Experimental Study on the Influence of Permeability Coefficient of

Granite Residual Soil

Hua Hu

1,2,3

and Zhirong Lin

1,2,3

School of Architecture and Civil Engineering, Xiamen University, Xiamen, China

Tan Kah Kee College, Xiamen University, Zhangzhou, China

Shenzhen Research Instiute, Xiamen University, Shenzhen, China

Keywords: Granite Residual Soil, Permeability Coefficient, Seepage Test.

Abstract: In order to study the influence of void ratio, seepage flow, confining pressure and principal stress difference

on the permeability coefficient of granite residual soil samples, four groups of seepage tests of 16 samples

were designed. The test results show that with the increase of initial void ratio, the permeability coefficient

increases gradually, and the final increase trend of permeability coefficient slows down; with the increase of

confining pressure, the permeability coefficient decreases gradually, and the decrease trend of permeability

coefficient slows down; with the increase of main stress, the permeability coefficient decreases gradually, and

the decrease trend of permeability coefficient slows down; with the increase of seepage flow rate The

permeability coefficient increases gradually, and the increasing trend of permeability coefficient becomes

larger.

1 INTRODUCTION

Granite residual soil is mainly distributed in the

southeast region with abundant rainfall in China,

where there are many granites. The granite in contact

with rain and air has changed its mineral composition

after weathering for a certain period of time, and the

internal structure of the soil has cracks. Under the

influence of the surrounding environment, the granite

has formed residual soil over time. Underground

geotechnical engineering is growing more and more

significant as the economy grows. The study of the

mechanical properties of granite residual soil is

inextricably linked to projects like subways, tunnels,

foundation pits, slope protection, and so forth.

Residual soil is easy to soften and disintegrate when

encountering water. Water will alter the internal

skeleton structure of the particles as it infiltrates, and

the penetration may have an impact or drag effect on

the soil particles. The more fine particles the

percolation force can carry away the larger the

percolation pores will be and the direction of the

percolation force is fixed to induce a rearrangement

of the particles. Additionally, more orderly pore

channels can also make the infiltration more smooth

and enhance the permeability characteristics of soil.

Seepage characteristics are of great significance for

many working conditions such as rainfall, water level

change and foundation pit drainage in practical

projects.

Liao Hongjian(Liao et al., 2005) et al. considered

the research of slope stability caused by the speed of

water level decline and the permeability

characteristics of soil, and combined with the

simulation calculation of seepage field in actual

working conditions, obtained the influence law of

water level decline and soil permeability coefficient

on the stability coefficient.Lu Yulin(Lu, 2018) et al.

consider the influence of coupled seismic and seepage

fields on the change of slope stability, combining the

common limit equilibrium theory with both

earthquake and percolation conditions to study and

refine the calculation method of stability coefficients.

Yan Fangfang(Yan et al,. 2019) et al. considered the

effect of different rainfall duration on the variation of

the water level line of the seepage field and the slope

instability slip surface. The simulation results showed

that the longer the rainfall duration the higher the

water level line the larger the slope slip surface, and

the rainfall had a greater effect on the surface layer of

the soil. Shi Zhenming(Shi et al,. 2016) et al.

considered the changing law of slope stability during

rainfall infiltration on multi-layered soil slopes,

improved the seepage field model, calculated the

strength parameters in the seepage process of

Hu, H. and Lin, Z.

Experimental Study on the Inﬂuence of Permeability Coefﬁcient of Granite Residual Soil.

DOI: 10.5220/0011953000003536

In Proceedings of the 3rd International Symposium on Water, Ecology and Environment (ISWEE 2022), pages 169-174

ISBN: 978-989-758-639-2; ISSN: 2975-9439

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

169

different soil layers and carried out numerical

simulations, and the results showed that the stability

coefficient of soil decreases as the depth of rainfall

infiltration increases. Liu Caihua(Liu et al, 2005) et

al. considered the influence of slope water level rise

on slope stability change, and the simulation results

showed that the slope stability coefficient first

decreased and then increased due to the effect of pore

water pressure during the water level rise, which was

also related to the attenuation of shallow strength

parameters. Liu Caihua(Liu et al, 2005) et al.

considered the impact of groundwater changes on

slope stability changes during the sudden drop of

reservoir water level, and analyzed a large number of

practical cases. The results showed that there was a

certain delay time for groundwater to drop after the

sudden drop of reservoir water level, which had an

impact on slope instability.Ma Mengxiang(Ma et al,

2018) et al. considered the effect of the rate of change

of water level rise and fall on the change of reservoir

slope stability, and the simulation study results

showed that the rate of change of water level has a

greater effect on slope stability, and the effect of

water level rise and fall on stability is different.

However, there are few research results on the

influence of various internal and external factors on

the permeability coefficient of residual soil.

Therefore, this paper mainly studies the influence of

pore ratio, seepage flow, confining pressure, principal

stress difference and other factors on the permeability

coefficient of granite residual soil samples under

constant waterhead.

2 EXPERIMENTAL

PROGRAMME

To investigate the effects of pore ratio, seepage flow

, confining pressure and main stress difference on the

penetration coefficient of granite residual soil

specimens, four sets of seepage tests with a total of 16

specimens were designed, in which specimens 1-4

were tested to study the effects of initial pore ratio on

the penetration coefficient, specimens 2-8 were tested

to study the effects of seepage flow rate on the

penetration coefficient, specimens 9-12 were tested to

study the effects of confining pressure on the

penetration coefficient, and specimens 13-16 were

tested to study the effects of different main stress

differences on the penetration coefficient.

Table 1

displays the test conditions for each group of tests.

Table 1.

number

Initial void

ratio

confining

pressure

（kPa）

Seepage

flow

（ml/min）

Principal

stress

difference

（kPa）

1 1.0 70 0.02 0

2 1.1 70 0.02 0

3 1.2 70 0.02 0

4 1.3 70 0.02 0

5 1.0 70 0.02 0

6 1.0 70 0.04 0

7 1.0 70 0.06 0

8 1.0 70 0.08 0

9 1.0 70 0.02 0

10 1.0 120 0.02 0

11 1.0 170 0.02 0

12 1.0 220 0.02 0

13 1.0 70 0.02 0

14 1.0 70 0.02 20

15 1.0 70 0.02 40

16 1.0 70 0.02 60

3 EXPERIMENTAL EQUIPMENT

AND TESTING

3.1 Experimental Equipment

The instrumentation used in this test is the SLB-1 type

stress-strain controlled triaxial shear permeability

tester, which can be used to conduct seepage shear

tests under constant water head and constant flow

conditions, respectively. The test equipment is shown

in Figure 1. The parameters that can be adjusted or

displayed for each function of the instrument are: the

controllable range of specimen axial pressure is 0-

20kN (±1%), the controllable range of strain in shear

test is 0.002-4mm/min (±10%), the controllable range

of stress in shear test is 0kN-20kN(±1%), the

controllable range setting value of specimen

circumferential pressure is 0.01-1.95MPa, the set

value of counterpressure in percolation test can be

controlled in the range of 0.01-0.99MPa(±0.5%FS),

the volume flow rate in constant flow percolation test

can be controlled in the range of 0.02-30ml/min, the

volume deformation ignores positive and negative

and the maximum deformation is 480ml.

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170

Figure 1: The stress-strain control shear penetrant triaxial

test apparatus

3.2 Experimental Testing

The test soil samples were taken from a granite

residual soil slope, firstly, all the soils were dried and

crushed, and then the soil was sieved with a

maximum particle size of 2mm sifter. The main

physical properties are shown in Table 2. The

specimen models used for the test were all

Φ39.1×80mm models. In order to prepare soil

samples with a specific initial pore ratio, the dry

density of the soil can be calculated based on the

required pore ratio, and then the mass of the required

soil can be calculated based on the already prepared

soil samples with a certain moisture content. The

specimen is saturated by means of vacuum pumping

and later solidified, and the solidification end

condition is set to be zero pore water pressure.

Table 2: Main physical property indexes of granite residual

soil.

Restricted

particle size

(mm)

Median

size

(mm)

proportion

Liquid

limit

(%)

Plastic

limit

(%)

Plasticity

index

0.006 0.0008 2.7065 46.5 23.1 23.4

The seepage test adopts the constant waterhead

seepage method. In the test, open the back pressure

valve and set the back pressure at the upper and lower

ends, and the numerical difference is the constant

head value. Set the back pressure at the upper end to

0 and the lower end to 50kPa. The constant waterhead

value is 50kPa.

4 EXPERIMENTAL RESULTS

AND ANALYSIS

4.1 Influence of Seepage Flow on

Permeability Coefficient

Triaxial seepage shear tests were conducted under

different initial pore ratio conditions according to the

experimental scheme. The permeation coefficients

obtained from the seepage tests are shown in Table 3.

The variation of the penetration coefficient with the

initial pore ratio is shown in Fig. 2.

Table 3: Effect of initial void ratio on permeability coeffi-

cient.

number

Initi-

void

ratio

confining

pressure

（kPa）

Seepage

flow

（ml/m-

in）

Principal

stress

differen-

（kPa）

Permeabil-

ity

coefficient

（cm/s）

HLL1 1.0 70 0.02 0 8.34E-07

HLL2 1.1 70 0.02 0 4.91E-06

HLL3 1.2 70 0.02 0 8.48E-06

HLL4 1.3 70 0.02 0 8.95E-06

According to the trend shown in the data in Fig.

2 and table 3, it can be seen that when the confining

pressure, flow rate and main stress are the same and

the initial pore ratio is within the range of 1.0-1.3 in

the test, the permeability coefficient increases with

the growth of the initial pore ratio, but the increasing

trend gradually slows down. The initial pore ratio

from 1.0 to 1.3 corresponds to an increase in the

permeability coefficient from 8.34E-07cm/s to

8.95E-06cm/s. The order of magnitude increases by

one level, thus showing the importance of the initial

pore ratio on the permeability coefficient.

Figure 2: Relationship between initial void ratio and per-

meability coefficient.

The larger the pore ratio, the better the

connectivity of the percolating pores and thus the

larger the contact surface of the percolating water

with the particles around the pores. With the gradual

increase of percolation force, the directional

percolation force promotes the orderly arrangement

of particles. The more orderly pore channels also lead

to smoother infiltration. The initial pore ratio in the

test increased from 1.0 to 1.3, and the corresponding

permeability coefficient increased from 8.34E-

07cm/s to 8.95E-06cm/s, but the increasing trend was

gradually slowing down.

Experimental Study on the Inﬂuence of Permeability Coefﬁcient of Granite Residual Soil

171

4.2 Influence of Initial Pore Ratio on

Permeability Coefficient

Triaxial seepage shear tests of remodeled soils were

conducted according to the test protocol at different

flow, the obtained permeability coefficients are

shown in Table 4, and the variation of permeability

coefficients with flow is shown in Fig. 3.

According to the data in Fig. 3 and table 4, when

the void ratio, confining pressure and principal stress

are the same in the test and the flow rate is within the

range of 0.02ml/min-0.08ml/min, the permeability

coefficient also increases with the growth of the flow

rate.

The permeability coefficient varies from 8.34E-

07cm/s to 2.97E-06cm/s in the flow variation range.

The overall variation of the permeability coefficient

changes greatly, which is an order of magnitude

higher. The permeability coefficient gradually

increases with the increase of the seepage pressure,

because the seepage flow directly affects the seepage

pressure.

The faster the rate of change in osmotic

pressure, the faster the rate of change in penetration

force and the increased ability to influence the

skeletal structure of the soil particles, resulting in

better pore connectivity.

Table 4: Effect of seepage flux on permeability coefficient.

number

Initial

void

ratio

Confine-

pressure

（kPa）

Seepage

flow

（ml/m-

in）

Principal

stress

differen-

（kPa）

Permeabili-

coefficient

（cm/s）

HLL5 1.0 70 0.02 0 8.34E-07

HLL6 1.0 70 0.04 0 1.25E-06

HLL7 1.0 70 0.06 0 1.96E-06

HLL8 1.0 70 0.08 0 2.97E-06

Figure 3: Relationship between seepage flux and per-

meability coefficient.

4.3 Influence of Confining Pressure on

Permeability Coefficient

Triaxial seepage shear tests of remodeled soils under

different confining pressure conditions were

conducted according to the test protocol, and the

obtained permeability coefficients are shown in Table

5, and the relationship between the permeability

coefficient and the change of confining pressure is

shown in Figure 4.

According to the data in Fig. 4 and table 5, when

the pore ratio, seepage flow and principal stress are

the same and the confining pressure is in the range of

70kpa-220kpa, the permeability coefficient decreases

with the increase of confining pressure. When the

confining pressure changes from 70kpa to 220kpa,

the corresponding permeability coefficient decreases

from 8.34E-07cm/s to 9.66E-08cm/s, and the

downward trend gradually slows down.

In the seepage test, an increase in confining

pressure can restrict the evolution of seepage

channels, shrink soil pores, boost soil compactness,

and weaken soil permeability.

Confining pressure's

capacity to alter the internal particle skeleton

structure of soil during consolidation is waning as it

increases.

The pore space is already quite small due

to the addition of some confining pressure, thus it is

challenging to further shrink the vacuum by raising

the confining pressure.

Table 5: Effect of confining pressure on permeability co-

efficient.

number

Initial

void

ratio

Confine-ng

pressure

（kPa）

Seepage

flow

（ml/m-

in）

Principal

stress

differen-ce

（kPa）

Permeabili-ty

coefficient

（cm/s）

HLL9

1.0 70 0.02 0 8.34E-07

HLL10

1.0 120 0.02 0 3.54E-07

HLL11

1.0 170 0.02 0 1.38E-07

HLL12

1.0 220 0.02 0 9.66E-08

Figure 4: Relationship between confining pressure and

permeability coefficient.

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172

4.4 Influence of Principal Stress

Difference on Permeability

Coefficient

Triaxial seepage shear tests of remodeled soils under

different principal stress differences were conducted

according to the test protocol, and the obtained

permeability coefficients are shown in Table 6, and

the variation of permeability coefficients with

principal stress is shown in Fig. 5.

The data in Figure 5 and Table 6 show that, in tests

with the same pore ratio, seepage flow rate, and

confining pressure, the permeability coefficient drops

as the main stress differential increases.

The main

stress difference varies from 0 kPa to 60 kPa, and the

corresponding permeability coefficient decreases

from 8.34E-07cm/s to 3.38E-07cm/s, which is a small

range of permeability coefficient reduction.

Table 6: Effect of principal stress difference on permea-

bility coefficient.

number

Initial

void

ratio

Confine-

pressure

（kPa）

Seepage

flow

（ml/m-

in）

Principal

stress

differen-

（kPa）

Permeabili-

coefficient

（cm/s）

HLL13

1.0 70 0.02 0 8.34E-07

HLL14

1.0 70 0.02 20 5.76E-07

HLL15

1.0 70 0.02 40 3.98E-07

HLL16

1.0 70 0.02 60 3.83E-07

Figure 5: Relationship between principal stress difference

and permeability coefficient.

On the one hand the applied principal stress

difference increases the vertical pressure on the soil

sample, and there will be less pore space after vertical

consolidation. On the other hand, the principal stress

difference may lead to local deformation of the soil,

and the cross-sectional area of seepage will increase.

The larger the principal stress difference is, the more

obvious the effect from local deformation will be and

the larger the area of seepage cross-section will be.

Therefore, the permeability coefficient decreases

with the increase of the principal stress difference.

5 CONCLUSIONS

(1) The permeability coefficient steadily rises as

the initial pore ratio rises, and the final growth trend

of the permeability coefficient slows down. The

larger the pore ratio, the better the connectivity of the

seepage pores, and the larger the contact surface

between the seepage water and the particles around

the pores. With the gradual increase of the seepage

force, the directional seepage force promotes the

orderly arrangement of particles, and the more

orderly pore channels can also make the penetration

more smooth.

(2) The permeability coefficient progressively rises

as the seepage flow rate rises, and the trend of rising

permeability coefficient quickens. Permeability

pressure is directly influenced by the size of the

seepage flow. The greater the rate of change in

permeability pressure, the greater the rate of change

in permeability, and the greater the ability to modify

the skeletal structure of soil particles, resulting in

improved pore connectivity.

(3) The permeability coefficient steadily drops as

confining pressure rises, and the rate at which it is

falling slows down. In the seepage test, an increase in

confining pressure can restrict the evolution of

seepage channels, shrink soil pores, boost soil

compactness, and weaken soil permeability.

Confining pressure's capacity to alter the internal

particle skeleton structure of soil during consolidation

is waning as it increases. The key point is that its

pores are already quite small when the confining

pressure is increased to a certain degree. It is

challenging to minimize the pores, even while the

confining pressure rises.

(4) The permeability coefficient steadily declines

as the major stress rises, and this decline trend

becomes slower. On the one hand, the application of

the primary stress difference will result in an increase

in the soil sample's vertical pressure ,and the pores for

vertical consolidation will be less. On the other hand,

applying the primary stress difference can cause

localized soil deformation and expand the seepage's

cross-sectional area. The influence of local

deformation is more visible and the region of seepage

cross-section is bigger as the major stress differential

increases. As a result, the permeability coefficient

similarly falls as the primary stress difference

increases.

Experimental Study on the Inﬂuence of Permeability Coefﬁcient of Granite Residual Soil

173

ACKNOWLEDGEMENTS

The authors would like to acknowledge financial

support from the Natural Science Foundation of

Xiamen city. Audit number of Xiamen Natural

Science Foundation: 3502Z20227323.

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