The results are compared against published noerosion, excessive erosion and continuing erosion thresholds. Using dispersive clay soils in hydraulic structures, embankment dams, or other structures such as roadway embankments can cause serious engineering problems if these soils are not identified and used appropriately. The crumb test, astm d6572, and double hydrometer test, astm d4221, usually define this. It is evident that some simplest embankment dams were constructed about 3000 years ago in the cradles of ancient cultures such as egypt, indian, sri lanka, peru. If you are not an asabe member or if your employer has not arranged for access to the fulltext, click here for options. When wet these soils are prone to compaction and water erosion. A non dispersive clay usually undergoes little erosion, even under sustained flow through the hole under a head of up to 40 inches. A rating of nd2, nd3, or nd4 indicates the soils are slightly to moderately dispersive. Dams founded on dispersive soils and rocks drilling and.
Internal erosion of dams and their foundationswill be most valuable to dam engineers, researchers and students who are involved in assessing the safety of embankment dams from internal erosion and piping. Many earth dams, hydraulic structures and other structures like road way embankments have suffered serious erosion problems and have failed due to the. Dams founded on dispersive soils and rocks drilling and grouting under difficult conditions. All southern municipalities have dispersive soil risks and tunnel erosion is not uncommon.
These soil is a major contributing factor to piping failure of embankment dams figure 2. Pdf for the pdf version or on the title for the html version. The erosion features such as rill and gully marks, channels. Geotechnical engineering of dams pdf download free ebooks. Coarsegrained, noncohesive soils, in general, erode more rapidly and have lower critical shear stresses than finegrained soils.
Dispersive soilscharacterization, problems and remedies irjet. Contractors bid to construct embankments with highcapacity machines on a. Photographs of failed embankments with antiseep collars dispersive clays are extremely erodible soils and cracks in the earthfill. Characteristics and problems of dispersive clay soils bureau of. Dams without filters and responding to seepage incidents. The region of tlemcen in algeria is well known for its rich water sources. Tim overhue dispersive soils are structurally unstable when wet and often lack structure when dry. Leaking farm dams department of primary industries. This problem is worldwide, and structural failures attributed to dispersive soils have occurred in many countries.
Many of these failures occurred in embankments constructed using dispersive clay soils. This paper deals with determination of physical and mechanical properties of dispersive soil. Typically dispersive soils are found in the subsoil as the topsoil is usually nondispersive. Unfortunately, this book cant be printed from the openbook. Experiential investigation on the stabilization of. Contact erosional behaviour of foundation of pavement. Soil type the soil used to build the embankment must be impermeable, so the embankment can hold water. Figure 1 shows the untreated dispersive soil with a standard hydrometer and parallel hydrometer test with an identical soil specimen, but without chemical dispersant. Dispersive clay soils collapse or disperse to form dissolved slurry when in contact. The most striking characteristics of dispersive formations such as weathered granite found in. The problems may occur suddenly and cause catastrophic failures. If you need to print pages from this book, we recommend downloading it as a pdf.
A rating of nd1 indicates the soil is not dispersive. Thousands of embankment dams exceeding 20 meters in height have been constructed throughout the world. The history of embankment dams is much earlier than that of concrete dams. Blanket treatment of embankment slopes and zoning plan for.
Base materials tested include both dispersive and nondispersive soils. As a result of its name, it is like a dispersive medium, where the soil particles are dispersed in the pore fluid between them. This is where base stability is of most concern and where a majority of the borings should be located, particularly if the nearsurface soils are expected to consist of soft finegrained deposits. Reclamations earth manual usbr, 1974, 1990 identifies the following criteria for. Pdf internal erosion resulted from dispersive soils in. It points out that there are aging processes, and a project may be developing aging characteristics which need to be. The paper comments on the validity of the adopted thresholds and the effectiveness of the nef test as a filter evaluation method.
Definition of dispersive soils dispersive soils are those which by the nature of their mineralogy, and the chemistry of the water in the soil, are susceptible to. Using dispersive clay soils in hydraulic structures, embankment dams, or other structures such as roadway, embankments can cause serious engineering problems if these soils are not stabilized and used appropriately. The piping failures of a number of homogeneous earth dams, erosion along channel or canal banks, and rainfall erosion of earthen structures have been attributed to the colloidal erosion along cracks or other flow channels formed in masses. Methods for assessment and identification of dispersive soils.
Southern africa has more than its fair share of dispersive soils and rocks. In such case, the dispersive soil particles can be easily transported through the large pores of the working platform layer under water movement, resulting in soil loss of the dispersive embankment and the subsequent settlement of the pavement layers. A second test, such as the double hydrometer test, should be performed to verify the dispersion characteristics of soils grading as a 3 or 4 in the crumb test and to detect any dispersive properties of soils grading as a 1 or 2. Movement of air and water into dispersive soils is poor, making them prone to waterlogging see farmnote 3862009 identifying dispersive soils. Soil mechanics note sm discusses dispersive clays in detail, including performing field tests to identify them. In such soils, the peculiar phenomenon happens with an increment in moisture content that sometimes inflicts significant damages on construction projects. Embankment dams were low on the scale of public confidence for many centuries. Dispersive soils can be caused by high sodium content i. Study the existence of dispersive assiut university. A dispersive clay soil will erode rapidly under a low 2inch head within 10 minutes of flow initiation. The safety of an ageing population of embankment dams is a cause for concern in many european countries. The soils that are highly susceptible to erosion and containing a high percentage of exchangeable sodium ions are called dispersive soils by sivapullaiah et al.
Internal erosion can initiate under low hydraulic gradients less than 0. Identification and management of dispersive soils electronic. Table 2 shows a high percentage of soils with dispersive characteristics, exhibited dispersion when tested by a double hydrometer test. Prepared by the ussd committee on materials for embankment dams. Dams constructed of earth and rock materials are generally referred to as embankment dams or filltype dams. Much research has been done and experience gained during recent decades to improve the identification process and to develop adequate preventive and remedial techniques to ensure successful and judicious utilization of these materials for embankment dams and. The problems related to dispersive soils are common through out the world. Some defensive measures may need to be incorporated into the. Embankment dams constructed of dispersive clays can fail, because of internal erosion through cracks or other opening in the fill. Pdf susceptibility of dispersive clay at grenada dam. Store the topsoil for completion of the embankment. Lime treatment of dams constructed with dispersive clay soils. Improving the characteristics of dispersive subgrade soils. An earthfill embankment dam is made by building a foundation wall that is embedded into the rock below the dam to prevent water flowing beneath it and then creating a core of impermeable clay on top of this figure 8.
Sinthe dam in myanmar sinthe dam 3 dam located in the nay pyi taw region. Using dispersive clay soils in hydraulic structures, embankment dams, or other structures such as canal lining, roadway embankments can cause serious engineering problems if these soils are not. This problem is worldwide, and structural failures attributed to dispersive clays have occurred in many countries. A rating of d1 or d2 indicates the soils are dispersive enough to require special designs if the soils must be used in the project. Using dispersive clay soils in hydraulic structures, embankment dams, or other. In cohesive soils the onset of internal erosion occurs when the shear stress imposed by water flow exceeds the critical shear stress of the soil, determined from the hole erosion test or similar. Knowledge of the erosion characteristics of the soil in the core of an embankment dam aids in the assessment of the likelihood of dam failure due to piping erosion. An overview paper based on the papers and discussion at the workshop describes the state of the art and research needs. Photographs of failed embankments with antiseep collars dispersive clays are extremely erodible soils and cracks in the earthfill surrounding the conduit were attributed to have caused these failures. Why dispersive soils and tunnel erosion are an issue. Smn17 summarizes the properties of dispersive clay soils, discukses the proper way. From a study of case histories, the features in an embankment dam. Often along a penetrating structure such as outlet works conduit, spillway wall, or floor slab. A questionnaire was sent to federal and state agencies, consulting firms, and private consultants experienced in the design and safety evaluation of embankment dams.
Use of dispersive soils in embankment dams causes serious problems that may be difficult to solve later unless this type of soil is adequately defined and properly used. Materials for embankment dams united states society on dams. Softening materials in contact with water including dispersive and expansive soils iv. Geotechnical failures case histories of construction on. For dispersive clay soils to erode, a concentrated leakage channel such as a crack even a very small crack must exist through an earth embankment. Earth dams constructed on dispersive soils have suffered internal and surface erosion. A european working group on internal erosion in embankment dams was formed in 1993 and has examined the hazard posed by internal erosion to existing dams. Manual, sustainable land use department of primary industries and water. Bureau of reclamation, earth manual, part 2, third edition, denver, co, 1990. Investigation of rate of erosion of soils in embankment dams. Above this the remaining structure is built from earth. Piping in an earth dam is the progressive internal erosion of the soil by the flow of water along preferred seepage paths such as cracks or sandy lenses traversing the width of the dam. Dispersive soils and their management department of primary.
Dispersive soils are not suitable for foundation or fill material in the construction of hydraulic earth structures. Dispersive clay soils are those with unique properties which under certain conditions deflocculate and are rapidly eroded and carried away by waterflow. Soil dispersivity is mainly due to the presence of exchangeable sodium present in the structure. The white paper is of interest to owners of dams and those responsible for the safety of existing dams. The paper provides an outline of important points that need to be recognized and understood when selecting material for use in embankment dams. Soil is the foundation material which supports loads from the overlaying structure. Soils that have a 1 or 2 crumb test reaction occasionally are shown to be dispersive in other tests or field performance. Chapter 9 embankments washington state department of. Dispersive formations consist of soils and rocks that deflocculate or disperse in water into its constituent particles such as sand, silt or clay. Pdf on jan 1, 2009, m hardie and others published dispersive soils and their management. Low pi silts, lean clays, fine sands, dispersive soils, collapsing soils backward erosion piping mechanism is common. Use of milk of lime for dispersive soil treatment in the.
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