|||||||||I|| US00509702A United States Patent (19) 11 Patent Number: 5,109,702 Charlie et al. 45) Date of Patent: . May 5, 1992 (54) METHOD FOR DETERMINING LIQUEFACTION POTENTIAL OF FOREIGN PATENT DOCUMENTS COHESIONLESS SOLS 124840 2/1986 U.S.S.R. .................................. 73/84 (75) Inventors: Wayne A. Charlie, Fort Collins, Primary Examiner-Robert Raevis Colo.; Leo W. Butler, Green Bay, Attorney, Agent, or Firm-Thomas C. Stover; Donald J. Wis. Singer (57) ABSTRACT 73) Assignee: The United States of America as A method for determining the liquefaction potential of represented by the Secretary of the cohesionless (granular) soils is provided in which a Air Force, Washington, D.C. rotational shear vane assembly having a plurality of radially disposed blades (herein a Piezovane) is (21) Appl. No.: 549,888 mounted to a shaft having a porewater pressure trans ducer mounted to such assembly and communicating to 22 Filed: Jun. 27, 1990 an outer edge of at least one the blades, with a torque (51) Int. C. ............................................... G01N3/00 transducer mounted to such shaft and a potentiometer 52 U.S. C. ........................................................ 73/84 connected to an upper portion of the shaft to measure Field of Search .................................... 73/784, 84 rotational displacement of such blades. The vane assem (58) bly blades are inserted into undisturbed soil and rotated (56) References Cited one or more turns to obtain porewater pressure re sponse measurements from the soil shear surface de U.S. PATENT DOCUMENTS fined by the blade ends along with torque and rotational 3,456,509 7/1969 Thordarson .......................... 73/406 displacement measurements. A porewater pressure in 3,561,259 2/1971 Barendse ... ... 73/84 crease indicates a contractive soil which has the poten 3,906,781 9/1975 Vlasblom .............................. 73/784 tial to liquefy (and cause landslides) while a porewater 4,408,481 10/1983 Sidey ....................................... 73/73 4,411,160 10/1983 Lutenegger et al. ................. 73/843 pressure decrease indicates a dilating soil which does 4,453,401 6/1984 Sidey ....................................... 73/73 not readily liquefy and is suitable for building thereon. 4,594,899 6/1986 Henke et al. .......................... 73/784 4,649,741 3/1987 Stron ...................................... 73/84 18 Claims, 4 Drawing Sheets U.S. Patent May 5, 1992 Sheet 1 of 4 5,109,702 FIG. 1 FIG. 2 U.S. Patent May 5, 1992 Sheet 2 of 4 5,109,702 56 45 FIG. 6 U.S. Patent May 5, 1992 Sheet 3 of 4 5,109,702 TEST 8 DISPLACEMENT VS SHEAR STRESS 1.1 CONTRACTIVE SAMPLE 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 O 2 4 6 8 10 12 14 16 18 20 22 24, 26 DISPLACEMENT cm) . FIG. 7 TEST 8 DISPLACEMENT VS VANE POREWATER 0.070 CONTRACTIVE SAMPLE 0.065 0.060 0.055 0.050 0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.00 0.005 Q999 -0.010Q995. - -0.015 O 2 4 6 8 1 0 1 2 4 16 18 20 22 24, 26 DISPLACEMENT cm) FIG. 8 U.S. Patent May 5, 1992 Sheet 4 of 4 5,109,702 TEST 4 DISPLACEMENT VS SHEAR STRESS 0.60 DILATING SAMPLE 0.55 0.50 O.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 -0.05 -0.10 -0.15 -0.20 -0.25 0 2 4 6 8 10 12 14, 16 18 20 22 24, 26 DISPLACEMENT cm) FIG. 9 TEST 4 DISPLACEMENT vs VANE PORWATER 0.045 DLATING SAMPLE 0.040 0.035 0.030 0.025 0.020 0.015 0.010 -0.005o lover -O.OO -0.015 0 2 4 6 8 to 12 14 16 18 20 22 24 26 DISPLACEMENT cm) FIG. 10 5,109,702 1 2 caused by the advancement of the cone, influences the METHOD FOR DETERMINING LIQUEFACTION porewater pressure response. Seismic Wave Tests POTENTIAL OF COHES ONLESS SOILS (SWT) are based on an empirical correlation between the velocity of shear waves and the occurrence or STATEMENT OF GOVERNMENT INTEREST 5 nonoccurence of liquefaction. The invention described herein may be manufactured Samples of the above penetration tests are disclosed and used by or for the Government for governmental in e.g., in U.S. Pat. No. 4,453,401 to Sidey (1984) and purposes without the payment of any royalty thereon. U.S. Pat. No. 4,594,899 to Henkel et al. (1976), which disclosures are subject to the drawbacks noted above, BACKGROUND OF THE INVENTION 10 relative to the SPT approach and CPT approach. 1. Field of the Invention There have also been attempts to measure soil lique This invention relates to a method for determining faction potential by employing a shear vane test. In this liquefaction potential of soils, particularly a method for approach a vane assembly, having a plurality of angu determining liquefaction potential, in-situ of cohesion larly spaced blades, is mounted to a drilling shaft, with less soils. 15 torque sensors mounted either on the blades or the 2. Description of the Prior Art drilling shaft. The so-mounted vane assembly is low Soil liquefaction results from increases in soil porewa ered on the drilling shaft, into soil, rotated and torque ter pressure induced by transient or repeated ground measurements taken. Subsequently, mathematical cal motions. Porewater pressure increases may be induced culations based on the respective torque measurements, by earthquakes, explosions, impacts and ocean waves. 20 result in an approximation of soil shear strength. Soil liquefaction occurs in water-saturated, cohesionless In another example of the prior art, a laboratory vane soils and causes a loss of soil strength that may result in apparatus has been constructed wherein 4 blades at the settlement of buildings, landslides, the failure of right angles are mounted on a rotational shaft with an earth dams and pipelines, or other hazards. Liquefaction aperture cut through one of the vanes which communi of sands and silts has been reported in almost all large 25 cates with the interior of said shaft and to the upper earthquakes around the world. For example, an earth portion thereof and thence to a hypodermic needle, for quake in 1964 caused more than one billion dollars in registering changes in pore pressure at the edge of such damages in Niigata, Japan. The Great Alaskan Earth vane. The vane apparatus was lowered into a container quake in 1964 destroyed large sections of Valdez and of cohesionless soil such as silt or sand. The vane blades Anchorage, and failed more than 250 bridges. The San 30 were rotated in the sand to shear same and describe a Fernando, Calif., earthquake of 1971 resulted in the liquefaction induced failure of the Lower Van Norman cylinder having the same dimensions as the (outer edges Dam. Most of the damage that occurred during these of the) vane blades. The blades were rotated slowly and earthquakes was due to widespread soil liquefaction. porewater pressure fluctuations noted on the calibra For existing and planned structures, e.g., large mine 35 tions of the hypodermic needle. A number of tests were tailing impoundments, earth fill dams, nuclear power accordingly run in dense sand (dilative condition) and plants and offshore structures, the liquefaction tenden loose sand (contractive condition) and the porewater cies of a site should be studied so that preventative steps pressure noted. It was found that in the dense sand one can be taken where possible. would obtain negative porewater pressure readings and Prior methods for evaluating liquefaction potential 40 that in loose sand, one would obtain positive porewater follow two basic approaches, laboratory tests and in pressure readings. The conclusion of such studies was situ test procedures. The laboratory approach requires that torque readings were distorted in cohesionless soils undisturbed samples. At the present time, there is not a so as to indicate, in dense sand, an inflated stress reading method for obtaining undisturbed samples which does while in loose sand, a deflated or reduced stress reading not alter the in-situ void ratio, structure, or stress state 45 relative to shear strength was indicated. That is, the during removal. There are also questions on which study concluded that one could not use rotating vane laboratory test is more representative of actual field shear tests to obtain accurate shear strength calculations conditions. As for the other approach, four in-situ tests in cohesionless soil but only in cohesive soil such as are being used to determine liquefaction potential. clay. The study thus recommends against the use of a These are (1) the Standard Penetration Test (SPT), (2) 50 rotational vane apparatus for making shear strength the Cone Penetration Test (CPT), (3) The Piezocone related measurements in a cohesionless soil, see Wilson, Penetration Test (PCPT) and (4) Seismic Wave Tests N. E., 1963 "Laboratory Vane Shear Tests and The (SWT). Influence of Pore-Water Stresses," ASTM, Special Tech The Standard Penetration Test (SPT) approach is nical Publication, No. 361, pp. 377-388. For a related based on an empirical correlation between the number 55 article see ASTM D 2573, 1972, re-approved 1978, of blows and the occurrence or nonoccurrence of lique "Standard Test Method for Field Vane Shear in Cohe faction at sites subjected to past earthquakes. The SPT sive Soil,' 1987, Annual Book of ASTM Standards, Vol data is sensitive to technique and can vary by more than 04.08, Phila, Pa., pp. 424-427. 50% among reputable drillers. The Cone Penetration Such article covers the field vane test in soft saturated Test (CPT) has several advantages over the SPT, but cohesive soils with guide lines for conducting the test like the SPT test, empirical correlations between pene and also a formula for calculating shear strength of the tration resistance and liquefaction potential are used.