Side-by-Side Correlation of Texas Cone Penetration and Standard Penetration Test Blowcount Values

This paper presents side-by-side comparisons of blowcount values for the Texas cone penetration (TCP) test and the standard penetration test (SPT). The comparisons yielded statistically-significant regression models for both coarse-grained soils and fine-grained soils. Consistent with expected trends and published data, the TCP–SPT relationship is nonlinear, with weak to fair correlation strength (R² = 23–44%). For TCP blowcounts (N_{60, TCP}) varying from 25 to 200 blows/30 cm (1 ft), corresponding SPT blowcounts (N_{60, SPT}) are typically 30–60% lower than N_{60, TCP} in fine-grained soils. Likewise, corresponding N_{60, SPT} blowcounts are 10–70% lower than N_{60, TCP} in coarse-grained soils, all other things being equal. Comparative data were obtained from published sources and from project-specific field research sites used for full-scale deep foundation load tests. The final dataset consisted of 225 test pairs obtained in similar soils and geomaterials, at equivalent depths, with all blowcounts normalized to 30 cm (12 in.) penetration (i.e., blows/30 cm or blows/ft) within the bounds of typical test precision, and corrected to 60% hammer efficiency. The generally weak correlations do not support conversion of N_{60, TCP} to N_{60, SPT} (or vice versa) to compute foundation capacity for final design. But, engineers can certainly get an intuitive feel about site conditions and preliminary foundation capacity by using the correlation equations to translate their knowledge of one test to the other. This study extends previous work by formally comparing and contrasting the similar yet different SPT and TCP test methods in such a way as to make the results useful to users of both tests and to the broader geotechnical engineering community.     

动力触探杆长适应性及其修正试验

西部地区河床深厚覆盖层勘探取样及工程特性是水电工程地质勘察中常遇技术难题,动力触探(dynamic penetration test,DPT)因操作简单、适用土类多而成为西部地区河床覆盖层原位测试首选方法.现行规范仅给出了20 m杆长范围的修正方法,但对超此范围重型、超重型动力触探杆长适用性及修正问题,长期以来业内则颇多争议却少有研究.鉴于此,利用现场试验与数值模拟相结合,通过对动力触探试验杆上各测点应变现场实测并得到各测点应力分布,再利用LS-DYNA软件进行反演分析并确定相关计算参数,而后进行杆长25 m、40 m、60 m、80 m、120 m的数值模拟计算得到了杆长适用范围及修正系数.试验研究方法及成果可供类似问题研究与深厚覆盖层地区工程勘察借鉴或参考.      

Geostatistical modelling of spatial and depth variability of SPT data for Bangalore

The purpose of this study is to develop a geostatistical model to evaluate the spatial and depth variability of Standard Penetration Test (SPT) data from Bangalore, India. The database consists of 766 boreholes spread over a 220 km² area, with several SPT values (N) in each of them. The geostatistical analysis is done for N corrected (N _corrected) values. The N _corrected value has been corrected for different parameters such as overburden stress, size of the bore hole, type of sampler, hammer energy and length of the connecting rod. The knowledge of the semivariogram of the SPT data is used with kriging theory to estimate the values at points in the subsurface of Bangalore where field measurements are not available. The model is used to compute the variance of estimated data. The model predicts reasonably well the SPT data. The geostatistical model provides valuable results that can be used for seismic hazard analysis, site response and liquefaction studies for the development of microzonation maps. The predicted N values from the developed model can also be used to estimate the subsurface information, allowable bearing pressure of soils and elastic modulus of soils.     

On the mechanics of dynamic penetration tests

This paper describes a numerical model developed to simulate the wave propagation in an elastic media that is applied to in situ dynamic penetration test devices currently used for site characterization. In the model, dynamic equilibrium equations are solved by finite difference analysis in the time domain to produce the discretization of a penetration system – including hammer, rod, penetrometer (or sampler) and soil. In standard penetration tests numerical simulations are shown to agree well with energy measurements derived from force and acceleration signals produced by the impact of a hammer. A parametric study allowed the identification of the relevant factors affecting penetration by demonstrating that the energy effectively delivered to the soil is a function of hammer height of fall and weight of both hammer and rods, as well as the permanent penetration of the penetrometer into the ground produced by a single stroke. Based on these evidences, an approach is suggested to compare results from different dynamic penetration tests without the need to rely on empirical correlations, which is achieved by demonstrating that different equipments should yield the same normalized energy once the influence of both the hammer and rod potential energies are properly considered.     

Site characterization model using least‐square support vector machine and relevance vector machine based on corrected SPT data (Nc)

Statistical learning algorithms provide a viable framework for geotechnical engineering modeling. This paper describes two statistical learning algorithms applied for site characterization modeling based on standard penetration test (SPT) data. More than 2700 field SPT values (N) have been collected from 766 boreholes spread over an area of 220 sqkm area in Bangalore. To get N corrected value (N_c), N values have been corrected (N_c) for different parameters such as overburden stress, size of borehole, type of sampler, length of connecting rod, etc. In three‐dimensional site characterization model, the function N_c=N_c (X, Y, Z), where X, Y and Z are the coordinates of a point corresponding to N_c value, is to be approximated in which N_c value at any half‐space point in Bangalore can be determined. The first algorithm uses least‐square support vector machine (LSSVM), which is related to a ridge regression type of support vector machine. The second algorithm uses relevance vector machine (RVM), which combines the strengths of kernel‐based methods and Bayesian theory to establish the relationships between a set of input vectors and a desired output. The paper also presents the comparative study between the developed LSSVM and RVM model for site characterization. Copyright © 2009 John Wiley & Sons, Ltd.     

矿山救援地面生命保障孔高效成孔关键技术

地面生命保障孔作为井下被困人员的保障通道,是矿山事故造成人员被困井下时重要的地面应急救援方案之一,面对救援区易坍塌、易漏失、涌水大、易斜地层等复杂条件,单一成孔工艺存在地层适应性匹配差、综合钻进效率低、透巷难度大等问题,无法满足救援要求。为形成生命保障孔高效成孔工艺技术体系,提高应急救援响应速度,从解决钻效低、透巷难等科学问题和关键技术入手,快速安全钻进和精准透巷是高效成孔的两个核心任务:围绕快速安全钻进,针对深厚覆盖层、复杂基岩层,开展高压射流、空气潜孔锤跟管、复合钻进、空气潜孔锤、双钻头自平衡等钻进工艺研究,形成了深厚覆盖层安全高效钻进、基岩层复合“一趟钻”提速增效、基岩层空气潜孔锤“一趟钻”提速增效等安全快速钻进技术组合;围绕精准透巷,依据不同钻进工艺孔身轨迹控制机理,阐述了复合钻进轨迹监测控制与空气钻进轨迹监测关键技术方法,针对应急救援现场大偏移井无法透巷难题,提出了超短距离螺旋纠偏技术。成果应用于宁夏梅花井矿生命保障孔工程试验,钻孔深度670.50 m,成孔孔径215.9 mm,用时46.83 h,平均钻速14.32 m/h,孔底水平偏移0.27 m,从开钻至下套管高效成孔总用时55 h,证明该工艺技术体系能确保生命保障孔在72 h黄金救援时间内高效成孔,为地面应急救援钻孔的施工提供技术支持。      

Real-time monitoring of SPT donut hammer motion and SPT energy transfer ratio using digital line-scan camera and pile driving analyzer

In order to investigate the effect of standard penetration test (SPT) hammer impact on the energy transfer ratio (ETR) and sampler penetration, the behavior of hammer and anvil is monitored by using a high-speed digital line-scan camera and the stress wave is measured by using a pile driving analyzer during SPTs. By analyzing the motions of the hammer and anvil, which are digitized using the image processing algorithm, two types of secondary impact are observed to exist. Type-I secondary impact is caused by the rapid downward anvil movement at time t ₁ + 2L/c and the re-contact of the following hammer on the rebounding anvil. Type-I secondary impact is dominant for N value smaller than 25 and it contributes to the ETR and additional sampler penetration. The time elapsed to type-I secondary impact decreases as N value increases. Type-II secondary impact is induced by the restrike of the pushed-up hammer on the resting anvil. Type-II secondary impact is dominant for N value greater than 50 and it has no influence on the ETR and the sampler penetration. The time elapsed to type-II secondary impact increases with the increase in N value.     

Development of analytical models to estimate the increase in pile capacity with time (pile setup) from soil properties

This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different bridge construction projects of Louisiana in order to develop analytical models to estimate the increase in pile capacity with time or pile setup. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers, pressure cells that were monitored during the whole testing period. Several static load tests (SLTs) and dynamic load tests were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. Measurements of load tests confirmed that pile capacity increases almost linearly with the logarithm of time elapsed after EOD. Case pile wave analysis program was performed on the restrikes data and was used along with the load distribution plots from the SLTs to evaluate the increase in skin friction capacity of individual soil layers along the length of the piles. The logarithmic linear setup parameter “A” for unit skin friction was calculated of the 70 individual clayey soil layers and was correlated with different soil properties such as undrained shear strength (S_u), plasticity index, vertical coefficient of consolidation (c_v), over consolidation ratio and sensitivity (S_t). Nonlinear multivariable regression analyses were performed, and three different empirical models are proposed to predict the pile setup parameter “A” as a function of soil properties. For verification, the subsurface soil conditions and setup information for additional 18 PSC piles collected from local database were used to compare the measured versus predicted “A” parameters from the proposed models, which showed good agreement.

     

Application of the Dynamic Cone Penetrometer (DCP) for determination of the engineering parameters of sandy soils

Determination of the in situ engineering properties of foundation materials has always been a challenge for geotechnical engineers and, thus, several methods have been developed so far. Dynamic Cone Penetration (DCP) test is one of the most versatile amongst them. In the present research, a light weight simple DCP device was developed and used for evaluation of the engineering properties of sandy soils in laboratory conditions. The device consisted of an 8-kg hammer that drops over a height of 575 mm, and drives a 60° cone tip with 20 mm base diameter into the ground. To control the validation of the results, laboratory direct shear and plate load tests were used as reference tests. The soil sample was a poorly graded sandy soil (SP) taken from alluvial deposits of the Tehran plain. All DCP tests and PLTs were undertaken on compacted soil in a mould with 700 mm diameter and 700 mm height. Based on the results of the experiments, the relationships between Dynamic Penetration Index (DPI), relative density (D_r), modulus of elasticity (E), shear modulus (G), modulus of subgrade reaction (K_S), and the friction angle of the soil were obtained with a high coefficient of determination (> 90%). The repeatability of the test results was also evaluated by calculating the coefficient of variations (C_v), which was less than 30% for all tests.     

关于黄土湿陷性评价和剩余湿陷量的新认识

在总结诸多大型浸水现场试验成果的基础上,提出了一些关于湿陷性评价方法和剩余湿陷量合理控制等问题的新认识,目的是为了修正自重湿陷性黄土场地的自重湿陷量计算值与其实测值之间的差异,并减小地基处理深度。在获取自重湿陷量的计算值时,引进了一个深度修正系数?,使自重湿陷量和湿陷量的计算值接近实测值,这在一定程度上降低了较深部位黄土的剩余湿陷量。在获取湿陷量计算值时,提出了扩大湿陷系数阈值(0.015)的方案,并与深度修正系数?联合使用,达到了扩大湿陷量的计算值和降低较深土层的剩余湿陷量的目的。提出了大厚度自重湿陷性黄土场地的湿陷临界深度的概念,通过若干资料将其初步确定为20²5 m之间,结合深度修正系数和扩大湿陷系数阈值方法,使用湿陷临界深度概念,可以更为有效地降低较深土层的剩余湿陷量。新的研究思路可为自重湿陷性黄土场地的类似工程和黄土规范的修订提供一定的参考。     

Effect of overburden pressure and degree of saturation on compressibility characteristics

The settlement of a structure founded on clay comprises of immediate and consolidation settlements. In the case of clays, consolidation settlement is more than immediate settlement. The parameters influencing consolidation settlement of a normally loaded clay layer are degree of saturation (S%), void ratio (e) of soil prior to excavation, amount of overburden (σ_o) removed, amount of rebound and intensity of loading (σ) upon building superstructure. This paper presents the effect of the above parameters on compressibility characteristics of a clay. The different steps undertaken for footing construction were simulated in the laboratory. Remoulded clay samples were prepared from oven-dry fraction passing 425 μm sieve. The density of the samples was kept constant at 13 kN/m³. Degree of saturation was varied at 25%, 50%, 75% and 100%. The surcharge on the samples (overburden in the case of field clay layer) was varied as 25 kPa, 50 kPa and 100 kPa. Compressibility characteristics such as initial compression under the applied surcharge (overburden), rebound upon removal of surcharge and recompression were studied through one-dimensional consolidation tests. The rate and amount of initial compression, rebound, e-σ and e-log σ curves, compression index (C_c), coefficient of compressibility (a_v) and coefficient of volume compressibility (m_v) were studied.     

空气潜孔锤在松散地层中的钻进试验

空气潜孔锤钻探工艺在基岩地区已是首选的一种技术。传统观念认为空气潜孔锤钻进工艺适用于坚硬岩石（硬、脆、碎地层）,在松散地层中则需要常规泥浆回转钻进或冲击钻进。通过典型松散地层的试验证明：空气潜孔锤在松散覆盖地层中可以实现正常的钻进,并且具有效率高、成本低、劳动强度小等优点,在粘土和潮湿粘土地层中钻进效率最高可达87和72 m/h。为解决页岩气、地热、煤层气、地下水等能源资源勘探时上覆地层的开孔或一开钻进提供了行之有效的方法,同时,也解决了缺水地区或严重漏失地层钻井液用水困难和传统开孔或一开泥浆回转钻探工艺复杂等问题。     

覆盖层绿色钻探新方法——空气潜孔锤取心跟管钻进

针对覆盖层的特征和钻进特点,结合环境保护对地质勘查的新要求,将常规回转取心钻进与潜孔锤跟管钻进优化组合,形成了一种覆盖层钻探新方法—空气潜孔锤取心跟管钻进。介绍了潜孔锤取心跟管钻进方法的要点;从钻探工程经济性和环保因素,提出以潜孔锤取心钻进为主、解决覆盖层钻进效率低和质量差等技术难题的新思路。     

基于CFD的高能射流式液动冲击器活塞与缸体密封特性研究

通过计算流体动力学分析与实验室测试,对SC-86H型高能射流式液动冲击器活塞与缸体密封特性进行研究,分析了活塞密封段长度、环状间隙尺寸、活塞往复运动速度、角速度以及活塞外表面螺旋槽螺距与半径等参数对射流式冲击器前后腔之间泄漏量的影响。结果表明:活塞密封段长度、环状间隙尺寸、角速度以及活塞表面螺旋槽螺距均对射流式液动冲击器性能影响较小;活塞运动速度与泄漏量近似成正比例关系;随着活塞螺旋槽半径的增大,泄漏量会明显增大。活塞回程与冲程初期阶段,活塞运动速度较小,活塞处瞬时泄漏量占进入缸体前后腔流体流量的比例较大,使活塞无法快速加速运动,尤其是当活塞杆直径较大时,回程阶段泄漏量对活塞运动的影响更显著,导致冲击器工作性能大幅下降,甚至无法工作。     

轻烃及硫化物气体测量找寻多金属隐伏矿方法试验

挥发性有机化合物及硫化物气体作指标勘查金属矿床的工作国内外均处于初试阶段。近几年我们用硫化氢、二氧化硫及轻烃气体(C₁—C₄烷烃和烯烃)作指标对十个不同景观条件不同地区的铅锌矿、铜钼矿、金矿、铜镍等多金属矿床进行了土壤及地表岩石测量勘查隐伏矿的方法试验,取得很好的结果。表明该方法是寻找多金属隐伏矿的一种有效的气体测量方法,它可用于寻找覆盖厚度几米到400多米运积物覆盖区隐伏矿及基岩面下埋藏400多米盲矿的地表土壤和岩石测量以及岩体评价找矿工作。试验结果还表明该方法用于岩石测量的效果优于土壤测量。     

动力触探杆长修正系数试验研究

动力触探是一种应用广泛的原位测试技术,其动探杆长最大可达到上百米,在实际应用中需要进行杆长修正,目前规范中关于动力触探杆长修正问题,给出了以牛顿弹性碰撞理论和弹性杆波动理论为基础的两种修正方法,依据两种理论得出的修正系数是截然不同的。动力触探试验成果应该如何进行杆长修正,是限制该方法应用的重大问题。针对动力触探杆长修正问题,提出了室内模型试验,并依据砂砾石和均质砂两种地基土进行不同杆长的重型动力触探模型试验,杆长分别为2.0、8.9、16.4、23.4、30.0、36.0 m。通过试验,得到重型动力触探杆长修正系数。分析认为,重型动力触探杆长修正规律符合牛顿弹性碰撞理论,且与地基土材料特性无关。     

Pull-out behaviour of steel grid soil reinforcement embedded in silty sand

This paper investigates the pull-out behaviour (particularly the bearing resistance) of a steel grid reinforcement embedded in silty sand using laboratory tests and numerical analyses. It is demonstrated that the various common analytical equations for calculating the bearing component of pull-out resistance give a wide range of calculated values, up to about 200% disparity. The disparity will increase further if the issue of whether to use the peak or critical state friction angle is brought in. Furthermore, these equations suggest that the bearing resistance factor, N_q, is only a function of soil friction angle which is not consistent with some design guidelines. In this investigation, a series of large scale laboratory pull-out tests under different test pressures were conducted. The test results unambiguously confirmed that the N_q factor is a function of test pressure. A modified equation for calculating N_q is also proposed. To have more in-depth understanding of the pull-out behaviour, the tests were modelled numerically. The input parameters for the numerical analysis were obtained from laboratory triaxial tests. The analysis results were compared with the experimental results. Good agreement between experimental and numerical results was achieved if the strain-softening behaviour from peak strength to critical state condition was captured by the soil model used.     

Heterogeneity of grain-size fractions of nanodiamonds from the Orgueil C1 meteorite

A model for the composition of meteoritic nanodiamonds is suggested based on analysis of the concentrations and isotopic compositions of C, N, and Xe in the nanodiamond-rich grain-size fractions, which were separated for the first time from the Orgueil CI chondrite. According to the model, meteoritic nanodiamond consists of two populations of grains (denoted C_HL and C_N). The size distributions of grains in populations in the C_HL and C_N populations are different: the C_HL population is finer grained than C_N. The grains of the C_HL population are characterized by a radial gradient in the carbon isotopic composition, and they contain implanted anomalous noble gases (HL component) and the heavy nitrogen isotope ¹⁵N. Following (Clayton et al., 1995), the probable astrophysical source of this population of nanodiamond grains is thought to be the mixing helium and hydrogen shells of a Type-II supernova, and the mechanism that produced these grains was the slow CVD process. The C_N population grains have homogeneous isotopic compositions of carbon (δ¹³C ≡–100‰) and nitrogen (δ¹⁵N ≡–400‰) and contain almost all nitrogen of the nanodiamond-rich fractions. This population of nanodiamond grains was likely formed by a fast unequilibrated process, when shock waves affected organic compounds or gas rich in C- and N-bearing compounds during the early evolution of the protosolar nebula. Calculations within the framework of the model show that the nanodiamond-rich fractions separated from the Orgueil meteorite have the C_N/C_HL ratios varying from 1 in the finest grained fraction to 10 in the coarse-grained one. At these proportions of the populations, weighted mean δ¹³C values of C_HL grains in the fractions lie within the range of 42 to 394‰, and the concentrations of ¹³²Xe-HL and ¹⁵N are (49–563) × 10^–8 cm³/gC and (1.1–6.2) × 10^–5 cm³/gC, respectively.     

Experimental study on the mechanical behaviors and particle breakage characteristics of calcareous sand from South China Sea under repeated one-dimensional impacts

The behavior of calcareous sand under repeated impact considerably differs from that of silica sand. Notably, calcareous sand is important in engineering projects in the South China Sea, such as pile driving. To understand the behavior of calcareous sand under multiple impacts, the improved split Hopkinson pressure bar (SHPB) system was selected for one-dimensional impact tests of silica and calcareous sand with particle sizes of 0.25–0.50 mm. The sand specimens were impacted 1, 3, 7 and 10 times. The test results reveal that the dynamic apparent stiffness of silica sand is approximately 6–8 times that of calcareous sand. The dynamic apparent modulus values of the two sands increase with an increase in the number of impacts, N. For calcareous sand, the compression index C_c decreases with an increase in N, and silica sand shows the opposite trend. The yield pressure p_c of calcareous sand under impact loading is approximately 40% of that of silica sand. With an increase in N, the energy absorption capacity, energy dissipation rate and damage variables of the two sands exhibit a downward trend. In addition, the energy absorption efficiency of calcareous sand is better than that of silica sand. During the process of impact, a large number of sand particles will break, and particle breakage will change the particle size distribution (PSD), thereby significantly affecting the physical and mechanical properties of the corresponding soil. Based on the test results and fractal theory, an evolution model is established to characterize the PSD evolution in the breakage state for uniformly graded calcareous sand. Moreover, a Markov chain model is proposed to describe the PSD evolution of nonuniformly graded specimens. The predicted results of both models show agreement with the experimental values.

     

Soil organic matter as an important contributor to Late Quaternary sediments of the tropical West African continental margin

The contribution of soil organic matter (SOM) to continental margins is largely ignored in studies on the carbon budget of marine sediments. Detailed geochemical investigations of late Quaternary sediments (245-0 ka) from the Niger and Congo deep-sea fans, however, reveal that C_org/N_tot ratios and isotopic signatures of bulk organic matter (δ¹³C_org) in both fans are essentially determined by the supply of various types of SOM from the river catchments thus providing a fundamentally different interpretation of established proxies in marine sciences. On the Niger fan, increased C_org/N_tot and δ¹³C_org (up to −17‰) were driven by generally nitrogen-poor but ¹³C-enriched terrigenous plant debris and SOM from C₄/C₃ vegetation/Entisol domains (grass- and tree-savannah on young, sandy soils) supplied during arid climate conditions. Opposite, humid climates supported drainage of C₃/C₄ vegetation/Alfisol/Ultisol domains (forest and tree-savannah on older/developed, clay-bearing soils) that resulted in lower C_org/N_tot and δ¹³C_org (< −20‰) in the Niger fan record. Sediments from the Congo fan contain a thermally stable organic fraction that is absent on the Niger fan. This distinct organic fraction relates to strongly degraded SOM of old and highly developed, kaolinite-rich ferallitic soils (Oxisols) that cover large areas of the Congo River basin. Reduced supply of this nitrogen-rich and ¹²C-depleted SOM during arid climates is compensated by an elevated input of marine OM from the high-productive Congo up-welling area. This climate-driven interplay of marine productivity and fluvial SOM supply explains the significantly smaller variability and generally lower values of C_org/N_tot and δ¹³C_org for the Congo fan records. This study emphasizes that ignoring the presence of SOM results in a severe underestimation of the terrigenous organic fraction leading to erroneous paleoenvironmental interpretations at least for continental margin records. Furthermore, burial of SOM in marine sediments needs more systematic investigation combining marine and continental sciences to assess its global relevance for long-term sequestration of atmospheric CO₂.