Shear Strength Increment Research Articles

Experimental study on the volume and strength change of an unsaturated silty clay upon freezing

In order to investigate the frost deformation and shear strength increment characteristics of unsaturated soil, a comprehensive experimental study was conducted to unsaturated slity clay samples with considering the influence of soil initial dry density and water content. Micro-structure observation tests, three-dimensional frost deformation tests, direct shear tests and soil compression tests are carried out. The frost deformation test results demonstrate that frost shrinkage happens when soil initial degree of saturation (Sr) is low, whereas frost heave and frost cracking happen when soil initial Sr is high. There is a critical degree of saturation at which frost shrinkage will turn into frost expansion. For the silty clay tested, this critical value is about 0.75. The frost shrinkage of soil is considered to be owing to the increase of cohesion upon freezing. The frost expansion of soil is induced by the fabric rearrangement which happens when pore-water changes into ice upon freezing. The shear strength test results demonstrate that soil friction angle does not vary much upon freezing, whereas soil cohesion increases a lot because of the generation of ice cementation and the increase of capillary cohesion. With assuming the increment of capillary cohesion upon freezing is equal to that upon drying for soil samples with same reduction of pore-water content, the ice cementation of frozen soil is found to be linear to its volumetric ice content. If the volume shrinkage induced by the increase of cohesion is assumed to be equal to that induced by the increase of mean principle stress with same values, the frost expansion induced by the water-ice phase transition is also linear to the volumetric ice content of unsaturated soil. Such linear relations seem to be unique and are applicable to unsaturated soil samples with any initial void ratio and water content.

Experimental in-plane performance of insulated concrete and brick masonry wall panels retrofitted using polymer composites

Masonry infilled reinforced concrete frame buildings built prior to the introduction of modern seismic provisions have been observed to undergo damage in and around the masonry infill walls during most recent moderate to severe earthquakes. Fibre reinforced cementitious matrix (FRCM) is one of several retrofitting options available to limit such earthquake induced damage to infill walls. An experimental program was undertaken herein to experimentally investigate the effectiveness of FRCM as a strengthening solution for vintage (i.e. built between 1880 and 1930) un-reinforced brick masonry (URM) and insulated concrete masonry (IMU) infill walls. A total of 16 masonry assemblages were tested under in-plane diagonal load, of these 8 were constructed replicating vintage URM whereas the remainder were constructed using modern IMU. IMU is a preferred masonry type in hot and humid regions owing to its superior insulting capability. Different polymer fabrics (i.e., carbon, glass and basalt) were applied over both faces of test walls, with two replicate test walls receiving the same FRCM strengthening details. One test wall of each masonry type was tested as-built to serve as a control specimen for comparison. One wall of each masonry type received two layers of basalt FRCM. The investigated aspects included stress-strain behaviour, stiffness, and ductility. Shear strength increment observed due to single layer of FRCM application was 422-778% for vintage URM and 307-415% for modern IMU. FRCM also substantially increased the ductility capacity of the masonry assemblages.

Fully bio-based soybean adhesive in situ cross-linked by interactive network skeleton from plant oil-anchored fiber

The fiber-reinforcement is an attractive strategy to enhance composites under the green development concept. However, the poor dispersion/interactivity of natural fiber and most petroleum-based modification strategies impede development of fiber-reinforced environmental composites. In this study, we employed a soybean oil derivative as a multi-functional cross-linker that reacted with kenaf fiber (KF) to synergistically improve the soybean flour (SF)-based adhesive. The biobased cross-linker, phosphate and epoxy groups-containing soybean oil (PESO), was synthesized via phosphoric acid ring-opening reaction from epoxidized soybean oil in certain extent. To provide reaction sites, the KF was surface-coated by poly (tannic acid) (PTA) to obtain a PTA-coated KF (TKF). The PESO cross-linker, with the role of epoxy groups, constructed an interactive network skeleton with TKF and formed in situ cross-linking reactions with SF matrix. In addition, the incorporated phosphate groups of PESO gave rise to interactions with hydroxyl of TKF and polysaccharide of SF further stabilizing cross-linking network as confirmed by fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. As expected, compared to pristine SF adhesive, the modified adhesive showed a significant increment in wet shear strength by 236.4% and also exhibited a favorable thermal stability. We envisage that this design may provide a new avenue for developing high-performance fully sustainable biomass composites.

Performance of reinforced recycled aggregate concrete beams in flexure: experimental and critical comparative analysis

The necessity of sustainable approaches in the construction sector persuades the researchers to utilize the recycled coarse aggregate (RCA) extracted from waste concrete and study the performance of structural members by substituting natural coarse aggregate (NCA) with the RCA. In the present context, the flexural performance of RAC beam was examined on fourteen numbers of beams by completely replacing the NCA with RCA and using four different longitudinal reinforcement ratios (ρ) of 1.61, 1.31, 0.75 and 0.42%. In order to improve the quality of RAC, the particle packing method (PPM) of mix design approach was employed along with the two stage mixing approach (TSMA). The improved mechanical properties owing to the combined effect of PPM design mix and TSMA are also translated in the flexural performance of RAC beams even at 100% use of RCA. A maximum reduction of 35, 4 and 5% in cracking load, yield load and ultimate load, respectively, are observed in RAC beams as compared to the conventional concrete beams. However, the undesirable shear tension mode of failure was witnessed for RAC beams at ρ = 1.61%. A database is prepared by compiling the reported experimental results of RAC beams with shear reinforcement in the available literature. The suitability of the existing expressions to predict the ultimate load is verified for RAC beams and it is observed that, the number of unconservative predictions is significant. In this scenario, an equation is proposed to predict the ultimate load of transversely reinforced RAC beams by operating the flexure database, which shows good correlation with the available experimental results. Further, the increment in shear strength of RAC beams due to the inclusion of stirrups is estimated by using the derived expression.

Analysis on Rockbolt Support Interaction with Roof Dilatancy Above Roadside Backfill Area in Gob-Side Entry Retaining

To overcome the challenge to the roof dilatancy deformation control above roadside backfill area of gob-side entry retaining for confining pressure decreasing, a mechanical model of rockbolt reinforcement to the roof above roadside backfill area was established. The shear strength of the shear sliding zone above roadside backfill area considering rockbolt support was deduced. Factors and effect of rockbolt reinforcement to the shear sliding zone of the roof above roadside backfill area based on the 3107 working face of Xinyuan coal mine were obtained. Moreover, a numerical model was established to analyze rockbolt support for roof dilatancy deformation control. Mechanical results show that the shear strength increment from rockbolt axial force is positively related with rockbolt arrange density and rockbolt pretension while the shear strength increment from rockbolt shear force is positively related with rockbolt diameter, rockbolt arrangement density. Numerical results indicate that rockbolt support improves the confining pressure environment around the gateway excavation and effectively restrains roof dilatancy deformation of lower confining pressure region. Field tests and field monitoring indicated that the gob-side entry retaining in the 3107 working face with a width of 2.0 m roadside backfill body and high-strength rockbolt support for the roof above roadside backfill area could meet the requirement for gas drainage and ventilation when 3107 working face was retreating.

Peat Soil Stabilization using Lime and Cement

This paper presents a study of the comparison between two additive Lime and Cement for treating peat soil in term of stabilization. Peat and organic soils are commonly known for their high compressibility, extremely soft, and low strength. The aim of this paper is to determine the drained shear strength of treated peat soil from Perlis for comparison purposes. Direct Shear Box Test was conducted to obtain the shear strength for all the disturbed peat soil samples. The quick lime and cement was mixed with peat soil in proportions of 10% and 20% of the dry weight peat soil. The experiment results showed that the addition of additives had improved the strength characteristics of peat soil by 14% increment in shear strength. In addition, the mixture of lime with peat soil yield higher result in shear strength compared to cement by 14.07% and 13.5% respectively. These findings indicate that the lime and cement is a good stabilizer for peat soil, which often experienced high amount of moisture content.

EFFECT OF DATES NUCLEUS POWDER ON SOME ENGINERRING PROPERTIES OF CLAYEY SOIL IN COMPARISON TO LIME

Clayey soils are widely spread over the world. The clay soils are used and need to improve it’s engineering properties.Therefore, the treatment is considered one of the available solution for this purpose. Due to the nature of clay particles a trice plasticity,highly in surface area and the ion exchangaple ...etc. these properties encourage the idea of using pozzolanic materials, particularly the lime as pozzolana source.The alternative source of pozzolan is a metakaolin materials generated from burning the organic materials which are widely available in Iraq (i.e. Dates nucleus). The Dates nuclei is a waste material, so these additives can help in reducing the contamination and improving the environment. In this study, dates nuclei powder (DNP) was used after burning it at 900oC for one hour and then mixed it with clayey soil in different by weight percentages. Hence, four percentages are selected (5%, 7.5%, 10%, and 15%) to study the effect of each addition on the shear strength of the clayey soil and the results are compared with the same soil that treated with lime. Many tests were conducted on ( the natural clay, clay-DNP and clay-lime) to evaluate the engineering characteristics and to explore best percentages that can used. Curing time (0, 7, 14, 28,90 and 180 days) was used to evaluate the effectiveness of pozzolanic reaction (emerges from DNP-soil mixture) with time. Interested results are found, the shear strength was increased to about six folds for 10%-DNP-soil at 180 days of curing. The liquid limit, plasticity index and the maximum dry density decreased in all percentages of DNP-Clay mixtures. On the other hand, the shear strength increment for DNP-Clay mixture after 180 days of curing is higher than that of Lime-Clay mixture for same period of curing. Forthermore, CBR results increased by six times for 10%DNP-Clay mixture for un-soaking conditions, while at soaking conditions, the increase was more than eleven times. The lime addition increase the CBR-value about three and eight times for unsoaking and soaking conditions, respectively.

Thermal cycling, shear and insulating characteristics of epoxy embedded Sn-3.0Ag-0.5Cu (SAC305) solder paste for automotive applications

In this study, lead free solder alloy paste is fabricated using Sn-3.0Ag-0.5Cu (SAC305) powder mixed with epoxy based polymer and flux. The solder paste is reflowed onto Cu pad of 1608 chip, and the surface insulation resistance (SIR) of the joint is measured. The thermal shock reliability of the solder/Cu joint from −40 °C to 125 °C for 1000 cycles of aging is investigated. Shear test is also performed on the joint after thermal cycling. The results show that the SIR of the reflowed solder bump is around 2.58 × 1013 Ω compared to 3.21 × 1013 Ω of the flux. An increased growth of Cu6Sn5 intermetallic compounds (IMCs) occurs at the solder/Cu bonding interface with increasing number of thermal cycles. There is no appreciable damage in epoxy containing solder paste up to 1000 cycles except the formation of voids and cracks. The shear force of epoxy containing solder joint after thermal cycling for 1000 cycles is ≈34 N over 29 N for SAC305 without epoxy. This shows around 14% increment in shear strength in the presence of epoxy due to the slower growth rate of Cu-Sn IMCs.

Soil-roots Strength Performance of Extensive Green Roof by Using Axonopus Compressus

Green roof technology has been proven to provide potential environmental benefits including improved building thermal performance, removal of air pollution and reduced storm water runoff. Installation of green roof also involved soil element usage as a plant growth medium which creates several interactions between both strands. This study was carried out to investigate the soil-roots strength performance of green roof at different construction period up to 4 months. Axonopus compressus (pearl grass) was planted in a ExE test plot with a designated suitable soil medium. Direct shear test was conducted for each plot to determine the soil shear strength according to different construction period. In addition, some basic geotechnical testing also been carried out. The results showed that the shear strength of soil sample increased over different construction period of 1st, 2nd, 3rd and 4th month with average result 3.81 kPa, 5.55 kPa, 6.05 kPa and 6.48 kPa respectively. Shear strength of rooted soil samples was higher than the soil samples without roots (control sample). In conclusion, increment of soil-roots shear strength was due to root growth over the time. The soil-roots shear strength development of Axonopus compressus can be expressed in a linear equation as: y = 0.851x + 3.345, where y = shear stress and x = time.

An experimental study on the shear strengthening of reinforced concrete deep beams with carbon fiber reinforced polymers

In recent years, Fiber Reinforced Polymers (FRP) have emerged as useful materials for structural strengthening and rehabilitation. The main aspire of this research is towards evaluating the efficiency of Carbon Fiber Reinforced Polymers (CFRP) in enhancing the shear strength of deep beams. The research work included construction and testing of eight (08) reinforced concrete deep beams. Two of the beams, designated as control beams, were without any shear reinforcement. Remaining six beams were divided into three groups, with each group having two identical beams. Beams in one of these groups were strengthened with conventional type of steel web reinforcement. Remaining two groups were strengthened externally by CFRP sheets with different orientations of CFRP. Magnitude of load causing shear cracks to initiate, and the failure load of each beam was recorded. Significant increase in overall load carrying capacities was observed with both CFRP sheets and web steel reinforcement. CFRP was found to be considerably effective in delaying the initial appearance of shear cracks, thereby improving the serviceability limit state of beams. Beams with CFRP orientation perpendicular to the shear cracks showed higher increment in shear strength. In conclusion, CFRP laminates could effectively be used to strengthen existing RC structures deficient in shear strength, and also to reduce/replace internal steel web reinforcement in new RC structures. Material cost comparison of CFRP reinforced beams with conventional web reinforcement is presented, and the general cost effectiveness of structural rehabilitation by means of CFRP is also discussed.

The Study of Soil-Roots Strength Performance of Soil Slope by Using Guinea Grass

Vegetation has been proven for establishing and implementing resistive measures against erosion and failure of slopes, river banks, removal of air pollution and reduced storm water runoff. Installation of cover crop involved soil element usage as growth medium which create several interaction between both strands. This study was carried out to investigate the soil strength performance by using Guinea grass at different construction period up to three months. Grass was planted in a 300 mm x 300 mm x 700 mm test plot with a suitable soil medium. Direct shear tests were conducted for each plot to determine the soil shear strength according to different construction period. Some basic geotechnical testing also were carried out. The results showed there is an increment in shear strength for soil sample over the time at various depths. During period of 1st, 2nd and 3rd month, the average shear stress of 100 mm depth was 50.56 kPa, 63.96 kPa, and 96.59 kPa respectively. Meanwhile, for 200 mm depth the result was 40.843 kPa, 53.91 kPa and 62.93 kPa respectively. Lastly, on 300 mm depth, shear stress was 37.21 kPa, 51.09 kPa, and 59.27 kPa respectively. Based on the result, the higher shear strength was obtained at different construction period and at varying depths. From the observation, roots mass increased for different construction period. In terms of tensile strength, the diameter of the root affects the rate of resistance against the tensile forces. This indicated that the roots structure growth affects the soil shear strength.

Biocementation Potential of Tropical Residue Soil Infused with Facultative Anaerobe Bacteria

Biomediated soil improvement, a promising new branch of microbial geotechnology; which involved multi disciplines has successfully attracted abundant attentions among researchers, geotechnical engineers, and other industries practitioners. Few of the researches were conducted to examine the potential implementation of this technique on tropical residue soil. However, the uncertainties outcomes and inconsistency of bio mediated soil improvement, especially on the clayed soil have made this technique remained at the laboratory stage. Therefore, this paper intended to provide better understanding of this technique by investigating the relation between the bacteria, cementation reagents, and tropical residue soil. The residual soil was mixed with facultative anaerobe bacteria, Bacillus Subtilis before it was compacted into a prefabricated PVC mould. The soil samples were treated with different treatment condition such as (1) control or untreated, (2) treated with cementation solution, (3) treated with bacteria only, and (4) treated with bacteria and Cementation reagent. A worth noting finding showed that the sample treated with bacteria and nutrient only has produced the highest increment of shear strength. This phenomenon might have been caused by the effect of the chemical reagent to the mineralogy of residue soil. The presence of the chemical reagents is believed to have weakened the shear strength of the tropical residual soil.

Stress–strain behavior of a silty soil reinforced with polyethylene terephthalate (PET)

In some cases, the production of solid waste is experiencing an uncontrolled and continuous increase, especially wastes from plastic products. Therefore, this study proposes an alternative reuse method for certain types of plastic waste (bottles and containers used for liquid storage that are processed using discrete fibers) in geotechnical construction projects. To this end, discrete polyethylene terephthalate (PET) fibers were randomly mixed with fine soil to modify their mechanical properties.The principal objective of this research was to study the mechanical behavior of a silty soil that was reinforced with aleatorily distributed PET fibers. To meet this objective, UU triaxial laboratory tests were performed on soil specimens with fiber contents of 0.0–1.0% of the soil dry weight. The test results indicated that the reinforced specimens presented an increment of shear strength that was associated with the increasing quantities of the PET fiber. Furthermore, the laboratory tests indicated that the reinforced soil had a greater deformation capacity, which can be a positive characteristic in some cases because the deformation capacity can reduce the risk of crack formation in certain soil layers for specific geotechnical problems.Finally, this reinforced soil presents interesting mechanical properties and could be used in structures that require a high deformation capacity, such as landfills, sewage treatment deposits and dams (among other uses), to prevent failures due to cracking and to prevent the possible leakage of contaminants or water. However, these issues are beyond the scope of this paper.

A Change of Undrain Shear Strength of Soft Ground during Consolidation Process

The purpose of this study is to investigate the undrain shear strength increment during consolidation process of soft clayey soils. Thirty kinds of laboratory triaxial tests have been performed using undisturbed and remolded Ariake clay samples with different degree of consolidation and 5 kinds of confining pressure. Test results show that well known linear equation proposed by Yamanouchi et al.(1982) is overestimated the strength of undisturbed soft clay ground in the process of consolidation. A new simple and reasonable exponential equation proposed in this paper.

철근콘크리트 깊은 보의 파괴거동과 전단강도 산정식

깊은 보의 파괴거동은 전단경간과 유효깊이의 비(a/d)에 따라 크게 변한다. a/d≤1.0의 깊은 보는 복부의 쪼갬현상과 하중점과 재하점 부근에서의 콘크리트의 연화현상을 동반하는 파괴모드가 지배적인 파괴모드가 되는 것과 복부에 배치된 전단철근은 보의 파괴모드를 변화시키는 역할을 하고, 이러한 목적으로 복부철근을 배근할 때에는 반드시 연직 및 수평철근을 동시에 사용하거나 또는 사인장균열에 직각을 이루도록 철근을 배치하여야 한다. 한편, 1.0＜a/d≤2.5의 깊은 보의 경우, 전단파괴시 주인장철근이 항복상태에 도달하지 않도록 충분히 배치되어져 있다면 복부에 배치된 수평철근으로 인한 전단강도 증가는 거의 기대하기 어렵다. 하지만 연직전단철근은 1.0＜a/d≤2.5의 깊은 보가 일찍 타이드아치기구로 전이되는 현상을 방지함으로서 전단강도를 증대시키는 역할을 한다. 본 연구에서는 깊은 보에 대한 기존의 실험연구로부터 얻어진 파괴거동과 그것에 영향을 미치는 주요 인자들에 대해 정성적으로 분석하고, 소성이론을 적용하여 파괴강도를 구하는데 기초가 되는 역학모델을 정의하였다. 또한 정의된 역학모델을 근거로 소성이론의 상계정리(upper bound theorem)를 적용하여 a/d가 1이하의 깊은 보에 대한 전단강도식을 이론적으로 유도하였다. 이 연구에서 제안된 전단강도 산정식은 a/d≤1.0의 깊은 보의 전단강도를 정확하게 예측하였다.

콘크리트포장 위 아스팔트 덧씌우기용 택코팅 재료의 접착강도특성 연구

PURPOSES: The performance of tack coat, commonly used for layer interface bonding, is affected by application rate and curing time. In this study, bonding strength tests were performed according to the application rate and curing time of asphalt emulsion. Based on finding from this study, optimum application rates and curing times are proposed. METHODS: In order to investigate bonding characteristic of asphalt emulsion, tests were performed on both asphalt concrete pavement and portland concrete pavement. Also, asphalt emulsions were tested at the application rate of 0, 0.2, 0.4, 0.6, and and at the curing time of 0, 0.5, 1, 2, and 24 hours. Pull-off test and shear bonding strength test, which commonly used for bonding strength measurement of asphalt emulsion, were adopted for this study. To assess field performance under different testing condition, asphalt emulsions were applied to in-service pavement. Throughout coefficient of determination analysis between material index properties from asphalt emulsion and mechanical response from bonding strength tests, performance correlativity was analyzed. RESULTS: Test results show that optimum application rate for asphalt overlay on asphalt concrete pavement (AOA) and asphalt overlay on concrete pavement (AOC) was and , respectively. According to the curing time increment, tensile strength and shear strength of AOC were increased to 22~44% and 20~39%, respectively. AOA case also show strength increment in tensile strength (42%) and shear strength (9%). We tested the applicability of tack coat materials at the field sites, and our findings demonstrated that the bonding (for D and E) and rapid curing (for B, C, and D, E) performances were superior than others. Among material index properties, there was a high correlation between penetration ratio and bonding strength test result. CONCLUSIONS : Result show that interlayer bonding strength was affected by asphalt emulsion type, application rate and curing time. AOC required slightly higher application () than AOA. Both AOA and AOC cases show higher strength at longer curing time. Up to 2hours of curing, rapid strength increments were observed, but strength increment ratio was decreased after 2hours of curing. From the observed correlation between penetration ratio and bonding strength, it is expected that penetration ratio can be used as one of important factors affecting bonding strength analysis.

Diagonal shear behaviour of unreinforced masonry wallettes strengthened using twisted steel bars

The in-plane shear behaviour of URM wallettes strengthened using near surface mounted high strength twisted stainless steel reinforcement (TSNSM) was investigated and in particular, the effectiveness of the reinforcing schemes to restrain the diagonal cracking failure mode was studied. A total of 17 URM wallettes, each being 1.2 m × 1.2 m in size, were structurally tested in induced diagonal compression. Of these, 3 wallettes were tested as-built and 14 wallettes were tested after being strengthened using different patterns of TSNSM bars. Several parameters pertaining to the in-plane shear behaviour of strengthened URM walls were investigated, including failure modes, shear strength, maximum drift, pseudo-ductility, and shear modulus. It was inferred from the results that as-built tested wallettes exhibited sudden post-peak strength degradation and failed along a stepped diagonal joint crack, whilst strengthened wallettes failed along distributed diagonal cracks in a more ductile fashion and exhibited a shear strength increment ranging from 114% to 189%.

Mechanical Behavior of the Soil-Root System

The reinforcement of soil by vegetation depends on the biomechanics, length, and morphology of roots. Often, morphology and length are simplified in root reinforcement models by assuming symmetry above and below the shear plane. For many root systems, however, the presence of root collars and lateral rootlets could be greater beneath the shear plane. This is not taken into account in current models, so the current study derives a set of analytical equations to account for these effects and thereby provide a more realistic model of root reinforcement. To gain a better understanding of the mechanical behavior of the soil-root system, the resulting simulation was also compared with that of the data produced by the existing model in the literature (Waldron and Dakessian, 1981). This comparison shows that as root morphology and length are taken into account, the shear strength increment obtained with the new equations could reach values 1.4 times greater than that of previous models when the shear bond strength is small. In contrast, if the shear bond strength is greater, an increase in the root embedment length only produces a minor effect on the shear strength increment. In addition, we note that if the root system has the same constituents, the influence of roots on the shear strength increment decreases with an increase in the depth ofthe shear plane. The influence of rooted soils with smaller shear bond strength is found to be more significant than that of rooted soils with greater shear bond strength.

3-D numerical investigations into the shear strength of the soil–root system of Makino bamboo and its effect on slope stability

This study attempts to quantify the reinforcement effect of the Makino bamboo ( Phyllostachys makinoi Hayata) root system on the stability of slopeland through numerical analyses and in situ tests. Based on the field surveys of Makino bamboo root morphology, a three-dimensional (3-D) numerical model of the soil–root system consisting of the reverse T-shape tap root and hair roots was developed and successfully applied to the finite element simulations of in situ pull-out tests. In the simulations, the soil mass was simulated by a soil element with a perfect elastic–plastic (or Mohr–Coulomb) material model whereas the root system was simulated by a ground anchor element with a linear elastic material model. In addition, a mechanical conversion model with simple mathematical form, which enables a direct transformation of the ultimate pull-out resistance into the shear strength increment of soil–root system was proposed. The conversion model offered a convenient way to quantify the reinforcement effect of the Makino bamboo root system required for the 3-D slope stability analyses. The numerical results indicated that the shear strength increment of the Makino bamboo soil–root system ranged from 18.4 to 26.3 kPa and its effect on the slope stability was insignificant when compared with those adverse influence factors such as the steep slope angle (=50–70°), shallow root depth (=0.8–1.0 m) and large growth height (>10 m) of the Makino bamboo forest slopeland. It can be also speculated that the tension cracks widespread over the slope surface due to the wind loading acting on the bamboo stems and the sequential rainwater infiltration is the dominating factor in the collapse failure of slopeland. For a Makino bamboo forest slopeland with medium slope (25° < slope angle β < 40°), the reinforcement effect of the Makino bamboo root system can mobilize its maximum stabilization capacity when compared with those of slopeland with mild ( β < 25°) and steep slopes ( β > 40°). Conclusively, the contribution of the Makino bamboo root system to the stability of slopeland is not as significant as expected.

The effect of root architecture on the shearing resistance of root-permeated soils

This paper aims to investigate the effect of the root architecture on the shear strength increment provided by plant roots in the soil. In situ shear tests were conducted for this purpose. Five plant species – Hibiscus tiliaceus L. (Linden hibiscus), Mallotus japonicus (Thunb.) Muell.-Arg. (Japanese Mallotus), Sapium sebiferum (L.) Roxb. (Chinese tallow tree), Casuarina equisetifolia L. (ironwood), and Leucaena leucocephala (Lam.) (white popinac) – were used in this study. Tensile tests on roots of various diameters and surveys on the root system structure were carried out for each of the plant species tested. The shear strength increments (Δ S) provided by the roots of Linden hibiscus, Japanese Mallotus, Chinese tallow tree, ironwood, and white popinac were 0.34 t R, 0.462 t R, 0.688 t R, 0.3 t R, and 0.87 t R, respectively, when t R was estimated on the basis of the tensile root strength crossing through the shear plane. The shear strength increment provided by plant roots with conspicuous oblique and vertical roots was greater than that of root structures in which lateral roots were dominant. In comparison with other types of root architecture, the R-type root architecture was found to be the most effective root system against shear failure in the soil. Its shear strength increment was slightly greater than that with the V-type root architecture, followed by the VH-type root architecture. The shear strength increment provided by plants with the H-type root architecture was less effective than that contributed by plant species with other types of root architecture.