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Table of Contents Page 1.0 1.1 1.2 1.3 2.0 3.0 4.0 5.0 6.0 7.
1.0: Introduction 1.1: GeoGauge® Benefits The Humboldt GeoGauge® is a hand-portable instrument that provides a simple, rapid and precise means of measuring in-place two key engineering and mechanical properties of prepared soil and aggregate, lift stiffness and material modulus. Compaction Quality Control (QC) of subgrades, bases and pavements based on modulus or stiffness, as enabled by the GeoGauge, will reduce compaction costs by 30% and roadway maintenance by at least 50%.
1.2: How The GeoGauge Works ® The GeoGauge measures a material’s mechanical impedance at the surface of the ground. In other words, it measures the force imparted to the soil and the resulting surface deflection as a function of frequency. Stiffness, force over deflection, follows directly from the impedance. The GeoGauge imparts very small displacements to the ground (< 1.27 x 10-6 m or <.00005") at 25 steady state frequencies between 100 and 196 Hz.
Many current methods of measuring material modulus or lift stiffness in the field require large forces to produce a measurable deflection. The GeoGauge uses technology borrowed from the military to measure very small deflections, allowing much smaller loads. The GeoGauge does not measure the deflection resulting from the GeoGauge weight. Rather, the GeoGauge vibrates, producing small changes in force that produce small deflections.
The GeoGauge can be used in the QC of stabilized materials. The QC method can determine how soon a material can bear construction loads, determine the ultimate strength from measurements at the time of installation or assure structural uniformity of the material. Appendix 2 is a case study of such a QC method on a cement treated bases. Appendix 3 is a case study of use on a lime treated subgrade.
2.0: Button (KeyPad) Functions ON Turns on the gauge. When pushed, the GeoGauge goes through an electronics check, displays the present battery voltage and finally displays the value of the previous or last measurement made. The gauge is then ready to perform a new measurement. OFF Turns off the gauge. SHIFT To execute any of the four buttons with a blue background ( “ERASE”, “PRINT”, “TEST”, “UNIT”), you must first press the “SHIFT” button.
MEAS 8 Starts the actual stiffness measurement. The measurement will be completed in about 70 seconds. Pressing “SHIFT” and then “MEAS” will enter the Poisson’s Ratio value display. Each successive pressing of the “SHIFT” and then “MEAS” buttons will enter the time/date display. Press “SAVE” to save the new entry. START Begins the viewing or scrolling through the saved measurement data.
3.0: Technical Specifications Conforms to ASTM D6758 Soil Measurement Range From To Stiffness MN/m (klbf/in) 3 (17) MN/m (klbf/in) (399) Young's Modulus MPa (kpsi) 26.2 (3.8) MPa (kpsi) 610 (89) Measurement Precision (typ., Coefficient of Variation): < 10 % Depth of Measurement (from surface): 220 to 310 mm (9 to 12 in.
4.0: Display Messages StiF SENS OvLOAD 5d noiS Announces the measured value of stiffness (MN/m), (displayed in ID window). The measured value of stiffness is displayed simultaneously in the STIFFNESS window. Indicates that the current measurement was aborted due to the sensors being overloaded. The word "SENS" is displayed in the ID/TARGET window and the word "OvLOAD"is displayed in the STIFFNESS window.
OVFLO 0.00 11 Indicates that the database memory is full. No additional measurements may be taken. You need to download or erase before additional measurements are taken. Indicates that the last measurement was not accepted due to one of two reasons. One, that the sensors overloaded due to softness or extreme hardness (too much movement). Two, that six or more of the 25 total frequencies were unacceptable from low Signal to Noise Ratio.
51-Y Young’s modulus in SI value, MPa. (Mega Pascals) Eg-5 Stiffness in English value, klbf/in. (kilo pounds force per inch) Eg-Y Young’s modulus in English value, ksi or kpsi (kips per square in.
5.0: Get Acquainted With The GeoGauge ® Before using the GeoGauge to make measurements that matter, get acquainted with it. Get used to what it takes to make a precise measurement. Get acquainted with how the stiffness of prepared materials varies. Select a site that is representative of the material you will be measuring. Bases or subbases with high aggregate contents should be avoided for awhile until the technician gains some experience.
variability. Be prepared to question and understand what you are doing with all the measurements you make, not just the GeoGauge. Process control for material structures is new and will take different thinking to effectively implement it. 6.0: GeoGauge Seating A good GeoGauge measurement arises from good seating, the foot to surface contact. It cannot be emphasized enough that preparing the soil surface is key to good seating.
7.0: Sequence Of Operations For A GeoGauge Stiffness/Modulus Measurement Making Stiffness Measurements With The GeoGauge Per The Following Procedure Conforms To ASTM D6758 • Inspect The Condition Of The GeoGauge Prior To Testing 1) Is the foot clean and free of soil and other debris? 2) Is the rubber seal in good condition? • Turn On The GeoGauge (press “ON” button) 1) The self-test will be run (electronics functionality). 2) Ensure battery voltage is adequate (> 7.5 V).
3) GeoGauge will display, in sequence: • Signal to Noise ratio (SNR) in dB [The stiffer the material, the closer this value will be to 10, indicating that more than usual attention should be paid to seating.] • The standard deviation (5d) of all 25 frequency dependent stiffness measurements relative to the displayed (average) value of stiffness [This number will be small for soft materials ( ~ 1 MN/m) and larger for hard materials (~ 5 MN/m).
8.0: Transit - Carrying Case The transit case has both key lock and combination lock. The combination is set at factory “0-0-0”. To re-set the combination number: 1) Open the case. Looking at the back of the lock inside the case you will see a change lever. Move this change lever from the normal position to the middle of the lock in the way that it hooks behind the change notch. Move it sideways and then up.
9) Turn the #1 switch to off. Turn off the unit by pressing the “OFF” button. Replace the display panel back onto the unit and lightly tighten the screws. The GeoGauge is ready for operation. Note: The gauge exterior is not water proof or dust proof. Attempts were made to make the gauge as tight as reasonable. Do not expose the gauge to precipitation.
Appendix 1 Stiffness Based Compaction QC Method
CASE STUDY: Stiffness Based Compaction QC of a Granular Subgrade Minnesota DOT District 2 423 West Zeh St. Thief River Falls, MN 56721 Traditional subgrade compaction QC test methods do not evaluate in-place material strength or the structural uniformity of each lift as placed. Evaluating these two factors is essential if cost is to be held to a minimum while assuring the performance needed for the roadways intended function and projected life.
The Humboldt GeoGauge is a 10” diameter, 11” tall, 22 lb. electro-mechanical instrument that when placed on the surface of the ground evaluates the stiffness of the top 9” to 12” of material. It vibrates the ground over a range of discrete frequencies, applies force, measures the resulting deflection and displays the results in about a minute.
The level of material compliance with the specification and small variability in the quality of compaction was unprecedented in the experience of MnDOT District 2. The real-time nature of the stiffness QC tests forced the continuous attention of the contractor to compaction quality as was evident by the sectionby-section adjustments in roller patterns and watering.
Appendix 2 Stiffness Based QC Method Used On A Stabilized Base
CASE STUDY: Micro-Cracking A Cement Treated Roadway Base To Minimize Shrinkage Cracks Texas A&M University The Citites of Bryan & College Station, TX The Cities of La Quinta & Santa Rosa, CA CEMEX For decades, cement-amending a roadway base has been a way of employing economical local materials in place of imported, high cost aggregate. These bases have the strength and low water permeability to potentially out perform flexible aggregate bases.
The Humboldt GeoGauge is a 10” diameter, 11” tall, 22 lb. electro-mechanical instrument that when placed on the surface of the ground evaluates the stiffness of the top 9” to 12” of material. It vibrates the ground over a range of discrete frequencies, applies force, measures the resulting deflection and displays the results in about a minute.
During 2004, CEMEX, the second largest supplier of cement products in North America, began to promote the use of the micro-cracking construction method in southern California. This prompted the adoption and successful use of the Bryan, Texas specification by the Cities of La Quinta and Santa Rosa, California in 2005. As shown in the figures below, the QC test data is very similar to that achieved in Texas three years earlier.
Appendix 3 Stiffness Based QC Method Used On A Stabilized Subgrade
DATA ANALYSIS SUMMARY: PREPARED FOR: Lime Stabilized Subgrade Koch Performance Roads, Inc. 4111 East 37th Street North Wichita, Kasas 67220 Virginia Route 288 February, 2003 The following represents a effort by Koch Performance Roads to quantify the performance of approximately 50 miles of lime stabilized, silty clay, ~ 12” thick subgrade which was part of the Koch managed reconstruction of Virginia (VA) Route 288. As with similar jobs managed by Koch (e.g.
The modulus cure rates for the individual sections generally follow that of the average (see Figure 2).
Appendix 4 GeoGauge® Verifier Mass Guide
Humboldt GeoGauge Verifier Mass Guide ® For use with C series Humboldt GeoGauge Purpose To verify or check the operation of the C series Humboldt H-4140 GeoGauge by running a measurement on top of the Verifier Mass. It is not intended to calibrate the GeoGauge. Equipment Required H-4140.20 Verifier Mass Assembly (10 kg with installed rubber isolation mounts) Operation 1) Place the Verifier Mass Assembly on a relative flat and rigid surface. The surface at this location should be approximately level.
10) Normally, five (5) measurements will be sufficient. Average the measurements for a result. Record all measurements and save the records for long term monitoring of GeoGauge operation. The values from each verifier measurement will oscillate up and down a small percentage and the average stiffness should be used to compare with the expected stiffness. It is not necessary to verify daily.
Appendix 5 GeoGauge Data Download Guide ®
Humboldt GeoGauge® Data Download Guide For use with C series Humboldt GeoGauge Purpose To download data from the C series Humboldt H-4140 GeoGauge to a PC. Equipment Required • H-4140.
Data Downloading 1) Repeat operations 1, 2 and 3 above. 2) Double click on the HyperTerminal icon selected earlier. 3) In the window that opens, Click “Transfer”. Click “Transfer Text”. Create a file for the data to be saved in. A new file name will have to be entered for each new download. A unique reference number and date are suggested. The file name must end with “.csv”. 4) Press the “Shift” key and then the “Print” key on the GeoGauge. Data should be seen streaming onto the screen immediately.
