Research on the Ductility Design of Concrete Anti - Slide Piles for

Building Slopes in Saline-Alkali Soil Areas of Lanzhou City

Xiaosen Li, Shanzhi Fan

, Haihong Zhang, Xingrong Liang and Wenjing Zhang

Gansu Provincial Transportation Research Institute Group Co., Ltd., Lanzhou 730000, China

Keywords: Saline Soil, Building Slope, Governance Project, Improved Concrete Anti-Slide Pile, Finite Element Analysis.

Abstract: This paper takes the newly built building slope in Lanzhou City, Northwest China as the engineering

background. In order to ensure the stability of the saline - alkali soil slope, the durability of the treatment

project, and the safety of the residential buildings on the top of the slope, improved concrete anti - slide piles

are adopted to protect the slope based on traditional reinforced concrete. The finite - element calculation

results show that, firstly, this method is one of the most effective ways to treat important saline - alkali soil

building slopes. Secondly, (1) the supporting effect of the anti - slide piles prevents the potential slip surface

from penetrating from the top to the bottom of the slope, and the horizontal displacement of the slope body is

the largest; (2) compared with the maximum displacement of the slope supported by ordinary concrete anti -

slide piles, the horizontal displacement of the slope supported by the improved anti - erosion concrete anti -

slide piles is the smallest. The displacement of the former along the entire length of the pile is smaller than

that of the latter, which is conducive to improving the stability of the slope. This method can provide a basis

and experience for similar building slopes in the future.

1 INTRODUCTION

As the level of national infrastructure construction

continues to improve and the transformation from

traditional civil infrastructure to smart civil

engineering is taking place, high - quality

development has also ushered in a change towards

new - quality productive forces. However, in

transportation engineering construction, slope

instability or the re - activation of old landslides are

inevitable problems. Liu and Sun (2013), Ruan et al.

(2005) believe that landslides are one of the common

issues in engineering geological disaster management;

Zhou (2004) argues that ground excavation and

rainfall are common factors triggering landslides;

Ying (2000) holds that anti - slide piles are the most

effective protective engineering measures for

landslides, especially large - scale ones; (Tang et al.,

2013; Wang, 1999) consider that the Lijiawan

landslide is a multi - layer and multi -

atened the

normal operation of the expressway and the personal

https://orcid.org/0009-0004-3893-9336

and property safety of the toll station; Zhang (1996),

Zhao et al., (2012) established a numerical model of

the landslide using finite element software, analyzed

the plastic zone, deformation mechanism and

characteristics of the landslide, and compared them

with the horizontal displacement and plastic zone

nephograms of the slope after support to verify the

treatment effect.

In this project, the excavation of the building

slope has formed a slope with a maximum height of

nearly 9 meters. The slope toe is almost vertical, and

the stability of the slope is average. The slope may

collapse at any time in case of rainfall or other adverse

geological conditions. There is a residential building

at the top of the slope, which is an important object to

be protected. The slope is classified as a second - level

slope. Due to the particularity of this project, factors

such as the corrosiveness of saline - alkali soil in

Lanzhou area to concrete structures are taken into

account in the slope design and calculation. Therefore,

it is necessary to improve the corrosion resistance of

concrete anti - slide piles.

Li, X., Fan, S., Zhang, H., Liang, X., Zhang and W.

Research on the Ductility Design of Concrete Anti - Slide Piles for Building Slopes in Saline-Alkali Soil Areas of Lanzhou City.

DOI: 10.5220/0013573900004671

In Proceedings of the 7th International Conference on Environmental Science and Civil Engineering (ICESCE 2024), pages 85-90

ISBN: 978-989-758-764-1; ISSN: 3051-701X

Figure 1: Location of the project.

2 PROJECT OVERVIEW

2.1 Engineering Background

Bashangdi, Yatou Village, Bali Town, Qilihe District,

Lanzhou City. It is adjacent to the village road on the

east side, with the (Zone B) of the community to its

north and high mountains to its west. The site was

originally arable land (the area near the road on the

east has been excavated down about 12 meters). The

slopes to be protected are those on the north and west

sides of a seven - storey residential building. This

location is part of the Chuandong Fold Belt within the

Sichuan Subsidence Fold Belt. Atmospheric

precipitation and surface runoff in summer are the

primary means of rainwater replenishment. The

western region of China has the most extensive

distribution of salt lakes. Notably, the salt lakes in the

Hexi Corridor area possess extremely strong

corrosiveness, and the content of SO42- is 4.2 times

the maximum value stipulated in the current railway

specifications, as depicted in Figure 1.

2.2 Topography and Geotechnical

Composition

According to the results of on - site investigation, the

geomorphic unit of this site is classified as the high

terrace of Yatou Village on the south bank of the

Yellow River. The original site had well - developed

valleys with deep cuts. After artificial excavation,

filling, leveling and transformation, the terrain is

relatively flat. The new project site is located in

Qilihe District, where mountains, ridges, terraces,

plains, beaches and gullies crisscross. According to

its geomorphic characteristics, it can be divided into

the southern rocky mountain area, the central loess

ridge area, and the northern river valley basin. The

terrain of the proposed project area is relatively

complex with large undulations. Among them, the

slope to be reinforced in the project is the slope where

Building No. 9 is located, and the elevation difference

ranges from 1.5 to 15.1 meters. The terrain and

geomorphology of the proposed slope have large

undulations, and there are mainly two types of

corresponding soil: (1) The soil in the project area is

mainly loess - like silt; (2) In the main agricultural

area of the project area, the surface is a vegetation soil

layer.

2.3 Meteorological and Hydrological

Conditions

Lanzhou has a continental climate in the middle

temperate zone, characterized by large temperature

differences, low precipitation, and a mild climate. It

is located in the transition zone between the monsoon

and non - monsoon climate regions, with a typical

temperate semi - arid climate. The average altitude of

the urban area is about 1520 meters, and the annual

average temperature is around 10℃. Surrounded by

mountains to the north and south, the climate is dry

with abundant sunshine, and both the annual and daily

temperature differences are relatively large. The

winter is long and relatively cold, with little rain and

snow; spring and summer are short, with relatively

high temperatures but no intense heat; autumn is short,

with a rapid temperature drop. The maximum rainfall

in Lanzhou over the years is 564.9mm, and the annual

average precipitation is 327mm. The annual average

the

ect

The slope

ICESCE 2024 - The International Conference on Environmental Science and Civil Engineering

Table 1: Soil parameters.

name

Characteristic

value of

foundation

bearing capacity

fak(KPa)

Poisson's ratio

Serious

γ(kN/m

)

cohesive

strength

c(kPa)

Friction

angle φ(°)

Natural

working

condition

Saturation

condition

Loess silt 120 0.28 16.0 17.0 20 26

Round gravel

soil

260 0.24 19.0 20.0 22 29

C30 anti-slide

pile

name

Poisson's ratio

Elastic

modulus

E(GPa)

Serious

γ(kN/m

）

Design

strength

(MPa)

Preparation

strength

(MPa)

control

rou

0.20 30.0 23.0 30.0

Experimental

group

0.19 32.7 23.1 38.2

temperature is 10.3℃, the average annual sunshine

hours are 2446 hours, and the frost - free period is

more than 180 days.

The maximum rainfall of 564.9mm in Lanzhou

over the years has a significant impact on the steep

slope on the south side of this project. Protective

measures should be taken for the southern part of the

slope protection area. This site is located in an arid

region (aridity index K≥1.5), and the foundation will

be in a weakly permeable layer with a water content

greater than 20%. The average temperature in the site

area in January is less than - 4.0℃, which belongs to

the frozen area, and the freezing depth of the site is

about 1.05 meters. According to the test results of on

- site samples sent to the laboratory and referring to

the evaluation criteria for the corrosiveness of site soil

in China's geotechnical code [1] "Code for

Geotechnical Investigation" (GB50021 - 2001), it is

determined that the soluble salts precipitated from the

site soil have slight corrosiveness to the concrete

structure and slight corrosiveness to the steel bars in

the reinforced concrete structure.

3 FINITE ELEMENT ANALYSIS

AND CALCULATION OF

SLOPE STABILITY AND ANTI-

SLIDE PILE

3.1 Geotechnical Parameters

Based on the on - site survey and drilling to obtain

core samples of rock and soil, the shear strength

parameters of the rock and soil were obtained through

laboratory tests. The rock and soil parameters are

shown in Table 1.

3.2 Calculation of Anti-Slide Pile

Since the maximum height of this slope is 9 meters,

the two - dimensional finite element software Plaxis

2D for geotechnical engineering deformation and

stability analysis is adopted. It can simulate the

nonlinearity of soil and rock, and the elastoplastic

constitutive model is the Mohr - Coulomb model. The

anti - slide piles are modeled as linear elastic non -

porous structures. Wang et al., (2019) added 5.305%

slag micro - powder and 0.014% polycarboxylate

high - performance water - reducing agent to the

concrete according to the mass ratio. This not only

improves the strength of the concrete but also

enhances its impermeability and the flexural capacity

of the anti - slide piles. The calculation formula for

the preparation strength of concrete is calculated

according to f = f.k + tσ. In the formula, f is the

preparation strength of concrete (MPa); f is the

strength standard value of concrete at the designed

age (MPa); t is the probability coefficient, and the

design strength guarantee rate is 95%.

In the finite element model, the Embedded pile

element model is used for anti - slide piles. The

embedded beam unit (embedded beam) is employed

to simulate the mechanical and engineering properties

of the piles, which can analyze the deformation,

internal force of the piles and the pile - soil interaction.

The diameter of the piles is 0.3 meters, and the center

- to - center spacing of the piles is 1.5 meters. Non -

large - diameter piles can ensure rapid convergence

Research on the Ductility Design of Concrete Anti - Slide Piles for Building Slopes in Saline-Alkali Soil Areas of Lanzhou City

under certain accuracy conditions. The Mohr -

Coulomb elastic - ideal plastic model (MC)

constitutive model for the soil can well simulate the

mechanical behavior of this kind of soil. A total of

2453 elements and 20720 nodes are divided, as

depicted in Figure 2. In order to determine whether

plasticity occurs in a calculation, a function of stress

and strain is introduced here as the yield function. The

ideal plastic model is a constitutive model with a

fixed yield surface. The two parameters of the plastic

model are the friction angle φ and the cohesion c.

These yield functions can jointly represent a

hexagonal pyramid in the principal stress space.

(

)

Horizontal dis

lacement of unsu

orted slo

(

)

(b) Horizontal displacement of ordinary concrete anti-slide pile (mm)

ICESCE 2024 - The International Conference on Environmental Science and Civil Engineering

(d) Horizontal displacement of ordinary concrete anti-slide pile and improved anti-erosion concrete anti-slide pile (mm)

Figure 2: The calculation result.

4 CONCLUSION

To ensure the stability of a 9 - meter - high building

slope, based on the on - site geotechnical sample

testing and slope stability calculations, the main

conclusions are as follows:

(1) Through on - site inspection and core -

sampling of geotechnical specimens, the corrosivity

of salt ions in the rock and soil, as well as

geotechnical parameters, were analyzed. The soluble

salts in the rock and soil have a slight corrosive effect

on the concrete structure.

(2) By calculating the stability coefficient of the 9

- meter - high building slope, it was found that the

slope stability is insufficient, especially under rainfall

or seismic conditions, where the stability further

decreases. Through comparative analysis of the

slope's stability, horizontal displacement of the slope

body, and the horizontal displacement variation along

the entire length of the anti - slide piles under natural

conditions, ordinary anti - slide pile retaining

conditions, and sulfate - resistant formulated concrete

anti - slide pile conditions, the horizontal

displacement of the slope follows the order: U1x

(natural slope) > U2x (ordinary concrete anti - slide

pile) > U3x (improved anti - erosion concrete anti -

slide pile). Under natural conditions, there is a

potential through - going slip surface from the top to

Research on the Ductility Design of Concrete Anti - Slide Piles for Building Slopes in Saline-Alkali Soil Areas of Lanzhou City

the bottom of the slope. The maximum water - level

displacement is 0.59 mm. The maximum

displacement of the slope supported by ordinary anti

- slide piles is 0.52 mm, and the maximum

displacement of the slope supported by the improved

anti - erosion concrete anti - slide piles is 0.40 mm.

The maximum displacement of the pile body is at the

pile top, and the displacement of the top of the

ordinary anti - slide pile is greater than that of the

improved anti - erosion concrete anti - slide pile.

(3) Considering the weak corrosivity of the saline

- alkali soil to concrete and the long - term durability

of anti - slide piles in the building slope, measures

such as increasing the thickness of the concrete

protective layer and adding slag micro - powder to the

mixture can improve the compactness and

impermeability of the concrete. By comparing and

analyzing the changes in the mechanical properties of

the anti - slide piles before and after improvement, it

was found that these measures can also save certain

costs. These technical measures can provide some

reference experience for similar projects in the future.

AUTHOR CONTRIBUTION

Xiaosen Li, Shanzhi Fan, Haihong Zhang,:

conceptualization, methodology, data curation,

writing-original draft preparation. Xingrong Liang,

Wenjing Zhang: visualization, investigation,

resources, project administration, supervision,

funding acquisition. Shanzhi Fan: review & editing.

FUNDING INFORMATION

This paper is supported by Key R&D Program of

Enterprise Project of Gansu Provincial Highway

Transportation Construction Group Co., Ltd. (GJJ-

ZH-2023-50).

DATA AVAILABILITY

The data used to support the findings of this study are

available from the corresponding author upon request.

CONFLICTS OF INTEREST

We declare that we do not have any commercial or

associative interest that represents a conflict of

interest in connection with the work submitted.

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