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1、1AS 1289.6.4.21998 Australian Standard Methods of testing soils for engineering purposes Method 6.4.2: Soil strength and consolidation testsDetermination of compressive strength of a soilCompressive strength of a saturated specimen tested in undrained triaxial compression with measurement of pore wa
2、ter pressure 1SCOPEThis method describes a basic test procedure applicable to cohesive soils and sets out a method for determining the compressive strength of a specimen of soil in a triaxial compression apparatus under conditions in which the cell pressure is maintained constant. There is no change
3、 in the total water content of the specimen during shearing and the pore pressure is monitored throughout the test (see Notes 1 and 2). The procedure is applicable only to fully saturated soils meeting the requirements stated herein. The test described is limited to specimens in the form of right cy
4、linders of height not less than twice, and not more than 2.5 times, the diameter of the cylinder (see Note 3). The shearing stage of the triaxial test in which an axial compressive load is applied to the specimen at a constant rate may be preceded by a saturation stage to bring the specimen to an ef
5、fectively fully saturated state or a dissipation stage, or both, where the specimen is allowed to consolidate under constant total stress conditions (see Note 4). Cohesionless materials may be tested by triaxial methods; however, special techniques are required for the specimen preparation, for whic
6、h information can be obtained from the reference sources (see Note 4). The specific conditions of any test procedure are defined by a geotechnical engineer who ensures the test method is appropriate for the data required. 2REFERENCEDDOCUMENTThefollowingdocumentisreferredtointhis Standard: AS 1289Met
7、hods of testing soils for engineering purposes 1289.2.1.1Method 2.1.1: Soil moisture content testsDetermination of the moisture content of a soilOven drying method (standard method) 3APPARATUSThe following apparatus is required and shall be operated in a room in which the temperature is maintained a
8、t a constant level 2C: (a)A triaxial test cell of dimensions appropriate to the size of the specimen, suitable for use with the selected fluid at the highest test pressure, and provided with a means of applying additional axial compressive load to the specimen through a loading ram. COPYRIGHT Access
9、ed by TAFE QUEENSLAND INSTITUTES on 19 Dec 2007 AS 1289.6.4.219982 The cell shall include a pedestal end cap of the same diameter as the test specimen. The vertical stress due to the mass of top cap shall not exceed 1% of the maximum principal stress difference. The upper end cap shall have a centra
10、l seating which will not transmit moment (a ball and cone assembly is suitable) to receive the loading ram. Both pedestal and top cap shall include porous plates to be in contact with the specimen. The porous plates shall be made of silicon carbide, aluminium oxide, sintered bronze or other material
11、s which are not attacked by soil or soil moisture. The plates shall be sufficiently rigid to withstand the pressures applied without changes in physical properties. The plates shall be sufficiently fine so that soil will not extrude into the pores, but shall be sufficiently coarse so as to have a pe
12、rmeability appreciably greater than the soil sample. A filter paper disc may be placed between the soil specimen and the porous plate. The end caps shall be capable of hydraulic connection outside the cell to pressure and drainage systems. The hydraulic line from one end plate shall be capable of be
13、ing connected to a pore pressure measurement system and closed off beyond the pore pressure measurement take-off (see Note 5). (b)Apparatus for applying, maintaining and measuring the desired pressure in the fluid within the cell to an accuracy of 5 kPa or to 1% of the applied pressure, whichever is
14、 the greater. (c)A machine capable of applying axial compression to the specimen at convenient speeds. A speed of application in the range 0.0005 mm to 5 mm per min is normally satisfactory. The machine shall be capable of applying an axial deformation of approximately one-third of the height of the
15、 specimen. (d)Apparatus for measuring the additional axial load on the specimen to an accuracy of 5 kPa in the deviator stress or 1% of the applied load, whichever is the greater. (e)Apparatus for measuring the axial deformation of the specimen to 0.02 mm, e.g. dial gauge or other device together wi
16、th an adjustable reference point attached to the cell. (f)Apparatus for measuring the pore pressure in the specimen with an accuracy not greater than 1% of the measured value. The volume change (V) in the pore pressure measuring system shall be not more than that given by the following equation: . .
17、 . 3(1) V V.u 0.5 10 6, in m2/kN where V = volume of the specimen, in cubic metres u = pore pressure, in kilopascals Where the system exceeds this value, a compensation system shall be employed. (g)Apparatus for applying back pressure to the specimen (where saturation of the specimen is necessary) t
18、o an accuracy of 5 kPa or 1%, whichever is greater. The control of this pressure shall be separate from the cell pressure (see Note 6). (h)Seamless rubber membrane in the form of a tube, open at both ends, of internal diameter equal to the specimen diameter and of length approximately 50 mm greater
19、than the height of the specimen. The membrane thickness should be selected having regard to the size, strength and nature of the soil to be tested. A thickness of 0.1 mm to 0.4 mm is normally satisfactory. (i)Membrane stretcher to suit the size of the specimen. COPYRIGHT Accessed by TAFE QUEENSLAND
20、INSTITUTES on 19 Dec 2007 3AS 1289.6.4.21998 (j)Rubber rings of circular cross-section and internal diameter slightly smaller than the diameter of the end caps. (k)Laboratory sampling tubes or a soil lathe, as required, for preparing test specimens of the required diameter directly from a block samp
21、le in the laboratory. Each tube shall have a sharp cutting edge at the inner surface. (l)Sample extruder. (m)Trimming device, e.g. split mould or mitre box and wire saw for obtaining plane ends normal to the axis of cylindrical specimens. (n)Mould or formers and auxiliary apparatus, for preparing re
22、moulded specimens. (o)Apparatus for the determination of moisture content as described in AS 1289.2.1.1. (p)A balance of appropriate capacity and a limit of performance not exceeding 0.2% of the mass of the wet specimen. 4PREPARATION OF SPECIMENSThe preparation of specimens shall be as follows: (a)O
23、btain from a sample a subsample of the desired diameter in one of the following ways, as appropriate (see Note 7): (i)From a thin-walled sample tube, extrude a sufficient length to provide a test specimen of the required dimensions. (ii)From a block sample, trim a soil cylinder of sufficient length
24、to provide a test specimen of the required dimensions. (iii)From a disturbed sample, compact a specimen to the desired moisture/density condition in the mould or former. (b)Place the subsample obtained by Step (a)(i) or Step (a)(ii), in the trimming device and prepare the ends, plane and parallel, t
25、o provide a test specimen of the required length. For a subsample obtained by Step (a)(iii), trim the ends before removing from the mould or former. 5PREPARATIONFORTESTSThepreparationfortestsshallbeasfollows (see Note 8): (a)Measure and record the length, the diameter and the mass of the sample to a
26、n accuracy that will enable the bulk density to be calculated to an accuracy of 1%. (b)Saturate the porous discs by boiling or vacuum impregnation. Place the porous discs above and below the specimen. Ensure that all lines connecting are filled with de-aired water (see Note 9). (c)Place the specimen
27、 on the pedestal and put the other end cap on top of the specimen. Using the membrane stretcher, place the rubber membrane around the specimen and seal the membrane to the pedestal and end cap by means of rubber rings. Where back pressure saturation or consolidation is to form part of the test, conn
28、ect a line from the upper porous disc to the cell base or other exit point. (d)Assemble the cell with the loading ram initially clear of the top cap of the specimen and place the cell containing the specimen in the loading machine. (e)Connectallremainingpressurecontrolandpressuremeasurementlinesto a
29、ppropriate apparatus, taking care to exclude air. The drainage or water supply to the specimen shall be at the opposite end to that connected to the pore pressure measurement apparatus during saturation or consolidation. COPYRIGHT Accessed by TAFE QUEENSLAND INSTITUTES on 19 Dec 2007 AS 1289.6.4.219
30、984 6BACK PRESSURE SATURATIONWhere it is required that the specimen shall be back pressure saturated to ensure near total saturation, the following procedure shall be adopted: (a)Initially apply a cell pressure up to about half the desired effective stress but in no circumstances higher than the fin
31、al proposed effective stress for the test. (b)Simultaneously apply a pressure increment of about 50 kPa to both the cell pressure and the back pressure systems. Monitor the pore pressure in the specimen at the opposite end to which the back pressure is applied. Apply a second equal increment to both
32、 systems when the measured pore pressure and back pressure are equal. The original difference in cell and back pressure has to be maintained throughout this stage (see Note 6). Continue with the above procedure applying the cell and back pressures in increments of about 50 kPa up to 200 kPa, then 10
33、0 kPa increments up to 500 kPa, then in one step to required back pressure (see Note 10). (c)On achieving an appropriate stable back pressure, the effectiveness of the saturation process shall be checked by closing off all drainage, increasing the cell pressure by a small amount, c, and measuring th
34、e consequent change in the pore pressure, u. The effective stress on the specimen during this stage shall not exceed that which is to be applied during the shearing stage. The resultant of u/cshould be not less than 0.95. Where u/cis less than 0.95, continue to increase the pressure in the cell and
35、back pressure systems in the sequence given in Step (b), maintaining the original value of excess cell pressure until u/cis 0.95 (see Note 11). 7PORE PRESSURE DISSIPATIONThe procedure for dissipation of excess pore pressure shall be as follows: (a)Where required, the excess pore pressure shall be al
36、lowed to dissipate to achieve the effective stress designated for the test. After back pressure saturation the designated test effective stress may be reached through either increasing the cell pressure or decreasing the back pressure (see Note 12). (b)The specimen may be allowed to consolidate by d
37、rainage through the porous disc at both ends of the specimen. Where the rate of dissipation of excess pore pressure is required to calculate a straining rate then the pore pressure shall be monitored by closing the drainage valve at the cap where the pore pressure measuring apparatus is connected (s
38、ee Note 13). NOTE: Appendix A gives a method of calculating the straining rate required for pore pressure equalization in saturated specimens. 8STRAINING RATEThe straining rate at which the axial force is applied to the specimen shall be sufficiently slow to enable full pore pressure equalization wi
39、thin the specimen at the time of failure. The required straining rate to ensure pore pressure equalization throughout the specimen may be obtained by calculation based on a knowledge of the coefficient of consolidation of the soil. NOTE: A method of calculating the appropriate straining rate is give
40、n in Appendix A (see Note 14). COPYRIGHT Accessed by TAFE QUEENSLAND INSTITUTES on 19 Dec 2007 5AS 1289.6.4.21998 9SHEARINGThe procedure for shearing shall be as follows: (a)Adjust the loading machine straining rate to that required by previous calculation in Clause 8. Check that cell and back press
41、ure required to give designated effective stress for the test are applied. (b)After allowing all excess pore pressure to dissipate to achieve the required effective stress, close all drainage outlets from the specimen, allowing only for pore pressure measurement. (c)Record the initial gauge readings
42、 then commence straining. Take a sufficient number of simultaneous readings of the gauges to define the stress/strain curve (see Note 15). (d)Continue the test until the required failure criteria has been reached (see Notes 16 and 17). (e)Reduce the cell pressure to zero, extract the specimen, and r
43、ecord the mode of failure (see Note 18). (f)Break open the specimen and take samples for the determination of moisture content in accordance with AS 1289.2.1.1 (see Note 19). Examine and record the nature of layers, stones, calcareous matter and other physical features. 10CALCULATIONSCalculations sh
44、all be made as follows: (a)Calculate the cross-sectional area (A) of the specimen, for each recorded point of thetestontheassumptionthatthespecimendeformsasarightcylinder (see Note 20). This area at any strain is given by the following equation: . . . 10(1)A Ao 1 where A= the cross-sectional area of
45、 the specimen for each recorded point of the test, in square millimetres Ao= initial cross-sectional area of the specimen, in square millimetres = LoL Lo where Lo= initial length of the specimen, in millimetres L= length of the specimen at the stage of the test at which the area (A) is to be determi
46、ned, in millimetres. (b)Calculate the effective stresses at failure (see Note 21 and 22) from the following equations: 1=. . . 10(2)106. Pf As + 3 uf and 3= 3 uf. . . 10(3) where 1= effective axial stress, in kilopascals 3= effective lateral stress, in kilopascals Pf= axial force at failure, in kilo
47、newtons As= specimen cross-sectional area at failure, in square millimetres uf= pore pressure at failure, in kilopascals 3= lateral stress, in kilopascals. COPYRIGHT Accessed by TAFE QUEENSLAND INSTITUTES on 19 Dec 2007 AS 1289.6.4.219986 11TEST REPORT 11.1Results and general informationThe followin
48、g results and general information shall be reported (see Note 23): (a)The value of the maximum effective principal stresses and the pore pressure at failure, in kilopascals. Where the results are obtained from multistage testing, this shall be stated along with the failure criteria adopted to conclu
49、de each stage of testing. (b)The axial straining rate(s) and the strain(s) at failure. (c)Dimensions of each test specimen, in millimetres, to the nearest millimetre. (d)Dry density, in tonnes per cubic metre, to the nearest 0.1. (e)Specimen moisture contents, initial and final, in accordance with AS 1289.2.1.1. (f)Initial effective cell pressure, in kilopascals, to the nearest kilopascal. (g)Plot of the stress/strain curve of the test with the axial strain as the abscissa and the principal stress difference as the ordinate. (h)A description of