The IS 2720 Part 21 (1977) lays down the standardized laboratory procedure for quantifying the total soluble solids in soil samples. This test is vital for geotechnical and civil engineers to evaluate soil quality by measuring soluble salts that influence soil characteristics and construction suitability. The code prescribes detailed steps including sample preparation, extraction, filtration, and residue measurement via gravimetric and conductimetric methods to ensure accurate and consistent soil analysis.
Overview
The IS 2720 Part 21 (1977) lays down the standardized laboratory procedure for quantifying the total soluble solids in soil samples. This test is vital for geotechnical and civil engineers to evaluate soil quality by measuring soluble salts that influence soil characteristics and construction suitability. The code prescribes detailed steps including sample preparation, extraction, filtration, and residue measurement via gravimetric and conductimetric methods to ensure accurate and consistent soil analysis.
Audience
Contents
Structure
This section defines the scope of determining total soluble solids in soil samples through a conductimetric and gravimetric approach. It outlines the procedures for sample preparation, filtration, residue drying, and calculation of soluble solids percentage, emphasizing the use of 50 ml filtrate and oven-dried soil mass. Included are notes on repeating tests for soils with solubility exceeding 2% and recommendations for accuracy using conductivity meters.
Details the essential instruments and materials needed for testing, such as porcelain or glass dishes for drying residues, conductivity meters or bridges for conductimetric measurements, ovens for drying soil, balances with specified precision, distilled water for extraction, and filtration materials. It also presents the key formula for calculating soluble solids percentage and provides operational flowcharts for the process.
Describes the method for collecting representative soil samples passing through a 2 mm sieve, oven drying at 105–110°C, and preparing approximately 10 g of soil for testing. The extraction involves shaking with distilled water, settling, and filtering using Whatman No. 42 filter paper. Emphasizes clarity of filtrate for precise residue determination and includes procedural diagrams.
Provides step-by-step instructions for conducting the test, including maintaining records using the prescribed proforma, preparing filtrate, drying residue, weighing, and calculating total soluble solids percentage. It highlights the importance of repeating the test when solubility exceeds 2%, and includes illustrative flow diagrams to support the process.
Focuses on the use and calibration of conductivity meters or bridges, specifying measurement ranges, accuracy requirements, and calibration with saturated calcium sulphate solution. Explains the calculation of specific conductivity using the cell constant and conductance, and guides on recording results as per standard protocols to ensure consistency.
Elaborates on the gravimetric approach where 50 ml of filtrate is evaporated and dried to obtain residue weight, used to calculate the percentage of soluble solids relative to the original soil sample. Also discusses the subsidiary conductimetric method as a quick qualitative assessment, with a table interpreting conductivity values in relation to soluble solids content.
Specifies the format and precision for presenting results, recommending reporting to the nearest 0.01% by weight of oven-dried soil. Includes the required proforma for data recording and interpretation of conductivity readings, with instructions on repeating tests for samples exceeding 2% solubility.
Covers the sensitivity requirements for physical and chemical balances, use of standard filter paper for filtration, and adherence to proforma for observation recording. Discusses rounding conventions and statistical considerations for precision, backed by equipment specifications and procedural flowcharts.
Summarizes important formulae and procedural notes, emphasizing the necessity to repeat tests when soluble solids exceed 2%. Reinforces the importance of careful recording, use of 50 ml filtrate, and adherence to standard procedures for reliable and comparable results.
Provides a detailed proforma for documenting all relevant parameters such as sample number, masses, filtrate volume, dish details, residue weight, and calculated soluble solids percentage. Includes conductivity interpretation guidelines and notes on test repetition for high solubility samples.
Clarifies the protocol for repeating the test when the soluble solids percentage exceeds 2%, specifying use of 50 ml distilled water, maintaining sample mass consistency, and following the same calculation and recording methods to ensure result accuracy and reliability.
Frequently Asked
The procedure involves taking approximately 10 grams of oven-dried soil, mixing it with distilled water, and stirring intermittently, either manually or mechanically, to create a suspension. After allowing the suspension to settle for about 30 minutes, the clear supernatant liquid is carefully decanted. Then, 50 ml of this filtrate is taken in a pre-weighed dish, evaporated by gentle heating, dried at 110°C until constant weight is reached, cooled in a desiccator, and weighed. The percentage of total soluble solids is then calculated based on the residue weight and original soil mass.
For the gravimetric method, essential equipment includes an evaporating dish or crucible, a precision balance, filtration apparatus, a drying oven, and a desiccator. For the conductimetric method, a conductivity meter or bridge along with standard calibration solutions, beakers, and stirring rods are required. These instruments ensure accurate quantification or rapid estimation of soluble solids affecting soil properties.
Conductivity readings are compared against standardized ranges: values below 1 millimho/cm indicate normal soluble solids content; 1 to 2 millimhos/cm suggest fairly good levels; 2 to 3 millimhos/cm denote high soluble solids; and readings above 3 millimhos/cm indicate very high soluble solids. Higher conductivity correlates with increased soluble salts in the soil, providing a quick qualitative assessment relative to the gravimetric method.
When soluble solids content surpasses 2%, it indicates a high concentration of soluble salts that may impact soil performance. It is advised to confirm these results using the gravimetric method by evaporating 50 ml of filtrate and calculating the residue percentage. Subsequently, assess the suitability of the soil for construction purposes; if deemed unsuitable, consider soil treatment or replacement. Further geotechnical investigations may be needed to understand the effects on soil behavior.
The calculation involves taking 50 ml of clear soil filtrate, evaporating the water to dryness in a pre-weighed dish, drying the residue at 110°C, cooling it in a desiccator, and weighing the residue. The percentage of total soluble solids is then computed by dividing the residue weight by the oven-dried soil sample weight and multiplying by 100. This gravimetric method provides an accurate quantification of soluble solids present.
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