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To explore the water resistance properties of lime soil ground, the physical and mechanical properties of lime soil with 5%, 10%, 15% and 20% lime content after long-term water immersion were studied by conducting unconfined compressive tests, density tests and water absorption tests. The results show that the stress–strain relationship curves of the lime soil during immersion are of the strain-softening type. The curves are multistage and nonlinear with evident peak values, and the lime soil achieves ductility and toughness with an increase in immersion time. The failure modes of the lime soil samples mainly include single slope shear failures, brittle splitting failures and conjugate shear failures, which are mainly affected by the lime content and immersion time. The strength of the lime soil decreases sharply in a short time while interacting with water. The strength slowly increases to 50.07–69.15% of the initial strength after immersion for a long time, i.e., still far less than the initial strength without immersion. Under long-term immersion, the water absorption of the lime soil increases gradually at the initial stage of immersion and then increases to a stable value of 16.76–21.67%. The change law of the wet density is essentially controlled by the water absorption. The strength of lime soil decreases significantly, and the water resistance capacity is poor after soaking; lime soil with 15% lime content has better engineering properties. It is recommended to apply lime soil with 15% lime content in practical engineering with a volume ratio of lime to soil of 3:7 and to avoid using lime soil materials in immersed or other dry-humid environments.

The exit slope of the Chenjiapo tunnel is located in Xuanen County, Hubei Province, China, and rainfall is one of the main factors inducing landslides. During the tunnel excavation, the left side of the front edge of the slope slid downward and caused a 6.27 × 104 m3-large landslide. Moreover, a 8.69 × 105 m3-large unstable slope was formed under the combined action of rainfall and the excavation. Because the front edge of the slope has been sliding, further tunnel excavation and extreme rainfall may induce massive landslides. This not only threatens the safe construction of the tunnel but also directly risks the operation safety of the expressway at a subsequent stage. To reveal the failure process of the Chenjiapo tunnel exit slope under extreme rainfall conditions, the slope stability is studied under five rainfall types and three rainfall intensities by conducting numerical simulations using the GeoStudio software. The results show that under the condition of front-peak rainfall, the safety factor of the slope first decreases and subsequently increases with increasing rainfall time. The slope is damaged at the 18th hour of the rainfall, and the plastic zone completely penetrates the upper soil layer at the end of the first day of the rainfall. In addition, the maximum horizontal displacement of the slope, which is up to 0.233 m, is the maximum among those under the five rainfall types. Under the conditions of equal-intensity, stepped, medium-peak, and back-peak rainfall, the safety factor of the slope decreases with increasing rainfall time. The slope begins to be destroyed between the second and the third days of the rainfall, and the plastic zone begins to be fully penetrated. Therefore, for the same rainfall time and total rainfall amount, the front-peak rainfall is the most harmful to the slope stability. Under 50, 70, and 90 mm/day rainfall intensities, the safety factor of the slope decreases with increasing rainfall time. Compared with the other two rain intensities, the slope is damaged first at the 27th hour under the 90 mm/day-rain intensity. At the end of the rainfall, the safety factor of the slope is the smallest under the rainfall intensity of 90 mm/day, which is 0.887. This indicates that a high rainfall intensity is associated with easy damage to the slope. After the rainfall, the safety factor of the slope immediately recovers, the horizontal displacement gradually rebounds, the distribution range of the plastic zone begins to decrease, and the slope returns to a stable state after 12 days of the rainfall ending. The exit slope of the Chenjiapo tunnel may fail under extreme rainfall conditions; therefore, it is urgent to adopt reinforcement measures, such as an anti-slide pile as the main support and drainage and sealing slope cracks as the auxiliary ones.

In order to reveal the creep laws of light weight soil, the compression creep characteristics of light weight soil mixed with Weihe River mud and EPS (expanded polystyrene) particles are researched by one-dimensional compression creep tests. The results show that the cementation structure strength of light weight soil becomes larger, and the creep deformation under the same load becomes smaller with the increasing of cement content and the decreasing of EPS particles content. For the same mixed ratio of light weight soil, when the load is larger, the deformation is greater, but the time of the deformation reaches the steady stage is shorter. With the increasing of the time, the deformation is increasing, finally it tends to be a stable value. There is no sharp creep stage, the deformation is attenuated creep. Light weight soil is a kind of structural soil, and it has a certain compression yield stress. When the load acting on the specimen is less than the compression yield stress of light weight soil, its cementation structure may still be intact, but the deformation is mainly due to the discharge of pore water and the movement of solid particles, and therefore deformation is small. When the load is greater than the compression yield stress of light weight soil, the cementation structure might have been collapsed, there is larger deformation for the EPS particles under pressure, the deformation of the samples is mainly the plastic deformation of the EPS particles, and therefore deformation is large. In the practice, the load should be controlled within the compression yield stress of light weight soil. According to the results, a power function empirical creep model is set up. Compared the test data with the model calculation data, it is found that when the axial load is less than the compression yield stress, the model can exactly reflect the creep laws of light weight soil in a certain time scale (e.g. 50 years), and it can provide a theoretical basis for the practical engineering.

To reveal the durability of light weight soil ground under water environment conditions, the influence laws of soaking time and dry–wet cycle times on mechanical properties of light weight soil are researched by density tests, unconfined compressive strength tests, water absorption tests and mass loss rate tests. Due to chemical compositions in the light weight soil interacting with each other, a kind of network cemented structure containing soft inclusions (expanded polystyrene beads) is formed in the specimens. Enough water has been provided for the mixed soil in the physical–chemical reaction process in the experiments, hydrolysis and hydration of cement, ion exchange, hardening reaction and carbonation action occur continuously. Under long term soaking conditions, the physical properties of light weight soil are extremely stable, the network cemented structure is the physical basis for the hydrophobicity. When soaking time is more than 90 days, the unconfined compressive strength of the specimens will reach a stable value gradually. Similarly, light weight soil does not appear cracking phenomenon, and keep the mechanical properties and material density stable under long term dry–wet cycle. Thus light weight soil has good water stability and durability, it is recommended that light weight soil can be widely used in civil engineering, such as ground improvement, soft subgrade engineering, embankment heightening, slope repair, excavation backfill, pipeline backfilling and so on.

To research the unconsolidated undrained shear strength and deformation properties of saturated cotton fiber reinforced soil, the shear strength of saturated fiber reinforced soil is studied through a series of unconsolidated undrained shear tests. The test results show that the stress–strain relationship of the fiber reinforced soil is strain hardening, and the failure mode of the samples is bulging failure. Tensile properties of fibers require a certain strain to be “mobilized”. When the strain is less, the fiber content and the fiber length have less influence on the principal stress difference, and the reinforcement effect is weak. The reinforcement effect enhances with the increasing of axial strain. The unconsolidated undrained shear strength of saturated fiber reinforced soil increases first and then decreases with the increasing of fiber content and fiber length. The strength is the best under the condition of 1.0% fiber content and 3.09 cm fiber length, and the strength of fiber reinforced soil increases by 63.5% compared with that of unreinforced soil. Fiber reinforcement can weaken the end effect of the samples, and effectively constrain the radial deformation of the soil. By analyzing the interaction modes between the fibers and the soil particles, it is found that the interaction modes are contact, bending and interweaving. These three actions provide the interfacial shear stress between the fibers and the soil particles, and the tensile stress of fibers to restrict the movement of soil particles, and the interactions improve the shear strength of soil.

In order to research the dynamic stress–strain relationship of EPS (expanded polystyrene) particles light weight soil, under the condition of fixed water content and fixed curing age, the dynamic deformation properties of light weight soil with different mixing ratios are researched by dynamic triaxial tests. The results show that at the same cycle number and dynamic stress, the dynamic strain of light weight soil decreases with the increasing of cement content and the decreasing of EPS particles content. The dynamic bearing capacity of EPS particles light weight soil with cement content in the range of 10–20% and EPS particles content in the range of 0.14–0.86% is 1.5–3 times that of remolded soil. It indicates that light weight soil possesses obvious dynamic bearing capacity. In addition, when the vibration frequency increases from 0.5 to 6 Hz, the bigger the loading rate is, the more uneven the distribution of the pore water pressure in the soil is, and the less deformation can occur, which means that there is a greater constraint on the development of pore water pressure and deformation. Thus at the same dynamic strain, the dynamic stress of light weight soil under bigger vibration frequency is greater. The shape of dynamic backbone curves of light weight soil conforms to hyperbola, and its nonlinear dynamic response process can be described by Hardin–Drnevich model. Different stress state tests are used to verify the applicability of Hardin–Drnevich model. It is found that the relative errors between the measured values and calculated values of backbone curves are less than 15% by analysing the test data. It shows that Hardin–Drnevich model can be used to describe the dynamic deformation characteristics of EPS particles light weight soil.

The exit slope of Chenjiapo Tunnel is located directly above the exit of Chenjiapo Tunnel on Enshi to Laifeng expressway. During the excavation of the exit of the right line of the tunnel, the left side of the front edge of the slope slips. Under the joint action of excavation and rainfall, a large landslide of 6.27×10 4 m 3 and a huge unstable slope of 8.69×10 5 m 3 are formed. The landslide body and unstable slope body not only cause the tunnel to be shut down, but also directly threaten the operation safety of the later expressway. Therefore, in order to study the stability change process of the exit slope of Chenjiapo tunnel under the condition of long-term rainfall, the finite element calculation of the slope is carried out by GeoStudio software. The results show that under the condition of long-term continuous rainfall, the safety factor of the slope decreases with the increased rainfall time, but the reduction rate gradually slows down, and finally tends to be stable. The safety factor of the slope is reduced from 1.187 in the natural state to 1.015, which indicates that the slope is still in a stable state under the condition of long-term continuous rainfall, but the safety reserve is not high, and it is easy to lose stability and damage due to the influence of external adverse factors. As the rainfall continues, the seepage line inside the slope is rising, and the saturated area of the soil at the toe of the slope is increasing. Until the slope begins to drain outwards, the seepage field inside the slope is basically stable. The maximum horizontal displacement of the slope increases with the increased rainfall time, but the increase rate gradually slows down until it tends to be stable. The maximum horizontal displacement of the slope occurred in the middle surface of the slope at the beginning of the rainfall, and gradually transferred to the toe of the slope within 7 days of the rainfall and continued until the end of the rainfall. At the end of the rainfall, the maximum horizontal displacement of the toe of the slope is 0.128 m, and the toe of the slope will be damaged first. At the beginning of the rainfall, the plastic zone of the slope is only scattered at the slope surface and the slope toe. And then as the rainfall continues, the distribution range of the plastic zone in the slope surface, the slope toe and the slide zone gradually widen, and the slope stability gradually decreases. The maximum horizontal displacement and plastic zone of the slope are concentrated at the toe of the slope, the slope presents obvious traction failure characteristics. According to the results of field survey, there are small-scale gravel soil collapses and shear outlets at the front edge of the slope, and the survey results are consistent with the simulation results. It is suggested to set up perfect drainage engineering in the middle and back of the slope, and set anti slide piles and drainage holes at the toe of the slope to reinforce the slope.

There are two types of discriminant methods for retaining wall with gentle back surface: Wei-ci Gu’ discriminant method and critical angle discriminant method. Discriminant formula of the retaining wall with gentle back surface is $$\alpha > \alpha_{cr} = f(\delta ,\varphi ,\beta )$$ . According to theoretical deduction, it is found that Wei-ci Gu’ analytic solution which can be used to calculate the earth pressure of retaining wall with gentle back surface includes an assumed condition: $$\delta \approx \varphi$$ . The essence of Wei-ci Gu’ discriminant method and critical angle discriminant method $$(\delta = \varphi )$$ is the same; moreover, the second sliding surface location which is decided by the two methods, respectively, is the same too. Active earth pressure of retaining wall with gentle back surface under different conditions is calculated through Coulomb’ earth pressure theory and earth pressure theory of retaining wall with gentle back surface, respectively. The results show that the earth pressure increases gradually with the increase in the wall-back’ dip angle and the backfill’ dip angle, and it decreases with the increased backfill’ internal friction angle. Under any conditions, if and only if $$\alpha \approx \alpha_{cr}$$ , the calculation results obtained by Coulomb’ earth pressure theory and earth pressure theory of retaining wall with gentle back surface are approximately equal. The examples show that when the requirements of retaining wall with gentle back surface are met ( $$\alpha > \alpha_{cr}$$ ), the bigger the difference between α and α cr is, the bigger the calculation results’ difference by the two methods is. Change β the maximum error between the two calculation results is 38.77 %. In order to avoid major cost waste, it is suggested that when $$\alpha > \alpha_{cr}$$ , the earth pressure should be calculated through earth pressure theory of retaining wall with gentle back surface.

To investigate the formation mechanism and the stability of Wanjia middle school slope in Wenchuan Earthquake Area, the macroscopic geological characteristics and the failure process of the landslide are researched by engineering geology analysis method, limit equilibrium method, and finit element method. The results show that after the Wenchuan Earthquake, retaining walls, houses and other infrastructure on the foot of Wanjia middle school slope were severely destroyed, 10 cm wide tension fracture appeared at the trailing edge of the slope. Wanjia middle school slope is a type of medium-sized soil landslide. The area of the deformation body is about 19,314 m2, the total volume of the deformation body is about 23 × 104 m3. There may be two potential sliding surfaces in the unstable slope: shallow and deep landslide. The analysis results of the limit equilibrium method and the finite element method show that: under dead weight, dead weight + rainstorm, dead weight + earthquake conditions, the plastic zone occurs mainly at the middle part or the trailing edge of the slope, and it doesn’t fully cut through the deep landslide body, so the deep landslide is stable. However, under rainstorm or earthquake conditions, the plastic zone almost completely cut thorough the shallow landslide body, it shows that the shallow landslide is in the understable–basic stable state. It is found that the results of finite element method is concordant with the results of the limit equilibrium method (F s = 1.06–1.29, the shallow landslide is in the basic stable–stable state). The calculation results show that shallow landslides are likely to occur in Wanjia middle school slope during a rainstorm or an earthquake, so monitoring and control of the slope should be strengthened. The shallow landslide should be managed by some measures, such as anti slide pile retaining structures and drainage works, and the dangerous rock bodies on the slope surface should be cleaned up.

To research the prescription of lightweight soil under an optimum water content condition, the influence of the water content on the material state should be completely removed. The optimum water content of different mixing ratios of lightweight soil can be obtained using the optimum water content model. The prescription formula and prescription optimization method of foamed particle lightweight soil were investigated using density tests and unconfined compressive strength tests. The results show that the density of lightweight soil is mainly affected by the content of expanded polystyrene (EPS) particles, and it decreases linearly with an increase in the EPS particle volume ratio. However, the effect of the cement content on the density of lightweight soil is very small and can be ignored. The unconfined compressive strength of lightweight soil increases linearly with the increase in cement content, and the strength growth rates are mainly affected by the different EPS particle contents. There is a minimum cement content; if the cement mixing ratio is lower than the minimum cement content, there will be no solidification effect for the cement. The unconfined compressive strength of lightweight soil decreases linearly with an increase in the EPS particle volume ratio, and the strength reducing rates are mainly affected by the different cement contents. There is a maximum content for the EPS particles; if the EPS particle volume ratio is more than the maximum content of EPS particles, the strength of the mixed soil will be completely lost. Considering the density, strength, and cost of mixed soil, two empirical prescription formulas were proposed: the positive correlation linear fitting method and the negative correlation linear fitting method.

To reveal the influence of material composition on mechanical properties of light-weight soil, stress-strain -volumetric strain characteristics and Poisson's ratio of mixed soil were researched by consolidated drained shear tests. The results show that light-weight soil is a kind of structural soil, so its mechanical properties are affected by mixed ratio and confining pressure, and mixed soil possesses structural yield stress. When confining pressure is less than the structural yield stress, strain softening occurs; when confining pressure is more than the structural yield stress, strain hardening is observed. There are two kinds of volume change behavior: shear contraction and shear dilatancy. Shear dilatancy usually leads to strain softening, but there isn't an assured causal relationship between them. Poisson's ratio of mixed soil is a variational state parameter with the change of stress state, it decreases with increased confining pressure, and it increases with increased stress level. When axial st...

To uncover the formation mechanism of the Houba landslide in the Three Gorges Reservoir Area in China, macroscopic deformation characteristics, matter and structural characteristics, and slope stability were investigated using geological field investigations, indoor and outdoor tests, mineral identification, etc. The results show that since a large deformation occurred in the Houba landslide in 2003, there has been no obvious overall deformation and the whole slope has been in a basic steady state since January 2004. Slope deformation mainly exists in the expansive soil layer from 0 to 5 m (surface-layer sliding zone), and there are some evidences suggesting activity at 20 m (shallow-layer sliding zone) and nearby 35 m (deep-layer sliding zone). The expansive soil in the surface layer has a thickness of approximately 5 m, is 25–35% chlorite and illite, and has a free swelling ratio of 25–80%, making it a weak-moderate expansive soil. The expansive soil also has strong hydrophilicity, and it is more sensitive to saturation changes. Its shear strength could be easily reduced by saturation–unsaturation cycles with the change of water table or rainfall, so the expansive soil itself creates a good condition for a gently inclined landslide. The surface-layer slope, shallow-layer slope and deep-layer slope are in steady states under natural and rainstorm conditions. However, the surface-layer landslide body on the back edge of the III–III′ profile is in a basic stable–unstable state under rainstorm conditions, and a surface-layer landslide may occur under continuous rainfall conditions. Many people live on the Houba landslide, and the coupling effect of expansive soil and rainfall could cause many more local landslides from the surface-layer expansive soil with a slope-free face. Some measures should be taken to control the landslide, such as surface draining, local landslide supporting and retaining, and reinforcing the front existing retaining wall.

Deformation characteristics of light weight soil with different EPS (expanded polystyrene) sizes were investigated by consolidation tests. The results show that the confined stress-strain relation curve is in S shape, which has a good homologous relation with e-p curve and e-lgp curve, and three types of curves reflect obvious structural characteristics of light weight soil. When cement mixed ratio and EPS volume ratio are the same for different specimens, structural strength decreases with the increase of EPS size, but compressibility indexes basically keep unchanged within the structural strength. The settlement of light weight soil can be divided into instantaneous settlement and primary consolidation settlement. It has no obvious rheology property, and 90% of total consolidation deformation can be finished in 1 min. Settlement-time relation of light weight soil can be predicted by the hyperbolic model. S-lgt curve of light weight soil is not in anti-S shape. It is proved that there is no secondary consolidation section, so consolidation coefficient cannot be obtained by time logarithm method. Structural strength and unit price decrease with the increase of EPS size, but the reducing rate of the structural strength is lower than that of the unit price, so the cost of mixed soil can be reduced by increasing the EPS size. The EPS beads with 3–5 mm in diameter are suggested to be used in the construction process, and the prescription of mixed soil can be optimized.

Silt is the dominant soil in the deposited soil in the Yellow River Delta, with special properties. In this article, based on the results of the dynamic triaxial tests, the following conclusions are drawn. Under the cycle loading, the development of dynamic pore water pressure in silt differs from the sand, and its curve can be fitted by hyperbola. In beginning silty soils' pore water pressure rose sharply, and then gradually become stable, and in this paper the causes were analyzed.

In order to reduce the hazards of earthquake disasters on human, basic principle of reducing vibration is discussed by establishing passive vibration isolation model. The calculation results show vibration can be reduced by isolation materials whose deformation modulus (stiffness) should be smaller and damping should be appropriate. Light reinforced soil is a good man-made material, its all physical mechanical parameters can be changed, and anti-pull capacity of soil can be increased. According to the basic principle of reducing vibration, reducing vibration idea using light reinforced soil is brought forward, and the idea has a very important significance for research on reducing earthquake disasters from the angle of ground and foundation.