Fill mass properties

The shear strength of the fill mass and the subsoil determines the resistance against shear failure. This is relevant for bearing capacity and slope stability. Sufficient resistance against shear failure must be guaranteed during and after the construction. Tests available for determination of the shear strength are referenced in Appendix B. 

Specifications for land reclamation projects sometimes include requirements with respect to the bearing capacity of the fill mass in view of the construction of shallow foundations. It is important to realise that the bearing capacity not only depends on the shear strength of the fill mass but also on the geometry, dimensions and depth of the foundation. The bearing capacity can be checked by direct and indirect methods. The following direct methods are available to measure the bearing capacity of the fill  

These tests are in more detail described in Appendix B. 

The bearing capacity can also be assessed based on indirect measurements such as CPTs and SPT s. The resistance measured in the fill correlates to a friction angle, which is used in a theoretical bearing capacity formula. Another option is to perform triaxial or direct shear tests on the fill material at its in-situ density in order to measure the actual friction angle. 

Slope failure can be a consequence of constructing side slopes which are too steep along the periphery of the reclamation area. Precipitous placing of fill on soft subsoil, without allowance for consolidation and subsequent increase of shear strength, may also result in geotechnical instability. In both cases circular or noncircular failure mechanisms can be developed. 

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In case no suitable quartz sands are available from a borrow area within a reasonable distance to the site, or from maintenance dredging or capital dredging, other fill materials may have to be used such as clay, carbonate sand or rock. These materials have a different mineralogy, particle size distribution, grain shape, etc. which results in different and/or unexpected fill mass properties. However, by adequately addressing the typical properties of these materials, it may be possible to construct a reclamation that meets the specifications. The possibilities and restrictions of the use of these materials for fill is described in Chapter 9. 

Fill mass properties related to method of placement... 

Depending on the future use of the reclamation area and the thickness of the fill, mud waves may result in inadequate fill mass properties. Following measures can be taken to prevent these mud waves ... 

If quality control after the construction of a reclamation reveals that certain parts do not have the specified fill mass properties then it is occasionally required to remove the poor quality fill material. However, ground improvement could be a viable alternative (in respect of quality, time and cost) to repair these deficiencies without the need to replace the inferior fill by higher quality material. 

Generally, ground improvement can be carried out at any location and at any time after construction of the reclamation. This makes it feasible to limit the improvement to those locations where it is actually required, for instance, along the alignment of a future road or runway or at the footprint of a structure. Should other locations also need better fill mass properties, then ground improvement can be undertaken where and whenever required. 

Usually the Contractor selects or proposes the most cost-effective and suitable construction method to realise the fill mass properties according to the performance requirements and within the boundary conditions. It is essential, however, that the designer of a hydraulic fill also has a thorough understanding of the possibilities and limitations of the various construction methods including dredging and reclamation operations and soil improvement techniques. 

Infiltration is the process by which water at ground surface enters the subsoil. The infiltration capacity depends on various fill mass properties such as permeability and storage capacity. 

Attaining symbiosis between the reclamation and civil works is often important. The required fill mass properties derived from an optimised structural design may, however, not always be technically and economically feasible given the boundary conditions (e.g., nature of existing subsoil, quality of the fill material available) and the dredging equipment available (see Figure 2.3). 

An overview of the most relevant dimensional and technical aspects to be monitored and tested for land reclamation projects is presented in Table 11.1. A subdivision is made with respect to the fill geometry, the fill material properties and the fill mass properties. 

Occasionally it may be preferable to directly measure the required fill mass properties. Zone Load Tests and, to a lesser extent, Plate Loading Tests give reliable information about the stiffness and the strength of the fill mass. 

An intermediate option is a form of contract in which the performance requirements (and possibly also the design methods) are specified. The definition of the required fill and fill mass properties (including possibly required soil improvement techniques) is done by the Contractor. 

Following fill mass properties are relevant for the design of a reclamation area and should be tested in the field. (See Section 12.4.9)... 

Various direct or indirect tests are available to assess these fill mass properties (see also Appendix B). 

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