Performance Analysis Of Sheet-pile-wall System In Expansive Soil Slope At Ji-Tu-Hun High-speed Rail In Seasonally Frozen Region

Strongly weathered and fully weathered expansive soil are more discovered in seasonally frozen region in recent years, there being rich shallow groundwater. China has entered a new period of accelerating the development of high-speed rail, therefore more and more high-speed rails are constructed in the complexly expansive soil slope field. For expansive soil slope, freezing-thawing cycles and engineering activities become important reasons which seriously affect stability of expansive soil slope.Hence retaining structure is carried out on slope as effective protective measures.Sheet-pile-wall system is widely used due to which has many advantages such as retaining stably, easy construction and so on. For the design and construction of sheet-pile-wall system, taking into account effect of freezing-thawing cycle, reducing project cost and enhancing stability of sheet-pile-wall system have become urgent problems to solve.Based on reviews of research at home and abroad, basic physical and mechanical test, conventional static triaxial test and static triaxial test considering effect of freezing-thawing cycle are conducted by relying on Ji-Tu-Hun high-speed rail.Afterwards, basic physical and mechanical properties, strength and deformation characteristics are obtained from these tests, which provide parameters for establishing numerical model of sheet-pile-wall system of typical section of Yanji segment. Finally important parameter analysis is finished to provide advices and references for the design and construction of sheet-pile-wall system in expansive soil slope in seasonally frozen region. The main contents and understandings obtained from this paper are as follows:Firstly, grain density test, grain analysis test, limit moisture content test, compaction test, free expansive rate test, and consolidation test are carried out for expansive soil of Yanji. After tests, the results show that the soil is both weak expansive soil and silty clay of middle compressibility.With the increase of numbers of freezing-thawing cycle, all of coefficient of compression, compression index and rebound index are increased gradually;however, modulus of compressibility is decreased.Then, conventional static triaxial test and static triaxial test considering effect of freezing-thawing cycle are operated for expansive soil of Yanji. Strength and deformation characteristics are obtained from these tests under different degree of compaction, different confining pressures, and different numbers of freezing-thawing cycle. The results show that stress-strain curve of samples are mostly hardening type.With increasing of degree of compaction, effective cohesion and friction angle are rised generally; while effective cohesion and friction angle trend to decreasing gradually with numbers of freezing-thawing cycle increasing. In general, all of static strength, elasticmodulus and shear strength of samples are descended gradually with the rising of numbers of freezing-thawing cycle; whereas all of those are raised with increasing of confining pressures and degree of compaction.Finally, the finite element numerical simulation and analysis for sheet-pile-wall system in expansive soil slope of Yanji are finished. The influences of different numbers of freezing-thawing cycle, pile length, pile width and pile height on characteristic of soil uplift, horizontal displacement of pile, soil pressure of pile back, stability of pile body are discussed. Meanwhile, these results show that with the increase of the excavation depth and numbers of freezing-thawing cycle, horizontal displacement of pile is rised,and stability of pile body is decreased; however, horizontal displacement of pile is declined and stability of pile body is increased with the rising of pile length, pile width and pile height. When designing sheet-pile-wall system, there is an optimal length of pile; increasing pile’s width and height will help to reduce the horizontal displacement of pile top and improve stability of pile body. Under the same cost, increasing pile’s height is more obvious effect than pile’s width.