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In clay one can usually have three types of landslip failure: clay creep, deep-seated soil slip and shallow slip

1. Clay creep: the surface of the clay gradually moves down the slope. In summertime the clay dries out, shrinks and cracks form. The weight of the clay above pushes down and the cracks fill up and become compacted. In wintertime, the clay absorbs water and expands again. But the new expansion tends to be downwards at right angles to the inclination of the slope rather than upwards along the line of the slope. The following summer the cycle repeats, and so the clay gradually moves down the hill. A problem with an insurance claim for this failure mode is that many insurers have never heard of clay creep or at least maintain they have not. As the clay expansion is lateral, one might regard it as a combination of diagonal heave and subsidence but most policies talk of vertical movement when dealing with subsidence and heave. 

3. A second type of landslip, the most usual, is like the third but is a shallow slip with the slip circle close to the sloping edge. 

2. The third form of landslip in clay is a more deep-seated type of movement in which the soil slips, often along the arc of a circle of similar failure plane. (See diagram). If the clay, as in one instance I dealt with, has a layer of more moist clay in it, then the failure surface will often be found to follow the plane of the higher moisture content. Sometimes a minor failure takes place, thus giving rise to a plane along which the moisture can travel. Thus, when boreholes are bored, a local zone of higher than usual moisture in the clay is indicative of the presence of a failure plane. If part of the house in question, or whatever structure is involved, is founded on the top part of the failure zone, then there will be a reduction in support of that part of the structure with consequential cracking and possibly eventual collapse.