10.2.2 Decreasing the creep influence

The definition of creep is given as the condition where deformation increases with time，provided the stress remains constant.Creep usually occurs in clayey soils.The softer the soils are，the more obvious the characteristics of creep could be.Creep relates to time and stress.It increases with the increase of the stress level and time and covers a long period of time.Since soils near the retaining wall and on the excavation surface may be on the verge of the ultimate condition，the stress level must be high.As a result，soils with prominent characteristics of creep are susceptible to over settlement.

To prevent creep from occurring，especially when excavating in soft clayey soils，struts have to be installed as soon as each stage of excavation is completed.Strut installation usually takes a few days in braced excavations.If the top⁃down construction is adopted，it takes a few weeks to construct floor slabs.During the process of strut installation or floor slab construction，creep may continue worsening.The expedient way to handle this is to lay a layer of pure cement，usually at least 10 cm thick，on the excavation surface as soon as the excavation stage is completed（which is also necessary in practice to facilitate the construction machines operating on the excavation surface）.It is not easy to examine the effect of such a measure in the prevention of creep though it is considered to be useful to a certain extent from both theoretical and empirical points of views.