GB/T 19274-2024Geosynthetics - Plastic geocell (English PDF)

3 Terms and definitions

3.1 Plastic geocell: a three-dimensional grid structure formed by joining strips made of plastic by various processes, which when opened out takes the form of a quadrilateral or polygonal honeycomb. Note: a single set of plastic geocell is shown in Figure 1, whose key identifies the junction at the middle of the strip between cells, the junction at the edge of the strip between cells, the nominal cell length, the nominal cell width, the cell height, which is the strip width, and the edge length and edge width of a single set of plastic geocell when fully opened out.

3.2 Fixed angle connection junctions: a junction at which the initial angle between the two adjacent strips is 90° before the plastic geocell is opened out. Note 1: the structure is shown in Figure 2. Note 2: rounding the fixed-angle junction with an arc helps to reduce the stress concentration caused by a sharp junction angle.

3.3 Unfixed angle connection junctions: a junction at which the initial angle between the two adjacent strips is 0° before the plastic geocell is opened out. Note: the structure is shown in Figure 3.

4 Classification and designation

4.1.1 Plastic geocells are classified by the raw material of the strip, the strip production process, the junction structure, the junction strength and the preset initial angle at the junction.

4.1.2 By raw material of the strip they are divided into polyethylene, polypropylene and polyester geocells.

4.1.3 By strip production process they are divided into the extruded type (E) and the stretched type (S).

4.1.4 By junction structure they are divided into the welded type (WC), the micro-pile fusion type (WZ), the injection moulded type (IC), the mortise and tenon type (MT) and the ring insert type (PC). Common junction structures are given in Annex A.

4.1.5 By junction strength, welded, micro-pile fusion, injection moulded and mortise and tenon plastic geocells are divided into types I, II, III, IV and V, and ring insert plastic geocells into types VI and VII.

4.1.6 By preset initial angle at the junction they are divided into the fixed-angle type and the unfixed-angle type.

4.2 Designation. The designation is built from the abbreviation of the raw material of the strip, the strip production process, the junction structure, the junction strength grade, the cell height, the nominal cell length, the nominal cell width and the preset initial angle at the junction, in the pattern: plastic geocell code, strip raw material abbreviation, strip production process, junction structure, junction strength grade, cell height, nominal cell length by nominal cell width, preset initial angle at the junction. Where the nominal cell length and the nominal cell width are the same, only one value is written. The code for a plastic geocell is GC. The abbreviations of the strip raw materials follow GB/T 1844.1-2022: PP for polypropylene, PE for polyethylene, PET for polyester. The cell height, the nominal cell length and the nominal cell width are nominal dimensional values in millimetres and the preset initial angle at the junction is in degrees. The listed values for each position are: the code GC; the strip raw material PE, PP or PET; the production process E for extruded and S for stretched; the junction structure WC for welded, WZ for micro-pile fusion, IC for injection moulded, MT for mortise and tenon, PC for ring insert and OT for other; and the junction strength grades I to VII.

Example 1: GC-PP-S-IC-V-50-400-90 denotes a plastic geocell (GC) with a stretched strip of polypropylene (PP), an injection moulded junction structure, junction strength grade V, a cell height of 50 mm, a nominal cell length of 400 mm, a nominal cell width of 400 mm and a preset initial angle at the junction of 90°.

Example 2: GC-PE-E-WC-I-200-400-0 denotes a plastic geocell (GC) with an extruded strip of polyethylene (PE), a welded junction structure, junction strength grade I, a cell height of 200 mm, a nominal cell length of 400 mm, a nominal cell width of 400 mm and a preset initial angle at the junction of 0°.

5 Materials

5.1 Base resin. Of the base resins used as the raw material of the plastic geocell strip, polyethylene shall meet GB/T 11115, polypropylene shall meet GB/T 12670 and polyester shall meet GB/T 17931.

5.2 Junction connectors. Plastic connectors with resistance to ageing may be used at the junctions of a plastic geocell, and metal connectors may also be used; the surface quality of a metal connector shall meet the surface treatment requirements of 6.4.2 of GB/T 27704-2011.

6 Requirements

6.1 Appearance. Table 1 has three columns, the item number, the item and the requirement, and covers three items. For the strip, the colour shall be even and the surface flat and free of bubbles, and holes or embossing may be made as required. For the junction, the requirement depends on the junction type: welded junctions shall be neatly arranged and free of detachment; micro-pile fusion junctions shall be neatly arranged and free of detachment; injection moulded junctions shall be even, free of short shots, bubbles and shrinkage distortion; mortise and tenon junctions shall grip the geocell strip firmly and be free of looseness and detachment; and ring insert junctions shall have the port of the insert closed with no opening. For the grid, the cell dimensions after opening out shall be even and the junctions free of missed connections and of detachment.

6.2 Dimensions and deviations. The opened-out dimensions of a single set of plastic geocell preferably are not smaller than 4 m by 5 m, and other opened-out dimensions may be agreed between supplier and purchaser. The dimensions and deviations of the plastic geocell shall meet Table 2, which fixes, against a cell height of 100 mm or less and a cell height of more than 100 mm, the tolerance on the cell height, a minimum strip thickness for the extruded type and for the stretched type, the nominal cell length and width range with a deviation for the extruded type and a deviation for the stretched type, and the nominal value and the tolerance of the preset initial angle at a fixed-angle junction. In the extracted text of Table 2 the cells of the strip thickness, cell dimension and junction angle columns cannot be attributed to either of the two cell height rows, so the numerical values of that table are not reproduced here.

6.3 Properties of the plastic geocell strip. Table 3 lists nine test items against six columns of raw material and production process, namely extruded and stretched polyethylene, extruded and stretched polypropylene, and extruded and stretched polyester. The items are tensile strength in kilonewtons per metre; tensile yield strain and tensile strain at break, both as a percentage; carbon black content as a percentage and carbon black dispersion, both applying only to black plastic geocell products to which carbon black has been added; oxidation induction time at 200 degrees Celsius in minutes; tensile load stress cracking in hours; retention of properties after artificial weathering as a percentage, which applies to fields of use such as green slope protection where the product is exposed outdoors for long periods; and retention of properties after exposure to chemical media as a percentage, which applies only to polyester geocells used where the ambient pH is below 5 or above 9. The tensile strength requirement runs, in the order of the six columns, not less than 20, 100, 23, 100, 30 and 120 kN/m. The carbon black content requirement is a single value covering the whole row, 2.0 % to 3.0 %. The carbon black dispersion requirement is a single value covering the whole row: of ten readings not more than one shall be grade three, and no reading shall be grade four or grade five. The retention of properties after artificial weathering is a single value covering the whole row, not less than 80 %. The retention of properties after exposure to chemical media is not less than 80 % for polyester and is not required for polyethylene and polypropylene. The tensile yield strain requirement runs, in the order of the six columns, not more than 15 %, not required, not more than 15 %, not required, not more than 15 % and not required. The tensile strain at break requirement runs not required, 8 % to 20 %, not required, 6 % to 15 %, not required and 8 % to 20 %. For the oxidation induction time row and the tensile load stress cracking row the extracted text carries fewer cells than there are columns, so those two rows cannot be attributed column by column and their values are not reproduced here.

6.4 Properties of the plastic geocell junction. The junctions of welded, micro-pile fusion, injection moulded and mortise and tenon plastic geocells shall meet Table 4 and those of ring insert plastic geocells shall meet Table 5. Table 4 gives three items against the five junction strength grades I to V, all in newtons per millimetre: junction tensile strength not less than 20, 36, 100, 160 and 240; junction tensile shear strength not less than 20, 36, 80, 100 and 120; and junction peel strength not less than 14, 18, 40, 80 and 120. Table 5 gives three items against the two junction strength grades VI and VII: junction tensile strength not less than 160 and 240 N/mm; peel force at the end of the ring insert not less than 300 N and 400 N; and pull-out force of the ring insert not less than 700 N and 1000 N.

7 Test methods

7.1 The conditioning of plastic geocell specimens and the standard test environment follow GB/T 2918, at a temperature of 23 °C +/- 2 °C and a relative humidity of 50 % +/- 10 %, the conditioning time being at least 24 h.

7.2 Appearance quality is judged by eye in natural light.

7.3 Dimensions and deviations. The plastic geocell is opened out on level ground and the largest edge length after full opening out is measured with a tape whose smallest division is not greater than 5 mm, in metres. The nominal cell dimensions and the cell height are measured with a gauge whose smallest division is not greater than 1 mm, in millimetres; for a curved strip the cell height is measured at five points spaced evenly between the two end points of the strip, the end points included. The strip thickness is measured with a gauge whose smallest division is not greater than 0.01 mm, in millimetres. Each dimension is taken as the arithmetic mean of five measurements. The opened-out edge length, the cell dimensions and the cell height are kept to whole numbers and the strip thickness to two decimal places. The preset initial angle at a fixed-angle junction is measured as laid down in Annex B.

7.4 Tensile strength, tensile yield strain and tensile strain at break follow GB/T 1040.3, with a type 5 specimen. For a stretched-type geocell the strip preferably is pulled over its whole width; a strip wider than 100 mm is cut down to 100 mm from one side. Specimens are cut lengthwise from the strip more than 20 mm from a junction, avoiding any holes already punched, at least five specimens being taken, and the test speed is 50 mm/min +/- 5 mm/min. The tensile strength of a stretched-type geocell is calculated by formula (1), in which the tensile strength is in kilonewtons per metre, the maximum initial force during the tensile test is in newtons and the minimum width of the specimen is in millimetres. The tensile strength is expressed as the arithmetic mean and kept to three significant figures.

7.5 to 7.8 Carbon black content follows GB/T 13021. Carbon black dispersion follows Annex E of GB/T 17643-2011. Oxidation induction time at 200 degrees Celsius follows GB/T 19466.6, the specimen being cut from a clean strip, the specimen mass 10 mg, an aluminium pan being used, the heating rate 20 °C/min and the isothermal temperature 200 °C, each sample being measured twice. For tensile load stress cracking, where the strip surface has no pattern the specimen is cut lengthwise from the strip more than 20 mm from a junction, avoiding any holes already punched, and the test then follows GB/T 41794; where the strip surface has a pattern, the strip is pressed into a test sheet as laid down in GB/T 1845.2 before the test.

7.9 Retention of properties after artificial weathering. Specimens are prepared by the method of 7.4 and weathered artificially as laid down in GB/T 16422.2 under the following conditions: a black panel temperature of 65 °C +/- 2.5 °C; an irradiance at 340 nm of 0.51 watts per square metre; a relative humidity of 50 % +/- 5 %; a spray cycle of 18 min +/- 0.5 min of water spray with 102 min +/- 0.5 min between sprays; and a test duration of 500 h. After weathering, the tensile strength of the strip is measured as laid down in 7.4 and the retention is calculated by formula (2), in which the retention is a percentage, and the two tensile strengths, after and before ageing or immersion, are in kilonewtons per metre. The result is expressed as the arithmetic mean and kept to two figures.

7.10 Retention of properties after exposure to chemical media. Specimens are prepared by the method of 7.4 and then tested as laid down in GB/T 11547, the reagents being a saturated calcium hydroxide solution and a sulfuric acid solution of pH 2, the immersion time 72 h and the immersion temperature 60 °C +/- 2 °C. After immersion the tensile strength of the strip is measured as laid down in 7.4 and the retention calculated by formula (2).

7.11 to 7.13 Junction tests. Junction tensile strength is tested by method C of GB/T 44569.1-2024, junction tensile shear strength by method A and junction peel strength by method B; in each case the result is the force divided by the cell height at the junction, in newtons per millimetre.

7.14 to 7.16 The peel force at the end of the ring insert is tested as laid down in Annex C and the pull-out force of the ring insert as laid down in Annex D. Measured or calculated values are judged as laid down in GB/T 8170, using the all-figure comparison method.

8 Inspection rules

8.1 Lot formation. A lot is made up of products of the same category and the same dimensions produced continuously from the same batch of raw material by the same process. A lot holds not more than 500 sets; if 7 d of production yields fewer than 500 sets, the output of those 7 d makes a lot.

8.2 Sampling. Product quality is determined lot by lot: three sets are drawn at random and inspected for the items of 6.1 and 6.2, and enough specimens for the items of 6.3 and 6.4 are then drawn at random from the samples that have passed.

8.3 Factory inspection. The inspection items are 6.1, 6.2 and the tensile strength, tensile yield strain and tensile strain at break of Table 3; for welded, micro-pile fusion, injection moulded and mortise and tenon plastic geocells the inspection items are those of Table 4, and for ring insert plastic geocells those of Table 5.

8.4 Type inspection. The items are all the requirements of clause 6, and type inspection is carried out once a year under normal conditions. It is also carried out when the raw material, the formulation or the production process of the product has changed appreciably; when production has stopped for more than 6 months and is resumed; when the factory inspection result differs appreciably from the last type inspection; and on the trial production and type approval of a new product or of an existing product transferred to another factory.

8.5.1 Where one of the requirements of 6.1 to 6.2 is not met, three further sets are drawn and tested; if all three pass, the inspection result is judged conforming, and if one of them fails, the inspection result is judged non-conforming.

8.5.2 Where one of the requirements of 6.3 to 6.4 is not met, a double sample is drawn from the original lot and retested; if an item still fails, the lot is judged non-conforming, and if the retest passes, the lot is judged conforming.

9 Marking, packaging, storage and transport

9.1 Marking. The product shall carry a certificate of conformity. The product identification shall include the name, the trade mark, the specification and model, the date of manufacture, the storage life, the batch number, the name and address of the manufacturing plant, the inspector's stamp and the standard number.

9.2 Packaging. Plastic geocells are bundled with plastic strapping in sets, the bundling being tight and even. Other forms of packaging may be agreed between supplier and purchaser.

9.3 Storage. Plastic geocells shall be stored in a warehouse away from heat sources and protected from direct sunlight; where they are stored outdoors, a cover shall be added. The storage life from the date of manufacture is generally not more than 12 months.

9.4 Transport. During loading, unloading and transport, plastic geocells shall not be heavily pressed, sharp tools such as iron hooks shall not be used, and scratching shall be avoided. They shall not be exposed to the sun during transport.

A Annex A (informative) Several common junction structures of plastic geocells

A.1 Welded junction: a connecting junction formed by fusing plastic geocell strips together by ultrasonic or a similar process.

A.2 Micro-pile fusion junction: a connecting junction formed by the mutual fusion of solid material projecting from the strip surface.

A.3 Injection moulded junction: a connecting junction formed by injecting a polymer melt into the connecting area of the plastic geocell strips and letting it cool.

A.4 Mortise and tenon junction: a connecting junction in which the plastic geocell strips are held by a mortise and tenon structural part.

A.5 Ring insert junction: a connecting junction formed by threading a ring insert through slits in the strips.

B Annex B (normative) Preset initial angle at a fixed-angle junction

B.1 Apparatus. The preset initial angle at a fixed-angle junction is measured with an angle gauge whose smallest division is not coarser than 1°.

B.2 Preparation of the specimen. The junction is cut off the plastic geocell with scissors or another tool and marked so that the same direction can be identified; not fewer than five sets are taken. The specimen is shown in Figure B.1, in which the strip length is not less than 100 mm.

B.3 Test procedure. The test is shown in Figure B.2 and runs as follows: the specimen is fixed to the work table with the strips perpendicular to the table surface; the angle gauge is placed between the two adjacent strips and turned until its outer side rests against the wrapping body, and the reading is recorded.

B.4 Calculation of the result. The preset initial angle at a fixed-angle junction is the arithmetic mean of five test values taken in the same direction, rounded to a whole number.

C Annex C (normative) Peel force at the end of the ring insert

C.1 Apparatus. The clamp is connected to the tensile machine and holds the peel fixture; a centring pin on it keeps the gripping faces in one plane and makes the long axis of the specimen coincide with the direction of pull along the centre line of the peel fixture. The peel fixture holds the ring insert and the width of the part gripping the specimen is 5 mm; it is shown in Figure C.1.

C.2 Preparation of the specimen. The test sample is taken from the plastic geocell, the ring insert being removed from the strip with scissors or another tool without damaging the connection point of the insert; not fewer than five inserts are taken. The preparation is shown in Figure C.2.

C.3 Test procedure. The upper and lower peel fixtures are clamped into the clamps and, once clamped, are made to sit in the middle of the two clamp jaws. The two legs of the ring insert specimen are placed in the jaws of the upper and lower peel fixtures with the connection point 5 mm from the edge of the jaw, and the bolts are tightened, the specimen and the fixture lying in one plane after clamping, as shown in Figure C.3. The tensile speed is set to 5 mm/min and the tensile machine started, pulling until the connection at the open end of the ring insert has peeled apart; the maximum force during the test is recorded, in newtons.

C.4 Calculation of the result. The peel force at the end of the ring insert junction is the arithmetic mean of five test values, kept to a whole number.

D Annex D (normative) Pull-out force of the ring insert

D.1 Apparatus. The pull-out fixture is shown in Figure D.1. Its upper part carries a pulling steel wire of not less than 1 mm diameter, which passes through the tail end of the ring insert and provides the vertical pull-out force; its lower part is a gripping fixture that holds the plastic geocell strip.

D.2 Preparation of the specimen. The ring insert is placed in the middle of the plastic geocell and not fewer than five sets are taken. The specimen is shown in Figure D.2, in which the strip length is not less than 150 mm.

D.3 Test procedure. The crosshead of the testing machine is adjusted and the whole strip placed in the jaws of the lower pull-out fixture, flush with the edge of the fixture, and the jaws locked. The pulling steel wire of the upper pull-out fixture is passed through the ring insert, the strip lying in the middle of the jaws, as shown in Figure D.1. The tensile speed is set to 5 mm/min and the tensile machine started, pulling until the ring insert has been pulled out; the mode of failure of the specimen is observed and the maximum force during the test recorded, in newtons.

D.4 Calculation of the result. The pull-out force of the ring insert is the arithmetic mean of five test values, rounded to a whole number.