Soft ground

Y) Vertical Recovery Test. The purpose of this test is to det causes of malfunctioning of artillery fuzes when the projectiles are fired at very high angles of elevation, such as 83 to 90° and are landed on their bases on soft ground. A fuze passes the test if it is landed without damage so that it can be examined. A detailed description of the test is given in the Journal of the JANAF (Joint Army-Navy-Air Force) Fuze Committee, Serial No 41 (July 1966) (p IIIB-14 of Ref 39)... 

Locomotion Need to move Walking on soft ground Loose housing, exercise yard, pasture Combination of hard flooring and littered areas... 

Resting behaviour Lying on soft ground Species-specific raising and lying down Litter Flexible side partitions of cubicles... 

Table 5.4-1. Oxide Composition of a hard and soft Ground Coat Enamel for Steel- plate (in % by weight).

Source Bergato, D.T. et al, "Soft Ground Improvement", p 24, ASCE Press, 1996. Reproduced by permission of ASCE, Reston, VA. 

C. Wayne Clough, W.H. Baker, and F. Mensah-Dwumah, Development of Design Procedures for Stabilized Soil Support Systems for Soft Ground Tunnelling, Final Report, Oct. 1978, Stanford University, Stanford, California. 

Early wells were sunk by ramming. This was replaced by rotary drilling, where the bit turns at 50 to 300 revolutions a minute. Different bits are used for soft or hard rocks or coring. They tend to crumble the rock. Drilling speed can vary from 8 inches an hour in hard rocks to 100 feet per hour in soft ground. 

Schmidt, B. 1989. Consolidation settlement due to soft ground tunneling. In FYoceedings of the Twelfth International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro. Rotterdam A.A. Balkema, pp. 797-800. 

Vane shear test correction factor as a function of plasticity index. (From Bjerrum, L., Embankments on soft ground. Proceedings on Performance of Earth Supported Structures, American Society of Civil Engineers, 11, 1-54, 1972. Reprinted with permission of ASCE.)... 

Bjerrum, L. 1972. Embankments on soft ground. Proceedings of the ASCE Conference on the Performance of Earth-Supported Structures, 2 1-54. 

Micro piles (a.k.a. mini piles) of diameter 150-300 mm are used especially for underpinning of existing structures in distress, as well as support for structures (buildings and bridges) in difficult ground conditions, particularly in shallow karsts limestone formations, boulders in granite formations as well as soft ground over shallow hard formation (Ooi et al. 2004). 

The usage of self-boring or displacement type pressuremeter may improve the results for tests carried out on soft ground. However, due to wider commercial availability, greater experience in... 

Yee (2004) has provided theoretical arguments as to why the FVS test is the preferred investigation method in investigating Su in soft ground over other in situ methods such as the pressuremeter. 

Yee TS. 2004. Shear strength and structural stability of construction in soft ground Proc. Malaysian Geotech. Conf. 2004, Kuala Lumpur 475 95. 

In a number of design situations, piles have to be designed for effect of lateral soil movement. These include piles in or near an embankment built on soft clay, bridge abutment piles in soft ground, piles adjacent to an excavation, piles in unstable slope and piles in a marginally stable riverbank. These piles are called passive piles (De Beer 1977). As these piles will experience additional stress and strain, failure to assess the effect in design will result in unacceptable pile movement or stress or both. 

Ting Tan (1997) reported another interesting case history of excessive movement of a riverside structure subjected to high fluctuating water level. Findings from this case history are significant because, in Malaysia, excessive structure movement of structures like wharves built in coastal (invariably soft ground) areas are not uncommon, but mechanism of such failure has not been identified before that. 

For unsymmetrical loading (like embankment on soft ground), soil movement profile can be simplified as shown in Figure 8.3(a). In the case of unstable slope, the most critical slip surface will be determined and a uniform soil movement to its full depth can be assumed as shown in Figure 8.3(b). 

It can be seen from the table that the steel H-pile has the best overall performance. It also has an advantage over the tubular steel pile in being the lower in displacement and thus causing lesser disturbance to the soft ground during pile driving. The concrete spun pile is unsuitable because of the low moment resistance. 

Cortlever, N.G. 2001. Design of double railway track on Augeo Pile System. Symposium on Soft Ground Improvement and Geosynthetic Application, AIT, Bangkok. 

Two types of reinforcement are commonly used. The first is a very thick steel pipe which is preferred for very soft ground. This pipe can also serve as the tube a manchettes . The second type of reinforcement is in the form of extra-large diameter steel bars. Cross-sections of typical micropiles with the two types of reinforcement are shown in Figure 12.23. 

Gue, S.S. Tan, Y.C. 2003. Prevention of failures of bridge foundation and approach embankment on soft ground. Proceedings of 2nd International Conference on Advances in Soft Soil Engineering and Technology. Putrajaya, Malaysia 245-258. 

Direct settlement of soft ground under loading can be of unacceptable proportions. Ideally, this should be a matter for design. In practice, natural variability of the ground or lack of knowledge of the founding materials may well mean some hazard is left to be determined at the construction stage. 

Soft ground may also create problems due to a requirement for flatter back slopes to excavations and by the lack of a firm platform for the operation of plant. Unconsolidated material can result in quicksand developing especially on flat estuarial areas. This is especially the case where dense sand material overlies soft material. 

Pisani, R., 2002. Footwear and soft ground interaction, PhD Thesis, Salford University, UK. http //usir.salford.ac.uk/2170/ [accessed 15 February 2012]. 

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