Thesis entitled "Relationship between Penetration Resistance and Stability-Compactability Characteristics of Soil" submitted by Nandita Rani Shaha, Issue P), Session: October 2006, has been accepted as satisfactory in partial fulfillment of the requirement for the degree of Master of Science in Civil Engineering (Geotechnical) on March 18, 2013. Last but not least, the author thanks the patience and encouragement of her mother, two sons and her loving husband during M. The strength and compressibility properties of the soil were determined from soil collected using Modified Shelby Tubes.
Practicing engineers usually rely on SPT field test data and correlations of SPT-N values with various soil parameters. Therefore, it is necessary to know the correlations between the SPT-N value and the clay soil parameter so that the SPT-N value can be used for foundation design. A linear relationship between unconfined compressive strength and SPT-N value was found for all soils, soft or hard, with low or high plasticity.
Reliable linear relationship between natural moisture content and SPT-N value was found for all sites.
INTRODUCTION
- General
- Background of the Study
- Objectives of the Study
- Methodology
- Organization of the Thesis
The relationships should be such that the in situ soil strength can be predicted simply by using some readily available in-situ soil parameters such as SPT N value, water content, void ratio, relative density, shear strength , compression coefficient, etc. it is necessary to know the correlations between the SPT-N value and the clay soil parameter so that the SPT-N value can be used for soft clay foundation design with great confidence. Therefore, correlation between SPT-N value and clay shear strength made using those unreliable field data may lead to inaccurate correlation.
This study was formulated to establish reliable correlation between SPT-N value and shear strength and compressibility characteristics. A Split barrel sample was used for identification of soil and undisturbed samples of the same depth were used to conduct unconfined compression test, consolidation test, Atterberg Limit test etc. In the second phase, both types of undisturbed and disturbed samples were taken to geotechnical laboratory to conduct unconfined compression test and consolidation tests and other tests to determine soil properties.
In the third phase, from field and laboratory test data at different locations, the correlation between SPT and other soil parameters.
LITERATURE REVIEW
- Introduction
- Standard Penetration Test (SPT)
- Purpose of Standard Penetration Test
- Undisturbed Sampling in Bangladesh
- Standard Shelby Tubes
- Correlation between SPT N-value and Unconfined Compressive Strength This correlation developed to get the unconfined compressive strength directly from
- Empirical Correlations for Compression Index
- Concluding Remarks
The main purpose of the test is to determine the shear strength of the soil and the main reason for its widespread use is that it is simple and inexpensive. The length of the open shoe will be 25 to 50 mm. The outer diameter of the split barrel sample is 50.8 mm. Internal wall friction is one of the main causes of specimen disturbance (Hvorslev, 1949).
They found that Skempton's pore pressure parameter, A at maximum deviator stress, Ap significantly decreased as the area ratio increased and the values of Ap of the "tube" samples with different area ratios were negative. Compared to the Ap values of the “in-situ” samples, the pore pressure responses of the “tube” samples collected with varying area ratios are found to be significantly lower, resulting in significantly lower Ap values. Most of the above-mentioned studies studied the relationship between SPT-N value and other soil parameters.
Most of the time, drop height was not controlled during SPT and non-standard Shelby tubing was used.
TEST PROGRAM
- General
- Major Mistakes of SPT in Bangladesh
- Height of fall of SPT Hammer
- Thickness of SPT Spoon Cutting Shoe
- Instrumentation
- Auto Trip Hammer
- Specification of SPT Spoon
- Fabrication of Standard Shelby Tube
- Field Testing Program
- Laboratory Test
In the field, the drop height can be controlled by engaging the skilled labor, by marking and using nut on the top of the guide rod and also by using automatic release hammer. The two halves of the tube can be separated once the shoe and head are loosened to allow the sample to be removed. An SPT hammer system (as shown in Figure 3.5) consists of the hammer itself, the mechanism that lifts and drops the hammer (the anvil, stem and anvil or drive head), and the operator.
Common practice in performing SPT is to raise the hammer 762mm using a rope wrapped around a rotating pulley, then smartly throw the rope to separate from the pulley, allowing the hammer to fall onto an anvil attached to the top of the stem drill bit. To eliminate the variability of the energy transmitted to the hammer, which is raised by the rope and pulley technique, the automatic trigger. These systems were also found to not provide the theoretical free-fall energy to the drill rods, possibly due to energy losses associated with the anvil system at the top of the drill stem.
In most cases, driving shoes made of SPT are sharper than that specified in ASTM. In Figure 3.2, the running shoe of the SPT spoon is an angle of 16º to 24º, and the cutting edge is not too sharp, which gives an erroneous value of SPT. Usually used in cohesive soils, this sampler is inserted into the soil layer, generally 152.4 mm (6") less than the length of the pipe.
The vacuum created by the check valve and cohesion of the sample in the tube causes the sample to be retained when the tube is withdrawn. Most of the Shelby tube samples used in Bangladesh have high area ratio, very rough inner surface, irregular diameter and no specification for cutting edge. The soil was loosened and broken up by the water jets and the up-and-down movement of the chisel.
The soil particles between the rods and the side of the borehole were flushed to the surface through the annular space between the borehole and the borehole. For the determination of the consolidation parameters such as compression index (Cc), coefficient of consolidation (cv), one-dimensional consolidation tests were performed on undisturbed cohesive soil samples collected from four locations.
RESULTS AND DISCUSSION
General
Grain Size Distribution
Atterberg Limits
USCS Classification of Soil Samples
Relationship between SPT and Unconfined Compressive Strength
The combined relationship between SPT and Unconfined Compressive Strength for stiff clayey soil is shown in Figure 4.3. The result of SPT (N) and qu is shown in fig 4.4 at Sheikh Abu Naser Hospital (SANH), Khulna. The result of SPT (N) and qu is shown in Figure 4.5 at Atomic Medical Centre, Khulna.
According to ASTM D2435-96, one-dimensional consolidation tests were conducted to determine the compressibility properties of undisturbed soil samples collected at various depths in eight boreholes. A linear correlation is found between the compression index and the SPT-N value, with the compression index decreasing with increasing SPT-N value. Because the soft territory compression index data turned out to be scattered and unreliable, the combined graphs also became unreliable.
Therefore, the compression index compared to the SPT-N value for Bhulta site can only be considered for stiff clay soils. The observed compression index Cc of soil samples in Bhulta (Narayanganj) area ranges from 0.09 to 0.161.
Correlation between Compression Index and PI/N
Relationship between Liquidity Index and SPT N value
Initial Void Ratio vs SPT-N Value
Relationship between Dry Density and SPT
Correlation between Compression Index and Liquid Limit
Relationship between Compression Index and Plasticity Index
Initial Void Ratio vs Compression Index
Natural Moisture Content vs Compression Index
A linear correlation is found between the Natural Moisture Content and the Compression Index, where the Natural Moisture Content increases as the Compression Index increases. Similar graph is shown for AMC, Khulna in Figure 4.43 and for SANH, Khulna in Figure 4.44 where the connection is similar to Bhulta, Narayanganj location. Since the natural moisture content data of soft soil areas and hard soil areas were not distributed.
Therefore natural moisture content vs compression index for Bhulta and Khulna site can be considered for both stiff clay soil and soft soil. The observed natural moisture content, ωn of soil samples at Bhulta (Narayanganj) area varies from 18.2 % to 35.3.
Comparison of New Relation vs Previous Relations
Categorizing by liquid limit two types of correlation are found in this study which are shown below:. In this study, the plastic limit varies from 10 to 23 percent and the liquid limit varies from 17 to 57 percent. By comparing the new relationship between qu and N value with previous correlations performed by other authors, it is observed that correlation is not unique.
It is more or less similar to the other authors. 1976) introduced different correlations between the compression index and the initial void ratio for different soil types. This study finds the empirical relationship between the compression index and the initial void ratio, as shown in Figure 4.46, including previous research. It turns out that all empirical relationships, including the current study, follow more or less the same trend.
The combined result of the compression index Cc and natural moisture content wn is shown in Figure 4.45. So the correlation developed for compaction index and natural moisture content can be used for all soil categories. Some correlations are given by Terzaghi and Peak (1967) for compressibility index and liquid limit.
Similar correlations were found for compressibility index and liquid limit established by some other authors, including the present study in Figure 4.48. The linear correlations were developed for different types of soil which differ for stiff or soft soil. This correlation is different for different types of soil. 1975) tested some natural deep sea soil samples and correlates with compression index and plasticity index.
Cc = 0.007Ip- 0.015 Combination of Bhulta and Khulna; (Fig. 4.37) The relationship between compression index and plastic limit that was established by several authors including the present study is shown in Figure 4.49. The relationships that develop for soft and hard soil follow the same trend.
Concluding Remarks
The correlation developed for compression index and natural moisture content could be used for all categories of soil. The linear correlations were developed between compression index and liquid limit for different types of soil varying for stiff or soft soil. Compared to the other authors' correlations, similar type of linear relationships are found between compression index and plastic limit.
Liquidity Index vs SPT
Initial Void Ratio vs SPT
CONCLUSION
- General
- Conclusions
- Recommendations for Future Study
