Limiting Base Moduli to Prevent Premature Pavement Failure

The liquefaction of gravelly soils during earthquakes remains a challenging hazard to evaluate because larger soil particles can interfere with traditional in situ tests such as the standard penetration test (SPT) and cone penetration test (CPT). This study investigates six sites affected by the 2020 Mw 6.4 Petrinja, Croatia earthquake, where gravelly liquefaction ejecta was observed. Subsurface investigations included boreholes to define the soil profile, shear wave velocity (Vs) profiling using the multichannel analysis of surface waves (MASW) and horizontal to vertical spectral ratio (HVSR), and large-diameter (74-mm) dynamic cone penetration tests (DPT). At several sites, DPT blow counts increased through silty clay surface layers, whereas CPT tip resistance from companion testing remained constant. The increase in DPT resistance was thus attributed to side friction along the drill rods, and two subsequent DPT soundings were conducted to isolate this effect: (1) a cased DPT (cDPT), where the overlying material was removed and the hole was cased to the target gravelly layer; and (2) an instrumented DPT (iDPT), used to measure the hammer energy transferred to the cone. Corrected DPT blow counts (N120′) and normalized shear wave velocities (Vs1) from critical gravelly layers were evaluated using recent probabilistic DPT- and Vs-based liquefaction triggering models. These methods correctly predicted liquefaction manifestation at each of the sites. Results support the continued development of energy-corrected DPT and Vs-based approaches for liquefaction assessment in gravelly soils and provide valuable case history data to continue refining probabilistic triggering relationships.

The aim of this research is studying the effect of base and subgrade layer local materials properties on the rutting damage of flexible pavement due to repeated traffic loading. The most roads in Baghdad city present severe rutting damage due to absence of quality control in the construction of granular unbounded pavement layer. Furthermore many trucks with overweight using the roads and high temperature in summer produced distresses and deterioration of flexible pavement. Flexible pavement analyses are performed using finite element method; a 3-D dimensional finite element model using ABAQUS (ver. 6.12-1) computer program are developed. The results obtained for base layer show reduction in rutting damage by about (58%) while subgrade layer provided damage reduction only (10%). Also the critical value for vertical compressive stresses is (480 kPa) below the wheel loading area which is about (70.9%) of the applied tire pressure and then decreased gradually with depth to about (118 kPa) approximately (17%) of the applied tire pressure within the base layer and remains almost constant with depth through the subgrade layer. And for horizontal stresses a high value was observed on surface of flexible pavement under the path of wheel load rather than the compressive stresses then decreased laterally with horizontal distance.The local untreated base material experience critical rut depth of (8 mm) at 1000 number of repetitions and for treatment base materials the number of load repetitions to cause damage rutting increased (10) times to about 10000 number of load repetitions.The treated base materials decreased the rutting damage factor. This implicates the main role of granular base layer in pavement system support to minimize the rutting damage.

Assessing subgrade strength using an instrumented dynamic cone penetrometer

An investigation was conducted to determine the root cause of the premature pavement failure. The premature pavement failure occurred in the form of rutting and alligator cracking. Although the affected portion was repaired by removing and replacing the top 75-mm asphalt concrete (AC), the repaired AC experienced recurring rutting and alligator cracking in a few weeks. Through extensive field and lab testing, it was found that the weak base is the root cause of the premature failure and the brittleness of the AC is secondary. However, both the base and AC were built according to plan and met the current material and field density requirements. It was concluded that density alone for construction quality control is not sufficient, as it was not able to protect against premature failures from occurring. Although there are many different ways to minimize premature failures, an immediate action is to include proof rolling in construction quality control. Proof rolling has been used with success to ensure proper compaction and to locate unstable areas, as the stability is greatly influenced by the degree of densification achieved during compaction.

A condition assessment procedure for pavement layers that uses multiload-level falling weight deflectometer (FWD) deflections is presented. A dynamic finite element program that incorporates a stress-dependent soil model was used to generate the synthetic deflection database. On the basis of the data in this database, the relationships between surface deflections and critical pavement responses, such as the stresses and strains in each layer, have been established. The FWD deflection data, distress survey results, temperature, and laboratory testing results used to develop this procedure were collected from the Long-Term Pavement Performance project database. Research efforts also focused on the effect of the FWD load level on the condition assessment procedure. The results indicate that the proposed procedure can estimate the asphalt concrete (AC), base, and subgrade layer conditions. The AC layer modulus and the tensile strain at the bottom of the AC layer were found to be better indicators of the condition of the AC layer than the deflection basin parameter. It was also found that the structurally adjusted base damage index and base curvature index were good indicators for prediction of the stiffness characteristics of the aggregate base and subgrade, respectively. An FWD test with a load of 71.2 kN or less does not improve the accuracy of this procedure. The results from the study of the nonlinear behavior of a pavement structure indicate that the deflection ratio obtained from multiload-level deflections can predict the type and quality of the base and subgrade materials.

The Falling Weight Deflectometer (FWD) is one of the most important non-destructive tests (NDT) used for pavement structural evaluation based on deflection measurements. Inverse analysis of FWD measurements—back-calculation—is a common process for obtaining the pavement layer moduli, including the subgrade soil, which are useful for estimating remaining pavement life for overlay design purposes. Based on a proficiency test (PT) involving testing devices from different manufacturers, the objective of this study is to analyze the influence of FWD uncertainty on the back-calculated flexible pavement and foundation layers moduli. A parametric study was performed considering the back-analysis of different asphalt pavements with regard to layer thickness and resilient modulus (unbound granular and asphalt concrete layers, including subgrade). It was concluded, in general, that FWD uncertainty could have an important influence on the layers modulus obtained from back-calculations. This influence was less significant in the case of asphalt concrete layers (±25%). The variation in resilient modulus was greater in the layers of the subgrade soil (−33 to +83%) and the unbound granular materials (−42 to +80%).

The recurrence of building collapses and resulting casualties is overwhelming in Lagos State as the state records the highest cases in recent times. This work used geophysical (Ground magnetic (GM) and Electrical resistivity imaging (ERI)) and geotechnical (Dynamic cone penetration test (DCPT)) methods in delineating the subsurface conditions for its competence in foundation structures. Ten profiles of 200 m ground magnetic data were collected at 2 m spacing likewise for Wenner arrays on each profile. DCPT data were collected at points 0 m, 50 m, 100 m,150 m, and 200m to the depth of 3 m on each of the profiles occupied by GM and ERI. The data obtained were processed and interpreted using RES2DINV software for ERI, Excel package for both Magnetic and DCPT. The ground magnetic results gives the minimum relative magnetic intensity as -1689.78 nT representing possible fault/fractured zone and maximum value of 2943 nTindicating area of competence for foundation structure. ERI results gives a resistivity value ranging from 2 Ωm – 7602 Ωm depicting four zones of incompetent/sub-competent clay/sandy clay, moderately competent clayey sand, competent sand and highly competent lateritic sand. DCPT results is in the average range 11.20% to 39.87% representing Clay materials fairly competent for foundation structures, sand and well graded gravel that is competent for construction purposes. To prevent building collapsed in the study area, areas of incompetent materials should be excavated, refill and compact with lateritic sand before foundation is put in place.

Geotextiles have been widely promoted for pavement structure, but only a few full-scale experiments have investigated the effects of geotextile reinforcement on pavement design. In this study, full-scale accelerated pavement testing (APT) was conducted on six pavement test sections with granular bases reinforced with various types of woven geotextiles. The control section had a granular base without any reinforcement. All sections were paved with Superpave® hot-mix asphalt (HMA). Base and subgrade materials were the same, but the test sections had varying thicknesses of base and asphalt layers. Each section was instrumented with two pressure cells at the top of the subgrade, six strain gauges on the geotextile, six H-bar strain gauges at the bottom of the asphalt layer, and two thermocouples. The sections were loaded to 250,000 to 400,000 repetitions of an 80-kN single-axle load of the APT machine. Mechanistic responses of the test sections were periodically monitored and analyzed. Rutting profile, pressure on the subgrade, strains in the geotextiles, and strains at the bottom of the HMA layer were measured. Falling weight deflectometer (FWD) tests were performed before and after loading. Reinforced-base sections with similar cross sections outperformed the control section in terms of rutting, and the reinforced-base layer reduced pressure on the subgrade. Backcalculated moduli from FWD tests demonstrated that the base layer in reinforced sections was significantly stronger than the control section base layer after loading. Strain measurements at the bottom of the HMA layer indicated that fatigue life of test sections did not improve with geotextile reinforcement.

Implementing a quality assurance (QA) process for compaction of aggregates using light weight deflectometer (LWD) requires construction of a 100 ft. long, 24 ft. wide test section prior to other uses. However, there are numerous cases where aggregates are used in construction of subgrade, subbase course, and base course in small areas, such as bridge approach, lane widening, patching, and shoulders, and construction of a test section is not possible. In addition, there are over 70 LWDs currently used in construction projects by Indiana Department of Transportation (INDOT). Maintaining a quality control process requires timely and appropriate calibration and verification of the LWD devices. This study performed intensive laboratory experiments on the aggregate materials commonly used by INDOT to determine the target deflection values for compaction QA and evaluate the effects of the moisture content and the interface condition of the inner wall of the Proctor mold on LWD test results. Intensive experiments were also performed in the test pits with LWD to determine the effect of the thickness of aggregate layer and close the gap between the LWD measurements made in-situ and in the Proctor mold. Extensive field LWD testing was conducted during construction of many projects in 2016 and 2017 to validate the compaction of various types of projects. Statistical tests were performed on historical compaction QA data from LWD testing and LWD verification data. It was concluded that moisture content has a significant effect on LWD deflection or modulus. Unbound aggregates compacted near the optimum moisture are capable of providing a stable modulus value when becoming wet and experiencing dramatic gains in modulus with decreasing the moisture content. Maximum allowable deflections were developed for QA of aggregate compaction, particularly in small areas. It was also found that annual verification is necessary to ensure repeatability of LWD deflection measurements. Recommendations were made for immediate and future implementations, such as improvement of the current field practice of compaction QA with LWD in terms of test frequency, test position, and moisture content test. Finally, it was recognized that urgent effort is needed to determine the optimum interval for LWD calibration and necessary training is needed to further improve compaction quality and consistency of compaction QA with LWD.

Dynamic cone penetration test (DCPT) is a fast, economical and easy to conduct. It is widely used to assess the strength of natural and compacted soils. The device is introduced in the 1950s. However, it was newly introduced in Iraq. This study aims to evaluate the potentials of DCP in geotechnical explorations in the gypseous soil since it covers a large area of the country and to obtain correlations with the California bearing ratios (CBR) and investigating the effect of gypsum on the CBR-DCP relationship. Field and Laboratory tests were conducted on soil sample retrieved from six sites with different gypsum contents (28-41) %. Laboratory tests include performing CBR and DCP tests in a cylindrical mold. A statistical analysis of the results shows that gypsum content is an affecting factor on DCP and good CBR-DCP correlations on gypsum content were obtained.

An accurate knowledge of ground properties is essential in the design of civil engineering structures and this information is usually obtained by a combination of in situ and laboratory testing. The interpretation of in situ testing depends in the main on empirical correlations with published data, whilst the usefulness of laboratory soil testing depends on how realistically the field conditions can be reproduced. This paper provides a comparative study of ground properties determined using a number of different techniques in a sequence of Pleistocene sands and gravels overlying till in the Vale of St Albans. In situ testing techniques included both static and dynamic cone penetration tests and also a limited number of self-boring pressuremeter tests in the sands. Recovery of bulk disturbed samples from the site enabled laboratory shear tests to be carried out on large samples of the soil compacted to their maximum density conditions. Values for modulus, angles of shearing resistance and relative density from the in situ and laboratory tests on the soil are compared, and these in turn are correlated with data published by others for similar soil types.

Laboratory evaluation of an indigenous developed light weight deflectometer as a quality control tool for pavement construction

The use of construction and demolition waste (CDW) aggregates in unbound road pavement layers is increasing. However, the lack of data on performance in the field has spurred this investigation into their in-situ properties. A lightweight deflectometer (LWD) is a fast and simulative testing device for estimating the elastic modulus of unbound pavement layers. A field test pit was built to run LWD measurements on an unbound subbase layer containing CDW aggregates compacted at different energy levels. To assess their stress-strain non-linear behaviour, several LWD drops were performed on the same location by varying (i) the loading mass, (ii) the drop height, and (iii) the plate diameter. A stress-hardening behaviour of in-situ CDW aggregates was observed, consistent with the stress dependent evolution of resilient modulus of granular material commonly recorded in laboratory tests. The LWD modulus was found to be dependent on the level of compaction energy but also sensitive to the mechanical response of the layer below. The outcomes at this test pit suggest it would be wise to consider the rational evaluation of the in-field stress dependent behaviour of unbound CDW granular materials at both the design stage and when devising quality acceptance procedures. Nonetheless, to have a comprehensive interpretation of LWD results a greater uniformity of material properties and a stronger control of construction procedures will be desired, especially when heterogenous materials such as CDW aggregates are investigated.

To reduce the use of natural aggregates commonly used in base layers, constructing recycled aggregate base (RAB) layers has gained popularity. However, in the literature, there is limited information about the engineering properties of recycled concrete aggregate (RCA) materials with different gradations and the blends of RCA and recycled asphalt pavement (RAP) materials. There is also a lack of practice in using a mechanistic-empirical (ME) design method to optimize RAB layer thicknesses. In this study, several full-scale test cells were built with RAB and natural aggregate base layers, and the physical and engineering properties of the base layer aggregates were determined in the laboratory. For long-term performance evaluation of the cells built in the field, falling weight deflectometer (FWD) tests were performed, rutting measurements were taken, and soil temperature was monitored over a period of two years. An ME design procedure was used to optimize RAB layer thicknesses.

Saturation effects on calcareous desert sands: Ismael, N F; Al-Khalidi, O; Mollah, M A Trans Res RecN1089, 1986, P39–48