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Application Example of Geosynthetic Clay Liner on Huge Artificial Lake

 1.Project Overview

Huizhou Fuli Hot Spring Hotel is located in Weipo Town, Huicheng District, Huizhou City, which the anti-seepage area of artificial lake is 35,000 m2, water storage capacity is 60,000 m3. As Party A has high requirements for artificial lake water saving and landscape effect, in order to ensure high-quality anti-seepage effect and maximize cooperation with the landscape, so geosynthetic clay liner is selected as the impervious material of lake bottom. Practice shows that the seepage prevention effect of geosynthetic clay liner is satisfactory. 
The general plan of artificial lake is shown in Figure 1.

2.Brief Introduction of Seepage Prevention Technology of Geosynthetic Clay Liner

a)Material Composition
Geosynthetic clay liner (hereinafter referred to as GCL) is a new type of environmentally friendly waterproof material. GCL consists of 3 layers: the upper and lower layers are geotextile, the one is geotextile cloth, and another is non-woven geotextile, with the main role of protection and reinforcement, so that is has a certain overall anti-shear strength and anti-tensile strength, and the middle of GCL is natural sodium bentonite grain layer.
The GCL made of natural sodium bentonite has the characteristics of strong ability of bounding water, and the bentonite particles in the laboratory conditions can be expanded to 15 ~ 17 times when meeting water, and then form a layer of dense colloid hat can effectively cut off the penetration of water.
The chemical composition shown in Table 1.
Silicon Dioxide Bauxite Crystal Water Ferric Chloride Magnesium Chloride Sodium Carbonate Lime Others
60 20 6 5 3 3 1 2
Table 1: The Chemical Composition of GCL
b)Material Advantages of GCL
GCL has the following advantages:
i.It has Strong anti-seepage ability, unique swelling capacity and high expansion ratio, which can penetrate into the crack gap within 2 mm of the concrete structure. It has the function of repairing the cracks by itself, even if the water leakage point exists, the bentonite will migrate and self-healing;
ii.It has a wide range of applications, the bentonite is fully wrapped by 2 layers of geotextile fiber with high tensile strength and erosion resistance, and it will not be reduced the impermeability when meeting the wet and freeze-thaw cycle, which can be constructed in the harsh climatic environment below -30℃.
iii.It has a convenient construction that can be easy to transport and install. GCL is soft and can be cut and stitched in an complicated shape, and the seams at the overlap just need to be sprinkled a certain amount of bentonite sealing powder that can meet the seepage prevention requirements;
iv. The chemical properties of GCL will not be affected by time and the surrounding material changes, so the product will not aging and corrosion like the polyurethane coating or other rubber-like waterproof material, with long service life;
v.The product is non-toxic, tasteless, pollution-free and will not cause harm to the human body and the surrounding environment.
c)The Key Technical Indexes of GCL (as shown in Table 2)
Items Performance Index Items Performanc
Expansion coefficient(mL/2g) ≥22 Tensile strength(vertical and horizontal)(kN/m) ≥10
Moisture content(%) ≤12 Peel strength(N) ≥65
Fluid loss(mL) ≤18 Bentonite quality per unit area(g/m²) ≥4500
Water permeability coefficient(cm/s)


Vertical water permeability coefficient(cm/s) ≤5 × 10-9
Tensile force(N) >422 Indicate flow[m³/(㎡·s)] ≤0.5
Impact resistance(N) >445 Anti-hydrostatic pressure(24h, 0.5MPa) No leakage

Table 2: The Key Technical Indexes of GCL

3.Construction Method

a)The Main Process of Construction
Construction processes: foundation treatment→material reception test before construction and stacking→treatment of soil sudgrade and check before acceptance→laying and check before acceptance of GCL→covering and compaction of plain soil at the lake bottom→Sand bottom backfilled with medium sand and pebbles→lakeshore slope covered with pebbles
The GCL construction of this project is divided into 6 sections for construction.
b)Treatment of Foundation and Soil Subgarde
The geological conditions of the bottom of the artificial lake is rather harsh,  and the silt layer is 7 ~ 9 m, so there is no construction operations at all. After the research, first, backfill the earthwork of 2m thick, and then use the cement spraying pile for foundation solidification treatment after the construction machinery can walk on. 
After the foundation solidification treatment, the lake bottom are mechanically and manually trimmed to meet the design elevation and shape requirements. The foundation surface must be smooth and with no vegetation, spikes, stones, sticks, construction debris and other foreign objects that may damage the GCL. Then compacted with a roller compactor to remove car prints, footprints and floor bumps. 
The soil subgrade compacted to the design elevation, which the flatness should meet the requirements, and after passing the acceptance of all parties, the GCL can be constructed.
c)Material Reception Test Before Construction
The GCL is required to provide the product certification, test reports and other relevant information before entering the site, and through the random inspection by the site supervision. The GCL of wide width should be selected a flat and dry place to stack up and covered with plastic sheeting.
d)Laying Method
According to the actual situation of the project and the condition of the machinery and equipment, a bulldozer shall be used for paving when laying the GCL on a lake bottom with a large area, and the other small areas or complex parts shall be manually laid.
i.Large-scale laying method is the bulldozers driving backwards, and spreading out the GCL that hung in front of bulldozers (As shown in Figure 2)
The laying and lapping of the GCL should be parallel with the incline direction of the slope. If the slope is greater than 1:4, within 1 m between the laying site and the top or bottom of the slope, the GCL must not have a transverse lap.
ii.Using the artificial laying method for the special parts or complex parts such as small area or retaining wall facades, according to the actual situation in the field, the GCL should be cut into small pieces, and when laying the irregular parts that should reduce the overlapped joint of the GCL.
e)Structural Measures
i.Laying towards: when laying the GCL, the black side should be paved on the soil subgrade, and the offwhite side should be faced the upstream face that is toward the surface of the lake.
ii.Plane laying method: the GCL connection is used the overlapping method, and the overlapping width should not be less than 100 mm, and the joint should be staggered laying by using the triangle shape method. At the same time, using the nails and washers with nails to compact the GCL, and evenly spread the bentonite sealing powder to enhance the waterproof effect (as shown in Figure 3).
iii.Waterproof structure of the lake bottom: In the GCL laying process, in case of lake bottom pipeline site or column root, the gap should be filled with bentonite sealing powder or bentonite sealing paste, and then laying the GCL (as shown in Figure 4).
iv.Overlapping method of vertical revetment: using the steel nails to fix the GCL at the pool wall, the vertical overlapping width should not be less than 100 mm (as shown in Figure 5).
v.The fixing method of the GCL of soft revetment or slope: the anchorage ditch with 300 mm × 300 mm is excavated around the revetment, burying the end of the GCL into the anchorage ditch, and filled with solid or compacted with concrete.
vi.The strengthen treatment of local damage: during the construction process, in case of local damage of the GCL, a complete GCL can be used to repair and cover in accordance with the size of the damage plus 100 mm.
vii.The seam of the bizarre part: in addition to using bentonite sealing powder to reinforce, but also the appearance of the joints need to be coated with the slurry bentonite to reinforce.
f)Surface Protection of GCL
i.The GCL must be immediately compacted by the clay of 150 ~ 200 mm thick after laying, and should be used the tire machinery not the crawler machinery. When the vehicles of transporting earthwork runs on the GCL, it should go straight slowly and straightly to try to avoid turning.
ii.It should be used the manpower to lay the medium sand with 100 ~ 150 mm thick and pebbles combined with water layer at the bottom of the lake after it backfilled the soil. The backfill should be strictly inspected, shall not contain sharp-edged stones, boulders and other debris, so as not to cause damage to the GCL.
iii.At the slope of the lake bank, the surface of the GCL shall be compacted with cement mortar of high-strength with 40 mm thick bricked with pebbles of 100 ~ s150 mm 

4.Construction Notes

a)On-site management personnel and construction technicians must be trained and instructed by the manufacturer on site to be familiar with product requirements and technical measures for construction. Before construction, technical personnel should submit technical explanations and fill in technical certificates.
b)Require suppliers to provide the factory certificate, product instructions, performance test reports, and the material test should be made in accordance with the requirements.
c)Laying, lapping and closing of GCL should meet the design requirements and construction specifications, and be solid and stable, no hollowing, no damage,no slipping, no tilting and no wrinkles and so on. 
d)The distance between the lapped joint of GCL and the nightside and sunny side should be not less than 200mm.
e)During the construction process, attention should be paid to pumping regularly to ensure that the underground water level is lower than the cushion under 200 mm.
f)The GCL laid on that day must be covered by the backfill or the temporary tarpaulin, and it can not has no covering to pass the night.
g)The GCL should be stacked at the scene designated place, using the wood braces and planks to keep the GCL away from the floor, and covered with plastic film, which should be avoided rain soaking, sun and damp.
h)Do not construct in rainy or windy conditions. In case of rain, the plastic sheet shall be used to cover the GCL immediately to avoid the rainwater soaking and scouring the GCL to affect the construction quality. If the GCL is hydrated without cover, it is necessary to replace the hydrated part.
i)Construction workers are not allowed to wear nail shoes, so as not to damage the GCL.


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