Akihiko TAKAHASHI

Experimental Study on Lane's Equation for  Ground still

Tokuzo HOSOYAMADA

　Ground still exists in one of river crossing structures installed to stabilize the riverbed and maintain the longitudinal / transverse shape of the river.Ground still is a design designed to drop running water by falling and generate hydraulic water to reduce flowing water.However, since the energy of the running water is concentrated in one place around the headgear, there are not many cases where Ground still is damaged and deformed.Especially on the hydrological phenomenon acting on riverbed ground such as seepage flow caused by water level difference between upstream and downstream, characteristics of river channel of each riverIt changes greatly depending on the structural condition of Ground still.And，Lane's Equation, which is used for designing a water shield that is a structure for preventing permeate flow etc., is an empirical formula, and verification is insufficient.For this reason, we focused on Lane's Equation and conducted research.
　For the experimental method, we installed Ground still and used "Tohoku Siliceous No. 5" as a ground material and gravel.The height of the upper part of the water tapping part was set to 300 mm, and seven rows were installed so that the protective bed block section was also horizontal.In this experiment, in order to observe the percolation flow, a pore pressure gauge was installed in the riverbed ground of the second row of the protective bed block at intervals of 40 mm at ground heights of 160 mm, 200 mm and 240 mm.Moreover, in order to set the penetration path length of Lane's Equation to one, the total length of the root insertion length of the water impermeability worker was set to 150 mm and Lane's Equation was calculated. As the design conditions were satisfied,Observation was carried out for 10 minutes in the experimental waterway for each waterproof installation case.In Case 1, one waterproof worker with a rooting length of 150 mm is installed in the upstream part of Ground still, the case 2 is a waterproof worker of 150 mm in the downstream part of Ground still, 100 mm in the upstream part of Ground still,Two waterproof workers of 50 mm were installed in the downstream part.We also conducted experiments on conditions that do not install a waterblocker.
　After the value of pore pressure increased in all cases, the value of pore water pressure stabilized and equilibrium was maintained at about 2 minutes of observation time.As a result of comparing the average values of three pore pressure gauges installed for each case, it was found that the condition without the water impermeability is greater than the condition where the pore water pressure after the stabilization is larger than the condition where the shock absorber is installed.Because it can be said that the influence of seepage flow is suppressed by the water implements calculated by Lane's Equation, it is judged that the calculation of the root length of Lane's Equation is valid.Moreover, when comparing the conditions installing the waterproof workers, Case 3, in which the water shield was divided into the upstream and the downstream, had a lower pore water pressure value of about 200㎩ as compared with the other cases, Even if the penetration path length is equal, it is thought that the influence of seepage flow will change depending on the number of installed positions of the waterblocker.In other words, it seems that there is room for improvement, such as adding water conditioner installation conditions to Lane's Equation.