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Publication Number: FHWA-RD-07-052
Date: September 2007

Long Term Pavement Performance Project Laboratory Materials Testing and Handling Guide

Protocol P54
Test Method for Unconfined Compressive Strengthof Subgrade Soils

This protocol describes the test method for determining the unconfined compressive strength of cohesive subgrade soil samples. This protocol is based on AASHTO T208-90 (Unconfined Compressive Strength of Cohesive Soil). The test shall be performed in accordance with this standard (AASHTO T208-90), as modified herein. Those sections of the AASHTO standard included in this protocol by reference and without modification shall be strictly followed. All other sections of this protocol shall be followed as herein written.

The referenced test method shall be performed on a representative subgrade sample obtained from one of the thin-walled tube samples obtained at designated A-Type sampling locations.

1. SCOPE

1.1 This test method covers the determination of the unconfined compressive strength of soils in the undisturbed condition using the strain-controlled application of the axial load.

2. REFERENCED DOCUMENTS

2.3 LTPP Protocols
P49 Determination of the Natural Moisture Content
P56 Unit Weight of Subgrade Soils

4. SIGNIFICANCE AND USE

4.3 Delete

6. PREPARATION OF TEST SPECIMENS

6.1 Add: For LTPP SPS materials testing, 2.8-inch (71-mm) diameter samples shall be obtained from the thin-walled tube samples.

6.2 Delete the last two sentences of Section 6.2.

Add: Secure a representative sample of cuttings for use in determining the specimen's moisture content.

6.3 Delete

6.4 Delete

7. PROCEDURE

7.3 Record all required data on Form T54.

8. CALCULATIONS

8.2 Add: Calculate the cross-sectional area to two decimal places.

8.4 Add: For LTPP materials testing purposes include the graph of the stress-strain curve with Form T54.

8.5 Calculate the dry density of the specimen in accordance with LTPP Protocol P56.

9. REPORT

Record the following on Form T54:

9.1 Sample identification shall include: Laboratory Identification Code, Region, State, State Code, Experiment Number, SHRP ID, Field Set Number, Sampling Area Number, Layer Number and Location Number.

9.2 Test identification shall include: LTPP Test Designation, LTPP Protocol Number, Laboratory Test Number and Test Date.

9.3 Test Results

9.3.1 Specimen height, in inches, to two decimal places.

9.3.2 Specimen diameter, in inches, to two decimal places.

9.3.3 Average cross-sectional area, in square inches (in2), to two decimal places.

9.3.4 Length-to-diameter ratio (L/D) to one decimal place.

9.3.5 Moisture content, in percent, to one decimal place.

9.3.6 Dry density, in lb/ft3 (pcf), to the nearest whole number.

9.3.7 The unconfined compressive strength (qu) in lb/in2 (psi) to the nearest whole number.

9.3.8 The average strain at failure, as a percentage, to the nearest 0.1 percent.

9.3.9 The average rate of strain to failure, as a percentage per minute, to the nearest 0.1 percent.

9.4 Comments shall include: LTPP standard comment code(s), as shown in Section 4.3 of the LTPP Laboratory Material Testing Guide, and any other note as needed.

LTPP LABORATORY MATERIAL HANDLING AND TESTING
LABORATORY MATERIAL TEST DATA

UNCONFINED COMPRESSIVE STRENGTH OF SUBGRADE SOIL

LAB DATA SHEET T54
SUBGRADE SOILS

LTPP TEST DESIGNATION SS10/LTPP PROTOCOL P54

LABORATORY PERFORMING TEST:______________________________________________________________

LABORATORY IDENTIFICATION CODE:__ __ __ __

REGION _________________ STATE ___________________ STATE CODE __ __

EXPERIMENT NO _____ SHRP ID __ __ __ __

SAMPLED BY: ______________________________________________ FIELD SET NO. __

DATE SAMPLED: __ __-__ __-__ __ __ __ SAMPLING AREA NO.: SA-______

1. LAYER NUMBER ______

2. LABORATORY TEST NUMBER __

3. LOCATION NUMBER __ __ __

4. LTPP SAMPLE NUMBER __ __ __ __

5. TEST RESULTS

  1. SPECIMEN HEIGHT, inches __ __.__ __
  2. SPECIMEN DIAMETER, inches __ __.__ __
  3. AVERAGE CROSS-SECTIONAL AREA, in2 __ __.__ __
  4. MOISTURE CONTENT, % __ __.__
  5. DRY DENSITY, pcf __ __ __.
  6. UNCONFINED COMPRESSED STRENGTH (qu), psi __ __ __.
  7. LENGTH-TO-DIAMETER RATIO (L/D) __.__
  8. AVERAGE STRAIN AT FAILURE, % __ __.__
  9. AVERAGE RATE OF STRAIN TO FAILURE, %/min __.__

6. COMMENTS

  1. CODE __ __ __ __ __ __
    __ __ __ __ __ __
  2. (b) NOTE ________________

7. TEST DATE __ __-__ __-__ __ __ __

GENERAL REMARKS:___________________________________________________________________________
SUBMITTED BY, DATECHECKED AND APPROVED, DATE
____________________________________________________________
LABORATORY CHIEF
Affiliation______________________
Affiliation______________________

 

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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