The aim of this paper is to evaluate the liquefaction-induced ground deformations of sand-like soils based on Cone Penetration Tests (CPT) at Semani site, Fieri prefecture in Albania. These tests are performed during the process of investigation of this area, in which a Liquid Natural Gas Terminal-Power Plant was supposed to be built. This paper presents the assessment of the liquefaction and of the liquefaction-induced ground deformations such as lateral spreading displacement and post-liquefaction reconsolidation settlement. The liquefaction-induced lateral spreading and post-liquefaction reconsolidation settlement are estimated based on CPT data according to the method in MNO-12 “soil liquefaction during earthquake”, presented by Idriss and Boulanger (2008). This evaluation is very important and should be taken into consideration for the design of engineering structures that will be constructed in this area. All the calculation’s results are shown in graphs. At the end, there are highlighted some conclusions regarding the liquefaction-induced ground deformations in this site.
The study area is located in the South Western part of the Hoxhara village, Fieri prefecture, near the Adriatic Coastline as shown in
more than 100 m. These deposits are represented by gravels, sands, silty sands, silty clays, and clays. The water table is 0.5 m to 1.5 m from the ground surface [
Area of Semaniis included in the Periadriatic Depression, strongly affected by post-Pliocene compression movements (here in after referred as PL-zone), wherein have been recorded numerous strong earthquakes. This one is characterized by high seismic activity.
According to Albanian Earthquake-Resistant Design Regulation KTP-N.2-89, the soil conditions in this area are classified as Category III. The Peak Ground Acceleration,
The highest magnitude recorded up to date is Ms = 6.2 during the Fier earthquake of 18th of March 1962, ac- cording to Sulstarova, et al., 2010. During this earthquake were seen the liquefaction phenomena and its conse- quences including ground settlement, lateral spreading and sands boil [
Analysis of the factors that control the liquefaction indicates that the soils in this site are susceptible to lique- faction. The design of engineering structures that will be constructed in this area requires evaluation of the li- quefaction and after that evaluation of the liquefaction-induced ground deformations. Different authors, such as Robertson and Wride 1998, Idriss and Boulanger 2008, Andrus and Stokoe 2000, have evaluated the liquefac- tion resistance of soil based on Standard Penetration Tests (here in after referred as SPT), Cone Penetration Tests (here in after referred as CPT), Shear Wave Velocity (here in after referred as Vs) data. The liquefaction- induced ground deformations can be evaluated based on the methods presented by Ishihara and Yoshimine 1992 and improved by different authors such as Zhang et al., 2004, Yoshimine 2006; Idriss and Boulanger 2008; Fred Yi 2010 for application to SPT, CPT, Vs data.
In this study these evaluations are conducted using 12 Cone Penetration Tests executed in this area by means of the equations presented by Idriss and Boulanger 2008.
The procedure of calculation includes the following steps:
1) Evaluation of the liquefaction potential based on CPT method presented by Idriss and Boulanger 2008;
2) Calculation of the maximum shear strain
3) Calculation of the lateral spreading and of the post-liquefaction reconsolidation settlement according to Idriss and Boulanger 2008.
Using the Simplified Procedure presented by Seed and Idriss 1971, the liquefaction is estimated based on the factor of safety against the triggering of liquefaction. The lateral spreading displacement and post-liquefaction reconsolidation settlement are calculated based on the maximum shear strain
The liquefaction-induced lateral spreading and post-liquefaction reconsolidation settlement for saturated clean sands and silty sands are estimated based on CPT data according to the presented method in MNO-12, “Soil li- quefaction during earthquake”, Idriss and Boulanger, 2008 [
Primarily the liquefaction potential based on Idriss and Boulanger 2008, is evaluated using the factor of safety against the triggering of liquefaction. Daja, et al., 2011 have also evaluated the potential of liquefaction in this area by means of the liquefaction probability. Comparing the results of these two methods is one of the aims of the paper.
Liquefaction estimation requires the evaluation of cyclic stress ratio and of cyclic resistance ratio. Cyclic stress ratiois evaluated according to Seed-Idriss Simplified Procedure using the calculated stress reduction coef- ficient based on the relation presented by Idriss, 1999 as a function of the depth and the highest earthquake rec- orded to date in study area (Ms = 6.2). Cyclic Resistance Ratio is calculated as a function of three parameters: 1) Equivalent clean-sand CPT penetration resistance that is used to account for the effects of nonplastic fines content on the liquefaction resistance; 2) Magnitude scaling factor MSF, calculated according to Idriss, 1999 based on the number of equivalent uniform stress cycles and earthquake magnitude; 3) Over burden correction factor,
After that the lateral spreading displacement and post-liquefaction reconsolidation settlement are calculated based on the maximum shear strain
The factor of safety against the triggering of liquefaction is defined as the ratio of cyclic resistance ratio
Cyclic Stress Ratio
corporates ground surface acceleration, total and effective stresses in the soil and nonrigidity of the soil column [
where
are in radians.
Idriss and Boulanger (2004) derived the following correlation between CRR and penetration resistance for the CPT. This correlation is used to evaluate the triggering of liquefaction in clean sands and silty sands.
where:
where:
FC = fines content;
The factor
where:
The above correlation for CRR is applicable to
where:
MSF = magnitude scaling factor, given by Idriss (1999) based on the number of equivalent uniform stress cycles and earthquake magnitude:
where:
It is calculated based on the relation given by Idriss and Boulanger (2004) [
where:
The coefficient
The maximum shear strain for a given factor of safety against liquefaction is estimated by combining expressions given by Yoshimine et al. (2006) with the additional constraint of a limiting shear strain as follow [
where:
where:
where:
Lateral displacement index, LDI suggested by Zhang et al. 2004 is calculated by integrating the maximum shear strains over the depth interval of concern.
The lateral displacement is calculated according to Zhang et al. 2004 [
where:
LD = lateral displacement;
LDI = lateral displacement index;
S = ground slope as a percentage.
Ishihara and Yoshimine (1992) observed that the volumetric strain that occurs during post-liquefaction reconso- lidation of clean sands was related to
where:
The ground surface settlement for one-dimensional reconsolidation is estimated by equating the vertical strains to the volumetric strains and then integrating the vertical strains over the depth interval of concern [
The results of the calculations are presented below in graphs for 12 CPT.
Factor of safety against liquefaction, liquefaction-induced maximum shear strain, lateral displacement index, lateral displacement, post-liquefaction reconsolidation strain and post-liquefaction reconsolidation settlement were calculated based on CPT data following the procedures presented in the previous sections. All the results are shown in Figures 2-5.
The analysis based on the factor of safety indicates liquefaction potential in this site. By comparing the results of this study with the results of the study of Daja et al. (2011) two intervals where the liquefaction is expected are almost at the same depth. The small differences might be due to the considered value of Ic = 2.8 by Daja et al.
Lateral displacement index and post-liquefaction reconsolidation settlement are calculated as a function of the maximum shear strains. According to Idriss and Boulanger 2008, the maximum shear strains that occurs at low factor of safety against liquefaction tend toward limiting values that decrease as the relative density of the sand
increases. The limiting shear strains are calculated as a function of the equivalent clean-sand CPT penetration resistance and are limited to about 50% for computing LDI from individual soundings.
The calculated liquefaction-induced lateral spreading and settlement in this site are as follow:
Post-Liquefaction Reconsolidation Settlement: 0.15 m (CPT-7) up to 0.27 m (CPT-10);
Lateral displacement index: 1.42 m (CPT-7) up to 2.88 m (CPT-1);
Lateral displacement: 0.28 m (CPT-7) up to 0.57 m (CPT-1);
These conclusions are very important for the design and construction of engineering structures in this site.
The following symbols are used in this paper:
burden stress