| There are many ancient dammed lakes in the Minjiang River Basin,forming a series of sediments,the most typical of which is the Diexi ancient dammed lakes sediments.Due to the lack of understanding of the engineering characteristics of the sediments,the problems such as insufficient roadbed subsidence,lack of bearing capacity,slope instability,soil erosion and so on,are appeared in the highway such as G213.Therefore,it is of great significance to study the engineering characteristics and disposal measures of the sediments of the ancient lake in the Diexi.Therefore,the study on the engineering characteristics and treatment measures of the sediment of the Diexi ancient dammed lake is of great significance to the construction of highway traffic in this region.Based on the data collection,literature review and field investigation,this paper understands the basic characteristics of the sediments of the ancient dammed lake in the Minjiang River,and analyzes the material composition by sampling test and parallel comparison method.Through the laboratory test of the original sample and the disturbance sample,the basic parameters of physical,hydrological and mechanical properties of the sediments were obtained,and the influencing factors of the indexes were fully analyzed,and and then a systematic understanding of its engineering geological characteristics were formed.This paper summarizes the main engineering geological problems of sediments,and analyzes the causes of the engineering characteristics,and puts forward effective control measures for concrete examples.The main findings of this study are as follows:(1)The sediments of Diexi ancient dammed lake distribute along the both sides of the Minjiang River from Xiaoguanzi to ZhenPing,extending about 30 Km,the maximum thickness of which is nearly 243 m.The sediment develop the horizontal bedding,wavy bedding and oblique bedding.Bedding appears color(gray,yellow)changes in the law,the thickness of the rhythm layer is generally 2-5cm.Affected by the earthquake,there are deformation structures such as volume,flame and saucer shaped structure.The main mineral compositions of the sediments are illite,chlorite,quartz,plagioclase,calcite and dolomite.The grain size was mainly composed of fine particles with an average content of 82.72%,and the content of powder was up to 78.5% with a mean value of 61.81%,and the content of clay was the second.Local areas such as Mizoguchi,dammed lake tail with high content of silty sand.The difference among the material composition of different color layers is obvious.(2)the natural density of the whole sediment of the paleo lake of the DieXi River changed greatly,being among 1.71~1.92g/cm3;the porosity was generally,and the moisture content was 6~22%.Plasticity difference is bigger,and Ip changes in 8~17.Permeability is small,and K value in 1.50E-07~5.39E-06.Expansion and contraction are poor,and inflation rate was less than 7%,which belongs to non expansive soil.According to the results of particle analysis and plastic test,the sediments are classified into clay,silty clay,silt and silt.There are some differences in the physical and hydro physical properties of the sediments:the permeability of silty and silt is better;but the density of silty clay and clay is larger,and the plasticity and the expansion and shrinkage are good.(3)The mechanics test shows that:(1)the sedimentation coefficient a1-2 of the DieXi ancient barrier lake is between 0.059 and 0.22MPa-1,which belongs to lower to medium compressible soil.The consolidation coefficient was at the level of 10-3,and the consolidation speed is slow.The compressibility of the composites increases with the increase of clay content or the increase of water content,and decreases sharply with the increase of the density.(2)The CU strength value of the direct shear test of sediments is close to the intensity of triaxial CU test,and the variation range is not largebut the extreme value of UU intensity is different,especially the Cu value of UU is as high as 93.1kPa,which is related to the matrix suction in unsaturated soil.When the content of fine particles is high and the degree of gradation is good,the shear strength is also large.With the increase of water content,the shear strength C increases first and then decreases.Although the value of ? is decreasing,but the regularity is not obvious.(3)The maximum dry density obtained by sedimentation in real time is 1.673~1.701g/cm3,and the optimum water content is 14.17 ~ 16.00%,and the difference is not significant.The higher the water content of the sediments,the higher the dry density,and the higher the ratio of low water content,the greater the impact on the sediment compaction.(4)The sediment was formed for a long time,the material with fine grained,and the density is often higher with a certain cement.Despite the disturbance of earthquake liquefaction phenomenon,but research shows that a recent earthquake has not formed in the signs of liquefaction in the deposited layer.By means of the critical standard penetration number method,it is concluded that there is no possibility of liquefaction in the natural state.(4)Due to the special engineering geological characteristics of the sediments of the sediments of the Diexi ancient Dammed Lake,there are some problems such as roadbed settlement,insufficient bearing capacity,slope slump and soil erosion in the distribution area.For the settlement of subgrade is too large or uneven settlement,the replacement or composite foundation treatment are suggested.The foundation of the bridge can be reinforced by Static Pressing Anchored Pile or micro-pile,and optimized with post-grouting pile.For the better stability of the slope,slope rate method can be used;When the stability is poor,retaining wall,soil nail wall,anchor frame,and other supporting measures are adopted.Slope protection should be combined with the slope greening,using three-dimensional vegetation net and so on,so as to form a systematic ecological protection system. |
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