This standard outlines the procedures for using field instrumentation to gauge swelling pressure in expansive soils, essential for designing foundations of light constructions like single or double-story buildings. It details the setup, installation, and measurement methods needed to accurately evaluate soil swelling pressures on-site, aiding engineers in foundation stability and risk reduction.
Overview
This standard outlines the procedures for using field instrumentation to gauge swelling pressure in expansive soils, essential for designing foundations of light constructions like single or double-story buildings. It details the setup, installation, and measurement methods needed to accurately evaluate soil swelling pressures on-site, aiding engineers in foundation stability and risk reduction.
Audience
Contents
Structure
This section defines the application range for field instrumentation to measure swelling pressure in expansive soils, focusing on foundation design for lightweight structures such as single- or double-storey buildings. It specifies the SI units employed and details rounding rules for test data, alongside maintenance recommendations for dial gauges to ensure precise measurements.
Key references related to the standard are presented alongside the SI units used for measurements. Instructions for proper care of dial gauges are reinforced here, including cleaning and dust protection, to maintain the reliability of swelling pressure readings.
This section describes the construction and specifications of essential equipment such as the rigid plate, chamber assembly, proving ring with dial gauge, guide frames, and augers. Detailed dimensions and material requirements are outlined to ensure the apparatus functions correctly in field conditions.
Guidelines for excavating the test pit and preparing the borehole are provided here, including dimensions, leveling techniques, and use of augers to maintain verticality. The importance of cleaning and leveling the borehole base before installation of the test assembly is emphasized.
Instructions for installing the rigid plate and chamber assembly into the borehole are detailed, covering steps such as positioning, vertical alignment, encasing the central pipe, and securing the reaction beam. The components required to apply initial pressure and measure swelling are also discussed.
This part outlines the procedure for conducting swelling pressure tests, including applying initial pressures, filling the pit with water, zeroing instruments, and recording readings of load and displacement over time. Tables and formulas for calculating stress and heave are included.
Essential precautions for maintaining dial gauges and other instruments are covered here, such as daily cleaning with a hairbrush and dust protection using polythene covers. Proper handling to prevent damage and ensure measurement accuracy is stressed.
Recommendations for regular maintenance and calibration of instruments are provided to guarantee consistent accuracy. Reference to relevant IS codes for calibration standards is included, along with instructions on rounding off test results in accordance with standard practices.
This section focuses on interpreting swelling pressure data, providing guidance on unit consistency, data validation, rounding rules, and documentation. The importance of thorough reporting for engineering assessments is underscored.
Frequently Asked
IS 11550 specifies a setup featuring a rigid circular plate approximately 15 mm thick and 11.2 cm in diameter, equipped with a centrally welded socket of 20 mm internal diameter and 40 mm height. A galvanized iron pipe (20 mm outside diameter) is attached vertically to this socket. This assembly is housed within a galvanized iron chamber 4 mm thick, allowing a 3 mm clearance around the plate, with a maximum height of 15 cm. The chamber is capped with a GI sheet top cover that has a socket allowing 2 mm clearance for the pipe. The entire assembly is lowered into a borehole where the plate rests on its base, with the central pipe encased by a 40 mm diameter pipe suspended using clamps to permit free movement. Initial pressure is applied through a proving ring and screw jack without exceeding the soil's overburden pressure. Finally, the pit is filled with water to ground level, and a dial gauge is fixed to measure the upward movement of the plate caused by soil swelling.
Before installing the test apparatus, IS 11550 recommends excavating a 1 m by 1 m pit to a depth of 0.25 m and ensuring the pit bottom is perfectly leveled. A borehole of 15 cm diameter is then drilled centrally using a spiral auger compliant with IS 10442. Verticality of the borehole is maintained using an auger boring guide as per IS 2720 Part 40. The borehole is extended to the desired depth with extension rods. All loose soil and debris must be removed from the borehole bottom, and the base should be leveled precisely using a plate bucket auger. This preparation ensures that the test assembly can be installed securely and measurements will be reliable.
The standard requires a proving ring coupled with a dial gauge to measure the force exerted by swelling soils, and a dial gauge mounted on a magnetic base for recording vertical displacement of the rigid plate. A spirit level ensures that the central pipe remains vertical during the test. A screw jack is used to apply initial pressure through the proving ring without exceeding the in-situ overburden stress. Additionally, a guide clamp and a reaction beam anchoring assembly stabilize the setup. The main components include the rigid plate and chamber assembly, central pipe, and galvanized iron encasing chamber, all designed to provide accurate readings of swelling pressure and associated soil movements.
Swelling pressure measurements must be recorded on a weekly basis over a period extending up to three months or until the readings from the proving ring stabilize, whichever occurs first. This protocol ensures that the swelling pressure data reflects steady-state soil behavior. The initial pressure applied should not exceed the overburden pressure at the borehole base. Regular monitoring facilitates accurate assessment of the swelling characteristics of expansive soils.
To uphold instrument precision during testing, IS 11550 recommends daily cleaning of dial gauges with a soft hair brush to remove dust and debris. Gauges should be loosely covered with polythene sheets to protect them from dust accumulation without trapping moisture. Maintaining the vertical alignment of observation rods is critical to prevent erroneous readings. Instruments must be handled carefully to avoid mechanical shocks or damage and calibrated periodically to retain accuracy. Proper storage in clean, dry environments when not in use also helps preserve instrument integrity.
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