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The sliding forms of weak sloped and horizontal subgrades during the sliding process differ. In addition, the sliding form of weakly sloped subgrades exhibits considerable slippage and asymmetry. The accuracy of traditional slice methods for computing the stability safety factor of weakly sloped subgrades is insufficient for a subgrade design. In this study, a novel modified Bishop method was developed to improve the accuracy of the stability safety factor for different inclination angles. The instability mechanism of the weakly sloped subgrade was considered in the proposed method using the “influential force” and “additional force” concepts. The “additional force” reflected the weight effect of the embankment fill, whereas the “influential force” reflected the effect of the potential energy difference. Numerical simulations and experimental tests were conducted to evaluate the advantages of the proposed modified Bishop method. Compared with the traditional slice method, the error between the proposed method and the exact value is less than 32.3% in calculating the safety factor.

Determining the maximum and minimum void ratios of granular soils is very important because it can be correlated with engineering behaviors such as soil permeability. Empirical relationships can be used for determining the void ratio, but they have many limitations related to the shape and the size distribution of the grains. Analytical methods improve the empirical relationships. In this paper, we present enhancements to the model of Chang et al. by combining the model of Youd et al., as Chang–Youd models, to make it more convenient and also to extend its usage to be suitable for determining the maximum void ratio. The Chang–Youd models are verified with experimental tests performed by the authors. Compared with the experimental results in the literature, the Chang–Youd models are also effective but more convenient and practical.

The regularity of dynamic change of real mesostructures of soil is the foundation of the macro- and mesointegrated research. Mesoscale research about continuous image acquisition in real soils, identifying and quantifying mesostructures, is the subject of current interest. Soil mesostructure measurement method is the basis of modeling, and the development of rapid, direct, and lower-cost methods has great practical value for engineering practice. Combined with conventional triaxial loading test equipment, optical measurement, mesoscopic imaging tracking system, and digital image technology, a new method for measuring the dynamic change of the soil mesostructure is designed. This integrated approach to observation and acquisition is realized by direct observation and continuous image capture for dynamic change of real mesostructures of soil. The methods are used to analyze the high compressibility of a certain clay, shear zone development of cement soil, and erosive effects of ecological soil in order to investigate the continuous variation of mesostructures during the shear test. The aim of this paper is to provide a simple, straightforward, continuous, and low-cost test method for revealing the characteristics of consecutive change of real mesostructures of soil in the conventional triaxial test.

The durability of lightweight cellular concrete (LCC) and the corresponding assessment method are studied in this paper to improve the utilization of LCC in subgrade construction engineering. The durability assessment method is established by combining the analytic hierarchy process (AHP) with fuzzy comprehensive evaluation (FCE). The main assessment processes are as follows. Firstly, based on the physical and mechanical properties of LCC, the influencing factors are selected in terms of preliminary design, construction technology, and operation and management after completion of construction. The grading standard of influencing factors is established as well. Secondly, a multilevel assessment model with targets level, criteria level, and indexes level is established. AHP determines the effective weight of the lower level relative to the upper level. The consistency check of the judgment matrix is conducted to prove the rationality of the distribution of influencing factors’ effect weight. Thirdly, the membership function which is suitable for each influencing factor is built to calculate the membership degree. Besides, the practicality and reliability of AHP combined with FCE are demonstrated through a practical engineering case, which is the third section of a highway in Guangdong Province, China.

This study attempted to establish a process that uses the ultrasonic wave transmission method to correlate the ultrasonic parameters with the material properties of Foamed Mixture Lightweight Soil (FMLS). The results were then applied for the defect detection of the FMLS embankment. First, the ultrasonic wave velocity (UPV) and amplitude (UPA) of FMLS with different mix proportions were collected continuously from 3rd day to 45th day in the curing age. The relationships between UPV versus FMLS elastic modulus, unconfined compressive strength, and density were calibrated. The variations in the ultrasonic parameters owing to the test distance and crack width were recorded. Then, the laboratory tests were reproduced through numerical simulation approach. Finally, the reliability and accuracy of the proposed detection method for FMLS were proved and validated through on-site tests. The proposed methodology, which is simple, stable, and reliable, was found to be suitable for the quality diagnosis of FMLS embankments after construction and during operation.

This paper proposes an incipient assessment method for postconstruction settlement of highway subgrade by using statistical analysis approach with an improved static loading test method, time-extended loading test. The time-extended loading residual settlement Sr(t) and settlement rate Vs(t) are calculated from the field test data. The test procedure and the corresponding experimental validations are presented. Based on the field test data, a probabilistic model is built to bridge the final residual settlement and the actual postconstruction settlements. The proposed time-extended loading test based assessment system has been validated through three operating and well-documented road sections. According to the validation results, the construction quality can be accurately evaluated at an early stage and the corresponding remedial measures can be applied timely.

This paper presents a postconstruction settlement prediction method for pile-soil composite subgrade based on the multilevel fuzzy comprehensive evaluation principle. In this method, the variation range of postconstruction settlement can be obtained from a simple calculation based on the basic data of actual engineering. Firstly, according to the characteristics of influencing factors in the construction of soft soil subgrade, the evaluation index set and two-level factor index sets were selected. The grading standards of the evaluation index and factor index were determined according to the allowable value of the standard and the numerical simulation results. Secondly, each factor index was standardized, and the normal distribution function in the form of exponential was used to construct the standard membership function for the first and second factor indexes. Finally, the comprehensive evaluation matrix of postconstruction settlement of composite subgrade was constructed based on the entropy weight method. The variation range of postconstruction settlement was predicted by the principle of maximum membership. The example analysis shows that the predicted results of the prediction method and the field measurement method are in good agreement, indicating that the proposed method can realize the postconstruction settlement prediction of composite subgrade, and the results are more accurate and more instructive.

Lightweight cellular concrete (LCC) has been widely used as a subgrade filling. The quality test of LCC during the pouring impacts the construction quality control and saves time, while few studies have been conducted on it. This study proposed the surface strength and strength along the depth of LCC in situ test devices and methods. Based on a practical engineering case in Guangdong Province, the quantitative measurement pouring interval between layers and the reasonable pouring thickness of a single layer was determined by the proposed measuring devices and methods.

In order to save soil resources and increase the utilization range of high liquid limit soil, the high liquid limit soil was improved by mixing sand, and the cost-effective sand mixing ratio was determined with the help of fuzzy comprehensive evaluation method. It is shown that the sand-mixing improvement method can significantly reduce the liquid limit and plasticity index of high liquid limit soil, and increase its value of California bearing ratio to meet the property requirements for embankment filling. The fuzzy comprehensive evaluation results show that the improvement effect and cost of sand-mixed high liquid limit soil reach a comprehensive optimal state when the sand mixing ratio is 20%.

To promote the utilization of fly-ash, based on the orthogonal experiment method, wet density and unconfined compressive strength of Foamed Mixture Lightweight Soil mixed with fly-ash and quicklime (FMLSF) are studied. It is shown that the wet density and unconfined compressive strength of FMLSF increase with the increase of cement content, while decreasing with the increase of foam content. With the mixing content of fly-ash increase, the wet density and unconfined compressive strength of FMLSF increase firstly and then decrease. Scanning Electron Microscope (SEM) tests show that ball effect or microaggregate effect of fly-ash improves the wet density and unconfined compressive strength of FMLSF. With the mixing content of quicklime increase, the wet density and unconfined compressive strength of FMLSF increase firstly within a narrow range and then decrease. In addition, the primary and secondary influence order on wet density and 28-day compressive strength of FMLSF are obtained, as well as the optimal mixture combination. Finally, based on two abutments in China, behind which they are filled with FMLSF and Foamed Mixture Lightweight Soil (FMLS), the construction techniques and key points of quality control behind abutment are compared and discussed in detail, and the feasibility of utilization fly-ash as FMLSF is verified by the experimental results.

This paper takes probability of status judgment, value-at-risk of foundation pit, and cost of monitoring items into consideration, which related to the influence of foundation pit risk event to establishing a loss function of monitoring items and constructing a model for setting optimizing monitoring items to maximize their effect at the lowest cost, based on Bayes theorem. The safety status of the foundation pit was divided into nine levels. Also divided was the security coefficients obtained by numerical calculating into discrete data based the reliability theory to establish an optimization model as the corresponding calculation method. By calculating and dividing the security coefficient of an engineering example, the foundation pit monitoring items were ascertained through the optimization model, and the results of optimization were analyzed.

Use the digital image processing method to describe the microstructure characteristics of different geotechnical materials. Firstly, the microstructure images of different geotechnical materials were obtained by Charged Coupled Device (CCD) camera and long distance microscope. Secondly, the clear parts of the same geotechnical material image which were taken at the same point but different focus were obtained by technology of multi-resolution wavelet transform in digital image processing method and combined to get a high definition image. And then the high definition images were enhanced by histogram equalization process to highlight the contrast ratio. Finally, the images were divided according to the threshold which was automatically extracted by the maximum deviation to extract the microstructure parameters of geotechnical material. After processing images of different geotechnical materials, it shows that the digital image processing technology which is studied could well apply to describe the microstructure characteristics of different geotechnical materials.

Firstly, the rationale of block theory and stochastic statistical method of rock joint structural planes were introduced, and the reformatory measure of the genetic algorithm was brought forward. Secondly, the change of the position, size and stability in differ trend of the tunnel in two groups of typical joint structure planes were simulated and analyzed based on the key block theory and stereographic projection method, and they were contrasted and analyzed in contrast with practical instance. At last, the best trend of the tunnel in the characteristic interval of joint structure planes was programmed and reckoned by using reformatory measure of the genetic algorithm. The results obtained show that it is economic and feasible to optimize tunnel's axis by using key block theory and the modified genetic algorithm, and it is very stated referenced worthiness in traffic programming, design and construction of the tunnel.

In order to reduce the economic loss of discarded or improved reclamation with high liquid limit soil, the fundamental characteristics of high liquid limit soil is studied through the lab tests, and aiming at different type of high liquid limit soil, the engineering characteristics of direct reclamation and the best improved schemes are researched based on the trial road sections. It is shown that high liquid limit clay and sand-carrying high liquid limit clay can be used directly as embankment, using pack-cover method in accordance with the technical specification in China, and the degree of the compaction can be controlled at 88%, with the filling height no more than 8m and the total height of embankment no more than 12m; high liquid limit silt and sand-carrying high liquid limit silt are not suitable to be filled directly because the (California Bearing Ratio) CBR can not satisfy the requirement of greater than or equal to 3%, and therefore they should be improved before use; high liquid limit silt ought to be improved with quicklime, the best weight percentage is 5%, while sand-carrying high liquid limit silt should be improved with sand, the best weight percentage is 25%.

Lime-ash is semi-rigid material. It widely used in the construction of the highway subbase. Studying on engineering characteristic of lime-ash is mature. but, it always separately considered static force and motive power on studying the characteristic of lime-ash. It is different from practical situation. So, loading motive power in the model first, then carrying out commom triaxial test. The testing method is more similar with practical situation. The testing can be used to study the strength of lime-ash. The result of testing can be used to compare the index of shear strength of loading motive power before and after. Practial designing can rely the analysis result.

In order to learn the microstructure mechanics property of lime solidify soil, the digital image tracking technology has been introduced and used to track the soil particles, based on the micro-images captured by the long work distance telecentric microscope lens. On one hand, the sample of lime solidify soil is made into cylinder specimen. One of the half-parts is taken as the experimental specimen. Then, the region plane observed in the middle of soil specimen is compartmentalized nine small regions. One of the small regions is the tracking objective. When the objective is tracked successfully, the images of nine regions under the same loads are captured. On the other hand, using the transformed correlation formula, the tracking speed is improved. Moreover, According to the characteristic of soil under loads, the objective is successfully tracked by selecting the rectangle template and rectangle search region. Finally, using the image processing method, the evolution regulations of the porosity of soil sample under uniaxial stress are obtained. That is, the porosity is increased with the rising stress. In conclusion, the microstructure characteristic of lime solidify soil is agree with the macro property of lime solidify soil.