Determination of the modulus of subgrade reaction (ks) is an essential geotechnical design parameter that describes the relationship between stress and the associated settlement of soils. The ks is typically obtained using a laborious and costly method called the plate load test (PLT), and thus, to overcome the limitations related to the PLT, determining an alternative testing technique that can easily predict the ks is a priority. The feasibility of using a light weight deflectometer (LWD), also known as the dynamic PLT, to determine the ks of unbound pavement layers was thus investigated in this research. Eighteen laboratory testing models of granular soils were prepared and tested using the dynamic PLT (LWD) in conjunction with the static PLT (PLT). The soils’ characteristics examined under both dynamic and static loading conditions were analyzed and correlated. A series of multiple nonlinear regression analyses were conducted using three groups of independent variables: (1) LWD measurements, (2) basic soil properties, and (3) LWD data plus basic soil properties. Several nonlinear regression models were developed to predict the modulus of subgrade reaction on the basis of the LWD measurements and selected soil characteristics. The results revealed that certain LWD measurements, including dynamic modulus (Ed), surface deflection (δ), and degree of compatibility (Dc), are strongly correlated with the results from PLT. Additionally, good correlations were identified between ks and maximum dry density, suggesting that using LWD measurements along with basic soil properties yields correlations with adequate prediction quality.

The subgrade soil layer is the most essential part of the pavement system. Many pavement failures can be associated with subgrade weak strength and stiffness qualities. Therefore, it is necessary to strengthen this layer before building the other pavement layers. One of the essential methods utilized to enhance the engineering characteristics of this layer is soil stabilization. Stabilization methods are many and varied, but chemical and mechanical stabilization are the most common. This research aims to evaluate the strength of stabilized soils by using a dynamic cone penetration (DCP) test. To achieve this aim, subgrade soil was provided from a roadway project in Kerbala city and stabilized with 2.5 and 5% of Portland cement by weight of the dry soil. Then, the cemented subgrade soil was reinforced with 6 and 12 mm of polypropylene discrete fiber. The fiber was added to the soil with the following contents: 0.5, 1, and 2%. The characteristics of stabilized soils were evaluated by determining three parameters: dynamic cone penetration index (DCPI), in-situ California bearing ratio (CBR), and bearing capacity obtained from the DCP test. The results showed that when Portland cement was increased from 0 to 2.5% and then to 5% by weight of the dry soil, the DCPI value gradually decreased while increasing both CBR and bearing capacity. However, adding 6 and 12 mm fiber contents (0.5, 1, and 2) to the cement–sand mixture containing 2.5 and 5% cement led to increased DCPI and a gradual decrease in CBR and bearing capacity. Also, the results showed that the DCPI for a 12 mm fiber is lower than that for 6 mm fibers, while the CBR and bearing capacity for a 12 mm fiber are greater than those of 6 mm fibers for all ratios. Accordingly, the results of the DCP tests showed that the most significant support for the soil is obtained when the soil is stabilized using 5% cement with 12 mm of fiber by weight of dry soil.

Subgrade soil is a natural formation utilised as a foundation for pavement layers, which means that it must be strong enough to support the pavement system. Subgrades such as loose sand, clay and silt soils thus need to be stabilised in order to improve in-situ performance. Several different geotechnical techniques have been utilised for soil stabilisation, and in this research, experimental work was carried out to examine the use of hydrated lime and waste plastic fibre as sustainable additives to enhance the characteristics of loose subgrade sand. The hydrated lime was added at several different percentages (4, 6, 8, and 10% by dry weight of soil), and the laboratory tests results revealed that adding 8% lime to the soil provided the best strength characteristics. The optimum lime-treated sandy soil was then reinforced by the addition of waste plastic fibre with lengths ranging from 5 to 20 cm added at three percentages (1, 2 and 3% by dry weight of soil). The dynamic behaviours of the reinforced stabilised soil in terms of surface deflection and dynamic modulus were evaluated using a light weight deflectometer test (LWD). The results illustrated that adding 10 cm waste plastic fibre at 3 wt.% content led to an increase in the dynamic modulus of 28.12% and a decrease in the surface deflection of 21.35% as compared to natural subgrade soil.

Shallow foundations are often the most economical option for building support, as they distribute structural weight to soil layers, require minimal earthwork, and do not necessitate specialized machinery. The most common type of soil in the city of Karbala is sandy soil. It is granular and loose by nature which has a relatively low bearing capacity. According to previous studies, the soil weakness is one of the problems with shallow foundation construction. Thus, the aim of this study is to improve the properties of the soil using geogrid reinforcement. Three critical parameters are examined, including depth, size, and number of geogrid layers in the soil reinforcement process to increase bearing capacity and decrease soil settling. The effect of geogrid depth (u) was studied by considering four depth ratios (u/B = 0.5, 1.0, 1.5, and 2.0) in order to determine the ideal depth of the geogrid layer, where (B) refers to the width of the footings. The results indicated that a decrease in depth ratio significantly increased the bearing capacity of footings built on reinforced soil layers compared to those built on natural soil, and the settlement reduction ratio (SRR) also increased. The size of the geogrid layer (i.e., width of the geogrid layer (b) was evaluated by evaluating four size ratios (b/B = 1.5, 3.0, 4.5, and 6.0). With an increasing size ratio of the geogrid layer, the bearing capacity ratio (BRC) was significantly improved. Additionally, the study examined the optimal number of geogrid layers, focusing on single and multiple layers with N = 1, 2, 3, and 4. The results showed a higher BRC for footings on reinforced soil layers, as well as a significant rise in SRR with an increase in the number of geogrid layers. Finally, it was concluded that the optimal depth ratio was u/B = 0.5, the size ratio was b/B = 4.5, and reinforced with three geogrid layers, which provided the highest bearing capacity and SRR. The experimental test results were verified by comparing them with those calculated using theoretically developed models. The variation between the experimental and theoretical results is reasonable, confirming that the experimental testing results exhibit a high degree of accuracy.

The long-term performance of asphalt pavements is influenced by the quality of the supporting subgrade, with subgrade required to prevent premature asphalt pave

Computing the axial load capacity of pile foundations is often challenging for geotechnical engineers. Different theoretical and empirical approaches were proposed for determining the ultimate bearing capacity. Among these approaches, the in situ testing methods are based on cone penetration test (CPT) measurements. This study compares five CPT methods in estimating the axial load capacity of precast concrete piles evaluated at four piling construction projects in Northwest and Central Florida. The analytical methods used in this work are the Aoki and De Alencar method (1975), the Schmertmann method (1978), the Bustamante and Gianeselli Laboratoire Central des Ponts et Chausees method (1982), the Eslami and Fellenius method (1997), and the Eurocode 7 (2007). The outcomes indicated that the Eurocode method 7 had the most increased load capacity estimates, whereas the Eslami and Fellenius method yielded the lowest estimates. The results also indicated that the Aoki and De Alencar (1975) method consistently demonstrated the slightest differences among these values, showing its potential for reliable and consistent pile-bearing capacity estimations.