10th Asian Regional Conference of IAEG (2015)

Experimental research of correlation on static and dynamic strength of clay
Junhui LUO (1), Linchang MIAO (1) and Guangfan LI (2)(1) Institute of Geotechnical Engineering of Southeast University, Nanjing, China
E-mail:jhluo85@hotmail.com(2) College of Civil Engineering of Hainan University, Haikou, China
Abstract
The LoadTrac II triaxial apparatus was employed to performed static, and thedynamic triaxial tests on Haikou red clay under consolidated undrained condition. The
properties of static and dynamic strength were comparative studied. It obtained static anddynamic strength parameters of Haikou red clay, and established the relation between
them. It turned out that: the result could benefit for accumulation of basic data which
includes the seismic design, seismic safety evaluation of Haikou city, and completingtheoretical system and engineering properties of Haikou red clay.
Keywords: triaxial, static, dynamic, strength, seismic safety1.

2.

Introduction

Experiment process

2.1 Test material
The project site is located on the Gao-Po Villageof Haikou in Hainan province. Using thin-walledsampler to take undisturbed soil at the scene, andsealing it with tape could keep the integrity of thesoil. According to soil test method standard, the soil
was carried back and sampled preparation in thelaboratory. From the routing soil tests, the propertiesof the physical and mechanical indexes were made asystematic study in table 1. And in the figure 1 wasshowed the thin-walled sampler and horizontal earthmoving. In order to have the sample matched thedynamic triaxial apparatus, the undisturbed soil
sample diameter was made into 35mm, and the heightwas 77mm.

China lies on the middle of the two seismic
activities
intheworld,andtheearthquake occurs frequently. Haikou City is thehighest seismic intensity capital city in our country.
China will construct the fourth astronautics launchingbase in Wenchang of Hainan, and also construct
highway in the Hainan median line, but there is noliterature of the Haikou red clay on the dynamic
characteristics, therefore, it is necessary to obtain thesoil property under the effect of earthquake (GuangXin Li, 2004; Shen Zhujiang, 1999).
Shear strength is one important subject of soilmechanics. The dynamic strength can be defined as:
under a certain vibration times N, to make the soil up
to a certain failure criteria demanded dynamic stressamplitude (Wang Wenshao, 1997). Current research
is more about dynamic and static strength, but lack ofanalysis of the association (Hyodo et al, 1999). In thispaper, the characteristics of static and dynamic
strength are studied on Haikou regional special red
clay. The test results and conclusion could
accumulate basic data for which includes the seismic
design, seismic safety evaluation of Haikou, andcould complete theoretical system and engineering
properties of Haikou red soil, providing reference
data for earthquake prevention measures.

Fig. 1 Undisturbed soil field sampling equipment andhorizontal bulldozing

110th Asian Regional Conference of IAEG (2015)

3.

Table 1 Physical properties of natural undisturbed redclay
Water
contentω(%)

specificgravity
dsLiquidLimit
I l (%)

Plasticlimit
I p (%)

35.5

2.74

56.9

31

Characteristics of static strength
The deviator stress can be expressed as  1   3 .

SpecificWeight (kN/m3)
16.9

During the shear test, deviator stress increased withthe increase of strain, and then reached the peakvalue ( 1   3 ) f . It can be seen from figure 4 that thedeviator stress increases dramatically when theconfining pressure goes up.

2.2 Test Equipment
The LoadTrac II triaxial apparatus was made by
GEO-COMP Company in picture 2; it could maketriaxial tests under static and cyclic load.

Fig. 4 Stress-strain curve under cu static
This paper chose 15% as the failure pressure todraw up the Mohr circle, and then obtains the CU
strength parameter: Ccu  17kPa,cu  110 ；Fig. 2 LoadTrac II triaxial apparatus
4.
2.3 Test procedure
Saturation: The undisturbed sample firstsaturated by the outdoor exhaust, followed by carbon
dioxide led to saturation of the sample, then the
instrument back-pressure saturated;
Consolidation: Specimens consolidated withisotropic consolidation. The numerical size ofconfining pressure were determined by the depth ofoverburden undisturbed soil, the confining pressures
were followed by 50, 75, 100, 150 kPa. When theexcess pore water pressure mainly dissipated, it wasthe end of consolidation.
Load: In the static load, set the shear rate as
0.5%/minis until strain was up to 15%. When dynamic loading, in order to prevent the triaxial chamberfrom driven, some measures were needed to fix infigure 3. It made axial strain of soil samples up to 5%
as vibration destroyed (Mitchell and King, 1977).

Analysis of dynamic strength
Cyclic test results are analyzed as follows:

（a）

（b）
Fig. 3 Consolidation process210th Asian Regional Conference of IAEG (2015)

these factors such as soil composition, status andstructure. The other is external factors, including
stress state (confining pressure, the principal stress),stress history, the principal stress direction, loading
rate and drainage conditions (Lee K L, 1979).
As can be seen from the figure, the higher theconfining pressure, the greater the damage to thedynamic shear stresses. Points of attachment tend toparallel the fitted straight line.
The nation norms proposed equivalent damaging
vibration times, according to the formula of theearthquake department to promote：（c）

M  0.68 I 0  0.98

（1）

Where M is the magnitude, I 0 is the intensity, forthe degree of fortification of Haikou；
M  0.68  8  0.98  6.42 , by checking the table,
it is obtained that the equivalent failure vibration
times in table 3 which equals 8 times in Haikou；
Table 3 Correlation of equivalent vibration times
to failure and the seismic magnitude
Effective consolidation
confining pressure/ kPa
Equivalent dynamic
stress amplitude/ kPa（d）Fig. 5 Cyclic strain-vibration time curve under
different confining pressure
The test data can be described through one
fitting line of equation: y  a  bx , where a, b, R
(correlation coefficient), parameter as follows:

5075

100150120

156

190

268

It is gained that dynamic stress in table 4
corresponds to 8 vibration times. Then, draw theMohrcircle
toget
dynamic
strengthparameters: Cd  19kPa , d  110 .
Table 4 Magnitude, equivalent failure vibration
time relationshipthe magnitude (M) 6.0 6.5 7.0
Vibration times the58 12equivalent damage
5.

7.5

8.0

15-20

26-30

A comparative study of dynamic and static
strength

5.1 Overview
The static loads of limit equilibrium state can be
described by limit stress circle Mohr. In the cycle,
limit equilibrium state can also be used Moore limit
stress circle, as shown in figure 7. According toMohr-Coulomb failure criterion, it should be:

Fig. 6 Dynamic Shear stress - failure vibration time
curve
Table 2 Form fitting line equation parameters
Straight lineABCDParametersa268.2 191.7 161.4 114.3
b-0.53 -0.61 -0.56 -0.42
R0.991 0.990 0.995 0.993

2 sin  ' 2c  cos 0 1  sin 
1  sin （2）In the same confining pressure  0' of dynamic
triaxial test, stress  d caused by the destruction of soil

Many factors affect the soil strength can bedivided into two categories. One is the soil itself,3

10th Asian Regional Conference of IAEG (2015)

samples could also be used Mohr-Coulomb failure
criterion, that is:d 

2 sin  ' 2cd  cos 0 
1  sin 
1  sin Although it can not only obtain the unification
conclusion from the two kind of cohesive soil experiments, but it turned out that the dynamic cohesiveforce was about 1.6-2.4 times the static cohesiveforce.

（3）

Combination (2) and (3):cd / c  1  (1 '0c tan  )( d /   1)

5.2 The analysis of strength comparative onHaikou red soil
According to the mentioned above, made staticand cyclic triaxial test on Haikou red clay, taking thestrain damage for failure criteria under isotropic consolidated undrained conditions.
It can be seen dynamic cohesive force slightly
larger than the static cohesion.

（4）

Table 6 Comparison of dynamic and staticstrength of Haikou red soil
Test materials
Haikou red clay
Static cohesive force :C（kPa）
17
Internal frictional angle:  ()11Dynamic cohesive force : c d (kPa )20
cd / c1.17

Fig. 7 Mohr-circle and failure envelope under staticand dynamic load
Therefore, if know the static strength parameters c and  , and dynamic strength of soils  d have6.

been identified under the consolidation pressure  0' ，
the dynamic cohesion cd can be determined from theCONCLUSION

The LoadTrac II triaxial apparatus which wasmade by GEOCOMP Company was employed toperformed static and dynamic triaxial tests on Haikou
red clay under isotropic consolidated undrainedcondition.
In the test procedure, in order to prevent thetriaxial chamber from driven when dynamic loading,some measures were needed to fix.
Choose strain failure criterion to analyze thecurrent results, get that there is a certain relation
Table 5 Static and dynamic test result of two
between the dynamic and static strength parameters.
kinds of clay
The cohesive is several multiple between the dynamicand static strength, and internal friction angle isVolcanic
Volcanic
Volcanic
decided by soil property, so dynamic and static
sedimentary
sedimentary
sedimentary
Test condition
clay
sandy
clay
sandy
clay
condition basic unchanged; Comparative study ofand result（Izu） （Shiroishi） （Shiroishi）
dynamic and static strength on Haikou red soil,
Gravity
the dynamic cohesive is 1.17 times than static
14.2
18.7
19.0
 (kN/m 3 )cohesive.
Water capacity
110－140
22－23
20－21w(%)
Acknowledgements
Plasticity index
30
1818
Ip
The authors are grateful to the Committee
Static cohesive
members for DPRI Publications, who made the2028
32
force c(kPa )previous versions of this instruction.
Internal
frictional angle
171416 ()Dynamic
cohesive force
485251

formula (4) ；Table 5 shows the test condition and the result ofJapan Shiroishi region volcano sedimentary clay, thesoil particle composition: gravel particle13%,
sand47%, powder particle 12% and clay particle
28%. Besides, some volcanic sediment of thecohesive soil test result of the Japanese Izu area islisted in the table 5 (Yasuhara et al., 1992).

cd (kPa )cd / c2.4

1.86

1.59410th Asian Regional Conference of IAEG (2015)

References
Guang-Xin Li. (2004): Advanced Soil Mechanics,
Tsinghua University Press.
Hyodo M, Hyde A F L, Yamamoto Y, Fujii T.
(1999): Cyclic shear strength of undisturbed andremolded marine clays, Soils and Foundations,Vol. 39, No. 2, pp. 45-48.
Lee K L. (1979): Cyclic strength of sensitive clay ofeastern Canada, Canadian Geotechnical Journal,
Vol. 16, No. 1, pp. 163-176.
Mitchell R J, King R D. (1977): Cyclic loading of an
Ottawa area champlain sea clay, Canadian
Geotechnical Journal, Vol. 14, No. 1, pp. 52-63.
Shen Zhujiang.( 1999): Theory of soil mechanics,
China Water Power Press.
Wang Wenshao. (1997): Soil liquefaction
characteristics of dynamic strength, Beijing:
China Electric Power Press.
Yasuhara K, Hirao K, Hyde A F L. (1992): Effects ofcyclic loading on undrained strength andcompressibility of clay, Soils and Foundations,Vol. 32, No. 1, pp. 100-48.

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