Geological Characteristics and Stability Evaluation of Wanjia Middle School Slope in Wenchuan Earthquake Area

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.     

Evaluation of Strength Characteristics of Tropical Black Clay Treated with Locust Bean Waste Ash

An expansive tropical black clay (also known as black cotton soil because the cotton plant thrives well on it) was treated with up to 15 % locust bean waste ash (LBWA) to assess its soil improvement potential. Samples were subjected to index, compaction using three energy levels (British Standard light, BSL, West African Standard, WAS or ‘Intermediate’ and British Standard heavy, BSH), shear strength (unconfined compressive strength, UCS), California bearing ratio, CBR and durability tests. Results obtained show that the natural soil is not suitable for road construction. The maximum dry density (MDD) and optimum moisture content (OMC) decreased and increased, respectively. Regardless of the compactive effort and curing period, strength and durability properties increased with higher LBWA content with the BSL effort recording the best improvement. However, based on durability results, the optimal 12.5 % LBWA treatment of black cotton soil did not satisfy criteria for its use in road construction as a stand alone additive. Also, significant improvement in soil properties was obtained using the BSL compactive effort, which is easily achieved in the field. The benefits of the application include reduction in the cost of soil improvement and the adverse environmental impact of locust bean waste.     

An Overview of Electrokinetic Consolidation of Soils

Electrokinetic stabilization is one of the techniques that improve the geotechnical properties of the soils. It was pioneered by Casagrande in late 1940s and has not seen much development since then, especially in large-scale field applications. Some bench scale studies have been carried out during the past two decades and there have been some small scale field studies and limited field applications, mostly on soft soils. Due to lack of understanding of the physiochemical and electrochemical changes in the soil during electrokinetic stabilization, uncertain energy costs, loss of efficiency with time and the corrosion of electrodes, this method is usually considered as a last resort for large-scale practical applications. The objective of this paper is to highlight the critical parameters affecting electrokinetic consolidation, and to discuss their effects on the efficiency of the process. A better understanding of these critical parameters and their effects will enable geotechnical engineers to design the electrokinetic consolidation operation more effectively and make it an economically viable process for many situations.     

Two Methods for Predicting Reliability Index and Critical Probabilistic Slip Surface of Soil Slopes

Two methods of reliability analysis of soil slopes are studied, and the representative flow charts of both methods are illustrated. Method 1 can predict the reliability index and the critical probabilistic slip surface directly and it is computational efficient, but it needs the development of new codes for integrating the reliability analysis code and the slope stability code. Method 2 makes the reliability analysis code call the slope stability analysis code directly, and each code can be considered as an intact part. The main result of Method 2 is the reliability index of soil slope. Combined with the proposed method for locating the critical slip surface, Method 2 can also predict the probabilistic slip surface. Although Method 2 needs much more callings of the subprogram of slope stability analysis code, it needs not the developing of new computer program. Thus, Method 2 is easy to use and can be applied to different reliability analysis methods and slope stability analysis methods.     

Evaluation of Curve Fitting Techniques in Deriving p–y Curves for Laterally Loaded Piles

The p–y method is one of the most popular methods for the analysis and design of laterally loaded piles. The mathematical relationship it provides between the bending moment, which can be easily measured at strain gauges along the pile, and the soil resistance and lateral pile displacement, facilitates the construction of p–y curves. Numerical techniques are required to fit smooth continuous curves to the discrete bending moment data in order to improve the accuracy of subsequent differentiation and integration operations. Due to the lack of guidance on the optimum positioning of strain gauges and the reliability and accuracy of curve fitting methods, a unifying study, inclusive of small (0.61 m) and large (3.8 and 7.5 m) diameter piles in clay, was carried out using 18 strain gauge layouts and cubic spline, cubic to quintic B-spline and 3rd to 10th degree global polynomial techniques. Bending moment data was obtained using 3D finite element analysis. Through a comprehensive evaluation, the cubic and cubic B-spline methods were found to be consistently accurate in deriving p–y curves for both the small and large diameter piles.     

Class I and Class II Rocks: Implication of Self-sustaining Fracturing in Brittle Compression

Tests to determine the complete stress–strain curve of rocks indicate whether the rocks can be classified a Class I or Class II. Class II rocks exhibits the potential for self-sustained failure in the post-peak region. The purpose of the research described in this paper was to investigate whether or not this self-sustained failure characteristic is related to the fragmentation of the rock. The aim of the research was, therefore, to determine possible relationships between fragmentation and various properties of several rocks types, including the influence of the Class II characteristic. Fragmentation of rock depends on its self-sustaining failure behaviour and the energy available in the post-peak region to shatter the rock. The correlation of static and dynamic rock properties with size of fragments resulting from compression tests demonstrate clear relationships of Class II rocks, but the same cannot be said for Class I rocks. Analyses of test results show that fragmentation increases with an increase in rock strength, and is explosive for Class II rocks. Probability density distributions were constructed to show the overall comparison of fragment sizes produced during failure of Class II and Class rocks. The calculated probability of passing at X₅₀ and X₁₀ sieve sizes show that Class II rocks as a group are more finely fragmented. It can therefore be concluded that, when breaking rocks under the same steady loading conditions, Class II rocks will show greater fragmentation than Class I rocks.     

Stabilization of Expansive Soil with Cement Kiln Dust and RBI Grade 81 at Subgrade Level

The present research work deals with an expansive high plastic clayey soil with cement kiln dust (CKD) and stabilizer (RBI Grade 81). The physical and engineering properties of soil are plasticity, compaction, unconfined compressive strength (UCS), consolidation and California bearing ratio (CBR) of the clayey soil and clay treated with CKD and stabilizer were determined. Soil chemistry was examined before and after treatment using scanning electron microscope (SEM) and elemental dispersive spectrometer. The clay mixed with CKD, CKD and RBI Grade 81 was found that optimum contents are 10 % (CKD), 15 % CKD with 4 % RBI Grade 81, respectively. The result indicates that CKD alone will decrease maximum dry density and increase optimum moisture content. CKD with RBI Grade 81 slightly increases maximum dry density and decreases optimum moisture content. UCS increased with CKD alone and CKD with RBI Grade 81 from 88.3 to 976 kN/m², respectively. CBR values were increased by the addition of CKD, CKD with RBI Grade 81 from 1.65 to 21.7 %. With the curing time of 3, 14 and 28 days, UCS and CBR values were increased due to pozzolanic reaction from cementations material. The treated soil has considerable reduction in compression index. SEM images clearly indicate the formation of CSH and CAH gel.     

The Blasting Test and Blasting Vibration Monitoring of Vertical Crater Retreat Mining Method in the Luohe Iron Mine

Because the land requisition and demolishing became difficult more and more, the mining scheme of Luohe iron mine was changed from caving method to filling method. In order to ensure the safety of the residence and the underground tunnel cavern within the mobile belt of the underground mining, the Luohe iron mine did the blasting test on the vertical crater retreat mining method and blasting vibration monitoring. The blasting experiments use common emulsified oil explosives and non-electric initiation system. The way of caved ore adopts the cutting groove and bench side. The NUBOX-6016 intelligent vibration monitor was chosen in the blasting vibration monitoring. Twice experiments on the blasting vibration monitoring were done on the surface or in the underground refuge cavern. The first test select the three monitoring points on the ground and the second select two monitoring points on the ground and a monitoring point in the underground refuge cavern. The blasting vibration monitoring data were conducted by the regression analysis in the Sodev’s empirical formula. The vibration attenuation formula about the underground blasting vibration transmitting in three directions is derived. The blasting test on the vertical crater retreat mining method and the blasting vibration were analyzed. It is estimated if the vibration damage possibly the surface buildings and related facilities of mine.     

Study on Strength Influence Mechanism of Fiber-Reinforced Expansive Soil Using Jute

This study was undertaken to research the effects of jute fiber content, fiber length, water content and dry density of reinforced and unreinforced soil on the strength influence mechanism by implementing a series of laboratory tests and analysis. The most efficient fiber reinforcement effects was achieved by means of adding jute fiber with content of 0.6 % and length of 6 mm into expansive soil specimen prepared at maximum dry density and optimum moisture content. The cohesion of reinforced specimens increased first with increasing fiber content and fiber length and then decreased with further increase in fiber content and fiber length. The internal friction angle of reinforced specimens were not affected significantly by fiber content and fiber length. Higher water content reduces the fiber reinforcement effects by means of acting as lubricant in the interface of fiber and soil particles. Fiber reinforcement effects is more prominent for specimens prepared at higher dry density by increasing the effective contact area of fiber/soil. The application prospect of soil reinforcement using natural fiber is impeded by the hydrophilic nature and biodegradability of natural fiber, thus, studies on using chemical additive to do surface treatment for natural fiber are needed to improve the interfacial interaction of fiber/soil so as to widen the application of natural fiber.