Most common procedures for homogenisation of natural soil prior to treatment, specimen preparation methods and curing conditions
| Preparation standards and reference | Natural soil homogenisation method | Mixer type | Mixing duration | Specimen mould | Number of layers in the mould | Moulding techniques | Curing conditions |
|---|---|---|---|---|---|---|---|
| Tokyo Institute of Technology, Japan (Kitazume et al., 2015) | Soil is homogenised by mixing with its initial water content | Domestic dough mixer with a 5000–30 000 cm3 mixing bowl | 10 min with occasional hand-mixing | Cylindrical plastic moulds with 50 mm diameter and 100 mm height | Three to six layers | Sample ends are properly sealed with specified sealants and stored at 20 ± 3°C for specified time at 95% relative humidity | |
| Sapienza University of Rome, Italy (Grisolia et al., 2012, 2013; Marzano et al., 2012) | The soil is homogenised by remixing alone. Water is added at this stage to adjust the soil water content | Hobart mixer | 10 min with occasional hand-mixing | Cylindrical plastic moulds with 50 mm diameter and 100 mm height. The largest particle contained within the specimen shall be smaller than one-fifth of the specimen diameter | Three layers | Each mould is covered with a sealant and stored in a special curing room at 95% relative humidity to prevent water evaporation from the specimen | |
| University of Coimbra, Portugal (Correia et al., 2013) | The soil is homogenised by remixing at a mixing speed of 136 revolutions per min (rpm). To readjust the soil water content, water is added to the soil as a slurry of water–binder mixture | Hobart mixer (model N50) | 3 min with a mixing speed of 136 rpm | Polypropylene random copolymer pipes, with 50·8 mm internal diameter and 330 mm height. The height of the sample is 140 mm, and the remaining height of the mould serves as a guide for the dead load, corresponding to a vertical pressure of 24 kPa. The mould has two holes near the top to allow the sample to submerse | Six layers (thickness/diameter ratio equal to 0·5) |
| A non-woven geotextile porous disc is placed at the bottom and top of the mould. Samples are stored at 20 ± 2°C for a specified time. A vertical pressure of 24 kPa is applied during curing |
| SGS, Sweden (Åhnberg and Andersson, 2011; Carlsten and Ekström, 1997) | The soil is first homogenised thoroughly by mixing the soil alone | Dough mixer or kitchen mixer with sufficient capacity and rpm | 5 min | The moulds used are plastic tubes commonly used for piston sampling in Sweden, with a diameter of 50 mm and a height of 170 mm | Four to five layers (about 30 mm thickness per layer) | Sample ends are properly sealed with specified sealants and stored at 7°C in a climate-controlled room | |
| JGS 0821 (JGS, 2005), Kitazume and Terashi (2013) | The soil is homogenised by stirring it using a mixer. The soil water content is adjusted by adding water | Domestic dough mixer with a 5000–30 000 cm3 mixing bowl | 10 min with occasional hand-mixing | Specimen moulds with 50 mm diameter and 100 mm height. The maximum grain size of the sieved sample should be less than one-fifth of the inner diameter of the mould | Three layers |
| Sample ends are properly sealed with specified sealants and stored at 20 ± 3°C for a specified time at 95% relative humidity |
| BRE (2002) | The soil is mixed until it becomes visually homogenous | Dough mixer or kitchen mixer with sufficient capacity and rpm | 5 min (depending on the soil type) | Plastic tubes or plastic-coated cardboard, 50 mm diameter and 100 mm height coated with oil or wax on the inner side | Four layers |
| No standard specified for humidity. Samples are stored at a constant temperature of 18–22°C in properly sealed conditions |
| Jacobson et al. (2003) | The conglomerate of soil is mixed thoroughly for 3–4 min | KitchenAid dough mixer with a dough hook. Outer spindle rotating at 155 rpm and the inner spindle at 68 rpm | 3–5 min | 50 mm diameter and 100 mm height | Four layers |
| Cured at 100% relative humidity (moist environment) and 20 ± 3°C for 7, 14, 28 and 56 d |
| Janz and Johansson (2002), Edstam (2000) | The soil is homogenised by mixing it alone for 2–6 min. This is normally done the day before the stabiliser is added | Kitchen mixer or concrete mixer | 4–10 min | The moulds used are plastic tubes commonly used for piston sampling in Sweden, with a diameter of 50 mm and a height of 170 mm | Layer thickness between 2 and 4 cm after compaction | The specimens containing only lime are stored at room temperature (+22°C) for the first 10 d and the remaining time at +7°C. Other specimens are stored at a temperature of +7°C all the time | |
| ASTM D 3551-17 (ASTM, 2017), ASTM D 5102-09 (ASTM, 2009), ASTM (1992) | Soil is air-dried for 24 h and mixed with a dry binder for 1 min or until the mixture is homogenised visually | Mechanical mixer capable of producing uniform and homogeneous mixtures | 5 min | Moulds with a minimum inside diameter 50 mm and length-to-diameter ratios between 2·0 and 2·5. The largest particle contained within the specimen shall be smaller than one-tenth of the specimen diameter | At least three layers |
| Compacted specimens are cured in an airtight, moisture-proof container at a temperature of 23 + 2°C |
| Federal Highway Administration Design Manual (Bruce et al., 2013) | The soil is mixed for approximately 3 min at the lowest setting of the mixer (approximate rotation of the mixing tool of 100–175 cycles/min). Water is added to adjust the soil water content | Kitchen mixer with a sufficient capacity | 10 min | 50 by 100 mm plastic moulds with lids | Three layers |
| Sealed specimens are cured under controlled conditions at 95–100% relative humidity and at a room temperature of 20–25°C |
| European standard EN 16907-4 (CEN, 2018) | The soil in the field is corrected to the particle size distribution before adding the binder by blending the soil alone to break up large blocks or boulders | Mechanical mixer capable of producing uniform and homogeneous mixtures | The mixing time is not specified, but the produced mixture should be homogenised | Different mould dimensions are used according to the compaction method used for preparing the sample and the maximum particle size permitted in the sample. The length-to-diameter ratio of the specimen is 2 | Layers | In a temperate region, sample ends are properly sealed with specified sealants and stored in the air at 20 ± 2°C for a specified time at relative humidity >90%. The sample is cured also in water. Other conditions can be adopted in a warmer or colder climate | |
| French standard NF EN 13286-53 (Afnor, 2005) and the technical guide by Laboratoire Central des Ponts et Chausses (LCPC, 2004) | The sample is disintegrated or homogenised for several minutes | Kitchen mixer with enough capacity | The mixing time is not specified, but the produced mixture should be homogenised | Cylindrical steel mould with different dimensions (35 × 70, 50 × 100 and 100 × 200 mm). The length-to-diameter ratio of the specimen is 2. The mould has flanged pistons (plugs) from both ends. It is used to produce a specimen with a density gradient such as the density in the central part being less than that at the ends | One layer |
| The sample is sealed and cured at control room temperature (20–25°C) |
| ASTM (1992) | The soil is air-dried for 24 h at room temperature and mixed with a dry binder for 1 min or until the mixture is homogenised visually. The soil is passed through sieve number 16 | Hand-mixing or using a mechanical mixer | The mixing time is not specified, but the produced mixture should be homogenised | Cylindrical steel mould with dimensions of 71 × 299 mm. The mould has flanged pistons from both ends to compress the specimens and produces a specimen with dimensions of 17 × 142 mm. The length-to-diameter ratio of the specimen is 2 | One layer |
| Compacted specimens are cured in a moist room |
| BSI (1990a, 1990b) | The untreated soil is mixed alone either by using a mechanical mixer or by hand | Kitchen mixer with a sufficient capacity | 10 min | Tapered mould with two steel plugs with the following dimensions: 50 × 100 mm for fine-grained soil and 100 × 200 mm for medium-grained soil | One layer for a 50 × 100 mm specimen and six layers for a 100 × 200 mm specimen | Specimens are coated with wax and cured at constant temperature of 20 ± 2°C |
| Preparation standards and reference | Natural soil homogenisation method | Mixer type | Mixing duration | Specimen mould | Number of layers in the mould | Moulding techniques | Curing conditions |
|---|---|---|---|---|---|---|---|
| Tokyo Institute of Technology, Japan ( | Soil is homogenised by mixing with its initial water content | Domestic dough mixer with a 5000–30 000 cm3 mixing bowl | 10 min with occasional hand-mixing | Cylindrical plastic moulds with 50 mm diameter and 100 mm height | Three to six layers | Tapping Rodding Dynamic compaction Static compaction | Sample ends are properly sealed with specified sealants and stored at 20 ± 3°C for specified time at 95% relative humidity |
| Sapienza University of Rome, Italy ( | The soil is homogenised by remixing alone. Water is added at this stage to adjust the soil water content | Hobart mixer | 10 min with occasional hand-mixing | Cylindrical plastic moulds with 50 mm diameter and 100 mm height. The largest particle contained within the specimen shall be smaller than one-fifth of the specimen diameter | Three layers | Tapping Rodding Dynamic compaction Static compaction No compaction | Each mould is covered with a sealant and stored in a special curing room at 95% relative humidity to prevent water evaporation from the specimen |
| University of Coimbra, Portugal ( | The soil is homogenised by remixing at a mixing speed of 136 revolutions per min (rpm). To readjust the soil water content, water is added to the soil as a slurry of water–binder mixture | Hobart mixer (model N50) | 3 min with a mixing speed of 136 rpm | Polypropylene random copolymer pipes, with 50·8 mm internal diameter and 330 mm height. The height of the sample is 140 mm, and the remaining height of the mould serves as a guide for the dead load, corresponding to a vertical pressure of 24 kPa. The mould has two holes near the top to allow the sample to submerse | Six layers (thickness/diameter ratio equal to 0·5) | Static compaction | A non-woven geotextile porous disc is placed at the bottom and top of the mould. Samples are stored at 20 ± 2°C for a specified time. A vertical pressure of 24 kPa is applied during curing |
| SGS, Sweden ( | The soil is first homogenised thoroughly by mixing the soil alone | Dough mixer or kitchen mixer with sufficient capacity and rpm | 5 min | The moulds used are plastic tubes commonly used for piston sampling in Sweden, with a diameter of 50 mm and a height of 170 mm | Four to five layers (about 30 mm thickness per layer) | Tapping Rodding Static compaction | Sample ends are properly sealed with specified sealants and stored at 7°C in a climate-controlled room |
| JGS 0821 ( | The soil is homogenised by stirring it using a mixer. The soil water content is adjusted by adding water | Domestic dough mixer with a 5000–30 000 cm3 mixing bowl | 10 min with occasional hand-mixing | Specimen moulds with 50 mm diameter and 100 mm height. The maximum grain size of the sieved sample should be less than one-fifth of the inner diameter of the mould | Three layers | No compaction | Sample ends are properly sealed with specified sealants and stored at 20 ± 3°C for a specified time at 95% relative humidity |
| The soil is mixed until it becomes visually homogenous | Dough mixer or kitchen mixer with sufficient capacity and rpm | 5 min (depending on the soil type) | Plastic tubes or plastic-coated cardboard, 50 mm diameter and 100 mm height coated with oil or wax on the inner side | Four layers | Static compaction | No standard specified for humidity. Samples are stored at a constant temperature of 18–22°C in properly sealed conditions | |
| The conglomerate of soil is mixed thoroughly for 3–4 min | KitchenAid dough mixer with a dough hook. Outer spindle rotating at 155 rpm and the inner spindle at 68 rpm | 3–5 min | 50 mm diameter and 100 mm height | Four layers | Tapping Static compaction | Cured at 100% relative humidity (moist environment) and 20 ± 3°C for 7, 14, 28 and 56 d | |
| The soil is homogenised by mixing it alone for 2–6 min. This is normally done the day before the stabiliser is added | Kitchen mixer or concrete mixer | 4–10 min | The moulds used are plastic tubes commonly used for piston sampling in Sweden, with a diameter of 50 mm and a height of 170 mm | Layer thickness between 2 and 4 cm after compaction | Tapping Static compaction | The specimens containing only lime are stored at room temperature (+22°C) for the first 10 d and the remaining time at +7°C. Other specimens are stored at a temperature of +7°C all the time | |
| ASTM D 3551-17 ( | Soil is air-dried for 24 h and mixed with a dry binder for 1 min or until the mixture is homogenised visually | Mechanical mixer capable of producing uniform and homogeneous mixtures | 5 min | Moulds with a minimum inside diameter 50 mm and length-to-diameter ratios between 2·0 and 2·5. The largest particle contained within the specimen shall be smaller than one-tenth of the specimen diameter | At least three layers | Tapping and kneading Dynamic compaction | Compacted specimens are cured in an airtight, moisture-proof container at a temperature of 23 + 2°C |
| The soil is mixed for approximately 3 min at the lowest setting of the mixer (approximate rotation of the mixing tool of 100–175 cycles/min). Water is added to adjust the soil water content | Kitchen mixer with a sufficient capacity | 10 min | 50 by 100 mm plastic moulds with lids | Three layers | Tapping Rodding | Sealed specimens are cured under controlled conditions at 95–100% relative humidity and at a room temperature of 20–25°C | |
| European standard EN 16907-4 ( | The soil in the field is corrected to the particle size distribution before adding the binder by blending the soil alone to break up large blocks or boulders | Mechanical mixer capable of producing uniform and homogeneous mixtures | The mixing time is not specified, but the produced mixture should be homogenised | Different mould dimensions are used according to the compaction method used for preparing the sample and the maximum particle size permitted in the sample. The length-to-diameter ratio of the specimen is 2 | Layers | Proctor equipment or vibrating table compaction Vibrating hammer Vibrocompression Static compression | In a temperate region, sample ends are properly sealed with specified sealants and stored in the air at 20 ± 2°C for a specified time at relative humidity >90%. The sample is cured also in water. Other conditions can be adopted in a warmer or colder climate |
| French standard NF EN 13286-53 ( | The sample is disintegrated or homogenised for several minutes | Kitchen mixer with enough capacity | The mixing time is not specified, but the produced mixture should be homogenised | Cylindrical steel mould with different dimensions (35 × 70, 50 × 100 and 100 × 200 mm). The length-to-diameter ratio of the specimen is 2. The mould has flanged pistons (plugs) from both ends. It is used to produce a specimen with a density gradient such as the density in the central part being less than that at the ends | One layer | Static compaction or compressing the specimen from both sides by a compression-testing machine with a sufficient force. The additional flanged piston parts are removed during the compression process | The sample is sealed and cured at control room temperature (20–25°C) |
| The soil is air-dried for 24 h at room temperature and mixed with a dry binder for 1 min or until the mixture is homogenised visually. The soil is passed through sieve number 16 | Hand-mixing or using a mechanical mixer | The mixing time is not specified, but the produced mixture should be homogenised | Cylindrical steel mould with dimensions of 71 × 299 mm. The mould has flanged pistons from both ends to compress the specimens and produces a specimen with dimensions of 17 × 142 mm. The length-to-diameter ratio of the specimen is 2 | One layer | Static compaction Dynamic compaction | Compacted specimens are cured in a moist room | |
| The untreated soil is mixed alone either by using a mechanical mixer or by hand | Kitchen mixer with a sufficient capacity | 10 min | Tapered mould with two steel plugs with the following dimensions: 50 × 100 mm for fine-grained soil and 100 × 200 mm for medium-grained soil | One layer for a 50 × 100 mm specimen and six layers for a 100 × 200 mm specimen | Constant compaction effort For 50 × 100 mm specimen For 100 × 200 mm specimen | Specimens are coated with wax and cured at constant temperature of 20 ± 2°C |
For each layer, the mould is tapped 50 times against the floor
Performed using an 8 mm dia. steel rod and tapping down (30 times) the mixture with the rod for each layer
Each layer is compressed by the weight of a rod (1·6 kg) and compacted by a falling weight (0·6 kg) using a special apparatus. The fall height is set to 10 cm, and the number of blows is five
Each layer is statically compressed with a vertical pressure of 25 kPa for 10 s using a heavy rod
Each layer is compacted by a falling weight (1·5 kg) using a special apparatus. The fall height is set to 10 cm and the number of blows to five
Simply consists of filling the mould by either pouring or placing in the case of mixtures with a higher consistency
For each layer, the mixture is tapped by hand and statically compressed with a vertical pressure of 100 kPa for 10 s. Finally, the surface is lightly scarified and another layer is introduced
Tapping of the mould is performed 30 times for each of the approximately 30 mm thick layers of the soil–binder mixture put into the mould. The filling is performed in four layers
A rod is used to compact/smooth out evenly each 20–30 mm thick layer of the soil–binder mixture by hand
Each layer with about 30 mm thickness is statically compressed with a vertical pressure of 100 kPa for 5 s to squeeze out air pockets from each layer
For each layer, the mould is lightly tapped against the floor, hitting the mould with a mallet, and subjecting the mould to vibration
Each layer with about 30 mm thickness is statically compressed with a vertical pressure of 100 kPa three times for 2 s to squeeze out air pockets from each layer
Each layer with about 25 mm thickness is statically compressed with a vertical pressure of 100 kPa for 5–10 s
A 1 kg heavy load is placed on each layer, and the mould is tapped three times against the floor
Each layer with about 30 mm thickness is statically compressed with a vertical pressure of 100–200 kPa for 5–10 s
Each layer is compacted to achieve standard compacting effort of 600 kN m/m3 according to ASTM D 698-12 (ASTM, 2012). Suitable for preparing a specimen at the desirable unit weight
The dimensions of the mould are a diameter of 100 ± 1 mm and a height of 120 ± 1 mm or a diameter of 150 ± 1 mm and a height of 120 ± 1 mm, and the maximum particle sizes allowed are 16 and 31·5 mm, respectively
The dimensions of the mould are a diameter of 100 ± 1 mm and a height of 100 ± 1 mm or a diameter of 150 ± 1 mm and a height of 150 ± 1 mm, and the maximum particle sizes allowed are 22 and 31·5 mm, respectively
The dimensions of the mould are a diameter of 100 ± 1 mm and a height of 100 or 200 mm or a diameter of 160 mm and a height of 160 or 320 mm, and the maximum particle sizes allowed are 22 and 31·5 mm, respectively
The dimensions of the mould are a diameter of 50 mm and a height of 50 or 100 mm or a diameter of 100 mm and a height 100 or 200 mm, and the maximum particle sizes allowed are 11·2 and 20 mm, respectively
Placing the soil–binder mixture inside the mould gently and uniformly as one layer with the tamping rod and then compacting the mixture inside the mould with 15 blows of the rammer dropped from a height of 300 mm
Placing the soil–binder mixture inside the mould as six layers and compacting each layer with 25 blows of a rammer dropped from a height of 300 mm
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