Sensitive clay

The presence of sensitive clay in a reclamation or borrow area involves some specific issues and challenges  

Sensitive clays can be very hazardous. Disturbances caused by dredging, construction activities or changes in chemical (e.g. salt) content of the groundwater can, for instance, result in a sudden loss of strength of sensitive clay. This may trigger a soil mass instability responsible for damage to equipment, structures or even loss of hfe. 

The sensitivity of clays is defined as the ratio of their undisturbed and remoulded strength, and varies from about 1.0 for heavily over-consolidated clays to values 

Control of sensitive clays is very difficult to achieve, apart from the obvious precaution of avoiding sources of disturbance like pile driving, excavation, etc. Exceeding a certain (peak) shear strength may result in a considerable loss in strength. Most measures focus on damage control rather than measures related to the clay sensitivity itself. Possible measures include  

Knowledge of the presence of sensitive clays at or near borrow and/or reclamation areas in the planning phase of a project is clearly of great importance. The selection of these areas depends on the risks imposed by these sensitive clays and the cost for precautionary or remedial measures. Since the precise combination of factors that determine the sensitivity of clay is still unknown, occurrence of sudden strength loss is difficult to predict. Therefore, laboratory tests are necessary when the presence of sensitive clays is likely. These tests include the determination of the strain rate dependent strength behaviour (Leroueil et al, 1985), mineralogical and chemical content, the moisture content and the particle size distribution. 

---

A variety of shale-protective muds are available which contain high levels of potassium ions (10). The reaction of potassium ions with clay, well known to soil scientists, results in potassium fixation and formation of a less water-sensitive clay. Potassium chloride, potassium hydroxide, potassium carbonate [584-08-7] (99), tetrapotassium pyrophosphate [7320-34-5] (100), and possibly the potassium salts of organic acids, such as potassium acetate [127-08-2] (101) and formate, have all been used as the potassium source. Potassium chloride is generally preferred because of its low cost and availabihty. 

Lefebvre, G., and LeBoeuf, D. 1987. Rate effects and cyclic loading of sensitive clays. Journal of the Geotechnical Engineering, ASCE, 113, No. 5, pp. 476-489. 

Mitchell, R. L., Sangrey, D. A., and Webb, G. S. (1972), Foundations in the crust of sensitive clay deposits, Proceedings on Performance of Earth and Earth Sup>ported Structures, Purdue University, Indiana, ASCE, 1, No.2, pp. 1051-1072. 

F Special study soils, e.g. liquefiable soils, sensitive clays, organic soils, soft clays > 36 m thick ... 

S2 Deposits of liquefiahle soils, of sensitive clays, or any other soil profile not included in types A - E or S1 ... 

The presence of sensitive clays may have a significant impact on the design of the reclamation and the foundations of the future structures. Further, due attention shall be paid to an appropriate execution method for the dredging and reclamation works. Engineers should be aware of the consequences preferably already during the initial design stage of the project. 

Reaction of low-salinity or high-pH fluid filtrate (pH 12) with formation minerals, causing swelling or dispersion of sensitive clays and migration of fines through clay effects or mineral dissolution ... 

S2 Liquefiable soils sensitive clays or any soil not of type A to E or S] ... 

---