Standard penetration tests were also carried out to observe the change in soil stiffness due to the installation of the sand pile. The test results show that the installation of granular piles increased the bearing capacity of the normal terrain. The costs of mat and precast piles increased by approximately 114% and 154%, respectively, compared to sand piles.
General
Historical Background
The vibro-compaction method is used to improve the density of cohesionless soil using a vibroflot that sinks into the soil under its own weight and with the help of water and vibration (Baumann and Bauer 1974 and Engelhardt and Kirsch 1975). The vibro-compozer method is popular in Japan and is used for stabilizing soft clays in the presence of a high water table (Aboshi et al. 1979, Aboshi and Suematsu 1985, and Barksdale 1981). Some research work was carried out at the Department of Civil Engineering, Khulna University of Engineering &.
Scope of this Study
The vibro-replacement method is used to improve cohesive soils, where more than 18% does not pass. In the borehole method, the piles are constructed by ramming granular material into the pre-drilled holes in stages using a heavy drop weight (usually from 15 to 20 KN) from a height of 1.0 to 1.5 m (Datye and Nagaraju 1975, Datye 1798, Datye and Nagaraju 1981 and Bergado et al. 1984). Once the field performance in increasing the load-bearing capacity of this technique is established, this ground improvement technique can be used for soft soils, especially for small projects.
Objectives of this Study
In Bangladesh, the dry shear method, another column installation practice, is used, i.e. wet replacement method using locally available SPT arrangement, can be used in Bangladesh. As this installation technique is simple, manual labor oriented and required instrument is available locally, the practicing engineers can suggest the customer to use this soil improvement technique to improve the soft soil and construct the structure on it. This study will be very useful to verify the applicability of this method in case of soft fine grained deposits in Khulna regions.
Layout of this study
General
For example, small embankments or shallow excavations may be found on a site that do not cause technical problems. But if higher embankments or deeper excavations are to be carried out on the same foundation, the excessive deformation may occur and cause structural failure. Moreover, the soil should not pose any problems if the implementation of an embankment after the long span is followed in a slow process by other constructions, allowing the soil to become sufficiently stable.
Foundation Practice in Soft Ground
However, the determination of these parameters cannot be clearly done in the past since the soil reactions are different for the applied methods and the respective objectives. In addition, it is of course true that the constraints related to soil characteristics are also significantly different depending on the allowable differential settlement and total foundation deformation for structures. However, if the embankment is not to be built in a very short time, a problem such as bearing capacity and consolidation in the long term will become serious problems.
Ground Improvement Techniques
- Preloading
- Deep densification of cohesion less soils
- Densification of soft soils
- Injection and grouting
- Soil reinforcement
- Stone columns
Since the beginning of the modern phase of soil improvement, several techniques have been developed. In many methods, dynamic loading is accompanied by displacement in the form of inserting a probe or constructing a sand or gravel column in-situ methods used for in-situ deep compaction of cohesion, minor soil include blasting, vibro-compaction, heavy stamping. Of the methods for soil improvement and soil reinforcement, none has been as intensively suitable and advanced in application in the last several years as soil reinforcement.
Method of Selection of Ground Improvement Techniques
Columnar Inclusions
Sand Compaction Piles (SCP)
And most recently it was used in part of the coastline at Taus Reclamation for the Malaysia-Singapore Second Crossing. The depth, size and spacing of the sand piles must be designed in accordance with the soil and load conditions. In the case of the North Eastern Coast project, the pile size was 0.8m with spacing varying from 1m to 1.5m to produce an area replacement ratio between 0.25 and 0.5.
Installation Techniques
- Vibro-displacement method
- Vibro-replacement method
- Vibro- compozer method
- Cased-borehole method
- Rammed-displacement method
In the vibratory method, the vibrated hole must remain open after the probe is pulled out. Sand compaction piles are constructed by driving the casing pipe to the desired depth using a heavy, vertical vibratory hammer mounted on top of the pipe. Sand compaction piles are constructed by driving the casing pipe to the desired depth with a heavy, vertical hammer mounted on top of the pipe.
Sensitivity of soft soil
The method is useful in developing countries using only indigenous equipment as opposed to the methods described above which require special equipment and trained personnel (Ranjan and Rao 1983 and Ranjan 1989). The casing is filled with a specific volume of sand and the casing is then repeatedly withdrawn and partially re-driven using the rammer starting from the bottom. Extra-sensitive clays, such as Mexico City clay, are generally derived from the decomposition of volcanic ash.
Effect of Sample Disturbance During Installation Technique
For most clays, sensitivity lies between 2 and 4, clays considered sensitive have S. values between 4 and 8. In the case of sensitive clays, reshaping causes a large reduction in strength. High sensitivity in clay is due to a well-developed flaky structure, which is disturbed when the soil is reformed. In the case of silty sand, disturbance affects the dynamic shear strength, but the drained shear strength of sand does not appear to be sensitive to disturbance of raw material if the density is unchanged (Mori and Koreeda 1979).
Design of Granular Piles
- Unit Cell Concept
- Area replacement ratio
- Failure mechanisms
- Ultimate bearing capacity of single and isolated granular pile
- Ultimate bearing capacity of group granular pile
Where o is the stress in the granular pile and ac is the stress in the surrounding cohesive soil. The magnitude of the stress concentration also depends on the relative stiffness of the granular pile and the surrounding soil. Most approaches to predicting the ultimate bearing capacity of a single, isolated granular pile have been developed based on the above assumptions.
Experimental Investigations
The instrumentation records showed that the columns had no apparent effect on the performance of the embankment. From the results, it was found that through the top of the piles up to a depth of 0.8m, bulging of granular piles occurred and increased the bearing capacity by about 1.5 times compared to that of its counterpart without a skirt. They prevent lateral deformation and thus increase the vertical bearing capacity of the piles.
Reinforcement increased the load-carrying capacity and stiffness of the granular piles by about four times compared to their unreinforced counterparts. It was found that the ultimate bearing capacity increases with the density of column and the pure gravel column shows higher capacity than that of the mixed counterparts. A drainage blanket of 0.25m thick consisting of clean sand was laid on top of the compacted granule piles.
The maximum stress concentration ratio was found to increase approximately linearly with the replacement ratio of the sand column. The study shows that the sand piles significantly improved the bearing capacity of the natural soil. The simple construction procedure and related equipment used in this project for the installation of the desired sand pile proved to provide a high degree of efficiency.
Field measurement shows that the load-bearing capacity of soft soil is significantly increased due to the installation of crushed piles regardless of the type of granular material.
General
Site Condition and Sub-Soil Properties
Location
For this study, the project site for field investigation is selected at KUET campus, Khulna. The location map of the researched site in the KUET campus is also shown in Fig.
POND
Selection of Improvement Technique
- Granular Piles
During the planning phase of any construction project, it is necessary to determine whether an improvement to the land is needed or whether construction can continue without any improvement. The methods suitable for the application of countermeasures are determined according to various conditions, such as structural conditions accompanying soil or ground conditions, construction site conditions, economic feasibility and execution conditions. In this study, granulated pile is considered as the soil improvement technique to increase the bearing capacity of the soft compressible soil.
Sand Piles
- Installation technique
- Materials of Granular Piles
- Physical properties of sand
- General
- Installation of Granular Piles
- Description of equipment
- Installation procedures
- Monitoring of construction process
- Installation sequences
- Field Investigations
- Methods of investigation
- Constraints of plate load test
- Plate Load Test on Natural Ground
- Plate Load Test on Improved Ground
- One month after sand pile installation
- One year after sand pile installation
- Standard Penetration Test on Improve Ground
- General
- Load Carrying Capacity of Single Sand Pile
- One month after sand pile installation
- Comparison of Plate Load Test Results
- One month after sand pile installation
- One year after sand pile installation
- Summary of the plate load test result -4'
- One month after sand pile installation
- One year after sand pile installation
- Comparison of Field Test Results with other Published Results
- Comparison of Cost for Sand Pile Solution with Conventional Foundation
- Summary
- Conclusions
There are (i) The plate load test immediately after sand pile installation and (ii) The plate load test one year after sand pile installation. To determine the load carrying capacity of a single sand pile slab, load testing was done. The bearing capacity of the single sand pile is 671.70kN/m2 for the deposit of 8.20 mm.
The field test result shows that the load bearing capacity of the single sand pile is 671.70 kN/m2 which is about 2.0 times less than that of natural soil. The bearing capacity of the single sand pile is 671.70kN/m2 for the settlement of 7.00 mm. The settlement profile of the single sand pile reinforced soil is shown in Fig 5.2 for the verification of load intensity.
The field test result shows that the load-bearing capacity of the single sand pile is 671.70 kN/m2 which is about 2.50 times less than that of natural soil. The slab load test on the sand pile immediately, i.e. one month after the installation of the sand pile. The result shows that the installation of crushed piles significantly increased the bearing capacity of the natural soil regardless of the materials.
The weight test of the slab showed that the bearing capacity of the improved terrain increased significantly due to the installation of granular piles. Taking into account the above values, the final bearing capacity of the sand pile is calculated as qUI1=134.63kN/m. The results show that the bearing capacity of the normal terrain increased significantly with the installation of granular piles.
The field investigation on the improved soil by plate load test revealed that the granulated piles significantly improved the bearing capacity of the natural soil. Standard Penetration Test (SPT) results also show that the significant improvement of the soil along the depth can be achieved as a result of the installation of granular piles.
