Polyurethane resin injection is a treatment being considered as a replacement for traditional methods of ground improvement. It has been used to re-level foundations and concrete slabs that have settled over time. Additional claimed benefits of the treatment have been noted recently, including improved factors of safety against soil liquefaction and reduced earthquake-induced settlements. To investigate the capability of the polyurethane resin injection treatment to mitigate liquefaction, two full-scale blast liquefaction tests were performed; one test was conducted in an improved panel (IP), an 8 m circular area treated with the polyurethane resin in a 1.2 m triangular grid from a depth of 1 to 6 m, and another test in an untreated 8 m circular area, the natural panel (NP). Each blast test was severe enough to produce liquefaction (ru ≈1.0) in the respective panel, with blast-induced settlements in the range of 70 to 80 mm. Despite similar levels of ground-surface settlement in the IP and NP, settlement within the top 6 m of the IP was about half that of the NP. A CPT-based predicted settlement for each panel was employed using the Zhang et al. (2002) methodology. Good correlation was found between the observed settlements and predicted settlements in both panels. Differential settlements across the panels were calculated based on ground-based lidar surveys, with a reduction of 42 to 49% between the IP and NP. The measured total and differential settlements following resin injection were at the bottom of the range observed in blast tests on a variety of shallow ground improvement methods conducted by the New Zealand Earthquake Commission in 2013. The persistence of the polyurethane resin injection ground improvement three years following its installation was indicated by the lasting increase of fundamental in situ test parameters. The results of the study indicate that resin injection is a viable method of ground improvement to reduce liquefaction-induced settlements by creating a stiffer surficial crust.

This study was designed to evaluate the ability of vertical drains to prevent liquefaction and limit associated settlement. Drain performance was investigated using full-scale tests with vertical drains in liquefiable sand using a laminar shear box with acceleration time histories applied at the base. Performance of the sand box with drains in these tests was compared with performance of the sane box without drains in previous tests. The test data was also used to create case histories which can be used for further research and calibration of computer models. Although some investigations regarding vertical drains have been performed with centrifuge tests, no full-scale drain installation had been tested previously. Two drain geometries were investigated, first with drains spaced at 4 feet and second with drains spaced at 3 feet, to determine the effect of spacing on drain effectiveness.Sand was hydraulically placed at a relative density of about 40%. Sensors to monitor pore water pressure, settlement, lateral displacement, and acceleration were placed in the laminar shear box. Three rounds of testing were performed with each drain configuration. Each round consisted of three tests, with peak sinusoidal acceleration levels of 0.05g, 0.1g, and 0.2g respectively, with 15 sinusoidal cycles in each case. A cone penetration test sounding was performed between each round as well as before and after testing to characterize the soil properties for each round.Prefabricated drains were effective at reducing excess pore pressure generation during shaking and increasing the rate of dissipation immediately following the shaking. Liquefaction induced settlement was typically reduced by about 50% relative to tests without drains. These results are in good agreement with results from previous centrifuge testing. Drains spaced closer together reduced the excess pore pressure that generated during shaking and increased the rate of pore pressure dissipation relative to tests with drains spaced further apart, but post-liquefaction settlements were similar. As the soil became denser, settlement decreased significantly, as did the time for pore pressures to dissipate.

Existing and novel laboratory techniques and equipment are used to produce comprehensive information on the liquefaction mitigation provided by granular drainage columnar inclusions in loose sand. Extensive use is made of bender-element testing techniques and the frequency dependence of such measurements is examined. Phase-sensitive detection is proposed as a new method to obtain the frequency response of the element data. The applicability of this technique is extended to provide a convenient and accurate method for determination of the time-of-flight of a shear-wave in sand. This technique is employed to measure the load share between sand and columnar components during triaxial testing. A novel low cost, high loading frequency, triaxial testing system is developed and preliminary testing is carried out on both pure sand samples and composite columnar samples. The testing programme examines aspects of liquefaction mitigation due to the rigidity of the columnar inclusions and due to the increased permeability of the columns. The laboratory results are verified by the application of existing analytical models. The equipment and techniques are used to investigate the feasibility of using recycled aggregates in place of stone backfill.

abstract: The dissimilatory reduction of nitrate, or denitrification, offers the potential of a sustainable, cost effective method for the non-disruptive mitigation of earthquake-induced soil liquefaction. Worldwide, trillions of dollars of infrastructure are at risk for liquefaction damage in earthquake prone regions. However, most techniques for remediating liquefiable soils are either not applicable to sites near existing infrastructure, or are prohibitively expensive. Recently, laboratory studies have shown the potential for biogeotechnical soil improvement techniques such as microbially induced carbonate precipitation (MICP) to mitigate liquefaction potential in a non-disruptive manner. Multiple microbial processes have been identified for MICP, but only two have been extensively studied. Ureolysis, the most commonly studied process for MICP, has been shown to quickly and efficiently induce carbonate precipitation on particle surfaces and at particle contacts to improve the stiffness, strength, and dilatant behavior of liquefiable soils. However, ureolysis also produces copious amounts of ammonium, a potentially toxic byproduct. The second process studied for MICP, denitrification, has been shown to precipitate carbonate, and hence improve soil properties, much more slowly than ureolysis. However, the byproducts of denitrification, nitrogen and carbon dioxide gas, are non-toxic, and present the added benefit of rapidly desaturating the treated soil. Small amounts of desaturation have been shown to increase the cyclic resistance, and hence the liquefaction resistance, of liquefiable soils. So, denitrification offers the potential to mitigate liquefaction as a two-stage process, with desaturation providing short term mitigation, and MICP providing long term liquefaction resistance. This study presents the results of soil testing, stoichiometric modeling, and microbial ecology characterization to better characterize the potential use of denitrification as a two-stage process for liquefaction mitigation. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

To investigate the liquefaction mitigation capability of Rammed Aggregate Piers® (RAP) in silty sand, blast liquefaction testing was performed at a soil profile treated with a full-scale RAP group relative to an untreated soil profile. The RAP group consisted of 16 piers in a 4x4 arrangement at 2 m center-to-center spacing extending to a depth of 9.5 m. Blasting around the untreated area induced liquefaction (ru ≈1.0) from 3 m to 11 m depth, producing several large sand boils, and causing settlement of 10 cm. In contrast, installation of the RAP group reduced excess pore water pressure (ru ≈0.75), eliminated sand ejecta, and reduced average settlement to between 2 to 5 cm when subjected to the same blast charges. Although the liquefaction-induced settlement in the untreated area could be accurately estimated using the CPT-based settlement approach proposed by Zhang et al. (2002), settlement in the RAP treated area was significantly overestimated with the same approach even after considering RAP treatment-induced densification. Analyses indicate that settlement after RAP treatment could be successfully estimated from elastic compression of the sand and RAP acting as a composite material. The composite reinforced soil mass, surrounded by liquefied soil, transferred load to the base of the RAP group inducing settlement in the non-liquefied sand below the group. This test program identifies a mechanism that explains how settlement was reduced for the RAP group despite the elevated ru values in the silty sands that are often difficult to improve with vibratory methods.

Liquefiable soils are common at ports due to the use of hydraulic fills for construction of waterfront facilities. Liquefaction-induced ground failure can result in permanent ground deformations that can cause loss of foundation support and structural damage. This can lead to substantial repair and/or replacement costs and business interruption losses that can have an adverse effect on the port and the surrounding community. Although numerous soil improvement methods exist for remediating a liquefaction-prone site, many of these methods are poorly suited for developed sites because they could damage existing infrastructure and disrupt port operations. An alternative is to use a passive remediation technique. Treating liquefiable soils with colloidal silica gel via permeation grouting has been shown to resist cyclic deformations and is a candidate to be used as a soil stabilizer in passive mitigation. The small-strain dynamic properties are essential to determine the response to seismic loading. The small-to-intermediate strain shear modulus and damping ratio of loose sand treated with colloidal silica gel was investigated and the influence of colloidal silica concentration was determined. The effect of introducing colloidal silica gel into the pore space in the initial phase of treatment results in a 10% to 12% increase in the small-strain shear modulus, depending on colloidal silica concentration. The modulus reduction curve indicates that treatment does not affect the linear threshold shear strain, however the treated samples reduce at a greater rate than the untreated samples in the intermediate-strain range above 0.01% cyclic shear strain. It was observed that the treated sand has slightly higher damping ratio in the small-strain range; however, at cyclic shear strains around 0.003% the trend reverses and the untreated sand begins to have higher damping ratio. Due to the nature of the colloidal silica gelation process, chemical bonds continue to form with time, thus the effect of aging on the dynamic properties is important. A parametric study was performed to investigate the influence of gel time on the increase in small-strain shear modulus. The effect of aging increases the small-strain shear modulus after gelling by 200 to 300% for the 40-minute-gel time samples with a distance from gelation (time after gelation normalized by gel time) of 1000 to 2000; 700% for the 2-hour-gel time sample with a distance from gelation of 1000; and 200 to 400% for the 20-hour-gel time samples with a distance from gelation of 40 to 100. The treatment of all potentially liquefiable soil at port facilities with colloidal silica would be cost prohibitive. Identifying treatment zones that would reduce the lateral pressure and resulting pile bending moments and displacements caused by liquefaction-induced lateral spreading to prevent foundation damage is an economic alternative. Colloidal silica gel treatment zones of varying size and location were evaluated by subjecting a 3-by-3 pile group in gently sloping liquefiable ground to 1-g shaking table tests. The results are compared to an untreated sample. The use of a colloidal silica treatment zone upslope of the pile group results in reduced maximum bending moments and pile displacements in the downslope row of piles when compared to an untreated sample; the presence of the treatment zone had minimal effect on the other rows of piles within the group.

Stone column treatment is commonly used to mitigate liquefaction hazard in sandy soils. Research and experience indicate that this method is effective for clean sands but that it may not be effective for silts and sands with fines contents greater than 15-20%. An alternative to the stone column method involves supplementing stone column treatment with pre-fabricated vertical wick drains installed prior to the stone columns installation. Although this method is used in practice, there has not been a formal academic study of its effectiveness. This thesis evaluates seven different case histories where wick drains were used and one where wick drains were not used, for comparison purposes. The site locations varied as well as the soil properties and treatment plans. CPT testing was done at 3 sites and SPT testing was performed at the other 5 sites. CPT data were correlated to SPT data to facilitate comparisons. One of the case histories includes a unique study in which three different variations of the stone column treatment were applied at the same site, providing a direct comparison of the effectiveness of each method. A 26% area replacement ratio (Ar) with drains was determined to be more effective overall than a 26% Ar without drains and more effective in increasing low initial blow counts than the 34% Ar without drains. The areas with drains were more likely to exceed the minimum project criteria consistently throughout the site. Significant scatter were observed in the results and probable causes for the scatter are noted. Final blow count coefficients of variation ranged from 28% to 77%. Increased fines contents required increased Ar in order to maintain similar average final blow counts. Site improvements were evaluated separately and collectively. Individual site results were compared to clean sand curves developed by Baez (1995). Sites with average fines contents less than 20% which were improved using drains and an 11-15% Ar treatment were comparable to clean sand sites without drains and with 5-10% Ar. To achieve similar improvement at sites with 40-46% fines necessitated drains and Ar values of 23-26%. Design recommendations are provided.

Stone columns are an established method of liquefaction mitigation in clean sands (fines content <15%). Although stone columns are considered less effective in silty soils, an increase in the area replacement ratio or the addition of wick drains may still produce improvement in the normalized blow count. Limited case histories are available with a direct comparison of the use of stone columns with and without wick drains at one location. The Salmon Lake Dam Modification project provided such a scenario. Two test sections were completed at the site prior to construction to determine the area replacement ratio for the final design as well as to compare the application of stone columns with and without wick drains. Visual observations of water and air escaping from wick drains within a distance of 15 ft of the stone column construction confirmed that drains aided in pore pressure dissipation. Test results indicated that stone column treatment with wick drains produced greater improvement in blow count than stone column treatment without drains. For the overall site, there was an increase in improvement ranging from 3 to 8 SPT blow counts. When compared to the results of a similar evaluation of a site in Ogden, Utah, which had a comparable fines content and an area replacement ratio of 26%, the increase in stone column effectiveness produced by adding wick drains was lower at the Salmon Lake Dam site. The increase in improvement at the Ogden, Utah site ranged from 12 to 18 SPT blow counts. At the Ogden site, wick drains were placed between every stone column while they were only placed between vertical rows of columns at Salmon Lake dam. Despite the beneficial effects provided by using wick drains with stone column treatment in silty soils, the performance was below what would be expected for stone column treatment without wick drains in clean sands with less than 15% fines. Stone column treatment also proved less effective in layers of sandy silt than in layers of silty sand, which was indicated by lower average improvement and more points of negative improvement in layers of sandy silt. Although several different area replacement ratios were analyzed (23, 27, 31, and 35%), no consistent trend towards greater improvement in blow count was seen as the replacement ratio increased beyond 23%.