1.1 目的和应用: 1.1.1 本指南总结了使用重力法评估地下条件的设备、现场程序和解释方法。然而，本标准不涉及海洋、航空或卫星重力测量的使用。 1.1.2 本指南中描述的重力法适用于各种地下条件的现场表征。 1.1.3 重力测量表明，由于地下土壤或岩石密度的横向差异或自然空隙或人为因素的存在，地球重力场发生变化- 制造结构。通过测量重力场的空间变化，可以确定地下条件的变化。 1.1.4 详细重力测量（通常称为微重力测量）用于近地表地质现场特征描述以及岩土、环境和考古研究。地质和岩土工程应用包括埋藏通道的位置、基岩结构特征、孔隙和洞穴以及基础中的低密度区。环境应用包括场地特征、地下水研究、垃圾填埋场特征和地下储罐的位置 ( 1. ) 2. . 1.2 限制: 1.2.1 本指南概述了重力法。它没有涉及重力理论、野外程序或数据解释的细节。为此目的，包含了大量参考文献，并被视为本指南的重要组成部分。建议重力法的用户熟悉引用的参考文献和指南 D420 , D5753 , D6235 和 D6429 ，和实践 D5088 和 D5608 . 1.2.2 本指南仅限于在陆地上进行的重力测量。重力法可适用于许多特殊用途: 在陆地、钻孔、水面、飞机和太空。本指南不包括对这些其他重力方法的讨论，包括垂直重力梯度测量。 1.2.3 本指南中建议的重力法方法是最常用、最广泛接受和已验证的方法。然而，可以替代技术上合理的重力法的其他方法或修改。 1.2.4 本指南提供了有组织的信息收集或一系列选项，并不推荐具体的行动方案。本文件不能取代教育、经验，应与专业判断一起使用。 并非本指南的所有方面都适用于所有情况。本ASTM文件不代表或取代必须根据其判断给定专业服务的充分性的谨慎标准，也不应在不考虑项目的许多独特方面的情况下应用本文件。本文件标题中的“标准”一词仅表示该文件已通过ASTM共识程序获得批准。 1.3 单位- 以国际单位制表示的数值视为标准值。本标准不包括其他计量单位。以国际单位制以外的单位报告试验结果不应视为不符合本试验方法。 1.4 注意事项: 1.4.1 本指南的用户有责任遵循设备制造商建议中的任何预防措施，并建立适当的健康和安全实践。 1.4.2 如果本指南用于有危险材料、操作或设备的场所，则本指南的用户有责任在使用前制定适当的安全和健康做法，并确定任何法规的适用性。 1.5 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 概念- 本指南总结了用于使用重力法确定密度变化引起的地下条件的设备、现场程序和解释方法。重力测量可用于绘制数百平方英里以上的主要地质特征，并检测土壤或岩石中较浅的较小特征。 在某些地区，重力法可以检测地下空洞。 5.1.1 重力法的另一个好处是，可以在许多文化发达地区进行测量，而其他地球物理方法可能不起作用。例如，可以在建筑物内进行重力测量；在城市地区；以及文化、电气和电磁噪声领域。 5.1.2 用重力法测量地下条件需要重力仪( 图1 )以及一种确定重力站位置和非常精确的相对高程的方法。 5.1.2.1 重力法中使用的测量单位是Gal（为了纪念伽利略），基于地球表面的引力。 地球表面的平均重力约为980 Gal。区域重力测量中常用的单位是mGal（10 −3. 加仑）。环境和工程应用的典型重力测量要求测量精度为几μgal（10 −6. Gals），它们通常被称为微重力测量。 5.1.2.2 详细重力测量通常使用密集的测量站（几米到大约100米），并使用能够读取几微伽的重力仪进行。详细调查用于评估当地地质或结构条件。 5.1.2.3 重力测量包括沿剖面线或网格在测站进行重力测量。在基站（稳定的无噪声参考位置）定期进行测量，以校正仪器漂移。 5.1.3 重力数据包含由深层区域效应和浅层局部效应组成的异常。微重力工作中感兴趣的是浅层局部效应。对原始现场数据进行了多次校正。这些校正包括纬度、自由空气高度、布格校正（质量效应）、地球潮汐和地形。减去区域趋势后，剩余或剩余的布格重力异常数据可以表示为剖面线( 图2 )或者在等高线图上。剩余重力异常图可用于定性和定量解释。Telford等人提供了重力法的其他详细信息 ( 5. ) ; 管家 ( 6. ) ; 内特尔顿 ( 7. ) ; 和Hinze ( 8. ) . 5.2.2 表1 表明沉积岩的密度通常低于火成岩和变质岩的密度。密度大致随地质年龄的增加而增加，因为较老的岩石通常孔隙较小，并且受到更大的压实。土壤和岩石的密度在很大程度上由未固结材料或岩石的原生和次生孔隙度控制。 5.2.3 背景条件和被映射的特征之间必须存在足够的密度对比度，才能检测到特征。一些重要的地质或水文地质边界可能没有现场可测量的密度对比，因此无法使用该技术进行检测。 5.2.4 虽然重力法测量地球材料密度的变化，但解释人员必须根据当地条件或其他数据或两者的知识解释重力数据，并得出地质上合理的解决方案。 5.3 设备: 5.3.1 用于表面重力测量的地球物理设备包括重力仪、获取位置的方法和非常精确地确定高程相对变化的方法。 重力仪设计用于测量重力场中极小的差异，因此是非常精密的仪器。重力仪在运输和搬运过程中容易受到机械冲击。 5.3.2 重力仪- 必须选择具有范围、稳定性、灵敏度和精度的重力仪进行预期测量。许多重力仪记录数字数据。这些仪器能够平均一系列读数，拒绝噪声数据，并显示特定台站的重力测量序列。电子控制重力仪可以实时校正较小的倾斜误差、仪器温度和长期误差- 术语漂移和固体潮。这些重力仪与计算机、打印机和调制解调器通信以进行数据传输。考夫曼 ( 10 ) 描述了适用于微重力测量的仪器。查平对重力仪进行了全面回顾 ( 11 ) . 5.3.3 定位- 微重力测量的位置控制应具有1米或更高的相对精度。在中纬度，水平南北（纬度）位置的可能重力误差约为1μGal/m。定位可以通过卷尺和罗盘、传统土地测量技术或差分全球定位系统（DGPS）获得。 5.3.4 立面图- 准确的相对高程测量对于微重力测量至关重要。高程变化3 mm可能导致1μGal的标称重力误差。因此，微重力测量的高程控制要求相对高程精度约为3 mm。高程通常是相对于现场的任意参考确定的，但也可以与高程基准挂钩。高程是通过仔细的光学水准测量或自动数字水准测量获得的。 5.4 限制和干扰: 5.4.1 地球物理方法固有的一般局限性: 5.4.1.1 所有地球物理方法的一个基本限制是，一组给定的数据不能与一组独特的地下条件相关联。 在大多数情况下，仅凭地表地球物理测量无法解决所有模糊问题，需要一些额外的信息，如钻孔数据。由于地球物理方法的固有局限性，仅重力测量永远不能被视为对地下条件的完整评估。重力测量与其他地质信息适当结合，是获取地下信息的一种高效、准确、经济的方法。 5.4.1.2 此外，所有地表地球物理方法固有地受到分辨率随深度降低的限制。 5.4. 2. 重力法的特定限制: 5.4.2.1 背景条件和被映射的特征之间必须存在足够的密度对比度，才能检测到特征。一些重要的地质或水文地质边界可能没有现场可测量的密度对比，因此无法使用该技术进行检测。仅对重力数据的解释并不能在可能的地质模型和单个现场数据集之间产生唯一的相关性。这种模糊性只能通过使用足够的支持性地质数据和有经验的翻译来解决。 5.4.2.2 环境、地质和文化条件造成的干扰: (1) 重力法对各种自然环境和文化源的噪声（振动）敏感。由地质因素引起的密度空间变化也可能产生不必要的噪声。 (2) 环境噪声源- 环境噪声源包括地震、微震、潮汐、风、雨和极端温度。 （a） 地震- 在重力观测中，局部地震很少成为问题。它们在给您带来不便之前就已经发生和消失了。然而，遥远的地震可能导致100μgal或更大的重力变化，周期为几十分钟或更长。 这些影响会使重力观测延迟数小时甚至数天。 （b） 微震- 微震是指由风、水或波浪等自然原因引起的微弱地震（警长） ( 1. ) ). 它们被认为与海岸线上的波浪作用和快速移动的压力锋的通过有关，其影响被视为重力数据中的正弦变化。它们的振幅很容易超过几十μgal。 （c） 固体潮- 太阳和月球潮汐对地球表面引力的影响高达300μGal，变化率高达1μGal/min。 这些固体固体潮是可预测的，可以作为重力数据校正程序的一部分进行校正。 （d） 风雨- 风和大雨会导致重力仪移动。重力仪应遮挡风雨。 （e） 极端温度- 短期内极端温度变化可能导致仪器漂移。为了尽量减少这种影响，重力仪应与极端加热或冷却隔离。作为重力测量的正常部分，通常通过重复基站测量和漂移校正来适应温度的缓慢逐渐变化。 （f） 地质噪声源- 地质噪声源可能包括土壤和岩石的自然空间分布及其密度的未知变化。 （g） 地形- 丘陵、山脉和山谷会影响重力测量。根据测量目标，可能需要进行地形校正（Hinze） ( 8. ) ). （h） 文化噪声源- 文化噪声源包括车辆、重型设备、火车甚至行走在重力仪附近的人的振动。 5.4.3 摘要- 在设计和执行重力测量的过程中，必须考虑环境、地质和文化噪声的来源，并注明发生时间和位置。 干扰的确切形式并不总是可预测的，因为它取决于噪声的类型和幅值以及与噪声源的距离。 5.5 替代方法- 在某些情况下，前面讨论的因素可能会妨碍重力法和其他地球物理方法的有效使用（指南 D6429 )或可能需要非地球物理方法来调查地下条件。

1.1 Purpose and Application: 1.1.1 This guide summarizes the equipment, field procedures, and interpretation methods for the assessment of subsurface conditions using the gravity method. However, this standard does not address the use of marine, airborne, or satellite gravity measurements. 1.1.2 The gravity method described in this guide is applicable to site characterization of a wide range of subsurface conditions. 1.1.3 Gravity measurements indicate variations in the earth's gravitational field caused by lateral differences in the density of the subsurface soil or rock or the presence of natural voids or man-made structures. By measuring spatial changes in the gravitational field, variations in subsurface conditions can be determined. 1.1.4 Detailed gravity surveys (commonly called microgravity surveys) are used for near-surface geologic site characterizations and geotechnical, environmental, and archaeological studies. Geologic and geotechnical applications include location of buried channels, bedrock structural features, voids, and caves, and low-density zones in foundations. Environmental applications include site characterization, groundwater studies, landfill characterization, and location of underground storage tanks ( 1 ) 2 . 1.2 Limitations: 1.2.1 This guide provides an overview of the gravity method. It does not address the details of the gravity theory, field procedures, or interpretation of the data. Numerous references are included for that purpose and are considered an essential part of this guide. It is recommended that the user of the gravity method be familiar with the references cited and with the Guides D420 , D5753 , D6235 , and D6429 , and Practices D5088 , and D5608 . 1.2.2 This guide is limited to gravity measurements made on land. The gravity method can be adapted for a number of special uses: on land, in a borehole, on water, and from aircraft and space. A discussion of these other gravity methods, including vertical gravity gradient measurements, is not included in this guide. 1.2.3 The approaches suggested in this guide for the gravity method are the most commonly used, widely accepted, and proven. However, other approaches or modifications to the gravity method that are technically sound may be substituted. 1.2.4 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education, experience, and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM document is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through the ASTM consensus process. 1.3 Units— The values stated in SI units are regarded as standard. No other units of measurement are included in this standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method. 1.4 Precautions: 1.4.1 It is the responsibility of the user of this guide to follow any precautions in the equipment manufacturer's recommendations and to establish appropriate health and safety practices. 1.4.2 If this guide is used at sites with hazardous materials, operations, or equipment, it is the responsibility of the user of this guide to establish appropriate safety and health practices and to determine the applicability of any regulations prior to use. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Concepts— This guide summarizes the equipment, field procedures, and interpretation methods used for the determination of subsurface conditions due to density variations using the gravity method. Gravity measurements can be used to map major geologic features over hundreds of square miles and to detect shallow smaller features in soil or rock. In some areas, the gravity method can detect subsurface cavities. 5.1.1 Another benefit of the gravity method is that measurements can be made in many culturally developed areas, where other geophysical methods may not work. For example, gravity measurements can be made inside buildings; in urban areas; and in areas of cultural, electrical, and electromagnetic noise. 5.1.2 Measurement of subsurface conditions by the gravity method requires a gravimeter ( Fig. 1 ) and a means of determining location and very accurate relative elevations of gravity stations. 5.1.2.1 The unit of measurement used in the gravity method is the Gal (in honor of Galileo), based on the gravitational force at the Earth's surface. The average gravity at the Earth's surface is approximately 980 Gal. The unit commonly used in regional gravity surveys is the mGal (10 −3 Gal). Typical gravity surveys for environmental and engineering applications require measurements with an accuracy of a few μGals (10 −6 Gals), they are often referred to as microgravity surveys. 5.1.2.2 A detailed gravity survey typically uses closely spaced measurement stations (a few meters to approximately 100 meters) and is carried out with a gravimeter capable of reading to a few μGals. Detailed surveys are used to assess local geologic or structural conditions. 5.1.2.3 A gravity survey consists of making gravity measurements at stations along a profile line or grid. Measurements are taken periodically at a base station (a stable noise-free reference location) to correct for instrument drift. 5.1.3 Gravity data contain anomalies that are made up of deep regional and shallow local effects. It is the shallow local effects that are of interest in microgravity work. Numerous corrections are applied to the raw field data. These corrections include latitude, free air elevation, Bouguer correction (mass effect), Earth tides, and terrain. After the subtraction of regional trends, the remainder or residual Bouguer gravity anomaly data may be presented as a profile line ( Fig. 2 ) or on a contour map. The residual gravity anomaly map may be used for both qualitative and quantitative interpretations. Additional details of the gravity method are given in Telford et al ( 5 ) ; Butler ( 6 ) ; Nettleton ( 7 ) ; and Hinze ( 8 ) . 5.2.2 Table 1 shows that densities of sedimentary rocks are generally lower than those of igneous and metamorphic rocks. Densities roughly increase with increasing geologic age because older rocks are usually less porous and have been subject to greater compaction. The densities of soils and rocks are controlled, to a very large extent, by the primary and secondary porosity of the unconsolidated materials or rock. 5.2.3 A sufficient density contrast between the background conditions and the feature being mapped must exist for the feature to be detected. Some significant geologic or hydrogeologic boundaries may have no field-measurable density contrast across them, and consequently cannot be detected with this technique. 5.2.4 While the gravity method measures variations in density in earth materials, it is the interpreter who, based on knowledge of the local conditions or other data, or both, must interpret the gravity data and arrive at a geologically reasonable solution. 5.3 Equipment: 5.3.1 Geophysical equipment used for surface gravity measurement includes a gravimeter, a means of obtaining position and a means of very accurately determining relative changes in elevation. Gravimeters are designed to measure extremely small differences in the gravitational field and as a result are very delicate instruments. The gravimeter is susceptible to mechanical shock during transport and handling. 5.3.2 Gravimeter— The gravimeter must be selected to have the range, stability, sensitivity, and accuracy to make the intended measurements. Many gravimeters record digital data. These instruments have the capability to average a sequence of readings, to reject noisy data, and to display the sequence of gravity measurements at a particular station. Electronically controlled gravimeters can correct in real time for minor tilt errors, for the temperature of the instrument, and for long-term drift and earth tides. These gravimeters communicate with computers, printers, and modems for data transfer. Kaufmann ( 10 ) describes instruments suitable for microgravity surveys. A comprehensive review of gravimeters can be found in Chapin ( 11 ) . 5.3.3 Positioning— Position control for microgravity surveys should have a relative accuracy of 1 m or better. The possible gravity error for horizontal north-south (latitude) position is about 1 μGal/m at mid-latitudes. Positioning can be obtained by tape measure and compass, conventional land survey techniques, or a differential global positioning system (DGPS). 5.3.4 Elevations— Accurate relative elevation measurements are critical for a microgravity survey. A nominal gravity error of 1 μGal can result from an elevation change of 3 mm. Therefore, elevation control for a microgravity survey requires a relative elevation accuracy of about 3 mm. Elevations are generally determined relative to an arbitrary reference on site but can also be tied to an elevation benchmark. Elevations are obtained by careful optical leveling or by automatic digital levels. 5.4 Limitations and Interferences: 5.4.1 General Limitations Inherent to Geophysical Methods: 5.4.1.1 A fundamental limitation of all geophysical methods is that a given set of data cannot be associated with a unique set of subsurface conditions. In most situations, surface geophysical measurements alone cannot resolve all ambiguities, and some additional information, such as borehole data, is required. Because of this inherent limitation in the geophysical methods, a gravity survey alone can never be considered a complete assessment of subsurface conditions. Properly integrated with other geologic information, gravity surveying is a highly effective, accurate, and cost-effective method of obtaining subsurface information. 5.4.1.2 In addition, all surface geophysical methods are inherently limited by decreasing resolution with depth. 5.4.2 Limitations Specific to the Gravity Method: 5.4.2.1 A sufficient density contrast between the background conditions and the feature being mapped must exist for the feature to be detected. Some significant geologic or hydrogeologic boundaries may have no field-measurable density contrast across them, and consequently cannot be detected with this technique. An interpretation of gravity data alone does not yield a unique correlation between possible geologic models and a single set of field data. This ambiguity can only be resolved through the use of sufficient supporting geologic data and by an experienced interpreter. 5.4.2.2 Interferences Caused by Ambient, Geologic, and Cultural Conditions: (1) The gravity method is sensitive to noise (vibrations) from a variety of natural ambient and cultural sources. Spatial variations in density caused by geologic factors may also produce unwanted noise. (2) Ambient Sources of Noise— Ambient sources of noise include earthquakes, microseisms, tides, winds, rain, and extreme temperatures. (a) Earthquakes— Local earthquakes seldom are a problem during gravity observations. They occur and are gone before they are any inconvenience. Distant earthquakes however, can lead to gravity changes of 100 μGals or more with periods of tens of minutes or more. These effects can delay gravity observations for several hours or even days. (b) Microseisms— Microseisms are defined as feeble earth tremors due to natural causes such as wind, water, or waves (Sheriff ( 1 ) ). They are believed to be related to wave action on shorelines and to the passage of rapidly moving pressure fronts whose effects are seen as sinusoidal variations in the gravity data. Their amplitude can readily exceed several tens of μGals. (c) Earth Tides— Solar and lunar tides affect the force of gravity at the Earth's surface by as much as 300 μGals with a rate of change as large as 1 μGal/min. These solid earth tides are predictable and can be corrected for as a part of gravity data correction procedures. (d) Wind and Rain— Wind and heavy rain can cause movement of the gravimeter. The gravimeter should be shielded from the wind and rain. (e) Extreme Temperatures— Extreme temperature changes over short periods of time can cause instrument drift. In order to minimize this effect, the gravimeter should be insulated from extreme heating or cooling. Slow gradual changes in temperature are normally accommodated by repeat base station measurements and drift corrections made as a normal part of the gravity survey. (f) Geologic Sources of Noise— Geologic sources of noise may include unknown variations in the natural spatial distribution of soil and rock and their densities. (g) Topography— Hills, mountains, and valleys affect gravity measurements. Depending on the objectives of the survey, topographic corrections may be needed (Hinze ( 8 ) ). (h) Cultural Sources of Noise— Cultural sources of noise include vibration from vehicles, heavy equipment, trains, and even persons walking near the gravimeter. 5.4.3 Summary— During the course of designing and carrying out a gravity survey, the sources of ambient, geologic, and cultural noise must be considered and time of occurrence and location noted. The exact form of the interference is not always predictable because it depends upon the type and magnitude of noise and distance from the source of noise. 5.5 Alternate Methods— In some cases, the factors previously discussed may prevent the effective use of the gravity method, and other geophysical (Guide D6429 ) or non-geophysical methods may be required to investigate subsurface conditions.