Emerging Construction Technologies - Humboldt Soil Stiffness Gauge

Emerging Technologies outside Civil, Mechanical, and Electrical

Emerging Technologies Research Breakthroughts

Soil-Stiffness Gauge for Soil Compaction Control

The Need

Soil stiffness and modulus are the most meaningful engineering parameters for soil structures. Until now, there were no practical and reliable means to rapidly measure the in-situ soil stiffness and elastic modulus of soils. Soil density has always been a surrogate and empirical specification that has some shortcomings.The primary motivations are due to the need to find an alternative to nuclear density gauges, drastically reduce laboratory results time, and validate and implement mechanistic design models.

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Using Humboldt's Stiffness Gauge devices

The Technology

The Humboldt Stiffness Gauge (HSG) enables both the design and construction to be controlled by the same physical parameters, namely stiffness and modulus. Used as a compaction process control tool, it brings the contractor closer to the real purpose of compaction, which is to improve the stability of the soil over the life of the structure. The HSG's sensitivity and ability to rapidly take large amounts of data at a site enables site profiling for intelligent analysis.

Lightweight and ease of use overcomes the inconvenience and impracticalities of density based measurements and in-situ plate load tests. The Humboldt Stiffness Gauge was developed from land-mine detection technology to improve the control of compaction. The gauge consists of four main parts: ring foot, shaker and sensors, microprocessor, and body. The ring foot couples the force into the soil and provides feedback to the sensors for accurate measurement of force and displacement. The shaker drives the ring foot from 100 to 200 HZ and the sensors measure the impedance (force and resulting surface velocity vs. time). The microprocessor computes the stiffness (force over displacement) at each of the 25 different frequencies and then displays the average of the 25 measurements. The body provides the protective housing as well as the reaction mass to couple the ring foot to the soil. The entire measurement process takes about one minute.

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The soil stiffness gauge

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Soil stiffness gauge principle

The Benefits

Validation of mechanistic design models.

Compaction process control via modulus.

Non-nuclear measurement of soil density.

Directly connects design and construction via stiffness and modulus.

Rapid soil characteristic.

Basis for performance specification.

Characterization and control of stabilized soil.

Simple to use, minimum training, no license or special handling required.

Status

The Humboldt Stiffness Gauge has recently been evaluated in one of the largest broad-based evaluation program for a single soil measurement device. Over twelve separate groups consisting of state DOTs, academic researchers, and private laboratories have participated in the program. The gauge is in use worldwide.

Construction Innovation Forum honored the Humboldt as one of the winners of 1999 Nova Award.

Barriers

Density based measurements are so ingrained in the construction industry that the most powerful tool, education, is being used to create the awareness of the benefits of stiffness and modulus. Nearly all measurements require ASTM or AASHTO standards. The ASTM standard covering the use of Humboldt Stiffness Gauge is currently being developed.

Points of Contact

Scott Fiedler, Product Manager, Humboldt Mfg. Co., 7300 West Agatite Avenue, Norridge, IL 60656 Phone: (800)544-7220 X 231, Fax: (708)456-5412.
Mel Main, Main Associates, 16 Vegas Drive, Hanover, PA 17331, Phone & Fax: (717) 637-8246.

References

1999 Nova Award Nominations, The Nova Award, Construction Innovation Forum Inc.
The Humboldt Stiffness Gauge: A Field Instrument for Acoustically Measuring Soil Stiffness, Humboldt Mfg. Co., 1998.
Recommendations for Making a "Good" Measurement with The Humboldt Stiffness Gauge, Humboldt Mfg. Co., 1998.

Disclaimer Statement

Neither the Construction Industry Institute nor Purdue University in any way endorses this technology or represents that the information presented can be relied upon without further investigation.

AN,JW