THE LIQUEFACTION POTENTIAL OF SANDY SILT LAYERS USING CPT TESTS: CASE STUDY FROM THE CASABLANCA TANGIER HIGH- SPEED RAIL LINE (LGV) IN MOROCCO

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume, Issue, October, pp., Article ID: IJCIET Available online at ISSN Print: - and ISSN Online: - IAEME Publication Scopus Indexed THE LIQUEFACTION POTENTIAL OF SANDY SILT LAYERS USING CPT TESTS: CASE STUDY FROM THE CASABLANCA TANGIER HIGH- SPEED RAIL LINE (LGV) IN MOROCCO S. Touijrate GIE Laboratory, Mohammadia School of Engineering, Mohammed V University Rabat, Morocco K. Baba GCE Laboratory, High School of Technology-Salé, Mohammed V University, Rabat, Morocco M. Ahatri and L. Bahi GIE Laboratory, Mohammadia School of Engineering, Mohammed V University Rabat, Morocco ABSTRACT The soils, during liquefaction, behave as a liquid and no longer support the shearing forces, which causes large deformations which subsequently affect the structures built on this soil. The objective of this study is to evaluate and estimate the liquefaction potential from the CPT tests using three semi-empirical methods, namely the Olsen method, Juang method and the Robertson method. Our case study is a section from the Casablanca-Tangier High-Speed Line exactly between PK + and PK +, and that is part of the basin Drader-Soueir which is located in the North-West of Morocco. This evaluation allowed us to conclude, on the one hand, that the study area has a high risk of liquefaction and, on the other hand, comparing the results of the three methods proposed. Keywords: Liquefaction, Soil, Earthquake, Semi-empirical methods, Cone penetration tests, Factor of safety. Cite this Article S. Touijrate, K. Baba, M. Ahatri and L. Bahi, The Liquefaction Potential of Sandy Silt Layers Using Cpt Tests: Case Study from the Casablanca Tangier High-Speed Rail Line (Lgv) in Morocco, International Journal of Civil Engineering and Technology, (),, pp. ()-(). editor@iaeme.com

2 S. Touijrate, K. Baba, M. Ahatri and L. Bahi. INTRODUCTION The liquefaction is a hazardous phenomenon which generally affects saturated pulverulent soils. Under dynamic cyclic loading and with the undrained conditions due to the intensity and speed of loading, the soil loses a part or the whole of its resistance. This loss is related to the increase of the pore pressure in the soil which leads to a reduction of the effective stress. Nowadays, several semi-empirical methods are used to quantify and evaluate the liquefaction potential. This potential reflects the soil ability to resist the cyclic shear efforts and is mainly dependent on the relative density, the particle size, the soil texture, the saturation degree and the earthquake magnitude. The liquefaction potential evaluation of the section from the High-Speed Line located in the Drader-Soueir basin (North-West of Morocco) is based on the data from six surveys CPT executed between the PK + and the PK +. The evaluation is based on the determination of the factor of safety and the liquefaction probability by three semi-empirical methods, which are the Olsen method (Olsen ), the Juang method (Juang and al.) and the Robertson method (Robertson and Wride ). These methods are based on the cyclic stresses evaluation using the CPT test data.. SEMI-EMPIRICAL METHODS USED IN THE EVALUATION The semi-empirical approaches evaluating the liquefaction potential are founded on the earthquakes observation, the liquefaction-induced effects, and the in-situ test results. The tests, which help to estimate the liquefaction potential, are mainly the Cone Penetration Test (CPT) and the Standard Penetration Test (SPT). These approaches can be divided into three categories: Approach by cyclic stresses; Approach by cyclic deformations; Energy approach. In this paper, the evaluation methods (Olsen, Juang and al., Robertson and Wride ) proposed are based on the cyclic stress approach using the CPT test data... Evaluating cyclic stress ratio The CSR estimate for the three methods studied is based on the simplified method of Seed and Idriss ( who proposed the following relationship: = =, () here is the average cyclic shear stress; is the maximum horizontal acceleration at the ground surface; g =, m²/s is the acceleration of gravity; is the initial vertical total stress; is the initial vertical effective stress;! is the stress reduction factor. The stress reduction coefficient! is expressed in terms of the depth by the following equations (Liao and Whitman ) : =,, %, =,%,, < % The Juang method (Juang and al.) used the equation () to calculate the CSR with the introduction of MSF coefficient that adjusts the CSR value to an earthquake magnitude of.. Equation () then becomes: () editor@iaeme.com

3 The Liquefaction Potential of Sandy Silt Layers Using Cpt Tests: Case Study from the Casablanca Tangier High-Speed Rail Line (Lgv) in Morocco = =, +, () Where MSF is expressed by the equation () according to I.M Idriss (Idriss and Boulanger ): +, = -,-. -, = + / +, -, / () is the earthquake magnitude... Evaluating cyclic resistance ratio The CRR evaluation in this study is based on the CPT test data, which is among the most common in-situ tests in Morocco.... Olsen method Olsen has simplified the CRR estimation by the equation (), based on the study of several parameters influencing soil liquefaction (Olsen ): =,,,+, ;, - < ; +, ; () With = > is the resistance of the tip from the CPT (friction ration) is a percentage expressed as: ; = ; A C D is sleeve friction resistance measured by CPT. ()... Juang method For the Juang method, the CRR is expressed by (Juang and al.): = EFG,+, IJ,AK I,- L Where: =, < K IJ,A = M N IJ +, - K, K +, M N =,ON P.,ON P < +,ON P -.ON P+. () () () () N = RO, ST I IJ P - +OST I,+,P²V, () F is normalized friction ratio defined as:, = ; A O P () editor@iaeme.com

4 S. Touijrate, K. Baba, M. Ahatri and L. Bahi... Robertson method The Robertson's CRR estimation (Robertson and Wride ) appears more difficult than the other two methods. The evaluation steps are summarized in Figure. This method is limited by a standardized the resistance of the tip less than and uses another criterion (liquidity limit and moisture content) to evaluate the liquefaction if Ic is greater than or equal to.... Evaluating factor of safety and liquefaction probability The factor of safety is expressed by the same equation for all methods based on the cyclic stress approach (Seed and Idriss ):, A = K () From the factor of safety coefficient, we can determine the liquefaction probability (Juang & al. ): WX = I IY, AK Z [ () Where: A = and B =, according to Olsen method (Olsen ); A =, and B =, according to Juang method (Juang and al.); A = and B =, according to Robertson and Wride method (Robertson and Wride ). editor@iaeme.com

5 The Liquefaction Potential of Sandy Silt Layers Using Cpt Tests: Case Study from the Casablanca Tangier High-Speed Rail Line (Lgv) in Morocco Figure Method for evaluating Cyclic Resistance Ratio (CRR) (Robertson and Wride ). CASE STUDY Our case study positioned at the southern section of the high-speed line linking Tanger and Casablanca, it is between the PK + and the PK +. Geographically, this section of the high-speed line is located in the North-West of Morocco, precisely, km South-East of Moulay Bousselham... Geological framework Geologically, the section studied is part of the Drader-Soueir basin, which belongs to a unit that extends from the Gharb plain's South to the Oued Loukkos in the North and is limited by the clay and marly pre-rif outcrops in the East. The unit is composed of the plio-quaternary soils that are quite varied but always more or less detrital (intercalation of sand, sandstone, sandstone limestone, sandy clay) resting on a very clear substratum formed by the Miocene blue marls (MAYCHOU ). editor@iaeme.com

6 S. Touijrate, K. Baba, M. Ahatri and L. Bahi Figure Satellite view of the section studied Figure The Pre-Rif Simplified Geological Map (MAYCHOU ) The soils in the area are profoundly influenced by the textural nature of their bedrock made of quaternary sands. The granulometric analysis shows that the majority of the soils in this area contain at least % of the total sands, the most often %. The clay contents are located in the to % except in depth where they sometimes reach to %. The deep horizon frequently includes calcareous kidneys and needles. editor@iaeme.com

7 The Liquefaction Potential of Sandy Silt Layers Using Cpt Tests: Case Study from the Casablanca Tangier High-Speed Rail Line (Lgv) in Morocco Table Olsen method results Zone Zone PK Classification Depth (m) Rf % rd CCR CSR Fs PL Sandy silt to clayey silt..... Clay..... Sand..... Silty sand to sandy silt.... Sandy silt to clayey silt..... Silty sand to sand..... Sandy silt to clayey silt Clayey silt to silty clay..... Fine clayey soil or sensitive silt.... Silty sand to sand.... Sandy silt to clayey silt Organic soils and peats..... Clay..... Silty sand to sand.... Fine clayey soil or sensitive silt..... Silty sand to sand..... Silty sand to sandy silt.... Silty sand to sandy silt..... Clayey silt to silty clay Clayey silt to clay... Clay.... Clay..... Sandy silt to clayey silt Silty sand to sand..... Silty sand to sandy silt.. Silty sand to sandy silt.... Clayey silt to clay..... Silty sand to sand Silty sand to sandy silt Clay.... Silty sand to sandy silt.... Silty sand to sand.... Clay Sand Table Juang method results Zone P K + + Classification Depth (m) Sandy silt to clayey silt. Clay. Sand. Silty sand to sandy silt. Sandy silt to clayey silt. Silty sand to sand. Sandy silt to clayey silt. Rf % rd... qc N F Cσ Ic qcn.cs CC R.... CS R Fs PL editor@iaeme.com

8 S. Touijrate, K. Baba, M. Ahatri and L. Bahi Clayey silt to silty clay Fine clayey soil or sensitive silt Silty sand to sand Sandy silt to clayey silt Organic soils and peats Clay Silty sand to sand Fine clayey soil or sensitive silt. Silty sand to sand Silty sand to sandy silt Silty sand to sandy silt Clayey silt to silty clay Clayey silt to clay Zone + Clay. Clay. Sandy silt to clayey silt. Silty sand to sand Silty sand to sandy silt Silty sand to sandy silt. Clayey silt to clay. Silty sand to sand Silty sand to sandy silt Clay Silty sand to sandy silt. Silty sand to sand. Clay Sand editor@iaeme.com

9 The Liquefaction Potential of Sandy Silt Layers Using Cpt Tests: Case Study from the Casablanca Tangier High-Speed Rail Line (Lgv) in Morocco Table Robertson and Wride results P K Classification Depth (m) Rf % Sandy silt to clayey silt.. Rd Q F qcn Ic Kc..... qcn. cs. CC R CS R Fs. PL. Clay Sand Silty sand to sandy silt Sandy silt to clayey silt.. Silty sand to sand Sandy silt to clayey silt Clayey silt to silty clay Fine clayey soil or sensitive silt Zone + Silty sand to sand.. Sandy silt to clayey silt.. Organic soils and peats Clay Silty sand to sand Fine clayey soil or sensitive silt Silty sand to sand Silty sand to sandy silt Silty sand to sandy silt.. Clayey silt to silty clay Clayey silt to clay Clay Clay.. Sandy silt to clayey silt.. Silty sand to sand Zone + Silty sand to sandy silt Silty sand to sandy silt editor@iaeme.com

10 S. Touijrate, K. Baba, M. Ahatri and L. Bahi + Clayey silt to clay.. Silty sand to sand.. Silty sand to sandy silt.. Clay. Silty sand to sandy silt.. Silty sand to sand.. Clay.. Sand The region's seismicity In Oued Drader, the maximum intensity is measured at near VII, but due to the proximity of the area to the critical seismic intensity regions, including a historical seismic site, and for safety measures, considers an intensity of IX. Many conversion laws between the intensity and the magnitude were developed by Cherkaoui (CHERKAOUI and ASEBRIY ) and Karnick (KARNIK ), thus allowing a correlation between the two parameters. For an intensity equal to IX, the Drader-Soueir basin magnitude retained is M =.. Given that the Oued Drader region is part of the Seismic Zone No. according to the RPS revised in, it is therefore considered a maximum acceleration of g (RPS ).. RESULTS AND DISCUSSION This study is based on data from surveys of the test CPT along the section between the PK + and PK + of the High-Speed Line. We have been able to evaluate the factor of safety and the liquefaction probability of each survey with the three methods already discussed. The results of this study are presented in the Table (), () and ()... Evaluating liquefaction potential According to the analysis of the CPT test data for the surveys, it is found that the most affected depths are between and m, with a high liquefaction probability at the silty and the sandy soils such as "the silty sand to sandy silt" where the PL exceeds for the three methods (Olsen, Juang and al., Robertson and Wride ) in the PK + survey and "the silts sensitive" also in the PK + survey. The PK + survey presents a low probability due to the important alternation of clay layers which are less susceptible to liquefaction. We can conclude that the region of the Drader-Souier basin can be considered as very susceptible to liquefaction, due, on the one hand, to the formations nature in the area, which are characterized by the existence of sand and silt layers alternate with more clayey layers, which are saturated with water because of the basin hydrogeological nature, on the other hand, with the seismic risk present in this region. editor@iaeme.com

11 The Liquefaction Potential of Sandy Silt Layers Using Cpt Tests: Case Study from the Casablanca Tangier High-Speed Rail Line (Lgv) in Morocco.. Comparison between methods results The three methods presented in this study are all of the cyclic stress approach and are all based on the CPT test data. To compare the three methods, the survey data for the PK + case were used. Figure presents the results obtained in terms of the factor of safety of the PK + case, where there are points for which the factor of safety is less than, which are therefore likely to liquefy. According to Figure, it is also observed that the variation in the factor of safety curves of the Juang method (Juang and al.) and Robertson method (Robertson and Wride ) is almost similar and the difference between the two curves due essentially to the introduction of the MSF factor in the CSR calculation (Figure ). On some beaches in depth, the Fs curves of Olsen method (Olsen ) and Robertson method (Robertson and Wride ) are almost identical. These observations on the safety factor are translated directly on the liquefaction probability curves (Figure ), the curves patterns are a little changed as the coefficients A and B change from one method to another. Depth (m) CSR PK + Olsen & Robertson Juang Depth (m) Olsen CRR PK + Robertson Juang editor@iaeme.com

12 S. Touijrate, K. Baba, M. Ahatri and L. Bahi For the calculation of CCR, the Olsen method (Olsen ) does not have a well-defined physical aspect. It is easy to exploit, but it does not predict all points likely to liquefy in the same way as the other two methods except for depths greater than m. It is therefore less safe than the other two. Moreover, the Olsen method (Olsen ) involves a Rf (friction ration) term which regularizes the CCR curve and therefore the factor of safety. Depth (m) qcn PK + Depth (m) qcn,cs PK + Juang Robertson Juang Robertson. CONCLUSION Based on the data from six surveys of the CPT test between the PK + and the PK + from the High-Speed Line, the liquefaction potential calculations were carried out using three methods based on the cyclic stress approach which are the Olsen method (Olsen ), the Juang method (Juang and al.) and the Robertson method (Robertson and Wride ). The results of these calculations allowed us to conclude that the Drader region presents a high risk of liquefaction due the geological, hydrogeological and seismic context of the region. We also compared the different methods used in this study and concluded that the Juang method (Juang and al.) seems to be the best choice among those proposed because of its very robust physical appearance, contrary to the Olsen method (Olsen ), and also is simpler than the Robertson method (Robertson and Wride ) which assumes a several corrections and is limited by a normalized resistance of the tip fewer than. REFERENCES [] Alain PECKER, livre de Dynamique des sols, Presse de l'école nationale des Ponts et Chaussées. [] Francesco Castelli, Antonio Cavallaro, Salvatore Grasso, Michele Maugeri, Fourth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. [] Francesco Castelli, Valentina Lentini, - Fifth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. [] G. Zhang; P. K. Robertson, and R. W. I. Brachman,, Project Engineer, EBA Engineering Consultants Ltd., - Ave., Edmonton AB, Canada TV B, Journal of geotechnical and geoenvironmental engineering ASCE. [] I.M. Idriss, R.W. Boulanger, Soil Dynamics and Earthquake Engineering (). [] Juang, C.H., Chen, C.H. and Mayne, P.W. (), Soils and Foundations, Vol., No., pp editor@iaeme.com

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