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Australia

A thłrd of all foundatlon investlgators perform other types of ponetratlon tesls (descrlbed later); however, Ihe proportion (2%) of foundatlon lnve8tlgation effort spent on these tests is very smali.

The conclusion that the state-of-lhe-art in drilling technlques has lmproved is further evidenced by the significant use of addltives in drilling mud to cope with difficult situations. such as artesian ground and marinę conditlons.

4. STANDARD PENETRATION TEST (S.P.T.)

The so-called “Standard" Penetratlon Test (S.P.T.) (FLETCHER, 1965. and Dlscusslons; IRELAND et al.. 1970. and Dlscusslons) Is the subject of one of the Australian Standard Methods of Testłng Soils for Englneerlng Purposes (STANDARDS ASSOCIATION OF AUSTRALIA. 1971). To add to the confusion, the Australian Standard method dlffers from those practised In other countrles such as the U.S.A. (ref: ASTM designation D1587-67), where the test originated.

4.1 Equłpment

All organisatlons use the standard weight and fali of hammer. Flve organisatlons use non-standard size spllt-barrel samplers. A serlously large percentage (40%) use non-standard rods (ł.e.. rods with a stlffness outside the rangę of AW to NW drill rods). •

Over half (58%) of the S.P.T. users sometlmes replace the normal cuttlng shoe wlth a solid cone point, malnly for testlng gravels and weathered rocks. and to a lesser extent boulders and cemented soils. Some of the morę questionable applications include stiff clay. water bearing sands. soft materials, and very soft marinę silt.

Its application to contlnuous testlng In sand is covered later In Section 6.1 under Other Types of Penetratlon Test.

Virtually every organisation uses a commercially available automatic trlp hammer, which practically ensures the correct energy input for each blow.

4.2 Technlques

4.2.1    Means ot Advance

The most common methods are augerlng without drilling fluid (91%), rotary drilling with drilling mud (60%), and rotary drilling with water (59%). Comparlng thłs sirvey with that conducted by AITCHISON and LANG (1963) ten years ago, two good trends appear: (1) the usage of percus9ion drilling has reduced (60% down to 40%) and (2) the usage of rotary drilling with drilling mud has greatly Increased (20% up to 60%).

An analysis of the replies revealed that some dublous or unsatisfactory practices exist. A large number of organisatlons stIII use percusslon drilling In granular soils below the water table, a technique which can produce erroneously Iow S.P.T. values. A larger number employ the equally poor technlque of auger boring (without any drilling fluid) In granular soils below the water tabte. Such soils should preferably be rotary drilled with drilling mud to prevent any loosening of the soli at the bottom of the borehołe, especially In artesian condltions. Unfortunately, these troublesome conditlons are not covered specifically in the Australian Standard.

4.2.2    Means ot Borehołe Stabłllsatlon

The most common method of borehołe stabłllsatlon is casing (86%); however, over half (54%) use the hollow auger, and well over half (60%) use drilling mud, which is preferable In certain condltions noted above. (The relevant percentsges found in the survey by AITCHISON and LANG (1963) are 76. 28. and 28% for casing. hollow auger. and drilling fluid, respectively.)

4.3 Use ot Resutts

4.3.1    Soils Tested

As expected, every organisation performs S.P.T.*s In sands. A high percentage (73%) also perfcrm S.P.T.'s In silts, where the results can be mlsleadlng (e.g., FLETCHER, 1965). Well over half perform S.P.T/s In clays (60%) and gravels (67%), though the results from both are known to be unreliable for design purposes. Those (57%) that use the S.P.T. in decomposed rocks would obtain only a rough Indlcation of the rock's hardness.

4.3.2    Presentatlon ot Results

The Australian Standard describes the standard method of reporting S.P.T. results. A comparison of the survey replies with this Standard reveals that (a) 37% present the ir normal test results in a non-standard manner, and (b) 21% do not allow the standard 6 in. (15cm) depth of penetratlon for seating.

In the case, tor example. where 60 blows only produce a penetratlon of 5 In. during seating, the Standard States that the results in this case should be reported as 60 blows for Initlal 5 In. A form that clearly indicates that the blows were recorded during seating rather than after seating, e.g. 60/5 in. (seating), should be permissible. An extremely high proportion (85%) do not present their results in this case in accordance with the Standard.

4.3.3    Use ot S.P.T. Results In Design

Excludłng boring contractors, the great majority (80%) of organisatlons use S.P.T. results in design, and a higher proportion (54%) of their investłgations involve the S.P.T. as a design tool, as distinct from an exploratory (41%) or control (5%) tool.

Many organisatlons (82%) apply corrections to the N-values used in design and these are matnly over-burden pressure (GIBBS and HOLTZ, 1957) and level of water table.

S.P.T. results are used primarlly to estimate the bearing capacity of footlngs on sands, settlements on sands, and the load capacity of piłeś in sands. They are also used to provide a rough estimate of the bearing capacity of footings and the load capacity of piles in cohesive soils. Several methods of using S.P.T. results are often employed by an organisation: the most common approaches for (i) bearing capacity on sands are those given by TERZAGHI and PECK (1948), Art. 54, and MEYERHOF (1956); (ii) settlements on sands glven by AL PAN (1964) and D’APPOLONIA (1970); and (iii) load capacity of piles in sands given by NORDLUND (1963) and MEYERHOF (1956). The charta produced by HOUGH (1957), p. 296 and 297, are often used to estimate the allowable bearing capacity on other soils.

5. OUASI-STATIC CONE PENETRATION TEST (C.P.TJ

The quasł-static cone penetratlon test is defined as a test that determines the components of penetratlon resistance - end-bearing and side friction - developed during the steady slow penetratlon of a pointed Steel rod into soli or soft rock. The qualifying term "quasl-static* is used to differentiate the test from the morę truły “stalle* cone penetratlon tests performed in