I would like to thank Hari Prasad who has continuously guided me from the beginning of the project to the end. I would like to thank Sasanka Mouli who was always there for me by giving his valuable advice when I was not able to cope with some of the situations in my life.
Overview
The present study investigates whether the bearing capacity of the foundation soil can be improved by installing reinforcement. The improvement in the bearing capacity of the foundation soil is quantified using a non-dimensional parameter – load improvement factor (If) – defined as the ratio between the bearing capacity of the reinforced soil foundation at a given settlement and the bearing capacity of the unreinforced soil foundation in the same settlement.
Objectives of the study
Organization of the study
Introduction
When the geosynthetics are placed in the soil, they provide additional shear strength to the soil mass. To be effective, the reinforcement placed in the soil must intersect the potential failure surfaces in the soil mass.
Background work
The test results showed that the compaction of the aggregate causes a significant increase in the value of the subgrade modulus. The test results showed that there was a significant increase in the magnitude of the BCR value when the Lr/B ratio remained at 4.
Introduction
Sand and Aggregate
Direct shear test
The number of blows required to compact the aggregate was obtained based on energy applied to the aggregate sample to the compaction energy in the standard compaction test and was found to be equal to 192. Two linear variable displacement transducers (LVDTs) were used to measure the horizontal displacement of the lower box and the vertical displacement of the sample. Adjustments were made to ensure that the center of the box matches exactly under the vertical load cell.
The vertical load cell was lowered until it touched the ball placed in the middle of the loading plate. The speed of movement was maintained at 1 mm/min and the shearing continued until the horizontal movement of the lower box reached a value of 50 mm.
Interface direct shear test
Reinforcement
Geogrid
Road mesh
Introduction
Instrumentation
Sample Preparation
The compaction of the sample was done by placing the plate vibrator on the sample and moving the plate vibrator uniformly across the test vessel. One bar pressure (100 kPa) and 0.25 bar (25 kPa) pressure were used to compress the sample to achieve a relative density equal to 70% and 50%, respectively. After the compaction of the sand layer was complete, the top surface of the compacted sand surface was leveled and measurements were taken to verify that each layer had been compacted to the required relative density.
In the case of aggregate layer overlying a sand layer, a 100 mm (h/W =0.5) thick layer of aggregate was placed over the prepared uniform sand layer and compacted.
Test Procedure
A square rigid plate with dimensions equal to 200 mm x 200 mm x 30 mm (length, width and thickness) was placed on the prepared sand bed. After sample preparation, the plunger was mounted on the actuator swivel and the actuator was moved down by enabling the manual command in the software (which will be discussed in section 4.6). The actuator was moved until the plunger touched the ball placed in the center of the square base.
For some tests to monitor the surface settlement profiles, four LVDTs were placed across the surface of the prepared bed at a distance of 150mm and 225mm on either side of the foundation. After the test was completed, the load and settlement values were obtained directly from the software.
Test Series
In this test series, two tests were conducted by preparing specimens with two relative densities (50% and 70%) using geogrid reinforcement, and the width of the reinforcement used in this test series was 4B.
Station manager software
The detailed step-by-step procedure for the operation of the station management software is given below. Multi-Purpose Testware is selected in the Station Manager window and the Hydraulic Power Unit (HPU) and Hydraulic Servo Manifold (HSM) in the Station Manager window are turned ON. After that, select the displacement mode in the manual command window and operate the movement of the actuator by enabling the manual command option.
The MPT procedure editor was used to enter the displacement rate as well as the total displacement. The detectors were used to set thresholds for displacement and force to ensure that the application of the load would automatically stop if it exceeded that particular threshold.
Check list used during the experiment
14 Once the test is complete, turn OFF the HPU and HSM and close the software.
Introduction
Load improvement factor
Unreinforced case
Sand alone
Results showed that as the thickness of the aggregate layer increases, there is an increase in the bearing pressure of the footing. As the width of the reinforcement increases from 3B to 5B, there was an increase in the bearing pressure. For a settlement ratio (s/B) of 10%, there was a 37.2% increase in the bearing pressure of the reinforced sand compared to the unreinforced sand prepared for 50%.
At a settlement ratio (s/B) of 10%, there was a 12.8% increase in the bearing capacity of reinforced sand prepared with 50%. For a settlement ratio (s/B) equal to 10%, there was a 12.8% increase in bearing pressure of the layer-reinforced geogrid multilayer system compared to the unreinforced multilayer system for 50% relative density of sand layers.
Layered systemte-Aggregate layer overlying sand layer
Effect of depth of the reinforcement
Sand alone
The geogrid was placed at an optimal depth of 0.45B and the rebar width was kept at 4B. Similarly, for a sand base prepared with a relative density of 70%, the load-bearing capacity of reinforced sand increased by 57% compared to unreinforced sand. Similarly, for sand layers prepared with a relative density of 70%, the load-bearing capacity of reinforced sand increased by 21.1% compared to unreinforced sand.
Optimum depth of the reinforcement when the geonet is placed in the aggregate layer is 0.3 times the width of the footing. Increasing the width of the reinforcement did not show a significant effect on the bearing capacity of the footing when geonet reinforcement was placed in aggregate.
Layered systemte-Aggregate layer overlying sand layer
Effect of width of the reinforcement
Sand alone
To determine the effect of reinforcement width on the load-settlement behavior of the footing, test series F was designed. As the reinforcement width increases from 3B to 5B, there was no improvement in the bearing pressure and so the reinforcement width was. The road grid was placed at the optimum depth of 0.3 B in the aggregate layer and the width of the road grid reinforcement was kept as 4B.
For a settlement ratio (s/B) equal to 10%, there was a 16.7% increase in the bearing pressure of the footing resting on a two-layer reinforced casing, compared to the bearing pressure of the footing resting on a single-layer reinforced casing for a relative density of 50%. For a relative density of 70%, there was a 15.5% increase in the bearing pressure of the base resting on a two-layer reinforced casing compared to the bearing pressure of the foot resting on a single layer reinforced casing.
Layered systemte-Aggregate layer overlying sand layer
Effect of relative density
Sand alone
For a settlement ratio (s/B) equal to 10%, in the case of sand bed prepared with a relative density of 50%, there was a 2.5% decrease in the bearing pressure of the footing when the road net was used instead of the geonet. For a relative density of sand beds equal to 70%, there was an increase of 4.7% in the bearing pressure of the subgrade when the road grid was used instead of the geogrid. For a settlement ratio (s/B) of 10%, there was a 37.2% increase in bearing pressure for footings resting on geonet reinforced sand compared to the unreinforced sand for 50% relative density.
No significant improvement in foundation bearing pressure with the inclusion of road grid compared to geogrid reinforcement. When a 100 mm thick layer of aggregate was placed over the sand, there was an increase in the bearing pressure of the foundation by 20.2% compared to unreinforced sand of 50% relative density.
Layered systemte-Aggregate layer overlying sand layer
Effect of type of reinforcement
Sand alone
In the case of a sand base prepared with a relative density of 70%, there was an increase in the bearing pressure of the foundation by 4.4% when the road grid was used instead of the geogrid, which is not a very significant improvement. The inclusion of reinforcement in the sand and also in the aggregate layer resulted in an increase in the bearing pressure of the foundation. By incorporating the geogrid into the sand layer at a depth of 0.45 B, there was an increase in the bearing pressure of the foundation by 66% compared to the unreinforced casing.
For a settlement ratio (s/B) equal to 10%, there was a 39.2% improvement in the bearing pressure of the footing resting on unreinforced sand prepared at 70% relative density compared to 50% relative density. While the increase in bearing pressure for the footing was equal to 57% for geogrid reinforced sand compared to unreinforced sand for 70% relative density.
Layered systemte-Aggregate layer overlying sand layer
Effect of number of reinforcement layers
Increasing the width of the geogrid reinforcement showed an increase in the bearing capacity of the base for placement ratio (s/B) >10% when the geogrid reinforcement was placed in the sand layer. Increasing the thickness of the aggregate layer such as 0.1B, 0.25B and 0.5B, there was an increase in the bearing pressure of the foundation. The inclusion of road mesh instead of geogrid reinforcement in the aggregate layer showed significant improvement in the bearing pressure of the base for 50% relative density compared to the layered system prepared with 70% relative density.
When two layers of geogrid reinforcement were included in the aggregate layer, for a settlement ratio (s/B) equal to 10%, there was an increase of 16.7% in the bearing pressure of the footing resting on two-layer reinforced casing compared with the bearing pressure of the footing resting on single layer reinforced casing for a relative density of 50%. For a relative density of 70%, for a settlement ratio of 10%, there was a 15.5% increase in the bearing pressure of the footing resting on two-layer reinforced casing, compared to the bearing pressure of the footing resting on single layer rest. reinforced case.
