Abstract:
Provided is a consolidometer and methods of its use. In its preferred embodiment, the device and methods permit accurate and convenient laboratory sampling of the selfweight consolidation of media, such as soft soil and soil slurries that may result from dredging operations. One option also provides for attaching sensors at locations along the consolidometer for taking data on additional characteristics of the media.

Description:
STATEMENT OF GOVERNMENT INTEREST  
       [0001] The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     
    
     
       BACKGROUND  
         [0002]    The field of the invention is laboratory evaluation and geo-technical testing of media, in particular an apparatus and methods of its use for evaluation of soft soils or soil slurry materials.  
           [0003]    Consolidation testing of soft soil or slurry materials using traditional geo-technical testing methods and equipment is not practically possible, but predicting the consolidation behavior of such materials is of paramount importance in designing for dredged material or mine waste disposal operations, for example. During laboratory self-weight consolidation for modeling the field behavior of media such as dredged or other slurry material, the material undergoes significant strain as pore fluid drains and the media particles compact in the mix. Such strain behavior is modeled differently from that of traditional consolidation behavior. Traditionally, self-weight consolidation is assumed to be negligible and the change in void ratio is assumed to vary directly with the change in the specimen (column) height. Needed is a device and method that overcomes limitations of traditional consolidation testing by allowing self-weight consolidation to freely occur and by enabling determination of void ratio changes directly from tests of the sampled media contained inside each insert in a stack (column).  
           [0004]    The only known means of characterizing discrete layer properties of a soft soil material has heretofore been accomplished using a method in which each ring is accessed by moveably sliding an enveloping outer shell in a downward direction. The moveable outer shell has contributed to difficulties in accomplishing accurate specimen testing by unduly disrupting the self-consolidation process, and often impinges on the inner rings.  
           [0005]    A preferred embodiment of the present invention enables practical laboratory testing of soft soils and slurries to be accomplished, while validating large strain consolidation theory assumptions.  
         SUMMARY  
         [0006]    A consolidometer for determining properties of media, in particular, self-weight consolidation, is provided. As well as solids, the media include fluids incorporating suspended or dissolved solids. It uses inserts that are placed in a stacked configuration in a longitudinal frame, generally set vertically on its base in a containment device. The frame supports the inserts, typically rings, such that any media under investigation is contained wholly within the interior volumes of the inserts, e.g., the annular volume of the stack of ring inserts. The frame may be a cylinder cut in half lengthwise to permit insertion and withdrawal of said ring inserts at locations along its length. Also provided is a collection device, typically a flat tray configured to abut and secure onto any one of the ring inserts and with bosses to fit recesses in the frame. It is used seriatim with the insert rings to collect samples along the length of the media column. The ring inserts are secured to the frame in any of a number of ways, a typical method using one or more set screws for each ring insert. When a sample is taken, the set screws are removed and the ring insert slid out of the stack. Optionally, sensors may be inserted in one or more ring inserts to take additional data on the column of media.  
           [0007]    Also provided is a method for determining properties of media, in particular, self-weight consolidation properties. Using a consolidometer that represents a preferred embodiment of the present invention, one fills the stacked inserts of the consolidometer with the media to be evaluated and allows the mediate to self-consolidate. The topmost inserts that no longer contain media are removed. Then, a sample collection device, such as a specially-configured flat tray, is attached to the topmost insert having media contained in its interior volume. The set screws, or other retaining devices, are removed from the insert and the insert is slid from its position on top of the stack out over the flat sample tray. By removing the insert the media contained therein is dropped onto the flat tray for subsequent transfer to a sample vial or like container. The process is then repeated for each insert in the stack. Optionally, one or more of the inserts may be fitted with one or more sensors that provide additional information about the media at that point in the stack, based on a pre-specified data collection protocol.  
           [0008]    Advantages of a preferred embodiment of the present invention include:  
           [0009]    higher accuracy of laboratory sampling by conducting sampling and testing at discrete spatial intervals;  
           [0010]    adaptable to various types of geo-technical test and evaluation;  
           [0011]    ease of taking samples with reduced spillage;  
           [0012]    multiple laboratory functions able to be provided with a given configuration;  
           [0013]    low skill level needed for operators implementing the methods of use;  
           [0014]    low cost of the capital equipment needed to implement;  
           [0015]    low maintenance cost of the capital equipment; and  
           [0016]    low overall cost to implement including cost of necessary supplemental fabrication material.  
           [0017]    A preferred embodiment of the present invention overcomes traditional geo-technical testing constraints encountered in laboratory investigations of soft soils or soil slurries because the invention allows for material sampling, material testing, and evaluation of material characteristics during the specimen&#39;s self-weight consolidation process. This enables accurate laboratory representation and modeling of soft soil or slurry self-weight consolidation processes occurring during dredged material disposal, mine tailing operations, or other soft sediment placement scenarios. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0018]    [0018]FIG. 1A is a rendering of a preferred embodiment of the present invention in use.  
         [0019]    [0019]FIG. 1B is a top view of one of the rings connected to a sampling tray.  
         [0020]    [0020]FIG. 1C is a top view of the sampling tray and its pertinent parts.  
         [0021]    [0021]FIG. 1D is a cross-sectional view of how the sampling tray fits to the device to permit taking individual samples within the vertical column.  
         [0022]    [0022]FIG. 2A is a top view of a ring insert with a groove for an O-ring.  
         [0023]    [0023]FIG. 2B is a top view of a ring insert with a rail for mounting in a track of a structure.  
         [0024]    [0024]FIG. 2C is a view of a cross-section at A-A through FIG. 2B.  
         [0025]    [0025]FIG. 2D is a top view of a ring insert with an outlet for installation of a sensor or transducer.  
         [0026]    [0026]FIG. 2E is a top view of a ring insert with a screen for performing specialized self-weight consolidation testing.  
         [0027]    [0027]FIG. 3A is a profile of a consolidometer that uses a flexible mount attached to a base as structure for mounting ring inserts.  
         [0028]    [0028]FIG. 3B is a profile of a consolidometer that uses a rigid mount attached to a base as structure for mounting ring inserts. 
     
    
     DETAILED DESCRIPTION  
       [0029]    A preferred embodiment of the present invention provides laboratory methods and devices for evaluation and geo-technical testing of media, such as soft soil or soil slurry materials, that are being investigated after self-weight consolidation.  
         [0030]    The soft soil or slurry is placed inside the stacked inserts  101  of the consolidometer  100  and allowed to consolidate under its own weight. Consolidation occurs as the pore fluid drains out of the soil matrix and the soil particles achieve an interlocking pattern that resists further consolidation. Since the soil sample remains constrained inside the stacked inserts, e.g., the annular volume of stacked insert rings  101 , essentially one-dimensional consolidation occurs, i.e., vertical consolidation. The soil&#39;s geo-technical properties may be determined in discrete vertical intervals by serially removing the stacked inserts  101 , i.e., insert rings  101 , collecting the media, typically soil, from each ring insert  101 , and preserving the sample for further geo-technical soil testing as required.  
       EXAMPLE I  
       [0031]    Refer to FIGS.  1 A- 1 D. A consolidometer  100  supports a column of stacked ring inserts  101 . In this embodiment, the structure  102  has a semi-circular shape for both its inner and outer sides to accommodate insertion and removal of the circular ring inserts  101 . The structure  102  and ring inserts  102  may be constructed of PLEXIGLAS™, or other transparent material, to enable visual recording of the self-weight consolidation process that is not possible using traditional methods and equipment. Further, the shape of the structure  102  and insert rings  101  shown in FIG. 1A is not required. Indeed, any polygon shape may be used so long as the inserts are matched to the shape of the structure. Refer to FIGS. 3A and 3B. FIG. 3A depicts flexible hold-downs  301  attached to a base  302 . FIG. 3B depicts rigid hold-downs  304  attached to a base  303 . Even a flat panel (not separately shown) may be used as the support structure provided the stackable inserts have a flat side with suitable interfacing means to the panel. Each ring insert  102  is vertically stacked into position against the structure  102 , each ring insert individually affixed to the structure  102  such as with set screws  103 , rail  202  in FIG. 2B and slotted track  203  in FIG. 2C, bolts, slidable clamps, spring clips, or other methods of temporary attachment (all latter not separately shown).  
         [0032]    The media, typically soil or slurry material, occupies the annular space  104  in each ring insert  101  and thus forms a continuous column, wholly contained within the insert rings  101 , whose total height depends on the total number of stacked ring inserts  101 , and whose height may precisely match that of the modeled in situ material “column.” As the media consolidates, the uppermost ring inserts  101  will lose media by subsidence, and the interface boundary between any pore fluid and media particles gradually moves down the column. At a selected time, most likely at the end of the media&#39;s primary consolidation period, remaining pore fluid with minimal amounts of media particles is drained, and all empty ring inserts  101  are disengaged from the structure  102 , removed, and laid aside. The contents of the uppermost ring insert  101  that contains media may be sampled by first removing the ring insert&#39;s constraints, typically set screws  103 . A sample collection device, typically a specially configured flat plate collector  105 , is positioned on the ring insert  102 . Next, the ring insert  101  is disengaged from the structure  102 , slowly removed by grasping the ring insert pull tab  110 , and sliding the ring insert  101  outward horizontally. Once the ring insert  101  is free of the structure  102 , its contents are deposited on the flat plate  105  by lifting it vertically from the flat plate collector  105 .  
         [0033]    The collection plate  105  attaches to the structure  102  at designated points  106  and provides a smooth surface onto which an outwardly-sliding ring insert  101  releases its contents. The collection plate  105  consists of a horizontal surface with protruding bosses  107  and a ring tab pull receptor  108  located on the underside of the collection plate  105  at the same end of the collection plate  105  as the bosses  107 . To affix the collection plate  105  at each ring insert  101 , the bosses  107  are inserted into openings  109  located on the structure&#39;s  102  outer flange, and the ring tab pull receptor  108  is positioned over and mated to a ring pull tab  110 . The collection plate  105  is disengaged from the ring insert  101  and structure  102  by lifting the collection plate  105  up and away from the ring pull tab receptor  109  while pulling horizontally away from the structure  102 . This disengages the bosses  107  from the recesses  109 .  
         [0034]    The process is repeated for each successive ring insert  101  in the column. At the conclusion of sampling, no ring inserts  101  remain attached to the structure  102 . The consolidometer  100  is cleaned of any remaining media and setup for future tests.  
       EXAMPLE II  
       [0035]    Refer to FIG. 2E. Another embodiment of the method and apparatus provides for specimen testing that conforms to one-dimensional large strain consolidation theory for singly-drained specimens. Replacing the bottom ring insert  101  with a porous plate  205  permits shorter-duration consolidation which conforms to one-dimensional large strain consolidation theory for doubly-drained specimens. Doubly-drained testing models a field site where, for example, dredged material is placed directly on a coarse-grained foundation allowing free drainage through the bottom of the dredged material.  
       EXAMPLE III  
       [0036]    Yet another embodiment may be used to obtain geo-technical information in addition to self-weight consolidation values. Refer to FIG. 2D. Each ring insert  101  may be tapped or provided with an opening or outlet  204  to attach a sensor or transducer (not separately shown). For example, pore fluid pressure sensors (not separately shown) may be attached to obtain pore fluid pressure variations during the consolidation process. Density measurements of the specimen as a function of column height may be made by attachment of suitable sensors on or about the periphery of either the structure  102  or the ring inserts  101 . The consolidometer  100  may be converted readily to enable traditional consolidation testing by adding an external loading device (not separately shown) capable of controlled displacement or controlled load increment. Refer to FIG. 2A. Further, the column may be made fluid tight with the addition of O-rings in the slots  201  shown.  
         [0037]    With such adaptation, a preferred embodiment of the present invention enables consolidation behavior testing throughout the entire range of a material&#39;s plausible pore fluid content. For example, the consolidation characteristics for a dredged material may be determined for its expected life cycle void ratio range from a suspended sediment state to a fully consolidated state, without the use of additional geo-technical testing equipment such as an oedometer.  
         [0038]    Although specific functions for consolidometers and methods of their use as multiple instruments are discussed, such as self-weight consolidation measurements and consolidation behavior testing, this does not exclude other functions using the described apparatus and method from falling within the ambit of the claims herein.