Soil–building Interaction under Surface Horizontal Strain Induced by Underground Mining

: Underground mining will cause the ground to deform, leading to the destruction of buildings. 8 Horizontal strain is one of the most important causes of damage to strip foundation buildings. However, 9 related research is insufficient, making the mechanism of building damage caused by horizontal strain 10 unclear and resulting in several difficulties in performing coal mining under villages. In this study, 11 interface slip and soil pressure caused by the horizontal strain of ground transfer between soil and 12 buildings are investigated, and stress concentration in buildings driven by soil movement is considered 13 the primary cause of building damage. The influences of the mechanical parameters of the soil and the 14 geometric parameters of building on stress distribution inside a building are analyzed by establishing a 15 stress distribution model of a building under different ground horizontal strain. Softening the foundation 16 or designing deformation joints inside a building can reduce the influence of horizontal strain on the 17 building. This research can provide an important reference for performing coal mining safely under 18 villages and designing building protection against ground horizontal strain.


Introduction 21
As one of the most important energy sources, coal will still be utilized on a large scale in the next 22 few decades. However, ground movement and deformation caused by underground coal mining cause 23 damages to adjacent buildings and endanger the safety of properties and residents [1][2]. Although ground 24 movement can be reduced via filling mining, strip mining, and harmonic mining, understanding how 25 ground deformation acts on buildings and the interaction between ground deformation and building 26 damage will promote the development of coal mining technology that can be performed safely under 27 villages and building protection technology against surface movement and deformation[3].

28
Three major types of ground deformation are caused by mining: inclination, ground bending, and 29 horizontal strain. Among which, inclination and ground bending are caused by ground subsidence, while 30 horizontal strain is caused by ground horizontal movement. Inclined deformation can easily lead to the 31 instability, or even collapse, of the foundation of high-rise buildings. Meanwhile, ground bending and 32 horizontal strain pose a greater threat to common strip foundation buildings in ordinary villages [4].

33
Research on building damage caused by ground deformation has been conducted from different 34 perspectives. Bakri hypothesized that tunnel excavation will cause a deflection change in buildings, 35 leading to their destruction. Thus, the influence of soil shear deformation should be considered when 36 studying the transfer of deformation from ground to buildings [5]. Kahi analyzed the soil-structure

52
Moosazadeh applied an artificial neural network model and the particle swarm optimization algorithm 53 to predict damage to buildings caused by surface deformation [13].

54
The primary research object of previous scholars is surface deformation caused by tunnel excavation, 55 in which ground bending is more evident and horizontal strain is less apparent. Ground surface horizontal 56 strain caused by underground coal mining is severe. If the damage mechanism of buildings caused by 57 horizontal strain is not studied, then developing effective protection methods for ground buildings against 58 underground coal mining will be impossible. The current study investigates the interaction mechanism 59 between soil and walls on the basis of the characteristics of surface horizontal strain caused by 60 underground coal mining. Then, it clarifies the internal stress accumulation characteristics of buildings 3 under different soil mechanics characteristics, building characteristics, and horizontal strains, and thus, 62 identifies the destruction law and mechanism of buildings under surface horizontal strain. Lastly, it 63 proposes protection methods for buildings under horizontal strain. This research can provide an important 64 reference for conducting coal mining under villages and designing building protection strategies.

65
Characteristics of ground horizontal strain caused by coal mining 66 After coal is mined underground, a subsidence basin with an area that is considerably larger than 67 the mining area will form on the ground. During subsidence, the surface will move to the center of the 68 subsidence basin. Horizontal strain of the surface will form as shown in Fig. 1

77
where e is the horizontal strain between two points on the surface, ui is the horizontal displacement of 78 the ith point, ui+1 is the horizontal displacement of the (i+1)th point, and li~i+1 is the horizontal distance 79 between the ith and (i+1)th monitoring points.

80
In China, the probability integral method is the leading strategy for mining subsidence 81 prediction[14] [15]. The basic model is as follows:

83
where W is the surface subsidence, m is the mining height, a is the coal seam dip, q is the subsidence 84 coefficient, r is primary influence radius, and s is the working face length.

85
Surface horizontal displacement U is related to subsidence, and its calculation formula is The prediction formula for surface horizontal strain e is Interaction between the building foundation and the soil

Interface slip between the soil and building the foundation 98
In accordance with a study, the contact relationship between rock and soil interfaces satisfies the    In accordance with Coulomb's shear strength criterion, the interface will be destroyed once the 108 interface tangential force reaches the maximum value that it can bear.  126 Active earth pressure state: As shown in Fig. 3, when the wall moves away from the soil, wedge 127 ABC slides into the same direction and wall pressure enters an active state. In such case, the relationship 128 between the lateral displacements of the wall Ua and the shear deformation of slip surface ε1 is as follows: where φ is the internal friction angle of the soil, H is the depth of foundation buried in soil.

6
In accordance with the principle of limit equilibrium, the critical depth of active earth pressure z is where  is bulk density of soil.

134
When the shear deformation of the soil ε1 increases from 0 to the ultimate shear strain εmax, the 135 pressure formed between the soil and the wall changes from static into active earth pressure. Assuming 136 that the stress-strain relationship in this process is a straight line, the relationship between wall lateral 137 pressure Paʹ and wall lateral displacement in an active state is as follows:

138
When H<z, where Pa is the total active earth pressure, and P0 is the static earth pressure.
where Pp is the total passive earth pressure.   ()

Analysis of additional stress in buildings under surface horizontal strain
x u x ex  (17) 180 The relative displacement between the transverse wall foundation and the soil is as follows:

181
' 2 x l ue  where sn 2 is the foundation bottom pressure, H is the foundation height, and h is the wall height.

212
The horizontal stress acting on the longitudinal wall through the combined forces on both sides of 213 the transverse wall is as follows:

215
At this moment, the horizontal stress in each part of the longitudinal wall foundation is as follows:

Stress distribution inside the foundation 219
On the basis of the soil experiment conducted by Wilson (2009), the internal cohesion is 14 kPa, the 220 internal friction angle is 44°, the shear modulus is 1.07 MPa, the ultimate shear strain is 1%, and the

Stress distribution in buildings under different factors 246
In accordance with the preceding analysis, the major factors that affect the relationship between

275
Friction angle in the soil: When surface horizontal strain is less than 1.5 mm/m, the additional 276 horizontal stress in the building foundation hardly changes with a change in the friction angle in the soil.

277
When surface horizontal strain is greater than 1.5 mm/m, the additional stress in the foundation increases 278 sharply with increasing internal friction angle. Simultaneously, the ultimate horizontal strain increases 279 with an increase in friction angle. When the internal friction angle is 20°, the extreme value of horizontal 280 strain is 4.5 mm/m and that of the additional stress is 0.65 MPa. When the internal friction angle reaches 281 45°, the extreme value of horizontal strain is 10 mm/m and that of stress is 1.5 MPa (Fig. 8d). A

325
Discussion 326 In the current study, a building is simplified into a strip structure, and the interaction between the

336
In the current work, contact between the foundation and the soil is studied, and the transmission and

364
After the second abrupt change, the growth rate of the additional stress rapidly decreases and then 365 gradually reaches its maximum value.

366
Through the analysis of the influences of soil and building parameters on the additional horizontal 367 stress, that the following conclusion are drawn.     In uences of soil and building parameters on the additional stress