numerical simulation, and field measurement. The results indicated that the bamboo grid

could enhance the shear strength of the reinforcement interface. The interface shear strength first

improved and then decreased with the decrease in grid spacing. The differential settlement was

significantly reduced after the reinforcement of the bamboo grid at the interface. Compared with

other reinforcement positions, setting the bamboo grid in the upper part of the embankment was the

most efficient and economical. When the grid spacing became dense, the reinforcement effect was

improved as the differential settlement decreased. However, the improvement in the reinforcement

effect by decreasing the grid spacing was limited, which meant there was an optimal grid spacing.

Keywords: bamboo grid; interface reinforcement; filled loess embankment; differential settlement;

numerical simulation

1. Introduction

Loess is widespread in Northwest China, with a range of over 631,000 km

, accounting

for 6.6% of the total area of the country [

]. With the rapid development of West China, a

large number of transportation infrastructure projects have been constructed in the loess

gully region. Similar to the embankment widening project [

–

], there usually exists

differential settlement at the interface between the filled and undisturbed soils for the filled

loess embankment in high and steep gullies. Excessive differential settlement would cause

various embankment and pavement diseases. The conventional method uses geosynthetics,

i.e., geogrids, to restrain the differential settlement of the embankment [

–

]. However,

a geogrid does not have bending capacity. It is not suitable for treating large differential

settlement of the embankment [10].

Bamboo has proven to be a good reinforcement material due to its excellent mechanical

properties [

] including flexural properties [

], easy availability, and green character-

istics [

]. Compared to the geogrid, the tensile strength of bamboo is nine times higher.

Although the tensile strength value of bamboo is reduced to some degree after chemical

treatment to increase durability, it is still higher than that of geosynthetics [

]. It can satisfy

the specification requirement for reinforcing the embankment of a highway and replace

the geogrid [

]. Compared to the high cost of geosynthetics [

], bamboo is cheaper

as well. Extensive studies have been performed on the reinforcement technology with

bamboo grid. As a kind of reinforcement material, a bamboo grid can significantly reduce

Buildings 2024, 14, 3423. https://doi.org/10.3390/buildings14113423 https://www.mdpi.com/journal/buildings

Buildings 2024, 14, 3423

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the compressibility of soil [

] and the settlement of the embankment [

–

], as well as

improve the bearing capacity of soil [

]. It was also employed to enhance slope stability,

which showed that the bamboo grid was able to resist the applied loads and maintain the

stability of the slope [

]. In terms of differential settlement treatment, Luo et al. [

]

compared the performance of the bamboo grid and geogrid set at the widening interface of

the embankment. The results showed that, after being reinforced with the bamboo grid

in the new fill, differential settlement on top of the embankment was effectively reduced,

and its reinforcement effect was better than that of the geogrid. To sum up, due to better

mechanical properties and reinforcement performance than traditional geogrids, bamboo

grids can be used to constrain the differential settlement of the filled loess embankment in

a high and steep gully.

Generally, to restrain the differential settlement of the widening embankment, rein-

forcement materials are used in three ways. The first is to set reinforcement materials only

in the new fill [

]. The second is to set reinforcement materials in the new fill and the

interface [

]. The final way is to set reinforcement materials both in the new fill and the

existing soil [

]. Similarly, to restrain the differential settlement of the filled embankment

in a high and steep gully, there will be several reinforcement schemes as well. This paper

only focuses on the scheme of setting reinforcement materials at the interface, as shown in

Figure 1.

Buildings 2024, 14, x FOR PEER REVIEW 2 of 21

technology with bamboo grid. As a kind of reinforcement material, a bamboo grid can

significantly reduce the compressibility of soil [19] and the settlement of the embankment

[20–22], as well as improve the bearing capacity of soil [23]. It was also employed to en-

hance slope stability, which showed that the bamboo grid was able to resist the applied

loads and maintain the stability of the slope [24,25]. In terms of diﬀerential settlement

treatment, Luo et al. [26] compared the performance of the bamboo grid and geogrid set

at the widening interface of the embankment. The results showed that, after being rein-

forced with the bamboo grid in the new fill, diﬀerential settlement on top of the embank-

ment was eﬀectively reduced, and its reinforcement eﬀect was better than that of the ge-

ogrid. To sum up, due to better mechanical properties and reinforcement performance

than traditional geogrids, bamboo grids can be used to constrain the diﬀerential settle-

ment of the filled loess embankment in a high and steep gully.

Generally, to restrain the diﬀerential settlement of the widening embankment, rein-

forcement materials are used in three ways. The first is to set reinforcement materials only

in the new fill [27,28]. The second is to set reinforcement materials in the new fill and the

interface [29]. The final way is to set reinforcement materials both in the new fill and the

existing soil [30]. Similarly, to restrain the diﬀerential settlement of the filled embankment

in a high and steep gully, there will be several reinforcement schemes as well. This paper

only focuses on the scheme of setting reinforcement materials at the interface, as shown

in Figure 1.

However, the interface reinforcement technology with bamboo grids has rarely been

studied. Therefore, it is necessary to study the reinforcement eﬀect of the bamboo grid set

at the interface and its influencing factors. In this study, a large-scale direct shear test was

conducted to analyze the shear characteristics of the interface between the reinforcement

materials and the reinforced soil. A settlement measurement of a practical engineering

case was conducted to study the settlement law of the filled loess embankment. By using

ABAQUS 2022 software, a numerical simulation was carried out, and the interface rein-

forcement eﬀect of the bamboo grid and its influential factors including reinforcement

position and grid spacing were analyzed.

Figure 1. Scheme of reinforcement materials only set at the interface.

2. Large-Scale Direct Shear Test

Interface characteristics between the bamboo grid and the reinforced soil have a sig-

nificant influence on the reinforcement eﬀect of the bamboo grid. To study the interface

characteristics, large-scale direct shear tests with diﬀerent reinforcement types and grid

spacings were conducted.

2.1. Test Materials

Moso bamboo aged 5 to 6 years old was selected for tests. The chest-height diameter

of these 5- to 6-year-old bamboos was more than 50 mm. The wall thickness was 2–3 mm.

The bamboo was processed into strips. The width of these strips was 20 mm. In practical

engineering cases which need long-term anticorrosion, bamboo is soaked in boric acid

Figure 1. Scheme of reinforcement materials only set at the interface.

However, the interface reinforcement technology with bamboo grids has rarely been

studied. Therefore, it is necessary to study the reinforcement effect of the bamboo grid set

at the interface and its influencing factors. In this study, a large-scale direct shear test was

conducted to analyze the shear characteristics of the interface between the reinforcement

materials and the reinforced soil. A settlement measurement of a practical engineering

case was conducted to study the settlement law of the filled loess embankment. By us-

ing ABAQUS 2022 software, a numerical simulation was carried out, and the interface

reinforcement effect of the bamboo grid and its influential factors including reinforcement

position and grid spacing were analyzed.

2. Large-Scale Direct Shear Test

Interface characteristics between the bamboo grid and the reinforced soil have a

significant influence on the reinforcement effect of the bamboo grid. To study the interface

characteristics, large-scale direct shear tests with different reinforcement types and grid

spacings were conducted.

2.1. Test Materials

Moso bamboo aged 5 to 6 years old was selected for tests. The chest-height diameter

of these 5- to 6-year-old bamboos was more than 50 mm. The wall thickness was 2–3 mm.

The bamboo was processed into strips. The width of these strips was 20 mm. In practical

engineering cases which need long-term anticorrosion, bamboo is soaked in boric acid

solution for 24 h first to prevent fungi, bacteria, and ants from proliferating inside the

bamboo. Then, asphalt paint is applied on the surface of the bamboo to prevent external

Buildings 2024, 14, 3423

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water from entering the bamboo, as well as to prevent boric acid loss. These processes do

not have a significant influence on the properties of bamboo. In this study, the direct shear

test was fast. Therefore, only asphalt paint was used for the anticorrosion of bamboo strips.

The bamboo strips were fixed at the intersections by 4 mm diameter steel wire. Thus, the

bamboo grids were formed, as shown in Figure 2. For better comparison, a geogrid was

also used. The biaxial geogrid (TGSG2020) used in the tests was made of polypropylene,

and the mesh size was 50 mm × 50 mm, as shown in Figure 3.

Buildings 2024, 14, x FOR PEER REVIEW 3 of 21

solution for 24 h first to prevent fungi, bacteria, and ants from proliferating inside the

bamboo. Then, asphalt paint is applied on the surface of the bamboo to prevent external

water from entering the bamboo, as well as to prevent boric acid loss. These processes do

not have a significant influence on the properties of bamboo. In this study, the direct shear

test was fast. Therefore, only asphalt paint was used for the anticorrosion of bamboo

strips. The bamboo strips were fixed at the intersections by 4 mm diameter steel wire.

Thus, the bamboo grids were formed, as shown in Figure 2. For better comparison, a ge-

ogrid was also used. The biaxial geogrid (TGSG2020) used in the tests was made of poly-

propylene, and the mesh size was 50 mm × 50 mm, as shown in Figure 3.

The loess used was obtained from a section of the National Highway of China. It was

completely renewed Quaternary soil with a color of brown-yellow. The basic mechanical

properties tests of the soil were conducted according to ASTM D698 and ASTM D4318.

The results are shown in Table 1.

Figure 2. Bamboo grid.

Figure 3. Geogrid.

Table 1. Basic mechanical properties of the test soil.

Material Density (g·cm

−3

)

Optimum

Moisture (%)

Maximum Dry

Density (g·cm

−3

)

Liquid Limit

(%)

Plastic Limit

(%)

Plasticity Index

Loess 1.62 11.94 1.95 25.1 17 8.1

2.2. Test Program

The test employed a large-scale direct shear apparatus that was designed and devel-

oped by Zhengzhou University, as shown in Figure 4. The size of the upper shear box was

500 mm × 500 mm × 150 mm, and the lower shear box was 650 mm × 500 mm × 150 mm.

According to the standard for direct shear tests (ASTM D5321/D5321M-14), the test

procedures were as follows. The soil was first air-dried and then mixed with its optimum