Mechanical degradation of unstabilized rammed earth (URE) wall under salts and rising damp attack effect

The long-term chemo–thermo–hydro–mechanical behavior, the salt migration, and the salt attack on unstabilized rammed earth have been rarely investigated in the literature. The authors simulated the mechanical degradation of a typical unstabilized rammed earth (URE) wall under salts and rising damp attack effect by using the finite element method. The simulation results show that the water/salinity in a freshly built rammed earth wall decreases/increases significantly due to the water evaporation and capillary effects after construction, and these effects are stabilized in the following 3 years. Globally, the wall is wetter, cooler, and saltier in winter than in summer and has a lower strength. The strength in the upper part of the wall is higher than in the lower part. In the first 4 years after construction, the strength in the upper part increases and then reaches an equilibrium stage with time, while the strength in the lower part increases and then has the tendency to decrease in the latter 3 years due to the accumulation of salt. The strength inconsistency may exist in the wall due to the combined effects of salt accumulation and water evaporation, and the strength on the surface may be higher or lower than that of the inside due to the changes of surrounding conditions with time. The simulation results show that the wall has the best mechanical performance without damp and salt attacks.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

τ _w (–):

The tortuosity factor

σ _B (–):

Stefan–Boltzmann constant

σ ₁ (MPa):

First principal stress

σ (MPa):

Cauchy stress

ρ _w (kg·m^{− 3}):

Density of liquid water

ρ _v (kg·m^{− 3}):

Density of water vapor

ρ _s (kg·m^{− 3}):

Particle density

ρ _eff (kg·m^{− 3}):

Effective density

ρ _a (kg·m^{− 3}):

Density of dry air

ν (–):

Poisson’s coefficient

μ _w (Pa·s):

Dynamic viscosity of water

μ _v (Pa·s):

Dynamic viscosity of water vapor

λ _eff (W·m^{− 1}·K^{− 1}):

Effective thermal conductivity

κ _rw (–):

Relative water permeability

θ_s (–):

Saturated volumetric water content

θ_r (–):

Residual volumetric water content

θ_L (–):

Lode angle

θ (–):

Volumetric water content

η _s (%):

Salinity

η _ini (%):

Initial salinity inside of the wall

ε _v (–):

Volumetric strain

ε _ij (–):

Engineering strain tensor

ε _e (–):

Emissivity of the wall

γ _d (kN·m⁻³):

Dry unit weight

β _inc (–):

Wall inclination angle

α _H (–):

Hellman exponent

α ₁, α _t (m):

Longitudinal and transverse dispersivities

x (m):

Position of soil particles

v _{x , y , z} (m·s^{− 1}):

Components of the velocity field v_w

v _wind0 (m·s^{− 1}):

The velocity of wind at H₀

v _wind (m·s^{− 1}):

The velocity of wind

v _w (m·s^{− 1}):

Water velocity vector

v _w (m·s^{− 1}):

Water velocity

v _v (m·s^{− 1}):

Water vapor velocity

v _a (m·s^{− 1}):

Dir air velocity

u _ref (MPa):

Constant for UCS₀

UCS (MPa):

Unconfined compressive strength with salt effect

u ₁ (–):

Constant parameter for UCS₀

u (m):

The displacement vector

u (m):

Soil particle displacement

t _T (day):

The phase of T

t _RH (day):

The phase of RH

t _ref (day):

Reference time period

T _ini (°C):

Wall temperature at the beginning

T _ext, T_int (°C):

External and internal temperature of the wall

T _av (°C):

Average temperature

T _am (°C):

Amplitude of temperature

t (s):

Time

T (K):

Temperature

S _r (–):

Saturation

Sh (–):

Sherwood number

Sc (–):

Schmidt number

s (MPa):

Total suction

R _s (W·m^{− 2}):

Shortwave radiation

R _Lg (W·m^{− 2}):

Ground longwave radiation

R _La (W·m^{− 2}):

Environmental longwave radiation

RH_ini (–):

Relative humidity of the wall at the beginning

RH_i (–):

The RH on the internal boundary surface

RH_ext, RH_int (–):

Wall external and internal RH

RH_e (–):

The RH on the external boundary surface

RH_av (–):

Average RH

RH_am (–):

Amplitude of RH

RH (–):

Relative humidity

Re (–):

Reynolds number

R (J·K⁻¹·mol⁻¹):

Gas constant

Q _r (W·m^{− 3}):

Heat source of radiation

Q _p (MPa):

The plastic potential

Q (W·m^{− 3}):

Additional heat source

q (W·m^{− 2}):

Conductive heat flux

p _sat (Pa):

Pressure of saturated water vapor

p _at (Pa):

Total atmospheric pressure

n _VG (–), m_VG (–):

Material-dependent constant parameters

n (–):

The normal vector

n (–):

Porosity

m _ws (kg·m^{− 3}·s^{− 1}):

Water source

M _w (kg·mol^{− 1}):

Molar mass of water

m _HB (–):

Constant parameter in Hoek and Brown criteria

m _evap (kg·m^{− 3}·s^{− 1}):

Water source of evaporation

M _a (kg·mol^{− 1}):

Molar mass of dry air

l _VG (–):

Constant value of Mualem equation

L _v (J·kg^{− 1}):

Latent heat of evaporation

L (m):

Length of the evaporative surface

K ₁, K ₃ (–):

Parameters for R_La

J ₂ (MPa²):

J₃ (MPa³), Second and third deviatoric stress invariants

h _t (W·m^{− 2}·K^{− 1}):

Surface heat transfer coefficient

h _m (m·s^{− 1}):

Surface moisture transfer coefficient

H ₀ (m):

Wind height

H (m):

Wall height

g (m·s^{− 2}):

Gravity acceleration

F _yield (MPa):

Yield surface

f _v (kg·m^{− 2}·s^{− 2}):

Body force vector

e _s (–):

Void ratio

E _ref (MPa):

Reference Young modulus

e ₁ (–):

Constant value for E

E (MPa):

Elastic modulus at failure

dσ _ij (MPa):

Stress increment

dλ (–):

Harding parameter

D _w (m²·s^{− 1}):

Diffusivity of liquid water

D _v (m²·s^{− 1}):

Diffusivity of water vapor

D (m):

Water head

C _wi0 (s²·m^{− 2}·K^{− 1}):

Constant value for h_m

C _w (J·kg^{− 1}·K^{− 1}):

Water specific heat capacity

C _v (J·kg^{− 1}·K^{− 1}):

Water vapor specific heat

c _s (mol·m³·s^{− 1}):

Source of the solute concentration

C _s (J·kg^{− 1}·K^{− 1}):

Soil particle specific heat capacity

C _m (m^{− 1}):

Specific water capacity

C _KC (m²):

Constant value in Kozeny–Carman equation

c _fi (–):

Fine content

C _eff (J·kg^{− 1}·K^{− 1}):

Effective specific heat capacity

C _e (m²·s^{− 1}):

Effective diffusion

C _d (m²·s^{− 1}):

Dispersion tensor

C _c (–):

Cloud cover factor

C _a (J·kg^{− 1}·K^{− 1}):

Dry air specific heat capacity

c (mol·m^{− 3}):

Mass concentration of the solute

a _{l b} (–):

Surface albedo

\({\varepsilon }_{ij}^{pl}\) (–):

Plastic strain tensor

\({\varepsilon }_{ij}^{el}\) (–):

Elastic strain tensor

\({d\varepsilon }_{kl}^{el}\) (–):

Elastic strain increment

\({D}_{ijkl}^{el}\) (MPa):

Elastic modulus tensor

The financial support from China Scholarship Council (CSC) is gratefully acknowledged.

Authors and Affiliations

1. ICUBE, UMR 7357, CNRS, INSA de Strasbourg, 24 Boulevard de la Victoire, 67084, Strasbourg, France

   Xiang Zhang & Hossein Nowamooz

Corresponding author

Correspondence to Xiang Zhang.

Conflict of interest

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