Profile of normalized earth pressures and c) Acceleration amplification factors 91 Figure 4.24 Effect of backfill material on the normalized profile of horizontal displacement for 0.3g_3Hz. 94 Figure 4.28 Effect of STC mixture on model response at 0.3g_5Hz: a) Displacements . profile; b) Incremental profile of earth pressures and c) Acceleration. profile of amplification factors ... 95 Figure 4.29 Histories of displacements at different heights for the STC0 model: a) Sikkim.
Introduction
Background
The use of materials obtained from waste tires in the construction industry serves to create a sustainable future. The use of tire-derived materials as alternative materials in construction, particularly in geotechnical applications, has been.
Broad Objective of the Present Study
Organization of Thesis
Full-scale model wall with different infill materials and the various parametric studies are presented and discussed. The study considers the geotechnical and structural design of retaining walls filled with different fill materials.
Literature Review
Introduction
Scrap Tire-Derived geomaterials and their mixtures
- Properties of scrap tire-derived geomaterials
- Properties of STD geomaterial mixtures
The shear strength of scrap tape derived (STD) geomaterials was determined using triaxial shear and direct shear box was reported by Bressette (1984), Ahmed (1993), Humphrey et al. Shear strength properties of different types of scrap tire derived geomaterials are summarized and presented in Table 2.4.
STD geomaterials and its mixtures For Geoengineering Applications
- Retaining Walls
- Highways/Embankments
- Foundations
- Drainage Layer in Embankment, Landfill Cover and Liner Systems
This confirmed that the use of a mixture of tire fragments and soil is a suitable way to prevent self-heating of tire fragments. 2.31 (a) and (b) show the Fourier amplitude spectrum (FAS) of horizontal and vertical ground acceleration.
Critical Appraisal of Literature
Clogging and permeability tests of the model also showed that the drainage layers of crushed tires have excellent properties to serve as an effective drainage medium. 2010) studied the use of tire fragments as a drainage layer in an embankment. They used 240 tons of waste tires that were used in the construction of drainage layers in the embankment. Pieces of tires may contain steel wires; therefore, any potential damage to the underlying geomembrane in the cap or liner system is a major concern.
This problem was investigated through field tests and large-scale laboratory model tests (Reddy and Saichek, 1998a) and it was determined that a geotextile pad is required to be placed between the geomembrane and the tire chips to protect the geomembrane. 2008) used tire shreds as a drainage material in the final cover at a landfill, checked its performance and found that it performed excellently.
Objectives and Scope of the Work
Few studies on STD geomaterials have shown that STD geomaterials can be adopted for both of the above solutions. Considering the importance of the public infrastructure facilities, such as retaining walls and their volume, a comprehensive study to demonstrate the benefits of using STD geomaterials in retaining wall applications is essential. Model studies on the performance of retaining walls using STD geomaterials and their mixtures are limited in the literature.
Evaluate the financial benefits through design and cost analysis of retaining walls using STD geomaterials.
Summary
Materials and Methods
Introduction
Materials
- Sand
- Tire chips
- Sand -Tire chips (STC) mixtures
- Optimum STC Mixture and Discussion
Sand and tire shred (STC) mixtures were prepared manually by adding tire shred (TC) to sand in selected mass ratios. The target (%WTCtargeted) and achieved (%WTCachieved) mass percentage of tire scraps evaluated from different test samples are shown in Table 3.4. It is observed that the values of dry unit mass decrease linearly with increasing percentage of tire fragments content in the STC mixture, which was due to the lower value of specific gravity of waste tire fragments than that of sand.
It is clear that the amount of tire chips has a significant influence on the shear behavior of the mixtures.
Shaking table facility and instrumentation
- Shaking table facility
- Instrumentations
Further, it can also be observed (Fig. 3.15) that at the optimum mix ratio of STC mixture, the dry unit weight was reduced by nearly 20%. The optimal mix ratio of STC mix works effectively as a lightweight material for geo-engineering applications such as retaining wall backfill, embankments and foundations. Calibration of these sensors is done by placing standard dead weights on top of the sensor and reading the output voltage through the data acquisition system.
Three linear variable differential transformers (LVDTs) (Fig. 3.17c) were used to record horizontal movements of the wall.
Model construction and testing procedure
- Retaining wall models backfilled with lightweight materials
- Retaining wall models with compressible inclusions
A backfill area of 800 mm × 580 mm in plan was adopted and filled to the full height of the wall (600 mm) with sand or other STC mixtures in various model tests. After the backfill has been completely filled to the full height of the wall (600 mm), a massive wooden platform is placed on the surface of the backfill to facilitate the application of the supplement with concrete blocks (Figure 3.18). The average dry unit weight of the tire particles obtained after filling and tamping was 6.43 kN/m3.
A photograph of the model wall mount mounted on the shaking table is shown in Fig.
Summary
Retaining Wall Models Backfilled with STC Mixtures
Introduction
Testing programme
However, during the real earthquake excitation, the model behavior will be significantly affected by different ground excitation parameters (the frequency content, intensity). Retaining wall models were also tested with different (STC mixtures) backfill materials by applying four real earthquake excitations with different frequency content and different magnitudes. It can be seen from the figure that these different ground motions have different levels, duration and frequency content of peak ground acceleration (PGA).
The model walls are equipped with accelerometers, earth pressure sensors, displacement transducers at different heights to monitor the retaining wall model response as discussed in the previous chapter.
Static response of Retaining wall Models
- Horizontal displacements
- Lateral earth pressures on wall models
- Comparison of experimetnal and theoretical results
4.8(a) shows the lateral earth pressures along the height of the wall for 'at rest', while,Fig. It can also be seen that the lateral earth pressures were influenced by the STC mixtures, resulting in the lowest earth pressures for STC30 model (Test T4). Lateral earth pressures in the range of 2.0 - 5.0 kPa for STC0 are recorded for surcharge variations from 1 to 10 kPa.
The maximum lateral ground pressure decreases with increasing tire swarf content up to STC30.
Wall Models Subjected to Sinusoidal Excitations
- Response of model wall backfilled with sand
- Response of model wall backfilled with different STC mixtures
Furthermore, the variation of maximum earth pressure with different STC mixtures (%TC) and its percentage reduction are shown in figure. Acceleration responses of retaining wall models with different STC mixtures are presented in terms of acceleration amplification factors. The figure shows that the maximum acceleration gain is located at the top of the wall in all STC mixtures.
4.23(c) presents the acceleration gain factors along the wall height of the model with different STC mixes.
Model Walls Subjected To Earthquake Excitations
- Response of model wall backfilled with sand
- Response of model wall backfilled with different STC mixtures
Wall displacement histories at the top for different models with STC mixtures subjected to SK EQ excitation are shown in Figs. The percentage reduction is calculated for all STC mixtures with reference to STC0 model wall. Displacement profiles (after the excitation) of the model walls with different STC mixtures for TK EQ excitation are shown in Fig.
The maximum incremental earth pressures are listed at the bottom for various STC mixes and its % reduction is shown in Figure 1.
Summary
Displacements and incremental lateral earth pressures are low for backfilled walls in STC mixes compared to the control case with sand alone. The acceleration amplifications were reduced with the increase of STC mixtures up to STC30 mixture. Dynamic excitation induced pressures were reduced by up to 80% compared to the control test (STC0) model wall.
Based on all the above observations, shredded tire chips mixed with sand can be effective backfill material for retaining wall structures for seismic prone regions.
Retaining Wall Models With Tire Chips Inclusions
Introduction
Testing programme
The model walls are equipped with earth pressure sensors, displacement transducers and accelerometers, at different heights, to monitor the response of the retaining wall model, as discussed in Chapter 3. The results are discussed in terms of displacements, incremental earth pressures and amplification factors at different heights. .
Static response of retaining wall Models
- Wall horizontal displacements
- Lateral earth pressure on wall models
5.8 (a and b) presents the lateral earthing pressures of the model walls along the height with different additional pressures for t/H=0.15, and t/H=0.3. It is observed that the lateral earth pressures are higher for both walls of the model for higher additional pressures. 5.8 (c) shows the comparison of lateral earth pressures along the height of the wall model with different t/H ratios, below 10 kPa.
Lateral earth pressures, in the range 3.5–6 kPa for t/H=0, are recorded for surcharge variations from 1 to 10 kPa.
Model Wall Response Subjected To Sinusoidal excitations
It can be seen from the figure that the displacements decrease significantly with the increase in the thickness of the compressible inclusion. It is observed from the figure that the increasing lateral soil pressures describe a decreasing trend with an increase in the thickness of the compressible inclusion. It is observed from the figure that the increasing lateral soil pressures are describing the downward trend with the increase in the thickness of the compressible inclusion.
Laboratory model tests showed that large reductions in lateral earth pressure were achieved when tire chips with a thickness of t/H = 0.30 were used as the vertical compressible containment.
Model Wall Response Subjected To irregular Earthquake Excitations
Horizontal displacements and rising soil pressures are reduced by using tire shreds as compressible inclusions. Lateral soil displacements and pressures are low when compressive embedment is provided behind the wall. The horizontal displacements and lateral soil pressures of the wall after the removal of the support are determined and shown in Fig.
Changes in horizontal displacements and lateral earth pressures along the height of the wall are shown in fig.
Discussion of maximum values
Summary
A series of model tests were carried out to investigate the performance of retaining walls with scrap tire discs as compressible confinement, subjected to static and dynamic loading conditions. Results were presented and discussed in terms of incremental earth pressure, horizontal displacements and acceleration amplifications. Belt discs of 180 mm thickness are able to minimize the displacements and have been found to be effective in acting as a seismic buffer.
The maximum horizontal displacement of wall models with compressible inclusions (waste tape discs) is reduced by up to 75%.
Numerical Simulations of Retaining Walls
Introduction
Overview of Flac 2D
The static and dynamic analysis options in FLAC2D allow the study of two-dimensional, plane strain or axisymmetric problems. Three aspects that the user must consider when preparing a FLAC model for dynamic analysis are: (1) dynamic loading and boundary conditions; (2) mechanical damping; and (3) wave transmission through the model. Dynamic input can be used in one of the following ways: (a) acceleration history;. b) speed history; (c) history of stress (or pressure); or (d) force history.
Material damping can be incorporated into numerical simulation to represent the magnitude of energy losses in the natural system subjected to dynamic loading.
Development of numerical wall models
- Numerical Grid
- Boundary Conditions
- Materials properties
- Selection of grid size
The construction sequence adopted in the numerical model is the same as in the physical model tests. Created grid 600mm high and 800mm long to represent the backfill of the model wall. The boundary conditions applied to the model represent the actual boundary of the physical model tests.
The properties of the various filler materials were adopted based on the discussions in Chapter 3.
Validation of numerical models
The results of numerical models are discussed in terms of backfill accelerations, horizontal displacements and incremental lateral earth pressures. Typical histories of accelerations, horizontal displacements and incremental lateral earth pressures during dynamic loading (a = 0.3g and f = 3 Hz), at different heights of retaining wall models are shown in Figure. Acceleration, displacement and earth pressure histories obtained from the numerical model are comparable to those from physical model tests reported in Chapter 4.
Further, the numerical wall models are well capturing the response of the physical wall models to the variation of infill materials, overburden pressures, dynamic base excitations.
Static Response of full scale Retaining Wall
- Effect of STC mixtures
- Effect of surcharge pressure
- Effect of length of STC mixture zone (b)
- Effect of tire chips as compressible inclusion
The full height of retaining wall models with five different aggregate pressures were considered to study the influence of the aggregate pressure on displacements, lateral earth pressures, shear and bending moments of the wall. The variation of wall displacements and lateral earth pressures along the height of the wall is shown in Figure 6.17(b) and shows the maximum earth pressure values with different aggregate pressures for different STC mixtures.
To study the effect of compressible confinement, tire chips have been used as compressible confinement with different thicknesses.
Dynamic Response of Retaining Wall
- Effect of frequency (f) of base excitation
- Effect of base acceleration (a) of base excitation
- Effect of STC mixtures
- Effect of surcharge pressure
This indicates that the frequency of the input motion is close to the fundamental frequency of the wall, resulting in higher wall responses. As discussed in the previous sections, maximum displacements were found at the top and maximum dynamic earth pressures, shear forces and bending moments were found at the bottom of the wall. The maximum horizontal displacement observed at the top of the wall is approximately 170.3 mm for STC0 backfill, while it decreases to approximately 74.75 mm with STC30 backfill.
The maximum shear force and bending moment occur at the bottom of the wall and lower values are observed for STC30.
Numerical study on cantilever retaining model walls
- Target physical model
- Development of numerical cantilever retaining wall
- Validation of numerical cantilever retaining wall model
Response of full scale cantilever wall models
- Effect of STC mixtures
- Effect of STC30 zone
Summary
Design and Cost Benefit analysis of Retaining Walls
Introduction
Optimum mixing ratio of STC mixture
Design of Retaining Walls
Cost benefit Analysis
Summary
Concluding Remarks
Summary of the thesis
Conclusions
Limitations of the study
Scope for Future Research
