Study On Permeability Of Saturated Soft Clay And Effects On Large Deformation Consolidation

As the change of the stress condition in soil stratum, the permeability may change correspondingly. There is distinct influence of permeability on excavation and preloading engineering in soft clay. It is significant in theory and engineering practice to study the permeability characteristic of soft soil in different loading conditions.Based on a series of laboratory seepage tests of the soft clay in Guangzhou Panyu, the permeability characteristics under loading and unloading are investigated. The influence of permeability on one dimensional large deformation consolidation is analyzed, by experience formula obtained from the tests.The testing results show that the permeability characteristics of soft clay can be reflected by the fitting relationship of permeability coefficient k and void ratio e, k(e) = k₀exp[Q(e-e₀)].Soft clay's permeability relates to its preconsolidation pressure p_c, it may change little whenupper load exceeds 4 p_c.Consolidation pressure affects the seepage velocity of water in soilmainly in initial loading stages, and with consolidation pressure increasing, seepage velocity gradually tends into a steady range. Loading path and unloading path affect little on permeability of soft clay. It's revealed that initial hydraulic gradient exists in soft clay, which accords with the Darcy's seepage law solely in different phases of hydraulic gradient. The seepage failure of soft clay is characterized by soil flowing when the sample there is no vertical pressure; whereas, when the vertical pressure acting on the soil, the effusing of little soil grain is the main form of seepage failure.The calculated results of large deformation consolidation theory indicate that the large deformation method is more accurate to predicate the time-dependent consolidation deformation, especially when the consolidation time is relatively finite, in this case, using Terzaghi consolidation method would bring unacceptable error. The permeability of soil layer has a sufficient impact on the transmission velocity and depth of upper load, enhancing the transmission velocity would greatly shorten the consolidation time. When the settlement of thicker compression stratum is calculated by means of large deformation method, which considering permeability coefficient varies with depth, it is necessary to take a discount for the stratum.