Through the analysis on subsidence control mechanism of solid backfilling mining, it can be concluded that subsidence reduces greatly because backfilling body occupies the mining  space, which means that it decreases the mining height。 Actually, the mining height of solid backfilling mining, which is called equivalent mining height, is the difference between the mining height and the height of backfilling body after long time compaction and rheology by overburden strata。 Similar material simulation and in-situ measurements of solid backfilling mining show that the subsidence basin by solid backfilling mining is the same as caving method with equivalent mining height。 So, the subsidence prediction of solid backfilling mining can be switched to the subsidence prediction by caving method with equivalent mining height。 The subsidence prediction parameters and methods of thin coal seams could be used

4 Subsidence control principles and design methods under buildings

4。1 Subsidence control principles

It can be known from the theoretical analysis of equivalent mining height that the key for subsidence reduction by solid backfilling mining is to reduce the mining height of coals。 While under a particular geological and mining condition, the strata movement and deformation values can be decided by the equivalent mining height。 The task of subsidence control of solid backfilling mining is that the surface movement caused by mining should be less than the fortification criteria of buildings。 Thus, subsidence control principles of solid backfilling mining can be described as follows。 The equivalent mining height is designed according to the fortification criteria of buildings and their attachment structures, which enables the ground movement and deformation caused by mining to be less than the corresponding fortification criteria。 Based on the experience of mining under buildings, subsidence and horizontal deformation are usually selected as the fortification criteria of buildings in coal mines:

Wz≤Wc

εz≤εc

for it。

In  the  subsidence  prediction  of  solid   backfilling

where Wz

is  the  maximum  subsidence  in  the building

method, how to determine the equivalent mining   height

area after mining with the designed working face; Wc      is

the fortification criterion of ground subsidence value    in

is the key issue。 The analysis of subsidence influence

factors   by   solid   backfilling   mining   shows   that the

designed  building  area; εz

is  the  maximum horizontal

deformation in the building area after mining with the

elements   affecting   the   equivalent   height   are:     the

thickness of coal seam, the movement of roof and    floor

designed working face; εc

is the fortification criterion of

before filling, the backfilling rate, the prime compression of the backfilling body, the residual compression of the backfilling body, etc。 Then the calculation of equivalent height can be pided in two parts:

1) The height of filling body (H0) filled into the goaf can be calculated with the following formula:

H0=H−Δ−δ (1)

where δ is the gap between the backfilling body and roof, Δ is the movement of roof and floor before filling, and H is the thickness of coal seam。

2) Equivalent height can be decided by the following formula: