Laboratory research shows that the compacted sandy soil with and without geotextile improves the bearing capacity of organic soils 1.5 times than untreated soils. This system improved the load-bearing capacity of a foundation more than twice that of an installation on untreated soil.
List of Tables
General
Soft soils create problems for the construction of massive structures such as buildings, roads and highways, railways, airfields, embankments, dams, storage tanks, parking lots and temporary work platforms due to the low shear strength and high compressibility. The outcome of the study can be used as a guideline for the selection of appropriate soil improvement method for the construction of safe and.
Background of this Study
In addition to the installation of granular columns in soft soil, the capacity of the column-improved soil can also be increased by placing a compacted granular fill with or without reinforcement, i.e. the total and differential settlement of the soft soil is significantly reduced due to the use of geosynthetic reinforced granular fill (Sliukla, S.K., 1995).
The Research Scheme
Improvement by compacted sand bed with inclusion of geotextile layer in connection with compacted sand column. To establish comparisons of the degree of improvement among the treated plots with respect to untreated soil based on the experimental results and predictions using the available empirical equations.
Organization of the Thesis
This chapter discusses the index and engineering properties of organic soil collected in the Khulna region, which was also used for the preparation of reconstituted organic soil. The fifth chapter describes comparisons of experimental findings with predicted values using available empirical equations applicable to the considered soil improvement conditions.
General
Soft Ground
- General properties of soft ground
- Geotechnical aspects of soft soils in Bangladesh
- The nature of organic soil
- The complexity of organic soil nature
In these floodplains, the process of soil formation dominates over sediment deposition, as evidenced by soil characteristics, i.e., the initial alluvial stratification has been separated from the biological mix; the subsoil has a developed structure and oxidized spots; and, in older soils, the topsoil has become acidic. Since there is a limit to the number of samples that can be taken, there is no guarantee that the soil parameters are truly representative of the field layers.
General Properties of Organic Soils
The weight of organic matter can be determined by heating the sample to ignite the organic matter. The presence of organic matter in soil is often overlooked, although it affects several important properties.
Preparation of Reconstituted Organic Ground
- Preparation of soil slurry
- Consolidation of Slurry
- Selection of Overburden Pressure
A 150 mm thick perforated RCC slab with geotextile was placed on top of the slurry so that the water could also flow upwards. Initially, the slurry was consolidated for about 24 hours due to its own weight and the weight of the porous RCC slab.
Ground Improvement Techniques
- Soil reinforcement
Current indications are that conventional sand drains installed to accelerate consolidation may soon become a thing of the past as a number of prefabricated drains come into widespread use. Chemical grouts have the advantages compared to specific grouts that they can penetrate into smaller pores, they have a better viscosity and there is better control over the setting time.
Method of Selection of Ground Improvement Technique
Foundation Practice on Soft Ground of Khulna Region
In the present study, the improvement of reconstituted organic soil collected at a selected location in Khulna region was improved with compacted sand column, compacted sand subgrade with and without geotextile, and additionally reinforced with compacted sand column.
Determination of Bearing Capacity by Established Method
- Terzaghi's bearing capacity equation
- Vesic's bearing capacity equation Use Hansen's equations above
A small difference: in the table above, the program BEARING.ExE can be displayed on diskette, depending on the computer used and whether or not it has a floating point.
MENEM MEN 00
Bearing capacity of footing on layered soils
Model tests show that when the top layer is very soft, it tends to. squeeze out from under the base and when stiff it tends to "punch" into the lower, softer layer. the ground can squeeze from underfoot. Include here the q contribution from d, and calculate q'uit for the bottom stratum using the base dimension B.
The Seilmeijer's bearing capacity method
Determination Bearing Capacity of Ground Treated by Granular Column
- Passive pressure condition
- Based on expansion of a cylinder
- Based on cavity expansion theory
- Ultimate capacity of stone column
- General shear failure
- Local shear failure
- Punching shear failure
- Factors affecting modes of failure
The stiffness index (Ir) is a function of the modulus of elasticity (E), Poisson's ratio (u), cohesion (c), angle of shear resistance (0) and effective mean normal stress (q) of the soil. The average shear resistance of the composite soil would be developed at the failure surface. Where D = diameter of the compacted stone column s = center-to-center distance between the stone columns.
Case Study
- Load distribution in improved clay by Leung and Tan
- Settlement response test by Juran
- Benefits due to the use of reinforcement by Rowe and Soderman
This experimental study demonstrates the significant influence of column drainage, soil consolidation, replacement factor and group effect on the settlement response of soft foundation soils reinforced by compacted sand columns. The consolidation and partial drainage of the soil during loading have an important effect on the load transfer mechanism and should be taken into account in the analysis/design procedure. Analysis of the loading tests indicates that elastic unit cell solutions provide a reasonable estimate of the strengthening effect on the settlement response of soft foundation soils.
Remarks
With geocell reinforcement, failure was not observed even at a settlement equal to approximately 45% of the footing width and a load eight times the ultimate bearing capacity of the unreinforced soil, while with planar reinforcement, failure occurred at a settlement of approximately 15% of the footing width and a load of approximately four times the ultimate bearing capacity of the unreinforced soil. For the case with randomly distributed reinforcing mesh, failure was recorded at a load of approximately 1.8 times the ultimate bearing capacity of the unreinforced soil and at a settlement of approximately 10% of the footing width (Dash et al., 2004).
CHAPTER THREE
STATEMENT OF THE PROBLEM AND LABORATORY INVESTIGATION
- General
- Statement of the Problem
- Work Plan
- Collection of Organic Soil for the Preparation of Reconstituted grounds
- Preservation of soil samples for the testing programme in the laboratory
- Storage of organic soil
- Properties of the Used Organic Soil and Sand
- Determination of physical properties
- Determination of index properties
- Determination of strength properties
- Preparation of Reconstituted Organic Grounds
- Preparation of reconstituted organic layer
- Placement of bottom sand layer
- Preparation of compacted sand bed over the reconstituted organic ground
- Installation of sand column in the reconstituted organic ground
- Summary of Test Grounds
Determination of physical, index and technical properties of collected organic soils used in the construction of reconstituted organic soils, using conventional laboratory test methods. The specific gravity of the collected and reconstituted organic soil was determined based on the Pycnometer method following the test standard ASTM D854. The strength properties of collected organic soil and sample of reconstituted organic soil were determined in the laboratory by performing unconfined compression test according to the test standard ASTM D2166.
WIsJD
Load
Compacted sand Column
Footing Load Test
- RCC footing and slab
- Hydraulic jack
- Dial gauge
In the experiment, a circular RCC base and an RCC plate were used to apply load to the test site. The foundation was poured in the laboratory with Portland cement and the ratio of the concrete mixture was 1:1.5:3. A hydraulic jack was used to apply preset pressure to the reconstituted organic slurry for the preparation of reconstituted soils and also to apply load to the foundation during the loading test.
1 ILI
Experimental set-up
Load-settlement test
The load intensity and settlement observation of the foundation test are plotted in the same way as shown in figure. IS recommends a log-log plot with two straight lines, the intersection of which is considered the yield point of the soil, as shown in figure. Where a load settlement curve does not indicate a marked breaking point, it can alternatively be assumed that failure corresponds to a settlement equal to the settlement of 25 mm, as shown in Figure 3.20 Determination of load capacity based on load intensity and settlement.
General
Load-settlement Results and Failure Pattern of Grounds
- Load-settlement behaviour and failure pattern of untreated grounds
- Load-settlement behaviour and failure patterns of treated grounds
Compacted sand column was used as an application of one of the four soil improvement conditions. The load-settlement curve of the soft soil improved by single compacted sand column showed no significant improvement. The geotextile sandwich compacted sand bed with compacted sand column not only reduces the excessive settlement but also brings uniformity in settlement under loading ie.
Evaluation of Bearing Capacity of Untreated and Treated Grounds
The ultimate net bearing capacity of the untreated soil was found to be 118 kPa by the settlement rate method. The contribution of sand and geotextile to the improvement of organic soils when used in compacted sand column and compacted sand bed are shown in Table 4.3. From the laboratory research it can be concluded that the sand provides strength effectively in the compacted sand bed and it is about 45% and the geotextile improves the bearing capacity of the organic soil about 22%.
General
- Bearing capacity of untreated grounds
- Bearing capacity of treated grounds
The bearing capacity equations proposed by Terzaghi (1943), Meyerliof (1963), Hansen (1970), Vesic (1973 and 1975) were used to determine the bearing capacity of reconstituted organic soils. Then, the bearing capacity of reconstituted organic soils treated with compacted sand bed with and without geotextile was determined by considering footing on layered soil. The bearing capacity of the treated plots was determined by considering the concept of layered soil and compacted sand column reinforcement.
Comparison of the Predicted and Measured Values of Bearing Capacity
Finally, reconstituted organic soils were treated with compacted sand bed with geotextile in conjunction with compacted sand column. The bearing capacity of reconstituted organic soil treated with compacted sand bed was determined by the layered soil equation, which was approx. 1.4 times than untreated soil. Finally, the reconstituted organic soil was treated with compacted sand bed with geotextile and compacted sand column.
4 CHAPTER SIX
CONCLUSIONS AND RECOMMENDATIONS
Conclusion
The results show that the soil improvement system, compacted sand bed with geotextile in conjunction with compacted sand column is more suitable for soft soil improvement considering the degree of improvement. Comparison of predicted and measured bearing capacity of improved footings reveals that the available empirical equations are adequate for predicting the bearing capacity of footings resting on sand column and footings treated with compacted sand bedding, but far over predict the same in the case of bases treated by compacted sand bed with geotextiles and compacted sand bed with geotextile in connection with the compacted sand column.
Limitations of the Study
The reconstituted organic soil can be improved by using a compacted sand base with two layers of geotextile to check the second soil improvement condition. Geotextile should be used on the bottom and top positions of the reconstituted organic soil as a good filter medium to prevent the possibility of sand clogging. A pore pressure transducer should be used to measure the pore pressure of the soil to the obtained soil with the same conditions in order to compare the corresponding behavior of the test soil.
Full load test of granular piles with different densities and different amounts of gravel and sand on soft Bangkok clay. The influence of Non-Woven Fabric Inclusions on the Sfress-Strain Behavior of a Soil Mass. Keynote Lecture, 4th International Conference on GeoFilters, Stellenbosch, South Africa, October, University of Witswatersrand, A.Fourie (Ed), ppl-63.
APPENDIX-A
APPENDIX-B
C-5: Bearing capacity of soil treated with a compacted sand base with geotextile and compacted sand base (G-5.1).
