Fractured Soil Foundation Bed Treatment Of Defects

Fissured clay, also known as expansive soil, is special clay distributed all over the world. This soil swell when possess water and shrink when loses water. The strength of the soil will reduce greatly because of the repetitive expansion and shrinkage. This will lead to great danger for the safety of engineering with pavement cracking, ground settlement and slope failure. In railway engineering there is slope failure, landslide, settlement of subgrade and shoulder of road pushing.Those diseases are concerned to soil ingredient, mineral composition, crystal structure and hydrophilic property, Minerals of clay are mainly kaolinite, montmorillonite and illite, which are composed of silica tetrahedral and hydroxo-aluminium octahedral. Crystal faces are combined by molecular bond, such as montmorillonite; this kind of combination is very weak and inserted by a great deal of polar water molecule and hydration cation, which results in soil disaggregation and losing the combination strength. Crystal faces of kaolinite are combined by hydrogen bond and th'ose of illite are combined by K"1" ion. This kind of combination is relatively stronger but the soil will soften for the minerals have excessive negative charge, which lead to adsorption polar water molecule.Because of the hydrophilic property of clay minerals and the repetitive dynamic load of the train the soil of subgrade will soften, which results in a lot of diseases of foundation bed such as mud pumping, settlement of ballast, etc. In order to repair those diseases measures are adopted, such as soil replacement, laying chloroprene rubber plates, strip geodrain or geotextile. Those measures could not meet the requirements because of the restrictions of construction condition, construction quality and materials quality. It is proved that mud pumping of foundation bed will recur not long after the construction of sand cushion, laying chloroprene rubber plates or geotextile, thus the above-mentioned measures are not adopted now. The only effective measure above mentioned is laying strip geodrain, which gains advantages of construction conveniently, application widely and the life span will be 36 years if the construction quality is guaranteed. On the other hand it demands tooverground the track and to limit the speed of train then affects the running of train. In addition multi section construction is impossible because the length of strip is long that limits the construction progress.In order to treat diseases of foundation bed effectively, Ankang railway engineering section and Southwest Jiaotong University developed a new pavement solvent, which is a polymer composed of acrylic acid and urea-formaldehyde plastics. This pavement solvent could be laid under track bed when middle repair. For this pavement solvent, it is controlled to solidify in 3 to 5 minutes, and the compressive strength within 2 hours is 177kpa, and can reach 522kPa after 25 hours; and the tensile strength within 6 hours is 140kpa, and foundation coefficient within 24 hours (Kao) is 180Mpa/m. This material possesses elastic property and performs satisfactorily, therefor it is named elastic pavement solvent. It is proved by practice that this material is worth popularizing.