【Discussion of the Day】Utilities – Water Resources and Hydropower – 20210531

1) Layout of the bottom contour line for the clay gate foundation: The main consideration is how to reduce the seepage pressure at the bottom of the gate in order to enhance the stability of the gate chamber. For this reason, impermeable barriers are often laid horizontally rather than using sheet piles, in order to avoid disrupting the natural structure of the soil and causing concentrated seepage. The drainage facilities can be moved forward to beneath the gate slab to reduce the seepage pressure on the slab and facilitate the accelerated consolidation of clay. (2) Layout of the underground contour line for sandy soil sluice foundations: aimed primarily at preventing seepage deformation and reducing leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of sheet piling and suspended piling can be used, with drainage facilities placed beneath the protective barrier ； If it is fine sand, short piles can be added at the upstream end of the covering to increase the seepage path and reduce the seepage gradient. When the sand layer is thin and there is an impermeable layer beneath it, It is best to use a tooth wall or sheet piling to cut through the sand layer, and provide drainage beneath the protective barrier. For silt foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piling. (3) Layout of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-reduction wells can be installed at the bottom of the stilling basin, extending into such confined water or permeable layer.

(1) Layout of the underground contour line for the clay gate foundation: The main consideration is how to reduce the seepage pressure at the bottom of the gate in order to improve the stability of the gate chamber. To this end, horizontal waterproofing is provided for the facilities upstream of the lock chamber, while the drainage facilities are arranged in the section downstream of the lock floor or beneath the bottom slab of the stilling basin. Sheet piles are generally not used to avoid damaging the structure of the natural soil and causing concentrated seepage.  (2) Layout of the underground contour line for sandy soil sluice foundations: primarily to prevent seepage deformation and reduce leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of covered and suspended sheet piles can be used, with the drainage facilities arranged below the stilling basin ； If it is fine sand, short piles can be added at the upstream end of the covering to increase the seepage path and reduce the seepage gradient. When the sand layer is thin and there is an impermeable layer beneath it, it is best to use toothed walls or sheet piling to cut through the sand layer, and to install drainage systems below the stilling basin. For silty foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piles. (3) Layout of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-reduction wells can be installed at the bottom of the stilling basin, extending down into that confined water or permeable layer

Layout of the underground contour line for clay gate foundations: Clay possesses cohesion and is less prone to piping, but it has a low friction coefficient. When arranging the underground contour line, the main consideration is how to reduce the seepage pressure at the base of the gate in order to enhance the stability of the gate chamber. ⑵Layout of the underground contour line for sandey soil foundations: When the foundation is made of sandey soil, its friction coefficient with the base plate is high, resulting in a poor ability to resist seepage deformation; moreover, its seepage coefficient is also high. Therefore, when designing the underground contour, the focus should be on preventing seepage deformation and reducing leakage. ⑶Arrangement of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-reduction wells can be installed at the bottom of the stilling basin, extending down into that confined water or permeable layer.

(1). Arrangement of the underground contour line for sluice foundations in cohesive soil: The main consideration is how to reduce the seepage pressure at the sluice bottom so as to enhance the stability of the sluice chamber. For this reason, impermeable barriers are often laid horizontally rather than using sheet piles, in order to avoid damaging the natural structure and causing concentrated seepage. The drainage facilities can be moved forward under the gate base slab to reduce the seepage pressure on the slab and facilitate faster consolidation of the clay. (2) Layout of the underground contour line for sandy soil sluice foundations: aimed primarily at preventing seepage deformation and reducing leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of covered and suspended sheet piles can be used, with the drainage facilities placed beneath the protective barrier; in the case of fine sand, short sheet piles can be added at the upstream end of the covered structure to increase the percolation path and reduce the percolation gradient. When the sand layer is thin and there is an impermeable layer beneath it, it is best to use tooth walls or sheet piling to cut through the sand layer, and to install drainage systems below the stilling basin. For silty foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piling. (3) Layout of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-reduction wells can be installed at the bottom of the stilling basin, extending down into that confined water or permeable layer.

The layout of the underground profile is closely related to the quality of the foundation soil, as described below. 1. Cohesive soil foundations: Cohesive soils possess cohesion, making them less prone to piping, but they have a low friction coefficient. Therefore, when arranging the underground profile, the drainage facilities can be moved forward under the gate floor to reduce the seepage pressure beneath it and facilitate faster consolidation of the clay (Figure 1), thereby improving the stability of the gate chamber. Seepage prevention measures often involve horizontal laying rather than the use of sheet piling, in order to avoid damaging the natural structure of the clay and creating concentrated seepage pathways between the sheet piling and the foundation. When a confined permeable layer is present in a cohesive soil foundation, vertical drainage should be considered to remove the confined water. 2. Sandy soil foundation: There is no cohesion between sand particles, making piping likely to occur; preventing seepage-induced deformation is the main consideration ； Sandy soil has a high friction coefficient, so the requirement to reduce seepage pressure is relatively low. When the sand layer is thick, a combination of paving and sheet piling can be used, with the drainage facilities arranged on the retaining wall. If necessary, an additional short pile can be installed at the front end of the bedding to increase the percolation path ； When the sand layer is thin and there is an impermeable layer beneath it, sheet piles can be inserted into that impermeable layer ； When the foundation is made of fine sandy soil, to prevent foundation liquefaction, the area around the gate foundation is often enclosed with sheet piles, along with an appropriate drainage system. Due to the effect of bidirectional head pressure, drainage facilities are installed on both the upstream and downstream sides of the sluice, while the impermeable barriers cannot be extended. During design, the side with a larger head difference should be given priority, with the other side serving as a secondary factor; in addition to reducing osmotic pressure, other measures should also be taken to improve the stability of the lock chamber.

Layout of the underground contour line for sluice foundations on cohesive soil: The main consideration is how to reduce the seepage pressure at the sluice bottom so as to enhance the stability of the sluice chamber. To this end, impermeable barriers are often laid horizontally rather than using sheet piling, in order to avoid disrupting the natural structure of the soil and causing concentrated seepage.

(1) Layout of the underground contour line for the clay gate foundation: The main consideration is how to reduce the seepage pressure at the bottom of the gate in order to enhance the stability of the gate chamber. For this reason, impermeable barriers are often laid horizontally rather than using sheet piles, in order to avoid disrupting the natural structure of the soil and causing concentrated seepage. The drainage facilities can be moved forward to beneath the gate slab to reduce the seepage pressure on the slab and facilitate the accelerated consolidation of clay. (2) Layout of the underground contour line for sandy soil sluice foundations: aimed primarily at preventing seepage deformation and reducing leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of sheet piling and suspended piling can be used, with drainage facilities placed beneath the protective barrier ； If it is fine sand, short piles can be added at the upstream end of the covering to increase the seepage path and reduce the seepage gradient. When the sand layer is thin and there is an impermeable layer beneath it, It is best to use a tooth wall or sheet piling to cut through the sand layer, and provide drainage beneath the protective barrier. For silt foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piling. (3) Layout of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-reduction wells can be installed at the bottom of the stilling basin, extending into such confined water or permeable layer.

1) Layout of the bottom contour line for the clay gate foundation: The main consideration is how to reduce the seepage pressure at the bottom of the gate in order to enhance the stability of the gate chamber. For this reason, impermeable barriers are often laid horizontally rather than using sheet piles, in order to avoid disrupting the natural structure of the soil and causing concentrated seepage. The drainage facilities can be moved forward to beneath the gate slab to reduce the seepage pressure on the slab and facilitate the accelerated consolidation of clay. (2) Layout of the underground contour line for sandy soil sluice foundations: aimed primarily at preventing seepage deformation and reducing leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of sheet piling and suspended piling can be used, with drainage facilities placed beneath the protective barrier ； If it is fine sand, short piles can be added at the upstream end of the covering to increase the seepage path and reduce the seepage gradient. When the sand layer is thin and there is an impermeable layer beneath it, It is best to use a tooth wall or sheet piling to cut through the sand layer, and provide drainage beneath the protective barrier. For silt foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piling. (3) Layout of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-reduction wells can be installed at the bottom of the stilling basin, extending into such confined water or permeable layer.

(1) Layout of the bottom contour line for clay gate foundations: The main consideration is how to reduce the seepage pressure at the base of the gate in order to enhance the stability of the gate chamber. To this end, impermeable barriers are often laid horizontally rather than using sheet piling, in order to avoid disrupting the natural structure of the soil and causing concentrated seepage. The drainage facilities can be moved forward to beneath the gate slab to reduce the seepage pressure on the slab and facilitate the accelerated consolidation of clay. (2) Layout of the underground contour line for sandy soil gates: primarily to prevent seepage deformation and reduce leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of sheet piling and suspended piling can be used, with drainage facilities placed beneath the protective barrier ； If it is fine sand, short piles can be added at the upstream end of the covering to increase the seepage path and reduce the seepage gradient. When the sand layer is thin and there is an impermeable layer beneath it, It is best to use a tooth wall or sheet piling to cut through the sand layer, and provide drainage beneath the protective barrier. For silt foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piling. (3) Layout of the underground contour line for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-relief wells can be installed at the bottom of the stilling basin, extending into such confined water or permeable layer.

(1) Layout of the underground contour line for the clay gate foundation: The main consideration is how to reduce the seepage pressure at the bottom of the gate in order to improve the stability of the gate chamber. To this end, horizontal waterproofing is provided for the facilities upstream of the lock chamber, while the drainage facilities are arranged in the section downstream of the lock floor or beneath the bottom slab of the stilling basin. Sheet piles are generally not used to avoid damaging the structure of the natural soil and causing concentrated seepage. (2) Layout of the underground contour line for sandy soil sluice foundations: aimed primarily at preventing seepage deformation and reducing leakage. For foundations with thick sand layers, such as coarse sand or gravel, a combination of covered and suspended sheet piles can be used, with the drainage facilities arranged below the stilling basin ； If it is fine sand, short piles can be added at the upstream end of the covering to increase the seepage path and reduce the seepage gradient. When the sand layer is thin and there is an impermeable layer beneath it, it is best to use toothed walls or sheet piling to cut through the sand layer, and to install drainage systems below the stilling basin. For silty foundations, to prevent liquefaction, a closed layout is generally adopted, with the foundation of the gate enclosed by sheet piles. (3) Layout of the underground contour lines for special foundations: When there is confined water or a permeable layer in a weakly permeable foundation, in order to reduce the adverse effects of the confined water on the stability of the lock chamber, drainage and pressure-relief wells can be installed at the bottom of the stilling basin, extending down into that confined water or permeable layer.