路基 挡土墙学习.pptx
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1、Reduce driving forces,increase resisting forces,or both.Driving forces reduced by excavation and drainage to reduce the hydrostatic pressures acting on the unstable zone.Resisting forces can be increased byObjective of Slope Stabilization/Protection第1页/共84页第2页/共84页第3页/共84页A technique to reduce the d
2、riving forces within a slide mass.Excavation and lightweight fill are two common ways to reduce driving forces.EXCAVATIONRemoving weight from the upper part of the slope(removal of the head of slide)Removing all unstable or potentially unstable materialsFlattening slopesBenchingUnloading第4页/共84页Rela
3、tively large quantities of materials are taken.Applied to existing failures.One to two times the quantity originally removed at the toe of the slope during construction should be excavated from the head.Removal of the Head of a Slide第5页/共84页Total removal of all unstable or potentially unstable mater
4、ials have practical limitations depending on the volume of the moving mass and space availability.The location of other structures and existing property lines preclude the use of this method.Total Removal 第6页/共84页One of the most widely applied and economical methods for improving slope stability.Fla
5、ttening of SlopesReduce the driving forces;Force the failure surface deeper into the ground where the soil is often firmer(less weathering,less dissipation).Mechanism depicting increase in stability by flattening of cut slope第7页/共84页Failure plane changed from base failure L1 to a new critical circle
6、 L2.Failure surface was lengthened and resisting forces were increased.Flattening of Slopes-Embankment第8页/共84页Critical circle passes through the toe of the slope.Larger new critical circle radius leads to large shearing resistance(proportional to the length of the failure surface).Flattening of Slop
7、es-Embankment第9页/共84页Slope flattening on translational failure.Length of failure surface with the weak stratum was increased to increase the sliding resistance.Flattening of Slopes-Embankment(软弱岩层)第10页/共84页To transform the behavior of one high slope into several lower ones.The bench should be suffic
8、iently wide.Benching of SlopesCohesive soilSoil with cohesive and frictional strength第11页/共84页In sloping ground,benching leads to higher overall slopes and greater excavation quantities.Benching will reduce subsequent maintenance costs and thereby offset increased construction costs.Benching of Slop
9、es第12页/共84页Also used to control erosion and to establish vegetation.Vertical heights of benches are typically 25-30.Drainage to convey runoff to a discharge outlet.Benching of Slopes第13页/共84页In embankment construction,lightweight fill can reduce driving forces of the slope and increase the stability
10、.Slag(矿渣),encapsulated sawdust,expanded shale(膨胀页岩),cinders(煤渣),shredded rubber tires,polystyrene foam(泡沫聚苯乙烯),and seashell.Selection of material depends on the cost and availability in local areas.Lightweight Fill第14页/共84页Sawdust and wood fiber used to replace soils from a landside head.Exposed woo
11、d fiber and sawdust decay with time.Asphalt encapsulation applied as a retardant.Lightweight FillExcavation and lightweight fill deal used by Washington DOT第15页/共84页A technique used to offset or counter the driving forces of a slope by an externally applied force system that increases the resisting
12、force.Buttressing(扶壁支撑扶壁支撑)第16页/共84页Used to provide sufficient dead weight near the toe of an unstable slope to prevent movement.Most practical way to arrest further movement of an unstable slope.Soil and Rock Fill崩积层第17页/共84页Used to provide weight at the toe of a slope and to increase the shear str
13、ength below the toe.Useful for embankments over soft soils where the ground at the toe can move upward and form a bulge.The additional load imposed by the counterberm may increase the driving force rather than provide added resistance against sliding.Counterberms第18页/共84页Counterberms increase the le
14、ngth and depth of the potential failure surfaces and increase the resisting moments.Counterberms第19页/共84页To provide additional sliding resistance for a counterberm or rocky/soil buttress.Main purpose-force the critical slip circle deeper into the stronger underlying formation,increasing the resistan
15、ce along the slip surface.Shear Keys第20页/共84页When the bottom of the footing is a show distance below grade on the low side of the wall and/or the lateral passive resistance of the soil is low,it may be necessary to use an extension below the footing called a shear key to increase the resistance to s
16、liding.Shear Keys in Retaining Wall第21页/共84页Involve the designed use of backfill soil and thin metallic strips,mesh or geosynthetic reinforcement mesh to form a gravity mass capable of supporting or restraining large imposed loads.Mechanically Stabilized Embankments(MSE)第22页/共84页Slope face:vertical
17、or inclined.Internal stability:reinforced soil structure be coherent and self-supporting under self-weight and external load.Reinforcement not fail in tension.External stability:Resist forces that can cause overturning,sliding at or below the base,and global instability.Like a conventional retaining
18、 wall.Granular backfill is commonly used in MSE slopes.Mechanically Stabilized Embankments(MSE)第23页/共84页Use old automobile tires as inclusions in the soil mass instead of the metal or nonmetal reinforcement in MSE walls.Pneusol(Tiresoil)第24页/共84页Proper water drainage-the most important slope stabili
19、zation technique.Drainage reduces:destabilizing hydrostatic and seepage forces and the risk of erosion and piping.Surface DrainageTo ensure surface runoff is carried away from and not seeping downwards into the slope.Catchment Parameters To Be ConsideredDrainage第25页/共84页Failure on potential slip sur
20、face passing below the phreatic surface.Methods to accomplish subsurface drainage are:Subsurface Drainage第26页/共84页Natural slope not reliable for subsurface drainage design as compared with engineered embankment slopes.Understand the slope geological structure and choose a drainage system to intersec
21、t major water-bearing layer.Use piezometers(压力计)to monitor pore pressure before and after construction.Also monitor drainage efficiency reduction from siltation,deterioration of seals,pumps breakdown.Subsurface Drainage第27页/共84页Subsurface Drainage第28页/共84页A thin layer(10)of poor-quality saturated so
22、il at a shallow depth(1ton/sq ft and 稠度0.8,no loss of load or movement with timeRetaining Wall-Tieback Walls第50页/共84页Retaining Wall-Tieback Walls第51页/共84页Retaining Wall-Tieback Walls第52页/共84页Vegetation(grass,shrubs,and trees),effective and advantageous for soil stabilization.Vegetative covering remo
23、ved after cuts and embankments;surface soil exposed and susceptible to runoff and wind attack.Vegetation stabilization by intertwining its roots,minimize seepage of runoff by intercepting rainfall,retard runoff velocityRelatively inexpensive,self-repairing,visually attractive,no heavy or elaborate e
24、quipment required.Susceptible to blight(枯萎)and drought,difficult on steep slopes.Vegetation第53页/共84页Vegetation-Root ReinforcementRoot reinforcement in soils provides apparent cohesion(冷杉)(桦树)(云杉木-铁杉属)第54页/共84页Interception and transportation of moisture by trees-maintain drier soils and mitigate or d
25、elay the onset of waterlogged or saturated soil conditions(slope failure).Felling trees-wetter soilsClimate determines the relative contribution of transportation and vegetative modification of soil moisture to prevent landslides.Precipitation greatly exceeds potential evapotranspiration(water in so
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