工程用途土壤试验方法 方法5.2.1：土壤压实和密度试验——使用修正压实功确定土壤的干密度/含水率关系

Methods of testing soils for engineering purposes

Method 5.2.1: Soil compaction and density tests—Determination of the dry density/moisture content relation of a soil using modified compactive effort

1 SCOPE

This Standard sets out a method for the determination of the relationship between the moisture content and the dry density of a soil, when compacted, using modified compactive effort (2703 kJ/m³). Compaction is conducted over a range of moisture contents to establish the maximum mass of dry soil per unit volume achievable for this compactive effort, and its corresponding moisture content. The procedure is applicable to that portion of a soil that passes the 37.5 mm sieve. Soil that passes the 19.0 mm sieve is compacted in a 105 mm diameter mould. Soil that contains more than 20% of material retained on the 19.0 mm sieve is compacted in a 152 mm diameter mould.

NOTE: Corrections for oversize material are not made in this method but may be made using AS 1289.5.4.1 when required for compaction control.

2 REFERENCED DOCUMENTS

The following documents are referred to in this Standard:

AS

1

3 APPARATUS

The following apparatus is required:

(a) Steel moulds, of size dependent on the maximum size of material being tested as follows:

(i) Compaction of material passing a 19.0 mm sieve Mould A: A cylindrical metal mould having an internal diameter of 105 mm and effective height of 115.5 mm fitted with a detachable baseplate and a removable collar assembly about 60 mm high, both of which can be firmly attached to the mould. A suitable design is shown in Figure 1 (see Table 1 for tolerances).

(ii) Compaction of that fraction of the soil material that passes the 37.5 mm sieve but contains more than 20% of material, which would be retained on a 19.0 mm sieve Mould B: A cylindrical metal mould having an internal diameter of 152 mm and effective height of 132.5 mm fitted with a detachable baseplate and a removable collar assembly about 60 mm high, both of which can be firmly attached to the mould. A suitable design is shown in Figure 1 (see Table 1 for tolerances).

NOTE: A mould meeting the requirements of AS 1289.6.1.1 used with a steel spacer disc of 150 ±0.5 mm diameter and of sufficient height to provide an effective specimen height of 132.5 mm is a satisfactory alternative to Mould B.

(b) A 4.9 kg steel rammer as shown in Figure 2 and of dimensions as shown in Table 1. The design of the hammer shall permit the hammer to fall freely through the specified drop height, and shall ensure that there is a clearance not greater than 6 mm between the wall of the mould and the hammer during use. Alternatively, a mechanical compactor may be used provided it meets the essential requirements of drop height, mass and energy input.

NOTE: A mechanical form of apparatus may be used, provided the essential dimensions are adhered to and the rammer has a free vertical fall of the correct height. It is also essential that the design of the machine is such that the mould rests on a solid base. When a 152 mm diameter mould is used in a mechanical compactor that does not permit the hammer to be moved to compact around the periphery of the mould, a sector foot having a cross-sectional area equivalent to the area of the circular rammer face may be used to enable uniform compaction over the complete area of soil in the mould. Wear in the support mechanism of a mechanical apparatus that rotates between blows may occur and cause energy to be absorbed in the mechanism. Therefore, at regular intervals, comparison checks should be made between maximum dry density and optimum moisture content test results obtained using hand compaction and those using mechanical compaction. The difference in maximum dry density obtained using a mechanical compactor should not differ from the value found using a hand compactor by more than ±2%.

(c) A level rigid foundation on which to compact the specimen, for example, a sound concrete floor about 100 mm or more in thickness or a concrete block of at least 100 kg mass.

(d) A balance of suitable capacity with a limit of performance not greater than ±5 g.

(e) Sieves, 37.5 mm and 19.0 mm complying with AS 1152.

(f) A strong spatula or a suitable knife.

(g) A steel straightedge, about 250 mm long, 25 mm wide and 3 mm thick, preferably with one bevelled edge.

(h) Miscellaneous mixing apparatus, such as a pan or bowl, spoon, trowels and water spray suitable for thoroughly mixing increments of water with the soil.

(i) A rule graduated in millimetres or a layer depth gauge.

2

Apparatus (continued)

(j) Sealable containers to prevent moisture loss.

(k) A sample extractor such as a jack, lever frame or other device suitable for extruding compacted soil specimens from the mould (optional).

(l) A soil grater for fine-grained soil (optional).

NOTES:

1 Either but not both of the tolerances may be exceeded provided that the tolerance of volume is not exceeded.

2 Either but not both of the tolerances may be exceeded provided that the tolerance of area is not exceeded. Diameter and radius of arc of segment are measured 3 mm behind the face of the rammer.

3 Either but not both of the tolerances may be exceeded provided that the appropriate tolerance of energy delivered per blow is not exceeded.

3

AS 1289.5.2.1—2003

Smooth finish on bore

Push fit

NOTE: This design has been found satisfactory, but alternative designs may be employed provided that the essential dimensions in Table 1 are met.

FIGURE 1 DETAILS OF TYPICAL TYPE A AND TYPE B MOULDS

4

4 PROCEDURE

Section detail showing clearance between rammer and wall of mould

PARTS LIST AND TYPICAL DIMENSION

NOTE: This design has been found satisfactory, but alternative designs and materials may be used provided that the essential requirements in Table 1 are met.

DIMENSIONS IN MILLIMETRES

FIGURE 2 4.9 kg RAMMER

The procedure shall be as follows:

(a) Prepare the sample in accordance with AS 1289.1.1.

(b) Screen the prepared sample over a 19.0 mm sieve. If necessary, brush fine material from the material retained on the sieve. Determine the mass of the retained material and calculate the percentage retained on the 19.0 mm sieve from the equation:

P_o = 100m_o / m .... (4)

where

P_o = percentage by mass of + 19.0 mm (oversize) material

m_o = wet mass of +19.0 mm (oversize) material, in grams

m = wet mass of total sample, before screening, in grams

5

AS 1289.5.2.1—2003

If P₀ is greater than 20%, screen the retained 19.0 mm material over a 37.5 mm sieve. Determine the mass of the retained 37.5 mm material and calculate the percentage retained on the 37.5 mm sieve using the above equation, substituting +37.5 mm for +19.0 mm in the equation notation.

If required, keep the material retained on the 19.0 mm, or 19.0 mm and 37.5 mm sieves for dry mass and volume determinations.

NOTE: It is necessary that the dry mass and volume of oversize material be determined if a correction is required to the maximum dry density and optimum moisture content as detailed in AS 1289.5.4.1.

(c) Select the size fraction and mould to be used in the compaction test using the criteria in Table 2.

Record the mould used; that is, A or B. When necessary, recombine the material passing the 37.5 mm sieve and that passing the 19.0 mm sieve and thoroughly mix.

(d) Split out four or more representative portions of the sieved soil, each of sufficient quantity to produce a compacted volume in excess of the volume of the mould.

NOTE: For material compacted in a 105 mm diameter mould, a mass of 2.5 kg will be adequate for most soils. A gravel may, however, require up to 3 kg, whilst it may be possible to use as low as 2 kg with a heavy clay. For material compacted in 152 mm diameter mould about 2.5 times the mass of the material required for a 105 mm diameter mould will be required. An extra portion may be required to determine initial moisture content to assist in determining the amount of water to be added, or removed.

(e) Take the portions of the soil as prepared in Step (d). Thoroughly mix each portion, adding or removing water so that the optimum moisture content is judged to be straddled. Use essentially equal increments of moisture between portions and ensure that the moisture steps are not excessive for the soil type.

NOTE: As a guide, suitable intervals of moisture content range between 1% for crushed rock and gravel and 2% to 3% for clays.

(f) Allow the soil portions to cure for an appropriate time for the soil type. Record the time of curing.

NOTE: It is important that the water is thoroughly mixed into and uniformly distributed through the soil since adequate mixing gives rise to variable test results. It is desirable to keep the mixed soil in a sealed container to allow the water to become more uniformly distributed throughout the soil before compaction. For materials of low plasticity and high permeability prepared in a moist condition close to optimum moisture content, little or no curing is required, but if the soil is a completely dry heavy clay up to seven days curing may be required before testing. The more clayey a soil, the more time required for the water to be uniformly distributed through it. Normally, soils should be cured for a minimum of 2 h.

(g) Clean the mould, collar and baseplate. Inspect and clean the rammer and ensure that it is free in the guide.

6