Theory Study On Design Parameters Of The Horizontal Drainage System Of Consolidation Method

Consolidation method is applied increasingly to improve the soft ground with the construction of high grade highways,airports, port harbors and large area reclamation projects. The drainage capacity of vitical drains has been paid more attention in the past,but drainage capacity of horizontal drainage system has been overlooked.Actually, whether the water in the sand mat can be drained effectively or not will affect improvement effect and construction time limit.The impact of horizontal drainage system on soft ground improvement is subsidiary stress decrease due to residual hydraulic head and ground settlement, and the change of drain boundary.The residual hydraulic head of sand mat formula was derived based on existed research and simplifed by using relationship between settlement and settlement velocity.On condition that underground water table outside project region was constant, subsidiary stress was derived by considering loading regime,settlement and residual hydraulic head.Consolidation equation was established based on a series of assumptions. Average consolidation degree was equal to Sc (t) divided by S c calculated by using e-p curve.Theoretical solution was derived under the condition of equal vertical strain. Total settlement varying with time ,which must be amended by experience coefficient, was derived by using theoretical solution and S c* calculated by using e-log(p) curve.Theoretical solution was verified by using typical project examples in ShenZhen area. Results indicated that computational methods were reasonable and theoretical solution was correct.The impact of settlement,residual hydraulic head and loading regime on settlement process was analysed based on theoretical solution. Results illustrated that ,first,if water in preloading area was not pumped out immediately or design of horizontal drainage system was defective,settlement and residual hydraulic head would affect improvement adversly;second, if water in preloading area was pumped out immediately and design of horizontal drainage system was reasonable,settlement would not affect improvement,but residual hydraulic head would affect improvement to a certain extent in consolidation process,not affect final effect. In the end,coeffective of residual hydrualic head was discussed.Results showed that the longer construction time limit was,the bigger designed coefficient of residual hydraulic head could be; and vice versa. Design parameters of horizontal drainage system were also dicussed based on change law of coefficient of residual hydrualic head.The results showed that blind drainage distance, thickness and permeability coefficient of sand mat affected ground settlelment process to some extent, so construction time limit and loading regime must be considered comprehensively when these parameters are designed.