| In northeast of China, turfy soil developed wide-ragingly, which is formed by vegetable remains at the action of oxidization and decomposition in surface marsh . The porosity ratio, moisture content, hydraulic permeability and organic content of this soil is high. It is called turfy soil. With the rapid development of national economic, especially with the police of exploitation in west China recently, line engineering which passes turfy soil region wide-ragingly is constructed speedily. These line engineering has crossed the turfy soil region inevitably. Turfy soil is defective soft soil foundation. Limit height is the maximum filled height which embankment can bear, with fast construction (not controlling the rate of filling) without foundation base reinforcement treating in the natural soft soil foundation. When design height surpasses limit height, the embankment or foundation base must be reinforced or taken some measures to safe reclamation and normal operation. Because the engineering geology property of turfy soil is worse, it is an unfavorable soft soil base as building foundation. Embankment stability and foundation settlement are the two technology key problems. Embankment stability is the basic problem . By comparison to general soft soil base, the bearing capacity of turfy soil base is low, compressibility is large. So collapsing is easy to happen. Thus the analysis of stability in road embankment and calculation of limit height have large effect on design,construction and usage to line engineering passing this type area. At present, the study on engineering characteristic and stability of turfy soil ground-soil is very few in both domestic and foreign materials. The geomorphic characteristic, the form condition mechanism, the basic attribute and the physics property of the turfy soil is studied primary by some scholars; Some scholars have probed in the limit height of soft base and reduce the height of speedway road band. But the study on the engineering geological characteristic of turfy soil and its usage as base of building is seldom. This treatise is on the base of national-road from Hegang to Dalian . By lots of indoor tests the physical and mechanics of turfy soil are achieved. On this base, the possible failure model of the whole road embankment is explore and the stability is analyzed to determine the limit height, which is the core of this treatise. These researches will supply theory base for design and construction of road project on this type of soft soil roadbed. Key content and study work: First, engineering geology analysis of test area. This test area lies in Dun-hua region, from k1+300 to k2+520. According to prior reconnaissance report, distribution characteristics of strata to turfy soil,clay soil and gravel in this test area, area and engineering characters are determined. Field reconnaissance and sampling work are finished. Second, Analysis of soft foundation stability. By the introduce of limit height, stability analysis principle of soft soil foundation and calculate method of limit height are explained. According to roadbed,arc method is used to calculate the stability of non-homogeneous foundation. At the meantime, the application of JANBU method incalculation to stability of road embankment. Third, indoor test and achievement analysis. Determination of physical and mechanical parameters of strata is finished, which mainly includes specific gravity,water content,c ,? value of horizontal and vertical to resistance shearing(filled material included).Engineering character of turfy soil is achieved: low specific gravity,high void ratio,high water content,high compressibility,low resistance shearing and remarkable anisotropic. Four,determination of limit height. Section k1+850 is choused to study whole damage of road embankment and foundation soil. To add the comparable result of stability coefficient to slip-circle in different damage location, during calculation, the shape of slip-circle in every place is same in one filled height. That is putting the slip-circle before lower-most point to every breakdown point. (a)Calculating the stability coefficient of slip-circle both in bottom of turfy soil and clay soil, after comparison, the possibility of slip-circle along clay soil bottom is larger. (b)Cross comparison in stability coefficient in one filled height. Damage happens in left shoulder of road,centerline and location both left and right 2.5m to centerline, those stability coefficients are calculated. At every damage place, slip-circle shears out from different trace. After comparison, the minimum value is achieved. (c) Longitudinal comparison to filled height and the corresponding minimum stability coefficients. Thus limit height is determined. Originality innovation of this treatise.(a)This study is mainly to engineering geology of turfy soil as roadbed.(b) The possible failure...
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