Chapter 2. Literature Review
2.4 Dynamic Studies on GRS Retaining Walls
2.4.2 Analytical studies
Literature Review 22 with small displacement while large vertical acceleration at top associated with large displacements.
static method based on the Mononobe-Okabe(1929) earth pressure theory was used to determine the values of the critical acceleration associated with each potential failure mechanism. Newmark’s sliding block displacement method and a number of empirical methods were used to estimate the permanent displacements of segmental retaining walls.
Fig. 2.13 Calculation of dynamic earth pressure under seismic loading (after Bathurst and Cai, 1995)
Fig. 2.14 Calculation of tensile load in a reinforcement layer due to dynamic earth pressure and wall inertia (after Bathurst and Cai, 1995)
Ling et al. (1997) proposed seismic design procedures for geosynthetic- reinforced soil structures. The procedures were based on a pseudo-static limit
Literature Review 24 equilibrium analysis, which considers horizontal acceleration and incorporates a permanent displacement limit. Internal and external stability analyses in the form of tieback analysis, compound stability analysis and direct sliding analysis were conducted to determine the required strength and length of geosynthetic.
Ismeik and Guler (1998) analyzed the effect of wall facing thickness on stability of full height concrete facing by using two-wedge failure mechanism. An analytical method had developed to correlate the effect of facing thickness with the amount of geosynthetic reinforcement required using limit equilibrium method.
Ling et al. (2001) studied the performance of several modular-block reinforced soil retaining walls and reinforced slopes during Chi Chi earthquake of Taiwan in 1999. They had studied six numbers of reinforced walls and emphasized on the proper seismic design of the reinforced soil wall. Ling (2001) discussed on application of sliding block theory to different geotechnical structures. The reinforced soil was divided into two zones (Fig. 2.15). In this study a simplified procedure was used with vertical acceleration to calculate yield acceleration and permanent displacement.
Fig. 2.15 Direct sliding of reinforced soil retaining wall (after Ling, 2001)
Huang et al. (2003) investigated four geosynthetic-reinforced soil modular block (GRS-MB) retaining walls that behaved differently during the 1999 Taiwan Chi-Chi earthquake by field surveying and soil testing. Pseudo-static analyses based on the two-wedge failure mechanism with contribution of facing and reinforcement facing connection strength was used to investigate the seismic stability of such GRS- MB walls. Newmark’s sliding block theory together with a ‘displacement diagram’
was used to evaluate the seismic displacements of the investigated walls.
Ling and Leschinsky (2005) studied several modular-block reinforced-soil retaining walls, which were failed during 1994 Northbridge earthquake and 1999 Chi- Chi earthquake. The results of analysis indicated that these walls had adequate internal stability under estimated site acceleration. But reinforcement length was inadequate to resist compound modes of failure where the potential failure surface extends beyond the reinforced zone. It was also observed that, the external stability was most critical in the presence of horizontal and vertical accelerations.
Huang and Wang (2005) presented a pseudo-static based approach for evaluating the mechanical effects of facing components on the seismic displacement of reinforced soil walls backfilled with cohesionless soils. A multi-wedge analysis method (Fig. 2.16) over the conventional two-wedge method was proposed for seismic stability of reinforced soil wall. It was also observed that structural facing component and connection strength between facing and reinforcement significantly increase the seismic stability.
Nimbalkar et al. (2006) determined the internal stability of reinforced soil wall under earthquake condition by pseudo-dynamic method. Pseudo-dynamic method adopted in the analysis considered the effect of phase difference in both the shear and primary wave traveling through the backfill due to seismic excitation. The horizontal
Literature Review 26 slice method was used for determining internal stability or for tieback analysis of the reinforced soil. Choudhury et al. (2007) presented external stability aspects of reinforced soil retaining walls.
Fig. 2.16 Failure mechanism and force equilibrium in multi-wedge method (after Huang and Wang, 2005)
Huang and Wu (2006 and 2007) calculated critical seismic coefficient (khcr) and seismic displacement of some idealized geosynthetic-reinforced walls with full- height rigid panel facing (GRS-FHR walls) using a pseudo-static-based multi-wedge method in association with Newmark’s sliding block theory. Empirical equations were developed for the values of critical seismic coefficient (khcr) as functions of internal friction angle (δs), the ratio between reinforcement length (L) and wall height (Ht) and other factors.
Nouri et al. (2008) studied the effects of horizontal and vertical pseudo- static forces on reinforced soil structures and evaluated the seismic stability of reinforced soil slopes and walls using horizontal slice method. It had been observed that the effect of horizontal seismic acceleration on the response of reinforced slopes and walls depends mainly on the geotechnical strength parameters. The effect of vertical
seismic acceleration on the performance of reinforced slopes was not significant for low values of horizontal seismic acceleration. But ignoring the effect of the amplification phenomenon could result in an underestimated design.
Reddy et al. (2008) analyzed pseudo-static seismic stability of reinforced soil wall considering displacements of the sliding mass obliquely to the alignment of reinforcement layers causing non-axial pull (Fig. 2.17). The transverse component of oblique pull generates additional stress and consequently larger pullout forces. The analysis for new Factors of safety had been carried out considering the additional stresses due to oblique pull.
Fig. 2.17 Reinforced wall with kinematics of deformation of the reinforcement (after Reddy et al., 2008)
Shekarian et al. (2008) developed a new analytical method to determine the extension force of reinforcements and the distribution of reinforced mass in the determination of active earth pressure on reinforced soil walls. The application of this approach suggested a pseudo-static method that compared with the results of MSEW software.
Ahmed and Choudhury (2008, 2012) and Choudhury and Ahmed (2009) developed a design methodology for waterfront reinforced soil retaining wall by considering both the hydrodynamic pressure and seismic forces acting simultaneously on the wall.
Literature Review 28 Huang et al. (2009) developed a seismic displacement criterion for conventional soil retaining walls based on the observations of a series of shaking table tests and seismic displacement analysis using Newmark’s sliding block theory taking into account the internal friction angle mobilization along the potential failure line in the backfill.
Basha and Babu (2009 and 2011) presented a method of evaluation of external and internal stability of reinforced soil walls subjected to earthquakes by pseudo- dynamic approach. The seismic reliability of the wall was evaluated by considering the different possible failure mechanism such as sliding along base, overturning about toe, bearing capacity and eccentricity of the resultant forces. Basha and Babu (2010) presented reliability based optimum design methods for assessing the external stability of reinforced soil walls.
Huang and Chen (2012) modified limit-equilibrium based internal and external stability analyses considering toe scouring. It was observed that a low reinforcement-facing connection result in full mobilization of reinforcement force in lower most layer of reinforcement and accelerated failure process. The wall with high connection strength collapse was due to bearing capacity failure of toe. A new Factors of safety of internal and external stability considering toe failure was developed.
Mojallal et al. (2012) used upper-bound limit equilibrium approach and Newmark’s sliding block theory to develop a group of charts to estimate the coefficient of yield acceleration and permanent sliding displacements of full-height rigid concrete faced reinforced wall. The effect of parameters such as vertical spacing of reinforcement, ratio of width to height of spacing, ratio of reinforcement length to height of facing and inter friction angle of soil on magnitude of permanent displacements on coefficient of yield acceleration were also being studied.