Liquefaction potential of reinforced soil by stone columns

ABSTRACT

Stone column installation is commonly employed to prevent liquefaction. Stone columns mitigate liquefaction by means of mainly three mechanisms which are drainage, stiffening and densification. A factor of safety against liquefaction $\mathit{FS}$is used to quantify liquefaction potential. The aim of this study was to assess the efficiency of stone columns as a liquefaction remediation based on twenty four case studies. In these cases, SPT and CPT tests were recorded before and after stone columns installation. It was found that the installation of stone columns considerably increased soil density mainly in clean to slightly silty sand. The average rate of increase in the penetration resistance $N_{1,60,\mathit{cs}}$ and $q_{\mathit{c}1\mathit{Ncs}}$ were about 31.13% to 69.29% and 57.10% to 318.28%, respectively. Furthermore, the cyclic shear stress ratio of reinforced soil can be reduced by 13.5% to 77.5% due to the stiffening improvement of stone columns. Densification and stiffening mechanisms have been investigated through several approaches. Their individual and combined effects have been analysed. Comparative results indicate that considering the densification and stiffening effects in liquefaction analyses improved considerably the performance of stone columns.

KEYWORDS:

• Liquefaction
• stone columns
• FS
• densification
• stiffening

List of Notation

$\mathit{A}$	=	tributary area which is equal to (As +Asc)
$a_{\mathit{max}}$	=	peak horizontal acceleration
$A_s$	=	plan area of the soil matrix
$A_{\mathit{sc}}$	=	stone column area
BPT	=	Becker Penetration Test
CPT	=	Cone Penetration Test
$C_B$	=	borehole diameter correction
$C_E$	=	energy correction
CN	=	overburden blow count correction
CR	=	drill rod length correction
CRR	=	Cyclic Resistance Ratio
CRRM = 7.5,1 atm	=	Cyclic Resistance Ratio of the soil adjusted to 1 atmosphere of effective overburden pressure for the earthquake magnitude M = 7.5
CS	=	sampler liner correction
CSR	=	cyclic Shear Stress Ratio
CSRSC	=	cyclic Shear Stress Ratio of reinforced soil by stone columns
dSC	=	diameter of the stone column
E	=	elastic modulus of the stone column
FC	=	fine content
F	=	factor of safety
g	=	acceleration of gravity
Gs	=	shear modulus of the initial soil
Gs	=	shear modulus of the stone column
$G_r\frac{{\mathit{G}}_{\mathit{SC}}}{G_S}$	=	shear modulus ratio
Gsc	=	equivalent shear modulus
KG	=	shear stress reduction factor
$K_{\sigma }$	=	overburden correction factor for the overburden stresses
M	=	earthquake magnitude
MSF	=	magnitude scaling factor for earthquakes of magnitude other than 7.5
N	=	SPT blow count value
n	=	vertical stress ratio
n0	=	ground improvement factor
N1,60	=	corrected N values for overburden, energy, equipment and procedure effects
N1,60,CS	=	corrected Nfor fines content FC
qC	=	cone tip resistance
qc1Ncs	=	equivalent clean-sand CPT penetration resistance
rd	=	shear stress reduction factor
SPT	=	standard penetration test
Vs	=	shear wave velocity
z	=	depth
${\mathrm{\varnothing }}_{\mathit{SC}}$	=	friction angle of stone column material
$\mathit{\eta }$	=	area replacement ratio
${\sigma }^{\nu }$	=	effective vertical overburden stress
${\sigma }_s$	=	vertical effective stress within the initial soil
${\sigma }_{\mathit{sc}}$	=	vertical effective stress within the stone column
$\mathit{\lambda }$	=	Waves’ length
V	=	Poisson’s ratio
Vs	=	Poisson’s ratio of the initial soil
VSC	=	Poisson’s ratio of the stone column
$N_{1,60}$	=	equivalent clean sand adjustment
$\mathit{\beta }$	=	improvement factor
${\sigma }_v$	=	total vertical overburden stress
$\mathit{\tau }$	=	average cyclic shear stress
${\tau }_s$	=	shear stress of initial soil
${\tau }_{\mathit{sc}}$	=	shear stress of stone column
${\lambda }_{\tau }$	=	shear strain ratio

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Some or all data, models, or code generated or used during the study are available from the corresponding author by request.