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To cure your subsidence, you obviously need someone to first find out the cause. A chartered engineer experienced in such matters will obtain the necessary information about the soil and match it with the cracking patterns in your walls. Having formed an idea about what is wrong, he/she will then arrange tests. Such tests may be as simple as drain testing or root analysis. With clay soil, it is also important to drill boreholes to obtain moisture profiles for the soil where the worst subsidence is located, at locations of suspected subsidence and also at a place away from any trees (but all boreholes will be located in areas of the same type of geology).

This helps the engineer to see if underpinning is needed and if so, how deep and how great an area is required. If chalk solution features are suspected, dynamic probes may be used. Where chalk voids as described above are found, these can be filled by pumping in grout. If subsidence seems to be caused by a leaking drain, the drain should obviously be repaired but underpinning may be needed, to ensure there is no other problem causing slight disturbance and allowing the subsidence to continue.

In most cases one tries to undertake underpinning or whatever other action is decided upon, before repairing any cracks, unless piles need to be driven next to an unsafe wall, which obviously must first be repaired to avoid it collapsing. Masonry repairs can be undertaken in several ways including injection with epoxy resin, local rebuilding of the wall, drilling holes for stainless steel bars with serrated surfaces and embedding stainless steel bars into the mortar courses.

Around the serrated surface of the bars, one places epoxy resin. Where the cracking is bad, more than one of these methods may be combined. To have your subsidence problems efficiently dealt with, I recommend you to engage the services of a chartered civil or structural engineer who has had formal training in the subject of soil mechanics and who has practical experience of analysing soil and designing foundations.