Earthworks treatment

Abstract

A method of extracting and treated dredged material to produce material suitable for use as a general engineering fill comprises the steps of: extracting a sedimentary material via a dredging process; testing the dredged sedimentary material to determine chemical and / or mechanical parameters of the dredged sedimentary material; incorporating a quicklime additive to the dredged sedimentary material to produce treated material; separating the treated material into two separate windrows, a first windrow for upper drier material, and a second windrow for lower wetter material; testing the upper and lower material to determine the moisture content, MC, and moisture condition value, MCV, of the upper and lower material; adding a cement binder to the upper material, and retesting the MC and MCV for the upper material; adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; and once the upper material and lower material have a MC and MCV above a defined threshold, using the upper and / or lower material as a general engineering fill.

Description

Field of the Invention This invention relates to a method of treating dredged material so the material can be reused during building works, or safely deposited in a landfill site. Background of the Invention It is well known to use dredging to widen and deepen an existing quay areas to allow larger ships to easily use the docks within these areas. Typically, the dredged material will be disposed of offsite, or it may be used in combination with alternative ground engineering or improvements such as piling or vibro improvement to allow construction within the material. Statements of Invention In an embodiment there is provided a method of extracting and treated dredged material to produce material suitable for use as a general engineering fill comprising the steps of: extracting a sedimentary material via a dredging process; testing the dredged sedimentary material to determine chemical and / or mechanical parameters of the dredged sedimentary material; incorporating a quicklime additive to the dredged sedimentary material to produce treated material; separating the treated material into two separate windrows, a first windrow for upper drier material, and a second windrow for lower wetter material; testing the upper and lower material to determine the moisture content, MC, and moisture condition value, MCV, of the upper and lower material; adding a cement binder to the upper material, and retesting the MC and MCV for the upper material; adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; and once the upper material and lower material have a MC and MCV above a defined threshold, using the upper and / or lower material as a general engineering fill. Preferably, the lime added to the dredged sedimentary material is between 1-5% quicklime additive. Further preferably, the quicklime additive is a 2% quicklime additive. In an embodiment, the steps of adding a cement binder to the upper material, and retesting the MC and MCV for the upper material; and adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; are repeated until the upper material and lower material have a MC and MCV above a defined threshold. In a preferred example, the threshold for the MCV is between 8-12%. Preferably, the threshold for the MC is less than 10%. Further preferably, the threshold for the MC is less than 4%. In an example, after the quicklime additive is added to the dredged sedimentary material, the material is sealed and left for at least 24hours before the remaining steps of the method are performed. Preferably, the cement binder added to the upper and lower material is a 2-4% cement binder. Further preferably, the cement binder is a 2% cement binder. In an embodiment, wherein the cement binder is mixed into the material using a soil stabilizer. Preferably, wherein the dredged sedimentary material is dredged from a riverbed or an estuary. In an example, the treated dredged material has a California Bearing Ratio of >3%. Further preferably, the treated dredged material is acceptable for use as engineering when it can be compacted to >95% of its dry density. In a embodiment, a solution was proposed to add lime and / or cement binder to modify the dredged material to achieve a moisture content that allowed the dredged material to be workable so it could be either re-used as an Engineering Fill material (according to standards for the site where the work will occur) or at least it could be taken off site to landfill, having had the moisture content reduced to an acceptable level for landfill. Preferably, an embodiment allows for re-using of seafloor / estuarine dredging material as a compliant Engineering fill in accordance with construction standards using lime and / or cement modification and stabilisation of the dredged material rather than disposing of the dredged material as a waste. Brief description of the figures Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Figure 1 is a flow chart of the steps according to an embodiment; Figure 2 shows an example retention area and stockpiles; Figure 3(a) shows cross sectional views of the upper and lower material from the retention area; Figure 3(b) shows an example cross sectional view of the upper material from the retention area as stored in stockpile 1; Figure 3(c) shows an example cross sectional view of the lower material from the retention area as stored in stockpile 1; Detailed description of Invention The present invention will now be described with reference to the accompanying drawing in which there is illustrated an example of a method for treating dredged material to reduce the moisture content of the dredged material so the dredged material can either be reused on site, or can be accepted at a landfill, so that it can be removed from the site. However, it will be appreciated that the present invention is not limited to the specific examples herein described and as illustrated in the accompanying drawings. Furthermore, because the illustrated embodiments of the present invention may, for the most part, be implemented using components known to those skilled in the art, details will not be explained in any greater detail than that considered necessary as illustrated below, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. A regeneration scheme was proposed to widen and deepen an existing quay area to allow larger ships to use the docks. Dredging of the estuary floor was required as part of this works. Approximately 100,000m3 of sedimentary substance from the estuary floor was dredged during the works. A significant issue with the dredged material, was that if it could not be used in the scheme as a fill material, then it would have had to be removed from site as a waste. As the material was so wet, with a high moisture content and behaved like a liquid with no strength, the local landfill sites would not accept it, without the material being treated to reduce the moisture content. The originally dredged material would be deemed unsuitable for re-use as an Engineered fill due to its excessive moisture content above what is known as the Optimum Moisture Content (OMC), which is the moisture level where the material can be compacted to its maximum density. Lowering the moisture in the dredged material to within around 10% of the OMC would likely make the dredged material workable, and a suitable earthworks material when it is within 2-4% of OMC. The Construction Industry generally deem earthworks materials acceptable for re-use if it can be compacted >95% of its maximum dry density with no less than 5% air voids. The key to achieving the construction standard for acceptable material is to control the moisture of the Engineered Fill. As well as achieving the required compaction and moisture levels, the material would need to have the required strength and stiffness for the proposed use in accordance with the Engineers Earthworks Specification, that would be produced for the proposed car park earthworks scheme. Generally, an earthworks material is required to achieve a California Bearing Ratio (CBR) of >3% within non-structural areas of a development and >5% CBR as Structural Fill. Typical Moisture Condition Values (MCV) of 8-12% are typically accepted for material suitable for compaction particularly during modification and stabilisation. As far as the Inventors are aware, using dredged material from estuaries or river beds has not been used for conventional earthworks and binder modification / stabilisation, rather other ground engineering and ground improvements have been used such as piling, vibro improvement etc or land spreading or disposal. The dredged material have been proposed to be used in earthworks, if the dredged material could not be reused in the earthworks, then it would need to be disposed off-site. The dredged material without any treatment was too wet to be used within earthworks, and if used it would not be compliant with any Earthworks Specification and the resulting soft ground would settle excessively. Even most ground improvement techniques such as vibro replacement or dynamic improvement would not be suitable for treating this excessively soft material. Piling would not be used in a car park due to it costs. Therefore, engineering the dredged material using binders to modify and stabilise the material was the only solution acceptable to try to produce suitable engineering fill from the dredged material. The first key challenge was to prove that the dredged sedimentary material would not contaminate the ground below and adjacent to where it would be placed or contaminate any nearby water bodies, including controlled water. Chemical soil and leachate testing was carried out on the dredged material before and after the dredged material had been treated, as described below, to assess the potential for the dredged material to decrease the land quality of the area of placement. The treatment as described below will make the dredged material usable, and it can be reused as engineering fill material. The dredging material was placed in designated retention areas, which were non-permeable areas so any leachates from the dredged material did not migrate into the surrounding land. The dredged material was classified as a waste, which would have had to be removed from site potentially as a hazardous waste. Because the dredged material contained a high moisture content and behaved more like a liquid with no strength, local landfill sites would not accept the dredged material with further treatment. Also because of its potential contamination chemical composition, it was not permitted to just let the dredged material drain. As the retention areas did not allow the water to drain, the dredged material could only be dried by the atmosphere. Unfortunately, air drying the dredged material from the surface did not significantly reducing the moisture content in the dredged material. As will be described in more detail below, initial laboratory chemical and geotechnical testing were performed on the dredged material, after the dredged material had been initially treated with lime to make the material usable, and then a trial modification of the treated dredged material was carried out, along with further testing of the modified dredged material, and use of the treated / modified dredged material as stabilisation earthworks. Figure 1 shows the steps of the method according to an embodiment: According to an embodiment, a method of extracting and treated dredged material to produce material suitable for use as a general engineering fill is described. In an embodiment there is provided a method of extracting and treated dredged material to produce material suitable for use as a general engineering fill comprising the steps of: extracting a sedimentary material via a dredging process; testing the dredged sedimentary material to determine chemical and / or mechanical parameters of the dredged sedimentary material; incorporating a quicklime additive to the dredged sedimentary material to produce treated material; separating the treated material into two separate windrows, a first windrow for upper drier material, and a second windrow for lower wetter material; testing the upper and lower material to determine the moisture content, MC, and moisture condition value, MCV, of the upper and lower material; adding a cement binder to the upper material, and retesting the MC and MCV for the upper material; adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; and once the upper material and lower material have a MC and MCV above a defined threshold, using the upper and / or lower material as a general engineering fill. Preferably, the dredged sedimentary material is dredged from a riverbed or an estuary. Initially, the method comprises extracting sedimentary substance from the riverbed or estuary floor through dredging operations at 102 with the dredged material placed in a retention area 202 for initial and testing . The dredged sedimentary material is tested to determine one or more chemical parameters of the dredged sedimentary material. As a result of these initial tests the dredged material in the retention area is designated as U1A (unsuitable material) in accordance with Series 600 of the Specification for Highway Works (SHW) and categorised as a waste product under the Waste Acceptance Criteria, attributable co its elevated moisture content and possible elevated chemical / metals characteristics at 104. Preferably, a quicklime additive is incorporated into the dredged sedimentary material in the retention area 202 to produce treated dredged material, the dredged material undergoes initial treatment through the incorporation of a quicklime additive at 106. In an example, the quicklime added to the dredged sedimentary material is between 1-5% quicklime additive. Preferably, the quicklime additive is a 2% quicklime additive. Preferably, after the quicklime additive is added to the dredged sedimentary material, the material is sealed and left for at least 24hours before the remaining steps of the method are performed. Subsequently the quicklime treated dredged material is placed into two separate windrows, one for upper drier material and one for lower wetter material. The material in the upper and lower material windrows is resampled and retested to assess moisture content (MC) and moisture condition value (MCV) at 108, to see if it is suitable for further use. In an example, the threshold for the MCV in the treated dredged material is between 8-12%. In a further example, the threshold for the MC is less than 10%, further preferably, the threshold for the MC is less than 4%. Figure 2 shows an example of the retention and trial areas. The retention area 202 is used for the initial testing and drying of the dredged material. After initial drying in the retention area the dredged material is separated into two different stockpiles, stockpile 1, 204, and stockpile 2, 206. Stockpile 1, 204 has the separated upper drier material from the retention area, and stockpile 2, 206, has the separated wetter material from the retention area. The properties of the two stockpiles will be determined by the necessary chemical and other tests. Figure 3 shows cross sectional views of the dredged material Figure 3(a) shows the material in the retention area, with the upper drier and lower wetter material layers 304, 306, before the layers are separated. Figure 3(b) shows a cross sectional view of stockpile 1, 204, with the upper drier material 304 from retention area 202. Figure 3(c) shows a cross sectional view of stockpile 2, 206, with the lower wetter material 304 from retention area 202. Stockpile 1, 204 the upper drier material from the retention area 202, initially exhibiting a lower as -excavated moisture content (MC), will now have attained an MC level closer to the optimum moisture content (OMC) requisite for its suitability as general fill material at 110. The MC value was determined by tests such as Earthworks and stiffness Testing (Moisture Condition Value (MCV), Compaction Curves, Unsoaked Laboratory CBR). Stockpile 2, 206, the lower wetter material from the retention area 202, initially exhibited a higher as -excavated moisture content (MC), and although the quicklime treatment for the material in this stockpile will have provided some improvement, following a period of being open to the atmosphere, additional lime will be necessary to render the material usable at 112. Again, the MC value was determined by tests such as Earthworks and stiffness Testing (Moisture Condition Value (MCV), Compaction Curves, Unsoaked Laboratory CBR). A cement binder is added to the upper drier material, and the MC and MCV of the upper drier material after the cement addition is determined. Preferably, the cement binder is a 2-4% cement binder. Further preferably, the cement binder is a 2% cement binder, mixed to the upper drier material using a soil stabilizer. Stockpile 1, 204, following the addition of 2% ordinary Portland cement (OPC), will likely now be deemed suitable for adjustment to its optimum moisture content (OM() range. The cement is also added for the purpose of binding the material to mitigate potential leaching of chemicals / metals at 114. The chemical / metals that may leach comprise one or more of Arsenic, Cadmium, Chromium, Copper, Mercury, Nickel, Lead, Antimony, Selenium, Vanadium, Chloride, Ammonical nitrogen, sulphate, cyanide (total and free) thiocyanate, complex cyanide, calcium, sodium, hexavalent chromium, aliphatic and aromatic hydrocarbons, petroleum hydrocarbons, benzene derivates, PCBs, and other hydrocarbons. A cement binder and lime additive are added to the lower wetter material, and the MC and MCV of the lower material are determined, after these additions. Preferably, the cement binder is a 2-4% cement binder. Further preferably, the cement binder is a 2% cement binder, mixed to the lower wetter material using a soil stabilizer. Stockpile 2,206, following the inclusion of 2%-4% lime preceding the addition of 2% ordinary Portland Cement (OPC), is suitable for adjustment to its optimum moisture content (OMC) range and for the purpose of binding the material to mitigate potential leaching of chemicals / metals at 116. The chemical / metals that may leach comprise one or more of Arsenic, Cadmium, Chromium, Copper, Mercury, Nickel, Lead, Antimony, Selenium, Vanadium, Chloride, Ammonical nitrogen, sulphate, cyanide (total and free) thiocyanate, complex cyanide, calcium, sodium, hexavalent chromium, aliphatic and aromatic hydrocarbons, petroleum hydrocarbons, benzene derivates, PCBs, and other hydrocarbons. In an embodiment, the steps of adding a cement binder to the upper material, and retesting the MC and MCV for the upper material; and adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; are repeated until the upper material and lower material have a MC and MCV above a defined threshold. When the upper drier material and lower wetter material have a MC and MCV above a defined threshold, then the upper drier and / or lower wetter material can be used as a general engineering fill. Alternatively, the upper drier material and lower wetter material can be safely disposed in landfill. In an example, the treated dredged material has a California Bearing Ratio of >3%. Preferably, the treated dredged material is acceptable for use as engineering when it can be compacted to >95% of its dry density. The dredged materials, initially classified as U1A (unacceptable material) in accordance with Series 600 of the Specification for Highway Works (SHW), can now be reassessed and re-classified to a Class 2A (wet cohesive) designation, rendering the treated dredged material now appropriate for utilisation as a general fill material in accordance with Series 600 of the Specification for Highway Works (SHW) at 118 The steps of the method 100 as outlined above, will now be described in more detail below. During the trial for modification of the dredged material, the dredged material was separated into two material types, these were the upper (drier) material and the lower (wetter) material, as shown as stockpiles 1 and 2, 204, 206 in figure 2. The upper drier material was drier due to it being more exposed to the atmosphere since it was deposited into the retention area . A layer of 400mm of material from the retention area was placed in a 2no. trial areas i.e. upper and lower material. That is the upper material, to a depth of 400mm is in stockpile 1, and the lower material of a depth of 400-800mm in the retention are is in stockpile 2. Each trial area (stockpile 1, 204, stockpile 2, 206)was separated into five linear areas and modified using a Binder Spreader to control the rate of distribution of the binder, and soil stabiliser with 1 to 5% lime, where each area contained 1%. 25%, 3%, 4% or 5% lime, and the material in each of the five areas was modified with lime and cement. The amount of lime used at this stage is dependent upon the results of the lab trials, and the end product use of the material Upon the results of laboratory testing and in-situ trial testing, the treated dredged material was moved to an different area, separate from the initial drying site and modified with a quicklime additive to produce a working material that could be used as an engineered fill subject to further drying or moisture modification. These further modifications may include moving material into the fill areas on top of the good material using a bulldozer or similar. Quicklime and / or cement will be evenly spread on the surface of the dredged material with a spreader / mixer. Wind speed and direction will be checked with a windsock, and work will stop if winds are high, as this is detrimental to the process. The powder additive and dredged material will be mixed thoroughly with a mixing drum to create a uniform mixture throughout the treatment depth. The treated dredged material will be compacted to ensure the reaction occurs around each soil particle. Quicklime reacts quickly, but it may need to slake longer and be rotovated again for proper pulverization. Finally, the treated dredged material will be compacted according to the Earthworks Specification. Therefore, the project had to achieve as a minimum an improvement of the dredged material so it could be sent to a landfill, but ideally improve the dredged material enough so it could be used as Engineered Fill. Both laboratory and in-situ geotechnical testing was required to demonstrate that the dredged material could be re-used as an Engineered Fill. The testing had to be demonstrated that the dredged material would not contaminate the existing ground it was proposed to be placed above, therefore chemical testing including leachate testing was conducted. Geotechnical laboratory testing was conducted to show that the dredged material could be used as an engineered fill once the moisture content of the dredged material was modified to a suitable level. A trial of placing and engineering the dredged material was also performed to allow the dredged material to be tested by geotechnical in-situ testing methods to assess how the dredged material performs in a real earthwork scenario. Once it was determined that the dredged material was not going to cause pollution, further testing could be carried out. The geotechnical properties of the dredged material were investigated to determine whether it would be a suitable material for earthworks, in terms of its stiffness and strength, and whether it was not going to swell or shrink due to organic matter decomposition or sulphate reactions. One or more of the following tests on the dredged material were scheduled: Geotechnical Chemical Tests including organic matter and Sulphates: This was to determine the levels of certain chemicals that may lead to retardation of lime / cement binder or lead to unacceptable swelling or shrinkage. Classification Testing (Atterberg limits, natural moisture content, particle size distribution, particle density}: This was to classify the material type in respect to Earthworks Standards. Earthworks and stiffness Testing (Moisture Condition Value (MCV), Compaction Curves, Unsoaked Laboratory CBR):- To determine if it would be a suitable earthworks material in its natural state, and determine moisture content range required to allow it to be used. Laboratory Trial Binder Tests (Soaked CBR): To trial the addition of lime and / or cement or other binders and additives- to improve the material into an acceptable earthwork material and assess the increase in stiffness and swell from adding binders. One or more of these tests may be performed at different stages in the method 100. The laboratorybased testing of the dredged material and the treated dredged material provided data that could be used to predict the performance of the dredged material during earthworks. Trials were carried out to test the actual performance of the dredged material within an earthwork's scenario and include insit stiffness testing such as plate load tests and Light Weight Deflectometer (LWD). All these trials and tests were used formulate a suitable binder mixture required to modify the dredged material so it could be used within a earthworks project, and not simply sent to landfill. The solution would need to satisfy the requirements that the dredged material could be reused as an Engineered Fill rather than disposing of the dredged material as waste. It would also allow a decision to be made to whether it was more beneficial to modify the dredged material to allow for disposal to landfill or to produce suitable earthworks fill material. Laboratory and in-situ trials have been performed, with the testing results showing that using lime and cement binder within the dredged material can achieve an acceptable stiffness to allow the dredged material be used as an Engineered Fill without unacceptable swelling. A binder mix has been formulated that would allow for the dredged material to be modified into a workable material that could be stockpiled, and used in different locations with the original site as engineering fill material. Available laboratory testing and site trials, suggested that modifying the dredged material with 2% lime, would result in a material that is workable with a CBR >3% when compacted. The whole 100,000m3 of the dredged material was lifted from the retention area and blended with 2% quicklime additive prior to stockpiling, in stockpiles 1 and 2, 204, 206.. Once stockpiled the quicklime was allowed to modify the dredged material in the stockpiles. The stockpiles 1, and 2 were sealed and to remain in place until the material is to be used as Engineered Fill. The sealing is done using a bulldozer then an excavator which rubs and seals the surface of the stockpiles. Further laboratory testing was carried out during this works to confirm the lime was working as expected on the material in the stockpiles, and to alter the binder mix if required. The testing also allows for monitoring any significant changes in the materials as they were processed. Typically standard swell tests will be carried out at 7 and 28 days of soaking, to help determine the effectiveness of the lime binder. Testing suggests that a moisture content of 18% is the optimum moisture content to allow the treated dredged material to be sufficiently compacted, and to be subsequently reused within the site. Moisture content values of 23-24% were typically achieved from testing of the lime modified dredged material from initial moistures of >40%. Thus, the treatment was successful in reducing the moisture content. This suggest that the dredged material is now workable. On-site visual observations also confirm this. At these moisture values, the dredged material was achieving CBR values of 3.0-3.3% when compacted in the laboratory with MCV values of 7.0-7.3%. These values show that the dredged material is close to being suitable for earthwork filling, and with slight air drying or binder modification during the earthworks phase, it would meet the requirements to be suitable for use. These modification steps are as follows: The material will be moved into the fill areas on top of the good material using a D6 dozer or similar. Quicklime and / or cement will be evenly spread on the surface with a spreader / mixer. Wind speed and direction will be checked with a windsock, and work will stop if winds are high. The powder additive and material wet of optimal will be mixed thoroughly with a mixing drum to create a uniform mixture throughout the treatment depth. The treated material will be compacted to ensure the reaction occurs around each soil particle. Quicklime reacts quickly, but it may need to slake longer and be rotovated again for proper pulverization. Finally, the material will be compacted according to the Earthworks Specification for the area. Modifying the dredged material with 2% lime has also achieved the secondary target of producing a workable material that could be accepted at a landfill. It was unknown whether the dredged material was both chemically and geotechnically suitable for re-use as an Engineered Fill. The dredged material were originally placed in retention areas, as shown in figure 2, which inhibited the water content to leachate into the surrounding ground but were of large surface area to allow the material in the retention area to air dry. Retention areas are preferably for this step due to the excessive high moisture content of the dredged material, and the size of the retention area that is used will be dependent on the amount of dredged material that will be placed in the retention area. Unfortunately, the dredged material did not dry enough in the retention area to allow the dredged material to be used as an earthwork's material, therefore the inventors of this application proposed the use of binders to modify and strengthen the dredged material. This solution would provide both financial and environmental benefits to the project. Financial benefits would need to positive when compared to disposal offsite. The environmental benefits would also be positive in respect to the waste hierarchy i.e. re-use rather than dispose. Re-using the dredged material would also reduce CO2 emissions in respect to the number of transport movements on and off site. The dredged material also contained elevated sulphates that could cause heave when lime or cement is added from the formation of the mineral ettringite. Heave in soils due to lime or cement stabilisation is the upward movement or expansion of soil. This occurs because of the following reasons: chemical Reactions, moisture absorption, freezing and thawing. In order to mitigate Heave the following should be completed: proper design and dosage: Use the correct amount of stabiliser. Adequate Mixing: Ensure thorough mixing for uniform reactions. Moisture Control: Manage moisture content during and after stabilisation. Sulphate Testing: Test for sulphates and use appropriate stabilisers to minimise expansion. The elevated organics could also retard the lime and cement from reacting, thus not reducing the moisture content and increasing strength. Initially chemical and geotechnical samples of the dredged material were sent to a laboratory for testing. These showed that the dredged material could be chemically re-used without contaminating the surrounding land. However, the dredged material contained excessive moisture to be a suitable fill material for earthworks. The organic matter and sulphate content also suggested that adding binder may also make the dredged material unsuitable for lime and cement stabilisation. Given that organic matter may retarred the binder from reacting due to low pH levels, and sulphate can cause excessive swelling of treated materials due to production of ettringite minerals. Given the results of the initial laboratory testing, further binder laboratory testing trials were carried out to investigate the effects of adding binder such as lime and cement, in respect to moisture reduction, and stiffness and strength gain. These further tests could also monitor the amount of swell over time. After reviewing the further laboratory testing, a trial was designed to simulate the actual stabilisation works within an allocated test area. Two trial areas (stockpiles 1 and 2, 204, 206) were constructed using the dredged material. Trial Pad No. 1, 204 was comprised of upper dredged material that had been more exposed to the atmosphere whilst in the retention area 202, and being at a higher elevation may have drained, thus a drier material than at depth. Trial Pad No.2, 206 was comprised lower dredged material from the retention area 202 that was less exposed and potentially wetter. Each stockpile pad was approximately 15m wide, 20m long and 400mm thick. The stockpiles 204,206 were further separated into 3m wide sections that were to be treated for different lime contents. The rational for this was that the more lime added, the higher reduction in moisture content achieved. 1 to 5% lime was added and mixed into the sections of each Pad using a Wirtgen 240 stabiliser, with section 1 receiving 1% lime, section 2 receiving 2% lime and so on. Once the lime was added and pulverised / mixed, further laboratory samples were sent to the laboratory and the treated material was sealed with a single pass of a roller and left for 24 hours to allow the lime to react. After 24 hours, 3% cement was added to the material and mixed with the soil Stabiliser. Further samples and MCV testing was carried out and within 2hrs the material was compacted with a roller. After 48 hours, in-situ LWD and plate load tests were carried out to confirm the stiffness of the stabilised material. Upon reviewing the results of the laboratory and in-situ testing, it was agreed that the dredging material will be lime modified in an area of the site, and temporary stockpiled (as previously described). This would initially allow the material to be moved to a landfill site, if required, and ideally confirm the material was suitable for re-use as an Engineered Fill. Laboratory and in-situ testing were carried out to determine the Engineering and chemical properties of the dredged material. In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the scope of the invention as set forth in the appended claims and that the claims are not limited to the specific examples described above. Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments. However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms 'a' or 'an,' as used herein, are defined as one or more than one. Also, the use of introductory phrases such as 'at least one' and 'one or more' in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles 'a' or 'an' limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases 'one or more' or 'at least one' and indefinite articles such as 'a' or 'an.' The same holds true for the use of definite articles. Unless stated otherwise, terms such as 'first' and 'second' are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A method of extracting and treated dredged material to produce material suitable for use as a general engineering fill comprising the steps of:extracting a sedimentary material via a dredging process;testing the dredged sedimentary material to determine chemical and / or mechanical parameters of the dredged sedimentary material;incorporating a quicklime additive to the dredged sedimentary material to produce treated material;separating the treated material into two separate windrows, a first windrow for upper drier material, and a second windrow for lower wetter material;testing the upper and lower material to determine a moisture content, MC, and moisture condition value, MCV, of the upper and lower material;adding a cement binder to the upper material, and retesting the MC and MCV for the upper material;adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; andonce the upper material and lower material have a MC and MCV above a defined threshold, using the upper and / or lower material as a general engineering fill.

2. The method as claimed in claim 1, wherein the lime added to the dredged sedimentary material is between 1-5% quicklime additive.

3. The method as claimed in claim 2 wherein the quicklime additive is a 2% quicklime additive.

4. The method as claimed in any preceding claim wherein the steps of adding a cement binder to the upper material, and retesting the MC and MCV for the upper material; and adding lime and a cement binder to the lower material, and retesting the MC and MCV of the lower material; are repeated until the upper material and lower material have a MC and MCV above a defined threshold.

5. The method as claimed in any preceding claim wherein the defined threshold for the MCV is between 8-12%.

6. The method as claimed in any preceding claim wherein the defined threshold for the MC is less than 10%.

7. The method as claimed in claim 6 wherein the threshold for the MC is less than 4%.

8. The method as claimed in any preceding claim wherein after the quicklime additive is added to 5 the dredged sedimentary material, the material is sealed and left for at least 24hours before the remaining steps of the method are performed.

9. The method as claimed in claim 8 wherein the cement binder added to the upper and lower material is a 2-4% cement binder.

10. The method as claimed in claim 9 wherein the cement binder is a 2% cement binder.10 11. The method as claimed in claim 9 or claim 10 wherein the cement binder is mixed into thematerial using a soil stabilizer.

12. The method as claimed in any preceding claim wherein the dredged sedimentary material is dredged from a riverbed or an estuary.

13. The method as claimed in any preceding claim wherein the treated dredged material has a15 California Bearing Ratio of >3%.

14. The method as claimed in any preceding claim wherein the treated dredged material is acceptable for use as engineering when it can be compacted to >95% of its dry density.

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